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GEOLOGICAL OBSERYATIONS 
 
MR. DARWIN'S LIFE AND WORKS. 
 
 /-■^LIFE AND LETTEKS OF CHARLES DARWIN, with an Autobio- 
 graphical Chapter. Edited by his Son, FRAif CIS Darwin, F.R.S. With Portraits 
 and Woodcuts. 3 yds. 8vo. 36*. (Murray.) 
 
 OAN ILLUSTRATED EDITION OF DARWIN'S VOYAGE OF A 
 
 NATURALIST ROUND THE WORLD IN H.M.S. ' BBAaLE ' With ViewP of 
 Places Vi:.ited and Described. By E. T. Pritchbtt. With Maps and 100 IlluscratioLS. 
 Medium 8vo. 21s. (Murray.) 
 
 s JOURNAL OF A NATURALIST DURING A VOYAGE ROUND 
 
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 A ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION. 
 '^ Libriry Edition. 2 vols. 12*. ; or Popalar Edition, 6i. (Murray.) 
 
 ly DJESCENT OF MAN, AND SELECTION IN RELATION TO SEX. 
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 \/VARIATION OF ANIMALS AND PLANTS UNDER DOMESTI- 
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 ^EXPRESSIONS OF THE EMOTIONS IN MAN AND ANIMALS. 
 
 ^ With Illustrations. 3 2s. (Murray.) 
 
 1 VARIOUS CONTRIVANCES BY WHICH ORCHIDS ARE FERTI- 
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 CROSS AND SELF-FERTILIZATION IN THE VEGETABLE 
 
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 LIFE OF ERASMUS DARWIN. With a Study of his Works by 
 
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 FACTS AND ARGUMENTS FOR DARWIN. By Fbitz Muller. 
 
 Translated by W. S. Dallas. Woodcuts. Post Svo. 6s. (Murray.) 
 
 /^THE STRUCTURE AND DISTRIBUTION OP CORAL REEFS. 
 
 With an Appendix by Prof. T. G. Bonney, D.Sc, F.R.S.; F.G.S. Third Edition. 
 With 3 Plates. Crown 8vo. 8s.. 6d. (Smith, Elder, & Co.) 
 
 , y^GEOLOGICAL OBSERVATIONS ON THE VOLCANIC ISLANDS 
 
 AND PARTS OF SOUTH AMERICA, visited during the Voyage of H.M.S. 
 'Beagle.' Third Edition, with Maps and Illustrations. Crown 8vo. 12s. Gd. 
 (Smith, Elder, & Co.) 
 
 A MONOGRAPH OF THE CIRRIPEDIA. With numerous Illustra- 
 tious. 2 vols. 8vo. (Ray Society. Hardwicke.) 
 
 A MONOGRAPH OF THE FOSSIL LEPADIDiE OR PEDUNCU- 
 LATED CIRRIPEDS OF GREAT BRITAIN. (Palseontographical Society, 1851). 
 
 A MONOGRAPH OF THE FOSSIL BALANID^ AND VERRUCID^ 
 
 OF GREAT BRITAIN. (Palseontographical Society, 1854.) 
 
GEOLOGICAL OBSERVATIONS 
 
 ON THE VOLCANIC ISLANDS AND PAETS OF SOUTH 
 
 AMEEICA VISITED DUEING THE VOYAGE 
 
 OF H.M.S. 'BEAGLE' 
 
 BY 
 
 CHAELES DAKWIN, M.A. F.K.S. &c. 
 
 AUTHOR OF ' THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS ' 
 ' THE OltKilN OF SPECIES ' ETC. 
 
 THIRD EDITION 
 
 WITH MAPS AND ILLUSTRATIONS 
 
 BOSTON COLLEGE 
 SCIENCE LIBRARY 
 
 LONDON 
 SMITH, ELDER, & CO., 15 WATERLOO PLACE 
 
 1891 
 
 [All rights r-eserved} 
 
295'd 
 
 S95 
 
 y!) 
 
 ^^^^.v 
 
 'n^ 
 
PEE FACE 
 
 TO 
 
 THE SECOND EDITION 
 
 The First Edition of my ' Geological Observations on 
 the Volcanic Islands,' visited during the voyage of 
 H.M.S. ' Beagle,' under the command of Capt. Fitz- 
 Eoy, E.N., was published, with the approval of the 
 Lords Commissioners of Her Majesty's Treasury, in the 
 year 1844 ; and my ' Observations on South America/ 
 in 1846. As both these works are now out of print, and 
 as I believe that they still contain matter of scientific 
 value, it has appeared to me advisable that they should 
 be republished. They relate to parts of the world 
 which have been so rarely visited by men of science, 
 that I am not aware that much could be corrected or 
 added from observations subsequently made. 
 
 Owing to the great progress which Geology has 
 made within recent times, my views on some few points 
 may be somewhat antiquated ; but I have thought it 
 best to leave them as they originally appeared. In 
 order to complete my account of the Geological Obser- 
 
vi Preface to the Second Edition. 
 
 vations made during the voyage of the ' Beagle,' I will 
 here give references to four papers which were separately- 
 published. First, ' On the Connection of certain Vol- 
 canic Phenomena in South America,' read in 1838, and 
 published in Volume V. of the ' Transactions of the 
 Geological Society.' Secondly, ' On the Distribution 
 of the Erratic Boulders and on the contemporaneous 
 Stratified Deposits of South America,' read in 1841, and 
 published in Volume VI. of the ' Transactions ' of the 
 same Society. Thirdly, ' An Account of the Fine Dust 
 which often falls on Vessels in the Atlantic Ocean : ' 
 'Proceedings of the Geological Society,' June 4, 1845. 
 Fourthly, on March 25, 1846, in the same Journal, 
 ' On the Geology of the Falkland Islands.' 
 
CONTENTS. 
 
 PART I. 
 CHAPTER I. 
 
 ST. JAGO, IN THE CAPE DE VERDE AECHIPELAGO. 
 
 Rocks of the lowest series — A calcareous sedimentary deposit, with 
 recent shells, altered by the contact of superincumbent lava, its 
 horizontality and extent — Subsequent volcanic eruptions, asso- 
 
 . ciated with calcareous matter in an earthy and fibrous form, and 
 often enclosed within the separate cells of the scoriae — Ancient 
 and obliterated orifices of eruption of small size — Difficulty of 
 tracing over a bare plain recent streams of lava — Inland hills of 
 more ancient volcanic rock — Decomposed olivine in large masses 
 — Feldspathic rocks beneath the upper crystalline basaltic strata 
 — Uniform structure and form of the more ancient volcanic 
 hills — Form of the valleys near the coast — Conglomerate now 
 forming on the sea beach ...... page 3 
 
 CHAPTER II. 
 
 FERNANDO NORONHA ; TERCEIEA ; TAHITI, ETC. 
 
 Fernando Noronha — Precipitous hill of phonolite. Terceira — 
 Trachytic rocks ; their singular decomposition by steam of high 
 temperature. Tahiti — Passage from wacke into trap ; singular 
 volcanic rock with the vesicles half filled with mesotype. Mau- 
 ritius — Proofs of its recent elevation — Structure of its more 
 ancient mountains ; similarity with St. Jago. St. Paul's 
 Rocks — Not of volcanic origin — their singular mineralogical 
 composition 27 
 
vili Contents. 
 
 CHAPTER III. 
 
 ASCENSIOIf. 
 
 Basaltic lavas — Numerous craters truncated on the same side — 
 Singular structure of volcanic bombs — Aeriform explosions — 
 Ejected granitic fragments — Trachytic rocks — Singular veins — 
 Jasper, its manner of formation — Concretions in pumiceous tuff 
 — Calcareous deposits and frondescent incrustations on the coast 
 — Remarkable laminated beds, alternating with, and passing 
 into obsidian— Origin of obsidian — Lamination of volcanic 
 rocks PAGE 40 
 
 CHAPTER IV. 
 
 ST. HELENA. 
 
 Lavas of the f eldspathic, basaltic, and submarine series — Section of 
 Flagstaff Hill and of the Barn — Dikes — Turk's Cap and Pros- 
 perous Bays — Basaltic ring — Central crateriform ridge, with an 
 internal ledge and a parapet — Cones of phonolite — Superficial 
 beds of calcareous sandstone — Extioct land-shells — Beds of 
 detritus — Elevation of the land — Denudation — Craters of 
 elevation .......... 83 
 
 CHAPTER V. 
 
 GALAPAGOS ARCHIPELAGO. 
 
 Chatham Island — Craters composed of a peculiar kind of tuff — 
 Small basaltic craters, with hollows at their bases— Albemarle 
 Island ; fluid lavas, their composition — Craters of tuff ; inclina- 
 tion of their exterior diverging strata, and structure of their 
 interior converging strata — James Island, segment of a small 
 basaltic crater ; fluidity and composition of its lava streams, and 
 of its ejected fragments — Concluding remarks on the craters 
 of tuff, and on the breached condition of their southern sides 
 — Mineralogical composition of the rocks of the archipelago 
 — Elevation of the land — Direction of the fissures of erup- 
 tion 110 
 
Contents. ix 
 
 CHAPTER YI. 
 
 TBACHYTE AND BASALT. — DISTEIBUTION OF VOLCANIC ISLES. 
 
 The sinking of crystals in fluid lava — Specific gravity of the consti- 
 tuent parts of trachyte and of basalt, and their consequent 
 separation — Obsidian — Apparent non-separation of the elements 
 of plutonic rocks — Origin of trap-dikes in the plutonic series- 
 Distribution of volcanic islands ; their prevalence in the great 
 oceans — They are generally arranged in lines — The central 
 volcanos of Von Buch doubtful — Volcanic islands bordering con- 
 tinents — Antiquity of volcanic islands, and their elevation in 
 mass — Eruptions on parallel lines of fissure within the same 
 geological period PAGE 132 
 
 CHAPTER VII. 
 
 AUSTEALIA; NEW ZEALAND; CAPE OF GOOD HOPE. 
 
 New South Wales — Sandstone formation — ^^Embedded pseudo-frag- 
 ments of shale — Stratification — Current- cleavage — Great valleys 
 — Van Diemen's Land — Palseozoic formation — Newer formation 
 with volcanic rocks — Travertin with leaves of extinct plants — 
 Elevation of the land — New Zealand — King George's Sound — 
 ■ Superficial ferruginous beds — Superficial calcareous deposits, 
 with casts of branches ; its origin from drifted particles of shells 
 and corals — their extent — Cape of Good Hope — Junction of the 
 granite and clay-slate — Sandstone formation . . . 146 
 
 APPENDIX TO PART I. 
 
 DESCRIPTION OP FOSSIL SHELLS, BY G. B. SO WEBBY, ESQ., P.L.S. 
 
 From a Tertiary deposit at St. Jago, in the Cape de Verde 
 
 Archipelago ......... 171 
 
 Extinct land-shells from St, Helena 17.S 
 
 Shells from the Paleozoic formation of Van Diemen's Land . 176 
 Description of Fossil Corals from the Paleozoic formation of 
 
 Van Diemen's Land, by W. Lonsdale, Esq., F.G.S. . .178 
 
X Contents. 
 
 FART II. 
 CHAPTER YIII. 
 
 ON THE ELEVATION OF THE EASTERN COAST OF SOUTH AMERICA. 
 
 Upraised Shells of La Plata — Bahia Blanca, Sand-dunes and 
 Pamice-pebbles — Step-formed Plains of Patagonia, with upraised 
 shells — Terrace-bounded Valley of Santa Cruz, formerly a Sea- 
 strait — Upraised shells of Tierra del Fuego — Length and breadth 
 of the elevated area — Equability of the movements, as shown by 
 the similar heights of the plains — Slowness of the elevatory pro- 
 cess — Mode of formation of the step-formed plains — Summary — 
 Great Shingle Formation of Patagonia ; its extent, origin, and 
 distribution — Formation of sea-cliffs . . . PAGE 189 
 
 CHAPTER IX. 
 
 ON THE ELEVATION OF THE WESTERN COAST OF SOUTH AMERICA. 
 
 Chonos Archipelago — Chiloe, recent and gradual elevation of, tradi- 
 tions of the inhabitants on this subject — Concepcion, earthquake 
 and elevation of. Valparaiso, great elevation of, upraised 
 shells, earth of marine origin, gradual rise of the land within the 
 historical period. Coquimbo, elevation of, in recent times ; 
 terraces of marine origin, their inclination, their escarpments 
 not horizontal — Guasco, gravel terraces of — Copiapo. Peru — 
 Upraised shells of Cobija, Iquique, and Arica — Lima, shell-beds 
 and sea-beach on San Lorenzo — Human remains, fossil earthen- 
 ware, earthquake debacle, recent subsidence — On the decay of 
 upraised shells — General summary ..... 232 
 
 CHAPTER X. 
 
 ON THE PLAINS AND VALLEYS OF CHILE : — SALIFEROUS StTPBB- 
 
 FICIAL DEPOSITS. 
 
 Basin-like plains of Chile ; their drainage, their marine origin — 
 Marks of sea-action on the eastern flanks of the Cordillera — 
 Sloping-terrace-like fringes of stratified shingle within the valleys 
 of the Cordillera ; their marine origin — Boulders in the valley of 
 the Cachapual — Horizontal elevation of the Cordillera — Forma- 
 
Contents. xi 
 
 tion of valleys — Boulders moved by earthquake-waves — Saline 
 superficial deposits — Bed of nitrate of soda at Iquique — Saline 
 incrustations — Salt-lakes of La Plata and Patagonia ; purity of 
 the salt ; its origin page 283 
 
 CHAPTER XI. 
 
 ON THE FOEMATIONS OF THE PAMPAS. 
 
 Mineralogical constitution — Microscopical structure — Buenos Ayres, 
 shells embedded in tosca-rock — Buenos Ayres to the Colorado — 
 S. Ventana — Bahia Blanca ; M. Hermoso, bones and infusoria of; 
 P. Alta, shells, bones, and infusoria of ; co-existence of the recent 
 shells and extinct mammifers — Buenos Ayres to St. Fe — 
 Skeletons of Mastodon — Infusoria — Inferior marine tertiary 
 strata, their age — Horse's tooth. Banda Oriental — Superficial 
 Pampean formation — Inferior tertiary strata, variation of, con- 
 nected with volcanic action ; Macruchenia Patachonica at S. 
 Julian in Patagonia, age of, subsequent to living mollusca and to 
 the erratic block period. Summary — Area of Pampean forma- 
 tion — Theories of origin — Source of sediment — Estuary origin — 
 Contemporaneous with existing mollusca — Kelations to under- 
 lying tertiary strata — Ancient deposit of estuary origin — Eleva- 
 tion and successive deposition of the Pampean formation — 
 Number and state of the remains of mammifers ; their habitation, 
 food, extinction, and range — Conclusion— Supplement on the 
 thickness of the Pampean Formation — Localities in Pampas at 
 which mammiferous remains have been found . . 313 
 
 CHAPTEE XII. 
 
 ON THE OLDER TERTIARY FORMATIONS OF PATAGONIA AND CHILE. 
 
 Rio Negro— S. Josef — Port Desire, white pumiceous mudstone with 
 infusoria — Port S. Julian — Santa Cruz, basaltic lava of — P. 
 Gallegos — Eastern Tierra del Fuego ; leaves of extinct beech 
 trees — Summary on the Patagonian tertiary formations — Tertiary 
 formations of the Western Coast — Chonos and Chiloe groups, 
 volcanic rocks of — Concepcion— Navidad — Coquimbo — Summary 
 — Age of the tertiary formations — Lines of elevation — Silicified 
 wood — Comparative ranges of the extinct and living Mollusca on 
 the West Coast of S. America — Climate of the tertiary period-^ 
 On the causes of the absence of recent conchiferous deposits on 
 the coasts of S. America — On the contemporaneous deposition 
 and preservation of sedimentary formations . , . 370 
 
xii Contents. 
 
 CHAPTER XIII. 
 
 PLUTONIC AND METAMORPHIC EOCKS : — CLEAVAGE AND FOLIATION. 
 
 Brazil, Bahia, gneiss with disjointed metamorphosed dikes — Strike 
 of foliation — Eio de Janeiro, gneiss-granite, embedded fragment 
 in, decomposition of — La Plata, metamorphic and old volcanic 
 rocks of — S. Ventana — Claystone porphyry formation of Pata- 
 gonia ; singular metamorphic rocks ; pseudo-dikes — Falkland 
 Islands, palaeozoic fossils of — Tierra del Fuego, clay -slate forma- 
 tion, cretaceous fossils of ; cleavage and foliation ; form of land — 
 Chonos Archipelago, mica- schists, foliation disturbed by granitic 
 axis ; dikes — Chiloe — Concepcion, dikes, successive formation of 
 — Central and Northern Chile — Concluding remarks on cleavage 
 and foliation — Their close analogy and similar origin — Strati- 
 fication of metamorphic schists — Foliation of intrusive rocks — 
 Kelation of cleavage and foliation to the lines of tension during 
 metamorphosis PAG-B 422 
 
 CHAPTER XIY. 
 
 CENTRAL CHILE : — STRUCTURE OP THE CORDILLERA. 
 
 Central Chile — Basal formations of the Cordillera — Origin of the 
 porphyritic claystone conglomerate — Andesite — Volcanic rocks 
 — Section of the Cordillera by the Peuquenes or Portillo Pass — 
 Great gypseous formation — Peuquenes line ; thickness of strata, 
 fossils of — Portillo line — conglomerate, orthitic granite, mica- 
 schist, volcanic rocks of — Concluding remarks on the denudation 
 and elevation of the Portillo line — Section by the Cumbre, or 
 Uspallata Pass — Porphyries — G-ypseous strata — Section near the 
 Puente del Inca; fossils of — Great subsidence — Intrusive por- 
 phyries — Plain of Uspallata — Section of the Uspallata chain — 
 Structure and nature of the strata — Silicified vertical trees — 
 Great subsidence — Granitic rocks of axis — Concluding remarks 
 on the Uspallata range ; origin subsequent to that of the main 
 Cordillera ; tv70 periods of subsidence ; comparison with the 
 Portillo chain 470 
 
 CHAPTER XY. 
 
 NORTHERN CHILE. — CONCLUSION. 
 
 Section from lUapel to Combarbala ; Gypseous formation with 
 silicified wood — Panuncillo — Coquimbo ; mines of Arqueros ; 
 section up^ valley; fossils — Guasco, fossils of — Copiapo section 
 
Contents. xiii 
 
 up valley ; Las Amolanas, silicified wood — conglomerates, nature 
 of former land, fossils, thickness of strata, great subsidence — 
 Valley of Despoblado, tufaceous fossils, deposit, complicated 
 dislocations of — Kelations between ancient orifices of eruption 
 and subsequent axes of injection — Iquique, Peru, fossils of, salt- 
 deposits — Metalliferous veins — Summary on the Porphyritic 
 conglomerate and Gypseous formations — Great subsidence with 
 partial elevations during the Cretaceo-oolitic period — On the 
 elevation and structure of the Cordillera — Eecapitulation on the 
 tertiary series — Relations between movements of subsidence and 
 volcanic action — Pampean formation — Recent elevatory move- 
 ments — Long-continued volcanic action in the Cordillera. Con- 
 clusion ......... PA^E 535 
 
 APPENDIX TO PAET II. 
 
 Descriptions of Tertiary Fossil Shells from South America, 
 
 by G. B. Sowerby, Esq., F.L S., &c 605 
 
 Descriptions of Secondary Fossil Shells from South America, 
 
 by Professor E. Forbes, F.R.S., &c 624 
 
 INDEX 629 
 
INSTKUCTIONS TO THE BINDER. 
 
 The Map of Ascension to be inserted at the beginning of Chap. TIL 
 The Map of South Ameeica „ „ „ Part II. 
 
 Plates I. to V. . . ,, ., end of the volume. 
 
PART I. 
 
 VOLCANIC ISLANDS 
 
 &C. 
 
 R 
 
CHAPTER I. 
 
 ST. JAGO, IN THE CAPE DE VERDE ARCHIPELAGO. 
 
 Mocks of the lowest series. — A calcareous sedimentary dejjosit, with 
 recent shells, altered hy the contact of su]^erincmnlient lava, its hori- 
 zcntality and extent — Subsequent volcanic eruptions, associated with 
 calcareous matter in an earthy and fibrous form, and often enclosed 
 within the separate cells of the scorics — Ancient and obliterated 
 orifices of eruption of small size — Difficulty of tracing over a bar 
 plain recent streams of lava — Inland hills of more ancient volcanic 
 rock — decomposed olivine in large m.asses — Feldspathic rocks beneath 
 the upper crystalline basaltic strata — Uniform structure and form of 
 the more ancient volcanic hills — Form of the valleys near the coast 
 — Conglomerate now forming on the sea heach. 
 
 The island of St. Jago extends in a NNW. and SSE. 
 direction, thirty miles in length by about twelve in 
 breadth. My observations, made during two visits, were 
 confined to the southern portion within the distance of 
 a few leagues from Porto Praya. The country, viewed 
 from the sea, presents a varied outline : smooth conical 
 hills of a reddish colour (like Red Hill in the accompany- 
 ing woodcut),^ and others less regular, flat-topped, and 
 of a blackish colour (like A, B, 0,) rise from successive, 
 step-formed plains of lava. At a distance, a chain of 
 mountains, many thousand feet in height, traverses the 
 interior of the island. There is no active volcano in 
 St, Jago, and only one in the group, namely at Fogo. 
 
 * The outline of the coast, the position of the villages, streamlets, 
 and of most of the hills in this woodcut, are copied from the chart 
 made on board H.M.S. ' Leven.' The square-topped hills (A, B C, &c.) 
 are put in merely by eye, to illustrate my description. 
 
 b2 
 
St /ago. 
 
 PART I. 
 
 The island since being inhabited has not suffered from 
 destructive earthquakes. 
 
 The lowest rocks exposed on the coast near Porto 
 Praya, are highly crystalline and compact ; they appear 
 to be of ancient, submarine, volcanic origin ; they are 
 unconformably covered by a thin, irregular, calcareous 
 deposit, abounding with shells of a late tertiary period ; 
 and this again is capped by a wide sheet of basaltic lava, 
 which has flowed in successive streams from the interior 
 
 No. 1. 
 
 Signal 
 Post Hill. 
 
 /r^ 
 
 Bibeira 
 
 G-rande. 
 
 %^-' Porto Praya. 
 PART OF ST. JAGO, ONE OP THE CAPE DE VERDE ISLANDS. 
 
 of the island, between the square-topped hills marked 
 A, B, 0, &c. Still more recent streams of lava have 
 been erupted from the scattered cones, such as Red and 
 Signal Post Hills. The upper strata of the square- 
 topped hills are intimately related in mineralogical 
 composition, and in other respects, with the lowest series 
 of the coast-rocks, with which they seem to be continuous. 
 Mineralogical description of the roc'ks of the lowest 
 series. — These rocks possess an extremely varying char- 
 acter ; they consist of black, brown and gray, compact, 
 
CHAP. I. 
 
 Calcareotts Deposit. 
 
 basaltic bases, with numerous crystals of augite, horn- 
 blende, olivine, mica, and sometimes glassy feldspar. 
 A common variety is almost entirely composed of crystals 
 of augite v^ith olivine. ]\iica, it is known, seldom occurB 
 where augite abounds ; nor probably does the present 
 case offer a real exception, for the mica (at least in my 
 best characterised specimen, in which one nodule of this 
 mineral is nearly half an inch in length,) is as perfectly 
 rounded as a pebble in a conglomerate, and evidently 
 has not been crystallised in the base, in which it is now 
 inclosed, but has proceeded from the fusion of some pre- 
 existing rock. These compact lavas alternate with tuffs, 
 amygdaloids and wacke, and in some places with coarse 
 conglomerate. Some of the argillaceous wackes are of 
 a dark green colour, others, pale yellowish-green, and 
 others nearly white ; I was surprised to find that some 
 of the latter varieties, even where whitest, fused into a 
 jet black enamel, whilst some of the green varieties 
 afforded only a pale gray bead. Numerous dikes, con- 
 sisting chiefly of highly compact augitic rocks, and of 
 gray amygdaloidal varieties, intersect the strata, which 
 have in several places been dislocated with considerable 
 violence, and thrown into highly-inclined positions. 
 One line of disturbance crosses the northern end of 
 Quail Island, (an islet in the bay of Porto Praya) and 
 can be followed to the mainland. These disturbances 
 took place before the deposition of the recent sediment- 
 ary bed ; and the surface, also, had previously been 
 denuded to a great extent, as is shown by many trun- 
 cated dikes. 
 
 Descrijption of the calcareous deposit overlying tlie 
 foregoing volcanic rochs. — This stratum is very con- 
 spicuous from its white colour, and from the extreme 
 regularity with which it ranges in a horizontal line for 
 some miles along the coast. Its average height above 
 
6 S^. J^S^' i*^^T I. 
 
 the sea, measured from the upper line of junction with 
 the superincumbent basaltic lava, is about sixty feet ; 
 and its thickness, although varying much from the 
 inequalities of the underlying formation, may be esti- 
 mated at about twenty feet. It consists of quite white 
 calcareous matter, partly composed of organic debris, 
 and partly of a substance which may be aptly compared 
 in appearance with mortar. Fragments of rock and 
 pebbles are scattered throughout this bed, often forming, 
 especially in the lower part, a conglomerate. Many 
 of the fragments of rock are whitewashed with a thin 
 coating of calcareous matter. At Quail Island, the 
 calcareous deposit is replaced in its lowest part by a 
 soft, brown, earthy tuff, full of Turritellse ; this is 
 covered by a bed of pebbles, passing into sandstone, and 
 miixed with fragments of echini, claws of crabs, and 
 shells; the oyster shells still adhering to the rock on 
 which they grew. Numerous white balls appearing like 
 pisolitic concretions, from the size of a walnut to that of 
 an apple, are embedded in this deposit ; they usually 
 have a small pebble in their centres. Although so like 
 concretions, a close examination convinced me that they 
 were Nulliporse, retaining their proper forms, but with 
 their surfaces slightly abraded : these bodies (plants as 
 they are now generally considered to be) exhibit under a 
 microscope of ordinary power, no traces of organisation 
 in their internal structure. Mr. George R. Sowerby 
 has been so good as to examine the shells which I col- 
 lected : there are fourteen species in a sufficiently perfect 
 condition for their characters to be made out with some 
 degree of certainty, and four which can be referred only 
 to their genera. Of the fourteen shells, of which a list 
 is given in the Appendix, eleven are recent species ; one, 
 though undescribed, is perhaps identical with a species 
 which I found living in the harbour of Porto Praya ; 
 
CHAP. I. Calcareous Deposit altered by Heat. 7 
 
 the two remaining species are unknown, and have been 
 described by Mr. Sowerby. Until the shells of this 
 Archipelago and of the neighbouring coasts are better 
 known, it would be rash to assert that even these two 
 latter shells are extinct. The number of species which 
 certainly belong to existing kinds, although few in 
 number, are sufficient to show that the deposit belongs 
 to a late tertiary period. From its mineralogical char- 
 acter, from the number and size of the embedded 
 fragments, and from the abundance of Patellge, and 
 other littoral shells, it is evident that the whole was 
 accumulated in a shallow sea, near an ancient coast-line. 
 Effects produced by the floiuing of the sujperincum- 
 hent hascdtic lava over the calcareous deposit. — These 
 effects are very curious. The calcareous matter is altered 
 to the depth of about a foot beneath the line of junction ; 
 and a most perfect gradation can be traced, from loosely 
 aggregated, small, particles of shells, corallines, and 
 NuUiporse, into a rock, in which not a trace of mechani- 
 cal origin can be discovered, even with a microscope. 
 Where the metamorphic change has been greatest, two 
 varieties occur. The first is a hard, compact, white, 
 fine grained rock, striped with a few parallel lines of 
 black volcanic particles, and resembling a sandstone, 
 but which, upon close examination, is seen to be crystal- 
 lised throughout, with the cleavages so perfect that they 
 can be readily measured by the reflecting goniometer. 
 In specimens, where the change has been less complete, 
 when moistened and examined under a strong lens, the 
 most interesting gradation can be traced, some of th© 
 rounded particles retaining their j)roper forms, and others 
 insensibly melting into the gi-anulo-crystalline paste. 
 The weathered surface of this stone, as is so frequently 
 the case with ordinary limestones, assumes a brick-red 
 colour. 
 
8 SL J ago. 
 
 PART I. 
 
 The second metamorphosed variety is likewise a hard 
 rock, but without any crystalline structure. It consists 
 of a white, opaque, compact, calcareous stone, thickly 
 mottled w^ith rounded, though regular, spots of a soft, 
 earthy, ochraceous substance. This earthy matter is of 
 a pale yellowish-brown colour, and appears to be a mix- 
 ture of carbonate of lime with iron ; it effervesces with 
 acids, is infusible, but blackens under the blowpipe, and 
 becomes magnetic. The rounded form of the minute 
 patches of earthy substance, and the steps in the progress 
 of their perfect formation, which can be followed in a 
 suit of specimens, clearly show that they are due either 
 to some power of aggregation in the earthy particles 
 amongst themselves, or more probably to a strong at- 
 traction between the atoms of the carbonate of lime, 
 and consequently to the segregation of the earthy ex- 
 traneous matter. I was much interested by this fact, 
 because I have often seen quartz rocks (for instance, in 
 the Falkland Islands, and in the lower Silurian strata of 
 the Stiper-stones in Shropshire), mottled in a precisely 
 analogous manner, with little spots of a white, earthy 
 substance (earthy feldspar ?) ; and these rocks, there 
 was good reason to suppose, had undergone the action of 
 heat, — a view which thus receives confirmation. This 
 spotted structure may possibly afford some indication in 
 distinguishing those formations of quartz, which owe 
 their present structure to igneous action, from those pro- 
 duced by the agency of water alone : a source of doubt, 
 which I should think from my own experience, that 
 most geologists, when examining arenaceo-quartzose dis- 
 tricts, must have experienced. 
 
 The lowest and most scoriaceous part of the lava, in 
 rolling over the sedimentary deposit at the bottom of 
 the sea, has caught up large quantities of calcareous 
 matter, which now forms a snow-white, highly crystalline, 
 
CHAP. I. Calcareous Deposit altei^ed by Heat. 9 
 
 basis to a breccia, including small pieces of black, glossy 
 scorige. A little above this, where the lime is less abun- 
 dant, and the lava more compact, numerous little balls, 
 composed of spicula of calcareous spar, radiating from 
 common centres, occupy the interstices. In one part of 
 Quail Island, the lime has thus been crystallised by the 
 heat of the superincumbent lava, where it is only 
 thirteen feet in thickness ; nor had the lava been origi- 
 nally thicker, and since reduced by degradation, as could 
 be told from the degree of cellularity of its surface. I 
 bave already observed that the sea must have been 
 shallow in which the calcareous deposit was accumulated. 
 In this case, therefore, the carbonic acid gas has been 
 retained under a pressure, insignificant compared with 
 that (a column of water, 1708 feet in height) originally 
 supposed by Sir James Hall to be requisite for this 
 «nd : but since his experiments, it has been discovered 
 that pressure has less to do with the retention of carbonic 
 acid gas, than the nature of the circumjacent atmo- 
 sphere ; and hence, as is stated to be the case by Mr. 
 Faraday,^ masses of limestone are sometimes fused and 
 crystallised even in common lime-kilns. Carbonate of 
 lime can be heated to almost any degree, according to 
 Faraday, in an atmosphere of carbonic acid gas, without 
 being decomposed ; and Gay-Lussac found that frag- 
 ments of limestone, placed in a tube and heated to a 
 -degree, not sufficient by itself to cause their decomposi- 
 tion, yet immediately evolved their carbonic acid, when 
 a stream of common air or steam was passed over them : 
 Gay-Lussac attributes this to the mechanical displace- 
 ment of the nascent carbonic acid gas. The calcareous 
 
 ' I am much indebted to Mr. E. W. Brayley in having given me 
 the following references to papers on this subject : Faraday, in the 
 
 * Edinburgh New Philosophical Journal,' vol. xv. p. 398 ; Gay-Lussac, 
 in ' Annales de Chem. et Phys.,' torn. Ixiii. p. 219, translated in the 
 
 * London and Edinburgh Philosophical Magazine,' vol. x. p. 496. 
 
lo St. J ago. 
 
 PART I. 
 
 matter beneatti the lava, and especially that forming the 
 crystalline spicula between the interstices of the scoriae, 
 although heated in an atmosphere probably composed 
 chiefly of steam, could not have been subjected to the 
 effects of a passing stream ; and hence it is, perhaps^ 
 that they have retained their carbonic acid, under a 
 small amount of pressure. 
 
 The fragments of scorige, embedded in the crystalline 
 calcareous basis, are of a jet black colour, with a glossy 
 fracture like pitchstone. Their surfaces, however, are 
 coated with a layer of a reddish-orange, translucent 
 substance, which can easily be scratched with a knife \ 
 hence they appear as if overlaid by a thin layer of rosin. 
 Some of the smaller fragments are partially changed 
 throughout into this substance : a change which appears 
 quite different from ordinary decomposition. At the 
 Galapagos Archipelago (as will be described in a future 
 chapter), great beds are formed of volcanic ashes and 
 particles of scoriae, which have undergone a closely^ 
 similar change. 
 
 The extent and liorizontcdity of the calcareous stratum^ 
 — The upper line of surface of the calcareous stratum, 
 which is so conspicuous from being quite white and so 
 nearly horizontal, ranges for miles along the coast, at 
 the height of about sixty feet above the sea. The sheet 
 of basalt, by which it is capped, is on an average eighty 
 feet in thickness. Westward of Porto Praya beyond 
 Red Hill, the white stratum with the superincumbent 
 basalt is covered up by more recent streams. North- 
 ward of Signal Post Hill, 1 could follow it with my 
 eye, trending away for several miles along the sea cliffs. 
 The distance thus observed is about seven miles ; but 
 I cannot doubt from its regularity that it extends much 
 farther. In some ravines at right angles to the coast,, 
 it is seen gently dipping towards the sea, probably witk 
 
CHAP. I. Calcareous Horizontal Deposit. 1 1 
 
 the same inclination as wlien deposited round tlie 
 ancient shores of the island. I found only one inland 
 section, namely, at the base of the hill marked A, where, 
 at the height of some hundred feet, this bed was ex- 
 posed ; it here rested on the usual compact augitic rock 
 associated with wacke, and was covered by the wide- 
 spread sheet of modern basaltic lava. Some exceptions 
 occur to the horizontality of the white stratum : at 
 Quail Island, its upper surface is only forty feet above 
 the level of the sea ; here also the capping of lava is 
 only between twelve and fifteen feet in thickness ; on 
 the other hand, at the NE. side of Porto Pray a 
 harbour, the calcareous stratum, as well as the rock on 
 which it rests, attain a height above the average level : 
 the inequality of level in these two cases is not, as I 
 believe, owing to unequal elevation, but to original 
 irregularities at the bottom of the sea. Of this fact, at 
 Quail Island, there was clear evidence in the calcareous 
 deposit being in one part of much greater than the 
 average thickness, and in another part being entirely 
 absent; in this latter case, the modern basaltic lavas 
 rested directly on those of more ancient origin. 
 
 Under Signal Post Hill, the white stratum dips 
 into the sea in a remarkable manner. This hill is 
 conical, 450 feet in height, and retains some traces of 
 having had a crateriform structure ; it is composed 
 chiefly of matter erupted posteriorly to the elevation of 
 the great basaltic plain, but partly of lava of apparently 
 submarine origin and of considerable antiquity. The 
 surrounding plain, as well as the eastern flank of this 
 hill, have been worn into steep precipices, overhanging 
 the sea. In these precipices, the white calcareous 
 stratum may be seen, at the height of about 70 feet 
 above the beach, running for some miles both north- 
 ward and southward of the hill, in a line appearing to 
 
I 2 St J^R'O- 
 
 PART I. 
 
 be perfectly horizontal ; but for a space of a quarter of 
 a mile directly under the hill, it dips into the sea and 
 disappears. On the south side the dip is gradual, on 
 the north side it is more abrupt, as is shown in the 
 woodcut. As neither the calcareous stratum, nor the 
 
 No. 2. 
 
 SIGNAL POST HILL. 
 
 A— Ancient volcanic rocks. B— Calcareous stratum. 
 
 — Upper basaltic lava. 
 
 superincumbent basaltic lava (as far as the latter can 
 be distinguished from the more modern ejections), 
 appear to thicken as they dip, I infer that these strata 
 were not originally accumulated in a trough, the 
 centre of which afterwards became a point of eruption ; 
 but that they have subsequently been disturbed and 
 bent. We may suppose either that Signal Post Hill 
 subsided after its elevation with the surrounding country, 
 or that it never was uplifted to the same height with it. 
 This latter seems to me the most probable alternative, 
 for during the slow and equable elevation of this portion 
 of the island, the subterranean motive power, from ex- 
 pending part of its force in repeatedly erupting volcanic 
 matter from beneath this point, would, it is likely, have 
 less force to uplift it. Something of the same kind 
 seems to have occurred near Eed Hill, for when tracing 
 upwards the naked streams of lava from near Porto 
 Praya towards the interior of the island, I was strongly 
 induced to suspect, that since the lava had flowed, the 
 slope of the land had been slightly modified, either by a 
 small subsidence near Red Hill, or by that portion of 
 the plain having been uplifted to a less height during 
 the elevation of the whole area. 
 
CHAP. I. Calcai^eotts Deposit, 13 
 
 The hasaltic lava, superincmnbent on the calcareous 
 deposit. — This lava is of a pale gray colour, fusing 
 into a black enamel; its fracture is rather earthy 
 and concretionary ; it contains olivine in small grains. 
 The central parts of the mass are compact, or at most 
 crenulated with a few minute cavities, and are often 
 columnar. At Quail Island this structure was assumed 
 in a striking manner; the lava in one part being 
 divided into horizontal laminaB, which became in another 
 part split by vertical fissures into five-sided plates ; and 
 these again, being piled on each other, insensibly 
 became soldered together, forming fine symmetrical 
 columns. The lower surface of the lava is vesicular 
 but sometimes only to the thickness of a few inches • 
 the upper surface, which is likewise vesicular, is divided 
 into balls, frequently as much as three feet in diameter 
 made up of concentric layers. The mass is composed of 
 more than one stream ; its total thickness being, on an 
 average, about eighty feet : the lower portion has cer- 
 tainly flowed beneath the sea, and probably likewise the 
 upper portion. The chief part of this lava has flowed 
 from the central districts, between the hills marked 
 A, B, 0, &c. in the woodcut-map. The surface of the 
 country, near the coast, is level and barren ; towards 
 the interior, the land rises by successive terraces, of 
 which four, when viewed from a distance, could be 
 distinctly counted. 
 
 Volcanic eruptions subsequent to the elevation of 
 the coastland ; the ejected matter associated with ea/t^thy 
 lime. — These recent lavas have proceeded from those 
 scattered, conical, reddish-coloured hills, which rise 
 abruptly from the plain-country near the coast. I 
 ascended some of them, but will describe only one, 
 namely, Red Hill, which may serve as a type of its class, 
 and is remarkable in some especial respects. Its height 
 
1 4 S^, J^S^- 
 
 PART I. 
 
 is about 600 feet ; it is composed of bright red, highly 
 scoriaceous rock of a basaltic nature ; on one side of its 
 summit there is a hollow, probably the last remnant of 
 a crater. Several of the other hills of this class, judging 
 from their external forms, are surmounted by much 
 more perfect craters. When sailing along the coast, it 
 was evident that a considerable body of lava had flowed 
 from Ked Hill, over a line of cliff about 120 feet ii; 
 height, into the sea : this line of cliflF is continuous 
 with that forming the coast, and bounding the plain on 
 both sides of this hill ; these streams, therefore, were 
 erupted, after the formation of the coast-clifis, from 
 Red Hill, when it must have stood, as it now does, 
 above the level of the sea. This conclusion accords 
 with the highly scoriaceous condition of all the rock on 
 it, appearing to be of subaerial formation ; and this is 
 important, as there are some beds of calcareous matter 
 near its summit, which might, at a hasty glance, have 
 been mistaken for a submarine deposit. These beds 
 consist of white, earthy, carbonate of lime, extremely 
 friable so as to be crushed with the least pressure ; the 
 most compact specimens not resisting the strength of 
 the fingers. Some of the masses are as white as quick- 
 lime, and appear absolutely pure ; but on examining 
 them with a lens, minute particles of scoriae can always 
 be seen, and I could find none which, when dissolved in 
 acids, did not leave a residue of this nature. It is, 
 moreover, difficult to find a particle of the lime which 
 does not change colour under the blowpipe, most of 
 them even becoming glazed. The scoriaceous frag- 
 ments and the calcareous matter are associated in the 
 most irregular manner, sometimes in obscure beds, but 
 more generally as a confused breccia, the lime in some 
 parts and the scoriae in others being most abundant. 
 Sir H. De la Beche has been so kind as to have some oi 
 
CHAP. I. Calcareous Matter entangled in Lava. 1 5 
 
 the purest specimens analysed, with a view to discover, 
 considering their volcanic origin, whether they con- 
 tained much magnesia ; but only a small portion was 
 found, such as is present in most limestones. 
 
 Fragments of the scoriae embedded in the calcareous 
 mass, when broken, exhibit many of their cells lined 
 and partly filled with a white, delicate, excessively 
 fragile, moss-like, or rather conferva-like, reticulation 
 of carbonate of lime. These fibres, examined under a 
 lens of one-tenth of an inch focal distance, appear 
 cylindrical ; they are rather above the xoVo ^^ ^^ inch 
 in diameter ; they are either simply branched, or more 
 commonly united into an irregular mass of net-work, 
 with the meshes of very unequal sizes and of unequal 
 numbers of sides. Some of the fibres are thickly 
 covered with extremely minute spicula, occasionally 
 aggregated into little tufts ; and hence they have a 
 hairy appearance. These spicula are of the same dia- 
 meter throughout their length ; they are easily detached, 
 so that the object-glass of the microscope soon becomes 
 scattered over with them. Within the cells of many 
 fragments of the scoria3, the lime exhibits this fibrous 
 structure, but generally in a less perfect degree. These 
 cells do not appear to be connected with one another. 
 There can be no doubt, as will presently be shown, that 
 the lime was erupted, mingled with the lava in its fluid 
 state ; and therefore I have thought it worth while to 
 describe minutely this curious fibrous structure, of which 
 I know nothing analogous. From the earthy condition 
 of the fibres, this structure does not appear to be related 
 to crystallisation. 
 
 Other fragments of the scoriaceous rock from this 
 hill, when broken, are often seen marked with short and 
 irregular white streaks, which are owing to a row of 
 separate cells being partly, or quite, filled with white 
 
1 6 S^. J ago. 
 
 PAET I. 
 
 calcareous powder. This structure immediately re- 
 minded me of tlie appearance in badly kneaded doughy 
 of balls and drawn-out streaks of flour, which have re- 
 mained unmixed with the paste ; and I cannot doubt 
 that small masses of the lime, in the same manner re- 
 maining unmixed with the fluid lava, have been drawn 
 out when the whole was in motion. I carefully ex- 
 amined, by trituration and solution in acids, pieces of 
 the scoriae, taken from within half-an-inch of those celLs 
 which were filled with the calcareous powder, and they 
 did not contain an atom of free lime. It is obvious 
 that the lava and lime have on a large scale been very 
 imperfectly mingled ; and where small portions of the 
 lime have been entangled within a piece of the viscid 
 lava, the cause of their now occupying, in the form of 
 a powder or of a fibrous reticulation, the vesicular 
 cavities, is, I think, evidently due to the confined gases 
 having most readily expanded at the points where the 
 incoherent lime rendered the lava less adhesive. 
 
 A mile eastward of the town of Praya, there is 
 a steep-sided gorge, about 150 yards in width, cutting 
 through the basaltic plain and underlying beds, but 
 since filled up by a stream of more modern lava. This 
 lava is dark gray, and in most parts compact and rudely 
 columnar; but at a little distance from the coast, it 
 includes in an irregular manner a brecciated mass of 
 red scoriae mingled with a considerable quantity of 
 white, friable, and in some parts, nearly pure earthy 
 lime, like that on the summit of Red Hill. This lava, 
 with its entangled lime, has certainly flowed in the 
 form of a regular stream ; and, judging from the shape 
 of the gorge, towards which the drainage of the country 
 (feeble though it now be) still is directed, and from the 
 appearance of the bed of loose water-worn blocks with 
 their interstices unfilled, like those in the bed of a 
 
CHAP. I. Calcareous Matter entangledin Lava. 17 
 
 torrent, on wliicli the lava rests, we may conclude that 
 the stream was of snbaerial origin. I was unable to 
 trace it to its source, but, from its direction, it seemed 
 to have come from Signal Post Hill, distant one mile 
 and a quarter, which, like Hed Hill, has been a point 
 of eruption subsequently to the elevation of the great 
 basaltic plain. It accords with this view, that I found 
 on Signal Post Hill, a mass of earthy, calcareous matter 
 of the same nature, mingled with scorise. I may here 
 observe that part of the calcareous matter forming the 
 horizontal sedimentary bed, especially the finer matter 
 with which the embedded fragments of rock are white- 
 washed, has probably been derived from similar volcanic 
 eruptions, as well as from triturated organic remains : 
 the underlying, ancient, crystalline rocks, also, are as- 
 sociated with much carbonate of lime, filling amygda- 
 loidal cavities, and forming irregular masses, the nature 
 of which latter I was unable to understand. 
 
 Considering the abundance of earthy lime near the 
 summit of Red Hill, a volcanic cone 600 feet in height, 
 of subaerial growth, — considering the intimate manner 
 in which minute particles and large masses of scorias 
 are embedded in the masses of nearly pure lime, and 
 on the other hand, the manner in which small kernels 
 and streaks of the calcareous powder are included in 
 solid pieces of the scoria, — considering, also, the similar 
 occurrence of lime and scoriae within a stream of lava, 
 also supposed, with good reason, to have been of modern 
 subaerial origin, and to have flowed from a hill, where 
 earthy lime also occurs : I think, considering these 
 facts, there can be no doubt that the lime has been 
 erupted, mingled with the molten lava. I am not 
 aware that any similar case has been described : it 
 appears to me an interesting one, inasmuch as most 
 geologists must have speculated on the probable 
 
 c 
 
 r 
 
1 8 SL y^£'^' 
 
 PAET I. 
 
 ejffects of a volcanic focus, bursting through deep-seated 
 beds of different mineralogical composition. The gi'eat 
 abundance of free silex in the trachytes of some coun- 
 tries (as described by Beudant in Hungary, and by 
 P. Scrope in the Panza Islands), perhaps solves the en- 
 quiry with respect to deep-seated beds of quartz ; and 
 we probably here see it answered, where the volcanic 
 action has invaded subjacent masses of limestone. One 
 is naturally led to conjecture in what state the now 
 earthy carbonate of lime existed, when ejected with the 
 intensely heated lava : from the extreme cellularity of 
 the scoria3 on Red Hill, the pressure cannot have been 
 great, and as most volcanic eruptions are accompanied 
 by the emission of large quantities of steam and other 
 gases, we here have the most favourable conditions, 
 according to the views at present entertained by 
 3hemists, for the expulsion of the carbonic acid.^ Has 
 the slow re-absorption of this gas, it may be asked, 
 given to the lime in the cells of the lava, that pecuKar 
 fibrous structure, like that of an efflorescing salt ? 
 Finally, I may remark on the great contrast in appear- 
 ance between this earthy lime, which must have been 
 heated in a free atmosphere of steam and other gases, 
 with the white, crystalline, calcareous spar, produced by 
 a single thin sheet of lava (as at Quail Island) rolling 
 over similar earthy lime and the debris of organic 
 remains, at the bottom of a shallow sea. 
 
 Signal Post Hill. — This hill has already been 
 
 ^ Whilst deep beneath the surface, the carbonate of lime was, I 
 presume, in a fluid state. Hutton, it is known, thought that all 
 amygdaloids were produced by drops of molten limestone floating 
 in the trap, like oil in water : this no doubt is erroneous, but if the 
 matter forming the summit of Eed Hill had been cooled under the 
 pressure of a moderately deep sea, or within the walls of a dike, 
 we should, in all probability, have had a trap rock associated with 
 large masses of compact, crystalline, calcareous spar, which, accord- 
 ing to the views entertained by many geologists, would have been 
 wrongly attributed to subsequent infiltration. 
 
CHAP. I. Small Orifices of Ertiption. 19 
 
 several times mentionedj especially with reference to 
 tte remarkable manner in whicli the white calcareous 
 stratum, in other parts so horizontal (Woodcut No. 2), 
 dips under it into the sea. It is a broad summit, with 
 obscure traces of a crateriform structure, and is com- 
 posed of basaltic rocks,^ some compact, others highly 
 cellular, with inclined beds of loose scoriee, of which 
 some are associated with earthy lime. Like Red Hill, 
 it has been the source of eruptions, subsequently to the 
 elevation of the surrounding basaltic plain ; but unlike 
 that hill, it has undergone considerable denudation, 
 and has been the seat of volcanic action at a remote 
 period, when beneath the sea. I judge of this latter 
 circumstance from finding on its inland flank the last 
 remnants of three small points of eruption. These 
 points are composed of glossy scoriae, cemented by 
 crystalline calcareous spar, exactly like the great sub- 
 marine calcareous deposit, where the heated lava has 
 rolled over it : their demolished state can, I think, be 
 explained only by the denuding action of the waves of 
 the sea. I was guided to the first orifice by observing 
 a sheet of lava, about 200 yards square, with steepish 
 sides, superimposed on the basaltic plain, with no adjoin- 
 ing hillock, whence it could have been erupted ; and 
 the only trace of a crater which I was able to discover, 
 consisted of some inclined beds of scorias at one of its 
 corners. At the distance of fifty yards from a second 
 level-topped patch of lava, but of much smaller size, I 
 
 ' Of these, one common variety is remarkable for being full of 
 small fragments of a dark jasper-red earthy mineral, which, when 
 examined carefully, shows an indistinct cleavage ; the little frag- 
 ments are elongated in form, are soft, are magnetic before and after 
 being heated, and fuse with difficulty into a dull enamel. This 
 mineral is evidently closely related to the oxides of iron, but I 
 cannot ascertain what it exactly is. The rock containing this 
 mineral is crenulated with small angular cavities, which are lined 
 and filled with yellowish crystals of carbonate of lime. 
 
 C2 
 
20 St. J ago. 
 
 PART I. 
 
 found an irregular circular group of masses of cemented, 
 scoriaceous breccia, about six feet in height, whicli 
 doubtless bad once formed the point of eruption. The 
 third orifice is now marked only by an irregular circle 
 of cemented scoriae, about four yards in diameter, and 
 rising in its highest point scarcely three feet above the 
 level of the plain, the surface of which, close ail round, 
 exhibits its usual appearance : here we have a hori- 
 zontal basal section of a volcanic spiracle, which, to- 
 gether with all its ejected matter, has been almost 
 totally obliterated. 
 
 The stream of lava, which fills the narrow gorge ^ 
 eastward of the town of Praya, judging from its course, 
 seems, as before remarked, to have come from Signal 
 Post Hill, and to have flowed over the plain, after its 
 elevation : the same observation applies to a stream 
 (possibly part of the same one) capping the sea cliffs, a 
 little eastward of the gorge. When I endeavoured to 
 follow these streams over the stony level plain, which is 
 almost destitute of soil and vegetation, I was much 
 surprised to find, that although composed of hard 
 basaltic matter, and not having been exposed to marine 
 denudation, all distinct traces of them soon become 
 utterly lost. But I have since observed at the Gala- 
 pagos Archipelago, that it is often impossible to follow 
 even great deluges of quite recent lava across older 
 * streams, except by the size of the bushes growing on 
 them, or by the comparative states of glossiness of their 
 surfaces, — characters which a short lapse of time would 
 be sufficient quite to obscure. I may remark, that in a 
 country, with a dry climate, and with the wind blowing 
 
 V The sides of this gorge, where the upper basaltic stratum is 
 intersected, are almost periDendicular. The lava, which has since 
 filled it up, is attached to these sides, almost as firmly as a dike is to 
 its walls. In most cases, where a stream of lava has flowed down a 
 valley, it is bounded on each side by loose scoriaceous masses. 
 
cHAr. J. Ancie^it Volcanic Hills. 21 
 
 always in one direction (as at the Cape de Verde Archi- 
 pelago), tlie effects of atmosplieric degradation are pro- 
 bably much greater than would at first be expected ; 
 for soil in this case accumulates only in a few protected 
 hollows, and being blown in one direction, it is always 
 travelling towards the sea in the form of the finest dust, 
 leaving the surface of the rocks bare, and exposed to 
 the full effects of renewed meteoric action. 
 
 Inland hills of more ancient volcanic rochs. — These 
 hills are laid down by eye, and marked as A, B, C, &c., 
 in the woodcut-map. They are related in mineralogical 
 composition, and are probably directly continuous with 
 the lowest rocks exposed on the coast. These hills, 
 viewed from a distance, appear as if they had once 
 formed part of an irregular table-land, and from their 
 corresponding structure and composition this probably 
 has been the case. They have flat, slightly inclined 
 summits, and are, on an average, about 600 feet in 
 height ; they present their steepest slope towards the 
 interior of the island, from which point they radiate 
 outwards, and are separated from each other by broad 
 and deep valleys, through which the great streams of 
 lava, forming the coast-plains, have descended. Their 
 inner and steeper escarpments are ranged in an ir- 
 regular curve, which rudely follows the line of the shore, 
 two or three miles inland from it. I ascended a few of 
 these hills, and from others, which I was able to examine 
 with a telescope, I obtained specimens, through the 
 kindness of Mr. Kent, the assistant-surgeon of the 
 ' Beagle '; although by these means I am acquainted with 
 only apart of the range, five or six miles in length, yet 
 I scarcely hesitate, from their uniform structure, to 
 aflirm that they are parts of one great formation, stretch- 
 ing round much of the circumference of the island. 
 
 The upper and lower strata of these hills differ 
 
2 2 St J ago. 
 
 PART I. 
 
 greatly in composition. The upper are basaltic, gener- 
 ally compact, but sometimes scoriaceous and amygda- 
 loidal, with associated masses of wacke : where the basalt 
 is compact, it is either fine-grained or very coarsely 
 crystallised ; in the latter case it passes into an augitic 
 rock, containing much olivine ; the olivine is either 
 colourless, or of the usual yellow and dull reddish 
 shades. On some of the hills, beds of calcareous matter, 
 both in an earthy and in a crystalline form, including 
 fragments of glossy scorige, are associated with the 
 basaltic strata. These strata differ from the streams of 
 basaltic lava forming the coast-plains, only in being 
 more compact, and in the crystals of augite, and in the 
 grains of olivine being of much greater size ; — characters 
 which, together with the appearance of the associated 
 calcareous beds, induce me to believe that they are of 
 submarine formation. 
 
 Some considerable masses of wacke, which are 
 associated with these basaltic strata, and which likewise 
 occur in the basal series on the coast, especially at 
 Quail Island, are curious. They consist of a pale 
 yellowish-green argillaceous substance, of a crumbling 
 texture when dry, but unctuous when moist : in its 
 purest form, it is of a beautiful green tint, with 
 translucent edges, and occasionally with obscure traces 
 of an original cleavage. Under the blowpipe it fuses 
 very readily into a dark gray, and sometimes even black 
 bead, which is slightly magnetic. From these char- 
 acters, I naturally thought that it was one of the pale 
 species, decomposed, of the genus augite ; —a conclusion 
 supported by the unaltered rock being full of large 
 separate crystals of black augite, and of balls and 
 irregular streaks of dark gray augitic rock. As the 
 basalt ordinarily consists of augite, and of olivine often 
 tarnished and of a dull red colour, I was led to examine 
 
CHAP. I. Ancient Volcanic Hills. 23 
 
 the stages of decomposition of this latter mineral, and 
 I found, to my surprise, that I could trace a nearly- 
 perfect gradation from unaltered olivine to the green 
 wacke. Part of the same grain under the blowpipe 
 would in some instances behave like olivine, its colour 
 being only slightly changed, and part would give a 
 black magnetic bead. Hence I can have no doubt that 
 the greenish wacke originally existed as olivine ; but 
 great chemical changes must have been effected during 
 the act of decomposition thus to have altered a very 
 hard, transparent, infusible mineral, into a soft, unctu- 
 ous, easily melted, argillaceous substance.^ 
 
 The basal strata of these hills, as well as some 
 neighbouring, separate, bare, rounded hillocks, consist 
 of compact, fine-grained, non-crystalline (or so slightly 
 as scarcely to be perceptible,) ferruginous feldspathic 
 rocks, and generally in a state of semi-decomposition. 
 Their fracture is exceedingly irregular, and splintery; 
 yet small fragments are often very tough. They 
 contain much ferruginous matter, either in the form of 
 minute grains with a metallic lustre, or of brown hair- 
 like threads : the rock in this latter case assuming a 
 pseudo-brecciated structure. These rocks sometimes 
 contain mica and veins of agate. Their rusty brown or 
 yellowish colour is partly due to the oxides of iron, but 
 
 * D'Aubuisson, 'Traite de Geognosie ' (torn. ii. p. 569), mentions, 
 on the authority of M. Marcel cle Serres, masses of green earth near 
 Montpellier, which are supposed to be due to the decomposition of 
 olivine. I do not, however, find, that the action of this mineral 
 under the blowpipe being entirely altered, as it becomes decom- 
 posed, has been noticed ; and the knowledge of this fact is im- 
 portant, as at first it appears highly improbable that a hard, 
 transparent, refractory mineral should be changed into a soft, 
 easily-fused, clay, like this of St. Jago, I shall hereafter describe 
 a green substance, forming threads within the cells of some vesicular 
 basaltic rocks in Van Diemeu's Land, which behave under the blow- 
 pipe like the green wacke of St. Jago ; but its occurrence in 
 cylindrical threads, shows it cannot have resulted from the decom- 
 position of olivine, a mineral always existing in the form of grains 
 or crystals. 
 
24 SL J^S^' 
 
 PAET I. 
 
 chiefly to innumerable, microscopically minute, black 
 specks, wliick, wben a fragment is heated, are easily 
 fused, and evidently are either hornblende or augite. 
 These rocks, therefore, although at first appearing like 
 baked clay or some altered sedimentary deposit, contain 
 all the essential ingredients of trachyte ; from which 
 they differ only in not being harsh, and in not con- 
 taining crystals of glassy feldspar. As is so often 
 the case with trachytic formation, no stratification is 
 here apparent. A person would not readily believe that 
 these rocks could have flowed as lava ; yet at St. Helena 
 there are well characterised streams (as will be described 
 in an ensuing chapter) of nearly similar composition. 
 Amidst the hillocks composed of these rocks, I found in 
 three places, smooth conical hills of phonolite, abound- 
 ing with fine crystals of glassy feldspar, and with needles 
 of hornblende. These cones of phonolite, I believe, 
 bear the same relation to the surrounding feldspathic 
 strata which some masses of coarsely crystallised augitic 
 rock, in another part of the island, bear to the surround- 
 ing basalt, namely, that both have been injected. The 
 rocks of a feldspathic nature being anterior in origin ta 
 the basaltic strata, which cap them, as well as to the 
 basaltic streams of the coast-plains, accords with the 
 usual order of succession of these two grand divisions of 
 the volcanic series. 
 
 The strata of most of these hills in the upper part, 
 where alone the planes of division are distinguishable, 
 are inclined at a small angle from the interior of the 
 island towards the sea-coast. The inclination is not the 
 same in each hill ; in that marked A it is less than 
 in B, D, or E ; in C the strata are scarcely deflected 
 from a horizontal plane, and in F (as far as I could 
 judge without ascending it) they are slightly inclined 
 in a reverse direction, that is, inwards and towards the 
 
CHAP. T. Valleys near the Coast. 25 
 
 centre of the island. Notwitlistanding these differences 
 of inclination, their correspondence in external form, 
 and in the composition both of their npper and lower 
 parts, — their relative position in one curved line, with 
 their steepest sides turned inwards, — all seem to show 
 that they originally formed parts of one platform ; 
 which platform, as before remarked, probably extended 
 round a considerable portion of the circumference of 
 the island. The upper strata, certainly flowed as lava, 
 and probably beneath the sea, as perhaps did the lower 
 feldspathic masses : how then come these strata to 
 hold their present position, and whence were they 
 erupted ? 
 
 In the centre of the island ^ there are lofty moun- 
 tains, but they are separated from the steep inland 
 flanks of these hills by a wide space of lower country : 
 the interior mountains, moreover, seem to have been 
 the source of those great streams of basaltic lava which, 
 contracting as they pass between the bases of the hills 
 in question, expand into the coast-plains. Round the 
 shores of St. Helena there is a rudely-formed ring of 
 basaltic rocks, and at Mauritius there are remnants of 
 another such a ring round part, if not round the whole, 
 of the island ; here again the same question immediately 
 occurs, how come these masses to hold their present 
 position, and whence were they erupted? The same 
 answer, whatever it may be, probably applies in these 
 three cases ; and in a future chapter we shall recur to 
 this subject. 
 
 Valleys near the coast. — These are broad, very flat, 
 
 ' I saw very little of the inland parts of the island. Near the 
 village of St. Domingo, there are magnificent cliffs of rather coarsely 
 crystallised basaltic lava. Following the little stream in this 
 valley, about a mile above the village, the base of the great cliff 
 was formed of a compact fine-grained basalt, conformably covered 
 by a bed of pebbles. Near Fuentes, I met with pap-formed hills of 
 the compact feldspathic series of rocks. 
 
26 St. J ago. 
 
 PAET I. 
 
 and generally bounded by low cliff-formed sides. Por- 
 tions of the basaltic plain are sometimes nearly or quite 
 isolated by tliem ; of wliicli fact, the place on which 
 the town of Praya stands offers an instance. The great 
 valley west of the town has its bottom filled up to a 
 depth of more than twenty feet by well-rounded pebbles, 
 which in some parts are firmly cemented together by 
 white calcareous matter. There can be no doubt, from 
 the form of these valleys, that they were scooped out by 
 the waves of the sea, during that equable elevation of 
 the land, of which the horizontal calcareous deposit, 
 with its existing species of marine remains, gives evi- 
 dence. Considering how well shells have been preserved 
 in this stratum, it is singular that 1 could not find even a 
 single small fragment of shell in the conglomerate at 
 the bottom of the valleys. The bed of pebbles in the 
 valley west of the town is intersected by a second valley 
 joining it as a tributary, but even this valley appears 
 much too wide and flat-bottomed to have been formed 
 by the small quantity of water, which falls only during 
 one short wet season ; for at other times of the year 
 these valleys are absolutely dry. 
 
 Recent conglomerate. — On the shores of Quail 
 Island, I found fragments of brick, bolts of iron, 
 pebbles, and large fragments of basalt, united by a 
 scanty base of impure calcareous matter into a firm 
 conglomerate. To show how exceedingly firm this recent 
 conglomerate is, I may mention, that I endeavoured 
 with a heavy geological hammer to knock out a thick 
 bolt of iron, which was embedded a little above low- 
 water mark, but was quite unable to succeed. 
 
27 
 
 CHAPTER II. 
 
 Fernando Noeonha — Precipitous Mil of pJionolite. Teeceira — 
 Tracliytio rocks ; their singiilar decomposition hy steam of high tem- 
 peratiore. Tahiti — Passage from wache into trap ; singular vol- 
 canic rock with tlie vesicles half filled with mesotype. Mauritius 
 — Proofs of its recent elevation — Structure of its more ancient 
 mountains ; similarity with St. Jago. St. Paul's Eocks — Not of 
 volcanic origin — their singular mineralogical composition. 
 
 Fernando Noronlia. — During our short visit at this 
 and the four following islands, I observed very little 
 worthy of description. Fernando ISToronha is situated 
 in the Atlantic Ocean, in lat. 3° 50' S., and 230 miles 
 distant from the coast of South America. It consists 
 of several islets, together nine miles in length by three 
 in breadth. The whole seems to be of volcanic origin ; 
 although there is no appearance of any crater, or of any 
 one central eminence. The most remarkable feature 
 is a hill 1,000 feet high, of which the upper 400 feet 
 consist of a precipitous, singularly shaped pinnacle, 
 formed of columnar phonolite, containing numerous 
 crystals of glassy feldspar, and a few needles of horn- 
 blende. From the highest accessible point of this hill, 
 I could distinguish in different parts of the group 
 several other conical hills, apparently of the same nature. 
 At St. Helena there are similar, great, conical, protu- 
 berant masses of phonolite, nearly 1,000 feet in height, 
 which have been formed by the injection of fluid feld- 
 spathic lava into yielding strata. If this hill has had. 
 
28 Terceira, 
 
 PAET I. 
 
 as is probable, a similar origin, denudation has been 
 liere effected on an enormous scale. Near tlie base of 
 this hill, I observed beds of white tuff, intersected 
 by numerous dikes, some of amygdaloidal basalt and 
 others of trachyte; and beds of slaty phonolite with 
 the planes of cleavage directed NW. and SE. Parts 
 of this rock, where the crystals were scanty, closely re- 
 sembled common clay-slate, altered by the contact of a 
 trap-dike. The lamination of rocks, which undoubtedly 
 have once been fluid, appears to me a subject well deserv- 
 ing attention. On the beach there were numerous frag- 
 ments of compact basalt, of which rock a distant fapade 
 of columns seemed to be formed. 
 
 Terceira in the Azores. — The central parts of this 
 island consist of irregularly rounded mountains of no 
 great elevation, composed of trachyte, which closely 
 resembles in general character the trachyte of Ascension,, 
 presently to be described. This formation is in many 
 parts overlaid, in the usual order of superposition, by 
 streams of basaltic lava, which near the coast compose 
 nearly the whole surface. The course which these 
 streams have followed from their craters, can often be 
 followed by the eye. The town of Angra is overlooked 
 by a crateriform hill (Mount Brazil), entirely built of 
 thin strata of fine-grained, harsh, brown-coloured tuff. 
 The upper beds are seen to overlap the basaltic streams 
 on which the town stands. This hill is almost iden- 
 tical in structure and composition with numerous crater- 
 formed hills in the Galapagos Archipelago. 
 
 UjffeGts of steam on the tr achy tic roclcs. — In the 
 central part of the island there is a S23ot, where steam 
 is constantly issuing in jets from the bottom of a small 
 ravine-like hollow, which has no exit, and which abuts 
 against a range of trachytic mountains. The steam is 
 emitted from several irregular fissures : it is scentless,. 
 
CHAP. II. 
 
 Terceira. 29 
 
 soon blackens iron, and is of much too liigli temperature 
 to be endured by tlie liand. The manner in which the 
 solid trachyte is changed on the borders of these orifices 
 is curious : first, the base becomes earthy, with red 
 freckles evidently due to the oxidation of particles of 
 iron ; then it becomes soft ; and lastly, even the crystals 
 of glassy feldspar yield to the dissolving agent. After 
 the mass is converted into clay, the oxide of iron seems 
 to be entirely removed from some parts, which are left 
 perfectly white, whilst in other neighbouring parts, 
 which are of the brightest red colour, it seems to be 
 deposited in greater quantity ; some other masses are 
 marbled with the two distinct colours. Portions of the 
 white clay, now that they are dry, cannot be distinguished 
 by the eye from the finest prepared chalk ; and when 
 placed between the teeth they feel equally soft-grained ; 
 the inhabitants use this substance for white-washing 
 their houses. The cause of the iron being dissolved in 
 one part, and close by being again deposited, is obscure ; 
 but the fact has been observed in several other places.^ 
 In some half-decayed specimens, I found small, globular, 
 aggregations of yellow hyalite, resembling gum-arabic, 
 which no doubt had been deposited by the steam. 
 
 As there is no escape for the rain-water, which 
 trickles down the sides of the ravine-like hollow, whence 
 the steam issues, it must all percolate downwards 
 through the fissures at its bottom. Some of the in- 
 habitants informed me that it was on record that 
 flames (some luminous appearance ?) had originally 
 proceeded from these cracks, and that the flames had 
 
 1 Spallanzani, Dolomieu and Hoffman have described similar 
 cases in the Italian volcanic islands. Dolomieu says the iron at the 
 Panza Islands is redeposited in the form of veins (p. 86, ' Memoire 
 surles Isles Ponces'). These authors likewise believe that the steam 
 deposits silica : it is now experimentally known that vapour of a 
 high temperature is able to dissolve silica. 
 
30 Tahiti. 
 
 PAET r. 
 
 been succeeded by the steam ; but I was not able to- 
 ascertain how long tbis was ago, or anytliing certain on 
 tbe subject. Wben viewing the spot, I imagined that 
 the injection of a large mass of rock, like the cone of 
 phonolite at Fernando Noronha, in a semi-fluid state, by 
 arching the surface might have caused a wedge-shaped 
 hollow with cracks at the bottom, and that the rain- 
 water percolating to the neighbourhood of the heated 
 mass, would during many succeeding years be driven, 
 back in the form of steam. 
 
 Tahiti (Otalieite). — I visited only a part of the- 
 north-western side of this island, and this part is en- 
 tirely composed of volcanic rocks. Near the coast there 
 are several varieties of basalt, some abounding with 
 large crystals of augite and tarnished olivine, others 
 compact and earthy, — some slightly vesicular, and 
 others occasionally amygdaloidal. These rocks are 
 generally much decomposed, and to my surprise, I found 
 in several sections that it was impossible to distinguish, 
 even approximately, the line of separation between the 
 decayed lava and the alternating beds of tuiff. Since 
 the specimens have become dry, it is rather more easy 
 to distinguish the decomposed igneous rocks from the 
 sedimentary tuffs. This gradation in character be- 
 tween rocks having such widely different origins, may I 
 think be explained by the yielding under pressure of 
 the softened sides of the vesicular cavities, which in 
 many volcanic rocks occupy a large proportion of their 
 bulk. As the vesicles generally increase in size and 
 number in the upper parts of a stream of lava, so would 
 the effects of their compression increase; the yielding, 
 moreover, of each lower vesicle must tend to disturb all 
 the softened matter above it. Hence we might expect 
 to trace a perfect gradation from an unaltered crystal- 
 line rock to one in which all the particles (although 
 
CHAP. II. 
 
 Tahiti. 3 1 
 
 originally forming part of the same solid mass) had 
 undergone mechanical displacement ; and such particles 
 could hardly be distinguished from others of similar 
 composition, which had been deposited as sediment. 
 As lavas are sometimes laminated in their upper parts, 
 even horizontal lines, appearing like those of aqueous 
 deposition, could not in all cases be relied on as a 
 criterion of sedimentary origin. From these considera- 
 tions it is not surprising that formerly many geologists 
 believed in real transitions from aqueous deposits, 
 through wacke, into igneous traps. 
 
 In the valley of Tia^auru, the commonest rocks are 
 basalts with much olivine, and in some cases almost 
 composed of large crystals of augite. I picked up some 
 specimens, with much glassy feldspar, approaching in 
 character to trachyte. There were also many large 
 blocks of vesicular basalt, with the cavities beautifully 
 lined with chabasie (?), and radiating bundles of meso- 
 type. Some of these specimens presented a curious 
 appearance, owing to a number of the vesicles being 
 half filled up with a white, soft, earthy mesotypic 
 mineral, which intumesced under the blowpipe in 
 a remarkable manner. As the upper surfaces in all 
 the half-filled cells are exactly parallel, it is evident 
 that this substance has sunk to the bottom of each cell 
 from its weight. Sometimes, however, it entirely fills 
 the cells. Other cells are either quite filled, or lined, 
 with small crystals, apparently of chabasie ; these 
 crystals, also, frequently line the upper half of the cells 
 partly filled with the earthy mineral, as well as the 
 upper surface of this substance itself, in which case the 
 two minerals appear to blend into each other. I have 
 never seen any other amygdaloid ^ with the cells half 
 
 * MacCulloch, however, has described and given a plate of 
 ' Geolog. Trans.,' 1st Series, vol. iv. p. 225) a trap rock, with cavities 
 
32 Tahiti. 
 
 PAET I. 
 
 filled in the manner here described ; and it is difficult 
 to imagine the causes which determined the earthy 
 mineral to sink from its gravity to the bottom of the 
 cells, and the crystalline mineral to adhere in a coating 
 of equal thickness round the sides of the cells. 
 
 The basaltic strata on the sides of the valley are 
 gently inclined seaward, and I nowhere observed any 
 sign of disturbance ; the strata are separated from each 
 other by thick, compact beds of conglomerate, in which 
 the fragments are large, some being rounded, but most 
 angular. From the character of these beds, from the 
 compact and crystalline condition of most of the lavas, 
 and from the nature of the infiltrated minerals, I was 
 led to conjecture that they had originally flowed beneath 
 the sea. This conclusion agrees with the fact that the 
 Rev. W. Ellis found marine remains at a considerable 
 height, which he believes were interstratified with 
 volcanic matter ; as is likewise described to be the case 
 by Messrs. Tyerman and Bennett at Huaheine, an island 
 in this same archipelago. Mr. Stutchbury also dis- 
 covered near the summit of one of the loftiest moun- 
 tains of Tahiti, at the height of several thousand feet, 
 a stratum of semi-fossil coral. None of these remains 
 have been specifically examined. On the coast, where 
 masses of coral rock would have afforded the clearest evi- 
 dence, I looked in vain for any signs of recent elevation. 
 For references to the above authorities, and for more 
 detailed reasons for not believing that Tahiti has been 
 recently elevated, I must refer to my volume on the 
 ' Structure and Distribution of Coral Reefs ' (p. 138 of 
 the 1st edit., or p. 182 of the 2nd. edit.). 
 
 filled up horizontally with quartz and chalcedony. The upper 
 halves of these cavities are often filled by layers, which follow each 
 irregularity of the surface, and bj'- little depending stalactites of the 
 same siliceous substances. 
 
CHAP, II. Mauiatius. 2i2i 
 
 Mauritius. — Approaching this island on the 
 northern or north-western side, a curved chain of bold 
 mountains, surmounted by rugged pinnacles, is seen to 
 rise from a smooth border of cultivated land, which 
 gently slopes down to the coast. At the first glance, 
 one is tempted to believe that the sea lately reached 
 the base of these mountains, and upon examination, 
 this view, at least with respect to the inferior parts of 
 the border, is found to be perfectly correct. Several 
 authors ^ have described masses of upraised coral rock 
 round the greater part of the circumference of the 
 island. Between Tamarin Bay and the Great Black 
 River I observed, in company with Capt. Lloyd, two 
 hillocks of coral rock, formed in their lower part of 
 hard calcareous sandstone, and in their upper of great 
 blocks, slightly aggregated, of Astraea and Madrepora, 
 and of fragments of basalt ; they were divided into beds 
 dipping seaward, in one case at an angle of 8°, and in 
 the other at 18°; they had a water- worn appearance^ 
 and they rose abruptly from a smooth surface, strewed 
 with rolled debris of organic remains, to a height of 
 about twenty feet. The Officier du Roi, in his most 
 interesting tour in 1768 round the island, has described 
 masses of upraised coral rocks, still retaining that moat- 
 like structure (see ' Coral Reefs,' 2nd edit. p. 69) 
 which is characteristic of the living reefs. On the 
 coast northward of Port Louis, I found the lava con- 
 cealed for a considerable space inland by a conglo- 
 merate of corals and shells, like those on the beach, 
 but in parts consolidated by red ferruginous matter. 
 
 ' Captain Carmichael, in Hooker's ' Bot. Misc.' vol. ii. p. 301. 
 Captain Lloyd has lately, in the • Proceedings of the Geological 
 Society ' (vol. iii. p. 317), described carefully some of these masses. 
 In the ' Voyage k I'lsle de France, par un Officier du Koi,' many 
 interesting facts are given on this subject. Consult also ' Voyage 
 aux Quatre Isles d'Afrique, par M. Bory St. Vincent.' 
 
 D 
 
34 Mauritms. part i. 
 
 M. Bory St. Vincent lias described similar calcareous beds 
 over nearly the whole of the plain of Pamplemousses. 
 Near Port Louis, when turning over some large stones, 
 which lay in the bed of a stream at the head of a pro- 
 tected creek, and at the height of some yards above the 
 level of spring tides, I found several shells of serpula 
 still adhering to their under sides. 
 
 The jagged mountains near Port Louis rise to a 
 height of between 2,000 and 3,000 feet ; they consist 
 of strata of basalt, obscurely separated from each other 
 by firmly aggregated beds of fragmentary matter ; and 
 they are intersected by a few vertical dikes. The 
 basalt in some parts abounds with large crystals of 
 augite and olivine, and is generally compact. The 
 interior of the island forms a plain, raised probably 
 about a thousand feet above the level of the sea, and 
 composed of streams of lava which have flowed round 
 and between the rugged basaltic mountains. These 
 more recent lavas are also basaltic, but less compact, 
 and some of them abound with feldspar, so that they 
 even fuse into a pale coloured glass. On the banks of 
 the Great River, a section is exposed nearly 500 feet 
 deep, worn through numerous thin sheets of the lava of 
 this series, which are separated from each other by beds 
 of scorias. They seem to have been of subaerial forma- 
 tion, and to have flowed from several points of eruption 
 on the central platform, of which the Piton du Milieu 
 is said to be the principal one. There are also several 
 volcanic cones, apparently of this modern period, round 
 the circumference of the island, esi3ecially at the 
 northern end, where they form separate islets. 
 
 The mountains composed of the more compact and 
 crystalline basalt, form the main skeleton of the island. 
 M. Bailly ^ states that they all ' se developpent autour 
 * * Voyage aux Terres Australes,' torn. i. p. 54. 
 
CHAP. II. Mauritius. 32 
 
 d'elle comme une ceinture d'immenses remparts, toutes 
 affectant une pente plus ou moins inclinee vers le rivage 
 de la mer ; tandis, au contraire, que vers le centre de 
 File elles presentent une coupe abrupte, et souvent 
 taillee a pic. Toutes ces montagnes sont formees de 
 couches paralleles inclinees du centre de I'ile vers la 
 mer.' These statements have been disputed, though 
 not in detail, by M. Quoy, in the voyage of Freycinet. 
 As far as my limited means of observation went, I 
 found them perfectly correct.^ The mountains on the 
 NW. side of the island, which I examined, namely, La 
 Pouce, Peter Botts, Corps de Garde, Les Mamelles, 
 and apparently another farther southward, have pre- 
 cisely the external shape and stratification described by 
 M. Bailly. They form about a quarter of his girdle of 
 ramparts. Although these mountains now stand quite 
 detached, being separated from each other by breaches, 
 even several miles in width, through which deluges of 
 lava have flowed from the interior of the island ; never- 
 theless, seeing their close general similarity, one must 
 feel convinced that they originally formed parts of one 
 continuous mass. Judging from the beautiful map of 
 the Mauritius, published by the Admiralty from a 
 French MS., there is a range of mountains (M. Bamboo) 
 on the opposite side of the island, which correspond in 
 height, relative position, and external form, with those 
 just described. Whether the girdle was ever complete 
 may well be doubted ; but from M. Bailly's statements, 
 and my own observations, it may be safely concluded that 
 mountains with precipitous inland flanks, and composed 
 of strata dipping outwards, once extended round a con- 
 siderable portion of the circumference of the island. 
 The ring appears to have been oval and of vast size ; its 
 
 M. Lesson, in his account of th island, in the voyage of the 
 Coquille, seems to follow M. Bailly's views. 
 
 d2 
 
36 Mauritius. part i. 
 
 shorter axis, measured across from the inner sides of 
 the mountains near Port Louis and those near Grand 
 Port, being no less than thirteen geographical miles in 
 length. M. Bailly boldly supposes that this enormous 
 gulf, which has since been filled up to a great extent 
 by streams of modern lava, was formed by the sinking 
 in of the whole upper part of one great volcano. 
 
 It is singular in how many respects those portions 
 of St. Jago and of Mauritius which I visited agree in 
 their geological history. At both islands, mountains 
 of similar external form, stratification, and (at least in 
 their upper beds) composition, follow in a curved chain 
 the coast-line. These mountains in each case appear 
 originally to have formed parts of one continuous mass. 
 The basaltic strata of which they are composed, from 
 their compact and crystalline structure, seem, when 
 contrasted with the neighbouring basaltic streams of 
 subaerial formation, to have flowed beneath the pressure 
 of the sea, and to have been subsequently elevated. 
 We may suppose that the wide breaches between the 
 mountains were in both cases worn by the waves, 
 during their gradual elevation — of which process, within 
 recent times, there is abundant evidence on the coast- 
 land of both islands. At both, vast streams of more 
 recent basaltic lavas have flowed from the interior of 
 the island, round and between the ancient basaltic hills ; 
 at both, moreover, recent cones of eruption are scattered 
 around the circumference of the island ; but at neither 
 have eruptions taken place within the period of history. 
 As remarked in the last chapter, it is probable that 
 these ancient basaltic mountains, which resemble (at 
 least in many respects) the basal and disturbed remnants 
 of two gigantic volcanos, owe their present form, struc- 
 ture, and position, to the action of similar causes. 
 
 8i. PauVs Rocks. — This small island is situated in 
 
CHAP. II. S^. PauV s Rocks. 37 
 
 the Atlantic Ocean, nearly one degree north of the 
 equator, and 540 miles distant from South America, in 
 29° 15' west longitude. Its highest point is scarcely 
 fifty feet above the level of the sea; its outline is 
 irregular, and its entire circumference barely three- 
 quarters of a mile. This little point of rock rises 
 abruptly out of the ocean ; and, except on its western 
 side, soundings were not obtained, even at the short 
 distance of a quarter of a mile from its shore. It is 
 not of volcanic origin ; and this circumstance, which is 
 the most remarkable point in its history (as will here- 
 after be referred to), properly ought to exclude it from 
 the present volume. It is composed of rocks, unlike 
 any which I have met with, and which I cannot charac- 
 terise by any name, and must therefore describe. 
 
 The simplest, and one of the most abundant kinds, 
 is a very compact, heavy, greenish-black rock, having 
 an angular, irregular fracture, with some points just 
 hard enough to scratch glass, and infusible. This 
 variety passes into others of paler green tints, less hard, 
 but with a more crystalline fracture, and translucent on 
 their edges ; and these are fusible into a green enamel. 
 Several other varieties are chiefly characterised by 
 containing innumerable threads of dark-green serpen- 
 tine, and by having calcareous matter in their inter- 
 stices. These rocks have an obscure, concretionary 
 structure, and are full of variously-coloured angular 
 pseudo fragments. These angular pseudo fragments 
 consist of the first-described dark green rock, of a brown 
 softer kind, of serpentine, and of a yellowish harsh stone, 
 which, perhaps, is related to serpentine rock. There 
 are other vesicular, calcareo-ferruginous, soft stones. 
 There is no distinct stratification, but parts are imper- 
 fectly laminated ; and the whole abounds with innu- 
 merable veins, and vein-like masses, both small and 
 
38 S^. Paul's Rocks. PAET I. 
 
 large. Of these vein-like masses, some calcareous ones^ 
 wliich contain minute fragments of shells, are clearly 
 of subsequent origin to the others. 
 
 A glossy incrustation. — Extensive portions of these 
 rocks are coated by a layer of a glossy polished sub- 
 stance, with a pearly lustre and of a grayish white 
 colour ; it follows all the inequalities of the surface, to 
 which it is firmly attached. When examined with a 
 lens, it is found to consist of numerous exceedingly thin 
 layers, their aggregate thickness being about the tenth 
 of an inch. It is considerably harder than calcareous 
 spar, but can be scratched with a knife ; under the 
 blowpipe it scales off, decrepitates, slightly blackens, 
 emits a fetid odour, and becomes strongly alkaline : it 
 does not effervesce in acids. ^ I presume this substance 
 has been deposited by water draining from the birds' 
 dung, with which the rocks are covered. At Ascension, 
 near a cavity in the rocks which was filled with a 
 laminated mass of infiltrated birds' dung, I found some 
 irregularly-formed, stalactitical masses of apparently 
 the same nature. These masses, when broken, had an 
 earthy texture ; but on their outsides, and especially at 
 their extremities, they were formed of a pearly sub- 
 stance, generally in little globules, like the enamel of 
 teeth, but more translucent, and so hard as just to 
 scratch plate-glass. This substance slightly blackens 
 under the blowpipe, emits a bad smell, then becomes 
 quite white, swelling a little, and fuses into a dull white 
 enamel ; it does not become alkaline ; nor does it 
 effervesce in acids. The whole mass had a collapsed 
 appearance, as if in the formation of the hard glossy 
 crust the whole had shrunk much. At the Abrolhos. 
 Islands on the coast of Brazil, where also there is much 
 
 • In my Journal I have described this substance ; I then believed 
 that it was an impure phosphate of lime. 
 
CHAP. II. St Paul' s Rocks. 39 
 
 birds' dung, I found a great quantity of a brown, 
 arborescent substance adhering to some trap-rock. In 
 its arborescent form, this substance singularly resembles 
 some of the branched species of ISTullipora. Under the 
 blowpipe, it behaves like the specimens from Ascension ; 
 but it is less hard and glossy, and the surface has not 
 the shrunk appearance. 
 
40 Ascension. 
 
 PART I. 
 
 CHAPTER III. 
 
 ASCENSION. 
 
 Basaltic lavas — Ntunerous craters truncated on the same side — 
 Singular structure of volcanic honibs — Aeriform explosions — Ideated 
 granitic fragments — Trachytic rocks — Singular veins — Jasper, its 
 manner of formation — Concretions in pumiceous tuff — Calcareous 
 deposits and frondescent incrustations on the coast — Rema/rltaVIe 
 Itivmiated heds, alternating with, and passing into obsidian — 
 Origin of obsidian — Lamination oj volcanic rocTis. 
 
 This island is situated in tlie Atlantic Ocean, in lat. 8° 
 S., long. 14° W. It has tlie form of an irregular triangle 
 (see accompanying Map), eacli side being about six 
 miles in length. Its highest point is 2,870 feet^ above 
 the level of the sea. The whole is volcanic, and, from 
 the absence of proofs to the contrary, I believe of sub- 
 aerial orgin. The fundamental rock is everywhere of 
 a pale colour, generally compact, and of a feldspathic 
 nature. In the SE. portion of the island, where the 
 highest land is situated, well characterised trachyte, 
 and other congenerous rocks of that varying family, 
 occur. Nearly the entire circumference is covered up 
 by black and rugged streams of basaltic lava, with here 
 and there a hill or single point of rock (one of which 
 near the sea-coast, north of the Fort, is only two or 
 three yards across) of the trachyte still remaining 
 exposed. 
 
 Basaltic rocks. — The overlying basaltic lava is in 
 
 * ' Geographical Journal,' vol. v. p. 243. 
 
<c,o^ 
 
 23' Longitude. 22' W. of GTecranch- 2l' 
 
 Landm.: SmiBi,Mder, & Co., lS,Waia-ho Place.. 
 
 Stojrfard^ GeotpvphicxiUstnKiJhment^onSaru 
 
CHAP. III. Basaltic Rocks. 41 
 
 some parts extremely vesicular, in others little so ; it is 
 of a black colour, but sometimes contains crystals of 
 glassy feldspar, and seldom mucli olivine. These 
 streams appear to have possessed singularly little 
 fluidity; their side walls and lower ends being very 
 steep, and even as much as between twenty or thirty 
 feet in height. Their surface is extraordinarily rugged, 
 and from a short distance appears as if studded with 
 small craters. These projections consist of broad, 
 irregularly conical, hillocks, traversed by fissures, and 
 composed of the same unequally scoriaceous basalt with 
 the surrounding streams, but having an obscure ten- 
 dency to a columnar structure ; they rise to a height 
 between ten and thirty feet above the general surface, 
 and have been formed, as I presume, by the heaping up 
 of the viscid lava at points of greater resistance. At 
 the base of several of these hillocks, and occasionally 
 likewise on more level parts, solid ribs, composed of 
 angulo-globular masses of basalt, resembling in size 
 and outline arched sewers or gutters of brickwork, but 
 not being hollow, project between two or three feet 
 above the surface of the streams; what their origin 
 may have been, I do not know. Many of the super- 
 ficial fragments from these basaltic streams present 
 singularly convoluted forms ; and some specimens could 
 hardly be distinguished from logs of dark-coloured wood 
 without their bark. 
 
 Many of the basaltic streams can be traced, either 
 to points of eruption at the base of the great central 
 mass of trachyte, or to separate, conical, red-coloured 
 hills, which are scattered over the northern and western 
 borders of the island. Standing on the central eminence, 
 I counted between twenty and thirty of these cones of 
 eruption. The greater number of them had their trun- 
 cated summits cut off obliquely, and they all sloped 
 
42 
 
 Ascension. 
 
 PAUT I. 
 
 towards tlie SE., whence the trade-wind blowsJ This 
 structure no doubt has been caused by the ejected 
 fragments and ashes being always blown, during erup- 
 tions, in greater quantity towards one side than towards 
 the other. M. Moreau de Jonnes has made a similar 
 observation with respect to the volcanic orifices in the 
 West Indian Islands. 
 
 Volcanic hombs. — These occur in great numbers 
 strewed on the ground, and some of them lie at con- 
 siderable distances from any points of eruption. They 
 vary in size from that of an apple to that of a man's 
 
 No. 3. 
 
 Fragment of a spherical volcanic bomb, -with the interior parts coarsely cellular 
 coated by a concentric layer of compact lava, and this again by a crust of finely 
 cellular rock. 
 
 body ; they are either spherical or pear-shaped, or^with 
 the hinder part (corresponding to the tail of a comet) 
 
 * M. Lesson, in the ' Zoology of the Voyage of the " Coquille " ' 
 (p. 490), has observed this fact. Mr. Hennah (• Geolog. Proceedings,' 
 1835, p. 189) further remarks that the most extensive beds of ashes 
 at Ascension invariably occur on the leeward side of the island. 
 
CHAP. iiT. Volcanic Bombs. 43 
 
 irregular, studded with projecting points, and even 
 concave. Their surfaces are rough, and fissured with 
 branching cracks ; their internal structure is either 
 irregularly scoriaceous and compact, or it presents a 
 symmetrical and very curious appearance. An irregular 
 segment of a bomb of this latter kind, of which I 
 found several, is accurately represented in the accom- 
 panying woodcut. Its size was about that of a man's 
 head. The whole interior is coarsely cellular ; the cells 
 averaging in diameter about the tenth of an inch ; but 
 nearer the outside they gradually decrease in size. This 
 part is succeeded by a well-defined shell of compact 
 lava, having a nearly uniform thickness of about the 
 third of an inch ; and the shell is overlaid by a some- 
 what thicker coating of finely cellular lava (the cells 
 varying from the fiftieth to the hundredth of an inch in 
 diameter), which forms the external surface : the line 
 separating the shell of compact lava from the outer 
 scoriaceous crust is distinctly defined. This structure 
 is very simply explained, if we suppose a mass of viscid, 
 scoriaceous matter, to be projected with a rapid, rota- 
 tory motion through the air ; for whilst the external 
 crust, from cooling, became solidified (in the state we 
 now see it), the centrifugal force, by relieving the 
 pressure in the interior parts of the bomb, would allow 
 the heated vapours to expand their cells ; but these 
 being driven by the same force against the already- 
 hardened crust, would become, the nearer they were to 
 this part, smaller and smaller or less expanded, until 
 they became packed into a solid, concentric shell. As 
 we know that chips from a grindstone ^ can be flirted 
 off, when made to revolve with sufficient velocity, we 
 need not doubt that the centrifugal force would have 
 power to modify the structure of a softened bomb, in 
 
 ' Nichol's ' Architecture of the Heavens.' 
 
44 
 
 Ascension. 
 
 PAKT I. 
 
 the manner here supposed. Geologists have remarked, 
 that the external form of a bomb at once bespeaks the 
 history of its aerial course, and we now see that the 
 internal structure can speak, with almost equal plainness, 
 of its rotatory movement. 
 
 M. Bory St. Vincent ^ has described some balls of 
 lava from the Isle of Bourbon, which have a closely 
 similar structure ; his explanation, however (if I under- 
 stand it rightly), is very different from that which I 
 have given ; for he supposes that they have rolled, like 
 snow-balls, down the sides of the crater. M. Beudant,^ 
 also, has described some singular little balls of obsidian, 
 never more than six or eight inches in diameter, which 
 he found strewed on the surface of the ground : their 
 form is always oval ; sometimes they are much swollen 
 in the middle, and even spindle-shaped : their surface 
 is regularly marked with concentric ridges and furrows, 
 all of which on the same ball are at right angles to one 
 axis : their interior is compact and glassy. M. Beudant 
 
 supposes that masses of lava, 
 when soft, were shot into the air, 
 with a rotatory movement round 
 the same axis, and that the form 
 and superficial ridges of the 
 bombs were thus produced. Sir 
 Thomas Mitchell has given me 
 what at first appears to be the 
 half of a much flattened oval ball 
 of obsidian ; it has a singular 
 artificial-like appearance, which 
 Volcanic bomb of obsidian from is Well represented (of the natural 
 ^ ^^^the lower size) in the accompanying wood- 
 cut. It was found in its pre- 
 
 No. 4. 
 
 Australia 
 
 gives a front view 
 
 a side view of the same ob 
 
 ject 
 
 * ' Voyage aux Quatre Isles d'Afrique,' torn. i. p. 222. 
 ^ ' Voyage en Hongrie,' torn, ii, p. 214. 
 
CHAP. III. Aeriforvt Explosions. 45 
 
 sent state, on a great sandy plain between the rivers 
 Darling and Murray, in Australia, and at the distance 
 of several hundred miles from any known volcanic 
 region. It seems to have been embedded in some 
 reddish tufaceous matter; and may have been trans- 
 ported either by the aborigines or by natural means. 
 The external saucer consists of compact obsidian, of a 
 bottle-green colour, and is filled with finely-cellular 
 black lava, much less transparent and glassy than the 
 obsidian. The external surface is marked with four 
 or five not quite perfect ridges, which are represented 
 rather too distinctly in the woodcut. Here then we 
 have the external structure described by M. Beudant, 
 and the internal cellular condition of the bombs from 
 Ascension. The lip of the saucer is slightly concave, 
 exactly like the margin of a soup-plate, and its inner 
 edge overlaps a little the central cellular lava. This 
 structure is so symmetrical round the entire circum- 
 ference, that one is forced to suppose that the bomb 
 burst during its rotatory course, before being quite 
 solidified, and that the lip and edges were thus slightly 
 modified and turned inwards. It may be remarked that 
 the superficial ridges are in planes, at right angles to an 
 axis, transverse to the longer axis of the flattened oval : 
 to explain this circumstance, we may suppose that when 
 the bomb burst, the axis of rotation changed. 
 
 Aeriform explosions. — The flanks of Green Moun- 
 tain and the surrounding country are covered by a 
 great mass, some hundred feet in thickness, of loose 
 fragments. The lower beds generally consist of fine- 
 grained, slightly consolidated tuffs,^ and the upper beds 
 of great loose fragments, with alternating finer beds.- 
 
 ' Some of this peperino, or tuff, is sufficiently hard not to bo 
 broken by the greatest force of the fingers. 
 
 2 On the northern side of the Green Mountain a thin seam, about 
 an inch in thickness, of compact oxide of iron, extends over a con- 
 
46 Ascension. 
 
 PAET I 
 
 One white ribbon-like layer of decomposed, pumiceous 
 breccia, was curiously bent into deep unbroken curves, 
 beneatb each of the larger fragments in the superin- 
 cumbent stratum. From the relative position of these 
 beds, I presume that a narrow-mouthed crater, standing 
 nearly in the position of Green Mountain, like a great 
 air-gun, shot forth, before its final extinction, this vast 
 accumulation of loose matter. Subsequently to this 
 event, considerable dislocations have taken place, and 
 an oval circus has been formed by subsidence. This 
 sunken space lies at the north-eastern foot of Green 
 Mountain, and is well represented in the accompanying 
 map. Its longer axis, which is connected with a NE. 
 and SW. line of fissure, is three-fifths of a nautical mile 
 in length ; its sides are nearly perpendicular, except in 
 one spot, and about 400 feet in height ; they consist, in 
 the lower part, of a pale basalt with feldspar, and in the 
 upper part, of the tuff and loose ejected fragments; 
 the bottom is smooth and level, and under almost any 
 other climate a deep lake would have been formed 
 here. From the thickness of the bed of loose fragments, 
 with which the surrounding country is covered, the 
 amount of aeriform matter necessary for their projection 
 must have been enormous ; hence we may suppose it 
 probable that after the explosions vast subterranean 
 caverns were left, and that the falling in of the roof of 
 one of these produced the hollow here described. At 
 the Galapagos Archipelago, pits of a similar character, 
 
 siderable area ; it lies conformably in the lower part of the stratified 
 mass of ashes and fragments. This substance is of a reddish-brown 
 colour, with an almost metallic lustre ; it is not magnetic, but be- 
 comes so after having been heated under the blowpipe, by which it 
 is blackened and partly fused. This seam of compact stone, by 
 intercepting the little rain-water which falls on the island, gives rise 
 to a small dripping spring, first discovered by Dampier. It is the 
 only fresh- water on the island, so that the possibility of its being in- 
 habited has entirely depended on the occurrence of this ferruginous 
 layer. 
 
CHAP. III. Ejected Granitic Fragments. 47 
 
 but of a niTich smaller size, frequently occur at the bases 
 of small cones of eruption. 
 
 JEjected granitic fragments. — In the neighbour- 
 hood of Green Mountain, fragments of extraneous rock 
 are not unfrequently found embedded in the midst of 
 masses of scoriae. Lieut. Evans, to whose kindness I 
 am indebted for much information, gave me several 
 specimens, and I found others myself. They nearly all 
 have a granitic structure, are brittle, harsh to the touch, 
 and apparently of altered colours. First, a white syenite, 
 streaked and mottled with red ; it consists of well 
 crystallised feldspar, numerous grains of quartz, and 
 brilliant, though small, crystals of hornblende. The 
 feldspar and hornblende in this and the succeeding 
 cases have been determined by the rejflecting gonio- 
 meter, and the quartz by its action under the blowpipe. 
 The feldspar in these ejected fragments, like the glassy 
 kind in the trachyte, is from its cleavage a potash- 
 feldspar. Secondly, a brick-red mass of feldspar, quartz, 
 and small dark patches of a decayed mineral; one 
 minute particle of which I was able to ascertain, by its 
 cleavage, to be hornblende. Thirdly, a mass of con- 
 fusedly crystallised white feldspar, with little nests of a 
 dark coloured mineral, often carious, externally rounded, 
 having a glossy fracture, but no distinct cleavage : from 
 comparison with the second specimen, I have no doubt 
 that it is fused hornblende. Fourthly, a rock, which 
 at first appears a simple aggregation of distinct and 
 large-sized crystals of dusky-coloured Labrador feldspar ;i 
 
 * Professor Miller has been so kind as to examine this mineral. 
 He obtained two good cleavages of 86° 30' and 86° 50'. The mean 
 of several, Mrhich I made, was 86° 30'. Prof. Miller states that these 
 crystals, when reduced to a fine powder, are soluble in hydrochloric 
 acid, leaving some undissolved silex behind ; the addition of oxalate 
 of ammonia gives a copious precipitate of lime. He further re- 
 marks, that according to Von Kobell, anorthite (a mineral occurring 
 in the ejected fragments at Mount Somna) is always white and 
 
48 Ascension, 
 
 PART I. 
 
 but in tlieir interstices there is some white granular 
 feldspar, abundant scales of mica, a little altered horn- 
 blende, and, as I believe, no quartz. I have described 
 these fragments in detail, because it is rare ^ to find 
 granitic rocks ejected from volcanos with their minerals- 
 unchanged^ as is the case with the first specimen, and 
 partially with the second. One other large fragment, 
 found in another spot, is deserving of notice ; it is a 
 conglomerate, containing small fragments of granitic^ 
 cellular, and jaspery rocks, and of hornstone porphyries, 
 embedded in a base of wacke, threaded by numerous 
 thin layers of a concretionary pitchstone passing into- 
 obsidian. These layers are parallel, slightly tortuous^ 
 and short ; they thin out at their ends, and resemble in 
 form the layers of quartz in gneiss. It is probable 
 that these small embedded fragments were not separately 
 ejected, but were entangled in a fluid volcanic rock, 
 allied to obsidian ; and we shall presently see that 
 several varieties of this latter series of rock assume a 
 laminated structure. 
 
 TracJiytic series of rocks. — Those occupy the mora 
 elevated and central, and likewise the south-eastern, 
 parts of the island. The trachyte is generally of a pale 
 brown colour, stained with small darker patches ; it 
 contains broken and bent crystals of glassy feldspar, 
 
 transparent, so that if this be the case, these crystals from Ascension 
 must be considered as Labrador feldspar. Prof. Miller adds, that 
 he has seen an account, in Erdmann's ' Journal f iir technische 
 Chemie,' of a mineral ejected from a volcano, which had the external 
 characters of Labrador feldspar, but difEered in the analysis from 
 that given by mineralogists of this mineral : the author attributed 
 this difference to an error in the analysis of Labrador feldspar, 
 which is very old. 
 
 1 Daubeny, in his work on Volcanos (p. 389), remarks that this 
 is the case ; and Humboldt, in his ' Personal Narrative ' (vol. i. 
 p. 236), says, ' In general, the masses of known primitive rocks, I 
 mean those which perfectly resemble our granites, gneiss, and mica- 
 slate, are very rare in lavas : the substances we generally denote by 
 the name of granite, thrown out by Vesuvius, are mixtures of 
 nepheline, mica, and pyroxene.' 
 
CHAP. III. Trachytic Rocks. 49 
 
 grains of specular iroil, and black microscopical points, 
 which latter, from being easily fused, and then becom- 
 ing magnetic, I presume are hornblende. The greater 
 number of the hills, however, are composed of a quite 
 white, friable stone, appearing like a trachytic tuJBT. 
 Obsidian, hornstone, and several kinds of laminated 
 feldspathic rocks, are associated with the trachyte. 
 There is no distinct stratification ; nor could I distin- 
 guish a crateriform structure in any of the hills of this 
 series. Considerable dislocations have taken place ; 
 and many fissures in these rocks are yet left open, or 
 are only partially filled with loose fragments. Within 
 the space,^ mainly formed of trachyte, some basaltic 
 streams have burst forth ; and not far from the summit 
 of Green Mountain, there is one stream of quite black, 
 vesicular basalt, containing minute crystals of glassy 
 feldspar, which have a rounded appearance. 
 
 The soft white stone above mentioned is remarkable 
 from its singular resemblance, when viewed in mass, to 
 a sedimentary tuflP : it was long before I could persuade 
 myself that such was not its origin; and other geologists 
 have been perplexed by closely similar formations in 
 trachytic regions. In two cases, this white earthy stone 
 formed isolated hills ; in a third, it was associated with 
 columnar and laminated trachyte ; but I was unable to 
 trace an actual junction. It contains numerous crystals 
 of glassy feldspar and black microscopical specks, and 
 is marked with small darker patches, exactly as in the 
 surrounding trachyte. Its basis, however, when viewed 
 under the microscope, is generally quite earthy; but 
 sometimes it exhibits a decidedly crystalline structure. 
 On the hill marked ' Crater of an old volcano,' it passes 
 
 ^ This space is nearly included by a line sweeping round Green 
 Mountain, and joining the hills, called the Weather Port Signal, 
 Holyhead, and that denominated (improperly in a geological sense) 
 ' the Crater of an old volcano.' 
 
 E 
 
50 Ascension. 
 
 PAET I. 
 
 into a pale greenish-gray variety, differing only in its 
 colour, and in not being so earthy ; the passage was in 
 one case effected insensibly ; in another, it was formed 
 by numerous, rounded and angular, masses of the green- 
 ish variety, being embedded in the white variety ; — in 
 this latter case, the appearance was very much like that 
 of a sedimentary deposit, torn up and abraded during 
 the deposition of a subsequent stratum. Both these 
 varieties are traversed by innumerable tortuous veins 
 (presently to be described), which are totally unlike 
 injected dikes, or indeed any other veins which I have 
 ever seen. Both varieties include a few scattered frag- 
 ments, large and small, of dark-coloured scoriaceous 
 rocks, the cells of some of which are partially filled with 
 the white earthy stone ; they likewise include some 
 huge blocks of a cellular porphyry.^ These fragments 
 project from the weathered surface, and perfectly re- 
 semble fragments embedded in a true sedimentary tuff. 
 But as it is known that extraneous fragments of cellu- 
 lar rock are sometimes included in columnar trachyte, 
 in phonolite,^ and in other compact lavas, this circum- 
 stance is not any real argument for the sedimentary 
 origin of the white earthy stone. ^ The insensible 
 passage of the greenish variety into the white one, 
 and likewise the more abrupt passage by fragments of 
 the former being embedded in the latter, might result 
 
 * The porphyry is dark coloured ; it contains numerous, often 
 fractured, crystals of white opaque feldspar, also decomposing 
 crystals of oxide of iron ; its vesicles include masses of delicate, 
 hair-like, crystals, apparently of analcime. 
 
 2 D'Aubuisson, * Traits de G-eognosie,' torn. ii. p. 548. 
 
 3 Dr. Daubeny (on Volcanos, p. 180) seems to have been led to 
 believe that certain trachytic formations of Iscnia and of the Puy 
 de Dome, which closely resemble these of Ascension, were of sedi- 
 mentary origin, chiefly from the frequent presence in them ' of 
 scorif orm portions, different in colour from the matrix.' Dr. Daubeny 
 adds, that on the other hand, Brocchi, and other eminent geologists, 
 have considered these beds as earthy varieties of trachyte ; he con- 
 siders the subject deserving of further attention. 
 
CHAP. III. 
 
 Veins. 5 1 
 
 from sliglit differences in the composition of the same 
 mass of molten stone, and from the abrading action of 
 one such part still fluid on another part already solidi- 
 fied. The curiously formed veins have, I believe, been 
 formed by siliceous matter being subsequently segre- 
 gated. But my chief reason for believing that these 
 soft earthy stones, with their extraneous fragments, are 
 not of sedimentary origin, is the extreme improbability 
 of crystals of feldspar, black microscopical specks, and 
 small stains of a darker colour occurring in the same 
 proportional numbers in an aqueous deposit, and in 
 masses of solid trachyte. Moreover, as I have remarked, 
 the microscope occasionally reveals a crystalline struc- 
 ture in the apparently earthy basis. On the other 
 hand, the partial decomposition of such great masses of 
 trachyte, forming whole mountains, is undoubtedly a 
 circumstance of not easy explanation. 
 
 Veins in the earthy tr achy tic masses. — These veins 
 are extraordinarily numerous, intersecting in the most 
 complicated manner both coloured varieties of the 
 earthy trachyte : they are best seen on the flanks of 
 the ' Crater of the old volcano.' They contain crystals 
 of glassy feldspar, black microscopical specks and little 
 dark stains, precisely as in the surrounding rock ; but 
 the basis is very different, being exceedingly hard, 
 compact, somewhat brittle, and of rather less easy 
 fusibility. The veins vary much, and suddenly, fi'om 
 the tenth of an inch to one inch in thickness ; they 
 often thin out, not only on their edges, but in their 
 central parts, thus leaving round, irregular apertures ; 
 their surfaces are rugged. They are inclined at every 
 possible angle with the horizon, or are horizontal ; they 
 are generally curvilinear, and often interbranch one 
 with another. From their hardness they withstand 
 weathering, and projecting two or three feet above the 
 
 e2 
 
52 Ascension. 
 
 PART I. 
 
 ground, they occasionally extend some yards in length ; 
 these plate-like veins, when struck, emit a sound, almost 
 like that of a drum, and they may be distinctly seen to 
 vibrate ; their fragments, which are strewed on the 
 ground, clatter like pieces of iron when knocked against 
 each other. They often assume the most singular 
 forms ; I saw a pedestal of the earthy trachyte, covered 
 by a hemispherical portion of a vein, like a great 
 umbrella, sufficiently large to shelter two persons. I 
 have never met with, or seen described, any veins like 
 these ; but in form they resemble the ferruginous seams, 
 due to some process of segregation, occurring not un- 
 commonly in sandstones, — for instance, in the New Red 
 sandstone of England. Numerous veins of jasper and 
 of siliceous sinter, occurring on the summit of this 
 same hill, show that there has been some abundant 
 source of silica, and as these plate-like veins diflFer from 
 the trachyte only in their greater hardness, brittleness, 
 and less easy fusibility, it appears probable that their 
 origin is due to the segregation or infiltration of silice- 
 ous matter, in the same manner as happens with the 
 oxides of iron in many sedimentary rocks. 
 
 Siliceous sinter and jasper. — The siliceous sinter 
 is either quite white, of little specific gravity, and with 
 a somewhat pearly fracture, passing into pinkish pearly 
 quartz; or it is yellowish white, with a harsh fracture, 
 and it then contains an earthy powder in small cavities. 
 Both varieties occur, either in large irregular masses 
 in the altered trachyte, or in seams included in broad, 
 vertical, tortuous, irregular veins of a compact, harsh, 
 stone of a dull red colour, appearing like a sandstone. 
 This stone, however, is only altered trachyte ; and a 
 nearly similar variety, but often honeycombed, some- 
 times adheres to the projecting plate-like veins, de- 
 scribed in the last paragraph. The jasper is of an ochre 
 
CHAP. III. Siliceous Sinter and Jasper, 53 
 
 yellow or red colour ; it occurs in large irregular masses ^ 
 and sometimes in veins, both in tlie altered trachyte 
 and in an associated mass of scoriaceous basalt. The 
 cells of the scoriaceous basalt are lined or filled with 
 fine, concentric layers of chalcedony, coated and studded 
 with bright-red oxide of iron. In this rock, especially 
 in the rather more compact parts, irregular angular 
 patches of the red jasper are included, the edges of 
 which insensibly blend into the surrounding mass ; 
 other patches occur having an intermediate character 
 between perfect jasper and the ferruginous, decomposed, 
 basaltic base. In these patches, and likewise in the 
 large vein-like masses of jasper, there occur little 
 rounded cavities, of exactly the same size and form 
 with the air-cells, which in the scoriaceous basalt are 
 filled and lined with layers of chalcedony. Small frag- 
 ments of the jasper, examined under the microscope, 
 seem to resemble the chalcedony with its colouring 
 matter not separated into layers, but mingled in the 
 siliceous paste, together with some impurities. I can 
 understand these facts, — namely, the blending of the 
 jasper into the semi-decomposed basalt, — its occurrence 
 in angular patches, which clearly do not occupy pre- 
 existing hollows in the rock, — and its containing little 
 vesicles filled with chalcedony, like those in the scori- 
 aceous lava, — only on the supposition that a fluid, 
 probably the same fluid which deposited the chalcedony 
 in the air-cells, removed in those parts where there 
 were no cavities, the ingredients of the basaltic rock, 
 and left in their place silica and iron, and thus pro- 
 duced the jasper. In some specimens of silicified wood, 
 I have observed, that in the same manner as in the 
 basalt, the solid parts were converted into a dark- 
 coloured homogeneous stone, whereas the cavities 
 formed by the larger sap-vessels (which may be com- 
 
54 Ascension. 
 
 PART I. 
 
 pared with the air-vesicles in the basaltic lava) and 
 other irregular hollows, apparently produced by decay, 
 were filled with concentric layers of chalcedony ; in this 
 case, there can be little doubt that the same fluid 
 deposited the homogeneous base and the chalcedonic 
 layers. After these considerations, I cannot doubt but 
 that the jasper of Ascension may be viewed as a volcanic 
 rock silicified, in precisely the same sense as this term 
 is applied to wood, when silicified ; we are equally 
 ignorant of the means by which every atom of wood, 
 whilst in a perfect state, is removed and replaced by 
 atoms of silica, as we are of the means by which the 
 constituent parts of a volcanic rock could be thus acted 
 on.^ I was led to the careful examination of these rocks, 
 and to the conclusion here given, from having heard 
 the Rev. Professor Henslow express a similar opinion, 
 regarding the origin in trap-rocks of many chalcedonies 
 and agates. Siliceous deposits seem to be very general, 
 if not of universal occurrence, in partially decomposed 
 trachytic tufis ; ^ and as these hills, according to the 
 view above given, consist of trachyte softened and 
 altered in situ^ the presence of free silica in this case 
 may be added as one more instance to the list. 
 
 Concretions in inimiceous tuff. — The hill, marked 
 
 ^ Beudant ('Voyage en Hongrie,' torn. iii. pp. 502, 504) describes 
 kidney-shaped masses of jasper-opal, which either blend into the 
 surrounding trachytic conglomerate, or are embedded in it like chalk- 
 flints ; and he compares them with the fragments of opalised wood, 
 whicb are abundant in this same formation, Beudant, however, 
 appears to have viewed the process of their formation rather as one 
 of simple infiltration than of molecular exchange ; but the presence 
 of a concretion, wholly different from the surrounding matter, if not 
 formed in a pre-existing hollow, clearly seems to me to require, either 
 £1 molecular or mechanical displacement of the atoms, which occu- 
 pied the space afterwards filled by it. The jasper-opal of Hungary 
 passes into chalcedony, and therefore in this case, as in that of Ascen- 
 sion, jasper seems to be intimately related in origin with chalcedony. 
 
 2 Beudant (' Voyage Min.' tom. iii. p. 507) enumerates cases in. 
 Hungary, Germany, Central France, Italy, Greece, and Mexico. 
 
OHAP. III. Concretions in Puiniceous Tuff. 55 
 
 in the map ' Crater of an old volcano,' iias no claims to 
 this appellation, which I could discover, except in being 
 surmounted by a circular, very shallow, saucer-like 
 summit, nearly half a mile in diameter. This hollow 
 has been nearly filled up with many successive sheets of 
 ashes and scoriae, of different colours, and slightly con- 
 solidated. Each successive saucer-shaped layer crops 
 out all round the margin, forming so many rings of 
 various colours, and giving to the hill a fantastic 
 appearance. The outer ring is broad, and of a white 
 colour ; hence it resembles a course round which horses 
 have been exercised, and has received the name of the 
 Devil's Riding School, by which it is most generally 
 known. These successive layers of ashes must have 
 fallen over the whole surrounding country, but they 
 have all been blown away except in this one hollow, 
 in which probably moisture accumulated, either during 
 an extraordinary year when rain fell, or during the 
 storms often accompanying volcanic eruptions. One of 
 the layers of a pinkish colour, and chiefly derived 
 from small, decomposed fragments of pumice, is remark- 
 able, from containing numerous concretions. These 
 are generally spherical, from half-an-inch to three 
 inches in diameter ; but they are occasionally cylin- 
 drical, like those of iron-pyrites in the chalk of Europe. 
 They consist of a very tough, compact, pale-brown 
 stone, with a smooth and even fracture. They are 
 divided into concentric layers by thin white partitions, 
 resembling the external superficies ; six or eight of 
 such layers are distinctly defined near the outside ; but 
 those towards the inside generally become indistinct, 
 and blend into a homogeneous mass. I presume that 
 these concentric layers were formed by the shrinking of 
 the concretion, as it became compact. The interior 
 part is generally fissured by minute cracks or septaria 
 
56 Ascension. 
 
 PAET I. 
 
 which are lined, both by black, metallic, and by other 
 white and crystalline specks, the nature of which I was 
 unable to ascertain. Some of the larger concretions 
 consist of a mere spherical shell, filled with slightly 
 consolidated ashes. The concretions contain a small 
 proportion of carbonate of lime : a fragment placed 
 under the blowpipe decrepitates, then whitens and 
 fuses into a blebby enamel, but does not become caustic. 
 The surrounding ashes do not contain any carbonate of 
 lime ; hence the concretions have probably been formed, 
 as is so often the case, by the aggregation of this sub- 
 stance. I have not met with any account of similar 
 concretions ; and considering their great toughness and 
 compactness, their occurrence in a bed, which probably 
 has been subjected only to atmospheric moisture, is 
 remarkable. 
 
 Formation of calcareous rocks on the sea-coast. — - 
 On several of the sea-beaches, there are immense accu- 
 mulations of small, well-rounded particles of shells and 
 corals, of white, yellowish, and pink colours, inter- 
 spersed with a few volcanic particles. At the depth of 
 a few feet, these are found cemented together into 
 stone, of which the softer varieties are used for build- 
 ing ; there are other varieties, both coarse and fine- 
 grained, too hard for this purpose : and I saw one 
 mass divided into even layers half-an-inch in thickness^ 
 which were so compact that when struck with a hammer 
 they rang like flint. It is believed by the inhabitants, 
 that the particles become united in the course of a 
 single year. The union is effected by calcareous 
 matter ; and in the most compact varieties, each 
 rounded particle of shell and volcanic rock can be dis- 
 tinctly seen to be enveloped in a husk of pellucid 
 carbonate of lime. Extremely few perfect shells are 
 embedded in these agglutinated masses ; and I have 
 
CHAP. III. Recent Calcareous Formation. 57 
 
 examined even a large fragment under a microscope, 
 without being able to discover the last vestige of striae 
 or other marks of external form : this shows how long 
 each particle must have been rolled about, before its 
 turn came to be embedded and cemented.^ One of the 
 most compact varieties, when placed in acid, was en- 
 tirely dissolved, with the exception of some flocculent 
 animal matter; its specific gravity was 2*63. The 
 specific gravity of ordinary limestone varies from 2*6 to 
 2'75 ; pure Carrara marble was found by Sir H. De la 
 Beche^ to be 2-7. It is remarkable that these rocks of 
 Ascension, formed close to the surface, should be nearly 
 as compact as marble, which has undergone the action 
 of heat and pressure in the plutonic regions. 
 
 The great accumulation of loose calcareous particles, 
 lying on the beach near the Settlement, commences in 
 the month of October, moving towards the SW., which, 
 as I was informed by Lieut. Evans, is caused by a change 
 in the prevailing direction of the currents. At this period 
 the tidal rocks, at the SW. end of the beach, where the 
 calcareous sand is accumulating, and round which the 
 currents sweep, become gradually coated with a calcare- 
 ous incrustation, half-an-inch in thickness. It is quite 
 white, compact, with some parts slightly spathose, and 
 is firmly attached to the rock. After a short time it 
 gradually disappears, being either redissolved, when 
 the water is less charged with lime, or more probably is 
 mechanically abraded. Lieut. Evans has observed these 
 facts, during the six years he has resided at Ascension. 
 The incrustation varies in thickness in difierent years : 
 in 1831 it was unusually thick. When I was there in 
 
 ' The eggs of the turtle being buried by the parent, sometimes 
 become enclosed in the solid rock. Mr. Lyell has given a figure 
 (' Principles of Geology,' book iii. ch. 17) of some eggs, containing 
 the bones of young turtles, found thus entombed. 
 
 '■* ' Researches in Theoretical Geology,' p. 12. 
 
58 Ascension. 
 
 PAET I. 
 
 July, there was no remnant of tlie incrustation ; but on 
 a point of basalt, from which the quarrymen had lately 
 removed a mass of the calcareous freestone, the incrusta- 
 .tion was perfectly preserved. Considering the position 
 of the tidal rocks, and the period at which they become 
 coated, there can be no doubt that the movement and dis- 
 turbance of the vast accumulation of calcareous particles, 
 many of them being partially agglutinated together, 
 cause the waves of the sea to be so highly charged 
 with carbonate of lime, that they deposit it on the first 
 objects against which they impinge. I have been in- 
 formed by Lieut. Holland. R.N., that this incrusta- 
 tion is formed on many parts of the coast, on most of 
 which, I believe, there are likewise great masses of 
 comminuted shells. 
 
 A frondescent calcareous incrustation. — In many 
 respects this is a singular deposit ; it coats through- 
 out the year the tidal volcanic rocks, that project from 
 
 No. 5. 
 
 An incrustation of calcareous and animal matter, coating the tidal rocks at 
 
 Ascension. 
 
 the beaches composed of broken shells. Its general 
 appearance is well represented in the accompanying 
 woodcut ; but the fronds or disks, of which it is com- 
 
OHAP. III. Calcareous Iitcrustation. 59 
 
 posed, are generally so closely crowded together as to 
 touch. These fronds have their sinuous edges finely 
 crenulated, and they project over their pedestals or 
 supports ; their upper surfaces are either slightly con- 
 cave, or slightly convex ; they are highly polished, and 
 •of a dark gray or jet black colour ; their form is irre- 
 gular, generally circular, and from the tenth of an inch 
 to one inch and a-half in diameter ; their thickness, or 
 amount of their projection from the rock on which they 
 stand, varies much, about a quarter of an inch being per- 
 haps most usual. The fronds occasionally become more 
 and more convex, until they pass into botryoidal masses 
 with their summits fissured ; when in this state, they are 
 glossy and of an intense black, so as to resemble some 
 fused metallic substance. I have shown the incrustation, 
 both in this latter and in its ordinary state to several 
 geologists, but not one could conjecture its origin, except 
 .that perhaps it was of volcanic nature ! 
 
 The substance forming the fronds has a very com- 
 pact and often almost crystalline fracture ; the edges 
 being translucent, and hard enough easily to scratch 
 calcareous spar. Under the blowpipe it immediately be- 
 comes white, and emits a strong animal odour, like that 
 from fresh shells. It is chiefly composed of carbonate 
 •of lime ; when placed in muriatic acid it froths much, 
 leaving a residue of sulphate of lime, and of an oxide of 
 iron, together with a black powder, which is not soluble 
 in heated acids. This latter substance seems to be car- 
 bonaceous, and is evidently the colouring matter. The 
 sulphate of lime is extraneous, and occurs in distinct, 
 excessively minute, lamellar plates, studded on the sur- 
 faces of the fronds, and embedded between the fine 
 layers of which they are composed ; when a fragment is 
 heated in the blowpipe, these lamellae are immediately 
 rendered visible. The original outline of the fronds 
 
6o Ascension. 
 
 PAET I. 
 
 may often be traced, either to a minute particle of shell 
 fixed in a crevice of the rock, or to several cemented 
 together; these first become deeply corroded, by the 
 dissolving power of the waves, into sharp ridges, and 
 then are coated with successive layers of the glossy^ 
 gray, calcareous incrustation. The inequalities of the 
 primary support afiect the outline of every successive 
 layer, in the same manner as may often be seen in 
 bezoar-stones, when an object like a nail forms the 
 centre of aggregation. The crenulated edges, how- 
 ever, of the frond appear to be due to the corroding 
 power of the surf on its own deposit, alternating with 
 fresh depositions. On some smooth basaltic rocks on 
 the coast of St. Jago, I found an exceedingly thin layer 
 of brown calcareous matter, which under a lens pre- 
 sented a miniature likeness of the crenulated and 
 polished fronds of Ascension ; in this case a basis was 
 not afforded by any projecting extraneous particles. 
 Although the incrustation at Ascension is persistent 
 throughout the year ; yet from the abraded appearance 
 of some parts, and from the fresh appearance of other 
 parts, the whole seems to undergo a round of decay 
 and renovation, due probably to changes in the formr 
 of the shifting beach, and consequently in the action 
 of the breakers : hence probably it is, that the incrusta- 
 tion never acquires a great thickness. Considering the 
 position of the incrusted rocks in the midst of the cal- 
 careous beach, together with its composition, I think 
 there can be no doubt that its origin is due to the dis- 
 solution and subsequent deposition of the matter com- 
 posing the rounded particles of shells and corals.^ 
 
 * The selenite, as I have remarked, is extraneous, and must have 
 been derived from the sea-water. It is an interesting circumstance 
 thus to find the waves of the ocean, sufficiently charged with sul- 
 phate of lime, to deposit it on the rocks, against which they dash 
 every tide. Dr. Webster has described (' Voyage of the " Chanti- 
 
-CHAP. III. Calcareous Incritstation. 6i 
 
 From tMs source it derives its animal matter, which 
 is evidently the colouring principle. The nature of 
 the deposit, in its incipient stage, can often be well 
 seen upon a fragment of white shell, when jammed be- 
 tween two of the fronds ; it then appears exactly like 
 the thinnest wash of a pale gray varnish. Its darkness 
 varies a little, but the jet blackness of some of the 
 fronds and of the botryoidal masses seems due to the 
 translucency of the successive gray layers. There is 
 however, this singular circumstance, that when de- 
 posited on the under side of ledges of rock or in fissures 
 it appears always to be of a pale, pearly gray colour 
 even when of considerable thickness : hence one is led 
 to suppose, that an abundance of light is necessary to 
 the development of the dark colour, in the same 
 manner as seems to be the case with the upper and ex- 
 posed surfaces of the shells of living mollusca, which 
 are always dark, compared with their under surfaces 
 and with the parts habitually covered by the mantle of 
 the animal. In this circumstance, — in the immediate 
 loss of colour and in the odour emitted under the blow- 
 pipe, — in the degree of hardness and translucency of 
 the edges, — and in the beautiful polish of the surface ^ 
 rivalling when in a fresh state that of the finest Oliva 
 there is a striking analogy between this inorganic in- 
 
 cleer," ' vol. ii. p. 319) beds of gypsum and salt, as much as two feet 
 in thickness, left by the evaporation of the spray on the rocks on 
 the windward coast. Beautiful stalactites of selenite, resembling 
 in form those of carbonate of lime, are formed near these beds. 
 Amorphous masses of gypsum, also, occur in caverns in the interior 
 of the island ; and at Cross Hill (an old crater) I saw a considerable 
 quantity of salt oozing from a pile of scoria. In these latter cases, 
 the salt and gypsum appear to be volcanic products. 
 
 > From the fact described in my ' Journal of Eesearches ' (p. 12), 
 of a coating of oxide of iron, deposited by a streamlet on the rocks 
 in its bed (like a nearly similar coating at the great cataracts of the 
 Orinooco and Nile), becoming finely polished where the surf acts, I 
 presume that the surf in this instance, also, is the polishing agent. 
 
62 Ascension. paet i. 
 
 crustation and the shells of living molluscous animals.^ 
 This appears to me to be an interesting physiological 
 fact.^ 
 
 Singular laminated beds alternating ivith and 
 jmssing into obsidian. — These beds occur within the 
 trachytic district, at the western base of Green Mountain^ 
 under which they dip at a high inclination. They are 
 only partially exposed, being covered up by modern 
 ejections ; from this cause, I was unable to trace their 
 junction with the trachyte, or to discover whether they 
 had flowed as a stream of lava, or had been injected 
 amidst the overlying strata. There are three principal 
 beds of obsidian, of which the thickest forms the base 
 of the section. The alternating stony layers appear to 
 me eminently curious, and shall be first described, and 
 afterwards their passage into the obsidian. They have 
 an extremely diversified appearance ; five principal 
 varieties may be noticed, but these insensibly blend 
 into each other by endless gradations. 
 
 First, — A pale gray, irregularly and coarsely lami- 
 nated,^ harsh- feeling rock, resembling clay-slate which 
 
 1 In the section descriptive of St. Paul's Eocks, I have described 
 a glossy, pearly substance, which coats the rocks, and an allied 
 stalactitical incrustation from Ascension, the crust of which re- 
 sembles the enamel of teeth, but is hard enough to scratch plate 
 glass. Both these substances contain animal matter, and seem ta 
 have been derived from water infiltering through birds' dung. 
 
 - Mr. Horner and Sir David Brewster have described (' Philo- 
 sophical Transactions,' 1836, p. 65) a singular ' artificial substance, 
 resembling shell.' It is deposited in fine, transparent, highly- 
 polished, brown-coloured laminse, possessing peculiar optical pro- 
 perties, on the inside of a vessel, in which cloth, first prepared with 
 glue and then with lime, is made to revolve rapidly in water. It is 
 much softer, more transparent, and contains more animal matter,, 
 than the natural incrustation at Ascension ; but we here again see 
 the strong tendency which carbonate of lime and animal matter 
 evince to form a solid substance allied to shell. 
 
 * This term is open to some misinterpretation, as it may be applied 
 both to rocks divided into laminae of exactly the same composition,, 
 and to layers firmly attached to each other, with no fissile tendency,., 
 but composed of different minerals, or of different shades of colour.. 
 
CHAP. III. Obsidian Formation. 63 
 
 has been in contact with a trap-dike, and with a frac- 
 ture of about the same degree of crystalline structure. 
 This rock, as well as the following varieties, easily fuse 
 into a pale glass. The greater part is honey-combed 
 with irregular, angular, cavities, so that the whole has 
 a curious appearance, and some fragments resemble in 
 a remarkable manner silicified logs of decayed wood. 
 This variety, especially where more compact, is often 
 marked with thin whitish streaks, which are either 
 straight or wrap round, one behind the other, the elon- 
 gated carious hollows. 
 
 Secondly, — A bluish gray or pale brown, compact, 
 heavy, homogeneous stone, with an angular, uneven, 
 earthy fracture ; viewed, however, under a lens of high 
 power, the fracture is seen to be distinctly crystalline, 
 and even separate minerals can be distinguished. 
 
 Thirdly, — A stone of the same kind with the last, 
 but streaked with numerous, parallel, slightly tortuous, 
 white lines of the thickness of hairs. These white lines 
 are more crystalline than the parts between them ; and 
 the stone splits along them : they frequently expand 
 into exceedingly thin cavities, which are often only 
 just perceptible with a lens. The matter forming the 
 white lines becomes better crystallised in these cavities, 
 and Prof. Miller was fortunate enough, after several 
 trials, to ascertain that the white crystals, which are the 
 largest, were of quartz,^ and that the minute green trans- 
 parent needles were augite, or, as they would more 
 generally be called, diopside : besides these crystals, 
 there are some minute, dark specks without a trace of 
 
 The term 'laminated,' in this chapter, is applied in these latter 
 senses ; where a homogeneous rock splits, as in the former sense, in 
 a given direction, like clay-slate, I have used the term ' fissile.' 
 
 ^ Professor Miller informs me that the crystals which he measured 
 had the faces P, z, m of the figure (147) given by Haidinger in his 
 Translation of Mohs : and he adds, that it is remarkable, that none of 
 them had the slightest trace of faces r of the regular six-sided prism. 
 
64 Ascension. 
 
 PART I. 
 
 crystallisation, and some fine, white, granular, crystal- 
 line matter whicli is probably feldspar. Minute frag- 
 ments of this rock are easily fusible. 
 
 Fourthly, — A compact crystalline rock, banded in 
 straight lines with innumerable layers of white and 
 gray shades of colour, varying in width from the -gV^h 
 to the YW^^ ^^ ^^ ^^^^ '■> ^^6se layers seem to be com- 
 posed chiefly of feldspar, and they contain numerous 
 perfect crystals of glassy feldspar, which are placed 
 lengthways ; they are also thickly studded with micro- 
 scopically minute, amorphous, black specks, which are 
 placed in rows, either standing separately, or more 
 frequently united, two or three or several together, into 
 black lines, thinner than a hair. When a small frag- 
 ment is heated in the blowpipe, the black specks are 
 easily fused into black brilliant beads, which become 
 magnetic, — characters that apply to no common mineral 
 except hornblende or augite. With the black specks 
 there are mingled some others of a red colour, which are 
 magnetic before being heated, and no doubt are oxide 
 of iron. Round two little cavities, in a specimen of 
 this variety, I found the black specks aggregated into 
 minute crystals, appearing like those of augite or horn- 
 blende, but too dull and small to be measured by the 
 goniometer ; in this specimen, also, I could distinguish 
 amidst the crystalline feldspar, grains, which had the 
 aspect of quartz. By trying with a parallel ruler, I 
 found that the thin gray layers and the black hair-like 
 lines were absolutely straight and parallel to each 
 other. It is impossible to trace the gradation from the 
 homogeneous gray rocks to these striped varieties, or 
 indeed the character of the different layers in the same 
 specimen, without feeling convinced that the more or 
 less perfect whiteness of the crystalline feldspathic 
 matter depends on the more or less perfect aggregation 
 
CHAP. III. Obsidian Formation. 65 
 
 of diffused matter, into the black and red specks of 
 hornblende and oxide of iron. 
 
 Fifthly, — A compact heavy rock, not laminated, 
 with an irregular, angular, highly crystalline, fracture ; 
 it abounds with distinct crystals of glassy feldspar, and 
 the crystalline feldspathic base is mottled with a black 
 mineral, which on the weathered surface is seen to be 
 aggregated into small crystals, some perfect, bat the 
 greater number imperfect. I showed this specimen to 
 an experienced geologist, and asked him what it was, 
 he answered, as I think every one else would have done, 
 that it was a primitive greenstone. The weathered 
 surface, also, of the foregoing (No. 4) banded variety, 
 strikingly resembles a worn fragment of finely laminated 
 gneiss. 
 
 These five varieties, with many intermediate ones, 
 pass and repass into each other. As the compact 
 varieties are quite subordinate to the others, the whole 
 may be considered as laminated or striped. The laminae, 
 to sum up their characteristics, are either quite straight, 
 or slightly tortuous, or convoluted ; they are all parallel 
 to each other, and to the intercalating strata of obsidian ; 
 they are generally of extreme thinness; they consist 
 either of an apparently homogeneous, compact rock, 
 striped with difierent shades of gray and brown colours, 
 or of crystalline feldspathic layers in a more or less 
 perfect state of purity, and of difierent thicknesses, with 
 distinct crystals of glassy feldspar placed lengthways, or 
 of very thin layers chiefly composed of minute crystals 
 of quartz and augite, or composed of black and red 
 specks of an augitic mineral and of an oxide of iron, 
 either not crystallised or imperfectly so. After having 
 fully described the obsidian, I shall return to the subject 
 of the lamination of rocks of the trachytic series. 
 
 The passage of the foregoing beds into the strata of 
 
66 Ascension. 
 
 PAET I. 
 
 glassy obsidian is effected in several ways : first, angulo- 
 nodiilar masses of obsidian, botli large and small, 
 abruptly appear disseminated in a slaty, or in an amor- 
 phous, pale-coloured feldspathic rock, with, a somewhat 
 pearly fracture. Secondly, small irregular nodules of 
 the obsidian, either standing separately, or united into 
 thin layers, seldom more than the tenth of an inch 
 in thickness, alternate repeatedly with very thin layers 
 of a feldspathic rock, which is striped with the finest 
 parallel zones of colour, like an agate, and which some- 
 times passes into the nature of pitchstone ; the interstices 
 between the nodules of obsidian are generally filled by 
 soft white matter, resembling pumiceous ashes. Thirdly, 
 the whole substance of the bounding rock suddenly 
 passes into an angulo-concretionary mass of obsidian. 
 Such masses (as well as the small nodules) of obsidian 
 are of a pale green colour, and are generally streaked 
 with different shades of colour, parallel to the laminae 
 of the surrounding rock ; they likewise generally con- 
 tain minute white sphserulites, of which half is some- 
 times embedded in a zone of one shade of colour, and 
 half in a zone of another shade. The obsidian assumes 
 its jet black colour and perfectly conchoidal fracture, 
 only when in large masses ; but even in these, on careful 
 examination and on holding the specimens in different 
 lights, I could generally distinguish parallel streaks of 
 different shades of darkness. 
 
 One of the commonest transitional rocks deserves in 
 several respects a further description. It is of a very 
 complicated nature, and consists of numerous thin, 
 slightly tortuous, layers of a pale-coloured feldspathic 
 stone, often passing into an imperfect pitchstone, alter- 
 nating with layers formed of numberless little globules 
 of two varieties of obsidian, and of two kinds of sphas- 
 rulites, embedded in a soft or in a hard pearly base. 
 
CHAP. III. 
 
 Obsidian Formation. 
 
 67 
 
 The spliaerulites are either white and translucent, or 
 dark brown and opaqne ; the former are quite spherical, 
 of small size, and distinctly radiated from their centre. 
 The dark brown sphaerulites are less perfectly round, 
 and vary in diameter from the -^-^^ to -g^th of an inch ; 
 when broken they exhibit towards their centres, which 
 are whitish, an obscure radiating structure; two of 
 them when united, sometimes have only one central 
 point of radiation ; there is occasionally a trace of a 
 hollow or crevice in their centres. They stand either 
 separately, or are united two or three or many together 
 into irregular groups, or more commonly into layers, 
 parallel to the stratification of the mass. This union 
 in many cases is so perfect, that the two sides of the 
 layer thus formed, are quite even ; and these layers, as 
 they become less brown and opaque, cannot be distin- 
 guished from the alternating layers of the pale-coloured 
 feldspathic stone. The sphserulites, when not united, 
 are generally compressed in the plane of the lamination 
 of the mass ; and in this same plane, they are often 
 marked internally, by zones of different shades of 
 
 No. 6. 
 
 C'paque brown sphferulites, drawn on an enlarged scale. The upper ones are ex- 
 ternally marked with parallel riilges. The internal radiating structure of the 
 lower ones, is much too plainly represented. 
 
 colour, and externally by small ridges and furrows. In 
 the upper part of the accompanying woodcut, the 
 
 F 2 
 
6 8 Ascension. 
 
 PAKT I. 
 
 spTiserulites with tlie parallel ridges and furrows are 
 represented on an enlarged scale, but tiiey are not well 
 executed ; and in tlie lower part, their usual manner of 
 grouping is shown. In another specimen, a thin layer 
 formed of the brown sphserulites closely united together, 
 intersects, as represented in the woodcut, No. 7, a layer 
 
 No. 7. 
 
 A layer formed by the union of minute brown spliEerulites, intersecting two other 
 jy similar layers : the whole represented of nearly the natural size. 
 
 of similar composition ; and after running for a short 
 space in a slightly curved line, again intersects it, and 
 likewise a second layer lying a little way beneath that 
 first intersected. The small nodules also of obsidian are 
 sometimes externally marked with ridges and furrows, 
 parallel to the lamination of the mass, but always less 
 plainly than the sphserulites. These obsidian nodules 
 are generally angular, with their edges blunted : they 
 are often impressed with the form of the adjoining 
 sphasrulites, than which they are always larger; the 
 separate nodules seldom appear to have drawn each other 
 out by exerting a mutual attractive force. Had I not 
 found in some cases, a distinct centre of attraction in 
 these nodules of obsidian, I should have been led to 
 have considered them as residuary matter, left during 
 the formation of the pearlstone, in which they are 
 embedded, and of the sphasrulitic globules. 
 
 The spheerulites and the little nodules of obsidian 
 in these rocks so closely resemble, in general form and 
 
CHAP. III. Obsidian Fomnation. 69 
 
 structure, concretions in sedimentary deposits, that one 
 is at once tempted to attribute to them an analogous 
 origin. They resemble ordinary concretions in the 
 following respects : in their external form, — in the union 
 of two or three, or of several, into an irregular mass, or 
 into an even-sided layer, — in the occasional intersection 
 of one such layer by another, as in the case of chalk- 
 flints, — in the presence of two or three kinds of nodules, 
 often close together, in the same basis, — in their fibrous, 
 radiating structure, with occasional hollows in their 
 centres, — in the co-existence of a laminary, concretionary, 
 and radiating structure, as is so well developed in the 
 concretions of magnesian limestone, described by Pro- 
 fessor Sedgwick.^ Concretions in sedimentary deposits, 
 it is known, are due to the separation from the sur- 
 rounding mass of the whole or part of some mineral 
 substance, and its aggregation round certain points of 
 attraction. Guided by this fact, I have endeavoured 
 to discover whether obsidian and the sphserulites (to 
 which may be added marekanite and pearlstone, both 
 of them occurring in nodular concretions in the trachytic 
 series) differ in their constituent parts, from the minerals 
 generally composing trachytic rocks. It appears from 
 three analyses, that obsidian contains on an average 76 
 per cent, of silica ; from one analysis, that sphgerulites 
 contain 79*12 ; from two, that marekanite contains 
 79'25 ; and from two other analyses, that pearlstone 
 contains 75 "62 of silica.^ Now, the constituent parts 
 of trachyte, as far as they can be distinguished, consist 
 of feldspar, containing 65*21 of silica ; or of albite, con- 
 taining 69*09 ; of hornblende, containing 55*27,^ and of 
 
 ^ • Geological Transactions,' vol. iii. part i. p. 37. 
 
 2 The foregoing analyses are taken from Eeudant, * Trait6 de 
 Mineralogie,' torn. ii. p. 113 ; and one analysis of obsidian, from 
 Phillips's • Mineralogy.' 
 
 ^ These analyses are taken from Von Kobell's ' Grundziige der 
 Mineralogie,' 1838. 
 
yo Ascensio7t. 
 
 PART I. 
 
 oxide of iron : so tliat the foregoing glassy concre- 
 tionary substances all contain a larger proportion of 
 silica than that occurring in ordinary feldspathic or 
 trachytic rocks. D'Aubuisson,^ also, has remarked on 
 the large proportion of silica compared with alumina, 
 in six analyses of obsidian and pearlstone given in 
 Brongniart's ^ Mineralogy.' Hence I conclude, that the 
 foregoing concretions have been formed by a process of 
 aggregation, strictly analogous to that which takes 
 place in aqueous deposits, acting chiefly on the silica, 
 but likewise on some of the other elements of the sur- 
 rounding mass, and thus producing the different con- 
 cretionary varieties. From the well-known effects of 
 rapid cooling ^ in giving glassiness of texture, it is 
 probably necessary that the entire mass, in cases like 
 that of Ascension, should have cooled at a certain rate ; 
 but considering the repeated and complicated alterna- 
 tions of nodules and thin layers of a glassy texture 
 with other layers quite stony or crystalline, all within 
 the space of a few feet or even inches, it is hardly 
 possible that they could have cooled at different rates, 
 and thus have acquired their different textures. 
 
 The natural sphserulites in these rocks ^ very closely 
 
 ' ' Traite de Geogn.' torn. ii. p. 535. 
 
 2 This is seen in the manufacture of common glass, and in 
 Gregory Watts's experiments on molten trap ; also on the natural 
 surfaces of lava-streams, and on the side-walls of dikes. 
 
 * I do not know whether it is generally known, that bodies having 
 exactly the same appearance as sphserulites, sometimes occur in 
 agates. Mr. Robert Brown showed me in an agate, formed within 
 a cavity in a piece of silicified wood, some little specks, which were 
 only just visible to the naked eye : these specks, when placed by 
 him under a lens of high power, presented a beautiful appearance : 
 they were perfectly circular, and consisted of the finest fibres of a 
 brown colour, radiating with great exactness from a common centre. 
 These little radiating stars are occasionally intersected, and portions 
 are quite cut off by the fine, ribbon-like zones of colour in the agate. 
 In the obsidian of Ascension, the halves of a sph^rulite often lie in 
 different zones of colour, but they are not cut off by them, as in the 
 agate. 
 
CHAP. III. Obsidian Formation. 7 1 
 
 resemble those produced in glass, when slowly cooled. 
 In some fine specimens of partially devitrified glass, 
 in tlie possession of Mr. Stokes, tlie spliserulites are 
 united into straight layers with even sides, parallel to 
 each other, and to one of the outer surfaces, exactly as 
 in the obsidian. These layers sometimes interbranch 
 and form loops ; but I did not see any case of actual 
 intersection. They form the passage from the perfectly 
 glassy portions, to those nearly homogeneous and stony, 
 with only an obscure concretionary structure. In the 
 same specimen, also, sphserulites differing slightly in 
 colour and in structure, occur embedded close together. 
 Considering these facts, it is some confirmation of the 
 view above given of the concretionary origin of the 
 obsidian and natural sph^erulites, to find that M. Dar- 
 tigues,^ in his curious paper on this subject, attributes 
 the production of sphgerulites in glass, to the different 
 ingredients obeying their own laws of attraction and 
 becoming aggregated. He is led to believe that this 
 takes place, from the difficulty in remelting sphserulitic 
 glass, without the whole be first thoroughly pounded 
 and mixed together ; and likewise from the fact, that 
 the change takes place most readily in glass composed 
 of many ingredients. In confirmation of M. Dartigues' 
 view, I may remark, that M. Fleurian de Bellevue ^ 
 found that the sphserulitic portions of devitrified glass 
 were acted on both by nitric acid and under the blow- 
 pipe, in a different manner from the compact paste in 
 which they were embedded. 
 
 Gomjparison of the ohsidian beds and alternating 
 strata of Ascension^ with those of other countries. — 
 I have been struck with much surprise, how closely the 
 excellent description of the obsidian rocks of Hungary, 
 
 1 ' Journal de Physique,' torn. 59 (1804), pp. 10, 12. 
 ' Idem, torn. 60 (1805), p. 418. 
 
72 Ascejtsion. 
 
 PAET I, 
 
 given by Beudant,^ and that by Humboldt, of tbe same 
 formation in Mexico and Peru,^ and likewise the descrip- 
 tions given by several authors ^ of the trachytic regions 
 in the Italian islands, agree with my observations at 
 Ascension. Many passages might have been transferred 
 without alteration from the works of the above authors, 
 and would have been applicable to this island. They 
 all agree in the laminated and stratified character of 
 the whole series ; and Humboldt speaks of some of the 
 beds of obsidian being ribboned like jasper."^ They all 
 agree in the nodular or concretionary character of the 
 obsidian, and of the passage of these nodules into layers. 
 They all refer to the repeated alternations, often in un- 
 dulatory planes, of glassy, pearly, stony, and crystalline 
 layers : the crystalline layers, however, seem to be much 
 more perfectly developed at Ascension, than in the 
 above-named countries. Humboldt compares some of 
 the stony beds, when viewed from a distance, to strata 
 of a schistose sandstone. Sphaorulites are described as 
 occurring abundantly in all cases ; and they everywhere 
 
 * ' Voyage en Hongrie,' torn. i. p. 330 ; torn. ii. pp. 221 and 315 f 
 torn. iii. pp. 369, 371, 377, 381. 
 
 2 ' Essai Geognostiqiae,' pp. 176, 326, 328. 
 
 ^ P. Scrope, in ' Geological Transactions,' vol. ii. (second series) 
 p. 195. Consult, also, Dolimieu's ' Voyage anx Isles Lipari,' and 
 D'Aubuisson, ' Traite de Geogn.' torn, ii, p. 534. 
 
 * In Mr. Stokes' fine collection of obsidians from Mexico, I 
 observe that the sphserulites are generally much larger than those of 
 Ascension ; they are generally white, opaque, and are united into 
 distinct layers : there are many singular varieties, different from 
 any at Ascension. The obsidians are finely zoned, in quite straight 
 or curved lines, with exceedingly slight differences of tint, of 
 cellularity, and of more or less perfect degrees of giassiness. Tracing 
 some of the less perfectly glassy zones, they are seen to become 
 studded with minute white sphferulites, which become more and 
 more numerous, until at last they unite and form a distinct layer : 
 on the other hand, at Ascension, only the brown sphEerulites unite 
 and form layers ; the white ones always being irregularly dis- 
 seminated. Some specimens at the Geological Society, said to 
 belong to an obsidian formation from Mexico, have an earthy frac- 
 ture, and are divided in the finest parallel laminge, by specks of a 
 black mineral, like the augitic or hornblendic specks in the rocks at 
 Ascension. 
 
CHAP. III. Obsidian Formation. 73 
 
 seem to mark the passage, from the perfectly glassy to 
 the stony and crystalline beds. Beudant's account ^ of 
 his ' perlite lithoide globulaire ' in every, even the 
 most trifling particular, might have been written for 
 the little brown sphgerulitic globules of the rocks of 
 Ascension. 
 
 From the close similarity in so many respects, be- 
 tween the obsidian formations of Hungary, Mexico, 
 Peru, and of some of the Italian islands, with that of 
 Ascension, I can hardly doubt that in all these cases, 
 the obsidian and the sphaerulites owe their origin to a 
 concretionary aggregation of the silica, and of some of 
 the other constituent elements, taking place whilst the 
 liquefied mass cooled at a certain required rate. It is, 
 however, well known, that in several places, obsidian, 
 has flowed in streams like lava ; for instance, at Tenerifie, 
 at the Lipari Islands, and at Iceland.^ In these cases, 
 the superficial parts are the most perfectly glassy, the 
 obsidian passing at the depth of a few feet into an opaque 
 stone. In an analysis by Vauquelin of a specimen of 
 obsidian from Hecla, which probably flowed as lava, the 
 proportion of silica is nearly the same as in the nodular 
 or concretionary obsidian from Mexico. It would be 
 interesting to ascertain, whether the opaque interior 
 portions and the superficial glassy coating contained 
 the same proportional constituent parts : we know from 
 M. Dufrenoy ^ that the exterior and interior parts of 
 the same stream of lava sometimes difier considerably 
 in their composition. Even should the whole body of 
 the stream of obsidian turn out to be similarly com- 
 
 ^ Beudant's ' Voyage,' torn. iii. p. 373. 
 
 - For Teneriffe, see Von Buch, ' Descript. des Isles Canaries,' pp. 
 184 and 190 ; for the Lipari Islands, see Dolimieu's ' Voyage,' p. 34 ; 
 for Iceland, see Mackenzie's ' Travels,' p. 369. 
 
 ^ ' Memoires pour servir ^ une Descript. Geolog. de la France,* 
 torn. iv. p. 371. 
 
74 Ascension. 
 
 PART I. 
 
 posed with nodular obsidian, it would only be necessary, 
 in accordance with, the foregoing facts, to suppose that 
 lava in these instances had been erupted with its ingre- 
 dients mixed in the same proportion, as in the concre- 
 tionary obsidian. 
 
 Lamination of volcanic roclis of the trachytic series. 
 
 We have seen that, in several and widely distant 
 countries, the strata alternating with beds of obsidian, 
 are highly laminated. The nodules, also, both large 
 and small, of the obsidian, are zoned with different 
 shades of colour; and I have seen a specimen from 
 Mexico in Mr. Stokes' collection, with its external 
 surface weathered ^ into ridges and furrows, correspond- 
 ing with the zones of different degrees of glassiness : 
 Humboldt,^ moreover, found on the Peak of Teneriffe, 
 a stream of obsidian divided by very thin, alternating, 
 layers of pumice. Many other lavas of the feldspathic 
 series are laminated ; thus, masses of common trachyte 
 at Ascension are divided by fine earthy lines, along 
 which the rock splits, separating thin layers of slightly 
 different shades of colour ; the greater number, also, of 
 the embedded crystals of glassy feldspar are placed 
 lengthways in the same direction. Mr. P. Scrope ^ has 
 described a remarkable columnar trachyte in the 
 Panza Islands, which seems to have been injected into 
 an overlying mass of trachytic conglomerate : it is 
 striped with zones, often of extreme tenuity, of dif- 
 ferent textures and colours; the harder and darker 
 
 ^ MacCuUocli states (' Classification of Eocks,' p. 531), that the 
 exposed surfaces of the pitchstone dikes in Arran are furrowed, 
 'with undulating lines, resembling certain varieties of marbled 
 paper, and which evidently result from some corresponding difference 
 of laminar structure.' 
 
 2 ' Personal Narrative,' vol. i. p. 222. 
 
 ' ' Geological Transactions,' vol. ii. (second series) p. 195. 
 
CHAP. III. Lammatioii of Trachytic Rocks. 75 
 
 zones appearing to contain a larger proportion of silica. 
 In another part of the island, there are layers of pearl- 
 stone and pitchstone, which in many respects resemble 
 those of Ascension. The zones in the columnar trachyte 
 are generally contorted; they extend uninterruptedly 
 for a great length in a vertical direction, and apparently 
 parallel to the walls of the dike-like mass. Von Buch^ 
 has described at Teneriffe, a stream of lava containing 
 innumerable, thin, plate-like crystals of feldspar, which 
 are arranged like white threads, one behind the other, 
 and which mostly follow the same direction. Dolimieu^ 
 also states, that the gray lavas of the modern cone of 
 Vulcano, which have a vitreous texture, are streaked 
 with parallel white lines : he further describes a solid 
 pumice-stoue which possesses a fissile structure, like 
 that of certain micaceous schists. Phonolite, which I 
 may observe is often, if not always, an injected rock, 
 also, often has a fissile structure ; this is generally due 
 to the parallel position of the embedded crystals of 
 feldspar, but sometimes, as at Fernando Noronha, seems 
 to be nearly independent of their presence.^ From 
 these facts we see, that various rocks of feldspathic 
 series have either a laminated or fissile structure, and 
 that it occurs both in masses, which have been injected 
 into overlying strata, and in others which have flowed 
 as streams of lava. 
 
 The laminae of the beds, alternating with the obsi- 
 dian at Ascension, dip at a high angle under the moun- 
 
 ' ' Description des lies Canaries,' p. 184. 
 
 ^ ' Voyage aux Isles de Lipari,' pp. 35 and 85. 
 
 ^ In this case, and in that of the fissile pumice-stone, the struc- 
 ture is very different froru that in the foregoing cases, where the 
 laminge consist of alternate laj^ers of different composition or texture. 
 In some sedimentary formations, however, which apparently are 
 homogeneous and fissile, as in glossy clay-slate, there is reason to 
 believe, according to D'Aubuisson, that the laminte are really due to 
 excessively thin, alternating, layers of mica. 
 
76 Lamination of Volcanic Rocks paet i. 
 
 tain, at the base of whicli tliey are situated ; and they 
 do not appear as if they had been inclined by violence. 
 A high inclination is common to these beds in Mexico^ 
 Peru, and in some of the Italian islands : ^ on the other 
 hand, in Hungary, the layers are horizontal ; the 
 laminae, also, of some of the lava-streams above referred 
 to, as far as I can understand the descriptions given. 
 of them, appear to be highly inclined or vertical. I 
 doubt whether in any of these cases, the laminas have 
 been tilted into their present position ; and in some 
 instances, as in that of the trachyte described by Mr. 
 Scrope, it is almost certain that they have been origin- 
 ally formed with a high inclination. In many of thesa 
 cases, there is evidence that the mass of liquefied rock 
 has moved in the direction of the laminae. At Ascen- 
 sion, many of the air-cells have a drawn-out appearance, 
 and are crossed by coarse semi-glassy fibres, in the 
 direction of the laminae; and some of the layers, sepa- 
 rating the sphserulitic globules, have a scored appear- 
 ance, as if produced by the grating of the globules. I 
 have seen a specimen of zoned obsidian from Mexico, 
 in Mr. Stokes' collection, with the surfaces of the best- 
 defined layers streaked or furrowed with parallel lines ; 
 and these lines or streaks precisely resembled those, 
 produced on the surface of a mass of artificial glass by 
 its having been poured out of a vessel. Humboldt, 
 also, has described little cavities, which he compares to 
 the tails of comets, behind sphserulites in laminated obsi- 
 dian rocks from Mexico, and Mr. Scrope has described 
 other cavities behind fragments embedded in his lami- 
 nated trachyte, and which he supposes to have been 
 
 * See Phillips's ' Mineralogy,' for the Italian Islands, p. 136. 
 For Mexico and Peru, see Humboldt's ' Essai Geognostique.' Mr. 
 Edwards, also, describes the high inclination of the obsidian rocks 
 of the Cerro del Navaja in Mexico, in the ' Proc. of the Geolog. Soc* 
 for June, 1838. 
 
CHAP. ni. of the Ti^achytic Series. yy 
 
 produced during the movement of the mass.^ From 
 such facts, most authors have attributed the lamination 
 of these volcanic rocks to their movement whilst lique- 
 fied. Although it is easy to perceive, why each separate 
 -air-cell, or each fibre in pumice-stone,^ should be drawn 
 out in the direction of the moving mass; it is by no 
 means at first obvious why such air-cells and fibres 
 should be arranged by the movement, in the same 
 planes, in laminae absolutely straight and parallel to 
 each other, and often of extreme tenuity ; and still less 
 obvious is it, why such layers should come to be of 
 slightly different composition and of different textures. 
 In endeavouring to make out the cause of the 
 lamination of the igneous feldspathic rocks, let us 
 return to the facts so minutely described at Ascension. 
 We there see, that some of the thinnest layers are 
 chiefly formed by numerous, exceedingly minute, though 
 perfect, crystals of different minerals ; that other layers 
 are formed by the union of different kinds of concre- 
 tionary globules, and that the layers thus formed, often 
 cannot be distinguished from the ordinary feldspathic 
 and pitchstone layers, composing a large portion of the 
 entire mass. The fibrous radiating structure of the 
 sphserulites seems, judging from many analogous cases, 
 to connect the concretionary and crystalline forces : the 
 separate crystals, also, of feldspar all lie in the same 
 
 ^ ' Geological Transactions,' vol. ii. (second series) p. 200, &c. 
 These embedded fragments, in some instances, consist of the lami- 
 nated trachyte broken off and ' enveloped in those parts, which still 
 remained liquid.' Beudant, also, frequently refers, in his great work 
 on ' Hungary ' (torn. iii. p. 386), to trachytic rocks, irregularly spotted 
 with fragments of the same varieties, which in other parts form the 
 parallel ribbons. In these cases, we must suppose, that after part 
 of the molten mass had assumed a laminated structure, a fresh 
 irruption of lava broke up the mass, and involved fragments, and 
 that subsequently the whole became relaminated. 
 
 * Dolimieu's ' Voyage,' p. 64. 
 
y^ Lamination of Volcanic Rocks paet i. 
 
 parallel planes.^ These allied forces, therefore, have 
 played an important part in the lamination of the mass, 
 but they cannot be considered the primary force ; for 
 the several kinds of nodules, both the smallest and the 
 largest, are internally zoned with excessively fine shades 
 of colour, parallel to the lamination of the whole ; and 
 many of them are, also, externally marked in the same 
 direction with parallel ridges and furrows, which have 
 not been produced by weathering. 
 
 Some of the finest streaks of colour in the stony 
 layers, alternating with the obsidian, can be distinctly 
 seen to be due to an incipient crystallisation of the 
 constituent minerals. The extent to which the minerals 
 have crystallised can, also, be distinctly seen to be 
 connected with the greater or less size, and with the 
 number, of the minute, flattened, crenulated air-cavities 
 or fissures. Numerous facts, as in the case of geodes, 
 and of cavities in silicified wood, in primary rocks, and 
 in veins, show that crystallisation is much favoured 
 by space. Hence, I conclude, that, if in a mass of 
 cooling volcanic rock, any cause produced in parallel 
 planes a number of minute fissures or zones of less 
 tension, (which from the pent-up vapours would often 
 be expanded into crenulated air-cavities), the crystal- 
 lisation of the constituent parts, and probably the for- 
 mation of concretions, would be superinduced or much 
 favoured in such planes ; and thus, a laminated struc- 
 ture of the kind we are here considering would be 
 generated. 
 
 That some cause does produce parallel zones of less 
 
 * The formation, indeed, of a large crystal of any mineral in a 
 rock of mixed composition implies an aggregation of the requisite 
 atoms, allied to concretionary action. The cause of the crystals of 
 feldspar in these rocks of Ascension, being all placed lengthways, is 
 probably the same with that which elongates and flattens all the 
 brown sph^rulitic globules (which behave like feldspar under the 
 blowpipe) in this same direction. 
 
CHAP. iir. of the Tr achy tic Series. 79 
 
 tension in volcanic rocks, during tlieir consolidation, we 
 must admit in the case of tlie thin alternate layers of 
 obsidian and pumice described by Humboldt, and of 
 the small, flattened, crenulated air-cells in the lami- 
 nated rocks of Ascension ; for on no other principle can 
 we conceive why the confined vapours should through 
 their expansion form air-cells or fibres in separate 
 parallel planes, instead of irregularly throughout the 
 mass. In Mr. Stokes' collection, I have seen a 
 beautiful example of this structure, in a specimen of 
 obsidian from Mexico, which is shaded and zoned, like 
 the finest agate, with numerous, straight parallel layers,, 
 more or less opaque and white, or almost perfectly 
 glassy ; the degree of opacity and glassiness depending 
 on the number of microscopically minute, flattened 
 air-cells ; in this case, it is scarcely possible to doubt 
 but that the mass, to which the fragment belonged, 
 must have been subjected to some, probably prolonged, 
 action, causing the tension slightly to vary in the suc- 
 cessive planes. 
 
 Several causes appear capable of producing zones of 
 different tension, in masses semi-liquefied by heat. In 
 a fragment of devitrified glass, I have observed layers 
 of sph^rulites which appeared, from the manner in 
 which they were abruptly bent, to have been produced 
 by the simple contraction of the mass in the vessel, in 
 which it cooled. In certain dikes on mount Etna, de- 
 scribed by M. Elie de Beaumont,^ as bordered by alter- 
 nating bands of scoriaceous and compact rock, one is 
 led to suppose that the stretching movement of the 
 surrounding strata, which originally produced the 
 fissures, continued whilst the injected rock remained 
 fluid. Guided, however, by Professor Forbes' ^ clear 
 
 ' ' Mem. pour servir,' &:c., torn. iv. p. 131. 
 
 2 'Edinburgh New Phil. Journal,' 1842, p. 350. 
 
So Lamination of Volcanic Rocks part i. 
 
 description of tlie zoned structure of glacier-ice, far the 
 most probable explanation of the laminated structure 
 of these feldspathic rocks appears to be, that they have 
 been stretched whilst slowly flowing onwards in a pasty 
 condition/ in precisely the same manner as Professor 
 Forbes believes, that the ice of moving glaciers is 
 stretched and fissured. In both cases, the zones may 
 be compared to those in the finest agates; in both, 
 they extend in the direction in which the mass has 
 flowed, and those exposed on the surface are generally 
 vertical : in the ice, the porous laminae are rendered 
 distinct by the subsequent congelation of infiltrated 
 water, in the stony feldspathic lavas, by subsequent 
 crystalline and concretionary action. The fragment of 
 glassy obsidian in Mr. Stokes' collection, which is zoned 
 with minute air-cells, must strikingly resemble, j udging 
 from Professor Forbes' descriptions, a fragment of the 
 zoned ice ; and if the rate of cooling and nature of the 
 mass had been favourable to its crystallisation or to 
 concretionary action, we should here have had the finest 
 parallel zones of different composition and texture. 
 In glaciers, the lines of porous ice and of minute 
 crevices seem to be due to an incipient stretching, 
 •caused by the central parts of the frozen stream moving 
 faster than the sides and bottom, which are retarded by 
 friction : hence in glaciers of certain forms and towards 
 the lower end of most glaciers, the zones become hori- 
 •zontal. May we venture to suppose that in the feld- 
 spathic lavas with horizontal laminae, we see an analo- 
 gous case ? All geologists, who have examined trachytic 
 regions, have come to the conclusion, that the lavas of 
 
 * I presume that this is nearly the same explanation which Mr. 
 
 Scrope had in his mind, when he speaks (' Geolog. Transact.' vol. ii. 
 
 second series, p. 228) of the ribboned structure of his trachytic rocks, 
 
 iaving arisen, from ' a linear extension of the mass, while in a state 
 
 <of imperfect liquidity, coupled with a concretionary process.' 
 
CHAP. III. of the Trachytic Series. 8i 
 
 this series have possessed an exceedingly imperfect 
 fluidity; and as it is evident that only matter thus 
 characterised would be subject to become fissured and 
 to be formed into zones of different tensions, in the 
 manner here supposed, we probably see the reason why 
 augitic lavas, which appear generally to have possessed 
 a high degree of fluidity, are not,^ like the feldspathic 
 lavas, divided into laminae of different composition and 
 texture. Moreover, in the augitic series, there never 
 appears to be any tendency to concretionary action, 
 which we have seen plays an important part in the 
 lamination of rocks of the trachytic series, or at least in 
 rendering that structure apparent. 
 
 Whatever may be thought of the explanation here 
 advanced of the laminated structure of the rocks of the 
 trachytic series, I venture to call the attention of geolo- 
 gists to the simple fact, that in a body of rock at 
 Ascension, undoubtedly of volcanic origin, layers often 
 of extreme tenuity, quite straight, and parallel to each 
 other, have been produced ; — some composed of distinct 
 crystals of quartz and diopside, mingled with amorphous 
 augitic specks and granular feldspar, — others entii^ely 
 composed of these black augitic specks, with granules 
 of oxide of iron, — and lastly, others formed of crystal- 
 line feldspar, in a more or less perfect state of purity, 
 together with numerous crystals of feldspar, placed 
 lengthways. At this island, there is reason to believe, 
 and in some analogous cases, it is certainly known, that 
 the laminae have originally been formed with their pre- 
 
 ' Basaltic lavas, and many other rocks, are not nnfrequently 
 divided into thick laminae or plates, of the same composition, which 
 are either straight or curved ; these being crossed by vertical lines 
 of fissure, sometimes become united into columns, Tbis structure 
 seems related, in its origin, to that by which many rocks, both 
 igneous and sedimentary, become traversed by parallel systems of 
 fissures. 
 
 G 
 
82 Lamination of Tr achy tic Rocks. paet i. 
 
 sent liigh inclination. Facts of this nature are mani- 
 festly of importance, with relation to the structural 
 origin of that grand series of plutonic rocks, which like 
 the volcanic have undergone the action of heat, and 
 which consist of alternate layers of quartz, feldspar, 
 mica, and other materials. 
 
S3 
 
 CHAPTER IV. 
 
 ST. HELENA. 
 
 Lavas ofthefeldspatliic, tasaltic, and submariiie series — Section Flag- 
 staff Hill and of the Barn — DiTies — Turh's Cap and Prosperous 
 Bays — Basaltic ring — Central crateriform ridge, with an internal 
 ledge and a parapet — Cones of phonolite — Superficial heds of cal- 
 careous sandstone — Extinct land-shells — Beds of detritus — Eleva- 
 tion of the land — Denudation — Craters of elevation. 
 
 The whole island is of volcanic origin ; its circumference, 
 according to Beatson,^ is about twenty-eiglit miles. 
 The central and largest part consists of rocks of a feld- 
 spathic nature, generally decomposed to an extraordi- 
 nary degree ; and when in this state, presenting a singu- 
 lar assemblage of alternating, red, purple, brown, yellow, 
 and white, soft, argillaceous beds. From the shortness 
 of our visit, I did not examine these beds with care ; 
 some of them, especially those of the white, yellow, 
 and brown shades, originally existed as streams of lava, 
 but the greater number were probably ejected in the 
 form of scoriae and ashes : other beds of a purple tint, 
 porphyritic with crystal-shaped patches of a vs^hite, soft 
 substance, which are now unctuous, and yield, like 
 wax, a polished streak to the nail, seem once to have 
 existed as solid claystone-porphyries : the red argil- 
 laceous beds generally have a brecciated structure, and 
 no doubt have been formed by the decomposition of 
 
 ^ Governor Beatson's ' Account of St. Helena.' 
 
 G 2 
 
84 ^^' Helena. 
 
 PAET I. 
 
 scoriae. Several extensive streams, however, belonging 
 to this series, retain their stony character; these are 
 either of a blackish-green colour, with minute acicular 
 crystals of feldspar, or of a very pale tint, and almost 
 composed of minute, often scaly, crystals of feldspar, 
 abounding with microscopical black specks; they are 
 generally compact and laminated ; others, however, of 
 similar composition, are cellular and somewhat decom- 
 posed. None of these rocks contain large crystals of 
 feldspar, or have the harsh fracture peculiar to trachyte. 
 These feldspathic lavas and tuffs are the uppermost or 
 those last erupted ; innumerable dikes, however, and 
 great masses of molten rock, have subsequently been 
 injected into them. They converge, as they rise, 
 towards the central curved ridge, of which one point 
 attains the elevation of 2,700 feet. This ridge is the 
 highest land in the island; and it once formed the 
 northern rim of a great crater, whence the lavas of this 
 series flowed : from its ruined condition, from the 
 southern half having been removed, and from the 
 violent dislocation which the whole island has under- 
 gone, its structure is rendered very obscure. 
 
 Basaltic series. — The margin of this island is 
 formed by a rude circle of great, black, stratified, ram- 
 parts of basalt, dipping seaward, and worn into cliffs, 
 which are often nearly perpendicular, and vary in 
 height from a few hundred feet to two thousand. 
 This circle, or rather horse-shoe shaped ring, is open to 
 the south, and is breached by several other wide spaces. 
 Its rim or summit generally projects little above the 
 level of the adjoining inland country; and the more 
 recent feldspathic lavas, sloping down from the central 
 heights, generally abut against and overlap its inner 
 margin ; on the north-western side of the island, how- 
 ever, they appear (judging from a distance) to have 
 
CHAP. lY. Basaltic Seine s. 85 
 
 flowed over and concealed portions of it. In some 
 parts, where the basaltic ring had been breached, and 
 the black ramparts stand detached, the feldspathic 
 lavas have passed between them, and now overhang 
 the sea-coast in lofty clijSs. The basaltic rocks are of a 
 black colour and thinly stratified ; they are generally 
 highly vesicular, but occasionally compact ; some ol 
 them contain numerous crystals of glassy feldspar and 
 octahedrons of titaniferous iron ; others abound with 
 crystals of augite and grains of olivine. The vesicles 
 are frequently lined with minute crystals (of chabasie ?) 
 and even become amygdaloidal with them. The 
 streams are separated from each other by cindery 
 matter, or by a bright red, friable, saliferous tuff, which 
 is marked by successive lines like those of aqueous 
 deposition ; and sometimes it has an obscure, concre- 
 tionary structure. The rocks of this basaltic series 
 occur nowhere except near the coast. In most volcanic 
 districts the trachytic lavas are of anterior origin to the 
 basaltic ; but here we see, that a great pile of rock, 
 closely related in composition to the trachytic family, 
 has been erupted subsequently to the basaltic strata : 
 the number, however, of dikes, abounding with large 
 crystals of augite, with which the feldspathic lavas have 
 been injected, shows perhaps, some tendency to a re- 
 turn to the more usual order of superposition. 
 
 Basal submarine lavas. — The lavas of this basal 
 series lie immediately beneath both the basaltic and 
 feldspathic rocks. According to Mr. Seale,^ they may 
 be seen at intervals on the sea-beach round the entire 
 island. In the sections which I examined, their nature 
 varied much ; some of the strata abound with crystals of 
 
 * ' Geognosy of the Island of St. Helena.' Mr. Seale has con- 
 structed a gigantic model of St. Helena, well worth visiting, which 
 is now deposited at Addiscombe College, in Surrey. 
 
S6 St Helena. 
 
 PAET I. 
 
 augite ; others are of a brown colour, either lami- 
 nated or in a rubbly condition ; and many parts are 
 highly amygdaloidal with calcareous matter. The 
 successive sheets are either closely united together, or 
 are separated from each other by beds of scoriaceous 
 rock and of laminated tujff, frequently containing well- 
 rounded fragments. The interstices of these beds are 
 filled with gypsum and salt ; the gypsum also sometimes 
 occurring in thin layers. From the large quantity of 
 these two substances, from the presence of rounded 
 pebbles in the tuffs, and from the abundant amygdaloids, 
 I cannot doubt that these basal volcanic strata flowed be- 
 neath the sea. This remark ought perhaps to be extended 
 to a part of the superincumbent basaltic rocks ; but on 
 this point, I was not able to obtain clear evidence. The 
 strata of the basal series, whenever I examined them, 
 were intersected by an extraordinary number of dikes. 
 
 Flagstaff Hill and the Barn. — I will now describe 
 some of the more remarkable sections, and will com- 
 mence with these two hills, which form the principal 
 external feature on the north-eastern side of the island. 
 The square, angular outline, and black colour of the 
 Barn, at once show that it belongs to the basaltic 
 
 No. 8. 
 
 FlagstaiF HiU. The Barn. 
 
 2,272 feet high. 2,015 feet high. 
 
 The double lines represent the basaltic strata ; the single, the basal submarine strata ; 
 the dotted, the upper feldspathic strata ; the dikes are shaded transversely. 
 
 series ; whilst the smooth, conical figure, and the 
 varied bright tints of Flagstafi* Hill, render it equally 
 clear, that it is composed of the softened, feldspathic 
 
CHAP. IV. Flagstaff Hill and the Barn, ^"j 
 
 rocks. These two lofty hills are connected (as is shown 
 in the accompanying woodcut) by a sharp ridge, 
 which is composed of the rubbly lavas of the basal 
 series. The strata of this ridge dip westward, the in- 
 clination becoming less and less towards the Flagstaff; 
 and the upper feldspathic strata of this hill can be seen, 
 though with some difficulty, to dip conformably to the 
 WSW. Close to the Barn, the strata of the ridge are 
 nearly vertical, but are much obscured by innumerable 
 dikes ; under this hill, they probably change from being 
 vertical into being inclined into an opposite direction ; 
 for the upper or basaltic strata, which are about 800 
 or 1,000 feet in thickness, are inclined north-eastward, 
 at an angle between thirty and forty degrees. 
 
 This ridge, and likewise the Barn and Flagstaff Hills, 
 are interlaced by dikes, many of which preserve a re- 
 markable parallelism in a NNW. and SSE. direction. 
 The dikes chiefly consist of a rock, porphyritic with 
 large crystals of augite ; others are formed of a fine- 
 grained and brown-coloured trap. Most of these dikes 
 are coated by a glossy layer,^ from one to two-tenths of 
 an inch in thickness, which, unlike true pitchstone, 
 fuses into a black enamel ; this layer is evidently ana- 
 logous to the glossy superficial coating of many lava 
 streams. The dikes can often be followed for great 
 lengths both horizontally and vertically, and they seem 
 to preserve a nearly uniform thickness : ^ Mr. Seale 
 
 ^ This circumstance has been observed (Lyell, 'Principles of 
 Geology,' vol. iv. chap. x. p. 9) in the dikes of the Atrio del Cavallo, 
 but apparently it is not of very common occurrence. Sir G. Mac- 
 kenzie, however, states (' Travels in Iceland,' p. 372) that all the 
 veins in Iceland have a ' black vitreous coating on their sides.' Capt. 
 Carmichael, speaking of the dikes in Tristan D'Acunha, a volcanic 
 island in the southern Atlantic, says (' Linneean Transactions,' vol. 
 xii. p. 485) that their sides, < where they come in contact with the 
 rocks, are invariably in a semi-vitrified state.' 
 
 2 ♦ Geognosy of the Island of St. Helena,' plate 5. 
 
88 SL Helena. part i 
 
 states, that one near the Barn, in a height of 1,260 feet, 
 decreases in width only four inches, — from nine feet at 
 the bottom, to eight feet and eight inches, at the top. 
 On the ridge, the dikes appear to have been guided in 
 their course, to a considerable degree, by the alterna- 
 ting soft and hard strata : they are often firmly united 
 to the harder strata, and they preserve their paral- 
 lelism for such great lengths, that in very many in- 
 stances it was impossible to conjecture, which of the 
 beds were dikes, stnd which streams of lava. The dikes, 
 though so numerous on this ridge, are even more 
 numerous in the valleys a little south of it, and to a 
 degree I never saw equalled anywhere else : in these 
 valleys they extend in less regular lines, covering the 
 ground with a network, like a spider's web, and with 
 some parts of the surface even appearing to consist 
 wholly of dikes, interlaced by other dikes. 
 
 From the complexity produced by the dikes, from 
 the high inclination and anticlinal dip of the strata of 
 the basal series, which are overlaid, at the opposite 
 ends of the short ridge, by two great masses of different 
 ages and of different composition, I am not surprised 
 that this singular section has been misunderstood. It 
 has even been supposed to form part of a crater ; but 
 so far is this from having been the case, that the summit 
 of Flagstaff Hill once formed the lower extremity of a 
 sheet of lava and ashes, which were erupted from the 
 central, crateriform ridge. Judging from the slope of 
 the contemporaneous streams in an adjoining and un- 
 disturbed part of the island, the strata of the Flagstaff 
 Hill must have been upturned at least twelve hundred 
 feet, and probably much more, for the great truncated 
 dikes on its summit show that it has been largely 
 denuded. The summit of this hill now nearly equals 
 in height the crateriform ridge; and before having 
 
CHAP. IV. Flagstaff Hill and the Barn. 89 
 
 been denuded, it was probably higher than this ridge, 
 from which it is separated by a broad and much lower 
 tract of country; we here, therefore, see that the lower 
 extremity of a set of lava-streams have been tilted up 
 to as great a height as, or perhaps greater height than, 
 the crater, down the flanks of which they originally 
 flowed. I believe that dislocations on so grand a scale 
 are extremely rare ^ in volcanic districts. The forma- 
 tion of such numbers of dikes in this part of the island 
 shows that the surface must here have been stretched to a 
 quite extraordinary degree ': this stretching, on the ridge 
 between Flagstafi" and Barn Hills, probably took place 
 subsequently (though perhaps immediately so) to the 
 strata being tilted ; for had the strata at that time 
 extended horizontally, they would in all probability 
 have been fissured and injected transversely, instead of 
 in the planes of their stratification. Although the 
 space between the Barn and Flagstaff Hill presents a 
 distinct anticlinal line extending north and south, and 
 though most of the dikes range with much regularity 
 in the same line, nevertheless, at only a mile due south 
 of the ridge the strata lie undisturbed. Hence the 
 disturbing force seems to have acted under a point, 
 rather than along a line. The manner in which it has 
 acted, is probably explained by the structure of Little 
 Stony-top, a mountain 2,000 feet high, situated a few 
 miles southward of the Barn ; we there see, even from 
 a distance, a dark-coloured, sharp, wedge of compact 
 columnar rock, with the bright-coloured feldspathic 
 strata, sloping away on each side from its uncovered 
 apex. This wedge, from which it derives its name of 
 Stony-top, consists of a body of rock, which has been 
 
 • M. Constant Prevost ('Mem. de la Soc. Geolog.' torn, ii.) 
 observes, that * les produits volcaniques n'ont que localement et 
 rarement meme derange le sol, ^ travers lequel ils se sont fait jour.' 
 
90 S^. Helena, 
 
 PAET I. 
 
 injected whilst liquefied into the overlying strata ; and 
 if we may suppose tliat a similar body of rock lies in- 
 jected, beneath the ridge connecting the Barn and Flag- 
 stafi*, the structure there exhibited would be explained. 
 TutUs Cap and, Tros'perous Bays. — Prosperous 
 Hill is a great, black, precipitous mountain, situated 
 two miles and a half south of the Barn, and composed, 
 like it, of basaltic strata. These rest, in one part, on 
 the brown-coloured, porphyritic beds of the basal series, 
 and in another part, on a fissured mass of highly scori- 
 aceous and amygdaloidal rock, which seems to have 
 formed a small point of eruption beneath the sea, con- 
 temporaneously with the basal series. Prosperous Hill, 
 like the Barn, is traversed by many dikes, of which the 
 greater number range north and south, and its strata 
 dip, at an angle of about 20°, rather obliquely from the 
 island towards the sea. The space between Prosperous 
 Hill and the Barn, as represented in this woodcut, con- 
 sists of lofty clifis, composed of the lavas of the upper 
 
 No. 9. 
 
 FlagstafE HiU. 
 Hold-fast-Tom. /-. 
 
 Prosperous Hill. The Barn. 
 
 The double lines represent the basaltic strata ; the single, the basal submariae strata ; 
 the dotted, the upper f eldspathic strata. 
 
 or feldspathic series, which rest, though unconform- 
 ably, on the basal submarine strata, as we have seen 
 that they do at Flagstaff Hill. But differently from 
 what occurs in that hill, these upper strata are nearly 
 horizontal, gently rising towards the interior of the 
 island; they are also composed of greenish-black, or 
 more commonly, pale brown, compact lavas, instead of 
 softened and highly coloured matter. These brown- 
 coloured, compact lavas, consist almost entirely of small 
 
CHAP. IV. TttrMs Cap and Prosperotts Bays, g i 
 
 o-limmering scales, or of minute acicular crystals, of 
 feldspar, placed close by the side of eacli other, and 
 abounding with minute black specks, apparently of 
 hornblende. The basaltic strata of Prosperous Hill 
 project only a little above the level of the gently-sloping, 
 feldspathic streams, which wind round and abut against 
 their upturned edges. The inclination of the basaltic 
 strata seems to be too great, to have been caused by 
 their having flowed down a slope, and they must have 
 been tilted into their present position before the erup- 
 tion of the feldspathic streams. 
 
 Basaltic ring. — Proceeding round the island, the 
 lavas of the upper series, southward of Prosperous Hill, 
 overhang the sea in lofty precipices. Further on, the 
 headland, called Great Stony-top, is composed, as I 
 believe, of basalt; as is Long Eange Point, on the 
 inland side of which, the coloured beds abut. On the 
 southern side of the island, we see the basaltic strata of 
 the South Barn, dipping obliquely seaward at a con- 
 siderable angle ; this headland, also, stands . a little 
 above the level of the more modern, feldspathic lavas. 
 Further on, a large space of coast, on each side of Sandy 
 Bay, has been much denuded, and there seems to be 
 left only the basal wreck of the great, central crater. 
 The basaltic strata reappear, with their seaward dip, at 
 the foot of the hill called Man-and -Horse ; and thence 
 they are continued along the whole north-western coast 
 to Sugar-Loaf Hill, situated near to the Flagstaff; and 
 they everywhere have the same seaward inclination, 
 and rest, in some parts at least, on the lavas of the basal 
 series. We thus see that the circumference of the 
 island is formed by a much-broken ring, or rather a 
 horse-shoe, of basalt, open to the south, and interrupted 
 on the eastern side by many wide breaches. The 
 breadth of this marginal fringe on the north-western 
 
92 St Helena. 
 
 PAET I. 
 
 side, where alone it is at all perfect, appears to vary 
 from a mile to a mile and a half. The basaltic strata, 
 as well as those of the subjacent basal series, dip, with 
 a moderate inclination, where they have not been sub- 
 sequently disturbed, towards the sea. The more broken 
 state of the basaltic ring round the eastern half, com- 
 pared with the western half of the island, is evidently 
 due to the much greater denuding power of the waves 
 on the eastern or windward side, as is shown by the 
 greater height of the cliffs on that side, than to leeward. 
 Whether the margin of basalt was breached, before or 
 after the eruption of the lavas of the upper series, is 
 doubtful ; but as separate portions of the basaltic ring 
 appear to have been tilted before that event, and from 
 other reasons, it is more probable, that some at least of 
 the breaches were first formed. Reconstructing in 
 imagination, as far as is possible, the ring of basalt, the 
 internal space or hollow, which has since been filled up 
 with the matter erupted from the great central crater, 
 appears to have been of an oval figure, eight or nine 
 miles in length by about four miles in breadth, and 
 with its axis directed in a NE. and SW. line, coincident 
 with the present longest axis of the island. 
 
 The central curved ridge. — This ridge consists, as 
 before remarked, of gray feldspathic lavas, and of red, 
 brecciated, argillaceous tuffs, like the beds of the upper 
 coloured series. The gray lavas contain numerous, 
 minute, black, easily fusible specks ; and but very few 
 large crystals of feldspar. They are generally much 
 softened; with the exception of this character, and of 
 being in many parts highly cellular, they are quite 
 similar to those great sheets of lava which overhang 
 the coast at Prosperous Bay. Considerable intervals 
 of time appear to have elapsed, judging from the 
 marks of denudation, between the formation of the 
 
CHAP. IV. 
 
 Central Cttrved Ridge, 
 
 93 
 
 successive beds, of which this ridge is composed. On 
 the steep northern slope, I observed in several sections 
 a much worn undulating surface of red tuff, covered 
 by gray, decomposed, feldspathic lavas, with only a 
 thin earthy layer interposed between them. In an 
 adjoining part, I noticed a trap-dike, four feet wide, 
 cut off and covered up by the feldspathic lava, as is 
 represented in the woodcut. The ridge ends on the 
 
 No. 10. 
 
 Dike. 
 1 — G-ray feldspathic lava. 
 
 2 — A layer, one iuch in thickness, of a reddish earthy matter. 
 3 — Brecciated, red, argillaceous tuff. 
 
 eastern side in a hook, which is not represented clearly 
 enough in any map which I have seen; towards the 
 western end, it gradually slopes down and divides into 
 several subordinate ridges. The best defined portion 
 between Diana's Peak and Nest Lodge, which supports 
 the highest pinnacles in the island varying from 2,000 
 to 2,700 feet, is rather less than three miles long in a 
 straight line. Throughout this space the ridge has 
 a uniform appearance and structure ; its curvature 
 resembles that of the coast-line of a great bay, being 
 made up of many smaller curves, all open to the south. 
 The northern and outer side is supported by narrow 
 ridges or buttresses, which slope down to the adjoining 
 country. ' The inside is much steeper, and is almost pre- 
 cipitous ; it is formed of the basset edges of the strata, 
 which gently decline outwards. Along some parts of 
 the inner side, a little way beneath the summit, a flat 
 ledge extends, which imitates in outline the smaller 
 curvatures of the crest. Ledges of this kind occur 
 
94 
 
 S^. Helena, pabt r. 
 
 not unfrequently within volcanic craters, and their 
 formation seems to be due to the sinking down of a 
 level sheet of hardened lava, the edges of which re- 
 main (like the ice ronnd a pool, from which the water 
 has been drained) adhering to the sides. ^ 
 
 In some parts, the ridge is surmounted by a wall 
 or parapet, perpendicular on both sides. Near Diana's 
 Peak this wall is extremely narrow. At the Galapagos 
 Archipelago I observed parapets, having a quite similar 
 structure and appearance, surmounting several of the 
 craters ; one, which I more particularly examined^ 
 was composed of glossy, red scoriaB firmly connected 
 together; being externally perpendicular, and extend- 
 ing round nearly the whole circumference of the crater^ 
 it rendered it almost inaccessible. The Peak of Tene- 
 rifie and Cotopaxi, according to Humboldt, are similarly 
 constructed ; he states ^ that ' at their summits a cir- 
 cular wall surrounds the crater, which wall, at a 
 distance, has the appearance of a small cylinder placed 
 on a truncated cone. On Cotopaxi^ this peculiar 
 structure is visible to the naked eye at more than 
 2,000 toises' distance ; and no person has ever reached 
 its crater. On the Peak of Teneriffe, the parapet is so 
 high, that it would be impossible to reach the caldera^ 
 if on the eastern side there did not exist a breach.' 
 The origin of these circular parapets is probably du& 
 to the heat or vapours from the crater, penetrating^ 
 and hardening the sides to a nearly equal depth, and 
 afterwards to the mountain being slowly acted on by 
 the weather, which would leave the hardened part^ 
 
 ^ A most remarkable instance of this structure is described in 
 Ellis's ' Polynesian Researches ' (second edit.), where an admirable 
 drawing is given of the successive ledges or terraces, on the borders 
 of the immense crater at Hawaii, in the Sandwich Islands. 
 
 2 < Personal Narrative,' voh i. p. 171. 
 
 ' Humboldt's 'Picturesque Atlas,' folio, pi. 10. 
 
CHAP. IT. Central C^trved Ridge. 95 
 
 projecting in tlie form of a cylinder or circular 
 parapet. 
 
 From the points of structure in tlie central ridge, 
 now enumerated, — namely, from tlie convergence to- 
 wards it of the beds of the upper series, — from the 
 lavas there becoming highly cellular, — from the flat 
 ledge, extending along its inner and precipitous side, 
 like that within some still active craters, — from the 
 parapet-like wall on its summit, — and lastly, from its 
 peculiar curvature, unlike that of any common line of 
 elevation, I cannot doubt that this curved ridge 
 forms the last remnant of a great crater. In endeavour- 
 ing, however, to trace its former outline, one is soon 
 baffled ; its western extremity gradually slopes down, 
 and, branching into other ridges, extends to the sea- 
 coast ; the eastern end is more curved, but it is only 
 a little better defined. Some appearances lead me to 
 suppose that the southern wall of the crater joined the 
 present ridge near Nest Lodge ; in this case the crater 
 must have been nearly three miles long, and about a 
 mile and a half in breadth. Had the denudation of 
 the ridge and the decomposition of its constituent 
 rocks proceeded a few steps farther, and had this ridge, 
 like several other parts of the island, been broken up 
 by great dikes and masses of injected matter, we should 
 in vain have endeavoured to discover its true nature. 
 Even now we have seen that at Flagstaff Hill the 
 lower extremity and most distant portion of one sheet 
 of the erupted matter has been upheaved to as great a 
 height as the crater down which it flowed, and pro- 
 bably even to a greater height. It is interesting thus 
 to trace the steps by which the structure of a volcanic 
 district becomes obscured, and finally obliterated : so 
 near to this last stage is St. Helena, that I believe no 
 one has hitherto suspected that the central ridge or 
 
96 St Helena, 
 
 PAET I. 
 
 axis of tlie island, is tlie last wreck of tiie crater, 
 wlience the most raodern volcanic streams were poured 
 forth. 
 
 The great hollow space or valley southward of the 
 central curved ridge, across which the half of the crater 
 must once have extended, is formed of bare, water- 
 worn hillocks and ridges of red, yellow, and brown 
 rocks, mingled together in chaos-like confusion, inter- 
 laced by dikes, and without any regular stratification. 
 The chief part consists of red decomposing scorige, 
 associated with various kinds of tuflp and yellow argil- 
 laceous beds, full of broken crystals, those of augite 
 being particularly large. Here and there masses of 
 highly cellular and amygdaloidal lavas protrude. From 
 one of the ridges in the midst of the valley, a conical 
 precipitous hill, called Lot, boldly stands up, and forms 
 a most singular and conspicuous object. It is com- 
 posed of phonolite, divided in one part into great 
 curved laminae, in another, into angular concretionary 
 balls, and in a third part into outwardly radiating 
 columns. At its base the strata of lava, tuff, and 
 scoriae, dip away on all sides : ^ the uncovered portion 
 is 197 ^ feet in height, and its horizontal section gives 
 an oval figure. The phonolite is of a greenish-gray 
 colour, and is full of minute acicular crystals of 
 feldspar; in most parts it has a conchoidal fracture, 
 and is sonorous, yet it is crenulated with minute air- 
 cavities. In a SW. direction from Lot, there are 
 some other remarkable columnar pinnacles, but of a 
 
 ^ Abich, in Ms ' Views of Vesuvius ' (plate vi.), has shown the 
 manner in which beds, under nearly similar circumstances, are tilted 
 up. The upper beds are more turned up than the lower ; and he 
 accounts for this, by showing that the lava insinuates itself hori- 
 zontally between the lower beds. 
 
 - This height is given by Mr. Seale, in his Geognosy of the island. 
 The height of the summit above the level of the sea, is said to be 
 1,444 feet. 
 
CHAP. IV. Hills of Phonolite. 97 
 
 less regular shape, namely, Lot's Wife, and the Asses 
 Ears, composed of allied kinds of rock. From their 
 flattened shape, and their relative position to each 
 other, they are evidently connected on the same line ot 
 fissure. It is, moreover, remarkable that this same 
 NE. and SW. line, joining Lot and Lot's Wife, 
 prolonged, would intersect Flagstaff Hill, which, as 
 before stated, is crossed by numerous dikes running 
 in this direction, and which has a disturbed structure, 
 rendering it probable that a great body of once fluid 
 rock lies injected beneath it. 
 
 In this same great valley there are several other 
 conical masses of injected rock (one, I observed, was 
 composed of compact greenstone), some of which are 
 not connected, as far as is apparent, with any line of 
 dike ; whilst others are obviously thus connected. Of 
 these dikes, three or four great lines stretch across the 
 valley in a NE. and SW. direction, parallel to that 
 one connecting the Asses' Ears, Lot's Wife, and pro- 
 bably Lot. The number of these masses of injected 
 rock is a remarkable feature in the geology of St. 
 Helena. Besides those just mentioned, and the hypo- 
 thetical one beneath Flagstaff Hill, there is Little 
 Stony-top and others, as I have reason to believe, at 
 the Man-and-Horse, and at High Hill. Most of these 
 masses, if not all of them, have been injected subse- 
 quently to the last volcanic eruptions from the central 
 crater. The formation of conical bosses of rock on 
 lines of fissure, the walls of which are in most cases 
 parallel, may probably be attributed to inequalities in 
 the tension, causing small transverse fissures ; and at 
 these points of intersection the edges of the strata 
 would naturally yield, and be easily turned upwards. 
 Finally, I may remark, that hiDs of phonolite every- 
 
 H 
 
98 SL Helena. 
 
 PART I. 
 
 where are apt ^ to assume singular and even grotesque 
 stapes, like that of Lot : the peak at Fernando Noronha 
 offers an instance ; at St. Jago, however, the cones 
 of phonolite, though tapering, have a regular form. 
 Supposing, as seems probable, that all such hillocks 
 or obelisks have originally been injected, whilst 
 liquefied, into a mould formed by yielding strata, as 
 certainly has been the case with Lot, how are we to 
 account for the frequent abruptness and singularity of 
 their outlines, compared with similarly injected masses 
 \, of greenstone and basalt? Can it be due to a less 
 perfect degree of fluidity, which is generally supposed 
 to be characteristic of the allied trachytic lavas ? 
 
 8ujpeTJicial deposits. — Soft calcareous sajidstone 
 occurs in extensive, though thin, superficial beds, both 
 on the northern and southern shores of the island. 
 It consists of very minute, equal-sized, rounded particles 
 of shells, and other organic bodies, which partially 
 retain their yellow, brown, and pink colours, and oc- 
 casionally, though very rarely, present an obscure trace 
 of their original external forms. I in vain endeavoured 
 to find a single unrolled fragment of a shell. The 
 colour of the particles is the most obvious character 
 by which their origin can be recognised, the tints 
 being affected (and an odour produced) by a moderate 
 heat, in the same manner as in fresh shells. The par- 
 ticles are cemented together, and are mingled with 
 some earthy matter : the purest masses, according to 
 Beatson, contain 70 per cent, of carbonate of lime. 
 The beds, varying in thickness from two or three feet 
 to fifteen feet, coat the surface of the ground ; they 
 generally lie on that side of the valley which is pro- 
 tected from the wind, and they occur at the height 
 
 * D'Aubuisson, in his ' Traite de Geognosie' (torn, ii. p. 540) 
 particularly remarks that this is the case. 
 
CHAP. IV. Superficial Calcareotts Beds. 99 
 
 of several hundred feet above ttie level of the sea. 
 Their position is the same, which sand, if now drifted 
 bv the trade-wind, would occupy; and no doubt they 
 thus originated, which explains the equal size and 
 minuteness of the particles, and likewise the entire 
 absence of whole shells, or even of moderately-sized 
 frao-ments. It is remarkable that at the present day 
 there are no shelly beaches on any part of the coast, 
 whence calcareous dust could be drifted and winnowed ; 
 we must, therefore, look back to a former period when 
 before the land was worn into the present great 
 precipices, a shelving coast, like that of Ascension, 
 was favourable to the accumulation of shelly detritus. 
 Some of the beds of this limestone are between 600 
 and 700 feet above the sea ; but part of this height 
 may possibly be due to an elevation of the land, sub- 
 sequent to the accumulation of the calcareous sand. 
 
 The percolation of rain-water has consolidated parts 
 of these beds into a solid rock, and has formed masses 
 of dark brown, stalagmitic limestone. At the Sngar- 
 Loaf quarry, fragments of rock on the adjoining slopes,^ 
 have been thickly coated by successive fine layers of 
 calcareous matter. It is singular, that many of these 
 pebbles have their entire surfaces coated, without any 
 point of contact having been left uncovered ; hence, 
 these pebbles must have been lifted up by the slow 
 deposition between them of the successive films of car- 
 bonate of lime. Masses of white, finely oolitic rock are 
 attached to the outside of some of these coated pebbles. 
 
 ^ In the earthy detritus on several parts of this hill, irregular 
 masses of very impure, crystallised sulphate of lime occur As this 
 substance is now being abundantly deposited by the surf at Ascen- 
 sion, it is possible that these masses may thus have originated ; but 
 if so, it must have been at a period when the land stood at a much 
 lower level. This earthy selenite is now found at a height of 
 between 600 and 700 feet. 
 
 H 2 
 
loo Sf. Helena. 
 
 PART I. 
 
 Von Bucli lias described a compact limestone at 
 Lanzarote, which seems perfectly to resemble the sta- 
 lagmitic deposition just mentioned : it coats pebbles, 
 •and in parts is finely oolitic : it forms a far-extended 
 layer, from one inch to two or three feet in thickness, 
 and it occurs at the height of 800 feet above the sea, 
 but only on that side of the island exposed to the violent 
 north-western winds. Yon Buch remarks,^ that it is 
 not found in hollows, but only on the unbroken and 
 inclined surfaces of the mountain. He believes, that 
 it has been deposited by the spray which is borne over 
 the whole island by these violent winds. It appears, 
 however, to me much more probable that it has been 
 formed, as at St. Helena, by the percolation of water 
 through finely comminuted shells : for when sand is 
 blown on a much exposed coast, it always tends to accu- 
 mulate on broad, even surfaces, which offer a uniform 
 resistance to the winds. At the neighbouring island, 
 moreover, of Fuerteventura,^ there is an earthy lime- 
 stone, which, according to Von Buch, is quite similar 
 to specimens which he has seen from St. Helena, and 
 which he believes to have been formed by the drifting 
 of shelly detritus. 
 
 The upper beds of the limestone, at the above- 
 mentioned quarry on the Sugar-Loaf Hill, are softer, 
 finer-grained and less pure, than the lower beds. They 
 abound with fragments of land-shells, and with some 
 perfect ones ; they contain, also, the bones of birds, and 
 the large eggs,^ apparently of water-fowl. It is pro- 
 bable that these upper beds remained long in an uncon- 
 
 ^ ' Description des Isles Canaries,' p. 293. 
 
 - Idem, pp. 314 and 374. 
 
 3 Colonel Wilkes, in a catalogue presented with some specimens 
 to the Geological Society, states that as many as ten eggs were found 
 h^ one person. Dr. Buckland has remarked (' Geolog. Trans.' vol. v. 
 p. 474) on these eggs. 
 
CHAP. lY. Extinct Land Shells. loi 
 
 solidated form, durmg which time, these terrestrial 
 productions were embedded. Mr. G. R. Sowerby has 
 kindly examined three species of land-shells, which I 
 procured from this bed, and his descriptions are given 
 in the Appendix. One of them is a Succinea, identical 
 with a species now living abundantly on the island : 
 the two others, namely, Gochlogena fossilis and Helix 
 hiplicata, are not known in a recent state : the latter 
 species was also found in another and different locality, 
 associated with a species of Gochlogena which i& un- 
 doubtedly extinct. 
 
 Beds of extinct land-shells. — Land-shells, all of 
 which appear to be species now extinct, occur embedded 
 in earth, in several parts of the island. The greater 
 number have been found at a considerable height on 
 Flagstaff Hill. On the NW. side of this hill, a rain- 
 channel exposes a section of about twenty feet in thick- 
 ness, of which the upper part consists of black vegetable 
 mould, evidently washed down from the heights above, 
 and the lower part of less black earth, abounding with 
 young and old shells, and with their fragments : part 
 of this earth is slightly consolidated by calcareous 
 matter, apparently due to the partial decomposition of 
 some of the shells. Mr. Seale, an intelligent resident, 
 who first called attention to these shells, gave me a 
 large collection from another locality, where the shells 
 appear to have been embedded in very black earth. 
 Mr. G. R. Sowerby has examined these shells, and has 
 described them in the Appendix. There are seven 
 species, namely, one Gochlogena, two species of the 
 genus Gochlicopa, and four of Helix : none of these are 
 known in a recent state, or have been found in any 
 other country. The smaller species were picked out of 
 the inside of the large shells of the Gochlogena aiiris- 
 'vulpina. This last-mentioned species is in many 
 
I02 Sf. Helena. 
 
 PART I. 
 
 respects a very singular one ; it was classed, even by 
 Lamarck, in a marine genus, and having thus been 
 mistaken for a sea-shell, and the smaller accompanying 
 species having been overlooked, the exact localities 
 where it was found have been measured, and the eleva- 
 tion of this island thus deduced ! It is very remarkable 
 that all the shells of this species found by me in one 
 spot, form a distinct variety, as described by Mr. 
 Sowerby, from those procured from another locality by 
 Mr. Seale. As this Cochlogena is a large and con- 
 spicuous shell, I particularly enquired from several 
 intelligent countrymen whether they had ever seen it 
 alive ; they all assured me that they had not, and they 
 would not even believe that it was a land animal : Mr. 
 Seale, moreover, who was a collector of shells all his 
 life at St. Helena, never met with it alive. Possibly 
 some of the smaller species may turn out to be yet 
 living kinds ; but, on the other hand, the two land-shells 
 which are now living on the island in great numbers, 
 do not occur embedded, as far as it is yet known, with 
 the extinct species. I have shown in my Journal,^ that 
 the extinction of these land-shells possibly may not be 
 an ancient event ; as a great change took place in the 
 state of the island about 120 years ago, when the old 
 trees died, and were not replaced by young ones, these 
 being destroyed by the goats and hogs, which had run 
 wild in numbers, from the year 1502. Mr. Seale states, 
 that on Flagstaff Hill, where we have seen that the 
 embedded land-shells are especially numerous, traces 
 are everywhere discoverable, which plainly indicate 
 that it was once thickly clothed with trees ; at present 
 not even a bush grows there. The thick bed of black 
 vegetable mould which covers the shell-bed, on the 
 
 ^ ' Journal of Researches,' 1845, p. 489. 
 
CHAP. IT. Elevation of the Land. 103 
 
 flanks of this hill, was probably washed down from the 
 upper part, as soon as the trees perished, and the shelter 
 afforded by them was lost. 
 
 'Elevation of the land. — Seeing that the lavas of 
 the basal series, which are of submarine origin, are 
 raised above the level of the sea, and at some places to 
 the height of many hundred feet, I looked out for 
 superficial signs of the elevation of the land. The 
 bottoms of some of the gorges, which descend to the 
 coast, are filled up to the depth of about a hundred 
 feet, by rudely divided layers of sand, muddy clay, and 
 fragmentary masses ; in these beds, Mr. Seale has found 
 the bones of the tropic-bird and of the albatross ; the 
 former now rarely, and the latter never visiting the 
 island. From the difference between these layers, and 
 the sloping piles of detritus which rest on them, I 
 suspect that they were deposited, when the gorges stood 
 beneath the sea. Mr. Seale, moreover, has shown that 
 some of the fissure-like gorges,^ become, with a concave 
 outline, gradually rather wider at the bottom than at 
 the top ; and this peculiar structure was probably 
 caused by the wearing action of the sea, when it entered 
 the lower part of these gorges. At greater heights, 
 the evidence of the rise of the land is even less clear : 
 nevertheless, in a bay-like depression on the table-land 
 behind Prosperous Bay, at the height of about 1,000 
 feet, there are flat-topped masses of rock, which it is 
 scarcely conceivable, could have been insulated from 
 the surrounding and similar strata, by any other agency 
 than the denuding action of a sea-beach. Much denu- 
 dation, indeed, has been effected at great elevations, 
 which it would not be easy to explain by any other 
 means: thus, the flat summit of the Barn, which is 
 
 ' A fissure-like gorge, near Stony-top, is said by Mr. Seale to be 
 840 feet deep, and only 115 feet in width. 
 
I04 SL H electa. 
 
 PAET I. 
 
 2,000 feet high, presents, according to Mr. Seale, a 
 perfect network of truncated dikes ; on hills like the 
 Flagstaff, formed of soft rock, we might suppose that 
 the dikes had been worn down and cut off by meteoric 
 agency, but we can hardly suppose this possible with 
 the hard, basaltic strata of the Barn. 
 
 Goasi denudation. — The enormous cliffs, in many 
 parts between 1,000 and 2,000 feet in height, with 
 which this prison-like island is surrounded, with the 
 exception of only a few places, where narrow valleys 
 descend to the coast, is the most striking feature in its 
 scenery. We have seen that portions of the basaltic 
 ring, two or three miles in length by one or two miles 
 in breadth, and from one to two thousand feet in height, 
 have been wholly removed. There are, also, ledges and 
 banks of rock, rising out of profoundly deep water, and 
 distant from the present coast between three and four 
 miles, which, according to Mr. Seale, can be traced to 
 the shore, and are found to be the continuations of 
 certain well-known great dikes. The swell of the 
 Atlantic Ocean has obviously been the active power in 
 forming these cliffs ; and it is interesting to observe 
 that the lesser, though still great, height of the cliffs 
 on the leeward and partially protected side of the 
 island, (extending from the Sugar-Loaf Hill to South. 
 West Point,) corresponds with the lesser degree of 
 exposure. When reflecting on the comparatively low 
 coasts of many volcanic islands, which also stand ex- 
 posed in the open ocean, and are apparently of consider- 
 able antiquity, the mind recoils from an attempt to 
 grasp the number of centuries of exposure, necessary to 
 have ground into mud and to have dispersed the enor- 
 mous cubic mass of hard rock which has been pared off 
 the circumference of this island. The contrast in the 
 superficial state of St. Helena, compared with the 
 
CHAP. lY. Cratej^s of Elevation, 105 
 
 nearest island, namely, Ascension, is very striking. At 
 Ascension, the surfaces of the lava-streams are glossy, as 
 if just poured forth, their boundaries are well defined, 
 and they can often be traced to perfect craters, whence 
 they were erupted ; in the course of many long walks, 
 I did not observe a single dike ; and the coast round 
 nearly the entire circumference is low, and has been 
 eaten back (though too much stress must not be placed 
 on this fact, as the island may have been subsiding) 
 into a little wall only from ten to thirty feet high. Yet 
 during the 340 years, since Ascension has been known, 
 not even the feeblest signs of volcanic action have been 
 recorded.^ On the other hand, at St. Helena, the course 
 of no one stream of lava can be traced, either by the 
 state of its boundaries or of its superficies ; the mere 
 wreck of one great crater is left ; not the valleys only, 
 but the surface of some of the highest hills, are inter- 
 laced by worn-down dikes, and, in many places, the 
 denuded summits of great cones of injected rock stand 
 exposed and naked ; lastly, as we have seen, the entire 
 circuit of the island has been deeply worn back into the 
 grandest precipices. 
 
 Craters of JElevatioii. 
 
 There is much resemblance in structure and in 
 geological history between St. Helena, St. Jago, and 
 Mauritius. All three islands are bounded (at least in 
 
 1 In the 'Nautical Magazine' for 1835, p. 642, and for 1838, p. 
 361, and in the ' Comptes Kendns,' April, 1838, accounts are given of 
 a series of Yolcanic phenomena — earthquakes — troubled water — 
 floating scoriae and columns of smoke — which have been observed at 
 intervals since the middle of the last century, in a space of open sea 
 between longitudes 20° and 22° west, about half a degree south of 
 the equator. These facts seem to show, that an island or an archi- 
 pelago is in process of formation in the middle of the Atlantic : a 
 line joining St. Helena and Ascension, prolonged, intersects this 
 slowly nascent focus of volcanic action. 
 
io6 SL Helena. 
 
 PABT I. 
 
 the parts which I was able to examine) by a ring of 
 basaltic mountains, now much broken, but evidently 
 once continuous. These mountains have, or apparently 
 once had, their escarpements steep towards the interior 
 of the island, and their strata dip outwards. I was 
 able to ascertain, only in a few cases, the inclination of 
 the beds ; nor was this easy, for the stratification was 
 generally obscure, except when viewed from a distance. 
 I feel, however, little doubt that, according to the re- 
 searches of M. Elie de Beaumont, their average in- 
 clination is greater than that which they could have 
 acquired, considering their thickness and compactness, 
 by flowing down a sloping surface. At St. Helena, 
 and at St. Jago, the basaltic strata rest on older^and 
 probably submarine beds of different composition. At 
 all three islands, deluges of more recent lavas have 
 flowed from the centre of the island, towards and be- 
 tween the basaltic mountains ; and at St. Helena the 
 central platform has been filled up by them. All 
 three islands have been raised in mass. At Mauritius 
 the sea, within a late geological period, must have 
 reached to the foot of the basaltic mountains, as it now 
 does at St. Helena ; and at St. Jago it is cutting back 
 the intermediate plain towards them. In these three 
 islands, but especially at St. Jago and at Mauritius, 
 when, standing on the summit of one of the old basaltic 
 mountains, one looks in vain towards the centre of the 
 island, — the point towards which the strata beneath 
 one's feet, and of the mountains on each side, rudely 
 converge, — for a source whence these strata could have 
 been erupted ; but one sees only a vast hollow platform 
 stretched beneath, or piles of matter of more recent 
 origin. 
 
 These basaltic mountains come, I presume, into 
 the class of Craters of elevation: it is immaterial 
 
CHAP. IV. Cratei^s of Elevation. 107 
 
 whether the rings were ever corapletely formed, for the 
 portions which now exist have so uniform a structure, 
 that, if they do not form fragments of true craters, 
 they cannot be classed with ordinary lines of elevation. 
 With respect to their origin, after having read the 
 works of Mr. Lyell,i and of MM. C. Prevost and Yirlet, 
 I cannot believe that the great central hollows have 
 been formed by a simple dome-shaped elevation, and 
 the consequent arching of the strata. On the other 
 hand, I have very great difficulty in admitting that 
 these basaltic mountains are merely the basal fragments 
 of great volcanos, of which the summits have either 
 been blown off, or more probably swallowed up by 
 subsidence. These rings are, in some instances, so 
 immense, as at St. Jago and at Mauritius, and their 
 occurrence is so frequent, that I can hardly persuade 
 myself to adopt this explanation. Moreover, I suspect 
 that the following circumstances, from their frequent 
 concurrence, are someway connected together, — a con- 
 nection not implied in either of the above views : 
 namely, first, the broken state of the ring, showing 
 that the now detached portions have been exposed to 
 great denudation, and in some cases, perhaps, rendering 
 it probable that the ring never was entire ; secondly, 
 the great amount of matter erupted from the central 
 area after or during the formation of the ring ; and 
 thirdly, the elevation of the district in mass. As far 
 as relates to the inclination of the strata being greater 
 than that which the basal fragments of ordinary vol- 
 canos would naturally possess, I can readily believe 
 that this iuclination might have been slowly acquired 
 by that amount of elevation, of which, according to 
 M. Elie de Beaumont, the numerous upfilled fissures or 
 
 • * Principles of Geology' (fifth edit.), vol. ii. p. 171. 
 
io8 S^. Helena, 
 
 PAET I. 
 
 dikes are tlie evidence and the measure, — a view 
 equally novel and important, wliicli we owe to ttie re- 
 searches of that geologist on Mount Etna. 
 
 A conjecture, including the above circumstances, 
 occurred to me, when, — with my mind fully convinced, 
 from the phenomena of 1835 in South America,^ that 
 the forces which eject matter from volcanic orifices and 
 raise continents in mass are identical, — I viewed that 
 part of the coast of St. Jago, where the horizontally 
 upraised, calcareous stratum dips into the sea, directly 
 beneath a cone of subsequently erupted lava. The 
 conjecture is that, during the slow elevation of a vol- 
 canic district or island, in the centre of which one or 
 more orifices continue o|)en, and thus relieve the sub- 
 terranean forces, the borders are elevated more than 
 the central area ; and that the portions thus upraised 
 do not slope gently into the central, less elevated area, 
 as does the calcareous stratum under the cone at St. 
 Jago, and as does a large part of the circumference of 
 Iceland,'^ but that they are separated from it by curved 
 
 ^ I have given a detailed account of these phenomena, in a paper 
 read before the Geological Society in March, 1838. At the instant 
 of time, when an immense area was convulsed and a large tract 
 elevated, the districts immediately surrounding several of the great 
 vents in the Cordillera remained quiescent ; the subterranean forces 
 being apparently relieved by the eruptions, which then recommenced 
 with great violence. An event of somewhat the same kind, but on 
 an infinitely smaller scale, appears to have taken place, according 
 to Abich (' Views of Vesuvius,' plates i. and ix.), within the great 
 crater of Vesuvius, where a platform on one side of a fissure was 
 raised in mass twenty feet, whilst on the other side, a train of small 
 volcanos burst forth in eruption. 
 
 2 It appears, from information communicated to me in the most 
 obliging manner by M. E. Eobert, that the circumferential parts of 
 Iceland, which are composed of ancient basaltic strata alternating 
 with tuff, dip inland, thus forming a gigantic saucer. M. Eobert 
 found that this was the case, with a few and quite local exceptions, 
 for a space of coast several hundred miles in length. I find this 
 statement corroborated, as far as regards one place, by Mackenzie, 
 in his ' Travels ' (p. 377), and in another place by some MS. notes 
 kindly lent me by Dr. Holland. The coast is deeply indented by 
 creeks, at the head of which the land is generally low. M. Eobert 
 
CHAP, IV. . Craters of Elevation, 109 
 
 faults. We might expect, from what we see along 
 ordinary faults, that the strata on the upraised side, 
 already dipping outwards from their original formation 
 as lava-streams, would be tilted from the line of fault, 
 and thus have their inclination increased. According 
 to this hypothesis, which I am tempted to extend only 
 to some few cases, it is not probable that the ring 
 would ever be formed quite perfect; and from the 
 elevation being slow, the upraised portions would 
 generally be exposed to much denudation, and hence 
 the ring become broken ; we might also expect to find 
 occasional inequalities in the dip of the upraised 
 masses, as is the case at St. Jago. By this hypothesis 
 the elevation of the districts in mass, and the flowing 
 of deluges of lava from the central platforms, are like- 
 wise connected together. On this view the marginal 
 basaltic mountains of the three foregoing islands might 
 still be considered as forming ^ Craters of elevation ; ' 
 the kind of elevation implied having been slow, and 
 the central hollow or platform having been formed, not 
 by the arching of the surface, but simply by that part 
 having been upraised to a less height. 
 
 informs me, that the inwardly dipping strata appear to extend as 
 far as this line, and that their inclination usually corresponds with 
 the slope of the surface, from the high coast-mountains to the low 
 land at the head of these creeks. In the section described by Sir 
 Gr. Mackenzie, the dip is 12°. The interior parts of the island chiefly 
 consist, as far as is known, of recently erupted matter. The great 
 size, however, of Iceland, equalling the bulkiest part of England, 
 ought perhaps to exclude it from the class of islands we have boen 
 considering ; but I cannot avoid suspecting that if the coast-moun- 
 tains, instead of gently sloping into the less elevated central area, 
 had been separated from it by irregularly curved faults, the strata 
 would have been tilted seaward, and a ' Crater of elevation,' like 
 that of St. Jago or that of Mauritius, but of much vaster dimensions, 
 would have been formed. I will only further remark, that the 
 frequent occurrence of extensive lakes at the foot of large volcanos, 
 and the frequent association of volcanic and fresh-water strata, 
 seem to indicate that the areas around volcanos are apt to be 
 depressed beneath the general level of the adjoining country, either 
 from having been less elevated, or from the eiiects of subsidence. 
 
I lo Galapagos Archipelago. paet i. 
 
 CHAPTER V. 
 
 GALAPAGOS ARCHIPELAGO. 
 
 Chatham Island — Craters composecl of a jyeculiar Mndoftuff — Small 
 dasaltic craters, 7vith hollorvs at their bases — Albemarle Island, Jluid 
 lavas, their comj^osition — Craters of tuff, ijiclination of tJteir ex- 
 terior diverging strata, and structure of their interior converging 
 strata — James Island, segment of a small basaltic crater ; fluidity 
 and composition of its lava streams, and of its ejected fragments — 
 Concluding remarks 07i the craters of tuff, and on the breached con* 
 dition of their southern sides — Mineralogical composition of the 
 rochs of the archipelago — Elevation of the land — Direction of the 
 fissures of eruption. 
 
 This arcliipelago is situated under the Equator, at a 
 distance of between five and six hundred miles from 
 tlie west coast of South America. It consists of five 
 principal islands, and of several small ones, which 
 together are equal in area,^ but not in extent of land, 
 to Sicily, conjointly with the Ionian Islands. They are 
 all volcanic : on two, craters have been seen in erup- 
 tion, and on several of the other islands, streams of 
 lava have a recent appearance. The larger islands are 
 chiefly composed of solid rock, and they rise with a 
 tame outline to a height of between one and four 
 thousand feet. They are sometimes, but not generally, 
 surmounted by one principal orifice. The craters vary 
 
 1 I exclude from this measurement, the small volcanic islands 
 of Culpepper and Wenman, lying seventy miles northward of the 
 group. Craters were visible on all the islands of the group, except 
 on Towers Island, which is one of the lowest ; this island is, however, 
 formed of volcanic rocks. 
 
CHAP. V. 
 
 Altered Tttff, 
 
 I II 
 
 in size from mere spiracles to huge caldrons several 
 miles in circumference ; they are extraordinarily 
 numerous, so that I should think, if enumerated, they 
 would be found to 'exceed two thousand ; they are 
 formed either of scoriae and lava, or of a brown coloured 
 tuff; and these latter craters are in several respects 
 
 Cidpep])er I. • 
 
 Wenman I, 
 
 No. 11. 
 
 I II 1 I I -1 
 
 Narborotigh I. %^ 1 
 
 Albemarle L 
 
 1^5 Ahincfdon I. 
 
 Hindloesl. 
 
 Tower I. 
 
 ■**^!\ James I. 
 % 
 ^ Indefatigable I. 
 
 Barring ton I. 
 
 Chatham 1. 
 
 Charles I. 
 
 GALAPAGOS ARCHIPELAGO. 
 
 Hoods I. 
 
 remarkable. The whole group was surveyed by the 
 officers of the Beagle. I visited myself four of the 
 principal islands, and received specimens from all the 
 others. Under the head of the different islands I will 
 describe only that which appears to me deserving of 
 attention. 
 
 Chatham Island. Graters composed of a singular 
 hind of tuff. — Towards the eastern end of this island 
 
112 Galapagos Archipelago. paet i. 
 
 there occur two craters composed of two kinds of tuff; 
 one kind being friable, like slightly consolidated ashes ; 
 and the other compact, and of a different nature from 
 anything which I have met with described. This 
 latter substance, where it is best characterised, is of a 
 yellowish-brown colour, translucent, and with a lustre 
 somewhat resembling resin ; it is brittle, with an 
 angular, rough, and very irregular fracture, sometimes, 
 however, being slightly granular, and even obscurely 
 crystalline : it can readily be scratched with a knife, 
 yet some points are hard enough just to mark common 
 glass ; it fuses with ease into a blackish-green glass. 
 The mass contains numerous broken crystals of olivine 
 and augite, and small particles of black and brown 
 scorise : it is often traversed by thin seams of calcareous 
 matter. It generally affects a nodular or concretionary 
 structure. In a hand specimen this substance would 
 certainly be mistaken for a pale and peculiar variety of 
 pitchstone; but when seen in mass its stratification, 
 and the numerous layers of fragments of basalt, both 
 angular and rounded, at once render its subaqueous 
 origin evident. An examination of a series of speci- 
 mens shows that this resin-like substance results from a 
 chemical change on small particles of pale and dark- 
 coloured scoriaceous rocks; and this change could be 
 distinctly traced in different stages round the edges of 
 even the same particle. The position near the coast 
 of all the craters composed of this kind of tuff or 
 peperino, and their breached condition, renders it 
 probable that they were all formed when standing im- 
 mersed in the sea; considering this circumstance, 
 together with the remarkable absence of large beds of 
 ashes in the whole archipelago, I think it highly 
 probable that much the greater part of the tuff has 
 originated from the trituration of fragments of the 
 
CHAP. V. A Itei^ed Tuff. 113 
 
 gray, basaltic lavas in the mouths of craters standing in 
 the sea. It may be asked whether the heated water 
 within these craters has produced this singular change 
 in the small scoriaceous particles, and given to them 
 their translucent, resin-like fracture? Or has the 
 associated lime played any part in this change ? I ask 
 these questions from having found at St. Jago, in the 
 Cape de Verde Islands, that where a great stream of 
 molten lava has flowed over a calcareous bottom into 
 the sea, the outermost film, which in other parts re- 
 sembles pitchstone, is changed, apparently by its 
 contact with the carbonate of lime, into a resin-like 
 substance, precisely like the best characterised speci- 
 mens of the tuff from this archipelago.^ 
 
 To return to the two craters : one of them stands at 
 the distance of a league from the coast, the intervening 
 tract consisting of a calcareous tuff, apparently of sub- 
 marine origin. This crater consists of a circle of hills, 
 some of which stand quite detached, but all have a very 
 regular, qua-qua versal dip, at an inclination of between 
 thirty and forty degrees. The lower beds, to the thick- 
 ness of several hundred feet, consist of the resin-like 
 stone, with embedded fragments of lava. The upper 
 beds, which are between thirty and forty feet in thick- 
 ness, are composed of a thinly stratified, fine-grained, 
 harsh, friable, brown- coloured tuff, or peperino.^ A 
 central mass without any stratification, which must 
 
 ^ The concretions containing lime, whicli I have described at 
 Ascension, as formed in a bed of ashes, present some degree of re- 
 semblance to this substance, but they have not a resinous fracture. 
 At St. Helena, also, I found veins of a somewhat similar, compact, but 
 non-resinous substance, occurring in a bed of pumiceous ashes, appa- 
 rently free from calcareous matter : in neither of these cases could 
 heat have acted. 
 
 2 Those geologists who restrict the term of ' tuff to ashes of a 
 white colour, resulting from the attrition of feldspathic lavas, would 
 call these brown- coloured strata 'peiDerino,' 
 
114 
 
 Galapagos Archipelago. 
 
 PAET I. 
 
 formerly have occupied the hollow of the crater, but is 
 now attached only to a few of the circumferential hills, 
 consists of a tuff, intermediate in character between 
 that with a resin-like, and that with an earthy fracture. 
 This mass contains white calcareous matter in small 
 patches. The second crater (520 feet in height) must 
 have existed until the eruption of a recent, great stream 
 of lava, as a separate islet ; a fine section, worn by the 
 sea, shows a grand funnel-shaped mass of basalt, sur- 
 rounded by steep, sloping flanks of tuff, having in parts 
 an earthy, and in others, a semi-resinous fracture. The 
 tuff is traversed by several broad, vertical dikes, with 
 smooth and parallel sides, which I did not doubt were 
 formed of basalt, until I actually broke off fragments. 
 These dikes, however, consist of tuff like that of the 
 surrounding strata, but more compact, and with a 
 
 hence we must conclude, that 
 
 smoother fracture 
 
 No. 12. 
 
 The Kicker Kock. 400 feet high. 
 
 fissures were formed and filled up with the finer mud 
 or tuff from the crater, before its interior was occupied, 
 as it now is, by a solidified pool of basalt. Other 
 fissures have been subsequently formed, parallel to 
 these singular dikes, and are merely filled with loose 
 rubbish. The change from ordinary scoriaceous parti- 
 cles to the substance with a semi-resinous fracture, 
 
CHAP. Y. Small Basaltic Craters. 115 
 
 could be clearly followed in portions of tlie compact 
 tuflP of these dikes. 
 
 At tlie distance of a few miles from these two 
 craters, stands tlie Kicker Rock, or islet, remarkable 
 from its singular form. It is unstratified, and is com- 
 posed of compact tuff, in parts baying tbe resin-like 
 fracture. It is probable that tbis amorphous mass, 
 like that similar mass in tbe case first described, once 
 filled up tbe central bollow of a crater, and tbat its 
 flanks, or sloping walls, bave since been worn quite 
 away by tbe sea, in wbicb it stands exposed. 
 
 Small hasaltic craters. — A bare, undulating tract, 
 at tbe eastern end of Cbatbam Island, is remarkable 
 from tbe number, proximity, and form of tbe small 
 basaltic craters with wbicb it is studded. Tbey consist, 
 either of a mere conical pile, or, but less commonly, of 
 a circle, of black and red, glossy scoriae, partially ce- 
 mented together. They vary in diameter from 30 to 
 150 yards, and rise from about 50 to 100 feet above 
 the level of the surrounding plain. From one small 
 eminence, I counted sixty of these craters, all of which 
 were within a third of a mile from each other, and 
 many were much closer. I measured the distance 
 between two very small craters, and found tbat it was 
 only thirty yards from the summit-rim of one to the 
 rim of the other. Small streams of black, basaltic lava, 
 containing olivine and much glassy feldspar, have flowed 
 from many, but not from all of these craters. The 
 surfaces of the more recent streams were exceedingly 
 rugged, and were crossed by great fissures ; the older 
 streams were only a little less rugged ; and they were 
 all blended and mingled together in complete confusion. 
 The different growth, however, of the trees on the 
 streams, often plainly marked their different ages. 
 Had it not been for this latter character, the streams 
 
 I 2 
 
1 16 Galapagos Archipelago. paet i. 
 
 could in few cases have been distinguished ; and, con- 
 sequently, this wide undulatory tract might have, (as 
 probably many tracts have,) been erroneously considered 
 as formed of one great deluge of lava, instead of by a 
 multitude of small streams, erupted from many small 
 
 orifices. 
 
 In several parts of this tract, and especially at the 
 base of the small craters, there are circular pits, with 
 l^erpendicular sides, from twenty to forty feet deep. At 
 the foot of one small crater, there were three of these 
 pits. They have probably been formed, by the falling 
 in of the roofs of small caverns.^ In other parts, there 
 are mammiform hillocks, which resemble great bubbles 
 of lava, with their summits fissured by irregular cracks, 
 which appeared, upon entering them, to be very deep ; 
 lava has not flowed from these hillocks. There are, 
 also, other very regular, mammiform hillocks, composed 
 of stratified lava, and surmounted by circular, steep- 
 sided hollows, which, I suppose have been formed by a 
 body of gas, first, arching the strata into one of the 
 bubble-like hillocks, and then, blowing ofi" its summit. 
 These several kinds of hillocks and pits, as well as the 
 numerous, small, scoriaceous craters, all show that this 
 tract has been penetrated, almost like a sieve, by the 
 passage of heated vapours. The more regular hillocks 
 could only have been heaved up, whilst the lava was in 
 a softened state.^ 
 
 * M. Elie de Beaumont has described (' Mem, pour servir,' &c., 
 tom. iv. p. 113) many ' petits cirques d'eboulement ' on Etna, of some 
 of wliicla the origin is historically known. 
 
 2 Sir G. Mackenzie (' Travels in Iceland,' pp. 389 to 892) has de- 
 scribed a plain of lava at the foot of Hecla, everyvt^here heaved up into 
 great bubbles or blisters. Sir George states that this cavernous lava 
 composes the uppermost stratum ; and the same fact is affirmed by 
 Von Buch ('Descript. des Isles Canaries,' p,159), with respect to the 
 basaltic stream near Rialejo, in Teneriffe. It appears singular that 
 it should be the upper streams that are chiefly cavernous, for one 
 sees no reason why the upper and lower should not have been equally 
 
CHAP. Y. Fluidity of diffe7^ent Lavas. iij 
 
 Albemarle Island. — This island consists of five, 
 great, flat-topped craters, wiiicli, together with the one 
 on the adjoining island of Narborough, singularly re- 
 semble each other, in form and height. The southern 
 one is 4,700 feet high, two others are 3,720 feet, a third 
 only 50 feet higher, and the remaining ones apparently 
 of nearly the same height. Three of these are situated 
 on one line, and their craters appear elongated in nearly 
 the same direction. The northern crater, which is not 
 the largest, was found by the triangulation to measure, 
 externally, no less than three miles and one-eighth of a 
 mile in diameter. Over the lips of these great, broad 
 caldrons, and from little orifices near their summits, 
 deluges of black lava have flowed down their naked sides. 
 
 Fluidity of dijferent lavas. — ISTear Tagus or Banks' 
 Cove, I examined one of these great streams of lava, 
 which is remarkable from the evidence of its former 
 high degree of fluidity, especially when its composition 
 is considered. Near the sea-coast this stream, is several 
 miles in width. It consists of a black, compact base, 
 easily fusible into a black bead, with angular and not 
 very numerous air-cells, and thickly studded with large, 
 fractured crystals of glassy albite,^ varying from the 
 
 afEected at different times ; — have the inferior streams flowed beneath 
 the pressure of the sea, and thus been flattened, after the passage 
 through them, of bodies of gas ? 
 
 * In the Cordillera of Chile, I have seen lava very closely resem- 
 bling this variety at the Galapagos Archipelago. It contained, how- 
 ever, besides the albite, well-formed crystals of augite,and the base 
 (perhaps in consequence of the aggregation of the augitic particles) 
 was a shade lighter in colour. I may here remark, that in all these 
 cases, I call the feldspathic crystals, alhite, from their cleavage- 
 planes (as measured by the reflecting goniometer) corresponding 
 with those of that mineral. As, however, other species of this genus 
 have lately been discovered to cleave in nearly the same planes with 
 albite, this determination must be considered as only provisional. I 
 examined the crystals in the lavas of many different parts of the 
 Galapagos group, and I found that none of them, with the exception 
 of some crystals from one part of James Island, cleaved in the 
 direction of orthite or potash-feldspar. 
 
ii8 Galapagos Archipelago, parti. 
 
 tenth of an inch to half-an-inch, in diameter. This 
 lava, although at first sight appearing eminently por- 
 phyritic, cannot properly be considered so, for the 
 crystals have evidently been enveloped, rounded, and 
 penetrated by the lava, like fragments of foreign rock 
 in a trap- dike. This was very clear in some specimens 
 of a similar lava, from Abingdon Island, in which the 
 only difference was, that the vesicles were spherical and 
 more numerous. The albite in these lavas is in a 
 similar condition with the leucite of Vesuvius, and with 
 the olivine, described by Von Buch,^ as projecting in 
 great balls from the basalt of Lanzarote. Besides the 
 albite, this lava contains scattered grains of a green 
 mineral, with no distinct cleavage, and closely resem- 
 bling olivine ; ^ but as it fuses easily into a green glass, 
 it belongs probably to the augitic family : at James 
 Island, however, a similar lava contained true olivine. 
 I obtained specimens from the actual surface, and from 
 a depth of four feet, but they differed in no respect. 
 The high degree of fluidity of this lava-stream was at 
 once evident, from its smooth and gently sloping sur- 
 face, from the manner in which the main stream was 
 divided by small inequalities into little rills, and es- 
 pecially from the manner in which its edges, far below 
 its source, and where it must have been in some degree 
 cooled, thinned out to almost nothing ; the actual 
 margin consisting of loose fragments, few of which were 
 larger than a man's head. The contrast between this 
 margin, and the steep walls, above twenty feet high, 
 bounding many of the basaltic streams at Ascension, is 
 very remarkable. It has generally been supposed that 
 lavas abounding with large crystals, and including 
 
 ' ' Description des Isles Canaries,' p. 295. 
 
 2 Humboldt mentions that he mistook a green aitgitio mineral, 
 occurring in the volcanic rocks of the Cordillera of Quito, for olivine. 
 
CHAP. V. Fhndity of different Lavas. 119 
 
 angular vesicles,^ have possessed little fluidity ; but we 
 see that the case has been very different at Albemarle 
 Island. The degree of fluidity in different lavas, does 
 not seem to correspond with any ajpjparent corresponding 
 amount of difference in their composition : at Chatham 
 Island, some streams, containing much glassy albite 
 and some olivine, are so rugged, that they may be com- 
 pared to a sea frozen during a storm ; whilst the great 
 stream at Albemarle Island is almost as smooth as a 
 lake when ruffled by a breeze. At James Island, black 
 basaltic lava, abounding with small grains of olivine, 
 presents an intermediate degree of roughness ; its sur- 
 face being glossy, and the detached fragments resem- 
 bling in a very singular manner, folds of drapery, cables, 
 and pieces of the bark of trees.^ 
 
 Graters of tuff. — About a mile southward of Banks' 
 Cove, there is a fine elliptic crater, about 500 feet in 
 depth, and three quarters of a mile in diameter. Its 
 bottom is occupied by a lake of brine, out of which 
 some little crateriform hills of tuff rise. The lower 
 beds are formed of compact tuff, appearing like a 
 
 ^ The irregailar and angular form of the vesicles is probably- 
 caused, by the unequal yielding of a mass composed, in almost equal 
 proportion, of solid crystals and of a viscid base. It certainly seems 
 a general circumstance, as might have been expected, that in lava, 
 which has possessed a high degTee of fluidity, as well as an even- 
 sized grain, the vesicles are internally smooth and spherical. 
 
 - A specimen of basaltic lava, with a few small broken crystals 
 of albite, given me by one of the ofl&cers, is perhaps worthy of de- 
 scription. It consists of cylindrical ramifications, some of which are 
 only the twentieth of an inch in diameter, and are drawTi out into 
 the sharpest iDoints. The mass has not been formed like a stalactite, 
 for the points terminate both upwards and downwards. Globules, 
 only the fortieth of an inch in diameter, have dropped from some of 
 the points, and adhere to the adjoining branches. The lava is vesi- 
 cular, but the vesicles never reach the surface of the branches, 
 which are smooth and glossy. As it is generally supposed that vesi- 
 cles are always elongated in the direction of the movement of the 
 fluid mass, I maj^ observe, that in these cylindrical branches, which 
 vary from a quarter to only the twentieth of an inch in diameter, 
 every air-cell is spherical. 
 
I20 Galapagos Archipelago. paet i. 
 
 subaqueous deposit ; whilst the upper beds, round the 
 
 entire circumference, consist of a harsh, friable tuflP, 
 
 of little specific gravity, but often containing fragments 
 
 of rock in layers. This upper tuff contains numerous 
 
 pisolitic balls, about the size of small bullets, which 
 
 differ from the surrounding matter, only in being 
 
 slightly harder and finer grained. The beds dip away 
 
 very regularly on all sides, at angles varying, as I 
 
 found by measurement, from 25 to 30 degrees. The 
 
 external surface of the crater slopes at a nearly similar 
 
 inclination; and is formed by slightly convex ribs, 
 
 like those on the shell of a pecten or scallop, which 
 
 become broader as they extend from the mouth of the 
 
 crater to its base. These ribs are generally from eight 
 
 to twenty feet in breadth, but sometimes they are aa 
 
 much as forty feet broad ; and they resemble old, 
 
 plastered, much flattened vaults, with the plaster 
 
 scaling off in plates : they are separated from each 
 
 other by gullies, deepened by alluvial action. At their 
 
 upper and narrow ends, near the mouth of the crater, 
 
 these ribs often consist of real hollow passages, like, 
 
 but rather smaller than, those often formed by the 
 
 cooling of the crust of a lava-stream, whilst the inner 
 
 parts have flowed onward ; — of which structure I saw 
 
 many examples at Chatham Island. There can be no 
 
 doubt but that these hollow ribs or vaults have been 
 
 formed in a similar manner, namely, by the setting 
 
 or hardening of a superficial crust on streams of mud, 
 
 which have flowed down from the upper part of the 
 
 crater. In another part of this same crater, I saw 
 
 open concave gutters between one and two feet wide, 
 
 which appear to have been formed by the hardening 
 
 of the lower surface of a mud-stream, instead of, 
 
 as in the former case, of the upper surface. From 
 
 these facts I think it is certain that the tuff must have 
 
CHAP. V. Craters of Ttiff. 121 
 
 flowed as mud.^ This mud may have been formed 
 either within the crater, or from ashes deposited on 
 its upper parts, and afterwards washed down by torrents 
 of rain. The former method, in most of the cases, 
 appears the more probable one ; at James Island, how- 
 ever, some beds of the friable kind of tuff extend so 
 continuously over an uneven surface, that probably 
 they were formed by the falling of showers of ashes. 
 
 Within this same crater, strata of coarse tuff, chiefly 
 composed of fragments of lava, abut, like a consoli- 
 dated talus, against the inside walls. They rise to a 
 height of between 100 and 150 feet above the surface 
 of the internal brine-lake ; they dip inwards, and are 
 inclined at an angle varying from 30 to 36 degrees. 
 They appear to have been formed beneath water, pro- 
 bably at a period when the sea occupied the hollow of 
 the crater. I was surprise to observe that beds having 
 this great inclination did not, as far as they could be 
 followed, thicken towards their lower extremities. 
 
 Banks' Cove. — This harbour occupies part of the 
 interior of a shattered crater of tuff larger than that 
 last described. All the tuff is compact, and includes 
 numerous fragments of lava; it appears like a sub- 
 aqueous deposit. The most remarkable feature in 
 this crater is the great development of strata con- 
 verging inwards, as in the last case, at a considerable 
 inclination, and often deposited in irregular curved 
 
 * This conclusion is of some interest, because M. Dufrenoy 
 C Mem. pour servir,' torn. iv. p. 274) has argued from strata of tuff, 
 apparently of similar composition with that here described, being 
 inclined at angles between 18° and 20°, that Monte Nuevo and some 
 other craters of Southern Italy have been formed by upheaval. 
 From the facts given above, of the vaulted character of the separate 
 rills, and from the tuff not extending in horizontal sheets round 
 these craterif orm hills, no one will suppose that the strata have here 
 been produced by elevation ; and yet we see that their inclination is 
 above 20^, and often as much as 30°. The consolidated strata, also, 
 of the internal talus, as will be immediately seen, dips at an angle 
 of above 30°. 
 
122 
 
 Galapagos Archipelago. 
 
 PAET I. 
 
 layers. These interior converging beds, as well as the 
 proper, diverging, crateriform strata, are represented 
 
 No. ] 3. 
 
 A sectional sketch of the headlands forming Banks' Cove, showing the diverging 
 crateriform strata, and the converging stratified talus. The highest point of 
 these hills is 817 feet above the sea. 
 
 in the accompanying rude, sectional sketch of the head- 
 lands, forming this Cove. The internal and external 
 strata differ little in composition, and the former have 
 evidently resulted from the wear and tear, and re- 
 deposition of the matter forming the external crateriform 
 strata. From the great development of these inner j 
 beds, a person walking round the rim of this crater - 
 might fancy himself on a circular anti-clinal ridge 
 of stratified sandstone and conglomerate. The sea is 
 wearing away the inner and outer strata, and especially 
 the latter ; so that the inwardly converging strata will, 
 perhaps, in some future age, be left standing alone — a 
 case which might at first perplex a geologist.^ 
 
 James Island. — Two craters of tuff on this island 
 are the only remaining ones which require any notice. 
 
 ' I believe that this case actually occurs in the Azores, where 
 Dr. Webster (' Description,' p. 185) has described a basin-formed, 
 little island, composed of strata of tuff, dipping inwards and 
 bounded externally by steep sea-worn cliffs. Dr. Daubeny supposes 
 (on Volcanos, p. 266), that this cavity must have^' been formed by a 
 circular subsidence. It appears to me far more probable, that we 
 here have strata which were originally deposited within the hollow 
 of a crater, of which the exterior walls have since been removed by 
 the sea. 
 
<jHAP. V. James Island, 123 
 
 One of them lies a mile and a-half inland from Puerto 
 ■Grande : it is circular, about the third of a mile in 
 diameter, and 400 feet in depth. It differs from all 
 the other tuff-craters which I examined, in having the 
 lower part of its cavity, to the height of between 100 
 and 150 feet, formed by a precipitous wall of basalt, 
 giving to the crater the appearance of having^burst 
 through a solid sheet of rock. The upper part of this 
 crater consists of strata of the altered tuff, with a 
 semi-resinous fracture. Its bottom is occupied by a 
 shallow lake of brine, covering layers of salt, which 
 rest on deep black mud. The other crater lies at the 
 distance of a few miles, and is only remarkable from 
 its size and perfect condition. Its summit is 1,200 
 feet above the level of the sea, and the interior hollow 
 is 600 feet deep. Its external sloping surface presented 
 -a curious appearance from the smoothness of the wide 
 layers of tuff, which resembled a vast plastered floor. 
 Brattle Island is, I believe, the largest crater in the 
 Archipelago composed of tuff; its interior diameter 
 is nearly a nautical mile. At present it is in a ruined 
 condition, consisting of little more than half a circle 
 open to the south ; its great size is probably due, in 
 part, to internal degradation, from the action of the sea. 
 Segment of a small basaltic crater. — One side of 
 Fresh-water Bay, in James Island, is bounded by a 
 promontory, which forms the last wreck of a great 
 crater. On the head of this promontory, a quadrant- 
 shaped segment of a small subordinate point of 
 eruption stands exj)osed. It consists of nine separate 
 little streams of lava piled u|)on each other ; and 
 of an irregular pinnacle, about fifteen feet high, of 
 reddish-brown, vesicular basalt, abounding with large 
 crystals of glassy albite, and with fused augite. 
 This pinnacle, and some adjoining paps of rock on 
 
124 
 
 Galapagos Archipelago. 
 
 PAET I, 
 
 the beach, represents the axis of the crater. The- 
 streams of lava can be followed up a litttle ravine, at 
 right angles to the coast, for between ten and fifteen 
 yards, where they are hidden by detritus : along the 
 beach they are visible for nearly eighty yards, and I 
 do not believe that they extend much farther. The 
 three lower streams are united to the pinnacle ; and at 
 the point of junction (as is shown in the accompanying 
 rude sketch made on the spot), they are slightly arched. 
 
 No. 14. 
 
 Segment of a very small orifice of eruption, en tlie beach of Tresh-water Bay., 
 
 as if in the act of flowing over the lip of the crater. 
 The six upper streams no doubt were originally united 
 to this same column before it was worn down by the 
 sea. The lava of these streams is of similar com- 
 position with that of the pinnacle, excepting that the 
 crystals of albite appear to be more comminuted, and 
 the grains of fused augite are absent. Each stream 
 is separated from the one above it by a few inches, or 
 at most by one or two feet in thickness, of loose frag- 
 mentary scoriae, apparently derived from the abrasion 
 of the streams in passing over each other. All these 
 streams are very remarkable from their thinness. I 
 carefully measured several of them ; one was eight inches 
 thick, but was firmly coated with three inches above, 
 
CHAP. V. Segment of a small Cratej . 125 
 
 and three inches below, of red scoriaceous rock (which 
 is the case with all the streams), making altogether a 
 thickness of fourteen inches : this thickness was pre- 
 served quite uniformly along the entire length of the 
 section. A second stream was only eight inches thick 
 including both the upper and lower scoriaceous surfaces. 
 Until examining this section, I had not thought it 
 possible that lava could have flowed in such uniformly 
 thin sheets over a surface far from smooth. These 
 little streams closely resemble in composition that 
 great deluge of lava at Albemarle Island, which like- 
 wise must have possessed a high degree of fluidity. 
 
 Pseudo-extraneous, ejected fragments. — In the 
 lava and in the scorise of this little crater, I found 
 several fragments, which, from their angular form 
 their granular structure, their freedom from air-cells 
 their brittle and burnt condition, closely resembled 
 those fragments of primary rocks which are occasionally 
 ejected, as at Ascension, from volcanos. These frag- 
 ments consist of glassy albite, much mackled, and with 
 very imperfect cleavages, mingled with semi-rounded 
 grains, having tarnished, glossy surfaces, of a steel-blue 
 mineral. The crystals of albite are coated by a red 
 oxide of iron, appearing like a residual substance ; and 
 their cleavage-planes also are sometimes separated by 
 excessively fine layers of this oxide, giving to the 
 crystals the appearance of being ruled like a glass 
 micrometer. There was no quartz. The steeLblue 
 mineral, which is abundant in the pinnacle, but which 
 disappears in the streams derived from the pinnacle 
 has a fused appearance, and rarely presents even a 
 trace of cleavage; I obtained, however, one measure- 
 ment, which proved that it was augite; and in one 
 other fragment, which differed from the others in 
 being slightly cellular, and in gradually blending into 
 
126 Galapagos Archipelago. paet i. 
 
 the surrounding matrix the small grains of this mineral 
 were tolerably well crystallised. Although there is sa 
 wide a difference in appearance between the lava of 
 the little streams, and especially of their red scoriaceous 
 crusts, and one of these angular ejected fragments, 
 which at first sight might readily be mistaken for 
 syenite, yet I believe that the lava has originated from 
 the melting and movement of a mass of rock of abso- 
 lutely similar composition with the fragments. Besides 
 the specimen above alluded to, in which we see a 
 fragment becoming slightly cellular, and blending into 
 the surrounding matrix, some of the grains of the steel- 
 blue augite also have their surfaces becoming very 
 finely vesicular, and passing into the nature of the 
 surrounding paste ; other grains are throughout, in an 
 intermediate condition. The paste seems to consist 
 of the augite more perfectly fused, or, more probably, 
 merely disturbed in its softened state by the movement 
 of the mass, and mingled with the oxide of u'on and 
 with finely comminuted, glassy albite. Hence pro- 
 bably it is that the fused albite, which is abundant 
 in the pinnacle, disappears in the streams. The albite 
 is in exactly the same state, with the exception of 
 most of the crystals being smaller in the lava and in 
 the embedded fragments ; but in the fragments they 
 appear to be less abundant : this, however, would 
 naturally happen from the intumescence of the augitic 
 base, and its consequent apparent increase in bulk. It 
 is interesting thus to trace the steps by which a com- 
 pact granular rock becomes converted into a vesicular,, 
 pseudo-porphyritic lava, and finally into red scoria3. 
 The structure and composition of the embedded fi.'ag- 
 ments show that they are parts either of a mass of 
 primary rock which has undergone considerable change 
 from volcanic action, or more probably of the crust of 
 
CHAP. V. Ejected Fragments. 127 
 
 a body cf cooled and crystallised lava, wliich has after- 
 wards been broken up and re-liquefied ; the crust being 
 less acted on by the renewed heat and movement. 
 
 Gonchiclinrj remarks on the tujff-craters. — These 
 craters, from the peculiarity of the resin-like substance 
 which enters largely into their composition, from their 
 structure, their size and number, present the most strik- 
 ing feature in the geology of this Archipelago. The 
 majority of them form either separate islets, or promon- 
 tories attached to the larger islands ; and those which 
 now stand at some little distance from the coast are 
 worn and breached, as if by the action of the sea. 
 From this general circumstance of their position, and 
 from the small quantity of ejected ashes in any part 
 of the Archipelago, I am led to conclude, that the tuff 
 has been chiefly produced, by the grinding together of 
 fragments of lava within active craters, communicating 
 with the sea. In the origin and composition of the 
 tuff, and in the frequent presence of a central lake of 
 brine and of layers of salt, these craters resemble, though 
 on a gigantic scale, the ' salses,' or hillocks of mud, which 
 are common in some parts of Italy and in other countries.^ 
 Their closer connection, however, in this Archipelago, 
 with ordinary volcanic action, is shown by the pools of 
 solidified basalt, with which they are sometimes filled up. 
 
 It at first appears very singular, that all the craters 
 formed of tuff have their southern sides, either quite 
 broken down and wholly removed, or much lower than 
 the other sides. I saw and received accounts of twenty- 
 eight of these craters ; of these, twelve form separate 
 
 * D'Aubiiisson's 'Traite de G6ognosie,' torn. i. p. 189. I may 
 remark, that I saw at Terceira, in the Azores, a crater of tuff or 
 peperino, very similar to these of the Galapagos Archipelago. From 
 the description given in Freycinet's ' Voyage,' similar ones occur at 
 the Sandwich Islands ; and probably they are present in many other 
 places. 
 
128 Galapagos Archipelago. paet i- 
 
 islets,^ and now exist as mere crescents quite open to 
 the south, with occasionally a few points of rock mark- 
 ing their former circumference ; of the remaining six- 
 teen, some form promontories, and others stand at a 
 little distance inland from the shore ; but all, have 
 their southern sides either the lowest, or quite broken 
 down. Two, however, of the sixteen had their northern 
 sides also low, whilst their eastern and western sides 
 were perfect. I did not see, or hear of, a single ex- 
 ception to the rule, of these craters being broken down 
 or low on the side, which faces a point of the horizon 
 between SE. and SW. This rule does not apply to 
 craters composed of lava and scorias. The explanation 
 is simple : at this Archipelago, the waves from the 
 trade-wind, and the swell propagated from the distant 
 parts of the open ocean, coincide in direction, (which 
 is not the case in many parts of the Pacific,) and with 
 their united forces attack the southern sides of all the 
 islands; and consequently the southern slope, even 
 when entirely formed of hard basaltic rock, is invariably 
 steeper than the northern slope. As the tuif-craters 
 are composed of a soft material, and as probably all, or 
 nearly all, have at some period stood immersed in the 
 sea, we need not wonder that they should invariably 
 exhibit on their exposed sides the effects of this great 
 denuding power. Judging from the worn condition of 
 many of these craters, it is probable that some have 
 been entirely washed away. As there is no reason to 
 suppose, that the craters formed of scoriae and lava 
 
 1 These consist of the three Grossman Islets, the largest of which 
 is 600 feet in height ; Enchanted Island ; Gardner Island (760 feet 
 high) : Champion Island (331 feet high) ; Enderby Island ; Brattle 
 Island ; two islets near Indefatigable Island ; and one near James 
 Island. A second crater near James Island (with a salt lake in its 
 centre) has its southern side only about twenty feet high, whilst the 
 other parts of the circumference are about 300 feet in height. 
 
CHAP. Y. Breached C^^aters. 129 
 
 were erupted wliilst standing in the sea, we can see 
 why the rule does not apply to them. At Ascension, it 
 was shown that the mouths of the craters, which are 
 there all of terrestrial origin, have been affected by the 
 trade wind ; and this same power might here, also, aid 
 in making the windward and exposed sides of some of 
 the craters originally the lowest. 
 
 Mineralogical com'position of the rocks. — In the 
 northern islands, the basaltic lavas seem generally to con- 
 tain more albite than they do in the southern half of the 
 Archipelago ; but almost all the streams contain some. 
 The albite is not unfrequently associated with olivine. 
 I did not observe in any specimen distinguishable 
 crystals of hornblende or augite ; I except the fused 
 grains in the ejected fragments, and in the pinnacle of 
 the little crater, above described. I did not meet with 
 a single specimen of true trachyte ; though some of the 
 'paler lavas, when abounding with large crystals of the 
 harsh and glassy albite, resemble in some degree this 
 rock ; but in every case the basis fuses into a black 
 enamel. Beds of ashes and far-ejected scoriae, as pre- 
 viously stated, are almost absent ; nor did I see a frag- 
 ment of obsidian or of pumice. Yon Buch^ believes 
 that the absence of pumice on Mount Etna is conse- 
 quent on the feldspar being of the Labrador variety ; 
 if the presence of pumice depends on the constitution 
 of the feldspar, it is remarkable, that it should be ab- 
 sent in this archipelago, and abundant in the Cordillera 
 of South America, in both of which regions the feld- 
 spar is of the albitic variety. Owing to the absence of 
 ashes, and the general indecomposable character of the 
 lava in this Archipelago, the islands are slowly clothed 
 with a poor vegetation, and the scenery has a desolate 
 and frightful aspect. 
 
 * * Description des Isles Canaries,' p. 328. 
 
 K 
 
130 Galapagos A7xhipelago. paet i. 
 
 Elevation of the land. — Proofs of the rising of the 
 land are scanty and imperfect. At Chatham Island, I 
 noticed some great blocks of lava, cemented by cal- 
 careous matter, containing recent shells; but they 
 occurred at the height of only a few feet above high- 
 water mark. One of the officers gave me some frag- 
 ments of shells, which he found embedded several 
 hundred feet above the sea, in the tuff of two craters, 
 distant from each other. It is possible, that these 
 fragments may have been carried up to their present 
 height in an eruption of mud ; but as, in one instance, 
 they were associated with broken oyster-shells, almost 
 forming a layer, it is more probable that the tuff was 
 uplifted with the shells in mass. The specimens are 
 so imperfect that they can be recognised only as be- 
 longing to recent marine genera. On Charles Island, 
 I observed a line of great rounded blocks, piled on the 
 summit of a vertical cliff, at the height of fifteen feet 
 above the line, where the sea now acts during the 
 heaviest gales. This appeared, at first, good evidence 
 in favour of the elevation of the land ; but it was 
 quite deceptive, for I afterwards saw on an adjoining 
 part of this same coast, and heard from eye-witnesses, 
 that wherever a recent stream of lava forms a smooth 
 inclined plane, entering the sea, the waves during gales 
 have the power of rolling ujp rounded blocks to a great 
 height, above the line of their ordinary action. As the 
 little cliff in the foregoing case is formed by a stream 
 of lava, which, before being worn back, must have en- 
 tered the sea with a gently sloping surface, it is possible 
 or rather it is probable, that the rounded boulders, 
 now lying on its summit, are merely the remnant of 
 those which had been rolled uj) during storms to their 
 present height. 
 
 Direction of the fissures of eruption. — The volcanic 
 
CHAP. V. Fissures of Eruption. 131 
 
 orifices in tHis group cannot be considered as indis- 
 criminately scattered. Three great craters on Albemarle 
 Island form a well marked line, extending NW. by N. 
 and SE. by S. Narborougb Island, and the great crater 
 on tbe rectangular projection of Albemarle Island, 
 form a second parallel line. To tbe east. Hood's 
 Island, and the islands and rocks between it and James 
 Island, form another nearly parallel line, which, when 
 prolonged, includes Culpepper and Wenman Islands, 
 lying seventy miles to the north. The other islands 
 lying farther eastward, form a less regular fourth line. 
 Several of these islands, and the vents on Albemarle 
 Island, are so placed, that they likewise fall on a set 
 of rudely parallel lines, intersecting the former lines at 
 right angles ; so that the principal craters appear to 
 lie on the points where two sets of fissures cross each 
 other. The islands themselves, with the exception of 
 Albemarle Island, are not elongated in the same direc- 
 tion with the lines on which they stand. The direction 
 of these islands is nearly the same with that which 
 prevails in so remarkable a manner in the numerous 
 archipelagos of the great Pacific Ocean. Finally, I may 
 remark, that amongst the Galapagos Islands there is no 
 one dominant vent much higher than all the others, 
 as may be observed in many volcanic archipelagos : the 
 highest is the great mound on the south-western ex- 
 tremity of Albemarle Island, which exceeds by barely 
 a thousand feet several other neighbouring craters. 
 
 K 2 
 
132 Trachyte and Basalt. parti. 
 
 CHAPTER VI. 
 
 TRACHYTE AND BASALT. — DISTRIBUTION OF VOLCANIC 
 
 ISLES. 
 
 The sinTiing of crystals in fluid lava — Specific gravity of the consti- 
 tuent parts of trachyte and of hasoM, and their consequeyit separa- 
 tion — Obsidian — Apparent non- separation of the element of plutonio 
 frocks — Origin of trap-dihes in the pliitonic series — JDistrihution of 
 'volcmtic islands ; their prevalence in the great oceans — They are 
 generally arranged in lilies — The central volcanos of Von Buch 
 doubtful — Volcanic islands bordering continents — Antiquity of 
 volcanic islands, and their elevation in mass — Eruptions on 
 parallel lines of fissure within the same geological period. 
 
 On the separation of the constituent minerals of lava., 
 according to their specific gravities. — One side of 
 Fresh-water Bay, in James Island, is formed by the 
 wreck of a large crater, mentioned in the last chapter, 
 of which the interior has been filled up by a pool of 
 basalt, about 200 feet in thickness. This basalt is of a 
 gray colour, and contains many crystals of glassy albite, 
 which become much more numerous in the lower, 
 scoriaceous part. This is contrary to what might have 
 been expected, for if the crystals had been originally 
 disseminated in equal numbers, the greater intumescence 
 of this lower scoriaceous part would have made them 
 appear fewer in number. Von Buch ^ has described a 
 stream of obsidian on the peak of Teneriffe, in which 
 
 ^ ' Description des Isles Canaries,' pp. 190 and 191. 
 
CHAP. VI. Trachyte and Basalt. 133 
 
 the crystals of feldspar become more and more numerous, 
 as the depth or thickness increases, so that near the 
 lower surface of the stream the lava even resembles a 
 primary rock. Yon Buch further states, that M. Dree, 
 in his experiments in melting lava, found that the 
 crystals of feldspar always tended to precipitate them^ 
 selves to the bottom of the crucible. In these cases, I 
 presume there can be no doubt ^ that the crystals sink 
 from their weight. The specific gravity of feldspar 
 varies 2 from 2*4 to 2*58, whilst obsidian seems com- 
 monly to be from 2*3 to 2-4 ; and in a fluidified state 
 its specific gravity would probably be less, which would 
 facilitate the sinking of the crystals of feldspar. At 
 James Island, the crystals of albite, although no doubt 
 of less weight than the gray basalt, in the parts where 
 compact, might easily be of greater specific gravity 
 than the scoriaceous mass, formed of melted lava and 
 bubbles of heated gas. 
 
 The sinking of crystals through a viscid substance 
 like molten rock, as is unequivocally shown to have 
 been the case in the experiments of M. Dree, is worthy 
 of further consideration, as throwing light on the sepa- 
 ration of the trachytic and basaltic series of lavas. 
 Mr. P. Scrope has speculated on this subject ; but he 
 
 ^ In a mass of molten iron, it is found (' Edinburgh New Philoso- 
 phical Journal,' vol. xxiv. p. ^^') that the substances, which have a 
 closer affinity for oxygen than iron has, rise from the interior of 
 the mass to the surface. But a similar cause can hardly apply to 
 the separation of the crystals of these lava streams. The cooling of 
 the surface of lava seems, in some cases, to have afEected its compo- 
 sition ; for Dufrenoy (' Mem. pour sei-vir,' tom. iv. p. 271) found that 
 the interior parts of a stream near Naples contained two-thirds of a 
 mineral which was acted on by acids, whilst the surface consisted 
 chiefly of a mineral unattackable by acids. 
 
 ^ I have taken the specific gravities of the simple minerals from 
 Von Kobell, one of the latest and best authorities, and of the rocks 
 from various authorities. Obsidian, according to Phillips, is 2-35 ; 
 and Jameson says it never exceeds 2*4 ; but a specimen from 
 Ascension, weighed by myself, was 2*42. 
 
134 Trachyte and Basalt. paej: i. 
 
 does not seem to have been aware of any positive facts, 
 such as those above given ; and he has overlooked one 
 very necessary element, as it appears to me, in the 
 phenomenon — namely, the existence of either the 
 lighter or heavier mineral in globules or in crystals. 
 In a substance of imperfect fluidity, like molten rock, 
 it is hardly credible, that the separate, infinitely small 
 atoms, whether of feldspar, augite, or of any other 
 mineral, would have power from their slightly different 
 gravities to overcome the friction caused by their 
 movement ; but if the atoms of any one of these 
 minerals became, whilst the others remained fluid, 
 united into crystals or granules, it is easy to perceive that 
 from the lessened friction, their sinking or floating power 
 would be greatly increased. On the other hand, if all 
 the minerals became granulated at the same time, it is 
 scarcely possible, from their mutual resistance, that any 
 separation could take place. A valuable, practical dis- 
 covery, illustrating the effect of the granulation of one 
 element in a fluid mass, in aiding its separation, has 
 lately been made : when lead containing a small pro- 
 portion of silver, is constantly stirred whilst cooling, it 
 becomes granulated, and the grains or imperfect crystals 
 of nearly pure lead sink to the bottom, leaving a 
 residue of melted metal much richer in silver ; whereas 
 if the mixture be left undisturbed, although kept fluid 
 for a length of time, the two metals show no signs of 
 separating.^ The sole use of the stirring seems to be. 
 
 ^ A full and interesting account of this discovery, by Mr. 
 Pattinson, was read before the British Association in September, 
 1838. In some alloys, according- to Turner (' Chemistry,' p. 210), 
 the heaviest metal sinks, and it appears that this takes place whilst 
 both metals are fluid. Where there is a considerable difference in 
 gravity, as between iron and the slag formed during the fusion of 
 the ore, we need not be surprised at the atoms separating, without 
 either substance being granulated. 
 
CHAP. Yi. Trachyte and Basalt. 135 
 
 the formation of detached granules. The specific 
 gravity of silver is 10*4, and of lead 11-35 : the granu- 
 lated lead, which sinks, is never absolutely pure, and 
 the residual fluid metal contains, when richest, only 
 Yj-g- part of silver. As the difference in specific gravity, 
 caused by the difierent proportions of the two metals, 
 is so exceedingly small, the separation is probably aided 
 in a great degree by the difference in gravity between 
 the lead, when granular though still hot, and when 
 fluid. 
 
 In a body of liquefied volcanic rock, left for some 
 time without any violent disturbance, we might expect, 
 in accordance with the above facts, that if one of the 
 constituent minerals became aggregated into crystals 
 or granules, or had been enveloped in this state from 
 some previously existing mass, such crystals or granules 
 would rise or sink, according to their specific gravity. 
 Now we have plain evidence of crystals being embedded 
 in many lavas, whilst the paste or basis has continued 
 fluid. I need only refer, as instances, to the several, 
 great, pseudo-porphyritic streams at the Galapagos 
 Islands, and to the trachytic streams in many parts of 
 the world, in which we find crystals of feldspar bent 
 and broken by the movement of the surrounding, semi- 
 fluid matter. Lavas are chiefly composed of three 
 varieties of feldspar, varying in specific gravity from 
 2*4 to 2*74 : of hornblende and augite, varying from 3*0 
 to 3*4; of olivine, varying from 3*3 to 3-4; and lastly, 
 of oxides of iron, with specific gravities from 4*8 to 5-2. 
 Hence crystals of feldspar, enveloped in a mass of 
 liquefied, but not highly vesicular lava, would tend to 
 rise to the upper parts ; and crystals or granules of the 
 other minerals, thus enveloped, would tend to sink. 
 We ought not, however, to expect any perfect degree 
 of separation in such viscid materials. Trachyte, 
 
136 Trachyte a7id Basalt. parti. 
 
 which consists chiefly of feldspar, with some hornblende 
 and oxide of iron, has a specific gravity of about 2*45 ; ^ 
 whilst basalt composed chiefly of augite and feldspar, 
 often with much iron and olivine, has a gravity of about 
 3-0. Accordingly we find, that where both trachytic 
 and basaltic streams have proceeded from the same 
 orifice, the trachytic streams have generally been first 
 erupted, owing, as we must suppose, to the molten lava of 
 this series having accumulated in the upper parts of 
 the volcanic focus. This order of eruption has been 
 observed by Beudant, Scrope, and by other authors ; 
 three instances, also, have been given in this volume. 
 As the later eruptions, however, from most volcanic^ 
 mountains, burst through their basal parts, owing to 
 the increased height and weight of the internal column 
 of molten rock, we see why, in most cases, only the 
 lower flanks of the central, trachytic masses, are en- 
 veloped by basaltic streams. The separation of the 
 ingredients of a mass of lava would, perhaps, sometimes 
 take place within the body of a volcanic mountain, if 
 lofty and of great dimensions, instead of within the 
 underground focus ; in which case, trachytic streams 
 might be poured forth, almost contemporaneously, or 
 at short recurrent internals, from its summit, and 
 basaltic streams from its base : this seems to have taken 
 place at Tenerifio.^ I need only further remark, that 
 from violent disturbances the separation of the two 
 series, even under otherwise favourable conditions, 
 would naturally often be prevented, and likewise their 
 
 ^ Trachyte from Java, was found by Yon Buch to be 2-47 ; from 
 Auvergne, by De la Beche, it was 2-42 ; from Ascension, by myself, 
 it was 2-4:2. Jameson and other authors give to basalt a specific 
 gravity of 3-0 ; but specimens from Auvergne were found, by De la 
 Beche, to be only 2-78 ; and from the Giant's Causeway, to be 2-91. 
 
 2 Consult Von Buch's well-known and admirable Description 
 Physique of this island, which might serve as a model of descriptive 
 geology. 
 
CHAP. VI. Trachyte and Basalt. 137 
 
 usual order of eruption be inverted. From the high 
 degree of fluidity of most basaltic lavas, these perhaps, 
 alone, would in many cases reach the surface. 
 
 As we have seen that crystals of feldspar, in the 
 instance described by Yon Buch, sink in obsidian, in 
 accordance with their known greater specific gravity, 
 we might expect to find in every trachytic district, 
 where obsidian has flowed as lava, that it had proceeded 
 from the upper or highest orifices. This, according to 
 Von Buch, holds good in a remarkable manner both at 
 the Lipari Islands and on the Peak of Tenerifie; at 
 this latter place obsidian has never flowed from a less 
 height than 9,200 feet. Obsidian, also, appears to have 
 been erupted from the loftiest peaks of the Peruvian 
 Cordillera. I will only further observe, that the specific 
 gravity of quartz varies from 2 '6 to 2*8 ; and therefore, 
 that when present in a volcanic focus, it would not tend 
 to sink with the basaltic bases ; and this, perhaps, 
 explains the frequent presence, and the abundance of 
 this mineral, in the lavas of the trachytic series, as 
 observed in previous parts of this volume. 
 
 An objection to the foregoing theory, will, perhaps, 
 be drawn, from the plutonic rocks not being separated 
 into two evidently distinct series, of different specific 
 gravities ; although, like the volcanic, they have been 
 liquefied. In answer, it may first be remarked, that 
 we have no evidence of the atoms of any one of the 
 constituent minerals in the plutonic series having been 
 aggregated, whilst the others remained fluid, which we 
 have endeavoured to show is an almost necessary con- 
 dition of their separation ; on the contrary, the crystals 
 have generally impressed each other with their forms. ^ 
 
 ' The crystalline paste of phonolite is frequently penetrated by 
 long needles of hornblende ; from which it appears, that the horn- 
 blende, though the more fusible mineral, has crystallised before, or 
 
138 Trachyte and Basalt. parti. 
 
 In tlie second place, the perfect tranquillity, under 
 wMch it is probable that the plutonic masses, buried at 
 profound depths, have cooled, would, most likely, be 
 highly unfavourable to the separation of their consti- 
 tuent minerals ; for, if the attractive force, which during 
 the progressive cooling draws together the molecules of 
 the different minerals, has power sufficient to keep 
 them together, the friction between such half-formed 
 crystals or pasty globules would effectually prevent the 
 heavier ones from sinking, or the lighter ones from 
 rising. On the other hand, a small amount of disturb- 
 ance, which would probably occur in most volcanic 
 foci, and which we have seen does not prevent the 
 separation of granules of lead from a mixture of molten 
 lead and silver, or crystals of feldspar from streams of 
 lava, by breaking and dissolving the less perfectly 
 formed globules, would permit the more perfect and 
 therefore unbroken crystals, to sink or rise, according 
 to their specific gravity. 
 
 Although in plutonic rocks two distinct species, 
 corresponding to the trachytic and basaltic series, do 
 not exist, I much suspect, that a certain amount of 
 separation of their constituent parts has often taken 
 place. I suspect this from having observed how fre- 
 quently dikes of greenstone and basalt intersect widely 
 
 at the same time with a more refractory substance. Phonolitej as far 
 as my observations serve, in every instance appears to be an injected 
 rock, like those of the plutonic series ; hence probably, like these 
 latter, it has generally been cooled without repeated and violent dis- 
 turbances. Those geologists who have doubted whether granite 
 could have been formed by igneous liquefaction, because minerals 
 of different degrees of fusibility impress each other with their forms, 
 could not have been aware of the fact of crystallised hornblende 
 penetrating phonolite, a' rock undoubtedly of igneous origin. The 
 viscidity, which it is now known, that both feldspar and quartz retain 
 at a temperature much below their points of fusion, easily explains 
 their mutual impressment. Consult on this subject Mr. Horner's 
 paper on Bonn, ' Geolog. Transact.' vol. iv. p. 439 ; and ' L'Institut,' 
 with respect to quartz, 1839, p. 161. 
 
CHAP. Yi. Trachyte and Basalt. 139 
 
 extended formations of granite and tlie allied meta- 
 m Orphic rocks. I liave never examined a district in 
 an extensive granitic region without discovering dikes ; 
 I may instance the numerous trap-dikes, in several 
 districts of Brazil, Chile, and Australia, and at the Cape 
 of Good Hope : many dikes likewise occur in the great 
 granitic tracts of India, in the north of Europe, and in 
 other countries. Whence, then, has the greenstone 
 and basalt, forming these dykes, come ? Are we to 
 suppose, like some of the elder geologists, that a zone 
 of trap is uniformly spread out beneath the granitic 
 series, which composes, as far as we know, the founda- 
 tions of the earth's crust ? Is it not more probable, that 
 these dikes have been formed by fissures penetrating 
 into partially cooled rocks of the granitic and meta- 
 morphic series, and by their more fluid parts, consisting 
 chiefly of hornblende, oozing out, and being sucked 
 into such fissures ? At Bahia, in Brazil, in a district 
 composed of gneiss and primitive greenstone, I saw 
 many dikes, of a dark augitic (for one crystal certainly 
 was of this mineral) or hornblendic rock, which, as 
 several appearances clearly proved, either had been 
 formed before the surrounding mass had become solid, 
 or had together with it been afterwards thoroughly 
 softened.^ On both sides of one of these dikes, the 
 gneiss was penetrated, to the distance of several yards, 
 by numerous, curvilinear threads or streaks of dark 
 matter, which resembled in form clouds of the class 
 called cirrhi-coma3 ; some few of these threads could be 
 traced to their junction with the dike. When examin- 
 
 ^ Portions of these dikes have been broken off, and are now sur- 
 rounded by the primarj^ rocks, with their laminge conformably wind- 
 ing round them. Dr. Hubbard, also (' Silliman's Journal,' vol. xxxiv. 
 p. 119), has described an interlacement of trap-veins in the granite 
 of the White Mountains, which he thinks must have been formed 
 when both rocks were soft. 
 
140 The Distribution of part i. 
 
 ing them, I doubted whether such hair-like and curvili- 
 near veins could have been injected, and I now suspect, 
 that instead of having been injected from the dike, 
 they were its feeders. If the foregoing view of the 
 origin of trap-dikes in widely extended granitic regions 
 far from rocks of any other formation, be admitted as 
 probable, we may further admit, in the case of a great 
 body of plutonic rock, being impelled by repeated 
 movements into the axis of a mountain-chain, that its 
 more liquid constituent parts might drain into deep 
 and unseen abysses ; afterwards, perhaps, to be brought 
 to the surface under the form, either of injected masses 
 of greenstone and augitic porphyry,^ or of basaltic 
 eruptions. Much of the difficulty which geologists 
 have experienced, when they have compared the com- 
 position of volcanic with plutonic formations, will, I 
 think, be removed, if we may believe, that most plutonic 
 masses have been, to a certain extent, drained of those 
 comparatively weighty and easily liquefied elements, 
 which compose the trappean and basaltic series of 
 rocks. 
 
 On tlie distribution of volcanic islands. — During 
 my investigations on coral-reefs, I had occasion to 
 consult the works of many voyagers, and I was invari- 
 ably struck with the fact, that with rare exceptions, the 
 innumerable islands scattered throughout the Pacific, 
 Indian, and Atlantic Oceans, were composed either of 
 
 * Mr. Phillips ('Lardner's Cyclopgedia,' vol. ii. p. 115) quotes Von 
 Buch's statement, that augitic porphyry ranges parallel to, and is 
 found constantly at the base of, great chains of mountains. 
 Humboldt, also, has remarked the frequent occurrence of trap-rock, 
 in a similar position ; of which fact I have observed many examples 
 at the foot of the Chilian Cordillera. The existence of granite in 
 the axes of great mountain chains is always probable, and I am 
 tempted to suppose, that the laterally injected masses of augitic 
 porphyry and of trap, bear nearly the same relation to the granitic 
 axes which basaltic lavas bear to the central trachytic masses, round 
 the flanks of which they have so frequently been erupted. 
 
CHAP. VI. Volcanic Islands. 141 
 
 volcanic, or of modern coral rocks. It would be tedious 
 to give a long catalogue of all the volcanic islands : but 
 the exceptions which I have found are easily enumer- 
 ated: in the Atlantic, we have St. Paul's Rock, de- 
 scribed in this volume, and the Falkland Islands, 
 composed of quartz and clay slate; but these latter 
 islands are of considerable size, and lie not very far 
 from the South American coast : ^ in the Indian Ocean, 
 the Seychelles (situated in a line prolonged from Mada- 
 gascar) consist of granite and quartz : in the Pacific 
 Ocean, New Caledonia, an island of large size, belongs 
 (as far as is known) to the primary class. New Zealand, 
 which contains much volcanic rock and some active 
 volcanos, from its size cannot be classed with the small 
 islands, which we are now considering. The presence 
 of a small quantity of non-volcanic rock, as of clay-slate 
 on three of the Azores,^ or of tertiary limestone at 
 Madeira, or of clay-slate at Chatham Island in the 
 Pacific, or of lignite at Kerguelen Land, ought not to 
 exclude such islands or archipelagos, if formed chiefly 
 of erupted matter, from the volcanic class. 
 
 The composition of the numerous islands scattered 
 through the great oceans being with such rare excep- 
 tions volcanic, is evidently an extension of that law, 
 and the effect of those same causes, whether chemical 
 or mechanical, from which it results, that a vast majority 
 of the volcanos now in action stand either as islands 
 
 * Judging from Forster's imperfect observation, perhaps Georgia 
 is not volcanic. Dr. Allan is my informant with regard to the 
 Seychelles. I do not know of what formation Rodriguez, in the 
 Indian Ocean, is composed. 
 
 2 This is stated on the authority of Count V. de Bedemar, with 
 respect to Flores and Graciosa (Charls worth 'Magazine of Nat. Hist.' 
 vol. i. p. 557). St, Maria has no volcanic rock, according to Captain 
 Boyd (Von Buch's ' Descript.' p. 365). Chatham Island has been 
 described by Dr. Dieffenbach,in the 'Geographical Journal,' 1841, p. 
 201. As yet we have received only imperfect notices on Kerguelen 
 Land, from the Antarctic Expedition. 
 
142 The Distribution of paet i. 
 
 in tlie sea, or near its shores. This fact of the ocean- 
 islands being so generally volcanic is also interesting 
 in relation to the nature of the mountain-cliains on 
 our continents, which are comparatively seldom vol- 
 canic ; and yet we are led to suppose that where our 
 continents now stand an ocean once extended. Do 
 volcanic eruptions, we may ask, reach the surface more 
 readily through fissures formed during the first stages 
 of the conversion of the bed of the ocean into a tract 
 of land ? 
 
 Looking at the charts of the numerous volcanic 
 archipelagos, we see that the islands are generally 
 arranged either in single, double, or triple rows, in 
 lines which are frequently curved in a slight degree.^ 
 Each separate island is either rounded, or more gene- 
 rally elongated in the same direction with the group 
 in which it stands, but sometimes transversely to it. 
 Some of the groups which are not much elongated 
 present little symmetry in their forms ; M. Virlet ^ 
 states that this is the case with the Grecian Archi- 
 pelago : in such groups I suspect (for I am aware how 
 easy it is to deceive oneself on these points), that the 
 vents are generally arranged on one line, or on a set 
 of short parallel lines, intersecting at nearly right 
 angles another line, or set of lines. The Galapagos 
 Archipelago offers an example of this structure, for 
 most of the islands and the chief orifices on the largest 
 island are so grouped as to fall on a set of lines ranging 
 about NW. by N., and on another set ranging about 
 WSW. : in the Canary Archipelago we have a simpler 
 structure of the same kind : in the Cape de Verde 
 
 ^ Professors William and Henry Darwin Rogers have lately in- 
 sisted much, in a memoir read before the American Association, on 
 the regularly curved lines of elevation in parts of the^ Appalachian 
 range. 
 
 * ' Bulletin de la Soc. Geolog. tom. iii. p. 110. 
 
CHAP. VI. Volcanic Islands. 143 
 
 group, whicli appears to be the least symroetrical of 
 any oceanic volcanic archipelago, a NW. and SE. 
 line formed by several islands, if prolonged, would 
 intersect at right angles a curved line, on which the 
 remaining islands are placed. 
 
 Von Buch ^ has classed all volcanos under two heads, 
 namely, central volcanoi^^ round which numerous erup- 
 tions have taken place on all sides, in a manner almost 
 regular, and volcanic chains. In the examples given 
 of the first class, as far as position is concerned, I can 
 see no grounds for their being called ' central ; ' and 
 the evidence of any difference in mineralogical nature 
 between central volcanos and volcanic chains appears 
 slight. No doubt some one island in most small 
 volcanic archipelagos is apt to be considerably higher 
 than the others ; in a similar manner, whatever the 
 cause may be, that on the same island one vent is 
 generally higher than all the others. Yon Buch does 
 not include in his class of volcanic chains small archi- 
 pelagos, in which the islands are admitted by him, as 
 •at the Azores, to be arranged in lines ; but when 
 viewing on a map of the world how perfect a series 
 exists from a few volcanic islands placed in a row to 
 a train of linear archipelagos following each other in 
 a straight line, and so on to a great wall like the 
 Cordillera of America, it is difficult to believe that 
 there exists any essential difference between short and 
 long volcanic chains. Von Buch^ states that his 
 volcanic chains surmount, or are closely connected 
 with, mountain-ranges of primary formation : but it 
 trains of linear archipelagos are, in the course of time, 
 by the long-continued action of the elevatory and 
 volcanic forces, converted into mountain-ranges, it 
 
 ' • Description des Isles Canaries,' p. 324. 
 « Idem, p. 393. 
 
144 ^-^^ Distribution of part i. 
 
 would naturally result tliat the inferior primary rocks 
 would often be uplifted and brought into view. 
 
 Some authors have remarked that volcanic islands 
 occur scattered, though at very unequal distances, along 
 the shores of the great continents, as if in some measure 
 connected with them. In the case of Juan Fernandez, 
 situated 330 miles from the coast of Chile, there was 
 undoubtedly a connection between the volcanic forces 
 acting under this island and under the continent, as 
 was shown during the earthquake of 1835. The 
 islands, moreover, of some of the small volcanic groups 
 which thus border continents, are placed in lines, re- 
 lated to those along which the adjoining shores of 
 the continents trend ; I may instance the lines of 
 intersection at the Galapagos, and at the Cape de 
 Verde Archipelagos, and the best marked line of the 
 Canary Islands. If these facts be not merely accidental, 
 we see that many scattered volcanic islands and small 
 groups are related not only by proximity, but in the 
 direction of the fissures of eruption to the neighbouring 
 continents — a relation, which Yon Buch considers, cha- 
 racteristic of his great volcanic chains. 
 
 In volcanic archipelagos, the orifices are seldom in 
 activity on more than one island at a time ; and the 
 greater eruptions usually recur only after long intervals. 
 Observing the number of craters, that are usually found 
 on each island of a group, and the vast amount of 
 matter which has been erupted from them, one is led 
 to attribute a high antiquity even to those groups, which 
 appear, like the Galapagos, to be of comparatively recent 
 origin. This conclusion accords with the prodigious 
 amount of degradation, by the slow action of the sea, 
 which their originally sloping coasts must have suffered, 
 when they are worn back, as is so often the case, into 
 grand precipices. We ought not, however to suppose. 
 
CHAP. Yi. Volcanic Islands. 145 
 
 in hardly any instance, that the whole body of matter, 
 forming a volcanic island, has been erupted at the 
 level, on which it now stands : the number of dikes, 
 which seem invariably to intersect the interior parts of 
 every volcano, show, on the principles explained by 
 M. Elie de Beaumont, that the whole mass has been 
 uplifted and fissured. A connection, moreover, between 
 volcanic eruptions and contemporaneous elevations in 
 mass ^ has, I think, been shown to exist, in my work on 
 Coral Reefs, both from the frequent presence of upraised 
 organic remains, and from the structure of the accom- 
 panying coral-reefs. Finally, I may remark, that in 
 the same Archipelago, eruptions have taken place within 
 the historical period on more than one of the parallel 
 lines of fissure : thus, at the Galapagos Archipelago, 
 eruptions have taken place from a vent on Narborough 
 Island, and from one on Albemarle Island, which vents 
 do not fall on the same line ; at the Canary Islands, 
 eraptions have taken place in TenerifFe and Lanzarote ; 
 and at the Azores, on the three parallel lines of Pico, 
 St. Jorge, and Terceira. Believing that a mountain- 
 axis differs essentially from a volcano, only in plutonic 
 rocks having been injected, instead of volcanic matter 
 having been ejected, this appears to me an interesting 
 circumstance ; for we may infer from it as probable, 
 that in the elevation of a mountain-chain, two or more 
 of the parallel lines forming it may be upraised and 
 injected within the same geological period. 
 
 ' A similar conclusion is forced on us, by the phenomena, which 
 accompanied the earthquake of 1835, at Conception, and which are 
 detailed in my paper (vol. v. p. 601) in the ' Geological Transactions.' 
 
146 New South Wales. part i. 
 
 CHAPTER VII. 
 
 New South Wales — Sandstone formation — Embedded ]}seudo-frag- 
 ments of shale — Stratification — Current- cleavage — Great valleys 
 — Van Diemen^s Land — Palceozoic formation — Newer formation 
 with volcanic rocks — Travertin with leaves of extinct plants — 
 Elevation of the land — New Zealand — King George's Sound — 
 Superficial ferruginous teds — Superficial calcareous deposits, with 
 casts of hra/nches — Their origin from drifted particles of shells and 
 corals — Their extend — Ca^pe of Good Hope — Junction of the granite 
 and clay -slate — Sandstone formation. 
 
 The Beaghj in her homeward voyage, touched at New- 
 Zealand, Australia, Van Diemen's Land, and the Cape 
 of Good Hope. In order to confine the Second Part of 
 these Geological Observations to South America, I will 
 here briefly describe all that I observed at these places 
 worthy of the attention of geologists. 
 
 New South Wales. — My opportunities of observa- 
 tion consisted of a ride of ninety geographical miles to 
 Bathurst, in a WNW. direction from Sydney. The 
 first thirty miles from the coast passes over a sandstone 
 country, broken up in many places by trap-rocks, and 
 separated by a bold escarpment overhanging the river 
 Nepean, from the great sandstone platform of the Blue 
 Mountains. This upper platform is 1,000 feet high at 
 the edge of the escarpment, and rises in a distance of 
 twenty-five miles to between 3,000 and 4,000 feet above 
 the level of the sea. At this distance the road descends 
 to a country rather less elevated, and composed in chief 
 part of primary rocks. There is much granite, in one 
 part passing into a red porphyry with octagonal 
 
CHAP. VII. Sandstone Platforms. i/^y 
 
 crystals of quartz, and intersected in some places hj 
 trap-dikes. Near the Downs of Bathurst I passed over 
 much pale-brown, glossy clay-slate, with the shattered 
 laminae running north and south : I mention this fact,, 
 because Captain King informs me that, in the country 
 a hundred miles southward, near Lake George, the 
 mica-slate ranges so invariably north and south that 
 the inhabitants take advantage of it in finding their 
 way through the forests. 
 
 The sandstone of the Blue Mountains is at least 
 1,200 feet thick, and in some parts is apparently of 
 greater thickness ; it consists of small grains of quartz,, 
 cemented by white earthy matter, and it abounds with 
 ferruginous veins. The lower beds sometimes alternate 
 with shales and coal : at Wolgan I found in carbona- 
 ceous shale leaves of the Glossopteris Broivnii, a fern 
 which so frequently accompanies the coal of Australia. 
 The sandstone contains pebbles of quartz ; and these 
 generally increase in number and size (seldom, however,, 
 exceeding an inch or two in diameter) in the upper 
 beds : I observed a similar circumstance in the grand 
 sandstone formation at the Cape of Good Hope. On 
 the South American coast, where tertiary aud supra- 
 tertiary beds have been extensively elevated, I re- 
 peatedly noticed that the uppermost beds were formed 
 of coarser materials than the lower : this appears to 
 indicate that, as the sea became shallower, the force of 
 the waves or currents increased. On the lower plat- 
 form, however, between the Blue Mountains and the 
 coast, I observed that the upper beds of the sandstone 
 frequently passed into argillaceous shale, — the effect, 
 probably, of this lower space having been protected 
 from strong currents during its elevation. The sand- 
 stone of the Blue Mountains evidently having been of 
 mechanical origin, and not having sufiered any meta- 
 
 i, 2 
 
148 New South Wales. paet i. 
 
 inorpliic action, I was surprised at observing that, in 
 some specimens, nearly all the grains of quartz were so 
 perfectly crystallised with brilliant facets that they 
 evidently had not in their j^resent form been aggregated 
 in any previously existing rock.^ It is difficult to 
 imagine how these crystals could have been formed ; 
 one can hardly believe that they were separately pre- 
 cipitated in their present crystallised state. Is it 
 possible that rounded grains of quartz may have been 
 acted on by a fluid corroding their surfaces, and de- 
 positing on them fresh silica ? I may remark that, in 
 the sandstone formation of the Cape of Good Hope, it 
 is evident that silica has been profusely deposited from 
 aqueous solution. 
 
 In several parts of the sandstone I noticed patches 
 of shale which might at the first glance have been 
 mistaken for extraneous fragments ; their horizontal 
 laminse, however, being parallel with those of the 
 sandstone, showed that they were the remnants of thin, 
 continuous beds. One such fragment (probably the 
 section of a long narrow strip) seen in the face of a cliff, 
 was of greater vertical thickness than breadth, which 
 proves that this bed of shale must have been in some 
 slight degree consolidated, after having been deposited, 
 and before being worn away by the currents. Each 
 patch of the shale shows, also, how slowly many of the 
 successive layers of sandstone were deposited. These 
 pseudo-fragments of shale will perhaps explain, in some 
 cases, the origin of apparently extraneous fragments in 
 
 ' I have lately seen, in a paper by Smith (the father of English 
 geologists), in the ' Magazine of Natural History,' that the grains of 
 quartz in the millstone grit of England are often crystallised. Sir 
 David Brewster, in a paper read before the British Association, 1840, 
 states, that in old decomposed glass, the silex and metals separate 
 into concentric rings, and that the silex regains its crystalline struc- 
 ture, as is shown by its action on light. 
 
CHAP. VII. Sandstone Platforms, 149 
 
 crystalline metamorphic rocks. I mention this, because 
 I found near Rio de Janeiro a well-defined angular 
 fragment, seven yards long by two yards in breadth, of 
 gneiss containing garnets and mica in layers, enclosed 
 in the ordinary, stratified, porphyritic gneiss of the 
 country. The laminge of the fragment and of the sur- 
 rounding matrix ran in exactly the same direction, but 
 they dipped at different angles. I do not wish to 
 afiirm that this singular fragment (a solitary case, as 
 far as I know) was originally deposited in a layer, like 
 the shale in the Blue Mountains, between the strata of 
 the porphyritic gneiss, before they were metamorphosed ; 
 but there is sufl&cient analogy between the two cases to 
 render such an explanation possible. 
 
 Stratification of the escarpment. — The strata of 
 the Blue Mountains appear to the eye horizontal ; but 
 they probably have a similar inclination with the sur- 
 face of the platform, which slopes from the west to- 
 wards the escarpment over the Nepean, at an angle of 
 one degree, or of one hundred feet in a mile.^ The 
 strata of the escarpment dip almost conformably with 
 its steeply inclined face, and with so much regularity, 
 that they appear as if thrown into their present position ; 
 but on a more careful examination, they are seen to 
 thicken and to thin out, and in the upper part to be 
 succeeded and almost capped by horizontal beds. These 
 appearances render it probable, that we here see an 
 original escarpment, not formed by the sea having 
 eaten back into the strata, but by the strata having 
 originally extended only thus far. Those who have 
 been in the habit of examining accurate charts of sea- 
 coasts, where sediment is accumulating, will be aware, 
 that the surfaces of the banks thus formed, generally 
 
 * This is stated on the authority of Sir T. Mitchell, in his 
 • Travels,' vol. ii. p. 357. 
 
150 New South Wales. paet i. 
 
 slope from the coast very gently towards a certain line 
 in the offing, beyond which the depth in most.cases sud- 
 denly becomes great. I may instance the great banks 
 of sediment within the West Indian Archipelago,^ 
 which terminate in submarine slopes, inclined at angles 
 of between 30 and 40 degrees, and sometimes even at 
 more than 40 degrees : every one knows how steep such 
 a slope would appear on the land. Banks of this nature, 
 if uplifted, would probably have nearly the same ex- 
 ternal form as the platform of the Blue Mountains, 
 where it abruptly terminates over the Nepean. 
 
 Current cleavage. — The strata of sandstone in the 
 low coast countrv, and likewise on the Blue Mountains, 
 are often divided by cross or current laminge, which 
 dip in different directions, and frequently at an angle 
 of forty-five degrees. Most authors have attributed 
 these cross layers to successive small accumulations on 
 an inclined surface ; but from a careful examination in 
 some parts of the ISTew E,ed sandstone of England, I 
 believe that such layers generally form parts of a series 
 of curves, like gigantic tidal ripples, the tops of which 
 have since been cut off, either by nearly horizontal 
 layers, or by another set of great ripples, the folds of 
 which do not exactly coincide with those below them. 
 It is well known to surveyors that mud and sand are dis- 
 turbed during storms at considerable depths, at least from 
 300 to 450 feet,^ so that the nature of the bottom even 
 becomes temporarily changed; the bottom, also, at a 
 
 ^ I have described these very curious banks in the Appendix 
 (2nd edit. p. 255) to my volume on the structure of Coral Eeefs. I 
 have ascertained the inclination of the edges of the banks, from 
 information given me by Captain B. Allen, one of the surveyors, and 
 by carefully measuring the horizontal distances between the last 
 sounding on the bank and the first in the deep water. Widely ex- 
 tended banks in all parts of the West Indies have the same general 
 form of surface. 
 
 2 See Martin White, on ' Soundings in the British Channel,' pp. 4 
 and 166. 
 
CHAP, VII. Great Valleys. 151 
 
 depth between 60 and 70 feet, has been observed ^ to be 
 broadly rippled. One may, therefore, be allowed to 
 suspect, from the appearances just mentioned in the 
 New Red sandstone, that at greater depths, the bed of 
 the ocean is heaped up during gales into great ripple- 
 like furrows and depressions, which are afterwards cut 
 off by the currents during more tranquil weather, and 
 again furrowed during gales. 
 
 Valleys in the sandstone platforms. — The grand 
 valleys, by which the Blue Mountains and the other 
 sandstone platforms of this part of Australia are pene- 
 trated, and which long offered an insuperable obstacle 
 to the attempts of the most enterprising colonist to 
 reach the interior country, form the most striking 
 feature in the geology of New South Wales. They are 
 of grand dimensions, and are bordered by continuous 
 lines of lofty cliffs. It is not easy to conceive a more 
 magnificent spectacle, than is presented to a person 
 walking on the summit-plains, when without any notice 
 he arrives at the brink of one of these cliffs, which are 
 so perpendicular, that he can strike with a stone (as I 
 have tried) the trees growing, at the depth of between 
 1,000 and 1,500 feet below him ; on both hands he sees 
 headland beyond headland of the receding line of cliff, 
 and on the opposite side of the valley, often at the 
 distance of several miles, he beholds another line rising 
 up to the same height with that on which he stands, 
 and formed of the same horizontal strata of pale sand- 
 stone. The bottoms of these valleys are moderately level, 
 and the fall of the rivers flowing in them, according to 
 Sir T. Mitchell, is gentle. The main valleys often send 
 into the platform great bay-like arms, which expand at 
 their upper ends ; and on the other hand, the platform 
 
 * M. Siau on the ' Action of Waves : ' ' Bdin. New Phil. Journ. 
 vol. xxxi. p. 245. 
 
152 New SotUk Wales. paet i. 
 
 often sends promontories into the valley, and even 
 leaves in them great, almost insulated, masses. So 
 continuous are the bounding lines of cliff, that to 
 descend into some of these valleys, it is necessary to go 
 round twenty miles ; and into others, the surveyors 
 have only lately penetrated, and the colonists have not 
 yet been able to drive in their cattle. But the most 
 remarkable point of structure in these valleys, is, that 
 although several miles wide in their upper parts, they 
 generally contract towards their mouths to such a degree 
 as to become impassable. The Surveyor-General, Sir 
 T. Mitchell,^ in vain endeavoured, first on foot and then 
 by crawling between the great fallen fragments of sand- 
 stone, to ascend through the gorge by which the river 
 Grose joins the Nepean ; yet the valley of the Grose in 
 its upper part, as I saw, forms a magnificent basin some 
 miles in width, and is on all sides surrounded by cliffs, 
 the summits of which are believed to be nowhere less 
 than 3,000 feet above the level of the sea. When cattle 
 are driven into the valley of the Wolgan by a path 
 (which I descended) partly cut by the colonists, they 
 cannot escape ; for this valley is in every other part 
 surrounded by perpendicular cliffs, and eight miles 
 lower down, it contracts, from an average width of half 
 a mile, to a mere chasm impassable to man or beast. 
 Sir T. Mitchell ^ states, that the great valley of the Cox 
 river with all its branches contracts, where it unites 
 with the Nepean, into a gorge 2,200 yards wide, and 
 about 1,000 feet in depth. Other similar cases might 
 have been added. 
 
 The first impression, from seeing the correspondence 
 
 ^ ' Travels in Australia,' vol. i. p. 154. — I must express my obliga- 
 tion to Sir T. Mitchell, for several interesting personal communica- 
 tions on the subject of these great valleys of New South Wales. 
 
 2 ' Idem,' vol. ii. p. 358, 
 
CHAP. VII. Great Valleys. 153 
 
 of the horizontal strata, on each side of these valleys 
 and great amphitheatre-like depressions, is that they 
 have been in chief part hollowed out, like other 
 valleys, by aqueous erosion ; but when one reflects on 
 the enormous amount of stone, which on this view 
 must have been removed, in most of the above cases 
 through mere gorges or chasms, one is led to ask 
 whether these spaces may not have subsided. But con- 
 sidering the form of the irregularly branching valleys, 
 and of the narrow promontories, projecting into them 
 from the platforms, we are compelled to abandon this 
 notion. To attribute these hollows to alluvial action, 
 would be preposterous ; nor does the drainage from 
 the summit-level always fall, as I remarked near 
 the Weatherboard, into the head of these valleys, but 
 into one side of their bay-like recesses. Some of the 
 inhabitants remarked to me, that they never viewed 
 one of these bay-like recesses, with the headlands re- 
 ceding on both hands, without being struck with their 
 resemblance to a bold sea-coast. This is certainly the 
 case ; moreover, the numerous fine harbours, with their 
 widely branching arms, on the present coast of New 
 South Wales, which are generally connected with the 
 sea by a narrow mouth, from one mile to a quarter of a 
 mile in width, passing through the sandstone coast-cliffs, 
 present a likeness, though on a miniature scale, to the 
 great valleys of the interior. But then immediately 
 occurs the startling difficulty, why has the sea worn out 
 these great, though circumscribed, depressions on a 
 wide platform, and left mere gorges, through which 
 the whole vast amount of triturated matter must have 
 been carried away ? The only light I can throw on 
 this enigma, is by showing that banks appear to be 
 forming in some seas of the most irregular forms, and 
 that the sides of such banks are so steep (as before 
 
154 New South Wales. paet i. 
 
 stated) that a comparatively small amount of subse- 
 quent erosion would form them into cliffs : that the 
 waves have power to form high and precipitous cliffs, 
 even in land-locked harbours, I have observed in many- 
 parts of South America. In the E-ed Sea, banks with 
 an extremely irregular outline and composed of sedi- 
 ment, are penetrated by the most singularly shaped 
 creeks with narrow mouths : this is likewise the case, 
 though on a larger scale, with the Bahama Banks. 
 Such banks, I have been led to suppose,^ have been 
 formed by currents heaping sediment on an irregular 
 bottom. That in some cases, the sea, instead of spread- 
 ing out sediment in a uniform sheet, heaps it round 
 submarine rocks and islands, it is hardly possible to 
 doubt, after having examined the charts of the West 
 Indies. To apply these ideas to the sandstone plat- 
 forms of New South Wales, I imagine that the strata 
 might have been heaped on an irregular bottom by the 
 action of strong currents, and of the undulations of an 
 open sea ; and that the valley-like spaces thus left un- 
 filled might, during a slow elevation of the land, have 
 had their steeply sloping flanks worn into cliffs; the 
 worn-down sandstone being removed, either at the time 
 when the narrow gorges were cut by the retreating sea, 
 or subsequently by alluvial action. 
 
 Van Diemen''s Land. 
 
 The southern part of this island is mainly formed of 
 mountains of greenstone, which often assumes a syenitic 
 
 ^ See the ' Appendix ' (2nd edit. pp. 251 and 255) to the ' Part 
 on Coral Eeefs.' The fact of the sea heaping up mud round a sub- 
 marine nucleus, is worthy of the notice of geologists : for outlayers 
 of the same composition with the coast-banks are thus formed ; and 
 these, if upheaved and worn into cliffs, would naturally be thought 
 to have been once connected together. 
 
CHAP. yn. Volcanic Rocks. 155 
 
 character, and contains mucli hyperstliene. These moun- 
 tains, in their lower half, are generally encased by strata 
 containing numerous small corals and some shells. 
 These shells have been examined by Mr. G. B. Sowerby, 
 and are described in the Appendix : they consist of two 
 species of Producta, and of six of Spirifera ; two of 
 these, namely, P. rugata and 8. rotundata, resemble, 
 as far as their imperfect condition allows of comparison, 
 British mountain-limestone shells. Mr. Lonsdale has 
 had the kindness to examine the corals ; they consist 
 of six undescribed species, belonging to three genera. 
 Species of these genera occur in the Silurian, Devonian, 
 and Carboniferous strata of Europe. Mr. Lonsdale 
 remarks, that all these fossils have undoubtedly a 
 Palseozoic character, and that probably they correspond 
 in age to a division of the system above the Silurian 
 formations. 
 
 The strata containing these remains are singular 
 from the extreme variability of their mineralogical 
 composition. Every intermediate form is present, 
 between flinty-slate, clay-slate passing into gray-wacke, 
 pure limestone, sandstone, and porcellanic rock; and 
 some of the beds can only be described as composed 
 of a siliceo-calcareo-clay slate. The formation, as far 
 as I could judge, is at least a thousand feet in thick- 
 ness : the upper few hundred feet usually consist of a 
 siliceous sandstone, containing pebbles and no organic 
 remains ; the inferior strata, of which a pale flinty slate 
 is perhaps the most abundant, are the most variable ; 
 and these chiefly abound with the remains. Between 
 two beds of hard crystalline limestone, near Newtown, 
 a layer of white soft calcareous matter is quarried, and 
 is used for whitewashing houses. From information 
 given to me by Mr. Frankland, the Surveyor-General, 
 it appears that this Palseozoic formation is found in 
 
15^ Vein Dieniens Land, paet i. 
 
 different parts of the whole island; from the same 
 authority, I may add, that on the north-eastern coast and 
 in Bass' Straits primary rocks extensively occur. 
 
 The shores of Storm Bay are skirted, to the height 
 of a few hundred feet, by strata of sandstone, contain- 
 ing pebbles of the formation just described, with its 
 characteristic fossils, and therefore belonging to a sub- 
 sequent age. These strata of sandstone often pass into 
 shale, and alternate with layers of impure coal; they 
 have in many places been violently disturbed. Near 
 Hobart Town, I observed one dike, nearly a hundred 
 yards in width, on one side of which the strata were 
 tilted at an angle of 60°, and on the other they were 
 in some parts vertical, and had been altered by the 
 effects of the heat. On the west side of Storm Bay, I 
 found these strata capped by streams of basaltic lava 
 with olivine ; and close by there was a mass of brecci- 
 ated scoria, containing pebbles of lava, which probably 
 marks the place of an ancient submarine crater. Two 
 of these streams of basalt were separated from each 
 other by a layer of argillaceous wacke, which could be 
 traced passing into partially altered scoriae. The 
 wacke contained numerous rounded grains of a soft, 
 grass-green mineral, with a waxy lustre, and translu- 
 cent on its edges : under the blowpipe it instantly 
 blackened, and the points fused into a strongly magnetic, 
 black enamel. In these characters, it resembles those 
 masses of decomposed olivine, described at St. Jago in 
 the Cape de Verde group ; and I should have thought 
 that it had thus originated, had I not found a similar 
 substance, in cylindrical threads, within the cells of the 
 vesicular basalt, — a state under which olivine never 
 appears ; this substance,^ I believe, would be classed as 
 bole by mineralogists. 
 
 ^ Chlorophgeite, described by Dr. MacCulloch (' Western Islands,' 
 
CHAP. VII. Travertin, with Extinct Plmits. 157 
 
 Travertin with extinct plants. — Behind Hobart 
 Town there is a small quarry of a hard travertin, the 
 lower strata of which abound with distinct impressions 
 of leaves. Mr. Robert Brown had the kindness to 
 look at my specimens, and he informed me that there 
 are four or five kinds, none of which he recognises as 
 belonging to existing species. The most remarkable 
 leaf is palmate, like that of a fan-palm, and no plant 
 having leaves of this structure has hitherto been dis- 
 covered in Van Diemen's Land. The other leaves do 
 not resemble the most usual form of the Eucalyptus, 
 (of which tribe the existing forests are chiefly com- 
 posed,) nor do they resemble that class of exceptions to 
 the common form of the leaves of the Eucalyptus, which 
 occur in this island. The travertin containing this 
 remnant of a lost vegetation, is of a pale yellow colour, 
 hard, and in parts even crystalline ; but not compact, 
 and is everywhere penetrated by minute, tortuous, 
 cylindrical pores. It contains a very few pebbles of 
 quartz, and occasionally layers of chalcedonic nodules, 
 like those of chert in our Greensand. From the pure- 
 ness of this calcareous rock, it has been searched for in 
 other places, but has never been found. From this 
 circumstance, and from the character of the deposit, it 
 was probably formed by a calcareous spring entering a 
 small pool or narrow creek. The strata have subse- 
 quently been tilted and fissured ; and the surface has 
 been covered by a singular mass, with which, also, a 
 large fissure has been filled up, formed of balls of trap 
 embedded in a mixture of wacke and a white, earthy, 
 alumino-calcareous substance. Hence it would appear, 
 
 vol. i. p. .504) as occurring in a basaltic amygdaloid, differs from this 
 substance, in remaining unchanged before the blowpipe, and in 
 blackening from exposure to the air. May we suppose that olivine, 
 in undergoing the remarkable change described at St. Jago, passes 
 through several states ? 
 
158 Van Diemens Land. paet i. 
 
 as if a volcanic eruption had taken place on the borders 
 of the pool, in which the calcareous matter was deposit- 
 ing, and had broken it up and drained it. 
 
 Elevation of the land. — Both the eastern and 
 western shores of the bay, in the neighbourhood of 
 Hobart Town, are in most parts covered to the height 
 of thirty feet above the level of high- water mark, with 
 broken shells, mingled with pebbles. The colonists 
 attribute these shells to the aborigines having carried 
 them up for food : undoubtedly, there are many large 
 mounds, as was pointed out to me by Mr. Frankland, 
 which have been thus formed; but I thiuk from the 
 numbers of the shells, from their frequent small size, 
 from the manner in which they are thinly scattered, 
 and from some appearances in the form of the land, 
 that we must attribute the presence of the greater 
 number to a small elevation of the land. On the shore 
 of Ralph Bay (opening into Storm Bay) I observed a 
 continuous beach about fifteen feet above high-water 
 mark, clothed with vegetation, and by digging into it, 
 pebbles encrusted with Serpulas were found : along the 
 banks, also, of the river Derwent, T found a bed ot 
 broken sea shells above the surface of the river, and at 
 a point where the water is now much too fresh for sea- 
 shells to live ; but in both these cases, it is just possible, 
 that before certain spits of sand and banks of mud in 
 Storm Bay were accumulated, the tides might have 
 risen to the height where we now find the shells.^ 
 
 1 It would appear that some changes are now in progress in Kalph 
 Bay, for I w^as assured by an intelligent farmer, that oysters were 
 formerly abundant in it, but that about the year 1834 they had, with- 
 out any apparent cause, disappeared. In the ' Transactions of the 
 Maryland Academy' (vol. i. part i. p. 28), there is an account by Mr. 
 Dacatel, of vast beds of oysters and clams having been destroyed by 
 the gradual filling up of the shallow lagoons and channels, on the shores 
 of the southern United States. At Chiloe, in South America, I heard 
 of a similar loss, sustained bv the inhabitants, in the disappearance 
 from one part of the coast of au edible species of Ascidia. 
 
CHAP. VII. Elevation of the Land. 159 
 
 Evidence more or less distinct of a change of level 
 between the land and water, has been detected on 
 almost all the land on this side of the globe. Capt. 
 Grey, and other travellers, have found in southern 
 Australia upraised shells, belonging either to the recent, 
 or to a late tertiary period. The French naturalists 
 in Baudin's expedition, found shells similarly circum- 
 stanced on the S.W. coast of Australia. The Rev. W. B. 
 Clarke ^ finds proofs of the elevation of the land, to the 
 amount of 400 feet, at the Cape of Good Hope. In the 
 neighbourhood of the Bay of Islands in New Zealand,^ 
 I observed that the shores were scattered to some height, 
 as at Van Diemen's Land, with sea-shells, which the 
 colonists attribute to the natives. Whatever may have 
 been the origin of these shells, I cannot doubt, after 
 having seen a section of the valley of the Thames River 
 (37° S.), drawn by the Rev. W. Williams, that the land 
 has been there elevated : on the opposite sides of this 
 great valley, three step-like terraces, composed of an 
 enormous accumulation of rounded pebbles, exa^tlv 
 correspond with each other : the escarpment of each 
 terrace is about fifty feet in height. No one after 
 having examined the terraces in the valleys on the 
 
 ' ' Proceedings of the Geological Society,' vol. iii. p. 420. 
 
 '^ I will here give a catalogue of the rocks which I met with near 
 the Bay of Islands, in New Zealand : — 1st, Much basaltic lava, and 
 scoriform rocks, forming distinct craters ; — 2nd, A castellated hill of 
 horizontal strata of flesh-coloured limestone, showing when fractured 
 distinct crystalline facets : the rain has acted on this rock in a 
 remarkable manner, corroding its surface into a miniature model of 
 an Alpine country : I observed here layers of chert and clay iron- 
 stone ; and in the bed of a stream, pebbles of clay-slate ; — 3rd, The 
 shores of the Bay of Islands are formed of a feldspathic rock, of a 
 bluish-gray colour, often much decomposed, with an angular frac- 
 ture, and crossed by numerous ferruginous seams, but without any 
 distinct stratification or cleavage. Some varieties are highly 
 crystalline, and would at once be pronounced to be trap ; others 
 strikingly resembled clay-slate, slightly altered by heat : I was iin- 
 able to form any decided opinion on this formation. 
 
1 6o King George s Souna. part i. 
 
 western shores of South America, which are strewed 
 with sea-shells, and have been formed during intervals 
 of rest in the slow elevation of the land, could doubt 
 that the New Zealand terraces have been similarly 
 formed. I may add, that Dr. Dieffenbach, in his de- 
 scription of the Chatham Islands,^ (S.W. of New Zealand) 
 states that it is manifest ' that the sea has left many 
 places bare which were once covered by its waters.' 
 
 King George's Sounds 
 
 This settlement is situated at the south-western 
 angle of the Australian continent : the whole country 
 is granitic, with the constituent minerals sometimes 
 obscurely arranged in straight or curved laminae. In 
 these cases, the rock would be called by Humboldt, 
 gneiss-granite, and it is remarkable that the form of 
 the bare conical hills, appearing to be composed of 
 great folding layers, strikingly resembles, on a small 
 scale, those composed of gneiss-granite at Rio de Janeiro, 
 and those described by Humboldt at Venezuela. These 
 plutonic rocks are, in many places, intersected by trap- 
 pean-dikes ; in one place, I found ten parallel dikes 
 ranging in an E. and W. line ; and not far off another 
 set of eight dikes, composed of a different variety of 
 trap, ranging at right angles to the former ones. I 
 have observed in several primary districts, the occur- 
 rence of systems of dikes parallel and close to each other. 
 
 Superficial, ferruginous beds. — The lower parts of 
 the country are everywhere covered by a bed, following 
 the inequalities of the surface, of a honeycombed sand- 
 stone, abounding with oxides of iron. Beds of nearly 
 similar composition are common, I believe, along the 
 whole western coast of Australia, and on many of the 
 
 ' ' Geographical Journal,' vol. xi. pp. 202, 205. 
 
CHAP. VII. Superficial Calcareoiis Deposit. i6i 
 
 East Indian islands. At the Cape of Good Hope, at 
 the base of the mountains formed of granite and capped 
 with sandstone, the ground is everywhere coated either 
 by a fine-grained, rubbly, ochraceous mass, like that at 
 King George's Sound, or by a coarser sandstone with 
 fragments of quartz, and rendered hard and heavy by 
 an abundance of the hydrate of iron, which presents, 
 when freshly broken, a metallic lustre. Both these 
 varieties have a very irregular texture, including spaces 
 either rounded or angular, full of loose sand; from 
 this cause the surface is always honey-combed. The 
 oxide of iron is most abundant on the edges of the 
 cavities, where alone it affords a metallic fracture. In 
 these formations, as well as in many true sedimentary 
 deposits, it is evident that iron tends to become aggre- 
 gated, either in the form of a shell, or of a network. 
 The origin of these superficial beds, though sufficiently 
 obscure, seems to be due to alluvial action on detritus 
 abounding with iron. 
 
 Superficial calcareo^is deposit. — A calcareous de- 
 posit on the summit of Bald Head, containing branched 
 bodies, supposed by some authors to have been corals, has 
 been celebrated by the descriptions of many distinguished 
 voyagers.^ It folds round and conceals irregular hum- 
 mocks of granite, at the height of 600 feet above the 
 level of the sea. It varies much in thickness ; where 
 stratified, the beds are often inclined at high angles, 
 even as much as at 30 degrees, and they dip in all 
 directions. These beds are sometimes crossed by 
 oblique and even- sided laminae. The deposit consists 
 either of a fine, white, calcareous powder, in which not 
 a trace of structure can be discovered, or of exceedingly 
 minute, rounded grains, of brown, yellowish, and pur- 
 
 ' I visited this hill, in company with Captain FitzRoy, and we 
 came to a similar conclusion regarding these branching bodies. 
 
 M 
 
1 62 King George s Sound. p^^rt i. 
 
 plisli colours ; both varieties being generally, but not 
 always, mixed with small particles of quartz, and being 
 cemented into a more or less perfect stone. The rounded 
 calcareous grains, when heated in a slight degree, in- 
 stantly lose their colours ; in this and in every other 
 respect, closely resembling those minute, equal-sized 
 particles of shells and corals, which at St. Helena have 
 been drifted up the sides of the mountains, and have 
 thus been winnowed of all coarser fragments. I cannot 
 doubt, that the coloured calcareous particles here have 
 had a similar origin. The impalpable powder has 
 probably been derived from the decay of the rounded 
 particles ; this certainly is possible, for on the coast of 
 Peru, I have traced large unbroken shells gradually 
 falling into a substance as fine as powdered chalk. 
 Both of the above-mentioned varieties of calcareous 
 sandstone frequently alternate with, and blend into, 
 thin layers of a hard substalagmitic ^ rock, which, even 
 
 * I adopt this term from Lieut. Nelson's excellent paper on the 
 Bermuda Islands (' Geolog. Trans.' vol. v. p. 106), for the hard, com- 
 paet, cream- or b'-r wn-coloured stone, without any crystalline struc- 
 ture, which so often accompanies superficial calcareous accumulations. 
 I have observed such superficial beds, coated with substalagmitic 
 rock, at the Cape of Good Hope, in several parts of Chile, and over 
 wide spaces in La Plata and Patagonia, Some of these beds have 
 been formed from decayed shells, but the origin of the greater 
 number is sufficiently obscure. The causes which determine water 
 to dissolve lime, and then soon to redeposit it, are not, I think, known. 
 The surface of the substalagmitic layers appears always to be 
 corroded by the rain-water. As all the above-mentioned countries 
 have a long dry season, compared with the rainy one, I should have 
 thought that the presence of the substalagmite was connected with 
 the climate, had not Lieut. Nelson found this substance forming 
 under sea- water. Disintegrated shell seems to be extremely soluble ; 
 of which I found good evidence, in a curious rock at Coquimbo in 
 Chile, which consisted of small, pellucid, empty husks, cemented 
 together. A series of specimens clearly showed that these husks 
 had originally contained small rounded particles of shells, which had 
 been enveloped and cemented together by calcareous matter (as 
 often happens on sea-beaches), and which subsequently had decayed, 
 and been dissolved by water, that must have penetrated through the 
 calcareous husks, without corroding them, — of which processes, every 
 stage could be seen. 
 
CHAP. VII. Superficial Calcareotts Deposit. 163 
 
 when the stone on each side contains particles of quartz, 
 is entirely free from them : hence we must suppose that 
 these layers, as well as certain vein-like masses, have 
 been formed by rain dissolving the calcareous matter 
 and re-precipitating it, as has happened at St. Helena. 
 Each layer probably marks a fresh surface, when the, 
 now firmly cemented, particles existed as loose sand. 
 These layers are sometimes brecciated and re-cemented, 
 as if they had been broken by the slipping of the sand 
 when soft. I did not find a single fragment of a sea- 
 shell ; but bleached shells of the Hdix melo, an existing 
 land species, abound in all the strata ; and I likewise 
 found another. Helix, and the case of an Oniscus. 
 
 The branches are absolutely undistinguishable in 
 shape from the broken and upright stumps of a thicket ; 
 their roots are often uncovered, and are seen to diverge 
 on all sides ; here and there a branch lies prostrate. 
 The branches generally consist of the sandstone, rather 
 firmer than the surrounding matter, with the central 
 parts filled, either with friable calcareous matter, or 
 with a substalagmitic variety ; this central part is also 
 frequently penetrated by linear crevices, sometimes, 
 though rarely, containing a trace of woody matter. 
 These calcareous, branching bodies, appear to have 
 been formed by fine calcareous matter being washed 
 into the casts or cavities, left by the decay of branches 
 and roots of thickets, buried under drifted sand. The 
 whole surface of the hill is now undergoing disintegra- 
 tion, and hence the casts, which are compact and hard, 
 are left projecting. In calcareous sand at the Cape of 
 Good Hope, I found the casts, described by Abel, quite 
 similar to these at Bald Head ; but their centres are 
 often filled with black carbonaceous matter, not yet 
 removed. It is not surprising, that the woody matter 
 should have been almost entirely removed from the 
 
 M 2 
 
1 64 King George s Sotind. part 1. 
 
 casts on Bald Head ; for it is certain, that many cen- 
 turies must have elapsed since the thickets were buried ; 
 at present, owing to the form and height of the narrow 
 promontory, no sand is drifted up, and the whole sur- 
 face, as I have remarked, is wearing away. We must, 
 therefore, look back to a period when the land stood 
 lower, of which the French naturalists ^ found evidence 
 in upraised shells of recent species, for the drifting on 
 Bald Head of the calcareous and quartzose sand, and 
 the consequent embedment of the vegetable remains. 
 There was only one appearance which at first made me 
 doubt concerning the origin of the cast, — namely, that 
 the finer roots from different stems sometimes became 
 united together into upright plates or veins ; but when 
 the manner is borne in mind in which fine roots often 
 fill up cracks in hard earth, and that these roots would 
 decay and leave hollows, as well as the stems, there is 
 no real difficulty in this case. Besides the calcareous 
 branches from the Cape of Good Hope, I have seen 
 casts, of exactly the same forms, from Madeira^ and 
 
 * See M. Peron's ' Voyage,' torn. i. p. 204. 
 
 2 Dr. J. Macaulay has fully described (' Edinb. New Phil, Journ.' 
 vol. xxix. p. 350) the casts from Madeira. He considers (differently 
 from Mr. Smith of Jordan Hill) these bodies to be corals, and the cal- 
 careous deposit to be of subaqueous origin. His arguments chiefly 
 rest (for his remarks on their structure are vague) on the great 
 quantity of the calcareous matter, and on the casts containing animal 
 matter, as shown by their evolving ammonia. Had Dr. Macaulay 
 seen the enormous masses of rolled particles of shells and corals on 
 the beach of Ascension, and especially on coral-reefs ; and had he 
 reflected on the effects of long-contmued, gentle winds, in drifting 
 up the finer particles, he would hardly have advanced the argument 
 of quantity, which is seldom trustworthy in geology. If the calca- 
 reous matter has originated from disintegrated shells and corals, the 
 presence of animal matter is what might have been expected. Mr. 
 Anderson analyzed for Dr. Macaulay part of a cast, and he found it 
 composed of — 
 
 Carbonate of lime 73-15 
 
 Silica 11-90 
 
 Phosphate of lime 8- 81 
 
 Animal matter ....... 4-25 
 
 Sulphate of lime . . a trace 
 
 98-li 
 
CHAP. Yii. Superficial Calcareous Deposit. 165 
 
 from Bermuda ; at this latter place, the surrounding 
 calcareous rocks, judging from the specimens collected 
 by Lieut. Nelson, are likewise similar, as is their sub- 
 aerial formation. Eeflecting on the stratification of 
 the deposit on Bald Head, — on the irregularly alter- 
 nating layers of substalagmitic rock, — on the uniformly 
 sized, and rounded particles, apparently of sea- shells 
 and corals, — on the abundance of land-shells throughout 
 the mass, — and finally, on the absolute resemblance of 
 the calcareous casts, to the stumps, roots, and branches 
 of that kind of vegetation, which would grow on sand- 
 hillocks, I think there can be no reasonable doubt, 
 notwithstanding the difierent opinion of some authors, 
 that a true view of their origin has been here given. 
 
 Calcareous deposits, like these of King George's 
 Sound, are of vast extent on the Australian shores. 
 Dr. Fitton remarks, that ' recent calcareous breccia (by 
 which term all these deposits are included) was found 
 during Baudin's voyage, over a space of no less than 
 25 degrees of latitude and an equal extent of longitude, 
 on the southern, western, and. north-western coasts. '^ 
 It appears also from M. Peron, with whose observations 
 and opinions on the origin of the calcareous matter and 
 branching casts mine entirely accord, that the deposit 
 is generally much more continuous than near King 
 George's Sound. At Swan Eiver, Archdeacon Scott ^ 
 states that in one part it extends ten miles inland. 
 Captain Wickham, moreover, informs me that during 
 his late survey of the western coast, the bottom of the 
 
 ' For ample details on this formation, consult Dr. Fitton's 
 'Appendix to Capt. King's Voyage.' Dr. Fitton is inclined to 
 attribute a concretionary origin to the branching bodies : I may 
 remark, that I have seen in beds of sand in La Plata cylindrical 
 stems which no doubt thus originated ; but they differed much in 
 appearance from these at Bald Head, and the other places above 
 specified. 
 
 2 ' Proceedings of Geolog. Soc' vol. i. p. 320. 
 
1 66 Cape of Good Hope. part i. 
 
 sea, wherever tlie vessel anchored, was ascertained by- 
 crow-bars being let down, to consist of white calcareous 
 matter. Hence it seems that along this coast, as at 
 Bermuda and at Keeling Atoll, submarine and sub- 
 aerial deposits are contemporaneously in process of 
 formation, from the disintegration of marine organic 
 bodies. The extent of these deposits, considering their 
 origin, is very striking ; and they can be compared in 
 this respect only with the great coral-reefs of the Indian 
 and Pacific Oceans. In other parts of the world, 
 for instance in South America, there are sujperficial 
 calcareous deposits of great extent, in which not a trace 
 of organic structure is discoverable ; these observations 
 would lead to the enquiry, whether such deposits may 
 not, also, have been formed from disintegrated shells 
 and corals. 
 
 Ca^e of Good Hope. 
 
 After the accounts given by Barrow, Carmichael, 
 Basil Hall, and W. B. Clarke of the geology of this 
 district, I shall confine myself to a few observations on 
 the junction of the three principal formations. The 
 fundamental rock is granite,^ overlaid by clay-slate : 
 the latter is generally hard, and glossy from containing 
 minute scales of mica ; it alternates with, and passes 
 into, beds of slightly crystalline, feldspathic, slaty rock. 
 This clay-slate is remarkable from being in some places 
 (as on the Lion's Rump) decomposed, even to the depth 
 of twenty feet, into a pale-coloured, sandstone-like rock, 
 which has been mistaken, I believe, by some observers, 
 
 1 In several places I observed in the granite, small dark-coloured 
 balls, composed of minute scales of black mica in a tough basis. In 
 another place, I found crystals of black schorl radiating from a 
 common centre. Dr. Andrew Smith found, in the interior parts of 
 the country, some beautiful specimens of granite, with silvery mica 
 radiating or rather branching, like moss, from central points. At 
 the Geological Society ,[there are specimens of granite with crystallised 
 feldspar branching and radiating in like manner. 
 
CHAP. Yii. Junction of Granite and Clay- Slate. 167 
 
 for a separate formation. I was guided by Dr. Andrew 
 Smith to a fine junction at Green Point between the 
 granite and clay-slate : the latter at the distance of a 
 quarter of a mile from the spot, where the granite 
 appears on the beach (though, probably, the granite is 
 much nearer underground), becomes slightly more com- 
 pact and crystalline. At a less distance, some of the 
 beds of clay- slate are of a homogeneous texture, and 
 obscurely striped with different zones of colour, whilst 
 others are obscurely spotted. Within a hundred yards 
 of the first vein of granite, the clay-slate consists of 
 several varieties ; some compact with a tinge of purple^ 
 others glistening with numerous minute scales of mica 
 and imperfectly crystallised feldspar ; some obscurely 
 granular, others porphyritic with small, elongated spots of 
 a soft white mineral, which being easily corroded, gives 
 to this variety a vesicular appearance. Close to the 
 granite, the clay-slate is changed into a dark-coloured, 
 laminated rock, having a granular fracture, wh ch is 
 due to imperfect crystals of feldspar, coated by minute, 
 brilliaut, scales of mica. 
 
 The actual junction between the granitic and clay- 
 slate districts extends over a width of about 200 yards, 
 and consists of irregular masses and of numerous dikes 
 of granite, entangled and surrounded by the clay-slate : 
 most of the dikes range in a NW. and SE. line, 
 parallel to the cleavage of the slate. As we leave the 
 junction, thin beds, and lastly, mere films of the altered 
 clay-slate are seen, quite isolated, as if floating, in the 
 coarsely-crystallised granite; but although completely 
 detached, they all retain traces of the uniform NW. 
 and SE. cleavage. This fact has been observed in 
 other similar cases, and has been advanced by some 
 eminent geologists,^ as a great difficulty on the ordinary 
 
 ' See M. Keilhau's ' Theory on Granite,' translated in the ' Edin- 
 burgh New Philosophical Journal,' vol. xxiv. p, 402. 
 
1 68 Cape of Good Hope, part i. 
 
 theory, of granite having been injected whilst liquefied; 
 but if we reflect on the probable state of the lower 
 surface of a laminated mass, like clay-slate, after having 
 been violently arched by a body of molten granite, we 
 may conclude that it would be full of fissures parallel 
 to the planes of cleavage; and that these would be 
 filled with granite, so that wherever the fissures were 
 close to each other, mere parting layers or wedges of 
 the slate would depend into the granite. Should, 
 therefore, the whole body of rock afterwards become 
 worn down and denuded, the lower ends of these de- 
 pendent masses or wedges of slate would be left quite 
 isolated in the granite ; yet they would retain their 
 proper lines of cleavage, from having been united, 
 whilst the granite was fluid, with a continuous covering 
 of cli^T -slate. 
 
 Following, in company with Dr. A. Smith, the line 
 of junction between the granite and the slate, as it 
 stretched inland, in a SE. direction, we came to a 
 place, where the slate was converted into a fine-grained, 
 perfectly characterised gneiss, composed of yellowish- 
 brown granular feldspar, of abundant black brilliant 
 mica, and of few and thin laminae of quartz. From 
 the abundance of the mica in this gneiss, compared 
 with the small quantity and excessively minute scales, 
 in which it exists in the glossy clay-slate, we must 
 conclude, that it has been here formed by the meta- 
 morphic action — a circumstance doubted, under nearly 
 similar circumstances, by some authors. The laminae 
 of the clay-slate are straight ; and it was interesting to 
 observe, that as they assumed the character of gneiss, 
 they became undulatory with some of the smaller 
 flexures angular, like the laminae of many true meta- 
 morphic schists. 
 
 Sandstone formation. — This formation makes the 
 
CHAP. VII. Sandstone Formation. 169 
 
 most imposing feature in the geology of Southern 
 Africa, The strata are in many parts horizontal, and 
 attain a thickness of about 2,000 feet. The sandstone 
 varies in character ; it contains little earthy matter, 
 but is often stained with iron ; some of the beds are 
 very fine-grained and quite white ; others are as com- 
 pact and homogeneous as quartz rock. In some places 
 I observed a breccia of quartz, with the fragments 
 almost dissolved in a siliceous paste. Broad veins of 
 quartz, often including large and perfect crystals, are 
 very numerous ; and it is evident in nearly all the 
 strata, that silica has been deposited from solution in 
 remarkable quantity. Many of the varieties of quartzite 
 appeared quite like metamorphic rocks ; but from the 
 upper strata being as siliceous as the lower, and from the 
 undisturbed junctions with the granite, which in many 
 places can be examined, I can hardly believe that these 
 sandstone-strata have been exposed to heat.^ On the 
 lines of junction between these two great formations, I 
 found in several places the granite decayed to the 
 depth of a few inches, and succeeded, either by a thin 
 layer of ferruginous shale, or by four or five inches in 
 thickness of the re-cemented crystals of the granite, on 
 which the great pile of sandstone immediately rested. 
 
 Mr. Schomburgk has described ^ a great sandstone 
 formation in northern Brazil, resting on granite, and 
 resembling to a remarkable degree, in composition and 
 in the external form of the land, this formation of the 
 Cape of Good Hope. The sandstones of the great plat- 
 forms of Eastern Australia, which also rest on granite, 
 differ in containing more earthy and less siliceous 
 
 * The Kev. W. B. Clarke, however, states, to my surprise 
 (' Geolog. Proceedings,' vol. iii. p. 422), that the sandstone in some 
 parts is penetrated by granitic dikes : such dikes must belong to an 
 epoch altogether subsequent to that when the molten granite acted 
 on the clay-slate. 
 
 2 ' Geographical Journal,' vol. x. p. 246. 
 
170 Cape of Good Hope. part i. 
 
 matter. No fossil remains have been discovered in 
 these three vast deposits. Finally, I may add that I 
 did not see any boulders of far-transported rocks at 
 the Cape of Good Hope, or on the eastern and western 
 shores of Australia, or at Van Diemen's Land. In the 
 northern island of New Zealand, I noticed some large 
 blocks of greenstone, but whether their parent rock was 
 far distant, I had no opportunity of determining. 
 
APPENDIX TO PART I. 
 
 DESCRIPTION OF FOSSIL SHELLS. 
 By G. B. SOWEKBY, Esq., F.L.S. 
 
 Shells from a Tertiary deposit, beneath a great basaltic 
 stream, at St. Jago in the Cape de Yerde Archipelago, 
 referred to at p. 6 of this volume. 
 
 1. LiTTOEiNA PLAi^AXis. G. Sowerby. 
 
 Testa suhovatd, crassd, IcBvigatd, anfractibus quatuor, spiraliter 
 striatis ; apertur a suhovatd ; labio columellari infimdque parte 
 anfractus ultimi planatis : long. 0"6, lat. 0"45, poll. 
 
 In stature and nearly in form this resembles a small periwinkle ; 
 it diliers, however, very materially in having the lower part of the 
 last volution, and the columellarlip as it were cut off and flattened, 
 as in the Purpuras. Among the recent shells from the same locality, 
 is one which greatly resembles this, and which may be identical, but 
 which is a very young shell, and cannot therefore be strictly com- 
 pared. 
 
 2. Ceeithium ^mtjltjm. G. Sowerby. 
 
 Testd oblongo-turritd, subventricosd, apice subulato, anfractibus^ 
 decern leviter spiraliter striatis, p?'imis serie unicd tuberculorum 
 instructis, intermediis irregulariter obsolete tuberculiferis, ultimo 
 longe tnajori absque tuherculis, sulcis duobus fere basalibv^ in- 
 structo ; labii externi margine interna intics crenulato : long. 1"8, 
 lat. 0-7, poll. 
 
 This species resembles so nearly one of the shells brought to- 
 gether by Lamarck, under the name of Cerithium Vertagus, that at 
 
172 Appendix to Part I. 
 
 first sight I thought it might be identical with it ; it may be easily- 
 distinguished, however, by its being destitute of the fold in the 
 centre of the columella so conspicuous in those shells. There is 
 only one specimen, which has unfortunately lost the lower part of 
 the outer hp, so that it is impossible to describe the form of the 
 aperture. 
 
 3. VEifTrs siMFLAisrs. G. Sowerhy. 
 
 Testa rotundatd, ventricosd, Iceviusculd, crassd; costis obiusis, 
 latiusculis, concentricis, antice posticeque tuberculatim solutis ; 
 area cardinali posticd alterm valvce latiusculd; impressione 
 suhumbonali posticd circulari: long. 1'8, alt. 1*8, lat. 1"5, 
 poll, 
 
 A shell which is intermediate in its characters, taking its 
 place between the Venus verrucosa of the British Channel and the 
 V. rosalina of Rang of the western coast of Africa, but sufficiently 
 distinguished from both by its broad, obtuse, concentric ribs, which 
 are divided into tubercles both before and hehind. It is also of a 
 more circular form than either of those species. 
 
 The following Shells, from the same bed, as far as they can 
 be distinguished, are known to be recent species : — 
 
 4. PuEPiJEA Ffcfs. 
 
 5. Amphidesma atjsteale. Soiverby. 
 
 6. Coifus VENTJLATirs. Lam. 
 
 7. FiSSTJEELLA COAECTATA. King. 
 
 8. Perista — two odd valves, but in such condition that it can- 
 not be identified. 
 
 9. Ostrea coen"fcopi^. Lam. 
 
 10. Aeca ovata. Lam. 
 
 11. Patella i^igeita. Budgin. 
 
 12. TUEEITELLA BICOTGTJLATA ? Lam. 
 
 13. Steombtjs — too much worn and mutilated to be identified. 
 
 14. HippoNTX EADIATA. Gray. 
 
 15. Natica usee. Valenciennes. 
 
 16. PECTEif, which in form resembles opercularis, but which is 
 distinguishable by several characters. There is only a single valve, 
 wherefore I cannot consider myself warranted to describe it. 
 
 17. Pupa sttbdiaphaij^a. King. 
 
 18. Tegchus — indeterminable. 
 
Appendix to Part I. 173 
 
 EXTINCT LAND-SHELLS FEOM ST. HELENA. 
 
 The following six species were found associated together, at 
 the bottom of a thick bed of mould; the last two species 
 namely, the Cochlogena fossilis and Helix hiplicata were 
 found, together with a species of Succinea now living on 
 the Island, in a very modern calcareous sandstone. 
 These Shells are referred to at p. 101 of this volume. 
 
 1. COCHLOGEI^A ATJEIS-VULPIISrA. De Fei'. 
 
 This species is well described and figured in Martini and Chem- 
 nitz's eleventh volume. Chemnitz expresses doubts as to what 
 genus it might properly be referred, and also a strong opinion un- 
 favourable to the conclusion that it should be regarded as a land- 
 shell. His specimens were bought at a public auction in Hamburg, 
 having been sent there by the late G. Humphrey, who appears 
 to have been very well acquainted with their real locality, and who 
 sold them for land-shells. Chemnitz, however, mentions one speci- 
 men in Spengler's collection, in a fresher condition than his own, 
 and which was said to be from China. The representation which he 
 has given is taken from this individual, and appears to me to have 
 been only a cleaned specimen of the St. Helena shell. It is easy to 
 suppose that a shell from St. Helena might have been either acci- 
 dentally or interestedly, after passing through two or three hands, 
 sold as a Chinese shell. I think it is not possible that a shell of 
 this species could have been really found in China ,• and among the 
 immense quantities of shells that come to this country from the 
 Celestial Empire, I have never seen one. Chemnitz could not bring 
 himself to establish anew genus for the reception of this remarkable 
 shell, though he evidently could not collate it with any of the then 
 known genera, and though he did not think it a land-shell, he has 
 called it Auris-vulpina. Lamarck has placed it as the second 
 species of his genus Struthiolaria, under the name of crenulata. 
 To this genus it does not however bear any affinity ; and there can 
 be no doubt about the correctness of De Ferussac's views, who 
 places it in the fourth division of his sub-genus Cochlogena : and 
 Lamarck would have been correct, according to his own principles 
 if he had placed it with his AuriculcB. A variety of this species 
 occurs, which may be characterised as follows : — 
 
 COCHLOGEl^A AUEIS-VIJLPINA, va?'. 
 
 Testa subpyramidali, aperturd breviori, labio tenuiori: long. 1-68 
 apertur(B 0*76, lat. 0*87, poll. 
 
 Obs. — The proportions of this differ from those of the usual 
 variety, which are as follows: — Length 1-65, of the aperture 1- 
 
174 
 
 Appendix to Part I. 
 
 width 0*96 inch. It is worthy of observation, that all the shells 
 of this variety came from a different part of the island, from the 
 foregoing specimens. 
 
 2. CocHLOGEiirA FOSsiLis. G. Sowerhy. 
 
 Testa ohlongd, crassiusculd, spwd suhacwminatd, obtusd, anfractibus 
 senis, suhventricosis, leviter sti'iatis, suturd profunde impt'essd ; 
 apertm'd suhovatd ; peritremate continuo, subincrassato ; umbilico 
 parvo : long. 0*8, lat. 0'37, poll. 
 
 This species is of the stature of C. Guadaloupensis, but may 
 easily be distinguished by the form of the volutions and the deeply- 
 marked suture. The specimens vary a little in their proportions. 
 This species was not obtained by Mr. Darwin, but is from the 
 collection of the Geological Society. 
 
 1. OoCHLicoPA STJBPLICATA. G. Sowerby. 
 
 Testa oblongd, subacuminato-pyra7nidali, apice obtuso, anfractibus 
 novem Icsvibus, postice subplicatis, suturd crenulatd ; aperturd 
 ovatd, postice acutd, labio externo tenui ; columelld obsolete sub- 
 truncatd ; umbilico minim o : long. 0*93, lat. 0'28, poll. 
 
 This and the following are placed with De Ferussac's sub-genus 
 Oochlicopa, because they are most nearly related to his Cochlicopa 
 folliculus. As species they are, however, both perfectly distinct, 
 being much larger, and not shining and smooth like C folliculus, 
 which is found in the south of Europe and at Madeira, Some very 
 young shells and an egg were found, which I conjecture to belong 
 to this species. 
 
 2. Cochlicopa tekbbelltjm. G. Sowerby. 
 
 Testd oblongd, cyliyidraceo-pyramidali, apice obtusiuseulo, anfractibus 
 septenis, Icevibus ; suturd postice crenulatd; aperturd ovali, 
 postice acutd, labio externo tenui, antice declivi; columelld 
 obsolete truncatd, umbilico minimo: long. 0"77, lat. 0*25, 
 poll. 
 
 This species differs from the last in being more cylindrical, and 
 in being nearly free, when full grown, from the obtuse folds of the 
 posterior volutions, as well as in the form of the aperture. The 
 young shells of this species are longitudinally striated, and they 
 have some very obsolete longitudinal folds. 
 
 1. Helix bilamellata. G. Soiverby. 
 
 Testd orbiculato-depressd, spird plana, anfractibus senis, ultimo 
 subtiis ventricoso, superne angulari ; umbilico parvo ; aperturd 
 
Appendix to Part I. 175 
 
 semilunaris superne extiis angulatd, labio externo tenui : interno 
 plicis duabus spiralibus, posticd majori: long. 0*15, lot. 0*33, 
 2wll. 
 
 The young shells of this species have very different proportions 
 from those marked above, their axis being nearly as great as their 
 width. The largest specimen is white, with irregular ferruginous 
 rays. This is very different from any known recent species, although 
 there are several to which it appears to have some analogy, such as 
 Helix epistylium or Cookiana, and H. gularis : in both of these, 
 however, the internal spiral plaits are placed within the outer wall 
 of the shell, and not upon the inner lamina, as in Helix hilamellata. 
 There is another recent species, which is somewhat analogous to 
 this ; it is as yet undescribed, and differs from this and from 
 Cookiana, in the circumstance of its possessing four internal spiral 
 plaits, two of which are placed within the outer, and two upon 
 the inner wall of the shell ; it was brought from Tahiti, in the 
 Beagle, 
 
 2. Helix poltodon. G. Sowerhy. 
 
 Testa orhiculato-subdepressd, anfractibus sex, rotundatis, striatis ; 
 aperturd semilunaris labio interno plicis tribus spiralibus, posticis 
 gradatim majoribus, externo intics dentibus quinque instructo ; 
 umbilico medioci'i : long. 0*07, lat. 0'15, poll. 
 
 This is somewhat related to Helix contorta of De Ferussac, 
 * Moll. terr. et fluv.' Tab. 61 A, f. 2 ; but differs from it in several 
 particulars. 
 
 3. Helix spurca. G. Sowerhy. 
 
 Testd suborbiculari, spird suhconoided, obtusd ; anfractibus quatuor 
 tumidis, suhstriatis ; aperturd 'magna ^peritremate tenui ; umbilico 
 parvo, profundo : long. 0*1, lat. 0'13, poll. 
 
 Easily distinguished from Helix polyodon, by its wide, toothless 
 aperture. 
 
 4. Helix biplicata. G. Sowerhy. 
 
 Testd orbiculato-depressd, anfractibus quinque rotundatis, striatis ; 
 aperturd semilunaris labio interno plicis duahus spiralibus, posticd 
 majori; umbilico magno : long. 0'04, lat. O'l, poll. 
 
 This must be regarded as perfectly distinct from Helix hilamellata. 
 on account of its form ; its umbilicus is much larger, its spire is not 
 flat, nor is the posterior edge of each volution angular. There are 
 specimens, which must be referred to this species, found wiih the 
 foregoing species, and with the Cochlogena fossilis, which latter is 
 associated with a living Succinea, in the modern calcareous sand- 
 stone. 
 
176 Appendix to Part I. 
 
 PALAEOZOIC SHELLS FROM VAN DIEMEN'S LAND, 
 befekeed to at p. 155 of this volume. 
 
 1. Peoducta EUGATA. 
 
 This is probably the same species with that named Producta 
 rugata by Phillips (' Geolog-y of Yorkshire/ part ii. plate vii. f. 16) : 
 it is, however, in too imperfect a condition to allow me to decide 
 positively. 
 
 2. Peoducta beachtth^eus. G. Sowerby. 
 
 Producta, Testa subtrapezifoi'mi, compressd, pa?'te anticd latiori, sub- 
 bilobd, posticd angustiori, lined cardinali brevi. 
 
 The most remarkable characters of this species are the shortness 
 of the hin»e-line, and the comparative width of the anterior part: 
 its outside is ornamented with small, blunt tubercles, irregularly 
 placed : it is in limestone, of the ordinary grey colour of mountain 
 limestone. Another specimen which I suppose to be an impression 
 of the inside of the flat valve, is in stone, of a light rasty-brown 
 colour. There is a third specimen, which I believe to be the im- 
 pression of the inside of the deeper valve, in a nearly similar stone, 
 accompanied by other shells. 
 
 1. Spieifeea subeabtata. G. So2oerbg. 
 
 Spirifera, Testd Icsvissimd, parte mediand lata, I'adiis lateralibus 
 utriusque lateris paucis, inconspicuis. 
 
 The breadth of this shell is rather greater than its length. The 
 rays of the lateral surfaces are very few and indistinct, and the 
 medial lobe is uncommonly large and wide. 
 
 2 Spieifeea eotundata? Phillips's ' Geology of Yorkshire,^ 
 
 pi. ix. f. 17. 
 
 Although this shell is not exactly like the figure above referred 
 to it would perhaps be impossible to find any good distinguishing 
 character. Our specimen is much distorted ; it is, moreover, an 
 example of that sort of accidental variation that shows how little 
 dependence, ought, in some instances, to be placed upon particular 
 characters ; for the radiating ribs of one side of one valve are much 
 more numerous and closer than those on the other side of the same 
 valve. 
 
Appendix to Part I. 177 
 
 3. Spiripeba teapezoibalis. G. Soiverhy. 
 
 Spirifei'a, Testa suhtetragond, mediand parte profundd, radiis non- 
 nuUis, subinconspicuis ; radiis later alihus utriusque lateris septem 
 ad octo distinctis: long. 1*5, lat. 2', poll. 
 
 There are two specimens of this, in a dark, rusty, gray limestone, 
 probahly bituminous. 
 
 Spirieeea teapezoidalis, var. ? G. Sowerhy. 
 
 Spirifera, Testd radiis lateralihus tripartitim divisis, lineis incrementi 
 antiquatis, cceteroquin omninb ad Spiriferam trapezoidaleni 
 simillimd. 
 
 At first I hesitated to unite this to Spirifera trapezoidalis, hut 
 observing that at the commencement the radiating ribs were simple, 
 and knowing that these are subject to variations, I have thought it 
 best merely to distinguish this specimen as a variety. 
 
 There are several other, probably distinct, species of Spiriferse, 
 but as these are only casts, it is obviously impossible to give the 
 external characters of the species. Since, however, they are very 
 remarkable, I have thought it advisable to give a name, together 
 with a short description of each. 
 
 4. Spieieeea paucicostata. G. Sowerhy. 
 
 Length equal to about two-thirds of its breadth ; ribs few and 
 variable. 
 
 6. Spieieeea Vespeetilio. G. Soiverby. 
 
 Breadth more than double its length, radiating ribs rather large, 
 distinct, and not numerous ; posterior inner surface covered with 
 distinct punctulations in both valves. 
 
 6. Spieieeea avicula. G. Sowerhy. 
 
 The proportions of this species are very remarkable, inasmuch 
 as it appears to have been nearly three times as wide as it is long ; 
 the radiating ribs are not very numerous, and the internal posterior 
 surface of one valve alone (the large valve) has been punctulated. 
 In its proportions it resembles Phillips's Spirifera convoluta, but as 
 our Sp. avicula is only a cast of the inside, its proportions are not 
 so abnormal as those of Sp. convoluta.^ 
 
 A specimen, which is very much pressed out of its natural shape, 
 but which still appears to differ somewhat in its proportions, shows 
 not only the cast of the inside, but also the impression of the out- 
 side ; its radiating ribs are very irregular, and numerous, but it 
 must be regarded as doubtful whether some of them be not principal 
 and others only interstitial : their irregularity renders it impossible 
 to decide. 
 
 ^ ' Geology of Yorkshire,' part ii. plate ix. f . 7. 
 
 N 
 
178 Appendix to Part I. 
 
 DESCRIPTION OF SIX SPECIES OF CORALS, 
 FROM THE PALEOZOIC FORMATION OF 
 VAN DIEMEN'S LAND. 
 
 By W. LONSDALE, Esq., F.G.S. 
 
 1. Stenopoea Tasmai^iensis, sp. n.^ 
 
 Branched^ branches cylindrical, variously inclined or contorted: 
 tubes more or less divergent; mouths oval, divisional ridges 
 strongly tuberculated ; indications of successive narrowing in 
 each tube, 1 — 2. 
 
 This coral, in its g-eneral mode of gTowth, resembles Calamopora 
 (Stenopora?) tumida, (Mr. Phillips, ^ Geol. of Yorkshire,' part ii. 
 pi. 1, fig. 62), but in the form of the mouth and other structural 
 details the differences are very great. Stenopora Tasmaniensis 
 attains considerable dimensions, one specimen being 4|- inches in 
 length and half an inch in diameter. 
 
 The branches have individually great uniformity in their circum- 
 ference, but they differ vs^ith respect to each other in the same speci- 
 men, and there is no definite method of subdivision or direction 
 of growth. The extremities are occasionally hollow ; and one 
 specimen, about 1^ inch in length, and half an inch in breadth, is 
 crushed completely flat. The tubes, in the best exposed cases, have 
 considerable length, springing almost solely from the axis of the 
 branch, and diverging very gently till they nearly reach the circum- 
 ference, where they bend outwards. In the body of the branch 
 the tubes are angular from lateral interference ; but, on approaching 
 the outer surface, they become oval in consequence of the inter- 
 spaces produced by the greater divergence. Their diameter is very 
 uniform throughout, with the exception of the narro wings near the 
 terminations of the full-grown tubes. The walls in the interior of 
 
 ^ Though the characters of this genus are unpublished, it has been 
 thought advisable not to give them fully in this notice, a very few 
 species only having been examined. The coral is essentially com- 
 posed of simple tubes, variously aggregated and radiating outwards. 
 The mouth is round or oblong, and surrounded by projecting walls, 
 having along the crest a row of tubercles. The mouth originally 
 oval is gradually narrowed ((Xrevds) by a band projecting from the 
 inner wall of the tube, and is finally closed. [Shortly after the pub- 
 lication of the first edition, Mr. Lonsdale informed me that he 
 believed this coral ought to have been included in the genus Tham- 
 nopora of Steininger.] 
 
Appendix to Part I. 179 
 
 the branches were apparently very thin, but there is a relatively 
 considerable thickness of matter at the circumference. No traces 
 of transverse diaphragms have been noticed within the tubes. 
 
 Oases illustrative of the changes to maturity and final oblitera- 
 tion in the oval termination of the tubes are rare, but the following 
 have been observed. Where the mouth becomes free and oval, the 
 walls are thin and sharp, and perpendicular within the tube. In 
 some cases they are in contact ; but, in others, they are separated 
 by grooves of variable dimensions, in which very minute foramina 
 or pores may be detected. As the mouth approaches towards 
 maturity, the grooves are more or less filled up, and the walls 
 thicken, a row of very minute tubercles being discoverable along 
 the crest. At this stage the inner side of the tube ceases to be 
 vertical, being lined by a very narrow inclined band. The mature 
 mouths are separated by a bold ridge, generally simple, but not 
 unfrequently divided by a groove ; the double as well as the single 
 ridge being surmounted by a row of prominent tubercles almost 
 in contact with each other. Only one example of the filling up 
 of the mouths has been observed, but it affords satisfactory evi- 
 dence of a gradual expansion of the inner band, before alluded to, 
 and a final meeting in the centre. In this extreme state, there is 
 a general blending of details, but the tubercles are for the most 
 part distinct. 
 
 In this species, proofs of a narrowing of the mouth previously 
 to the formation of the perfect tube, and the final contraction, are 
 not very prominently exhibited in the long cylindrical straight 
 branches ; but near the point where the tubes bent outwards there 
 is an annular indentation, which may be traced successively from 
 cast to cast in a lineal direction, parallel to the surface ; and be- 
 tween the prominent narrowing and the perfect surface, the walls 
 of the tubes were slightly rugose. In another short branch, be- 
 lieved to belong to this species, but in which the tubes diverged 
 outwards very rapidly, the narrowing is strongly marked, but not 
 to an equal extent throughout the specimen. 
 
 The matrix, in which the fossil is imbedded, is a coarse calca- 
 reous shale, or a gray limestone ; and in which occur also Fenestella 
 internaia, &c. 
 
 2. STETiTOPOKA. OVATA, Sp. n. 
 
 Branched, hraneJies oval; tubes relatively short, divergence great; 
 mouths round; contractions or irregularities of grmvth nu- 
 merous. 
 
 The characters of this species have been very imperfectly ascer- 
 tained. The branches are not uniformly oval, even in apparently 
 the same fragment. The tubes diverged rapidly along the line of 
 the major axis, and had but a very limited vertical growth. Their 
 casts exhibit a rapid succession of irregularities of development. 
 The mouths, as far as they can be determined, were round or 
 
 N 2 
 
1 8o Appendix to Part I. 
 
 sliglitly oval, and the dividing, tuberculated ridges sharp ; but in 
 consequence of the outer surface not being exposed, their perfect 
 characters, and the changes incidental upon growth, could not be 
 ascertained. 
 
 The coral is imbedded in a dark gray limestone. 
 
 1. Fenestella ampla, sp. n. 
 
 Cup-shaped; celluliferous surface internal ; branches dichotomous, 
 broad, fiat, thin ; Tneshes oval ; rows of cells numerous, rarely 
 limited to two, alternate ; transverse connecting processes some- 
 times cellular ; inner layer of non-cellular surface very fibrous ; 
 external layer very granular, non-fibrous ; gemmuliferous vesicle ? 
 small. 
 
 Some of the casts of this coral have a general resemblance to 
 Fenestella polyporata, as represented in Captain Portlock's ' Report 
 on the Geology of Londonderry,' pi. xxii. A. fig. la. Id; but 
 there is no agreement between the Van Diemen's Land fossil and 
 the structure of that species as given in PI. xxii. fig. 3, of the 
 same work, or in Mr. Phillips's original figures, ' Geology of York- 
 shire,' part ii., pi. i. figs. 19, 20. A general resemblance also exists 
 between Fenestella ampla and a coral obtained by Mr. Murchison 
 from the carboniferous limestone of Kossatchi Datchi, on the eastern 
 flank of the Ural Mountains, but there is again a marked difference 
 in structural details. 
 
 Fenestella ampla attained considerable dimensions, fragments 
 apparently of one specimen covering an area of 4|- inches by 3 
 inches; and it displays considerable massiveness of outline, the 
 branches at the points where they dichotomise often exceeding the 
 tenth of an inch in breadth. 
 
 In the general aspect of the coral a considerable uniformity pre- 
 vails, but the branches vary in breadth, swelling out greatly near the 
 bifurcations ; nevertheless, there is no marked difierence of character 
 between the base and the upper part of the cup, even in the number 
 of the rows of cells. 
 
 In the best state of the cellular surface, which has been noticed, 
 the mouths of the cells are relatively large, round or oval, and are 
 defined by a slightly raised margin ; and an undulating, thread-like 
 ridge winds between them, dividing the interspaces into lozenge- 
 shaped areas. The rows of cells, immediately preceding the bifurca- 
 tion, sometimes amount to ten, and after the separation generally 
 exceed two. The mouths of the lateral rows project into the 
 meshes ; and the transverse connecting processes are sometimes 
 cellular. The interspaces between the mouths, as well as the un- 
 dulating ridges, are granular, or very minutely tuberculated. In- 
 ternally, the cells exhibit the usual oblique arrangement, overlaying 
 each other and terminating abruptly against the dorsal part of the 
 branch. The perfect casts of the cellular surface give the reverse 
 
Appendix to Part I. 1 8 1 
 
 of the characters just noticed, but more generally the impressions 
 display scarcely a trace of any other structure than longitudinal 
 rows of circular mouths. 
 
 On the inner layer of the non-cellular surface, twenty well- 
 marked parallel fibres, with intermediate narrow grooves or corre- 
 sponding casts, may sometimes be detected, and the number is 
 always considerable. The mode of preservation did not permit the 
 true nature of the fibres to be discovered, but in consequence of 
 what has been noticed in other species, it is inferred that they are 
 tubular. Their range is considerable, but in the specimen, which 
 exhibits their structure most fully, they are frequently cut off" by 
 circular foramina. Their perfect surface is minutely granular. 
 The outer layer, or back of the branches, is composed of an uniform 
 crust without any indications of fibres, but covered with numerous 
 microscopic papillae, and corresponding pores penetrating the sub- 
 stance of the layer. 
 
 The onlyindications of gemmuliferous vesicles, are small circular 
 pits occasionally situated over the mouth, and agreeing in position 
 with the vesicles, which in other cellular genera, have been con- 
 sidered as gemmuliferous. In the Russian specimen before alluded 
 to, casts of similar pits are very uniformly distributed between the 
 casts of the mouths. 
 
 The youngest state of the coral has not been noticed, nor have 
 any marked changes incident upon age, except the gradual thicken- 
 ing of the non-cellular surface, by the coating over of the fibrous 
 layer. 
 
 The matrix of the specimens is a dark gray splintery or an earthy 
 limestone. 
 
 2. Fenestella ii<rTEEi<rATA, sp. n. 
 
 Cup-shaped; celluliferous surface internal; branches dichotomous, 
 compressed, breadth variable ; meshes oblong, narrow ; rows of 
 cells 2 — 5, divided by longitudinal ridges ; transverse connecting 
 processes short without cells ; non-cellular surface, inner lager, 
 sharply fibrous, outer layer, minutely granular. 
 
 By the delicacy of its structure, this species is easily distinguish- 
 able from Fen. ampla ; and in the rows of cells varying from two 
 to five, as well as in their mode of development, there are further 
 well-marked differences. It appears to have attained considerable 
 dimensions, fragments having been noticed an inch and a-half in 
 length and an inch in breadth. 
 
 The branches vary in width, swelling out gradually towards the 
 bifurcations, but without any alteration in the form or size of the 
 meshe« ; and as far as the state of the specimens will permit an 
 opinion to be formed, no marked changes occurred during the deve- 
 lopment of the cup, except one about to be noticed. On the cellu- 
 liferous surface of the branches, considerable, but uniform, altera- 
 tions take place between the successive bifurcations. For a short 
 
1 82 Appendix to Pai4 I. 
 
 distance above the point of separation, the branch is narrow and 
 angular, and traversed along the centre by a ridge, and there is only 
 one row of cellular mouths on each side. As the branch grew, the 
 ridge widened, and ultimately became celluliferous, a row of mouths 
 springing from its place {internata). The three ranges of cellular 
 openings are, in this state of the branch, separated by two ridges, 
 and these, as the development advanced, again widened and became 
 cellular, the five rows being divided by four ridges. This appears 
 to be the extreme stage of growth, another bifurcation taking place 
 immediately after. In the earliest formed part of the cup only two 
 or three rows of mouths prevail ; and where the number is greater, 
 a certain amount of irregularity in the linear arrangement is percep- 
 tible, resulting from the lateral expansion of the branch. 
 
 In the best preserved specimens, the mouths are relatively large, 
 round or oval, and the margin is slightly raised. In the middle 
 rows they are parallel, or nearly parallel, and in the direction of the 
 axis of the branch ; but in the side rows they are often obliquely 
 placed, inclining towards the meshes. In these nearly perfect speci- 
 mens the dividing ridges are thread-like and slightly waved, but 
 there is no trace of the lozenge-shaped compartments so distinctly 
 exhibited in Fenestella ampla. The interspaces between the mouths 
 are flat or slightly convex. In specimens less finely preserved, or 
 deprived of the original surface, the mouths are not uniform in out- 
 line, and have no projecting margin. The diverging ridges are also 
 relatively broader ; and the whole surface, including the transverse 
 connecting processes, is granular or minutely tuberculated. 
 
 The inner layer of the non-cellular surface is sharply fibrous, and 
 the same structure may be more or less clearly detected in the 
 transverse, connecting processes. The number of fibres on the 
 branches do not apparently exceed twelve, and they are in general 
 less numerous. Their range is considerable, additional ones being 
 interpolated as the branch widens ; and their surface is minutely 
 tuberculated. No separate, circular foramina were noticed. The 
 outer layer is uniformly granular, where completed, but every inter- 
 mediate state from the sharply fibrous may be traced on the same 
 specimen. 
 
 No distinct proofs of gemmuliferous vesicles have been observed, 
 but in a specimen, which is believed to exhibit impressions of this 
 species, there are occasionally to be detected, near the mouths, 
 hemispherical casts, perfectly rounded on the surface, and evidently 
 unconnected immediately with the interior of the cells, and which 
 it is presumed may represent those vesicles. Fenestella internata 
 appears to be an abundant fossil, one slab nearly eight inches long 
 and six wide, being covered on both sides with fragments of it, 
 and numerous smaller specimens occur in the collection. The 
 matrix is chiefly a coarse gray calcareous shale, but it is sometimes 
 a splintery limestone, or a hard ferrr.-'nous or light-coloured clay- 
 stone. 
 
Appendix to Part I. 1 8 
 
 o 
 
 3. Fenestella eossula, sp. n. 
 
 Cup-shaped, celluliferous surface internal; hranches dichotonious, 
 slender; meshes oval; roios of cells, Uuo ; transverse processes 
 non-cellvlar ; inner layer of non-celluliferous surface minutely 
 fibrous ,* external layer smooth or granular. 
 
 In general aspect and structural details, this species bears a great 
 resemblance to Fenestella Jlustracea of the niagnesian limestone of 
 England (Retepora flustracea, ' Geol. Trans.,' 2nd series, vol. iii. 
 pi. xii. f. 8), but it differs from it in the peculiar character ex- 
 hibited in the cast of the celluliferous surface, the nature of which 
 will be given in noticing that surface. 
 
 The principal specimen is a nearly perfect cup \^ inch in height, 
 and about two inches across the widest, compressed part. There 
 are no marked variations of character, but occasionally, irregu- 
 larities of growth, due, apparently, to accidents during progressive 
 development. 
 
 The following details have been obtained from casts, no perfect 
 surface having been noticed. — The branches had great uniformity of 
 dimensions, swelling but very slightly at the distant points of bifur- 
 cation, and their thickness was apparently nearly equal to their 
 breadth. The cast of the cellular surface is traversed along the 
 centre by a sharp narrow trench (fossula), with nearly vertical 
 sides, the distinguishing character between this species and Fen. 
 flustracea. The cylindrical casts of the mouths, or the interior of 
 the cells, are arranged in a single row on each side of the trench, 
 and no increase of number is clearly perceptible at the bifurcations. 
 Along the centre of the trench is a row of indentations or minute 
 conical pits, a character noticeable in other species, particularly in 
 Fen. flustracea. They are plainly not casts of cellular openings, 
 but of relatively large papillae. Traces of such projections have 
 also been noticed in several other instances. 
 
 The mouths of the cells, in the minute fragment which has been 
 obtained exhibiting them, are large, round, slightly projecting, and 
 not very distant, and in the same atom is an imperfect keel. The 
 remains of the non-cellular surface exhibit no characters requiring 
 notice, but indications of a striated and smooth layer have been 
 observed. 
 
 The two specimens which afforded these structural details have 
 a matrix of dark-coloured, hard limestone. 
 
 HeMITRTPA SEXAJfTGULA, Sp. n. 
 
 Net-ivork fine, hexagonal ; meshes round in double rows. 
 
 The coral to which the above inefficient characters are applied, 
 is imbedded in the shaly surface of a dark, hard limestone. It is 
 
184 Appendix to Part I. 
 
 about an inch in breadth and half an inch in height, and consists of 
 two layers of net- work, — one presenting quadrangular meshes, and 
 the other hexagonal, with a round, inner area ; and over a consider- 
 able part of the specimen, the quadrangular net-work has been 
 removed, whereby the connexion of the two structures is perfectly 
 exposed. 
 
 This fossil is believed to agree completely in its essential generic 
 characters with those of Hemitrypa (' Pal. Foss. Cornwall,' p. 27), 
 but its state of preservation, and some facilities afforded by it for 
 determining structural details, have led to an inference respecting 
 its nature somewhat different from that given in the work just 
 quoted. 
 
 The inner surface of Hemitrypa oculata (Joe. cit.) is described as 
 ' marked with radiating ridges,' having intervening ^ oval depres- 
 sions, which penetrate only half through the substance of the coral, 
 and nowhere reach the outer surface.' The equivalent portion of 
 the Van Diemen's Land specimen agrees perfectly with this state- 
 ment, except in the form of the meshes or depressions ; it is, how- 
 ever, not merely ' like some Fenestellae,' but it possesses all the 
 essential characters of that genus, and is believed to be a fragment 
 of Fen. fossula. This inference is drawn from a minute portion 
 mechanically detached, and which exhibited a row of large, round, 
 projecting, cellular mouths. The external surface of Hem. oculata 
 is described as 'wholly covered with numerous round pores or 
 cells ' — ^ associated in double rows,' and the corresponding portion 
 of Hem. sexangula has been ascertained to consist also of a similar 
 surface of double rows of round meshes or ' pores,' but with hexa- 
 gonal boundaries ; and they are shown, as exhibited by the speci- 
 men in its imbedded state, to penetrate to the surface of the Fene- 
 stella or quadrangular net-work. 
 
 These details are conceived to be sufficient to establish a generic 
 agreement between the Van Diemen's Land coral and Hemitrypa 
 oculata ; and an examination of an Irish specimen of that genus 
 has fully confirmed the structural details exhibited in the ' inner 
 surface ' of the specimen to which, provisionally, the name of Hemi- 
 trypa sexangula is applied. 
 
 Of the true nature of the ' external ' net-work no opinion is 
 ventured. It is formed almost entirely of dark gray, calcareous 
 matter, filling apparently an originally cellular structure ; but there 
 are also a few small patches of the outer covering, consisting of an 
 opaque white crust on the surface, which was originally in contact 
 with the external net-work. That it was a parasite little doubt 
 is entertained ; and the interesting agreement between the space 
 occupied by the double row of meshes, and that of the parallel 
 branches of the Fenestella, arises apparently from the latter having 
 afforded suitable base lines for attachment. In the Van Diemen's 
 Land specimen, the agreement is marked by an increased breadth in 
 the net-work, and by a row of projecting points. There is also a re- 
 markable agreement between the arrangement of the mouths of the 
 
Appe7tdix to Pai^t I. 185 
 
 Fenestella and the meshes of the ' inner ' net- work. Similar con- 
 formities are admirably shown in Mr. Phillips's excellent figures 
 (^ Pal. Foss.' pi. xiii. f. 38). 
 
 The solid portions of the structure being exceedingly fine, resem- 
 bling the thread of the most delicate lace, attempts to discover satis- 
 factorily internal characters proved unsuccessful, except in one place, 
 where a true cellular arrangement was believed to be visible.^ 
 Of the nature of the investing crust, nothing also has been deter- 
 mined. 
 
 Though the name Hemitrypa may be objectionable, as applied 
 to the corals under consideration, it has been thought right to re- 
 tain the word, until the lull characters of the genus shall have 
 been ascertained. 
 
 Falmofth, January 1844. 
 
 ' A Codrington lens, balf-an-inch in diameter, was invariably 
 used in examining the corals described in this notice. 
 
PART II. 
 
 SOUTH AMEEICA, 
 
CHAPTER VIII. 
 
 ON THE ELEVATION OF THE EASTERN COAST OF SOUTH 
 
 AMERICA. 
 
 Upraised Shells of La Plata — Bahia Blanca, Sand-dimes and Pumice- 
 pebbles — Step-formed Plains of Patagonia, with upraised Shells — 
 Terrace-bounded Valley of SoMta Cruz, formerly a Sea-strait — Tip- 
 raised Shells of T terra del Fu£go — Length a,nd breadth of the 
 elevated area — Equability of the movements, as shown by the similar 
 heights of the plains — Slowness of the elevatory process — Mode of 
 formation of the step-formed plains — Summary — Great Shingle 
 Formation of Patagonia ; its extent, origin, and distribution — 
 'Formation of sea-cliffs. 
 
 In the following Part, which treats of the geology of 
 South America, and almost exclusively of the parts 
 southward of the Tropic of Capricorn, I have arranged 
 the chapters according to the age of the deposits, occa- 
 sionally departing from this order, for the sake of geo- 
 graphical simplicity. 
 
 The elevation of the land within the recent period, 
 and the modifications of its surface through the action 
 of the sea (to which subjects I paid particular attention) 
 will be first discussed ; I will then pass on to the tertiary 
 deposits, and afterwards to the older rocks. Only those 
 districts and sections will be described in detail which 
 appear to me to deserve some particular attention ; and 
 I will, at the end of each chapter, give a summary of 
 the results. We will commence with the proofs of the 
 upheaval of the eastern coast of the continent, from 
 the Rio Plata southward; and, in the next chapter. 
 
I go Elevation oj La Plata. part ir. 
 
 follow up the same subject along the shores of Chile aud 
 Peru . 
 
 On the northern bank of the great estuary of the 
 Rio Plata, near Maldonado, I found at the head of a 
 lake, sometimes brackish but generally containing fresh 
 water, a bed of muddy clay, six feet in thickness, with 
 numerous shells of species still existing in the Plata, 
 namely, the Azarob lahiata, d'Orbig., fragments of 
 Mytilus eduliformis, d'Orbig., Paludestrina Isahellei, 
 d'Orbig., and the Solen Garihceus, Lam., which last was 
 embedded vertically in the position in which it had 
 lived. These shells lie at the height of only two feet 
 above the lake, nor would they have been worth mention- 
 ing, except in connection with analogous facts. 
 
 At Monte Video, I noticed near the town, and along 
 the base of the mount, beds of a living Mytilus, raised 
 some feet above the surface of the Plata : in a similar 
 bed, at a height from thirteen to sixteen feet, M. Isabella 
 collected eight species, which, according to M. d'Or- 
 bigny,^ now live at the mouth of the estuary. At 
 Oolonia del Sacramiento, further westward, I observed 
 at the height of about fifteen feet above the river, there 
 of quite fresh water, a small bed of the same Mytilus, 
 which lives in brackish water at Monte Video. Near the 
 mouth of the Uruguay, and for at least thirty-five miles, 
 northward, there are at intervals large sandy tracts, 
 extending several miles from the banks of the river, 
 but not raised much above its level, abounding with 
 small bivalves, which occur in such numbers that at 
 the Agraciado they are sifted and burnt for lime. 
 Those which I examined near the A. S. Juan were much 
 worn : they consisted of Madra Isahellei, d'Orbig., 
 mingled with few of Venus sinuosa, Lam., both in- 
 ^ ' Voyage dans rAmerique Merid. : Part. Geolog.' p. 21. 
 
CHAP. Till. Elevation of La Plata. 191 
 
 habiting, as I am informed by M. d'Orbigny, brackish 
 water at the mouth of the Plata, nearly or quite as salt 
 as the open sea. The loose sand, in which these shells 
 are packed, is heaped into low, straight, long lines of 
 dunes, like those left by the sea at the head of many 
 bays. M. d'Orbigny has described ^ an analogous phe- 
 nomenon on a greater scale, near San Pedro on the 
 river Parana, where he found widely extended beds and 
 hillocks of sand, with vast numbers of the Azaraj 
 labiata, at the height of nearly 100 feet (English) 
 above the surface of that river. The Azara inhabits 
 brackish water, and is not known to be found nearer to 
 San Pedro than Buenos Ayres, distant above 100 miles 
 in a straight line. Nearer Buenos Ayres, on the road 
 from that place to San Isidro, there are extensive beds, 
 as I am informed by Sir Woodbine Parish,^ of the Azara 
 lahiata, lying at about forty feet above the level of the 
 river, and distant between two and three miles from it. 
 These shells are always found on the highest banks in 
 the district : they are embedded in a stratified earthy 
 mass, precisely like that of the great Pampean deposit 
 hereafter to be described. In one collection of these 
 shells, there were some valves of the Venus sinuosa^ 
 Lam., the same species found with the Mactra on the 
 banks of the Uruguay. South of Buenos Ayres, near 
 Ensenada, there are other beds of the Azara, some of 
 which seem to have been embedded in yellowish, cal- 
 careous, semi-crystalline matter ; and Sir W. Parish 
 has given me from the banks of the Arroyo del Tristan, 
 situated in this same neighbourhood, at the distance of 
 above a league from the Plata, a specimen of a pale- 
 reddish, calcareo-argillaceous stone (precisely like parts 
 of the Pampean deposit, the importance of which fact 
 
 ^ ' Voyag-e dans TAmerique Merid. : Part. Geolog.' p. 43. 
 2 ' Buenos Ayres,' &c., by Sir "Woodbine Parish, p. 168. 
 
192 
 
 Elevation of La Plata. 
 
 PART II. 
 
 will be referred to in a succeeding chapter), abounding 
 witb shells of an Azara, much worn, but which in 
 general form and appearance closely resemble, and are 
 probably identical with, the A. lahiata. Besides these 
 shells, cellular, highly crystalline rock, formed of the 
 casts of small bivalves, is found near Ensenada ; and 
 likewise beds of sea-shells, which from their appearance 
 appear to have lain on the surface. Sir W. Parish has 
 given me some of these shells, and M. d'Orbigny pro- 
 nounces them to be, 
 
 1. Buccinanops globulosum, 
 
 d'Orbig. 
 
 2. Qlivancillaria auricularia, 
 
 do. 
 
 3. Venus flexnosa, Lam. 
 
 4. Cvtheraea (imperfect). 
 
 5. Mactra Isabellei, d'Orbig. 
 
 6. Ostrea pulchella, do. 
 
 Besides these. Sir W. Parish procured ^ (as named 
 by Mr. G. B. Sowerby) the following shells : — 
 
 7. Voluta colocynthis. 
 
 8. V. angulata. 
 
 9. Buccinum (not spec. ?). 
 
 All these species (with, perhaps, the exception of 
 the last) are recent, and live on the South American 
 coast. These shell-beds extend from one league to six 
 leagues from the Plata, and must lie many feet above 
 its level. I heard, also, of beds of shells on the Som- 
 borombon, and on the Rio Salado, at which latter 
 place, as M. d'Orbigny informs me, the Mactra Isabellei 
 and Venus sinuosa are found. 
 
 During the elevation of the Provinces of La Plata, 
 the waters of the ancient estuary have but little affected 
 (with the exception of the sand-hills on the banks of 
 the Parana and Uruguay) the outline of the land. 
 M. Parchappe,^ however, has described groups of sand- 
 dunes scattered over the wide extent of the Pampas 
 
 * • Buenos Ayres,' &c., by Sir W. Parish, p. 168. 
 
 * D'Orbigny's ' Voyage Geolog.' p. 44. 
 
CHAP. Yiii. Elevation of Bahia Blanca. 193 
 
 soutliward of Buenos Ayres, whicli M. d'Orbigny attri- 
 butes with much probability to the action of the sea, 
 before the plains were raised above its level. ^ 
 
 Southiuard of the Plata. — The coast as far as Bahia 
 Blanca (in lat. 39° S.) is formed either of a horizontal 
 range of cliffs, or of immense accumulations of sand- 
 dunes. Within Bahia Blanca, a small piece of table- 
 land, about twenty feet above high-water mark, called 
 Punta Alta, is formed of strata of cemented gravel and 
 of red earthy mud, abounding with shells (with others 
 lying loose on the surface), and the bones of extinct 
 mammifers. These shells, twenty in number, together 
 with a Balanus and two corals, are all recent species, 
 still inhabiting the neighbouring seas. They will be 
 enumerated in the eleventh Chapter, when describing 
 the Pampean formation ; five of them are identical 
 with the upraised ones from near Buenos Ayres. The 
 northern shore of Bahia Blanca is, in main part, formed 
 
 * Before proceeding to the districts southward of La Plata, it may 
 be worth while just to state, that there is some evidence that the 
 coast of Brazil has participated in a small amount of elevation. Mr. 
 Burchell informs me, that he collected at Santos (lat. 24° S.) oyster- 
 shells, apparently recent, some miles from the shore, and quite above 
 the tidal action. Westward of Rio de Janeiro, Capt. Elliot is asserted 
 (see Harlan, ' Med. and Phys, Res.,' p. 35, and Dr. Meigs, in ' Trans. 
 Amer, Phil, Soc.'), to have found human bones, encrusted with sea- 
 shells, between fifteen and twenty feet above the level of the sea. 
 Between Rio de Janeiro and Cape Frio I crossed sandy tracts 
 abounding with sea- shells, at the distance of a league from the coast; 
 but whether these tracts have been formed by upheaval, or through 
 the mere accumulation of drift sand, I am not prepared to assert. 
 At Bahia (lat. 13° S.), in some parts near the coast, there are traces 
 of sea-action at the height of about twenty feet above its present 
 level ; there are also, in many parts, remnants of beds of sandstone 
 and conglomerate with numerous recent shells, raised a little above 
 the sea-level. I may add, that at the head of Bahia bay there is a 
 formation, about forty feet in thickness, containing tertiary shells 
 apparently of fresh- water origin, now washed by the sea and en- 
 crusted with Balani ; this appears to indicate a small amount of 
 subsidence subsequent to its deposition. At Pernambuco (lat. 8° 
 S.), in the alluvial or tertiary cliffs, surrounding the low land on 
 which the city stands, I looked in vain for organic remains, or other 
 evidence of changes in level. 
 
 O 
 
194 Elevation of Bahia Blanca. paet h. 
 
 of immense sand-dunes, resting on gravel with recent 
 shells, and ranging in lines parallel to the shore. These 
 ranges are separated from each other by flat spaces, 
 composed of stiff impure red clay, in which, at the 
 distance of about two miles from the coast, I found by 
 digging, a few minute fragments of sea-shells. The 
 sand-dunes extend several miles inland, and stand on a 
 plain, which slopes up to a height of between one and 
 two hundred feet. Numerous, small, well rounded 
 pebbles of pumice lie scattered both on the plain and 
 sand-hillocks : at Monte Hermoso, on the flat summit 
 of a cliff, I found many of them at a height of 120 feet 
 (angular measurement) above the level of the sea. 
 These pumice pebbles, no doubt, were originally brought 
 down from the Cordillera by the rivers which cross the 
 continent, in the same way as the river Negro anciently 
 brought down, and still brings down, pumice, and as 
 the river Ohupat brings down scoriae : when once de- 
 livered at the mouth of a river, they would naturally 
 have travelled along the coasts, and been cast up, dur- 
 ing the elevation of the land, at different heights. The 
 origin of the argillaceous flats, which separate the 
 parallel ranges of sand-dunes, seems due to the tides 
 here having a tendency (as I believe they have on most 
 shoal-protected coasts) to throw up a bar parallel to 
 the shore, and at some distance from it ; this bar 
 gradually becomes larger, affording a base for the 
 accumulation of sand-dunes, and the shallow space 
 within then becomes silted up with mud. The repe- 
 tition of this process, without any elevation of the land, 
 would form a level plain traversed by parallel lines of 
 sand-hillocks ; during a slow elevation of the land, the 
 hillocks would rest on a gently inclined surface, like 
 that on the northern shore of Bahia Blanca. I did not 
 observe any shells in this neighbourhood at a greater 
 
CHAP. Yiii. Elevation of Bahia Blanc a. 195 
 
 height than twenty feet ; and therefore the age of the 
 sea-drifted pebbles of pumice, now standing at the height 
 of 120 feet, must remain uncertain. 
 
 The main plain surrounding Bahia Blanca I esti- 
 mated at from 200 to 300 feet ; it insensibly rises 
 towards the distant Sierra Yentana. There are in this 
 neighbourhood some other and lower plains, but they 
 do not abut one at the foot of the other, in the manner 
 hereafter to be described, so characteristic of Patagonia. 
 The plain on which the settlement stands is crossed by 
 many low sand-dunes, abounding with the minute shells 
 of the Paludestrina aiistralis, d'Orbig., which now lives 
 in the bay. This low plain is bounded to the south, 
 at the Cabeza del Buey, by the cliff-formed margin 
 of a wide plain of the Pa.mpean formation, which I 
 estimated at sixty-feet in height. On the summit of 
 this cliff there is a range of high sand-dunes extending 
 several miles in an east and west line. 
 
 Southward of Bahia Blanca, the river Colorado 
 flows between two plains, apparently from thirty to 
 forty feet in height. Of these plains, the southern one 
 slopes up to the foot of the great sandstone plateau of 
 the Rio Negro ; and the northern one against an escarp- 
 ment of the Pampean deposit ; so that the Colorado 
 flows in a valley fifty miles in width, between the upper 
 escarpments. I state this, because on the low plain at 
 the foot of the northern escarpment, I crossed an im- 
 mense accumulation of high sand-dunes, estimated by 
 the Gauchos at no less than eight miles in breadth. 
 These dunes range westward from the coast, which is 
 twenty miles distant, to far inland, in lines parallel to 
 the valley ; they are separated from each other by 
 argillaceous flats, precisely like those on the northern 
 shore of Bahia Blanca. At present there is no source 
 whence this immense accumulation of sand could pro- 
 
 o 2 
 
1 96 Elevation of Patagonia. part h. 
 
 ceed ; but if, as I believe, the upper escarpments once 
 formed the shores of an estuary, in that case the sand- 
 stone formation of the river Negro would have afforded 
 an inexhaustible supply of sand, which would naturally 
 have accumulated on the northern shore, as on every 
 part of the coast open to the south winds between Bahia 
 Blanca and Buenos Ayres. 
 
 At San Bias (40° 40' S.), a little south of the 
 mouth of the Colorado, M. d'Orbigny ^ found fourteen 
 species of existing shells (six of them identical with 
 those from Bahia Blanca), embedded in their natural 
 positions. From the zone of depth which these shells 
 are known to inhabit, they must have been uplifted 
 thirty-two feet. He also found, at from fifteen to 
 twenty feet above this bed, the remains of an ancient 
 beach. 
 
 Ten miles southward, but 120 miles to the west, at 
 Port S. Antonio, the Officers employed on the Survey 
 assured me that they saw many old sea-shells strewed 
 on the surface of the ground, similar to those found on 
 other parts of the coast of Patagonia. At San Josef, 
 ninety miles south in nearly the same longitude, I found, 
 above the gravel, which caps an old tertiary forma- 
 tion, an irregular bed and hillocks of sand, several feet 
 in thickness, abounding with shells of Patella deamrita^ 
 Mytilus Magelkmicus, the latter retaining much of its 
 colour ; Fiisus MagellaniGus, (and a variety of the same) 
 and a large Balanus (probably B. Tulijjo), all now found 
 on, this coast : I estimated this bed at from eighty to 
 one hundred feet above the level of the sea. To the 
 westward of this bay, there is a plain estimated at be- 
 tween 200 and 300 feet in height : this plain seems, 
 from many measurements, to be a continuation of the 
 sandstone platform of the river Negro. The next 
 * ' Voyage,' &c. p. 54. 
 
CHAP. Yiii. Elevation of Patagonia. 197 
 
 place southward, where I landed, was at Port Desire, 
 340 miles distant ; but from the intermediate districts 
 I received, through the kindness of the Officers of the 
 Survey, especially from Lieut. Stokes and Mr. King, 
 many specimens and sketches, quite sufficient to show 
 the general uniformity of the whole line of coast. I 
 may here state, that the whole of Patagonia consists of 
 a tertiary formation, resting on and sometimes sur- 
 rounding hills of porphyry and quartz : the surface is 
 worn into many wide valleys and into level step-formed 
 plains, rising one above another, all capped by irregular 
 beds of gravel, chiefly composed of porphyritic rocks. 
 This gravel formation will be separately described at 
 the end of the chapter. 
 
 My object in giving the following measurements 
 of the plains, as taken by the Officers of the Survey, 
 is, as will hereafter be seen, to show the remarkable 
 equability of the recent elevatory movements. Round 
 the southern parts of Nuevo Gulf, as far as the River 
 Chupat, (seventy miles southward of San Josef) there 
 appear to be several plains, of which the best defined 
 are here represented. 
 
 No. 15. 
 Section of Step-formed Plains South of Nuevo Gulf. 
 350 ft. An. M. 200-220 An. M. 80 Est. 
 
 ( V_ ^^ ^ 
 
 West. ' • _ — _ >^ East. 
 
 Level of sea. Scale ^ of inch to 100 feet vertical. 
 
 N.B. — An. M. always stands for angular or trigonometrical measurement. 
 Ba. M. „ barometrical measurement. 
 
 Est. „ estimation by the Oflacers of the Survey. 
 
 The upper plain is here well defined (called Table 
 
 Hills) ; its edge forms a cliff or line of escarpment 
 
 many miles in length, projecting over a lower plain. 
 
 The lowest plain corresponds with that at San Josef 
 
 with the recent shells on its surface. Between this 
 
198 Elevation of Patagonia. part n. 
 
 lowest and tlie uppermost plain, there is probably more 
 than one step-formed terrace : several measurements 
 show the existence of the intermediate one of the height 
 given in the diagram. 
 
 Near the north headland of the great Bay of St. 
 George (100 miles south of the Chupat), two well 
 marked plains of 250 and 330 feet were measured : 
 these are said to sweep round a great part of the Bay. 
 At its south headland, 120 miles distant from the north 
 headland, the 250 feet plain was again measured. In 
 the middle of the bay, a higher plain was found at 
 two neighbouring places (Tilli Roads and 0. Marques) 
 to be 580 feet in height. Above this plain, towards 
 the interior, Mr. Stokes informs me that there were 
 several other step formed plains, the highest of which 
 was estimated at 1,200 feet, and was seen ranging at 
 apparently the same height for 150 miles northward. 
 All these plains have been worn into great valleys and 
 much denuded. The following section is illustrative of 
 the general structure of the great Bay of St. George. 
 
 No. 16. 
 Section of Plains in the Bay of St. George. 
 
 1,200 feet Est. Not measured. 
 
 I'> 580 An. M. 330 An. M. 250 An. M. 
 ^ ' , 
 
 Level of sea. Scale ^'q of incli to 100 feet rertical. 
 
 At the south headland of the Bay of St. George (near 
 0. Three Points) the 250 plain is very extensive. At 
 Port Desire (forty miles southward) I made several 
 measurements with the barometer of a plain, which 
 extends along the north side of the port and along the 
 open coast, and which varies from 245 to 255 feet in 
 
CHAP. VIII. Elevation of Patagonia. 1 99 
 
 height : this plain abuts against the foot of a higher 
 plain of 330 feet, which extends also, far northward 
 along the coast, and likewise into the interior. In the 
 distance a higher inland platform was seen, of which 
 I do not know the height. In three separate places, I 
 observed the cliff of the 245-255 feet plain, fringed by 
 a terrace or narrow plain estimated at about 100 feet 
 in height. These plains are represented in the fol- 
 lowing section : — 
 
 No. 17. 
 Section of Plains at Port Desire. 
 
 Not Measured. 
 
 a3 M oj O +3 isj iQ ^ 
 
 mPQ 
 
 ?,^^« ^.§43 
 
 100 ft. Est. 
 
 Level of sea. Scale /q of inch to 100 feet vertical. 
 
 In many places, even at the distance of three and 
 four miles from the coast, I found on the gravel-capped 
 surface of the 245-255 feet, and of the 330 feet plain, 
 shells of Mytilus Magellanicus^ M. edulis, Patella 
 deaurita, and another Patella, too much worn to be 
 identified, but apparently similar to one found abun- 
 dantly adhering to the leaves of the kelp. These 
 species are the commonest now living on this coast. 
 The shells all appeared very old : the blue of the 
 mussels was much faded ; and only traces of colour 
 could be perceived in the Patellas, of which the outer 
 surfaces were scaling off. They lay scattered on the 
 smooth surface of the gravel, but abounded most in 
 certain patches, especially at the heads of the smaller 
 valleys : they generally contained sand in their insides ; 
 and I presume that they have been washed by alluvial 
 action out of thin sandy layers, traces of which may 
 sometimes be seen covering the gravel. The several 
 
200 Elevation of Patagonia. part u. 
 
 plains have very level surfaces ; but all are scooped out 
 by numerous, broad, winding, flat-bottomed valleys, in 
 which, judging from the bushes, streams never flow. 
 These remarks on the state of the shells, and on the 
 nature of the plains, apply to the following cases, so 
 need not be repeated. 
 
 Southward of Port Desire, the plains have been 
 greatly denuded, with only small pieces of table-land 
 marking their former extension. But opposite Bird Is- 
 land, two considerable step-formed plains were measured, 
 and found respectively to be 350 and 590 feet in height. 
 This latter plain extends along the coast close to Port 
 St. Julian (110 miles south of Port Desire); where we 
 have the following section : — 
 
 950 ft. An. M. 
 
 
 No. 18. 
 Section of Plains at Port St. Julian. 
 
 560 An. M. 
 
 430 An. M. 
 
 
 +3 
 
 o 
 
 05 
 
 O 03 
 CO O 
 
 1 
 
 
 
 1 
 
 \ 
 
 J 
 
 
 
 
 Xi^ 
 
 Level of sea. Scale Jg of inch to 100 feet vertical. 
 
 The lowest plain was estimated at ninety feet : it is 
 remarkable from the usual gravel-bed being deeply 
 worn into hollows, which are filled up with, as well as 
 the general surface covered by, sandy and reddish earthy 
 matter : in one of the hollows thus filled up, the skeleton 
 of the Macrauchenia Patachonica^ as will hereafter be 
 described, was embedded. On the surface and in the 
 upper parts of this earthy mass, there were numerous 
 shells of Mytilus Magellanicus and M. edulis, Patella 
 deaurita, and fragments of other species. This plain 
 is tolerably level, but not extensive ; it forms a pro- 
 montory seven or eight miles long, and three or four 
 wide. The upper plains in the above diagram were 
 
CHAP. Yiii. Elevation of Patagonia. 201 
 
 measured by the Officers of the Survey ; they were all 
 capped by thick beds of gravel, and were all more or 
 less denuded : the 950 plain consists merely of separate, 
 truncated, gravel-capped hills, two of which, by measure- 
 ment, were found to differ only three feet. The 430 
 feet plain extends, apparently with hardly a break, to 
 near the northern entrance of the Rio Santa Cruz (fifty 
 miles to the south) ; but it was there found to be only 
 330 feet in height. 
 
 On the southern side of the mouth of the Santa Cruz 
 we have the following section, which I am able to give 
 with more detail than in the foregoing cases : — 
 
 No. 19. 
 Section of Plains at tlie moutti of the Rio Santa Cruz. 
 840 ft. An. M. 710 An. M. • 
 
 
 Level of sea. Scale -^ of inch to 100 feet vertical. 
 
 The plain marked 355 feet (as ascertained by the 
 barometer and by angular measurement) is a continua- 
 tion of the above-mentioned 330 feet plain : it extends 
 in a NW. direction along the southern shores of the 
 estuary. It is capped by gravel, which in most parts is 
 covered by a thin bed of sandy earth, and is scooped out 
 by many flat-bottomed valleys. It appears to the eye 
 quite level, but in proceeding in a SSW. course, towards 
 an escarpment distant about six miles, and likewise 
 ranging across the country in a NW. line, it was found 
 to rise at first insensibly, and then for the last half mile, 
 sensibly, close up to the base of the escarpment : at 
 this point it was 463 feet in height, showing a rise of 
 108 feet in the six miles. On this 355 to 463 feet 
 plain, I found several shells of Mytilus Magellanicns 
 
202 Valley of Santa Cruz, part n, 
 
 and of a Mytilus, whicli Mr. Sowerby informs me is yet 
 unnamed, tliough well known as recent on this coast ; 
 Patella deaurita ; Fusiis, I believe, Magellanicus, but 
 the specimen has been lost ; and at the distance of four 
 miles from the coast, at the height of about 400 feet, 
 there were fragments of the same Patella and of a 
 Voluta (apparently V. ancilla) partially embedded in 
 the superficial sandy earth. All these shells had the 
 same ancient appearance with those from the foregoing 
 localities. As the tides along this part of the coast 
 rise at the Syzygal period forty feet, and therefore form 
 a well-marked beach-line, I particularly looked out for 
 ridges in crossing this plain, which, as we have seen, 
 rises 108 feet in about six miles, but I could not see 
 any traces of such. The next highest plain is 710 feet 
 above the sea ; it is very narrow, but level, and is 
 capped with gravel ; it abuts to the foot of the 840 
 feet plain. This summit-plain extends as far as the 
 eye can range, both inland along the southern side of 
 the valley of the Santa Cruz, and southward along the 
 Atlantic. 
 
 TJie Valley of the B. Santa Cruz. — This valley runs 
 in an east and west direction to the Cordillera, a dis- 
 tance of about 160 miles. It cuts through the great 
 Patagonian tertiary formation, including, in the upper 
 half of the valley, immense streams of basaltic lava, 
 which, as well as the softer beds, are capped by gravel ; 
 and this gravel, high up the river, is associated with a 
 vast boulder formation.^ In ascending the valley, the 
 plain which at the mouth on the southern side is 355 
 feet high, is seen to trend towards the corresponding 
 plain on the northern side, so that their escarpments 
 appear like the shores of a former estuary, larger than 
 
 ' I have described this formation in a paper in the ' Geological 
 Transactions,' vol. vi. p. 415. 
 
CHAP. VIII. Valley of Santa Criiz, 205 
 
 the existing one : the escarpments, also, of the 840 feet 
 summit-plain (with a corresponding northern one, 
 which is met with some way up the valley), appear like 
 the shores of a still larger estuary. Farther up the val- 
 ley, the sides are bounded throughout its entire length 
 by level, gravel-capped terraces, rising above each other 
 in steps. The width between the upper escarpments is 
 on an average between seven and ten miles ; in one 
 spot, however, where cutting through the basaltic lava, 
 it was only one mile and a half. Between the escarp- 
 ments of the second highest terrace the average width 
 is about four or five miles. The bottom of the valley, 
 at the distance of 110 miles from its mouth, begins 
 sensibly to expand, and soon forms a considerable plain, 
 440 feet above the level of the sea, through which the 
 river flows in a gut from twenty to forty feet in depth. 
 1 here found, at a point of 140 miles from the Atlantic, 
 and seventy miles from the nearest creek of the Pacific, 
 at the height of 410 feet, a very[old and worn shell of 
 Patella deaurita. Lower down the valley, 105 miles 
 from the Atlantic (long. 71° W.), and at an elevation 
 of about 300 feet, I also found, in the bed of the river, 
 two much worn and broken shells of the Valuta ancilla^ 
 still retaining traces of their colours ; and one of the 
 Patella deaurita. It appeared that these shells had 
 been washed from the banks into the river ; considering 
 the distance from the sea, the desert and absolutely 
 unfrequented character of the country, and the very 
 ancient appearance of the shells (exactly like those 
 found on the plains nearer the coast), there is, I think, 
 no cause to suspect that they could have been brought 
 here by Indians. 
 
 The plain at the head of the valley is tolerably 
 level, but water-worn, and with many sand-dunes on it 
 like those on a sea-coast. At the highest point to which 
 
204 Valley of Santa Cruz, paet u. 
 
 we ascended, it was sixteen miles wide in a north and 
 soutli line ; and forty-five miles in length in an east 
 and west line. It is bordered by the escarpments, one 
 above the other, of two plains, which diverge as they 
 approach the Cordillera, and consequently resemble, at 
 two levels, the shores of great bays facing the moun- 
 tains ; and these mountains are breached in front of the 
 lower plain by a remarkable gap. The valley, therefore, 
 of the Santa Cruz consists of a straight broad cut, 
 about ninety miles in length, bordered by gravel-capped 
 terraces and plains, the escarpments of which at both 
 ends diverge or expand, one over the other, after the 
 manner of the shores of great bays. Bearing in mind 
 this peculiar form of the land — the sand-dunes on the 
 plain at the head of the valley — the gap in the Cordil- 
 lera, in front of it — the presence in two places of very 
 ancient shells of existing species — and lastly, the cir- 
 cumstance of the 355 to 453 feet plain, with the 
 numerous marine remains on its surface, sweeping from 
 the Atlantic coast, far up the valley, I think we must 
 admit, that within the recent period, the course of the 
 Santa Cruz formed a sea-strait intersecting the con- 
 tinent. At this period, the southern part of South 
 America consisted of an archipelago of islands 360 
 miles in a N. and S. line. We shall presently see, that 
 two other straits also, since closed, then cut through 
 Tierra del Fuego ; I may add, that one of them must 
 at that time have expanded at the foot of the Cordillera 
 into a great bay (now Otway Water) like that which 
 formerly covered the 440 feet plain at the head of the 
 Santa Cruz. 
 
 I have said that the valley in its whole course is 
 bordered by gravel-capped plains. The following sec- 
 tion, supposed to be drawn in a N. and S. line across 
 the valley, can scarcely be considered as more than 
 
CHAP. VIII. Valley of Santa Ci^uz. 205 
 
 illustrative ; for during our hurried ascent it was im- 
 possible to measure all tlie plains at any one place. 
 
 No. 20. 
 
 Nortli and South Section across the Terraces bounding the Valley of 
 the Elver Santa Cruz, high up Its coui'se. 
 
 A south. A north. 
 
 \^ 
 
 ±5 S. 
 
 
 
 Ds. 
 
 E. 
 
 Dn. 
 
 
 ii u. / 
 
 
 
 ~\ "^^ 
 
 
 
 
 
 
 "^N 
 
 
 
 
 /~^ 
 
 
 
 
 
 
 V 
 
 ■^ r- 
 
 / 
 
 
 
 1,122 ft. 869 ft. 639 ft. Bed of 639 ft. 869 ft. 1,122 ft. 
 
 river. 
 
 The height of each terrace above the level of the river, is shown by the number 
 under it. Vertical scale -j^ of inch to a 100 feet ; but terrace E being only 
 twenty feet above the river, has necessarily been raised. The horizontal dis- 
 tances much contracted ; the distance from the edge of A n. to A s. being on an 
 average from seven to ten miles. 
 
 At a point nearly midway between the Cordillera and 
 the Atlantic, I found the plain (A north) 1,122 feet 
 'i/bove the river ; all the lower plains on this side were 
 here united into one great broken cliff: at a point 
 sixteen miles lower down the stream, I found by 
 measurement and estimation that B {n) was 869 above 
 the river : very near to where A (7^) was measured, 
 {n) was 639 above the same level : the terrace D (71) 
 was nowhere measured : the lowest E (?i) was in many 
 places about twenty feet above the river. These plains 
 or terraces were best developed where the valley was 
 widest; the whole five, like gigantic steps, occurred 
 together only at a few points. The lower terraces are 
 less continuous than the higher ones, and appear to be 
 entirely lost in the upper third of the valley. Terrace 
 C (s), however, was traced continuously for a great 
 distance. The terrace B (71), at a point of fitty-five 
 miles from the mouth of the river, was four miles in 
 width; higher up the valley this terrace (or at least 
 the second highest one, for I could not always trace it 
 continuously) was about eight miles wide. This second 
 
2o6 Valley of Santa Cruz, part h. 
 
 plain was generally wider than the lower ones — as 
 indeed follows from the valley from A {ii) to A (s) 
 being generally nearly double the width from B (?i) 
 to B (s). Low down the valley, the summit-plain A (s) 
 is continuous with the 840 feet plain on the coast, but it 
 is soon lost or unites with the escarpment of B (s). 
 The corresponding plain A (??/), on the north side of the 
 valley, appears to range continuously from the Cordil- 
 lera to the head of the present estuary of the S. Cruz, 
 where it trends northward towards Port St. Julian. 
 Near the Cordillera the summit-plain on both sides of 
 the valley is between 3,200 and 3,300 feet in height ; 
 at 100 miles from the Atlantic, it is 1,416 feet, and on 
 the coast 840 feet, all above the sea-beach ; so that in 
 a distance of 100 miles the plain rises 576 feet, and 
 much more rapidly near to the Cordillera. The lower 
 terraces B and C also appear to rise as they run up the 
 valley; thus D (?^), measured at two points twenty- 
 four miles apart, was found to have risen 185 feet. 
 From several reasons I suspect, that this gradual 
 inclination of the plains up the valley, has been chiefly 
 caused by the elevation of the continent in mass, 
 having been the greater the nearer to the Cordillera. 
 
 All the terraces are capped with well-rounded gravel, 
 which rests either on the denuded and sometimes 
 furrowed surface of the soft tertiary deposits, or on the 
 basaltic lava. The difference in height between some 
 of the lower steps or terraces seems to be entirely 
 owing to a difference in the thickness of the capping 
 gravel. Furrows and inequalities in the gravel, where 
 such occur, are filled up and smoothed over with sandy 
 earth. The pebbles, especially on the higher plains, 
 are often whitewashed, and even cemented together by 
 a white aluminous substance ; and I occasionally found 
 this to be the case with the gravel on the terrace D. 
 
CHAP. VIII. Valley of Santa Cruz. 207 
 
 I could not perceive any trace of a similar deposi- 
 tion on tlie pebbles now thrown up by the river, and 
 therefore I do not think that terrace D was river- 
 formed. As the terrace E generally stands about 
 twenty feet above the bed of the river, my first impres- 
 sion was to doubt whether even this lowest one could 
 have been so formed ; but it should always be borne in 
 mind, that the horizontal upheaval of a district, by in- 
 creasing the total descent of the streams, will always 
 tend to increase, first near the sea-coast and then 
 farther and farther up the valley, their corroding and 
 deepening powers : so that an alluvial plain, formed 
 almost on a level with a stream, will, after an elevation 
 of this kind, in time be cut through, and left standing 
 at a height never again to be reached by the water. 
 With respect to the three upper terraces of the S. Cruz, 
 I think there can be no doubt, that they were modelled 
 by the sea, when the valley was occupied by a strait, in 
 the same manner (hereafter to be discussed), as the 
 greater, step-formed, shell-strewed plains along the 
 coast of Patagonia. 
 
 To return to the shores of the Atlantic the 840 
 feet plain, at the mouth of the Santa Cruz, is seen ex- 
 tending horizontally far to the south ; and I am in- 
 formed by the Officers of the Survey, that bending round 
 the head of Coy Inlet (sixty-five miles southward), it 
 trends inland. Outliers of apparently the same height 
 are seen forty miles farther south, inland of the river 
 Gallegos; and a plain comes down to Cape Gregory 
 (thirty-five miles southward), in the Strait of Magellan, 
 which was estimated at between 800 and 1,000 feet 
 in height, and which, rising towards the interior, is 
 capped by the boulder formation. South of the Strait 
 of Magellan, there are large outlying masses of appa- 
 rently the same great table-land, extending at intervals 
 
2o8 Concluding Remaj'ks on the part it, 
 
 along tlie eastern coast of Tierra del Fuego : at two 
 places here, 110 miles apart, this plain was found to be 
 950 and 970 feet in height. 
 
 From Coy Inlet, where the high summit-plain 
 trends inland, a plain estimated at 350 feet in height, 
 extends for forty miles to the river Gallegos. From 
 this point to the Strait of Magellan, and on each side 
 of that Strait, the country has been much denuded and 
 is less level. It consists chiefly of the boulder forma- 
 tion, which rises to a height of between 150 and 250 
 feet, and is often capped by beds of gravel. At N.S. 
 Gracia, on the north side of the Inner Narrows of the 
 Strait of Magellan, I found on the summit of a cliff, 
 160 feet in height, shells of existing Patellae and Mytiliy 
 scattered on the surface and partially embedded in 
 earth. On the eastern coast, also, of Tierra del Fuego, 
 in latitude 53° 20' S., I found many Mytili on some 
 level land, estimated at 200 feet in height. Anterior 
 to the elevation attested by these shells, it is evident 
 by the present form of the land, and by the distribution 
 of the great erratic boulders ^ on the surface, that two 
 sea-channels connected the Strait of Magellan both 
 with Sebastian Bay and with Otway Water. 
 
 Concluding remarlis on the recent elevation of the 
 south-eastern coasts of America, and on the action of 
 the sea on the land. — Upraised shells of species, still ex- 
 isting as the commonest kinds in the adjoining sea, occur, 
 as we have seen, at heights of between a few feet and 410 
 feet, at intervals from latitude 33° 40' to 53° 20' South. 
 This is a distance of 1,180 geographical miles — about 
 equal from London to the North Cape of Sweden. As 
 the boulder formation, extends with nearly the same 
 height 150 miles south of 53° 20', the most southern 
 point where I landed and found upraised shells; and 
 
 ^ ' Geolog. Transactions,' vol. vi. p, 419. 
 
CHAP. viiT. Area of Recent Elevation. 209 
 
 as the level Pampas ranges many hundred miles north- 
 ward of the point, where M. d'Orbigny found at the 
 height of 100 feet beds of the Azara, the space in a 
 north and south line, which has been uplifted within 
 the recent period, must have been much above the 
 1,180 miles. By the term ' recent,' I refer only to that 
 period within which the now living mollusca were 
 called into existence ; for it will be seen in the eleventh 
 Chapter, that both at BahiaBlanca and P. S. Julian, the 
 mammiferous quadrupeds which co-existed with these 
 shells belong to extinct species. I have said that the 
 upraised shells were found only at intervals on this line 
 of coast, but this in all probability may be attributed 
 to my not having landed at the intermediate points ; 
 for wherever I did land, with the exception of the 
 river Negro, shells were found : moreover, the shells 
 are strewed on plains or terraces, which, as we shall 
 immediately see, extend for great distances with a 
 uniform height. I ascended the higher plains only in 
 a few places, owing to the distance at which their 
 escarpments generally range from the coast, so that I 
 am far from knowing that 410 feet is the maximum of 
 elevation of these upraised remains. The shells are 
 those now most abundant in a living state in the 
 adjoining sea.^ All of them have an ancient appear- 
 ance ; but some, especially the mussels, although lying 
 fully exposed to the weather, retain to a considerable 
 extent their colours : this circumstance appears at first 
 surprising, but it is now known that the colouring 
 principle of the Mytilus is so enduring, that it is pre- 
 served when the shell itself is completely disintegrated. ^ 
 
 ' Capt. King, ' Voyages of Adventure and Beagle,' vol. i. pp. i\ 
 and 133. 
 
 ^ See Mr. Lyell's ' Proofs of a Gradual Eising in Sweden,' in the 
 ' Philosoph. Transact.' 1835, p. 1. See also Mr. Smith, of Jordan 
 Hill, in the ' Edin. New Phil. Journal,' vol. xxv. p. 393. 
 
 P 
 
2IO Area of Recent Elevation, part n. 
 
 Most of the shells are broken ; I nowhere found two 
 valves united ; the fragments are not rounded, at least 
 in none of the specimens which I brought home. 
 
 With respect to the breadth of the upraised area in 
 an east and west line, we know from the shells found at 
 the inner Narrows of the Strait of Magellan, that the 
 entire width of the plain, although there very narrow, 
 has been elevated. It is probable that in this southern- 
 most part of the continent, the movement has extended 
 under the sea far eastward ; for at the Falkland Islands, 
 though I could not find any shells, the bones of whales 
 have been noticed by several competent observers, lying 
 on the land at a considerable distance from the sea, and 
 at the height of some hundred feet above it.^ More- 
 over, we know that in Tierra del Fuego the boulder for- 
 mation has been uplifted within the recent period, and a 
 similar formation occurs ^ on the north-western shores 
 (Byron Sound) of these islands. The distance from 
 this point to the Cordillera of Tierra del Fuego, is 360 
 miles, which we may take as the probable width of the 
 recently upraised area. In the latitude of the R. Santa 
 Cruz, we know from the shells found at the mouth and 
 head, and in the middle of the valley, that the entire 
 width (about 160 miles) of the surface eastward of the 
 Cordillera has been upraised. From the slope of the 
 plains, as shown by the course of the rivers, for several 
 degrees northward of the S. Cruz, it is probable that the 
 elevation attested by the shells on the coast has likewise 
 extended to the Cordillera. When, however, we look as 
 far northward as the provinces of La Plata, this conclusion 
 
 * 'Voyages of the Adventure and Beagle,' vol. ii. p. 227. And 
 Bougainville's 'Voyage,' tome i. p. 112. 
 
 2 I owe this fact to the kindness of Capt. Sulivan, K.N., a highly 
 competent observer, I mention it more especially, as in my Paper 
 (p. 427) on the Boulder Formation, I have, after having examined 
 the northern and middle parts of the eastern island, said that the 
 formation was here wholly absent. 
 
CHAP. VIII. Unifor^n Height of Terraces. 211 
 
 would be very hazardous ; not only is the distance from 
 Maldonado (where I found upraised shells) to the 
 Cordillera great, namely, 760 miles, but at the head 
 of the estuary of the Plata, a NNE. and SSW. range 
 of tertiary volcanic rocks has been observed,^ which 
 may well indicate an axis of elevation quite distinct 
 from that of the Andes. Moreover, in the centre of 
 the Pampas in the chain of Cordova, severe earthquakes 
 have been felt ; ^ whereas at Mendoza, at the eastern 
 foot of the Cordillera, only gentle oscillations, trans- 
 mitted from the shores of the Pacific, have ever been 
 experienced. Hence the elevation of the Pampas may 
 be due to several distinct axes of movement ; and we 
 cannot judge, from the upraised shells round the estuary 
 of the Plata, of the breadth of the area uplifted within 
 the recent period. 
 
 Not only has the above specified long range of coast 
 been elevated within the recent period, but I think it 
 may be safely inferred from the similarity in height of 
 the gravel-capped plains at distant points, that there 
 has been a remarkable degree of equability in the 
 elevatory process. I may premise, that when I mea-r 
 sured the plains, it was simply to ascertain the heights 
 at which shells occurred ; afterwards, comparing these 
 measurements with some of those made during the 
 Survey, I was struck with their uniformity, and accord- 
 
 ' This volcanic formation will be described in Chapter XI. It is 
 not improbable that the height of the upraised shells at the head 
 of the estuary of the Plata, being greater than at Bahia Blanca or 
 at San Bias, may be owing to the upheaval of these latter places 
 having been connected with the distant line of the Cordillera, whilst 
 that of the provinces of La Plata was in connection with the adjoin- 
 ing tertiary volcanic axis. 
 
 ^ See Sir W. Parish's work on ' La Plata,' p. 242. For a notice of 
 an earthquake which drained a lake near Cordova, see also Temple's 
 ' Travels in Peru.' Sir W. Parish informs me, that a town between 
 Salta and Tucuman (north of Cordova) was formerly utterly over- 
 thrown by an earthquake. 
 
 p 2 
 
2 1 2 Uniform Height of Terraces. part ir. 
 
 ingly tabulated all those which represented the sum- 
 mit-edges of plains. The extension of the 330 to 355 
 feet plain is very striking, being found over a space of 
 500 geographical miles in a north and south line. A 
 table of the measurements is here given. The angular 
 measurements and all the estimations are by the Officers 
 of the Survey; the barometrical ones by myself: — 
 
 Gallegos River to Coy Inlet (partly angular meas. and partly 
 
 estim.) . . . 
 South Side of Sa^nta Cruz (ang. and barom. meas.) . 
 
 North Side of do. (ang. m.) 
 
 Bird Island, plain opposite to (ang. m.) 
 Port Desire, plain extending far along coast (barom. m.) 
 St. George's Bay, north promontory (ang. m.) . 
 Table Land, south of New Bay (ang. m.) . 
 
 Feet. 
 
 , 350 
 , 355 
 , 330 
 , 350 
 . 330 
 . 330 
 , 350 
 
 A plain, varying from .245 to 255 feet, seems to 
 extend with much uniformity from Port Desire to the 
 north of St. George's Bay, a distance of 170 miles; 
 and some approximate measurements, also given in the 
 following table, indicate the much greater extension of 
 780 miles.: — 
 
 Feet. 
 
 Coy Inlet, south of (partly ang. m. and partly estim.) 200 to 300 
 
 Port Desire (barom. m.) 245 to 255 
 
 C. Blanco (ang. m.) 250 
 
 North Promontory of St. George's Bay (ang. m.) .. 250 
 
 ^outh of New Bay (aag. m.) 200 to 220 
 
 TS^orth of S. Josef (estim.) 200 to 300 
 
 Plain of Kio Negro (ang. m.) . . . . . 200 to 220 
 
 Bahia Blanca (estim.) . . . . . . 200 to 300 
 
 The extension, moreover, of the 560 to 580, and of 
 the 80 to 100 feet, plains is remarkable, though some- 
 what less obvious than in the former cases. Bearing 
 in mind that I have not picked these measurements 
 out of a series, but have used all those which repre- 
 sented the edges of plains, I think it scarcely possible 
 that these coincidences in height should be accidental. 
 We must therefore conclude that the action, whatever 
 it may have been, by which these plains have been 
 
CHAP. Yiii. Uniform Height of Terraces. 2 1 
 
 o 
 
 modelled into their present forms, has been singularly 
 uniform. 
 
 These plains or great terraces, of which three and 
 ■four often rise like steps one behind the other, are 
 formed by the denudation of the old Patagonian 
 tertiary beds, and by the deposition on their surfaces of 
 a mass of well-rounded gravel, varying, near the coast, 
 from ten to thirtv-five feet in thickness, but increasiner 
 in thickness towards the interior. The gravel is often 
 capped by a thin irregular bed of sandy earth. The 
 plains slope up, though seldom sensibly to the eye, 
 from the summit-edge of one escarpment to the foot of 
 the next highest one. Within a distance of 150 miles, 
 between Santa Cruz to Port Desire, where the plains 
 are particularly well developed, there are at least seven 
 stages or steps, one above the other. On the three 
 lower ones-, namely, those of 100 feet, 250 feet, and 
 350 feet in height, existing littoral shells are abundantly 
 strewed, either on the surface, or partially embedded in 
 the superficial sandy earth. By whatever action these 
 three lower plains have been modelled, so undoubtedly 
 have all the higher ones, up to a height of 950 feet at 
 S. Julian, and of 1,200 feet (by estimation) along St. 
 George's Bay. I think it will not be disputed, con- 
 sidering the presence of the upraised marine shells, that 
 the sea has been the active power during stages of some 
 kind in the elevatory process. 
 
 We will now briefly consider this subject : if we 
 look at the existing coast-line, the evidence of the 
 great denuding power of the sea is very distinct ; for, 
 from Cape St. Diego, in lat. 54° 30' to the mouth of 
 the Rio Negro, in lat. 31° (a length of more than 800 
 miles), the shore is formed, with singularly few excep- 
 tions, of bold and naked cliffs : in many places the 
 cJiifs are high ; thus, south of the Santa Cruz, they are 
 
214 Nature of the Elevation. part n. 
 
 between 800 and 900 feet in height, with their hori- 
 zontal strata abruptly cut off, showing the immense 
 mass of matter which has been removed. Nearly this 
 whole line of coast consists of a series of greater or 
 lesser curves, the horns of which, and likewise certain 
 straight projecting portions, are formed of hard rocks ; 
 hence the concave parts are evidently the effect and the 
 measure of the denuding action on the softer strata. 
 At the foot of all the cliffs, the sea shoals very gradually 
 far outwards ; and the bottom, for a space of some 
 miles, everywhere consists of gravel. I carefully ex- 
 amined the bed of the sea off the Santa Cruz, and found 
 that its inclination was exactly the same, both in 
 amount and in its peculiar curvature, with that of the 
 355 feet plain at the same place. If, therefore, the 
 coast, with the bed of the adjoining sea, were now sud- 
 denly elevated 100 or 200 feet, an inland line of cliffs, 
 that is an escarpment, would be formed, with a gravel- 
 capped plain at its foot gently sloping to the sea, and 
 having an inclination like that of the existing 355 feet 
 plain. From the denuding tendency of the sea, this 
 newly formed plain would in time be eaten back into a 
 cliff: and repetitions of this elevatory and denuding 
 process would produce a series of gravel-capped, sloping 
 terraces, rising one above another, like those fronting 
 the shores of Patagonia. 
 
 The chief difficulty (for there are other inconsider- 
 able ones) on this view, is the fact, — as far as I can 
 trust two continuous lines of soundings carefully taken 
 between Santa Cruz and the Falkland Islands, and 
 several scattered observations on this and other coasts, — 
 that the pebbles at the bottom of the sea quicMy and 
 regularly decrease in size with the increasing depth 
 and distance from the shore, whereas in the gravel on 
 the sloping plains, no such decrease in size was per- 
 
CHAP. VIII. Elevation Gradual. 2 1 5 
 
 ceptible. The following table gives tlie average result 
 of many soundings off the Santa Cruz : — 
 
 Under two miles from the shore, many of the pebbles were of 
 large size mingled with some small ones. 
 
 Distance 
 
 
 Depth. 
 
 Size of Pebbles. 
 
 3 to 4 miles from the shore. 
 
 11 to 12 fathoms. 
 
 As large as walnuts ; mingled 
 
 
 
 
 
 in every case with some 
 
 
 
 
 
 smaller ones. 
 
 6 to 7 miles 
 
 do. 
 
 17 to 19 
 
 do. 
 
 As large as hazel nuts. 
 
 10 to 11 miles 
 
 do. 
 
 23 to 25 
 
 do. 
 
 From three to four tenths of 
 an inch in diameter. 
 
 12 miles 
 
 do. 
 
 30 to 40 
 
 do. 
 
 Two -tenths of an inch. 
 
 22 to 150 miles 
 
 do. 
 
 45 to 65 
 
 do. 
 
 One-tenth of an inch, to the 
 finest sand. 
 
 I particularly attended to the size of the pebbles on 
 the 355 feet Santa Cruz plain, and I noticed that on 
 the summit-edge of the present sea-cliffs many were 
 as large as half of a man's head ; and in crossing from 
 these cliffs to the foot of the next highest escarpment, 
 a distance of six miles, I could not observe any increase 
 in their size. We shall presently see that the theory 
 of a slow and almost insensible rise of the land, will 
 explain all the facts connected with the gravel-capped 
 terraces, better than the theory of sudden elevations of 
 from one to two hundred feet. 
 
 M. d'Orbigny has argued, from the upraised shells 
 at San Bias being embedded in the positions in which 
 they lived, and from the valves of the Azara labiata 
 high on the banks of the Parana being united and un- 
 rolled, that the elevation of Northern Patagonia and of 
 La Plata must have been sudden ; for he thinks, if it 
 had been gradual, these shells would all have been 
 rolled on successive beach-lines. But in protected bays, 
 such as in that of Bahia Blanca, wherever the sea is 
 accumulating extensive mud-banks, or where the winds 
 quietly heap up sand-dunes, beds of shells might assuredly 
 be preserved buried in the positions in which they had 
 lived, even whilst the land retained the same level ; any, 
 the smallest, amount of elevation would directly aid in 
 
:2 1 6 Elevation Gradual. part n. 
 
 their preservation. I saw a multitude of spots in Bahia 
 Blanca where this might have been effected; and at 
 Maldonado it almost certainly has been effected. In 
 speaking of the elevation of the land having been slow, 
 I do not wish to exclude the small starts which accom- 
 pany earthquakes, as on the coast of Chile ; and by such 
 movements beds of shells might easily be uplifted, even 
 in positions exposed to a heavy surf, without undergoing 
 any attrition : for instance, in 1835, a rocky flat off the 
 island of Santa Maria was at one blow upheaved above 
 high-water mark, and was left covered with gaping and 
 putrefying mussel-shells, still attached to the bed on 
 which they had lived. If M. d'Orbigny had been aware 
 of the many long parallel lines of sand-hillocks, with 
 infinitely numerous shells of the Mactra and Yenus, at 
 a low level near the Uruguay ; if he had seen at Bahia 
 Blanca the immense sand-dunes, with water- worn pebbles 
 of pumice, ranging, in parallel lines, one behind the other 
 up a height of at least 120 feet ; if he had seen the sand- 
 dunes, with the countless Paludestrinas, on the low plain 
 near the Fort at this place, and that long line on the edge 
 of the cliff, sixty feet higher up ; if he had crossed that 
 long and great belt of parallel sand-dunes, eight miles in 
 width, standing at the height of from forty to fifty feet 
 above the Colorado, where sand could not now collect, — 
 I cannot believe he would have thought that the eleva- 
 tion of this great district had been sudden. Certainly the 
 sand-dunes (especially when abounding with shells), 
 which stand in ranges at so many different levels, must 
 all have required long time for their accumulation ; and 
 hence I do not doubt that the last 100 feet of elevation 
 of La Plata and Northern Patagonia has been exceed- 
 ingly slow. 
 
 If we extend this conclusion to Central and Southern 
 Patagonia, the inclination of the successively rising 
 
(?HAP. VIII. Elevation Gradual. 217 
 
 gravel-capped plains can be explained quite as well, as 
 by the more obvious view already given of a few com- 
 paratively great and sudden elevations ; in either case 
 we must admit long periods of rest, during which the 
 sea ate deeply into the land. Let us suppose the 
 present coast to rise at a nearly equable, slow rate, yet 
 sufficiently quick to prevent the waves quite removing 
 each part as soon as brought up ; in this case every 
 portion of the present bed of the sea will successively 
 form a beach-line, and from being exposed to a like 
 action will be similarly affected. It cannot matter to 
 what height the tides rise, even if to forty feet as at 
 Santa Cruz, for they will act with equal force and in 
 like manner on each successive line. Hence there is 
 no difficulty in the fact of the 855 feet plain at Santa 
 Cruz sloping up 108 feet to the foot of the next highest 
 escarpment, and yet having no marks of any one par- 
 ticular beach-line on it ; for the whole surface on this 
 view has been a beach. I cannot pretend to follow out 
 the precise action of the tidal waves during a rise of 
 the land, slow, yet sufficiently quick to prevent or check 
 denudation : but if it be analogous to what takes place 
 on protected parts of the present coast, where gravel is 
 now accumulating in large quantities,^ an inclined 
 surface, thickly capped by well-rounded pebbles of 
 about the same size, would be ultimately left. On the 
 gravel now accumulating, the waves, aided by the wind, 
 sometimes throw up a thin covering of sand, together 
 with the common coast-shells. Shells thus cast up by 
 gales, would, during an elevatory period, never again 
 be touched by the sea. Hence, on this view of a slow 
 and gradual rising of the land, interrupted by periods 
 
 ' On the eastern side of Chiloe, which island we shall see in the 
 next chapter is now rising, T observed that all the beaches and exten- 
 sive tidal fiats were formed of shingle, 
 
2 1 8 Summary of Results. part n. 
 
 of rest and denudation, we can understand the pebbles 
 being of about the same size over the entire width of 
 the step-like plains, — the occasional thin covering of 
 sandy earth, — and the presence of broken, unrolled 
 fragments of those shells, which now live exclusively 
 near the coast. 
 
 Summary of Results. — It may be concluded that 
 the coast on this side the continent, for a space of at 
 least 1,180 miles, has been elevated to a height of 100 
 feet in La Plata, and of 400 feet in Southern Patagonia, 
 within the period of existing shells, but not of existing 
 mammifers. That in La Plata the elevation has been 
 very slowly effected : that in Patagonia the movement 
 may have been by considerable starts, but much more 
 probably slow and quiet. In either case, there have 
 been long intervening periods of comparative rest,^ 
 during which the sea corroded deeply, as it is still cor- 
 roding, into the land. That the periods of denudation 
 and elevation were contemporaneous and equable over 
 great spaces of coast, as shown by the equable heights 
 of the plains ; that there have been at least eight 
 periods of denudation, and that the land, up to a height 
 of from 950 to 1,200 feet, has been similarly modelled 
 and affected : that the area elevated, in the southern- 
 most part of the continent, extended in breadth to 
 the Cordillera, and probably seaward to the Falkland 
 Islands ; that northward, in La Plata, the breadth is 
 unknown, there having been probably more than one 
 axis of elevation ; and finally, that, anterior to the 
 elevation attested by these upraised shells, the land was 
 divided by a Strait where the river Santa Cruz now 
 
 ' I say comparative and not a'bsolute rest, because the sea acts, 
 as we have seen, with great denuding power on this whole line of 
 coast ; and therefore, during an elevation of the land, if excessively 
 slow (and of course during a subsidence of the land), it is quite 
 possible that lines of cliff might be formed. 
 
CHAP. VIII. Gravel Formation of Patagonia. 2 1 9 
 
 flows, and. tliat farther southward there were other sea- 
 straits, since closed. I may add, that at Santa Cruz, 
 in lat. 50° S., the plains have been uplifted at least 
 1,400 feet, since the period when gigantic boulders 
 were transported between sixty and seventy miles from 
 their parent rock, on floating icebergs. 
 
 Lastly, considering the great upward movements 
 which this long line of coast has undergone, and the 
 proximity of its southern half to the volcanic axis of 
 the Cordillera, it is highly remarkable that in the many 
 fine sections exposed in the Pampean, Patagonian 
 tertiary, and Boulder formations, I nowhere observed 
 the smallest fault or abrupt curvature in the strata. 
 
 Gravel Formation of Patagonia. 
 
 P I will here describe in more detail than has been as 
 yet incidentally done, the nature, origin, and extent of 
 the great shingle covering of Patagonia : but I do not 
 mean to affirm that all of this shingle, especially that 
 on the higher plains, belongs to the recent period. A 
 thin bed of sandy earth, with small pebbles of various 
 porphyries and of quartz, covering a low plain on the 
 north side of the Eio Colorado, is the extreme northern 
 limit of this formation. These little pebbles have 
 probably been derived from the denudation of a more 
 regular bed of gravel, capping the old tertiary sand- 
 stone plateau of the Rio Kegro. The gravel-bed near 
 the Eio Negro is, on an average, about ten or twelva 
 feet in thickness ; and the pebbles are larger than on 
 the northern side of the Colorado, being from one to 
 two inches in diameter, and composed chiefly of rather 
 dark-tinted porphyries. Amongst them I here first 
 noticed a variety often to be referred to, namely, a 
 peculiar gallstone-yellow siliceous porphyry, frequently. 
 
2 20 Gravel Formation of Patagonia, paet ir. 
 
 but not invariably, containing grains of quartz. The 
 pebbles are embedded in a white gritty calcareous 
 matrix very like mortar, sometimes merely coating 
 with a whitewash the separate stones, and sometimes 
 forming the greater part of the mass. In one place I 
 saw in the gravel concretionary nodules (not rounded) 
 of crystallized gypsum^ some as large as a man's head. 
 I traced this bed for forty-five miles inland, and was 
 assured that it extended far into the interior. As the 
 surface of the calcareo-argillaceous plain of Pampean 
 formation, on the northern side of the wide valley of 
 the Colorado, stands at about the same height with the 
 mortar-like cemented gravel capping the sandstone on 
 the southern side, it is probable, considering the appa- 
 rent equability of the subterranean movements along 
 this side of America, that this gravel of the Rio Negro 
 and the upper beds of the Pampean formation north- 
 ward of the Colorado, are of nearly contemporaneous 
 origin, and that the calcareous matter has been derived 
 from the same source. 
 
 Southward of the Rio Negro, the cliffs along the 
 great bay of S. Antonio are capped with gravel : at San 
 Josef, I found that the pebbles closely resembled those 
 on the plain of the Rio Negro, but that they were not 
 cemented by calcareous matter. Between San Josef 
 and Port Desire, I was assured by the Officers of the 
 Survey that the whole face of the country is coated with 
 gravel. At Port Desire and over a space of twenty-five 
 miles inland, on the three step-formed plains and in the 
 valleys, I everywhere passed over gravel which, where 
 thickest, was between thirty and forty feet. Here, as 
 in other parts of Patagonia, the gravel, or its sandy 
 covering, was, as we have seen, often strewed with re- 
 cent marine shells. The sandy covering sometimes 
 ^lls up furrows in the gravel, as does the gravel in the 
 
CHAP. Yiii. Gravel Formation of Patagonia. 221 
 
 underlying tertiary forniations. The pebbles are fre- 
 quently whitewashed and even cemented together by 
 a peculiar, white, friable, aluminous, fusible, substance^ 
 which I believe is decomposed feldspar. At Port Desire, 
 the gravel rested sometimes on the basal formation of 
 porphyry, and sometimes on the upper or the lower 
 denuded tertiary strata. It is remarkable that most 
 of the porphyritic pebbles differ from those varieties of 
 porphyry which occur here abundantly in situ. The 
 peculiar gallstone-yellow variety was common, but less 
 numerous than at Port S. Julian, where it formed 
 nearly one-third of the mass of gravel ; the remaining 
 part there consisting of pale gray and greenish por- 
 phyries with many crystals of feldspar. At Port S. 
 Julian, I ascended one of the flat-topped hills, the de- 
 nuded remnant of the highest plain, and found it, at 
 the height of 950 feet, capped with the usual bed of 
 gravel. 
 
 Near the mouth of the Santa Cruz, the bed of gravel 
 on the 355 feet plain is from twenty to about thirty- 
 five feet in thickness. The pebbles vary from minute 
 ones to the size of a hen's egg, and even to that of half 
 a man's head ; they consist of paler varieties of porphyry 
 than those found farther northward, and there are fewer 
 of the gallstone-yellow kind ; pebbles of compact black 
 clay-slate were here first observed. The gravel, as we 
 have seen, covers the step-formed plains at the mouth, 
 head, and on the sides of the great valley of the Santa 
 Cruz. At a distance of 110 miles from the coast, the 
 plain has risen to the height of 1,416 feet above the 
 sea ; and the gravel, with the associated great boulder 
 formation, has attained a thickness of 212 feet. The 
 plain, apparently with its usual gravel covering, slopes 
 up to the foot of the Cordillera to the height of between 
 3,200 and 3,300 feet. In ascending the valley, the 
 
2 2 2 Gravel Formation of Patagonia, part h. 
 
 gravel gradually becomes entirely altered in character : 
 high lip, we have pebbles of crystalline feldspathic rocks, 
 compact clay-slate, quartzose schists and pale-coloured 
 porphyries ; these rocks, judging both from the gigantic 
 boulders in the surface and from some small pebbles 
 embedded beneath 700 feet in thickness of the old 
 tertiary strata, are the prevailing kinds in this part of 
 the Cordillera ; pebbles of basalt from the neighbouring 
 streams of basaltic lava are also numerous ; there are 
 few or none of the reddish or of the gallstone-yellow 
 porphyries so common near the coast. Hence the 
 pebbles on the 350 feet plain at the mouth of the Santa 
 Cruz cannot have been derived (with the exception of 
 those of compact clay-slate, which, however, may equally 
 well have come from the south) from the Cordillera in 
 this latitude ; but probably, in chief part, from farther 
 north. 
 
 Southward of the Santa Cruz, the gravel may be 
 seen continuously capping the great 840 feet plain : at 
 the Rio Gallegos, where this plain is succeeded by a 
 lower one, there is, as I am informed by Captain Suli- 
 van, an irregular covering of gravel from ten to twelve 
 feet in thickness over the whole country. The district 
 on each side of the Strait of Magellan is covered up 
 either with gravel or the boulder formation : it was 
 interesting to observe the marked difference between 
 the perfectly rounded state of the pebbles in the great 
 shingle formation of Patagonia, and the more or less 
 angular fragments in the boulder formation. The 
 pebbles and fragments near the Strait of Magellaji 
 nearly all belong to rocks known to occur in Fuegia. 
 I was therefore much surprised in dredging south of 
 the Strait to find, in lat. 54° 10^ south, many pebbles 
 of the gallstone-yellow siliceous porphyry ; I procured 
 others from a great depth off Staten Island, and others 
 
CHAP. VIII. Gravel Formation of Patagonia. 223 
 
 were brought me from tlie western extremity of the 
 Falkland Islands.^ The distribution of the pebbles of 
 this peculiar porphyry, which I venture to affirm is not 
 found in situ either in Fuegia, the Falkland Islands, 
 or on the coast of Patagonia, is very remarkable, for 
 they are found over a space of 840 miles in a north and 
 south line, and at the Falklands, 300 miles eastward of 
 the coast of Patagonia. Their occurrence in Fuegia 
 and the Falklands may, however, perhaps be due to 
 the same ice-agency by which the boulders have been 
 there transported. 
 
 We have seen that porphyritic pebbles of a small 
 size are first met with on the northern side of the Eio 
 Colorado, the bed becoming well developed near the 
 Rio Negro : from this latter point I have every reason 
 to believe that the gravel extends uninterruptedly over 
 the plains and valleys of Patagonia for at least 630 
 nautical miles southward to the Rio Gallegos. From 
 the slope of the plains, from the nature of the pebbles, 
 from their extension at the Rio Negro far into the 
 interior, and at the Santa Cruz close up to the Cor- 
 dillera, I think it highly probable that the whole breadth 
 of Patagonia is thus covered. If so, the average width 
 of the bed must be about 200 miles. Near the coast 
 the gravel is generally from ten to thirty feet in thick- 
 ness ; and as in the valley of Santa Cruz it attains, at 
 some distance from the Cordillera, a thickness of 214 
 feet, we may, I think, safely assume its average thick- 
 
 ^ At my request, Mr. Kent collected for me a bag of pebbles from 
 the beach of White Kock harbour, in the northern part of the sound, 
 between the two Falkland Islands. Out of these well-rounded 
 pebbles, varying in size from a walnut to a hen's egg, with some 
 larger, thirty-eight evidently belonged to the rocks of these islands ; 
 twenty-six were similar to the pebbles of porphyry found on the 
 Patagonian plains, which rocks do not exist in situ in the Falklands ; 
 one pebble belonged to the peculiar yellow siliceous porphyry ; thirty 
 were of doubtful origin. 
 
2 24 Gravel Formation of Patagonia, part n. 
 
 ness over the wliole area of 630 by 200 miles, at fifty 
 feet! 
 
 The transportal and origin of this vast bed of pebbles 
 is an interesting problem. From the manner in which 
 they cap the step-formed plains, worn by the sea within 
 the period of existing shells, their deposition, at least 
 on the plains up to a height of 400 feet, must have 
 been a recent geological event. From the form of the 
 continent, we may feel sare that they have come from 
 the westward, probably, in chief part from the Cordillera, 
 but, perhaps, partly from unknown rocky ridges in the 
 central districts of Patagonia. That the pebbles have 
 not been transported by rivers, from the interior towards 
 the coast, we may conclude from the fewness and small- 
 ness of the streams of Patagonia : moreover, in the case 
 of the one great and rapid river of Santa Cruz, we have 
 good evidence that its transporting power is very trifling. 
 This river is from 200 to 300 yards in width, about 
 seventeen feet deep in its middle, and runs with a sin- 
 gular degree of uniformity five knots an hour, with no 
 lakes and scarcely any still reaches : nevertheless, to 
 give one instance of its small transporting power, upon 
 careful examination, pebbles of compact basalt could 
 not be found in the bed of the river at a greater distance 
 than ten miles below the point where the stream rushes 
 over the debris of the great basaltic clifis forming its 
 shore : fragments of the cellular varieties have been 
 washed down twice or thrice as far. That the pebbles 
 in Central and Northern Patagonia have not been trans- 
 ported by ice-agency, as seems to have been the case to 
 a considerable extent farther south, and likewise in the 
 northern hemisphere, we may conclude, from the absence 
 of all angular fragments in the gravel, and from the 
 complete contrast in many other respects between the 
 shingle and neighbouring boulder formation. 
 
CHAP. VIII. Distribution of Gravel. 225 
 
 Looking to the gravel on any one of tlie step-formed 
 plains, I cannot doubt, from the several reasons assigned 
 in this chapter, that it has been spread out and levelled 
 by the long-continued action of the sea, probably during 
 the slow rise of the land. The smooth and perfectly 
 rounded condition of the innumerable pebbles alone 
 would prove long-continued action. But how the whole 
 mass of shingle on the coast-plains has been transported 
 from the mountains of the interior, is another and more 
 diflScult question. The following considerations, how- 
 ever, show that the sea by its ordinary action has con- 
 siderable power in distributing pebbles. A table has 
 already been given, showing how very uniformly and 
 gradually ^ the pebbles decrease in size with the gradu- 
 ally seaward increasing depth and distance. A series 
 of this kind irresistibly leads to the conclusion, that 
 the sea has the power of sifting and distributing the 
 loose matter on its bottom. According to Martin 
 White,^ the bed of the British Channel is disturbed 
 during gales at depths of sixty-three and sixty-seven 
 fathoms, and at thirty fathoms, shingle and fragments 
 of shells are often deposited, afterwards to be carried 
 away again. Ground-swells, which are believed to be 
 
 ^ I may mention, that at the distance of 150 miles from the 
 Patagonian shore I carefully examined the minute -rounded particles 
 in the sand, and found them to be fusible like the porphyries of the 
 great shingle bed. I could even distinguish particles of the gall- 
 stone yellow porphyry. It was interesting to notice how gradually 
 the particles of white quartz increased, as we approached the Falk- 
 land Islands, which are thus constituted. In the whole line of 
 soundings betw^een these islands and the coast of Patagonia dead or 
 living organic remains were most rare. On the relations between 
 the depth of water and the nature of the bottom, see Martin White 
 on ' Soundings in the Channel,' pp. 4, 6, 175 ; also Captain Beechey's 
 ' Voyage to the Pacific,' chap, xviii. 
 
 ^ ' Soundings in the Channel,' pp. 4, 166. M, Siau states 
 (' Edin. New Phil. Jour.' vol. xxxi, p. 246), that he found the sedi- 
 ment, at a depth of 188 metres, arranged in ripples of different 
 degrees of fineness. There are some excellent discussions on this 
 and allied subjects in Sir H. De la Beche's ' Theoretical Eesearches.' 
 
 Q 
 
2 26 Distribution of Gravel. part ii. 
 
 caused by distant gales, seem especially to affect the 
 bottom : at sucb times, according to Sir R. Scbom- 
 burgk,^ tbe sea to a great distance round the "West 
 Indian Islands, at depths from five to fifteen fathoms, 
 becomes discoloured, and even the anchors of vessels 
 have been moved. There are, however, some difficulties 
 in understanding how the sea can transport pebbles 
 lying at the bottom, for, from experiments instituted 
 on the power of running water, it would appear that 
 the currents of the sea have not sufficient velocity to 
 move stones of even moderate size : moreover, I have 
 repeatedly found in the most exposed situations that 
 the pebbles which lie at the bottom are encrusted with 
 full-grown living corallines, furnished with the most 
 delicate, yet unbroken spines : for instance, in ten 
 fathoms water off the mouth of the Santa Cruz, many 
 pebbles, u.nder half an inch in diameter, were thus 
 coated with Flustracean zoophytes.^ Hence we must 
 conclude that these pebbles are not often violently dis- 
 turbed : it should, however, be borne in mind that the 
 growth of corallines is rapid. The view, propounded 
 by Prof Playfair, will, I believe, explain this apparent 
 difficulty, — namely, that from the undulations of the 
 sea tending to lift up and down pebbles or other loose 
 bodies at the bottom, such are liable, when thus quite 
 or partially raised, to be moved even by a very small 
 
 1 ' Journal of Eoyal Geograph. Soc' vol. v, p. 25. It appears from 
 Mr. Scott Eussell's investigations (see Mr. Murchison's ' Anniver. 
 Address Geolog. Soc' 1843, p. 40), that in waves of translation the 
 motion of the particles of water is nearly as great at the bottom as 
 at the top. 
 
 2 A pebble, one and a half inch square and half an inch thick, was 
 given me, dredged up from twenty-seven fathoms depth off the west- 
 ern end of the Falkland Islands, where the sea is remarkably stormy, 
 and subject to violent tides. This pebble was encrusted on all sides 
 by a delicate living coralline. I have seen many pebbles from depths 
 between forty and seventy fathoms thus encrusted ; one from the 
 latter depth off Cape Horn. 
 
CHAP. VIII. Distribution of Gravel. 227 
 
 force, a little onwards. We can tlius understand how 
 oceanic or tidal currents of no great strength, or that 
 recoil movement of the bottom- water near the land, 
 called by sailors the ' undertow ' (which I presume must 
 extend out seaward as far as the hreaking waves impel 
 the surface-water towards the beach), may gain the 
 power during storms of sifting and distributing pebbles 
 even of considerable size, and yet without so violently 
 disturbing them as to injure the encrusting corallines.^ 
 The sea acts in another and distinct manner in 
 the distribution of pebbles, namely by the waves on the 
 beach. Mr. Palmer,^ in his excellent memoir on this 
 subject, has shown that vast masses of shingle travel 
 with surprising quickness along lines of coast, according 
 to the direction with which the waves break on the 
 beach, and that this is determined by the prevailing 
 direction of the winds. This agency must be powerful 
 in mingling together and disseminating pebbles derived 
 from different sources : we may, perhaps, thus under- 
 stand the wide distribution of the gallstone-yellow 
 porphyry ; and likewise, perhaps, the great difference in 
 the nature of the pebbles at the mouth of the Santa 
 
 ^ I may take this opportunity of remarking on a singular but 
 very common character in the form of the bottom, in the creeks 
 which deeply penetrate the western shores of Tierradel Fuego; namely, 
 that they are almost invariably much shallower close to the open sea 
 at their mouths than inland. Thus, Cook, in entering Christmas 
 Sound, first had soundings in thirty-seven fathoms, then in fifty, then 
 in sixty, and a little farther in no bottom, with 170 fathoms. The 
 sealers are so familiar with this fact, that they always look out for 
 anchorage near the entrances of the creeks. See, also, on this subject, 
 the ' Voyage of the Adventure and Beagle,' vol. i. p. 375, and ' Appen- 
 dix,' p. 313. This shoalness of the sea-channels near their entrances 
 probably results from the quantity of sediment formed by the wear 
 and tear of the outer rocks exposed to the full force of the open sea. 
 I have no doubt that many lakes, for instance in Scotland, which are 
 very deep within, and are separated from the sea apparently only by 
 a tract of detritus, were originally sea-channels with banks of this 
 nature near their mouths, which have since been upheaved. 
 
 2 ' Philosophical Transactions,' 1834, p. 576. 
 
 q2 
 
2 28 Formation of Sea-Cliffs. paet n. 
 
 Cruz from those in the same latitude at the head of the 
 valley. 
 
 I will not pretend to assign to these several and 
 complicated agencies their shares in the distribution of 
 the Patagonian shingle ; but from the several considera- 
 tions given in this chapter, and I may add, from the 
 frequency of a capping of gravel on tertiary deposits in 
 all parts of the world, as I have myself observed and 
 seen stated in the works of various authors, I cannot doubt 
 that the power of widely dispersing gravel is an ordinary 
 contingent on the action of the sea ; and that even in 
 the case of the great Patagonian shingle-bed we have 
 no occasion to call in the aid of debacles. I at one 
 time imagined that perhaps an immense accumulation 
 of shingle had originally been collected at the foot of 
 the Cordillera; and that this accumulation, when up- 
 raised above the level of the sea, had been eaten into 
 and partially spread out (as off the present line of coast) ; 
 and that the newly-spread out bed had in its turn been 
 upraised, eaten into, and re-spread out ; and so onwards, 
 until the shingle, which was first accumulated in great 
 thickness at the foot of the Cordillera, had reached in 
 thinner beds its present extension. By whatever means 
 the gravel formation of Patagonia may have been dis- 
 tributed, the vastness of its area, its thickness, its 
 superficial position, its recent origin, and the great 
 degree of similarity in the nature of its pebbles, all 
 appear to me well deserving the attention of geologists, 
 in relation to the origin of the widely-spread beds of 
 conglomerate belonging to past epochs. 
 
 Formation of Cliffs. — "When viewing the sea- worn 
 cliffs of Patagonia, in some parts between 800 and 900 
 feet in height, and formed of horizontal tertiary strata, 
 which must once have extended far seaward — or again, 
 when viewing the lofty cliffs round many volcanic 
 
CHAP. Till. Formation of Sea-Cliffs. 
 
 229 
 
 islands, in which the gentle inclination of the lava- 
 streams indicates the former extension of the land, a 
 difficulty often occurred to me, namely, how the strata 
 could possibly have been removed by the action of the 
 sea at a considerable depth beneath its surface. The 
 following section, which represents the general form of 
 the land on the northern and leeward side of St. Helena 
 (taken from Mr. Seal's large model and various measure- 
 ments), and of the bottom of the adjoining sea (taken 
 chiefly from Captain Austin's survey and some old 
 charts) , will show the nature of this difficulty : — 
 
 No. 21. 
 Section of Coast Cliffs and Bottom of Sea, off tlie Island of St. Helena. 
 
 1,600 feet 
 ibove sea. 
 
 30 fath. 
 
 100 fa. 250 fa. 
 
 Level of sea. 
 
 Bottom rocky 
 only to a depth of 
 fiTB or six fathoms. 
 
 Mud and sand. 
 
 Vertical and horizontal scale, two inches to a nautical mile. The point marked 
 1,600 feet is at the foot of High Knoll ; point marked 510 feet is on the edge of 
 Ladder Hill. The strata consist of basaltic streams. 
 
 If, as seems probable, the basaltic streams were 
 originally prolonged with nearly their present inclina- 
 tion, they must, as shown by the dotted line in the 
 section, once have extended at least to a point, now 
 covered by the sea to a depth of nearly thirty fathoms : 
 but I have every reason to believe they extended con- 
 siderably farther, for the inclination of the streams is 
 less near the coast than farther inland. It should also 
 be observed, that other sections on the coast of this 
 island would have given far more striking results, but 
 I had not the exact measurements ; thus, on the wind- 
 ward side, the clifis are about 2,000 feet in height and 
 
230 Formation of Sea-Cliffs. pakt n. 
 
 the cut-off lava streams very gently inclined, and the 
 bottom of the sea has nearly a similar slope all round 
 the island. How, then, has all the hard basaltic rock, 
 which once extended beneath the surface of the sea, 
 been worn away ? According to Captain Austin, the 
 bottom is uneven and rocky only to that very small 
 distance from the beach within which the depth is from 
 five to six fathoms ; outside this line, to a depth of 
 about 100 fathoms, the bottom is smooth, gently in- 
 clined, and formed of mud and sand; outside the 100 
 fathoms, it plunges suddenly into unfathomable depths, 
 as is so very commonly the case on all coasts where 
 sediment is accumulating. At greater depths than the 
 five or six fathoms, it seems impossible, under existing 
 circumstances, that the sea can both have worn away 
 hard rock, in parts to a thickness of at least 150 feet, 
 and have deposited a smooth bed of fine sediment. 
 Now, if we had any reason to suppose that St. Helena 
 had, during a long period, gone on slowly subsiding, 
 every difficulty would be removed : for looking at the 
 diagram, and imagining a fresh amount of subsidence, 
 we can see that the waves would then act on the coast- 
 cliffs with fresh and unimpaired vigour, whilst the 
 rocky ledge near the beach would be carried down to 
 that depth, at which sand and mud would be deposited 
 on its bare and uneven surface : after the formation 
 near the shore of a new rocky shoal, fresh subsidence 
 would carry it down and allow it to be smoothly 
 covered up. But in the case of the many cliff-bounded 
 islands, for instance in some of the Canary Islands and 
 of Madeira, round which the inclination of the strata 
 shows that the land once extended far into the depths 
 of the sea, where there is no apparent means of hard 
 rock being worn away — are we to suppose that all these 
 islands have slowly subsided ? Madeira, I may remark, 
 
CHAP. Tin. Formation of Sea-Cliffs. 231 
 
 has, according to Mr. Smith of Jordan-hill, subsided. 
 Are we to extend this conclusion to the high, cliff- 
 bound, horizontally- stratified shores of Patagonia, off 
 which, though the water is not deep even at the dis- 
 tance of several miles, yet the smooth bottom of pebbles 
 gradually decreasing in size with the increasing depth, 
 and derived from a foreign source, seem to declare that 
 the sea is now a depositing and not a corroding agent ? 
 I am much inclined to suspect, that we shall hereafter 
 find in all such cases, that the land with the adjoining 
 bed of the sea has in truth subsided : the time will, I 
 believe, come, when geologists will consider it as im- 
 probable, that the land should have retained the same 
 level during a whole geological period, as that the 
 atmosphere should have remained absolutely calm 
 during an entire season. 
 
 k 
 
232 Elevation of Chiloe. pabt n. 
 
 CHAPTER IX. 
 
 ON THE ELEVATION OF THE WESTERN COAST OF SOUTH 
 
 AMERICA. 
 
 Chonos Archipelago — Chiloe, recent and gradual elevation of, tradi- 
 tions of the iQihahitants on this subject — Conee2)cion, earthquake and 
 elevation of. — Valpaeaiso, great elevation of, upraised shells, earth 
 of marine origin, gradual rise of the land within the historical 
 period. — Coquimbo, elevation of, in recent times, terraces of marine 
 origin, their inclination, their escarpments not horizontal — Guasco, 
 gravel terraces of — Copiapo. — Peru — Upraised shells of Codija, 
 Iquique, and Arica — Lima, shell-l)eds and sea-heach on San Lorenzo, 
 Human remains, fossil earthenware, earthqiiahe dehacle, recent sub- 
 sidence — On the decay of upraised shells — General summary. 
 
 Commencing at the south and proceeding northward, 
 the first place at which I landed, was at Cape Tres 
 Montes, in lat. 46° 35^ Here, on the shores of Christ- 
 mas Cove, I observed in several places a beach of 
 pebbles with recent shells, about twenty feet above 
 high-water mark. Southward of Tres Montes (between 
 lat. 47° and 48°), Byron ^ remarks, ' we thought it very 
 strange, that upon the summits of the highest hills 
 were found beds of shells, a foot or two thick.' In the 
 Chonos Archipelago, the island of Lemus (lat. 44° 30') 
 was, according to M. Coste,^ suddenly elevated eight 
 feet, during the earthquake of 1839 : he adds, ' des 
 roches jadis toujours couvertes par la mer, restant 
 aujourd'hui constamment decouvertes.' In other parts 
 
 1 ' Narrative of the Loss of the Wager,' 
 
 2 ' Comptes Rendus,' October 1838, p. 706. 
 
CHAP. IX. Elevation of Chiloe. 233 
 
 of this archipelago, I observed two terraces of gravel, 
 abutting to the foot of each other : at Lowe's Harbour 
 (43° 48'), under a great mass of the boulder formation, 
 about 300 feet in thickness, I found a layer of sand, 
 with numerous comminuted fragments of sea-shells, 
 having a fresh aspect, but too small to be identified. 
 
 The Island of Ghiloe. — The evidence of recent 
 elevation is here more satisfactory. The bay of San 
 Carlos is in most parts bounded by precipitous clifi"s 
 from about ten to forty feet in height, their bases 
 being separated from the present line of tidal action 
 by a talus, a few feet in height, covered with vegetation. 
 In one sheltered creek (west of P. Arena) instead of a 
 loose talus, there was a bare sloping bank of tertiary 
 mudstone, perforated, above the line of the highest 
 tides, by numerous shells of a Pholas now common in 
 the harbour. The upper extremities of these shells, 
 standing upright in their holes with grass growing out 
 of them, were abraded about a quarter of an inch, to 
 the same level with the surrounding worn strata. In 
 other parts, I observed (as at Pudeto) a great beach, 
 formed of comminuted shells, twenty feet above the 
 present shore. In other parts, again, there were small 
 caves worn into the foot of the low clifis, and protected 
 from the waves by the talus with its vegetation : one 
 such cave which I examined, had its mouth about 
 twenty feet, and its bottom, which was filled with sand 
 containing fragments of shells and legs of crabs, from 
 eight to ten feet above high-water mark. From these 
 several facts, and from the appearance of the upraised 
 shells, I inferred that the elevation had been quite 
 recent ; and on inquiring from Mr. Williams, the Port- 
 master, he told me he was convinced that the land had 
 risen, or the sea fallen, four feet within the last four 
 years. Daring this period, there had been one severe 
 
234 Elevation of Chiloe. pabt n. 
 
 earthquake, but no particular change of level was then 
 observed ; from the habits of the people who all keep 
 boats in the protected creeks, it is absolutely impossible 
 that a rise of four feet could have taken place suddenly 
 and been unperceived. Mr. Williams believes that the 
 change has been quite gradual. Without the elevatory 
 movement continues at a quick rate, there can be no 
 doubt that the sea will soon destroy the talus of earth 
 at the foot of the cliffs round the bay, and will then 
 reach its former lateral extension, but not of course its 
 former level : some of the inhabitants assured me, that 
 one such talus, with a footpath on it, was even already 
 sensibly decreasing in width. 
 
 I received several accounts of beds of shells, existing 
 at considerable heights in the inland parts of Chiloe ; 
 and to one of these, near Catiman, I was guided by a 
 countryman. Here, on the south side of the peninsula 
 of Lacuy, there was an immense bed of the Yenus 
 costellata and of an oyster, lying on the summit-edge 
 of a piece of table land, 350 feet (by the barometer) 
 above the level of the sea. The shells were closely 
 packed together, embedded in and covered by, a very 
 black, damp peaty mould, two or three feet in thick- 
 ness, out of which a forest of great trees was growing. 
 Considering the nature and dampness of thispeaty soil, 
 it is surprising, that the fine ridges on the outside of 
 the Venus are perfectly preserved, though all the 
 shells have a blackened appearance. I did not doubt 
 that the black soil, which, when dry, cakes hard, was 
 entirely of terrestrial origin, but on examining it under 
 the microscope, I found many very minute rounded 
 fragments of shells, amongst which I could distinguish 
 bits of serpulse and mussels. The Venus costellata, 
 and the ostrea (0. edulis, according to Captain King) 
 are now the commonest shells in the adjoining bays. 
 
€HAP. IX. Elevation of Chiloe. 235 
 
 In a bed of shellsj a few feet below the 350 feet bed, I 
 found a born of the little Cervus Jiumilis^ wbicb now 
 inhabits Cbiloe. 
 
 The eastern or inland side of Cbiloe, with its many 
 adjacent islets, consists of tertiary and boulder deposits, 
 worn into irregular plains capped by gravel. Near 
 Castro, and for ten miles southward, and on the islet of 
 Lemuy, I found the surface of the ground to a height 
 of between twenty and thirty feet above high- water 
 mark, and in several places apparently up to fifty feet, 
 thickly coated by much comminuted shells, chiefly of 
 the Venus costellata and Mytilus Ghiloensis ; the 
 species now most abundant on this line of coast. As 
 the inhabitants carry immense numbers of these shells 
 inland, the continuity of the bed at the same height 
 was often the only means of recognising its natural 
 origin. Near Castro, on each side of the creek and 
 rivulet of the Gamboa, three distinct terraces are seen : 
 the lowest was estimated at about 150 feet in height, 
 and the highest at about 500 feet, with the country 
 irregularly rising behind it; obscure traces, also, of 
 these same terraces could be seen along other parts of 
 the coast. There can be no doubt that their three 
 escarpments record pauses in the elevation of the 
 island. I may remark that several promontories have 
 the word Huapi, which signifies in the Indian tongue, 
 island, appended to them, such as Huapilinao, Huapi- 
 lacuy, Caucahuapi, etc. ; and these, according to Indian 
 traditions, once existed as islands. In the same manner 
 the term Pulo in Sumatra is appended ^ to the names 
 of promontories, traditionally said to have been islands ; 
 in Sumatra, as in Chiloe, there are upraised recent 
 shells. The Bay of Carelmapu, on the mainland north 
 
 * Marsden's ' Sumatra,' p. 31. 
 
236 Elevation of Concepcion. paet n. 
 
 of Chiloe, according to Agiierros/ was in 1643 a good 
 harbour ; it is now quite useless, except for boats. 
 
 Valdivia. — I did not observe here any distinct proofs 
 of recent elevation ; but in a bed of very soft sandstone, 
 forming a fringe-like plain, about sixty feet in height^ 
 round the hills of mica-slate, there are shells of Mytilus, 
 Crepidula, Solen, Novaculina, and Oytheraea, too im- 
 perfect to be specifically recognised. At Imperial, 
 seventy miles north of Valdivia, Agiierros ^ states that 
 there are large beds of shells, at a considerable distance 
 from the coast, which are burnt for lime. The island 
 of Mocha, lying a little north of Imperial, was uplifted 
 two feet,^ during the earthquake of 1835. 
 
 Concepcion. — I cannot add anything to the excellent 
 account by Captain FitzHoy^ of the elevation of the 
 land at this place, which accompanied the earthquake 
 of 1835. I will only recall to the recollection of 
 geologists, that the southern end of the island of St. 
 Mary was uplifted eight feet, the central part nine, and 
 the northern end ten feet ; and the whole island more 
 than the surrounding districts. Great beds of mussels, 
 patellge, and chitons still adhering to the rocks were 
 upraised above high-water mark ; and some acres of a 
 rocky flat, which was formerly always covered by the 
 sea, was left standing dry, and exhaled an offensive 
 smell, from the many attached and putrefying shells. 
 
 ^ ' Descripcion Hist, de la Provincia de Chiloe,' p. 78. From the 
 account given by the old Spanish writers, it would appear that several 
 other harbours, between this point and Concejpcion, were formerly 
 much deeper than they now are. 
 
 - 'Descripc. Hist.' p. 25. 
 
 ^ ' Voyages of Adventure and Beagle,' vol. ii. p. 415. 
 
 * Ibid. vol. ii. p. 412 et seq. In vol. v. (p. 601) of the 'Geolo-' 
 gical Transactions,' I have given an account of the remarkable vol- 
 canic phenomena, which accompanied this earthquake. These 
 phenomena appear to me to prove that the action, by which large 
 tracts of land are uplifted, and by which volcanic eruptions are 
 produced, is in every respect identical. 
 
CHAP. IX. Elevation of Concepcion. 237 
 
 It appears from the researches of Capt. FitzEoy that 
 both the island of St. Mary and Concepcion (which was 
 uplifted only four or five feet) in the course of some 
 weeks subsided, and lost part of their first elevation. 
 I will only add as a lesson of caution, that round the 
 sandy shores of the great Bay of Concepcion, it was 
 most difficult, owing to the obliterating efiects of the 
 great accompanying wave, to recognise any distinct 
 evidence of this considerable upheaval ; one spot must 
 be excepted, where there was a detached rock which 
 before the earthquake had always been covered by the 
 sea, but afterwards was left uncovered. 
 
 On the island of Quiriquina (in the Bay of Concep- 
 cion), I found, at an estimated height of 400 feet, 
 extensive layers of shells, mostly comminuted, but some 
 perfectly preserved and closely packed in black vege- 
 table mould ; they consisted of Concholepas, Fissurella, 
 Mytilus, Trochus, and Balanus. Some of these layers 
 of shells rested on a thick bed of bright-red, dry, friable 
 earth, capping the surface of the tertiary sandstone, 
 and extending, as I observed whilst sailing along the 
 coast, for 150 miles southward: at Valparaiso, we shall 
 presently see that a similar red earthy mass, though 
 quite like terrestrial mould, is really in chief part of 
 recent marine origin. On the flanks of this island of 
 Quiriquina, at a less height than the 400 feet, there 
 were spaces several feet square, thickly strewed with 
 fragments of similar shells. During a subsequent visit 
 of the Beagle to Concepcion, Mr. Kent, the assistant- 
 surgeon, was so kind as to make for me some measure- 
 ments with the barometer : he found many marine 
 remains along the shores of the whole bay, at a height 
 of about twenty feet ; and from the hill of Sentinella 
 behind Talcahuano, at the height of 160 feet, he col- 
 lected numerous shells, packed together close beneath 
 
238 Elevation of Coficepcion. paet 11, 
 
 the surface in black earth, consisting of two species 
 of Mytilus, two of Crepidula, one of Concholepas, of 
 Fissurella, Venus, Mactra, Turbo, Monoceros, and the 
 Balanus |jsi^^aCTfs» These shells were bleached, and 
 within some of the Balani other Balani were growing, 
 showing that they must have long lain dead in the sea. 
 The above species I compared with living ones from 
 the bay, and found them identical ; but having since 
 lost the specimens, I cannot give their names : this is 
 of little importance, as Mr. Broderip has examined a 
 similar collection, made during Capt. Beechey's expedi- 
 tion, and ascertained that they consisted of ten recent 
 species, associated with fragments of Echini, crabs, and 
 Flustr^ ; some of these remains were estimated by 
 Lieut. Belcher to lie at the height of nearly a 1,000 feet 
 above the level of the sea.^ In some places round the 
 bay, Mr. Kent observed that there were beds formed 
 exclusively of the Mytilus Ghiloensis : this species now 
 lives in parts never uncovered by the tides. At con- 
 siderable heights, Mr. Kent found only a few shells ; 
 but from the summit of one hill, 625 feet high, he 
 brought me specimens of the Concholepas, Mytilus 
 Ghiloensis, and a Turbo, These shells were softer and 
 more brittle than those from the height of 164 feet; 
 and these latter had obviously a much more ancient 
 appearance than the same species from the height of 
 only twenty feet. 
 
 Coast north of Concepcion. — The first point exa- 
 mined was at the mouth of the Rapel (160 miles N. of 
 Concepcion and sixty miles S. of Valparaiso), where I 
 observed a few shells at the height of 100 feet, and 
 some barnacles adhering to the rocks three or four feet 
 above the highest tides : M. Gay ^ found here recent 
 
 ^ 'Zoology of Capt. Beechey's Voyage,' p. 162. 
 2 'Annates des Scienc. Nat.' Avril 1833. 
 
CHAP. IX. Elevation of Valparaiso. 239 
 
 shells at the distance of two leagues from the shore. 
 Inland there are some wide, gravel-capped plains, inter- 
 sected by many broad, flat-bottomed valleys (now carry- 
 ing insignificant streamlets) with their sides cut into 
 successive wall-like escarpments, rising one above 
 another, and in many places, according to M. Gay, 
 worn into caves. The one cave (C. del Obispo) which 
 I examined, resembled those formed on many sea-coasts, 
 with its bottom filled with shingle. These inland 
 plains, instead of sloping towards the coast, are inclined 
 in an opposite direction towards the Cordillera, like the 
 successively rising terraces on the inland or eastern side 
 of Chiloe : some points of granite, which project through 
 the plains near the coast, no doubt once formed a chain 
 of outlying islands, on the inland shores of which 
 the plains were accumulated. At Bucalemu, a few 
 miles northward of the Rapel, I observed at the foot 
 and on the summit-edge of a plain, ten miles from the 
 coast, many recent shells, mostly comminuted, but 
 some perfect. There were, also, many at the bottom of 
 the great valley of the Maypu. At San Antonio, shells 
 are said to be collected and burnt for lime. At the 
 bottom of a great ravine (Quebrada Onda, on the road 
 to Oasa Blanca), at the distance of several miles from 
 the coast, I noticed a considerable bed, composed ex- 
 clusively of Mesodesma donaciforme^ Desh., lying on a 
 bed of muddy sand : this shell now lives associated 
 together in great numbers, on tidal flats on the coast of 
 Chile. 
 
 Val2Jaraiso. 
 
 During two successive years I carefully examined, 
 part of the time in company with Mr. Alison, into all 
 the facts connected with the recent elevation of this 
 neighbourhood. In very many parts a beach of broken 
 
240 Elevation of Valparaiso. paet n. 
 
 shells, about fourteen or fifteen feet above high-water 
 mark, may be observed; and at this level the coast- 
 rocks, where precipitous, are corroded in a band. At 
 one spot, Mr. Alison, by removing some birds' dung, 
 found at this same level barnacles adhering to the rocks. 
 For several miles southward of the bay, almost every 
 flat little headland, between the heights of 60 and 230 
 feet (measured by the barometer), is smoothly coated 
 by a thick mass of comminuted shells, of the same 
 species, and apparently in the same proportional num- 
 bers with those existing in the adjoining sea. The 
 Concholepas is much the most abundant, and the best 
 preserved shell; but I extracted perfectly preserved 
 specimens of the Fisstirella hiradiata, a Trochus and 
 Balanus (both well known, but according to Mr. Sowerby 
 yet unnamed) and parts of the Mytilus Chiloensis. 
 Most of these shells, as well as an encrusting Nullipora, 
 partially retain their colour; but they are brittle, and 
 often stained red from the underlying brecciated mass 
 of primary rocks ; some are packed together, either in 
 black or reddish mould; some lie loose on the bare 
 rocky surfaces. The total number of these siiells is 
 immense ; they are less numerous, though still far from 
 rare up a height of 1,000 feet above the sea. On the 
 summit of a hill, measured 557 feet, there was a small 
 horizontal band of comminuted shells, of which many 
 consisted (and likewise from lesser heights) of very 
 young and small specimens of the still living Con- 
 cholepas, Trochus, Patell83, Orepidulge, and of Mytilus 
 Magellanicus (?) : ^ several of these shells were under 
 a quarter of an inch in their greatest diameter. My 
 
 ^ Mr. Cuming informs me that he does not think this species 
 identical with, though closely resembling, the true M. 3Iagella7iicus 
 of the southern and eastern coast of South America ; it lives abun- 
 dantly on the coast of Chile. 
 
CHAP. Tx. Elevation of Valparaiso. 241 
 
 attention was called to this circnmstance by a native 
 fisherman, whom I took to look at these shell-beds ; 
 and he ridiculed the notion of such small shells having 
 been brought up for food ; nor could some of the species 
 have adhered when alive to other larger shells. On 
 another hill, some miles distant, and 648 feet high, I 
 found shells of the Concholepas and Trochus, perfect, 
 though very old, with fragments of Mytilus Chiloensis, 
 all embedded in reddish-brown mould : I also found 
 these same species, with fragments of an Echinus and 
 of Balanus psittacus, on a hill 1,000 feet high. Above 
 this height, shells became very rare, though on a hill 
 1,300 feet high,^ I collected the Concholepas, Trochus, 
 Fissurella, and a Patella. At these greater heights the 
 shells are almost invariably embedded in mould, and 
 sometimes are exposed only by tearing up bushes. 
 These shells obviously had a very much more ancient 
 appearance than those from the lesser heights ; the 
 apices of the Trochi were often worn down ; the little 
 holes made by burrowing animals were greatly en- 
 larged ; and the Concholepas was often perforated quite 
 through, owing to the inner plates of shell having 
 scaled off. 
 
 Many of these shells, as I have said, were packed in, 
 and were quite filled with, blackish or reddish-brown 
 earth, resting on the granitic detritus. I did not doubt 
 until lately that this mould was of purely terrestrial 
 origin, when with a microscope examining some of it 
 from the inside of a Concholepas from the height of 
 about 100 feet, I found that it was in considerable part 
 composed of minute fragments of the spines, mouth- 
 bones and shells of Echini, and of minute fragments, 
 
 ^ Measured by the barometer : the highest point in the range 
 behind Valparaiso I found to be 1,626 feet above the level of the 
 sea. 
 
 R 
 
242 Elevation of Valparaiso, paet n. 
 
 of chiefly very young Patellee, Mytili, and other species. 
 I found similar microscopical fragments in earth filling 
 up the central orifices of some large Fissurellse. This 
 earth when crushed emits a sickly smell, precisely like 
 that from garden-mould mixed with guano. The earth 
 accidentally preserved within the shells, from the greater 
 heights, has the same general appearance, but it is a 
 little redder ; it emits the same smell when rubbed, but 
 I was unable to detect with certainty any marine remains 
 in it. This earth resembles in general appearance, as 
 before remarked, that capping the rocks of Quiriquina 
 in the Bay of Concepcion, on which beds of sea-shells 
 lay. I have, also, shown that the black, peaty soil, in 
 which the shells at the height of 350 feet at Chiloe 
 were packed, contained many minute fragments of 
 marine animals. These facts appear to me interesting, 
 as they show that soils, which, would naturally be con- 
 sidered of purely terrestrial nature, may owe their origin 
 in chief part to the sea. 
 
 Beino^ well aware from what I have seen at Chiloe 
 and in Tierra del Fiiego, that vast quantities of shells 
 are carried, during successive ages, far inland, where the 
 inhabitants chiefly subsist on these productions, I am 
 bound to state that at greater heights than 557 feet, 
 where the number of very young and small shells proved 
 that they had not been carried up for food, the only 
 evidence of the shells having been naturally left by the 
 sea, consists in their invariable and uniform appearance 
 of extreme antiquity — in the distance of some of the 
 places from the coast, in others being inaccessible from 
 the nearest part of the beach, and in. the absence of 
 fresh water for men to drink — in the shells not lying 
 in heaps, — and, lastly, in the close similarity of the 
 soil in which they are embedded, to that which lower 
 
CHA.P. IX. Elevation of Valparaiso, ■ 243 
 
 down can be unequivocally shown to be in great part 
 formed from the debris of the sea animals.^ 
 
 With respect to the position in which the shells lie, 
 I was repeatedly struck here, at Concepcion, and at 
 Other places, with the frequency of their occurrence on 
 the summits and edges either of separate hills, or of 
 little flat headlands often terminating precipitously 
 over the sea. The several above-enumerated species of 
 Mollusca, which are found strewed on the surface of 
 the land from a few feet above the level of the sea up 
 to the height of 1,300 feet, all now live either on the 
 beach, or at only a few fathoms' depth : Mr. Edmonston, 
 in a letter to Prof. E. Forbes, states that in dredging 
 in the Bay of Valparaiso, he found the common species 
 of Concholepas, Fissurella, Trochus, Monoceros, Chi- 
 tons, &c. living in abundance from the beach to a depth 
 of seven fathoms ; and dead shells occurred only a few 
 fathoms deeper. The common Turritella cingulata 
 was dredged up living at even from ten to fifteen 
 fathoms ; but this is a species which I did not find here 
 amongst the upraised shells. Considering this fact of 
 the species being all littoral or sub-littoral, considering 
 their occurrence at various heights, their vast numbers, 
 and their generally comminuted state, there can be 
 little doubt that they were left on successive beach-lines 
 
 ^ In the ' Proceedings of the Geolog. Soc' vol. ii. p. 446, I have 
 given a brief account of the upraised shells on the coast of Chile, 
 and have there stated that the proofs of elevation are not satisfactory 
 above the height of 230 feet. I had at that time unfortunately over- 
 looked a separate page written during my second visit to Valparaiso, 
 describing the shells now in m}^ possession from the 557 feet hill ; I 
 had not then unpacked my collections, and had not reconsidered 
 the obvious appearance of greater antiquity of the shells from the 
 greater heights, nor had I at that time discovered the marine origin of 
 the earth in which many of the shells are packed. Considering these 
 facts, I do not now feel a shadow of doubt that the shells, at the 
 height of 1,.800 feet, have been upraised by natural causes into their 
 present position. 
 
 e2 
 
244 Elevation of Valparaiso part n. 
 
 during a gradual elevation of the land. The presence, 
 however, of so many whole and perfectly preserved 
 shells appears at first a difficulty on this view, consider- 
 ing that the coast is exposed to the full force of an 
 open ocean : but we may suppose, either that these 
 shells were thrown during gales on flat ledges of rock 
 just above the level of high- water mark, and that 
 during the elevation of the land they were never again 
 touched by the waves, or, that during earthquakes, such 
 as those of 1822, 1835, and 1837, rocky reefs covered 
 with marine-animals were at one blow uplifted above 
 the future reach of the sea. This latter explanation is, 
 perhaps, the most probable one with respect to the beds 
 at Concepcion entirely composed of the Mytilus Chi- 
 loensis^ a species which lives below the lowest tides ; 
 and likewise with respect to the great beds, occurring 
 both north and south of Valparaiso, of the Mesodesma 
 donaciforme, — a shell which, as I am informed by Mr. 
 Cuming, inhabits sand-banks at the level of the lowest 
 tides. But even in the case of shells having the habits 
 of this Mytilus and Mesodesma, beds of them, wherever 
 the sea gently throws up sand or mud, and thus protects 
 its own accumulations, might be upraised by the slowest 
 movement, and yet remain undisturbed by the waves of 
 each new beach-line. 
 
 It is worthy of remark, that nowhere near Valparaiso 
 above the height of twenty feet, or rarely of fifty feet, 
 I saw any lines of erosion on the solid rocks, or any 
 beds of pebbles ; this, I believe, may be accounted for 
 by the disintegrating tendency of most of the rocks in 
 this neighbourhood. Nor is the land here modelled 
 into terraces : Mr. Alison, however, informs me, that 
 on both sides of one narrow ravine, at the height of 
 300 feet above the sea, he found a succession of rather 
 indistinct step-formed beaches, composed of broken 
 
CHAP. IX. within the Historical Period. 245 
 
 shells, whicli together covered a space of about eighty 
 feet vertical. 
 
 I can add nothing to the accounts already published 
 of the elevation of the land at Valparaiso/ which ac- 
 companied the earthquake of 1822 : but I heard it 
 confidently asserted, that a sentinel on duty, immedi- 
 ately after the shock, saw a part of a fort, which pre- 
 viously was not within the line of his vision, and this 
 would indicate that the uplifting was not horizontal : 
 it would even appear from some facts collected by Mr. 
 Alison, that only the eastern half of the bay was then 
 elevated. Through the kindness of this same gentle- 
 man, I am able to give an interesting account of the 
 changes of level, which have supervened here within 
 historical periods: about the year 1680 a long sea-wall 
 (or Prefil) was built, of which only a few fragments 
 now remain; up to the year 1817, the sea often broke 
 over it, and washed the houses on the opposite side of 
 the road (where the prison now stands) ; and even in 
 1819, Mr. J. Martin remembers walking at the foot of 
 this wall, and being often obliged to climb over it to 
 escape the waves. There now stands (1834) on the 
 seaward side of this wall, and between it and the beach, 
 in one part a single row of houses, and in another part 
 two rows with a street between them. This great 
 extension of the beach in so short a time cannot be 
 attributed simply to the accumulation of detritus ; for 
 a resident engineer measured for me the height between 
 the lowest part of the wall visible, and the present 
 beach-line at spring-tides, and the difference was eleven 
 fe'et six inches. The church of S. Augustin is believed 
 to have been built in 1614, and there is a tradition that 
 
 » Dr. Meyen (' Reise urn Erde,' Th. I. s. 221) found in 1831 sea- 
 weed and other bodies still adhering to some rocks which during the 
 shock of 1822 were lifted above the sea. 
 
246 Elevation of Coquzmbo. pabt n. 
 
 the sea formerly flowed very near it ; by levelling, its 
 foundations were found to stand nineteen feet six inches 
 above the highest beach-line ; so that we see in a period 
 of 220 years, the elevation cannot have been as much 
 as nineteen feet six inches. From the facts given with 
 respect to the sea-wall, and from the testimony of the 
 elder inhabitants, it appears certain that the change in 
 level began to be manifest about the year 1817. The 
 only sudden elevation of which there is any record 
 occurred in 1822, and this seems to have been less than 
 three feet. Since that year, I was assured by several 
 competent observers, that part of an old wreck, which 
 is firmly embedded near the beach, has sensibly 
 emerged ; hence here, as at Chiloe, a slow rise of the 
 land appears to be now in progress. It seems highly 
 probable that the rocks which are corroded in a band 
 at the height of fourteen feet above the sea were acted 
 on during the period, when by tradition the base of 
 S. Augustin church, now nineteen feet six inches above 
 the highest water-mark, was occasionally washed by 
 the waves. 
 
 Valparaiso to Coquimbo. — For the first seventy- 
 five miles north of Valparaiso I followed the coast-road, 
 and throughout this space I observed innumerable 
 masses of upraised shells. About Quintero there are 
 immense accumulations (worked for lime) of the Meso- 
 desma donaciforme, packed in sandy earth, they abound 
 chiefly about fifteen feet above high-water, but shells 
 are here found, according to. Mr. Miers,^ to a height of 
 500 feet, and at a distance of three leagues from the 
 coast : I here noticed barnacles adhering to the rocks 
 three or four feet above the highest tides. In the 
 
 * ' Travels in Chile,' vol. i. pp. 458, 395. I received several similar 
 accounts from the inhabitants, and was assured that there are many 
 shells on the plain of Casa Blanca, between Valparaiso and Santiago, 
 at the height of 800 feet. 
 
CHAP. IX. Elevation of Coqttmtbo, 247 
 
 neighbourliood of Plazilla and Catapilco, at heiglits of 
 between 200 and 300 feet, the number of comminuted 
 shells, with some perfect ones, especially of the Meso- 
 desma, packed in layers, was truly immense : the land 
 at Plazilla had evidently existed as a bay, with abrupt 
 rocky masses rising out of it, precisely like the islets in 
 the broken bays now indenting this coast. On both 
 sides of the rivers Ligua, Longotomo, Guachen, and 
 Quilimari, there are plains of gravel about 200 feet in 
 height, in many parts absolutely covered with shells. 
 Close to Conchalee, a gravel-plain is fronted by a lower 
 and similar plain about sixty feet irt height, and this 
 again is separated from the beach by a wide tract of 
 low land : the surfaces of all three plains or terraces 
 were strewed with vast numbers of the Concholepas, 
 Mesodesma, an existing Venus, and other still existing 
 littoral shells. The two upper terraces closely resemble 
 in miniature the plains of Patagonia ; and like them 
 are furrowed by dry, flat-bottomed, winding valleys. 
 Northward of this place I turned inward ; and therefore 
 found no more shells . but the valleys of Chuapa, Illapel, 
 and Limari, are bounded by gravel- capped plains, often 
 including a lower terrace within. These plains send 
 bay- like arms between and into the surrounding hills ; 
 and they are continuously united with other extensive 
 gravel-capped plains, separating the coast mountain- 
 ranges from the Cordillera. 
 
 Coqnimho. 
 
 A narrow fringe-like plain, gently inclined towards 
 the sea, here extends for eleven miles along the coast, 
 with arms stretching up between the coast-mountains, 
 and likewise up the valley of Coquimbo : at its southern 
 extremity it is directly connected _^with the plain of 
 
248 Elevation of Coquimbo. - paet n. 
 
 Limari, out of which hills abruptly rise like islets, and 
 other hills project like headlands on a coast. The 
 surface of the fringe-like plain appears level, but differs 
 insensibly in height, and greatly in composition, in 
 different parts. 
 
 At the mouth of the valley of Coquimbo, the surface 
 consists wholly of gravel, and stands from 300 to 350 
 feet above the level of the sea, being about 100 feet 
 higher than in other parts. In these other and lower 
 parts, the superficial beds consist of calcareous matter, 
 and rest on ancient tertiary deposits hereafter to be 
 described. The uppermost calcareous layer is cream- 
 coloured, compact, smooth-fractured, sub-stalactiform, 
 and contains some sand, earthy matter, and recent shells. 
 It lies on, and sends wedge-like veins into,^ a much 
 more friable, calcareous, tuff-like variety; and both 
 rest on a mass about twenty feet in thickness, formed 
 of fragments of recent shells, with ;a few whole ones, 
 and with small pebbles firmly cemented together. This 
 latter rock is called by the inhabitants losa^ and is used 
 for building; in many parts it is di\dded into strata, 
 which dip at an angle of ten degrees seaward, and ap- 
 pear as if they had originally been heaped in successive 
 layers (as may be seen on coral-reefs) on a steep beach. 
 This stone is remarkable from being in parts entirely 
 formed of empty, pellucid capsules or cells of calcareous 
 matter, of the size of small seeds : a series of specimens 
 unequivocally showed that all these capsules once con- 
 tained minute rounded fragments of shells which have 
 
 * In many respects this upper hard, and the underlying more 
 friable varieties, resemble the great superficial beds at King George's 
 Sound in Australia, which I have described in Chapter VII. p. 161. 
 There could be little doubt that the upper layers there have been 
 hardened by the action of rain on the friable calcareous matter, and 
 that the whole mass has originated in the decay of minutely commi- 
 nuted sea-shells and corals. 
 
CHAP. IX. 
 
 Elevation of Coquimbo, 
 
 249 
 
 since been gradually dissolved by water percolating 
 through the mass.^ 
 
 The shells embedded in the calcareous beds forming 
 the surface of this fringe-like plain, at the height of 
 from 200 to 250 feet above the sea, consist of, 
 
 1. Venus opaca. 
 
 2. Mulinia Byronensis. 
 
 3. Pecten purpuratus. 
 
 4. Mesodesma donaciforme. 
 
 5. Turritella cingulata. 
 
 6. Monoceros costatum. 
 
 7. Concholepas Peruviana. 
 
 8. Troclius (common Valpa- 
 
 raiso species). 
 
 9. Calyptrsea Byronensis. 
 
 Although these species are all recent, and are all 
 found in the neighbouring sea, yet I was particularly 
 struck with the difference in the proportional numbers 
 of the several species, and of those now cast up on the 
 present beach. I found only one specimen of the Con- 
 cholepas, and the Pecten was very rare, though both 
 these shells are now the commonest kinds, with the 
 exception, perhaps, of the Oalyptrcea radians, of which 
 I did not find one in the calcareous beds. I will not 
 pretend to determine how far this difference in the 
 proportional numbers depends on the age of the deposit, 
 and how far on the difference in nature between the 
 present sandy beaches and the calcareous bottom, on 
 which the embedded shells must have lived. 
 
 On the bare surface of the calcareous plain, or in a 
 thin covering of sand, there were lying at a height from 
 200 to 252 feet, many recent shells, which had a much 
 fresher appearance than the embedded ones : fragments 
 of the Concholepas, and of the common Mytilus, still 
 retaining a tinge of its colour, were numerous, and 
 altogether there was manifestly a closer approach in 
 proportional numbers to those now lying on the beach. 
 In a mass of stratified, slightly agglutinated sand, which 
 in some places covers up the lower half of the seaward 
 
 ^ I have already had occasion to describe this rock in Chapter VII. 
 
250 
 
 Elevation of Coquimbo. 
 
 PART II. 
 
 escarpment of the plain, the included shells appeared to 
 be in exactly the same proportional numbers with those 
 on the beach. On one side of a steep-sided ravine, 
 cutting through the plain behind Herradura Bay, I 
 observed a narrow strip of stratified sand, containing 
 similar shells in similar proportional numbers : a section 
 of the ravine is represented in the following diagram, 
 which serves also to show the general composition of the 
 plain. I mention this case of the ravine chiefly because 
 without the evidence of the marine shells in the sand, 
 any one would have supposed that it had been hollowed 
 out by simple alluvial action. 
 
 No. 22. 
 
 Section of Plain of Coquimbo. 
 B Surface of plain 252 feet above sea. B 
 
 
 
 F y^f:^. 
 
 Level of sea. 
 
 A. stratified sand, witb recent sbells in same proportions as on the beacb, half filling 
 
 up a ravine, 
 
 B. Surface of plain with scattered shells in nearly same proportions as on the beach. 
 
 C. Upper calcareous bed, ) with recent shells, but not in same propor- 
 
 D. Lower calcareous sandy bed (Losa), ) tions as on the beach. 
 
 E. Upper ferrugino-sandy old tertiary stratum, ) with all, or nearly all, extinct 
 
 F. Lower old tertiary stratum, J shells. 
 
 The escarpment of the fringe-like plain, which 
 stretches for eleven miles along the coast, is in some 
 parts fronted by two or three narrow, step-formed ter- 
 races, one of which at Herradura Bay expands into a 
 small plain. Its surface was there formed of gravel, 
 cemented together by calcareous matter ; and out of it 
 I extracted the following recent shells, which are in 
 a more perfect condition than those from the upper 
 t)lain : — 
 
CHAP. IX. 
 
 Elevation of Coqui7nbo. 251 
 
 1. Calyptrfea radians. 
 '2. Turritella cingulata. 
 
 3. Oliva Peruviana. 
 
 4. Mures labiosus, var. 
 
 5. Nassa (identical with a living 
 species). 
 
 6. Solen Dombeiana. 
 
 7. Pecten purpiiratus. 
 
 8. Venus Chilensis. 
 
 9, Amphidesma rugulosum. The 
 small irregular v^rinkles of the 
 posterior part of this shell are 
 rather stronger than in the 
 recent specimens of this species 
 from Coquimbo. (G. B. 
 Sowerby.) 
 
 10. Balanus (identical with liv- 
 ing species). 
 
 On tlie syenitic ridge, whicli forms tlie southern 
 boundary of Herradura Bay and Plain, I found the 
 Concholepas and Turritella cingulata (mostly in frag- 
 ments), at tlie height of 242 feet above the sea. I could 
 not have told that these shells had not formerly been 
 brought up by man, if I had not found one very small 
 mass of them cemented together in a friable calcareous 
 tuff. I mention this fact more particularly, because I 
 carefully looked, in many apparently favourable spots 
 at lesser heights on the side of this ridge, and could not 
 find even the smallest fragment of a shell. This is only 
 one instance out of many, proving that the absence of 
 sea-shells on the surface, though in many respects inex- 
 plicable, is an argument of very little weight in opposi- 
 tion to other evidence on the recent elevation of the 
 land. The highest point in this neighbourhood at which 
 I found upraised shells of existing species was on an 
 inland calcareous plain, at the height of 252 feet above 
 the sea. 
 
 It would appear from Mr. Caldcleugh's researches,^ 
 that a rise has taken place here within the last century 
 and a half ; and as no sudden change of level has been 
 observed during the not very severe earthquakes, which 
 have occasionally occurred here, the rising has probably 
 been slow, like that now, or quite lately, in progress at 
 Chiloe and at Valparaiso : there are three well-known 
 rocks, called the Pelicans, which in 1710, according to 
 
 Proceedings of the Geological Society,' vol. ii. p. 446. 
 
252 Elevation of Coquimbo. paet ir. 
 
 Feuillee, were a flew dleau^ but now are said to stand 
 twelve feet above low- water mark : the spring- tides rise 
 here only five feet. There is another rock, now nine 
 feet above high-water mark, which in the time of Freziei" 
 and of Feuillee rose only five or six feet out of water. 
 Mr. Caldcleugh, I may add, also shows (and I received 
 similar accounts) that there has been a considerable 
 decrease in the soundings during the last twelve years 
 in the Bays of Coquimbo, Ooncepcion, Valparaiso, and 
 Guasco ; but as in these cases it is nearly impossible to 
 distinguish between the accumulation of sediment and 
 the upheavement of the bottom, I have not entered into 
 any details. 
 
 Valley of Coquimbo. — The narrow coast-plain sends, 
 as before stated, an arm, or more correctly a fringe on 
 both sides, but chiefly on the southern side, several 
 miles up the valley. These fringes are worn into steps 
 or terraces, which present a most remarkable appear- 
 ance, and have been compared (though not very cor- 
 rectly) by Capt. Basil Hall, to the parallel roads of Glen 
 Roy in Scotland : their origin has been ably discussed 
 by Mr. Lyell.^ The first section which I will give, is 
 not drawn across the valley, but in an east aud west 
 
 No. 23. 
 
 East and West Section through the Terraces at Coquimbo, where they debouch 
 from the Valley, aud front the Sea. 
 
 364 feet. ^^'l 
 
 
 D. 
 
 . 120 feet. 
 
 (B.) 
 70 feet. 
 
 
 
 
 (A.) 
 25 feet 
 
 N^ 
 
 
 
 
 Level of sea. Town of Coquimbo. 
 
 Vertical scale —^h of inch to 100 feet : horizontal scale much contracted. 
 
 line at its mouth, where the step-formed terraces de- 
 bouch and present their very gently inclined surfaces 
 towards the Pacific. 
 
 * ' Principles of Geology ' (1st edit.), vol. iii. p. 131. 
 
CHAP. IX. Gravel-Terraces of Coquimbo. 253 
 
 The bottom plain (A) is about a mile in width, and 
 rises quite insensibly from the beach to a height of 
 twenty-five feet at the foot of the next plain : it is sandy, 
 and abundantly strewed with shells. 
 
 Plain or terrace (B) is of small extent, and is almost 
 concealed by the houses of the town, as is likewise the 
 escarpment of terrace (C). On both sides of a ravine, 
 two miles south of the town, there are two little ter- 
 races, one above the other, evidently corresponding with 
 (B) and (C) ; and on them marine remains of the species 
 already enumerated were plentiful. Terrace (E) is very 
 narrow, but quite distinct and level ; a little southward 
 of the town there were traces of a terrace (D) inter- 
 mediate between (E) and (C). Terrace (F) is part of 
 the fringe-like plain, which stretches for the eleven 
 miles along the coast ; it is here composed of shingle, 
 and is 1 00 feet higher than where composed of calca- 
 reous matter. This greater height is obviously due to 
 the quantity of shingle, which at some former period 
 has been brought down the great valley of Coquimbo. 
 
 Considering the many shells strewed over the ter- 
 races (A) (B) and (C), and a few miles southward on 
 the calcareous plain, which is continuously united with 
 the upper step-like plain (F), there cannot, I apprehend 
 be any doubt, that these six terraces have been formed 
 by the action of the sea ; and that their five escarp- 
 ments mark so many periods of comparative rest in the 
 elevatory movement, during which the sea wore into 
 the land. The elevation between these periods may 
 have been sudden and on an average not more than 
 seventy-two feet each time, or it may have been gradual 
 and insensibly slow. From the shells on the three 
 lower terraces, and on the upper one, and I may add on 
 the three gravel-capped terraces at Conch alee, being all 
 littoral and sub-littoral species, and from the analogical 
 
2 54 Gravel-Terraces of Coquimbo part ir. 
 
 facts given at Valparaiso, and lastly from the evidence 
 of a slow rising lately or still in progress here, it appears 
 to me far more probable, that the movement has been 
 slow. The existence of these successive escarpments, 
 or old cliff-lines, is in another respect highly instructive, 
 for they show periods of comparative rest in the eleva- 
 tory movement, and of denudation, which would never 
 even have been suspected from a close examination of 
 many miles of coast southward of Coquimbo. 
 
 . We come now to the terraces on the opposite sides 
 of the east and west valley of Coquimbo : the following 
 section is taken in a north and south line across the 
 valley at a point about three miles from the sea. The 
 valley measured from the edges of the escarpments of 
 the upper plain (F) (F) is about a mile in width ; but 
 from the bases of the bounding mountains it is from 
 three to four miles wide. The terraces marked with 
 an interrogative do not exist on that side of the valley, 
 but are introduced merely to render the diagram more 
 intelligible. 
 
 No. 24. 
 
 North and South Section across the Valley of Coquimbo. 
 
 
 
 
 
 South 
 
 
 B? 
 
 C 
 
 D? 
 
 E P 
 
 A 
 
 i 
 w — ' 
 
 ,/^ 
 
 Level of sea. 
 
 Vertical scale yoth of inch to 100 feet : horizontal scale much contracted : terraces 
 marked with (?) do not occur on that side of the valley, and are introduced only 
 to make the diagram more intelligible. A river and bottom-plain of valley C, E, 
 and P, on the south side of valley, are respectively, 197, 377, and 420 feet above 
 the level of the sea. 
 
 A A The bottom of the vaUey, believed to be 100 feet above the sea : it is continu- 
 ously united with the lowest plain (A) of the former section. 
 
 B This terrace higher up the valley expands considerably ; seaward it is soon lost, 
 its escarpment being united with that of (0) : it is not developed at all on the 
 south side of the valley. 
 
 C This terrace like the last, is considerably expanded higher up the valley. These 
 two terraces apparently correspond with (B) and (C ) of the foi-mer section. 
 
 D is not well developed in the line of this section ; but seaward it expands into a 
 plain : it is not present on the south side of the valley ; but it is met with, as 
 stated under the former section, a little south of the town. 
 
CHAP. IX. not Horizojital. 255 
 
 E is well developed on the south side, but absent on the north side of the valley ; 
 though not continuously united with (B) of the former section, it apparently 
 corresponds with it. 
 
 F This is the surface-plain, and is continuously united with that which stretches 
 like a fringe along the coast. In ascending the valley it gradually becomes 
 narrower, and is at last, at the distance of about ten miles from the sea, reduced 
 to a row of flat-topped patches on the sides of the mountains. None of the lower 
 terraces extend so far up the vaUey. 
 
 These five terraces are formed of shingle and sand ; 
 three of them, as marked by Capt. Basil Hall (namely, 
 B, C, and F), are much more conspicuous than the others. 
 From the marine remains copiously strewed at the 
 mouth of the valley on the lower terraces, and south- 
 ward of the town on the upper one, they are, as before 
 remarked, undoubtedly of marine origin ; but within 
 the valley, and this fact well deserves notice, at a dis- 
 tance of from only a mile and a half to three or four 
 miles from the sea, I could not find even a fragment of 
 a shelL 
 
 P: On the inclination of the terraces of Coquimho 
 ' and on the upper and hasal edges of their esca/rpments 
 not being horizontal. — The surfaces of these terraces 
 slope in a slight degree, as shown by the last two sections 
 taken conjointly, both towards the centre of the valley, 
 and seawards towards its mouth. This double or 
 diagonal inclination, which is not the same in the 
 several terraces, is, as we shall immediately see, of 
 simple explanation. There are, however, some other 
 
 points which at first appear by no means obvious 
 
 namely, first, that each terrace, taken in its whole 
 breadth from the summit-edge of one escarpment to 
 the base of that above it, and followed up the valley, is 
 not horizontal ; nor have the several terraces, when 
 followed up the valley, all the same inclination; thus 
 I found the terraces C, E, and F, measured at a point 
 about two miles from the mouth of the valley, stood 
 severally between fifty-six to seventy-seven feet higher 
 than at the mouth. Again, if we look to any one line 
 
256 Gravel-Terraces of Coquimbo part n. 
 
 of cliff or escarpment, neither its summit-edge nor its 
 base is horizontal. On the theory of the terraces having 
 been formed during a slow and equable rise of the land, 
 with as many intervals of rest as there are escarpments, 
 it appears at first very surprising that horizontal lines 
 of some kind should not have been left on the land. 
 
 The direction of the diagonal inclination in the 
 different terraces being different, — in some being direc- 
 ted more towards the middle of the valley, in others 
 more towards its mouth, — naturally follows on the 
 view of each terrace, being an accumulation of successive 
 beach-lines round bays, which must have been of dif- 
 ferent forms and sizes when the land stood at different 
 levels : for if we look to the actual beach of a narrow 
 creek, its slope is directly towards the middle ; whereas, 
 in an open bay, or slight concavity on a coast, the slope 
 is towards the mouth, that is, almost directly seaward ; 
 hence as a bay alters in form and size, so will the direc- 
 tion of the inclination of its successive beaches become 
 changed. 
 
 If it were possible to trace any one of the many 
 beach-lines, composing each sloping terrace, it would 
 of course be horizontal ; but the only lines of demarca- 
 tion are the summit and basal edges of the escarpments. 
 Now the summit-edge of one of these escarpments 
 marks the furthest line or point to which the sea has 
 cut into a mass of gravel sloping seaward ; and as the 
 sea will generally have greater power at the mouth than 
 at the protected head of a bay, so will the escarpment 
 at the mouth be cut deeper into the land, and its 
 summit-edge be higher ; consequently it will not be 
 horizontal. With respect to the basal or lower edges 
 of the escarpments, from picturing in one's mind ancient 
 bays entirely surrounded at successive periods by cliff- 
 formed shores, one's first impression is that they at least 
 
CHAP. IX. not Horizontal. 257 
 
 necessarily must be horizontal, if tlie elevation has been 
 horizontal. But here is a fallacy : for after the sea has, 
 during a cessation of the elevation, worn cliffs all round 
 the shores of a bay, when the movement recommences, 
 and especially if it recommences slowly, it might well 
 happen that, at the exposed mouth of the bay, the 
 waves might continue for some time wearing into the 
 land, whilst in the protected and upper parts successive 
 beach-lines might be accumulating in a sloping surface 
 or terrace at the foot of the cliffs which had been lately 
 reached : hence, supposing the whole line of escarpment 
 to be finally uplifted above the reach of the sea, its 
 basal line or foot near the mouth will run at a lower 
 level than in the upper and protected parts of the bay ; 
 consequently this basal line will not be horizontal. And 
 it has already been shown that the summit-edges of 
 each escarpment will generally be higher near the 
 mouth (from the seaward sloping land being there most 
 exposed and cut into) than near the head of the bay ; 
 therefore the total height of the escarpments will be 
 greatest near the mouth ; and further up the old bay 
 or valley they will on both sides generally thin out and 
 die away : I have observed this thinning out of the 
 successive escarpment at other places besides Coquimbo ; 
 and for a long time I was quite unable to understand 
 its meaning. The following rude diagram will perhaps 
 render what I mean more intelligible ; it represents a 
 bay in a district which has begun slowly rising. Before 
 the movement commenced, it is supposed that the 
 waves had been enabled to eat into the land and form 
 cliffs, as far up, but with gradually diminishing power, 
 as the points A A : after the movement had commenced 
 and gone on for a little time, the sea is supposed still to 
 have retained the power, at the exposed mouth of the 
 bay, of cutting down and into the land as it slowly 
 
 S 
 
258 Gravel-Terraces of Coquimbo part 11. 
 
 emerged ; but in the upper parts of the bay it is 
 supposed soon to have lost this power, owing to the more 
 
 No. 25. 
 
 protected situation and to the quantity of detritus 
 brought down by the river ; consequently low land was 
 there accumulated. As this low land was formed during 
 a slow elevatory movement, its surface will gently slope 
 upwards from the beach on all sides. Now, let us 
 imagine the bay, not to make the diagram more com- 
 plicated, suddenly converted into a valley : the basal 
 line of the cliffs will of course be horizontal, as far as 
 the beach is now seen extending in the diagram; but 
 in the upper part of the valley, this line will be higher, 
 the level of the district having been raised whilst the 
 low land was accumulating at the foot of the inland 
 cliffs. If, instead of the bay in the diagraui being 
 suddenly converted into a valley, we suppose with much 
 more probability it to be upraised slowly, then the 
 waves in the upper parts of the bay will continue very 
 gradually to fail to reach the cliffs, which are now in 
 the diagram represented as washed by the sea, and 
 
CHAP. IX. not Horizontal. 259 
 
 which, consequently, will be left standing higher and 
 higher above its level ; whilst at the still exposed mouth, 
 it might well happen that the waves might be enabled 
 to cut deeper and deeper, both down and into the cliffs, 
 as the land slowly rose. 
 
 The greater or lesser destroying power of the waves 
 at the mouths of successive bays, comparatively with 
 this same power in their upper and protected parts, will 
 vary as the bays become changed in form and size, and 
 therefore at different levels, at their mouths and heads, 
 more or less of the surfaces between the escarpments, 
 (that is, the accumulated beach-lines or terraces) will 
 be left undestroyed : from what has gone before we can 
 see that, according as the elevatoiy movements after 
 each cessation recommence more or less slowly, according 
 to the amount of detritus delivered by the river at the 
 heads of the successive bays, and according to the degree 
 of protection afforded by their altered forms, so will a 
 greater or less extent of terrace be accumulated in the 
 upper part, to which there will be no surface at a cor- 
 responding level at the mouth : hence we can perceive 
 why no one terrace, taken in its whole breadth and 
 followed up the valley, is horizontal, though each 
 separate beach-line must have been so; and why the 
 inclination of the several terraces, both transversely, 
 and longitudinally up the valley, is not alike. 
 
 I have entered into this case in some detail, for I 
 was long perplexed (and others have felt the same 
 difficulty) in understanding how, on the idea of an 
 equable elevation with the sea at intervals eating into 
 the land, it came that neither the terraces nor the upper 
 nor lower edges of the escarpments were horizontal. 
 Along lines of coast, even of great lengths, such as that 
 of Patagonia, if they are nearly uniformly exposed, the 
 corroding power of the waves will be checked and 
 
 s2 
 
26o G rave I- Terraces of Coqtiimbo part n. 
 
 conquered by tlie elevatory movement, as often as it 
 recommences, at about the same period ; and hence the 
 terraces, or accumulated beach-lines, will commence 
 being formed at nearly the same levels : at each suc- 
 ceeding period of rest, they will, also, be eaten into at 
 nearly the same rate, and consequently there will be a 
 much closer coincidence in their levels and inclinations, 
 than in the terraces and escarpments formed round 
 bays with their different parts very differently exposed 
 to the action of the sea. It is only where the waves 
 are enabled, after a long lapse of time, slowly to corrode 
 hard rocks, or to throw up, owing to the supply of 
 sediment being small and to the surface being steeply 
 inclined, a narrow beach or mound, that we can expect, 
 as at Glen Roy in Scotland,^ a distinct line marking an 
 old sea-level, and which will be strictly horizontal, if 
 the subsequent elevatory movements have been so : for 
 in these cases no discernible effects will be produced, 
 except during the long intervening periods of rest; 
 whereas in the case of step-formed coasts, such as those 
 described in this and the preceding chapter, the terraces 
 themselves are accumulated during the slow elevatory 
 process, the accumulation commencing sooner in pro- 
 tected than in exposed situations, and sooner where 
 there is copious supply of detritus than where there is 
 little ; on the other hand, the steps or escarpments are 
 formed during the stationary periods, and are more 
 deeply cut down and into the coast-land, in exposed 
 than in protected situations ; — the cutting action, more- 
 over, being prolonged in the most exposed parts, both 
 during the beginning and ending, if slow, of the upward 
 movement. 
 
 Although in the foregoing discussion I have assumed 
 the elevation to have been horizontal, it may be sus- 
 * 'Philosophical Transactions,' 1839, p. 39. 
 
<3HAP. IX. 710 1 Horizontal. 261 
 
 pected, from the considerable seaward slope of the 
 terraces, both up the valley of S. Cruz and up that of 
 Coquimbo, that the rising has been greater inland than 
 nearer the coast. There is reason to believe,^ from the 
 effects produced on the water- course of a mill during 
 the earthquake of 1822 in Chile, that the upheaval one 
 mile inland was nearly double, namely, between five 
 -and seven feet, to what it was on the Pacific. We know, 
 also, from the admirable researches of M. Bravais,^ that 
 in Scandinavia the ancient sea-beaches gently slope 
 from the interior mountain-ranges towards the coast, 
 ^nd that they are not parallel one to the other, showing 
 that the proportional difference in the amount of eleva- 
 tion on the coast and in the interior, varied at different 
 periods. 
 
 Goquimho to Guasco. — In this distance of ninety 
 miles, I found in almost every part marine shells up to 
 :a height of apparently from 200 to 300 feet. The 
 <iesert plain near Choros is thus covered ; it is bounded 
 by the escarpment of a higher plain, consisting of pale- 
 coloured, earthy, calcareous stone, like that of Coquimbo, 
 with the same recent shells embedded in it. In the 
 valley of Chaiieral, a similar bed occurs in which, dif- 
 ferently from that of Coquimbo, I observed many shells 
 •of the Concholepas : near Cuasco the same calcareous 
 bed is likewise met with. 
 
 In the valley of Guasco, the step-formed terraces of 
 ^avel are displayed in a more striking manner than at 
 any other point. I follow^ed the valley for thirty-seven 
 miles (as reckoned by the inhabitants) from the coast 
 to Ballenar : in nearly the whole of this distance, five 
 
 * Mr. Place, in the ' Quarterly Journal of Science,' 1824, vol. xvii. 
 p. 42. 
 
 2 ' Voyages de la Comm. du Nord,' &c. : also, ' Comptes Kendus,' 
 Oct. 1842. 
 
262 Grave I- Terraces of G tease 0. part ii, 
 
 grand terraces, running at corresponding heights on 
 both sides of the broad valley, are more conspicuous 
 than the three best developed ones at Coquimbo. They 
 give to the landscape the most singular and formal 
 aspect; and when the clouds hung low, hiding the 
 neighbouring mountains, the valley resembled in the 
 most striking manner that of Santa Oruz. The whole 
 thickness of these terraces or plains seems composed of 
 gravel, rather firmly aggregated together, with occasional 
 parting seams of clay : the pebbles on the upper plain 
 are often white-washed with an albuminous substance, 
 as in Patagonia. Near the coast I observed many sea- 
 shells on the lower plains. At Freyrina (twelve miles 
 up the valley), there are six terraces beside the bottom- 
 surface of the valley : the two lower ones are here only 
 from 200 to 300 yards in width, but higher up the 
 valley they expand into plains : the third terrace is 
 generally narrow : the fourth I saw only in one place, 
 but there it was distinct for the length of a mile : the 
 fifth is very broad : the sixth is the summit-plain, 
 which expands inland into a great basin. Not 
 having a barometer with me, I did not ascertain the 
 height of these plains, but they appeared consider- 
 ably higher than those at Coquimbo. Their width 
 varies much, sometimes being very broad, and some- 
 times contracting into mere fringes of separate flat- 
 topped projections, and then quite disappearing: at 
 the one spot, where the fourth terrace was visible, the 
 whole six terraces were cut off for a short space by one 
 single bold escarpment. Near Ballenar (thirty-seven 
 miles from the mouth of the river), the valley between 
 the summit-edges of the highest escarpment is several 
 miles in width, and the five terraces on both sides are 
 broadly developed : the highest cannot be less than 
 600 feet above the bed of the river, which itself must, 
 
CHAP. IX. Gravel-Terraces of Copiapo. 263 
 
 I conceive, be some hundred feet above tbe sea. A 
 
 north and south section across the valley in this part is 
 
 here represented. 
 
 No. 26. 
 
 North and South Section across the Valley of Guasco, and of a plain north of it. 
 Cforth. South, 
 
 "X- 
 
 Kiver of Guasco. A/ 
 
 \ 
 
 Town of Ballenar. 
 
 On the northern side of the valley the summit-plain 
 of gravel (A) has two escarpments, one facing the valley, 
 and the other a great basin-like plain (B), which 
 stretches for several leagues northward. This narrow 
 plain (A) with the double escarpment, evidently once 
 formed a spit or promontory of gravel, projecting into 
 and dividing two great bays, and subsequently was 
 worn on both sides into steep cliffs. Whether the 
 several escarpments in this valley were formed during 
 the same stationary periods with those of Coquimbo 
 I will not pretend to conjecture ; but if so, the inter- 
 vening and subsequent elevatory movements must have 
 been here much more energetic, for these plains cer- 
 tainly stand at a much higher level than do those of 
 Coquimbo. 
 
 Copiapo. — From Guasco to Copiapo, I followed the 
 road near the foot of the Cordillera, and therefore saw 
 no upraised remains. At the mouth, however, of the 
 valley of Copiapo there is a plain, estimated by Meyen ^ 
 between fifty and seventy feet in height, of which the 
 upper part consists chiefly of gravel, abounding with 
 recent shells, chiefly of the Concholepas, Venus Dombeyi, 
 and Galyptrcea trochiformis. A little inland, on a 
 plain estimated by myself at nearly 300 feet, the upper 
 
 » ♦ Eeise urn die Erde.' Th. 1. s. 372, et seq. 
 
264 Gravel-Terraces of Copiapo. part u, 
 
 stratum was formed of broken shells and sand cemented 
 by white calcareous matter, and abounding with em- 
 bedded recent shells, of which the Mulmia Byronensis 
 and Peden ])urpuratus were the most numerous. The 
 lower plain stretches for some miles southward, and for 
 an unknown distance northward, but not far up the 
 valley; its seaward face, according to Meyen, is worn 
 into caves above the level of the present beach. The 
 valley of Copiapo is much less steeply inclined and less 
 direct in its course than any other valley which I saw 
 in Chile ; and its bottom does not generally consist of 
 gravel : there are no step-formed terraces in it, except at 
 one spot near the mouth of the great lateral valley of 
 the Despoblado where there are only two, one above the 
 other : lower down the valley, in one place I observed 
 that the solid rock had been cut into the shape of a 
 beach and was smoothed over with shingle. 
 
 Northward of Copiapo, in lat. 26° S., the old voyager 
 Wafer ^ found immense numbers of sea-shells some 
 miles from the coast. At Cobija (lat. 22° 34'), M. 
 d'Orbigny observed beds of gravel and broken shells, 
 containing ten species of recent shells ; he also found, 
 on projecting points of porphyry, at a height of 300 
 feet, shells of Concholepas, Chiton, Calyptrsea, Fissurella, 
 and Patella, still attached to the spots on which they 
 had lived. M. d'Orbigny argues from this fact, that 
 the elevation must have been great and sudden : ^ to 
 
 ^ Burnett's ' Collection of Voyages,' vol. iv. p. 193. 
 
 ^ ' Voyage. Part. Geolog.' p, 9i. M. d'Orbigny (p. 98) in sum- 
 ming up, says, ' S'il est certain (as he believes) que tous les terrains 
 en pente, compris entre la mer et les montagnes sont I'ancien rivage 
 de la mer, on doit supposer, pour I'ensemble, un exhaussement qui ne 
 serait pas moindre de deux cent metres ; il faudrait supposer encore 
 que ce soulevement n'a point ete graduel ; . . . mais qu'il resulterait 
 d'une seule et meme cause fortuite,' &c. Now, on this view, when 
 the sea was forming the beach at the foot of the mountains, many 
 shells of Concholepas, Chiton, Calyptreea, Fissurella, and Patella 
 (which are known to live close to the beach), were attached to rocks 
 
CHAP. IX. Elevation of the Coast of Peru. 265 
 
 me it appears far more probable that tbe movement 
 was gradual, witb small starts as during the earth- 
 quakes of 1822 and 1835, by which whole beds of shells 
 attached to the rocks were lifted above the subsequent 
 reach of the waves. M. d'Orbigny also found rolled 
 pebbles, extending up the mountain to a height of at 
 least 600 feet. At Iquique (lat. 20° 12' S.), in a great 
 accumulation of sand, at a height estimated between 150 
 and 200 feet, I observed many large sea-shells which I 
 thought could not have been blown up by the wind to 
 that height. Mr. J. H. Blake has lately ^ described 
 these shells : he states that ' inland toward the moun- 
 tains they form a compact uniform bed, scarcely a trace 
 of the original shells being discernible; but as we 
 approach the shore, the forms become gradually more 
 distinct till we meet with the living shells on the coast.' 
 This interesting observation, showing by the gradual 
 decay of the shells how slowly and gradually the coast 
 must have been uplifted, we shall presently see fully 
 confirmed at Lima. At Arica (lat. 18" 28'), M. 
 d'Orbigny ^ found a great range of sand-dunes, four- 
 teen leagues in length, stretching towards Tacna, in- 
 cluding recent shells and bones of Cetacea, and reach- 
 ing up to a height of 300 feet above the sea. Lieut. 
 Freyer has given some more precise facts : he states ^ 
 that the Morro of Arica is about 400 feet high ; it is 
 worn into obscure terraces, on the bare rock of which 
 he found Balini and Milleporae adhering. At the 
 
 at a depth of 300 feet, and at a depth of 600 feet several of these 
 same shells were accumulating in great numbers in horizontal beds. 
 From what I have myself seen in dredging, I believe this to be 
 improbable in the highest degree, if not impossible ; and I think 
 every one who has read Prof. E, Porbes's excellent researches on the 
 subject, will without hesitation agree in this conclusion. 
 
 ' Silliman's ' Amer. Jour, of Science,' vol. xliv. p. 2. 
 
 '^ ' Voyage,' &c. p. 101. 
 
 ' In a letter to Mr. Lyell, 'Geolog. Proc' vol. ii. p. 179. 
 
266 Elevation of Lima. part n. 
 
 height of between twenty and thirty feet the shells 
 and corals were in a quite fresh state, but at fifty feet 
 they were much abraded ; there were, however, traces 
 of organic remains at greater heights. On the road 
 from Tacna to Arequipa, between Loquimbo and 
 Moquegua, Mr. M. Hamilton ^ found numerous recent 
 sea-shells in sand, at a considerable distance from the 
 sea. , 
 
 lAma. 
 
 Northward of Arica, I know nothing of the coast 
 for about a space of five degrees of latitude ; but near 
 Callao, the port of Lima, there is abundant and 
 very curious evidence of the elevation of the land. 
 The island of San Lorenzo is upwards of 1,000 feet 
 high ; the basset edges of the strata composing the 
 lower part are worn into three obscure, narrow, sloping 
 steps or ledges, which can be seen only when standing 
 on them : they probably resemble those described by 
 Lieut. Freyer at Arica. The surface of the lower ledge^ 
 which extends from a low cliff" overhanging the sea to 
 the foot of the next upper escarpment, is covered by an 
 enormous accumulation of recent shells.^ The bed is 
 level, and in some parts more than two feet in thick- 
 ness; I traced it over a space of one mile in length, 
 and heard of it in other places : the uppermost part is 
 eighty-five feet by the barometer above high-water 
 mark. The shells are packed together, but not strati- 
 fied ; they are mingled with earth and stones, and are 
 generally covered by a few inches of detritus ; they 
 rest on a mass of nearly angular fragments of the 
 underlying sandstone, sometimes cemented together by 
 
 ^ ' Edin. New Phil. Jour.' vol. xxx. p. 155. 
 
 - M. Cheyalier, in the ' Voyage of the Bonite,' observed these 
 shells; but his specimens were lost. — ' L'Institut,' 1838, p. 151.. 
 
CHAP, IX. 
 
 Elevation of Lima. 
 
 267 
 
 common salt. I collected eighteen species of shells of 
 all ages and sizes. Several of the univalves had evi- 
 dently long lain dead at the bottom of the sea, for 
 their insides were incrusted with Balani and Serpnlge. 
 All, according to Mr. G. B. Sowerby, are recent species : 
 they consist of — 
 
 1 . My tilus Mageilanicus : same as 
 
 that found at Valparaiso, and 
 there stated to be probably 
 distinct from the true 31. 
 Magellanicus of the east 
 coast. 
 
 2. Venus costellata, Sowb. 'Zool, 
 
 Proc' 
 
 3. Pecten purpuratus, Lam. 
 
 4. Chama, probably echinulata, 
 
 Brod. 
 
 5. Calyptrsea Byronensis, Gray. 
 6. radians (Trochus, 
 
 Lam.). 
 
 7. Fissurella affinis, Gray. 
 
 8. biradiata, Trembly. 
 
 9. Purpura chocolatta, Duclos. 
 
 Peruviana, Gray. 
 
 labiata, Gray. 
 
 buxea (Murex, Brod.). 
 
 Concholepas Peruviana. 
 
 Nassa, related to reticulata. 
 
 15. Triton rudis, Brod. 
 
 16. Trochus, not yet described, 
 
 but well ^ known and very 
 common. 
 17 and 18. Balanus, two species, 
 - both common on the coast. 
 
 10 
 11 
 12 
 13 
 14 
 
 These upraised shells appear to be nearly in the 
 same proportional numbers — with the exception of 
 the Crepidulge being more numerous — with those on 
 the existing beach. The state of preservation of the 
 different species differed much ; but most of them were 
 much corroded, brittle, and bleached : the upper and 
 lower surfaces of the Concholepas had generally quite 
 scaled off: some of the Trochi and Fissurellas still 
 partially retain their colours. It is remarkable that 
 these shells, taken all together, have fully as ancient an 
 appearance, although the extremely arid climate appears 
 highly favourable for their preservation, as those from 
 1,300 feet at Valparaiso, and certainly a more ancient ap- 
 pearance than those from 500 to 600 feet from Valparaiso 
 and Concepcion : at which places 1 have seen grass and 
 other vegetables actually growing out of the shells. 
 Many of the univalves here at San Lorenzo were filled 
 and united together by pure salt, probably left by the 
 
26S Fossil Remains of Human Art. part u. 
 
 evaporation of the sea-spray, as tlie land slowly emerged.* 
 On the highest parts of the ledge, small fragments of 
 the shells were mingled with, and evidently in process 
 of reduction into, a yellowish-white, soft, calcareous 
 powder, tasting strongly of salt, and in some places as 
 fine as prepared medicinal chalk. 
 
 Fossil Remains of Human Art. — In the midst of 
 these shells on San Lorenzo, I found liglit corallines, 
 the horny ovule-cases of Mollusca, roots of sea-weed,^ 
 bones of birds, the heads of Indian corn and other 
 vegetable matter, a piece of woven rushes, and another 
 of nearly decayed cotton string. I extracted these re- 
 mains by digging a hole, on a level spot ; and they had 
 all indisputably been embedded with the shells. I 
 compared the plaited rush, the cotton string, and Indian 
 €orn, at the house of an antiquary, with similar objects, 
 taken from the Huacas or burial-grounds of the ancient 
 Peruvians, and they were undistinguishable ; it should 
 be observed that the Peruvians used string only of 
 •cotton. The small quantity of sand or gravel with the 
 shells, the absence of large stones, the width and thick- 
 ness of the bed, and the time requisite for a ledge to 
 
 ' The underlying sandstone contains true layers of salt ; so that 
 the salt may possibly have come from the beds in the higher parts 
 of the island ; but I think more probably from the sea-spray. It is 
 generallj'- asserted that rain never falls on the coast of Peru ; but this 
 is not quite accurate ; for, on several days, during our visit, the so- 
 called Peruvian dew fell in sufficient quantity to make the streets 
 muddy, and it would certainly have washed so deliquescent a sub- 
 stance as salt into the soil. I state this because M. d'Orbigny, in 
 discussing an analogous subject, supposes that I had forgotten that 
 it never rains on this whole line of coast. See Ulloa's ' Voyage ' (vol. 
 ii. ' Eng. Trans,' p. 67) for an account of the muddy streets of Lima, 
 and on the continuance of the mists during the whole winter. Kain, 
 a,lso, falls at rare intervals even in the driest districts, as, for in- 
 stance, during forty days, in 1726, at Chocope (7° 46') ; this rain 
 entirely ruined ('Ulloa,' &c. p. 18) the mud-houses of the inhabi- 
 tants. 
 
 ^ Mr. Smith of Jordanhill found pieces of sea- weed in an upraised 
 pleistocene deposit in Scotland. See his admirable Paper in the 
 * Edin. New. Phil. Journal,' vol. xxv. p. 384. 
 
CHAP. IX. Fossil Remains of Htwimi Art, 269 
 
 be cut into tlie sandstone, all show that these remains 
 were not thrown high up by an earthquake-wave : on 
 the other hand, these facts, together with the number 
 of dead shells, and of floating objects, both marine and 
 terrestrial, both natural and human, render it almost 
 certain that they were accumulated on a true beach, 
 since upraised eighty-five feet, and upraised this much 
 since Lidian man inhabited Peru. The elevation 
 may have been, either by several small sudden starts, 
 or quite gradual ; in this latter case the unrolled shells 
 having been thrown up during gales beyond the reach 
 of the waves which afterwards broke on the slowly 
 emerging land. I have made these remarks, chiefly 
 because I was at first surprised at the complete differ- 
 ence in nature, between this broad, smooth, upraised 
 bed of shells, and the present shingle-beach at the foot 
 of the low sandstone-cliffs ; but a beach formed, when 
 the sea is cutting into the land, as is shown now to be 
 the case by the low bare sandstone-cliffs, ought not to 
 be compared with a beach accumulated on a gently in- 
 clined rocky surface, at a period when the sea (probably 
 owing to the elevatory movement in process) was not 
 able to eat into the land. With respect to the mass of 
 nearly angular, salt-cemented fragments of sandstone 
 which lie under the shells, and which are so unlike the 
 materials of an ordinary sea-beach ; I think it probable 
 after having seen the remarkable effects ^ of the earth- 
 quake of 1835, in absolutely shattering as if by gun- 
 powder the surface of the primary rocks near Concepcion 
 that a smooth bare surface of stone was left by the sea 
 covered by the shelly mass, and that afterwards when 
 upraised, it was superficially shattered by the severe 
 shocks so often experienced here. 
 
 * I have described these effects in my ' Journal of Researches ' p 
 303, 2nd edit., 1845. 
 
270 Fossil Earthenware near Lima, paet n. 
 
 The very low land surrounding the town of Callao, 
 is to the south joined by an obscure escarpment to a 
 hio"her plain (south of Bella Vista), which stretches 
 along the coast for a length of about eight miles. This 
 plain appears to the eye quite level ; but the sea-cliffs 
 show that its height varies (as far as I could estimate) 
 from 70 to 120 feet. It is composed of thin, sometimes 
 waving, beds of clay, often of bright red and yellow 
 colours, of layers of impure sand, and in one part with 
 a great stratified mass of granitic pebbles. These beds 
 are capped by a remarkable mass, varying from two to 
 six feet in thickness, of reddish loam or mud, containing 
 many scattered and broken fragments of recent marine 
 shells, sometimes though rarely single large round 
 pebbles, more frequently short irregular layers of fine 
 gravel, and very many pieces of red coarse earthenware, 
 which from their curvatures must once have formed 
 parts of large vessels. The earthenware is of Indian 
 manufacture; and I found exactly similar pieces acci- 
 dentally included within the bricks, of which the neigh- 
 bouring ancient Peruvian burial-mounds are built. 
 These fragments abounded in such numbers in certain 
 spots, that it appeared as if waggon-loads of earthen- 
 ware had been smashed to pieces. The broken sea- 
 shells and pottery are strewed both on the surface, and 
 throughout the whole thickness of this upper loamy 
 mass. I found them wherever I examined the cliffs, 
 for a space of between two and three miles, and for 
 half a mile inland ; and there can be little doubt that 
 this same bed extends with a smooth surface several 
 miles further over the entire plain. Besides the little 
 included irregular layers of small pebbles, there are 
 occasionally very obscure traces of stratification. 
 
 At one of the highest parts of the cliff, estimated 
 120 feet above the sea, where a little ravine came down, 
 
<!HAP. IX. Fossil Earthenware near Lima. 271 
 
 there were two sections, at right angles to each other, 
 of the floor of a shed or building. In both sections or 
 faces, two rows, one over the other, of large round stones 
 could be distinctly seen; they were packed close to- 
 gether on an artificial layer of sand two inches thick, 
 which had been placed on the natural clay-beds; the 
 round stones were covered by three feet in thickness of 
 the loam with broken sea-shells and pottery. Hence, 
 before this widely spread-out bed of loam was deposited, 
 it is certain that the plain was inhabited; and it is 
 probable, from the broken vessels being so much more 
 abundant in certain spots than in others, and from the 
 underlying clay being fitted for their manufacture, that 
 the kilns stood here. 
 
 The smoothness and wide extent of the plain, the 
 bulk of matter deposited, and the obscure traces of 
 stratification seem to indicate that the loam was de- 
 posited under water ; on the other hand, the presence 
 of sea-shells, their broken state, the pebbles of various 
 sizes, and the artificial floor of round stones, almost 
 prove that it must have originated in a rush of water 
 fi:"om the sea over the land. The height of the plain, 
 namely, 120 feet, renders it improbable that an earth- 
 quake-wave, vast as some have here been, could have 
 broken over the surface at its present level ; but when 
 the land stood eighty-five feet lower, at the period when 
 the shells were thrown up on the ledge at S. Lorenzo 
 and when as we know man inhabited this district, such 
 an event might well have occurred ; and if we may fur- 
 ther suppose, that the plain was at that time converted 
 into a temporary lake, as actually occurred, during the 
 earthquakes of 1713 and 1746, in the case of the low 
 land round Callao owing to its being encircled by a 
 high shingle- beach, all the appearances above described 
 will be perfectly explained. I must add, that at a 
 
272 Recent Subsidence near Lima. part h. 
 
 lower level near tlie point wliere tlie present low land 
 round Callao joins the higher plain, there are appear- 
 ances of two distinct deposits both apparently formed 
 by debacles : in the upper one, a horse's tooth and a 
 dog's jaw were embedded ; so that both must have been 
 formed after the settlement of the Spaniards : accord- 
 ing to Acosta, the earthquake- wave of 1586 rose eighty- 
 four feet. 
 
 The inhabitants of Callao do not believe, as far as I 
 could ascertain, that any change in level is now in pro- 
 gress. The great fragments of brickwork, which it is- 
 asserted can be seen at the bottom of the sea, and which 
 have been adduced as a proof of a late subsidence, are, 
 as I am informed by Mr. Gill, a resident engineer, 
 loose fragments; this is probable, for 1 found on the 
 beach, and not near the remains of any building, masses 
 of brickwork, three and four feet square, which had 
 been washed into their present places, and smoothed 
 over with shingle during the earthquake of 1746. The 
 spit of land, on which the ruins of Old Callao stand, is 
 so extremely low and narrow, that it is improbable in 
 the highest degree that a town should have been founded 
 on it in its present state ; and I have lately heard ^ that 
 M. Tschudi has come to the conclusion, from a com- 
 parison of old with modern charts, that the coast both 
 south and north of Callao has subsided. I have shown 
 that the island of San Lorenzo has been upraised eighty- 
 five feet since the Peruvians inhabited this country ; 
 and whatever may have been the amount of recent sub- 
 sidence, by so much more must the elevation have ex- 
 ceeded the eighty-five feet. In several places ^ in this 
 
 1 I am indebted for this fact to Dr. E. Dieffenbach. I may add 
 that there is a tradition, that the islands of San Lorenzo and Fronton 
 were once joined, and that the channel between S. Lorenzo and the 
 mainland, now above two miles in width, was so narrow that cattle 
 used to swim over. 
 
 2 ' Observaciones sobre el Clima del Lima,' par Dr. H. Unanue, 
 
CHAP. IX. Decay of Upraised Sea-Shells. 273 
 
 neisflibourliood, marks of sea-action liave been observed : 
 Ulloa gives a detailed account of such appearances at a 
 point five leagues northward of Callao : Mr. Cruikshank 
 found near Lima successive lines of sea-clifis, with 
 rounded blocks at their bases, at a height of 700 feet 
 above the present level of the sea. 
 
 On the Decay of upraised Sea-Shells. — I have 
 stated that many of the shells on the lower inclined 
 ledge or terrace of San Lorenzo are corroded in a pecu- 
 liar manner, and that they have a much more ancient 
 appearance than the same species at considerably greater 
 heights on the coast of Chile. I have, also, stated that 
 these shells in the upper part of the ledge, at the height 
 of eighty-five feet above the sea, are falling, and in 
 some parts are quite changed into a fine, soft, saline, cal- 
 careous powder. The finest part of this powder has been 
 analysed for me, at the request of Sir H. De la Beche, 
 by the kindness of Mr. Trenham Reeks of the Museum 
 of Economic Geology; it consists of carbonate of lime 
 in abundance, of sulphate and muriate of lime, and of 
 muriate and sulphate of soda. The carbonate of lime 
 is obviously derived from the shells ; and common salt 
 is so abundant in parts of the bed, that, as before 
 remarked, the univalves are often filled with it. The 
 sulphate of lime may have been derived, as has probably 
 the common salt, from the evaporation of the sea-spray, 
 during the emergence of the land ; for sulphate of lime 
 is now copiously deposited from the spray on the shores 
 of Ascension.^ The other saline bodies may perhaps 
 have been partially thus derived, but chiefly, as I con- 
 clude from the following facts, through a difierent 
 means. 
 
 p. 4. — UUoa's ' Voyage,' vol. ii. ' Eng. Trans.' p. 97.— For Mr. Cmik- 
 shank's observations, see Mr. Lyell's ' Principles of Geology' (1st 
 edit.), vol. iii. p. 130. 
 
 ' See my discussion on a calcareous incrustation in Chapter IH 
 
2 74 Decay of Upraised Sea-Shells, part n. 
 
 On most parts of the second ledge or old sea-beach, 
 at a height of 170 feet, there is a layer of white powder 
 of variable thickness, as much in some parts as two 
 inches, lying on the angular, salt-cemented fragments 
 of sandstone and under about four inches of earth, which 
 powder, from its close resemblance in nature to the 
 upper and most decayed parts of the shelly mass, I can 
 hardly doubt originally existed as a bed of shells, now 
 much collapsed and quite disintegrated. I could not 
 discover with the microscope a trace of organic structure 
 in it ; but its chemical constituents, according to Mr. 
 Reeks, are the same as in the powder extracted from 
 amongst the decaying shells on the lower ledge, with 
 the marked exception that the carbonate of lime is 
 present in only very small quantity. On the third and 
 highest ledge, I observed some of this powder in a 
 similar position, and likewise occasionally in small 
 patches at considerably greater heights near the summit 
 of the island. At Iquique, where the whole face of the 
 country is covered by a highly saliferous alluvium, and 
 where the climate is extremely dry, we have seen that, 
 according to Mr. Blake, the shells which are perfect 
 near the beach become, in ascending, gradually less 
 and less perfect, until scarcely a trace of their original 
 structure can be discovered. It is known that car- 
 bonate of lime and common salt left in a mass together,^ 
 and slightly moistened, partially decompose each other : 
 now we have at San Lorenzo and at Iquique, in the 
 shells and salt packed together, and occasionally mois- 
 
 * I am informed by Dr. Kane, through Mr. Reeks, that a manu- 
 factory was established on this principle in France, but failed from 
 the small quantity of carbonate of soda produced. Sprengel 
 ('G-ardeners' Chron.' 1845, p. 157) states, that salt and carbonate of 
 lime are liable to mutual decomposition in the soil. Sir H. De la 
 Beche informs me, that calcareous rocks, washed by the spray of the 
 sea, are often corroded in a peculiar manner ; see also on this latter 
 subject ' Gardeners' Chron.' p. 675, 1844. 
 
CHAP. IX. Recent Elevatory Movements. 275 
 
 tened by the so-called Peruvian dew, the proper elements 
 for this action. We can thus understand the peculiar 
 corroded appearance of the shells on San Lorenzo, and 
 the great decrease of quantity in the carbonate of lime 
 in the powder on the upper ledge. There is, however, 
 a great difficulty on this view, for the resultant salts 
 should be carbonate of soda and muriate of lime ; the 
 latter is present, but not the carbonate of soda. Hence 
 I am led to the j^erhaps unauthorised conjecture (which 
 I shall hereafter have to refer to) that the carbonate of 
 soda, by some unexplained means, becomes converted 
 into a sulphate. 
 
 If the above remarks be just, we are led to the very 
 unexpected conclusion, that a dry climate, by leaving 
 the salt from the sea-spray undissolved, is much less 
 favourable to the preservation of upraised shells than 
 a humid climate. However this may be, it is interest- 
 ing to know the manner in which masses of shells, 
 gradually upraised above the sea-level, decay and finally 
 disappear. 
 
 Summary on the recent Elevation of the West 
 Coast of South Ammnca. — We have seen that upraised 
 marine remains occur at intervals, and in some parts 
 almost continuously, from lat. 45° 35' to 12° S., along 
 the shores of the Pacific. This is a distance, in a north 
 and south line, of 2,075 geographical miles. From 
 Byron's observations, the elevation has no doubt extended 
 sixty miles farther south; and from the similarity in 
 the form of the country near Lima, it has probably 
 extended many leagues farther north.^ Along this 
 great line of coast, besides the organic remains, there 
 are in very many parts, marks of erosion, caves, ancient 
 
 * 1 may take this opportunity of stating that in a MS. in the 
 Geological Soc. by Mr. Weaver, it is stated that beds of oj^sters and 
 other recent shells are found thirty feet above the level of the sea, 
 in many parts of Tampico, in the Gulf of Mexico. 
 
 t2 
 
276 Rece7it Elevatory Movements, paet 11. 
 
 beaclies, sand-dunes, and successive terraces of gravel, 
 all above tlie present level of tlie sea. From the steep- 
 ness of the land on tliis side of the continent, shells 
 have rarely been found at greater distances inland than 
 from two to three leagues ; but the marks of sea-action 
 are evident farther from the coast ; for instance, in the 
 valley of Guasco, at a distance of between thirty and 
 forty miles. Judging from the upraised shells alone, 
 the elevation in Chiloe has been 350 feet, at Concepcion 
 certainly 625 feet, and by estimation 1,000 feet; at 
 Valparaiso 1,300 feet; at Ooquimbo 252 feet; north- 
 ward of this place, sea-shells have not, I believe, been 
 found above 300 feet; and at Lima they were falling 
 into decay (hastened probably by the salt) at eighty-five 
 feet. Not only has this amount of elevation taken 
 place within the period of existing Mollusca and Cir- 
 ripedes ; but their proportional numbers in the neigh- 
 bouring sea have in most cases remained the same. 
 Near Lima, however, a small change in this respect 
 between the living and the upraised was observed : at 
 Coquimbo this was more evident, all the shells being 
 existing species, but with those embedded in the upper- 
 most calcareous plain not approximating so closely in 
 proportional numbers, as do those that lie loose on its 
 surface at the height of 252 feet, and still less closely 
 than those which are strewed on the lower plains, which 
 latter are identical in proportional numbers with those 
 now cast up on the beach. From this circumstance, 
 and from not finding, upon careful examination, near 
 Coquimbo any shells at a greater height than 252 feet, 
 I believe that the recent elevation there has been much 
 less than at Valparaiso, where it has been 1,300 feet, 
 and I may add, than at Concepcion. This considerable 
 inequality in the amount of elevation at Coquimbo and 
 Valparaiso, places only 200 miles apart, is not im- 
 
CHAP. IX. a7id Action of Sea on the Land. 277 
 
 probable, considering, first, tbe diiference in the force 
 and number of the shocks now yearly affecting different 
 parts of this coast; and, secondly, the fact of single 
 areas, such as that of the province of Concepcion, having 
 been uplifted very unequally during the same earth- 
 quake. It would, in most cases, be very hazardous to 
 infer an inequality of elevation, from shells being found 
 on the surface or in superficial beds at different heights ; 
 for we do not know on what their rate of decay depends ; 
 and at Coquimbo one instance out of many has been 
 given, of a promontory, which, from the occurrence of 
 one very small collection of lime-cemented shells, has 
 indisputably been elevated 242 feet, and yet on which, 
 not even a fragment of shell could be found on careful 
 examination between this height and the beach, although 
 many sites appeared very favourable for the preservation 
 of organic remains : the absence, also, of shells on the 
 gravel-terraces a short distance up the valley of Co- 
 quimbo, though abundant on the corresponding terraces 
 at its mouth, should be borne in mind. 
 
 There are other epochs, besides that of the existence 
 of recent Mollusca, by which to judge of the changes 
 of level on this coast. At Lima, as we have just seen, 
 the elevation has been at least eighty-five feet, within 
 the Indo-human period; and since the arrival of the 
 Spaniards in 1530, there has apparently been a sinking 
 of the surface. At Valparaiso, in the course of 220 
 years, the rise must have been less than nineteen feet ; 
 but it has been as much as from ten to eleven feet in 
 the seventeen years subsequently to 1817, and of this 
 rise only a part can be attributed to the earthquake 
 of 1822, the remainder having been insensible and 
 apparently still, in 1834, in progress. At Ohiloe the 
 elevation has been gradual, and about four feet during 
 four years. At Coquimbo, also, it has been gradual, 
 
278 Recent Elevatory Movements, part n. 
 
 and in the course of 150 years has amounted to several 
 feet. The sudden small upheavals, accompanied by 
 earthquakes, as in 1822 at Valparaiso, in 1835 at Con- 
 cepcion, and in 1837 in the Chonos Archipelago, are 
 familiar to most geologists, but the gradual rising of 
 the coast of Chile has been hardly noticed ; it is, how- 
 ever, very important, as connecting together these two 
 orders of events. 
 
 The rise of Lima, having been eighty-five feet within 
 the period of man, is the more surprising if we refer to 
 the eastern coast of the continent, for at Port S. Julian, 
 in Patagonia, there is good evidence (as we shall here- 
 after see) that when the land stood ninety feet lower, 
 the Macrauchenia, a mammiferous beast, was alive ; 
 and at Baliia Blanca, when it stood only a few feet 
 lower than it now does, many gigantic quadrupeds 
 ranged over the adjoining country. But the coast of 
 Patagonia is some way distant from the Cordillera, and 
 the movement at Bahia Blanca is perhaps no ways 
 connected with this great range, but rather with the 
 tertiary volcanic rocks of Banda Oriental, and therefore 
 the elevation at these places may have been infinitely 
 slower than on the coast of Peru. All such speculations, 
 however, must be vague, for as we know with certainty 
 that the elevation of the whole coast of Patagonia has 
 been interrupted by many and long pauses, who will 
 pretend to say that, in such cases, many and long periods 
 of subsidence may not also have been intercalated ? 
 
 In many parts of the coast of Chile and Peru there 
 are marks of the action of the sea at successive heights 
 on the land, showing that the elevation has been inter- 
 rupted by periods of comparative rest in the upward 
 movement, and of denudation in the action of the sea. 
 These are plainest at Chiloe, where, in a height of about 
 500 feet, there are three escarpments, — at Coquimbo, 
 
CHAP. IX. and Action of Sea on the Land, 279 
 
 where, in a height of 364 feet, there are five, — at Guasco, 
 where there are six, of which five may perhaps cor- 
 respond with those at Ooquimbo, but if so, the subse- 
 quent and intervening elevatory movements have been 
 here much more energetic, — at Lima, where, in a height 
 of about 250 feet, there are three terraces, and others, 
 as it is asserted, at considerably greater heights. The 
 almost entire absence of ancient marks of sea-action at 
 defined levels along considerable spaces of coast, as near 
 Valparaiso and Concepcion, is highly instructive, for as 
 it is improbable that the elevation at these places alone 
 should have been continuous, we must attribute the 
 absence of such marks to the nature and form of the 
 coast-rocks. Seeing over how many hundred miles of 
 the coast of Patagonia, and on how many places on the 
 shores of the Pacific, the elevatory process has been 
 interrupted by periods of comparative rest, we may 
 conclude, conjointly with the evidence drawn from 
 other quarters of the world, that the elevation of the 
 land is generally an intermittent action. From the 
 quantity of matter removed in the formation of the 
 escarpments, especially of those of Patagonia, it appears 
 that the periods of rest in the movement, and of denu- 
 dation of the land, have generally been very long. In 
 Patagonia, we have seen that the elevation has been 
 equable, and the periods of denudation synchronous 
 over very wide spaces of coast ; on the shores of the 
 Pacific, owing to the terraces chiefly occurring in the 
 valleys, we have not equal means of judging on this 
 point ; and the very different heights of the upraised 
 shells at Coquimbo, Valparaiso, and Concepcion seem 
 directly opposed to such a conclusion. 
 
 Whether on this side of the continent the elevation, 
 between the periods of comparative rest when the 
 escarpments were formed, has been by small sudden 
 
2 8o Recent Elevatory Movements, pakt iu 
 
 starts, such as those accompanymg recent earthquakes, 
 or, as is most probable, by such starts conjointly with a 
 gradual upward movement, or by great aud sudden 
 upheavals, I have no direct evidence. But as on the 
 eastern coast, I Avas led to think, from the analogy of 
 the last hundred feet of elevation in La Plata, and from 
 the nearly equal size of the pebbles over the entire 
 width of the terraces, and from the upraised shells 
 being all littoral species, that the elevation had been 
 gradual ; so do I on this western coast, from the analogy 
 of the movements now in progress, and from the vast 
 numbers of shells now living exclusively on or close to 
 the beach, which are strewed over the whole surface of 
 the land up to very considerable heights, conclude, that 
 the movement here also has been slow and gradual, 
 aided probably by small occasional starts. We know 
 at least that at Coquimbo, where five escarpments occur- 
 in a height of 364 feet, that the successive elevations, 
 if they have been sudden, cannot have been very great. 
 It has, I think, been shown that the occasional preserva- 
 tion of shells, unrolled and unbroken, is not improbable 
 even during a quite gradual rising of the land ; and 
 their preservation, if the movement has been aided by 
 small starts, is quite conformable with what actually 
 takes place during recent earthquakes. 
 
 Judging from the present action of the sea, along 
 the shores of the Pacific, on the deposits of its own 
 accumulation, the present time seems in most places to 
 be one of comparative rest in the elevatory movement, 
 and of denudation of the land. Undoubtedly this is 
 the case along the whole great length of Patagonia. 
 At Ghiloe, however, we have seen that a narrow sloping 
 fringe, covered with vegetation, separates the present 
 sea-beach from a line of low cliffs, which the waves 
 lately reached; here, then, the land is gaining in 
 
CHAP. ix. and Action of Sea on the Land. 281 
 
 breadth and heiglit, and the present period is not one 
 of rest in the elevation and of contingent denudation ; 
 but if the rising be not prolonged at a quick rate, there 
 is every probability that the sea will soon regain its 
 former horizontal limits. I observed similar low slop- 
 ing fringes on several parts of the coast, both northward 
 of Valparaiso and near Coquimbo; but at this latter 
 place, from the change in form which the coast has 
 undergone since the old escarpments were worn, it may 
 be doubted whether the sea, acting for any length of 
 time at its present level, would eat into the land ; for 
 it now rather tends to throw up great masses of sand. 
 It is from facts such as these that I have generally used 
 the term comjywrcdwe rest^ as applied to the elevation 
 of the land; the rest or cessation in the movement 
 being comparative both with what has preceded it and 
 followed it, and with the sea's power of corrosion at 
 each spot and at each level. Near Lima, the cliff- 
 formed shores of San Lorenzo, and on the mainland 
 south of Callao, show that the sea is gaining on the 
 land ; and as we have here some evidence that its 
 surface has lately subsided or is still sinking, the periods 
 of comparative rest in the elevation and of contingent 
 denudation, may probably in many cases include periods 
 of subsidence. It is only, as was shown in detail when 
 discussing the terraces of Coquimbo, when the sea with 
 difficulty and after a long lapse of time has either 
 corroded a narrow ledge into solid rock, or has heaped 
 up on a steep surface a narrow mound of detritus, that 
 we can confidently assert that the land at that level and 
 at that period long remained absolutely stationary. In 
 the case of terraces formed of gravel or sand, although 
 the elevation may have been strictly horizontal, it may 
 well happen that no one level beach-line may be trace- 
 able, and that neither the terraces themselves nor the 
 
282 Recent Elevatory Movements, paet h. 
 
 summit nor basal edges of their escarpments may be 
 horizontal. 
 
 Finally, comparing the extent of the elevated area, 
 as deduced from the upraised recent organic remains, 
 on the two sides of the continent, we have seen that on 
 the Atlantic, shells have been found at intervals from 
 eastern Tierra del Fuego for 1,180 miles northward, 
 and on the Pacific for a space of 2,075 miles. For a 
 length of 775 miles, they occur in the same latitudes 
 on both sides of the continent. Without taking this 
 circumstance into consideration, it is probable from 
 the reasons assigned in the last chapter, that the entire 
 breadth of the continent in Central Patagonia has been 
 uplifted in mass ; but from other reasons there given, it 
 would be hazardous to extend this conclusion to La 
 Plata. From the continent being narrow in the south- 
 ernmost parts of Patagonia, and from the shells found 
 at the Inner Narrows of the Strait of Magellan, and 
 likewise far up the valley of the S. Cruz, it is probable 
 that the southern part of the western coast, which was 
 not visited by me, has been elevated within the period 
 of recent Mollusca : if so, the shores of the Pacific 
 have been continuously, recentlj'', and in a geological 
 sense synchronously upraised, from Lima for a height of 
 2,480 nautical miles southward, — a distance equal to that 
 from the Red Sea to the North Cape of Scandinavia ! 
 
28. 
 
 CHAPTER X. 
 
 ON THE PLAINS AND VALLEYS OF CHILE: — SALIFEROUS 
 SUPERFICIAL DEPOSITS. 
 
 JBasm-like plains of Chile ; their drainage, their marine origin — 
 Marks of sea-action on the eastern flanks of the Cordillera — Sloping 
 terrace-like fringes of stratified shingle within the valleys of the 
 Cordillera; their marine origin — Bonlders in the valley of the 
 Cachapual — Horizontal elevation of the Cordillera — Formation of 
 valleys — Boulders moved by earthquake-waves — Saline supei'fcial 
 deposits — Bed of 7iitrate of soda at Iquique — Saline incrustations — 
 Salt lakes of La Plata and Patagonia : purity of the salt ; its origin. 
 
 The space between tlie Cordillera and the coast of Chile is 
 on a rude average from eighty to above one hundred 
 miles in width ; it is formed, either of an almost 
 continuous mass of mountains, or more commonly of 
 several nearly parallel ranges, separated by plains ; in 
 the more southern parts of this province the mountains 
 are quite subordinate to the plains; in the northern 
 part the mountains predominate. 
 
 The basin-like plains at the foot of the Cordillera 
 are in several respects remarkable ; that on which the 
 capital of Chile stands is fifteen miles in width, in an 
 east and west line, and of much greater length in a 
 north and south line ; it stands 1,750 feet above the sea; 
 its surface appears smooth, but really falls and rises 
 in wide gentle undulations, the hollows corresponding 
 with the main valleys of the Cordillera : the striking 
 manner in which it abruptly comes up to the foot of 
 
284 Basin-like Plahis of Chile. paet ii, 
 
 this great range has been remarked by every author ^ 
 since the time of Molina. Near the Cordillera it is 
 composed of a stratified mass of pebbles of all sizes, 
 occasionally including rounded boulders : near its 
 western boundary, it consists of reddish sandy clay, 
 containing some pebbles and numerous fragments of 
 pumice, and sometimes passes into pure sand or into 
 volcanic ashes. At Podaguel, on this western side of 
 the plain, beds of sand are capped by a calcareous 
 tuff, the uppermost layers being generally hard and 
 substalagmitic, and the lower ones white and friable, 
 both together precisely resembling the beds at Co- 
 quimbo, which contain recent marine shells. Abrupt, 
 but rounded, hummocks of rock rise out of this plain : 
 those of Sta. Lucia and S. Cristoval are formed of 
 greenstone-porphyry almost entirely denuded of its 
 original covering of porphyritic claystone breccia; on 
 their summits, many fragments of rock (some of them 
 kinds not found in situ) are coated and united together 
 by a white, friable, calcareous tuff, like that found at 
 Podaguel. When this matter was deposited on the 
 summit of S. Cristoval, the water must have stood 
 946 feet ^ above the surface of the surrounding plain. 
 
 To the south this basin-like plain contracts, and 
 rising scarcely perceptibly with a smooth surface, 
 
 ^ This plain is partially separated into two basins by a range of 
 hills ; the southern half, according to Meyen (' Eeise um Erde,' Th. i. 
 8.274), falls in height, by an abrupt step, of between fifteen and twenty 
 feet. 
 
 2 Or 2,690 feet above the sea, as measured barometrically by Mr. 
 Eck. This tuff appears to the eye nearly pure ; but when placed in 
 acid it leaves a considerable residue of sand and broken crystals, 
 apparently of feldspar. Dr. Meyen (' Reise,' Th. i. s. 269) says, he 
 found a similar substance on the neighbouring hill of Dominico (and 
 I found it also on the Cerro Blanco), and he attributes it to the 
 weathering of the stone. In some places which I examined, its bulk 
 put this view o£ its origin quite out of question ; and I should much 
 doubt whether the decomposition of a porphyry would, in any case, 
 leave a crust chiefly composed of carbonate of lime. The white 
 crust, which is commonly seen on weathered feldspathic rocks, 
 does not appear to contain any free carbonate of lime. 
 
CHAP. X. B asin- like Plai7is of Chile. 285 
 
 passes througli a remarkable level gap in the moun- 
 tains, forming a true land-strait, and called the Angostura. 
 It then immediately expands into a second basin-formed 
 plain : this again to the south, contracts into another 
 land-strait, and expands into a third basin, which, how- 
 ever, falls suddenly in level about forty feet. This third 
 basin, to the south, likewise contracts into a strait, and 
 then again opens into the great plain of S. Fernando, 
 stretching so far south that the snowy peaks of the dis- 
 tant Cordillera are seen rising above its horizon as above 
 the sea. These plains, near the Cordillera, are generally 
 formed of a thick stratified mass of shingle ; ^ in other 
 parts, of a red sandy clay, often with an admixture of pu- 
 miceous matter. Although these basins are connected to- 
 gether like a necklace, in a north and south line, by smooth 
 land-straits, the streams which drain them do not all flow 
 north and south, but mostly westward, through breaches 
 worn in the bounding mountains ; and in the case of 
 the second basin, or that of Rancagua, there are two 
 distinct breaches. Each basin, moreover, is not drained 
 singly : thus, to give the most striking instance, but 
 not the only one, in proceeding southward over the 
 plain of Rancagua, we first find the water flowing 
 northward to and through the northern land-strait ; 
 then, without crossing any marked ridge or water-shed, 
 we see it flowing south-westward towards the northern 
 one of the two breaches in the western mountainous 
 boundary ; and lastly, again without any ridge, it flows 
 'towards the southern breach in these same mountains. 
 Hence the surface of this one basin-like plain, appear- 
 ing to the eye so level, has been modelled with great 
 nicety, so that the drainage, without any conspicuous 
 
 ' The plain of S. Fernando has, according to MM. Meyen and 
 Gay (' Eeise,' &c. Th. i. ss. 295 and 298), near the Cordillera, an 
 upper step-formed plain of clay, on the surface of which they found 
 numerous blocks of rocks, from two or three feet long, either lying 
 single or piled in heaps, but all arranged in nearly straight lines. 
 
286 Basin- like Plains of Chile. paet ii. 
 
 watersheds, is directed towards three openings in the 
 encircling mountains.^ The streams flowing from the 
 three southern basin-like plains, after passing through 
 the breaches to the west, unite and form the river 
 Rapel, which enters the Pacific near Navidad. I 
 followed the southernmost branch of this river, and 
 found that the basin or plain of S. Fernando is con- 
 tinuously and smoothly united with those plains, 
 which were described in the ninth chapter, as being 
 worn near the coast into successive cave-eaten escarp- 
 ments, and still nearer to the coast, as being strewed with 
 upraised recent marine remains. 
 
 I might have given descriptions of numerous other 
 plains of the same general form, some at the foot of 
 the Cordillera, some near the coast, and some half-way 
 between these points. I will allude only to one other, 
 namely, the plain of Uspallata, lying on the eastern 
 or opposite side of the Cordillera, between that great 
 range and the parallel lower range of Uspallata. 
 According to Miers, its surface is 6,000 feet above the 
 level of the sea : it is from ten to fifteen miles in 
 width, and is said to extend with an unbroken surface 
 for 180 miles northwards: it is drained by two rivers 
 passing through breaches in the mountains to the east. 
 On the banks of the E. Mendoza it is seen to be 
 composed of a great accumulation of stratified shingle, 
 estimated at 400 feet in thickness. In general appear- 
 ance, and in numerous points of structure, this plain 
 closely resembles those of Chile. 
 
 The origin and manner of formation of the thick 
 beds of gravel, sandy clay, volcanic detritus, and cal- 
 careous tufiP, composing these basin-like plains, is very 
 
 1 It appears from Capt. Herbert's account of the Diluvium of the 
 Himalaya (' Gleanings of Science,' Calcutta, vol. ii. p. 164), that 
 precisely similar remarks apply to the drainage of the plains or 
 valleys between those great mountains. 
 
CHAP. X. Basin- like Plains of Chile. 287 
 
 important ; because, as we shall presently show, they 
 send arms or fringes far up the main valleys of the 
 Cordillera. Many of the inhabitants believe that these 
 plains were once occupied by lakes, suddenly drained ; 
 but I conceive that the number of the separate breaches 
 at nearly the same level in the mountains surrounding 
 them, quite precludes this idea. Had not such distin- 
 guished naturalists as MM. Meyen and Gay stated 
 their belief that these deposits were left by great 
 debacles rushing down from the Cordillera, I should 
 not have noticed a view, which appears to me from 
 many reasons improbable in the highest degree — 
 namely, from the vast accumulation of ivell-rounded 
 pebbles — their frequent stratification with layers of 
 sand — the overlying beds of calcareous tuff — this same 
 substance coating and uniting the fragments of rock 
 on the hummocks in the plain of Santiago — and lastly 
 even from the worn, rounded, and much denuded state 
 of these hummocks, and of the headlands which pro- 
 ject from the surrounding mountains. On the other 
 hand, these several circumstances, as well as the con- 
 tinuous union of the basins at the foot of the Cor- 
 dillera, with the great plain of the Eio Eapel which 
 still retains the marks of sea-action at various levels, 
 and their general similarity in form and composition 
 with the many plains near the coast, which are either 
 similarly marked or are strewed with upraised marine 
 remains, fully convince me that the mountains bound- 
 ing these basin-plains were breached, their islet-like 
 projecting rocks worn, and the loose stratified detritus 
 forming their now level surfaces deposited, by the sea, 
 as the land slowly emerged. It is hardly possible to 
 state too strongly the perfect resemblance in outline be- 
 tween these basin-like, long, and narrow plains of Chile, 
 (especially when in the early morning the mists hang- 
 
288 Basin- like Plains of Chile. part n. 
 
 ing low represented water,) and the creeks and fiords 
 now intersecting tlie southern and western scores of 
 the continent. We can on this view of the sea, when 
 the land stood lower, having long and tranquilly 
 occupied the spaces between the mountain-ranges, un- 
 derstand how the boundaries of the separate basins 
 were breached in more than one place; for we see that 
 this is the general character of the inland bays and 
 channels of Tierra del Fuego ; we there, also, see in 
 the sawing action of the tides, which flow with great 
 force in the cross channels, a power sufficient to keep 
 the breaches open as the land emerged. We can 
 further see that the waves would naturally leave the 
 smooth bottom of each great bay or channel as it be- 
 came slowly converted into land, gently inclined to as 
 many points as there were mouths, through which the 
 sea finally retreated, thus forming so many water-sheds, 
 without any marked ridges, on a nearly level surface. 
 The absence of marine remains in these high inland 
 plains cannot be properly adduced as an objection to 
 their marine origin : for we may conclude, from shells not 
 being found in the great shingle beds of Patagonia, 
 though copiously strewed on their surfaces, and from 
 many other analogous facts, that such deposits are 
 eminently unfavourable for the embedment of such 
 remains ; and with respect to shells not being found 
 strewed on the surface of these basin-plains, it was 
 shown in the last chapter that remains thus exposed in 
 time decay and disappear. 
 
 1 observed some appearances on the plains at the 
 eastern and opposite foot of the Cordillera which are 
 worth notice, as showing that the sea there long acted 
 at nearly the same level as on the basin-plains of Chile. 
 The mountains on this eastern side are exceedingly 
 abrupt; they rise out of a smooth, talus-like, very 
 
CHAP. X. Sea-action at Eastern Foot of Andes. 289 
 
 gentle, slope, from live to ten miles in width (as repre- 
 sented in the following diagram), entirely composed of 
 
 No. 27. 
 Section of tlie Plain at the Eastern Foot of the Chilian Cordillera. 
 
 Cordillera. Talus-plain. Level surface, Gravel 
 
 2,700 feet above sea. terraces. 
 
 perfectly rounded pebbles, often white-washed with an 
 aluminous substance like decomposed feldspar. This 
 sloping plain or talus blends into a perfectly flat space 
 a few miles in width, composed of reddish impure clay, 
 with small calcareous concretions as in the Pampean 
 deposit, — of fine white sand with small pebbles in 
 layers, — and of the above-mentioned white aluminous 
 earth, all interstratified together. This flat space runs 
 as far as Mendoza, thirty miles northward, and stands 
 probably at about the same height, namely, 2,700 feet 
 (Pentland and Miers) above the sea. To the east it 
 is bounded by an escarpment, eighty feet in height 
 running for many miles north and south, and composed 
 of perfectly round pebbles, and loose, white-washed or 
 embedded in the aluminous earth : behind this escarp- 
 ment there is a second and similar one of gravel. 
 Northward of Mendoza, these escarpments become 
 broken and quite obliterated; and it does not appear that 
 they ever enclosed a lake-like area : I conclude, there- 
 fore, that they were formed by the sea, when it reached 
 the foot of the Cordillera, like the similar escarpments 
 occurring at so many points on the coasts of Chile and 
 Patagonia. 
 
 The talus-like plain slopes up with a smooth 
 surface into the great dry valleys of the Cordillera. On 
 each hand of the Portillo valley, the mountains are 
 
 U 
 
290* Sloping Tei'races of Gravel paet n 
 
 formed of red granite, mica-slate, and basalt, which all 
 have suffered a truly astonishing amount of denudation ; 
 the gravel in the valley, as well as on the talus-like 
 plain in front of it, is composed of these rocks ; but at 
 the mouth of the valley, in the middle (height proba- 
 bly about 3,500 feet above the sea), a few small isolated 
 hillocks of several varieties of porphyry project, round 
 which, on all sides, smooth and often white-washed 
 pebbles of these same porphyries, to the exclusion of 
 all others, extend to a circumscribed distance. Now, 
 it is difficult to conceive any other agency, except the- 
 quiet and long- continued action of the sea on thes& 
 hillocks, which could have rounded and white-washed 
 the fragments of porphyry, and caused them to radiate 
 from such small and quite insignificant centres, in the 
 midst of that vast stream of stones which has descended 
 from the main Cordillera. 
 
 Slojying Terraces of Gravel in the Valleys of the 
 Cordillera. — All the main valleys on both flanks of the 
 Chilian Cordillera have formerly had, or still have, their 
 bottoms filled up to a considerable thickness by a mass 
 of rudely stratified shingle. In central Chile, the 
 greater part of this mass has been removed by the 
 torrents ; cliff-bounded fringes, more or less continuous, 
 being left at corresponding heights on both sides of 
 the valleys. These fringes, or as they may be called 
 terraces, have a smooth surface, and as the valleys rise, 
 they gently rise with them : hence they are easily irri- 
 gated, and afford great facilities for the construction of 
 the roads. From their uniformity, they give a re- 
 markable character to the scenery of these grand, wild, 
 broken valleys. In width, the fringes vary much, 
 sometimes being only broad enough for the roads, and 
 sometimes expanding into narrow plains. Their sur- 
 faces, besides gently rising up the valley, are slightly 
 
CHAP. X, in the Valleys of the Cordillei^a. 291 
 
 inclined towards its centre in such a manner as to 
 show that the whole bottom must once have been filled 
 up with a smooth and slightly concave mass, as still are 
 the dry unfurrowed valleys of northern Chile. Where 
 two valleys unite into one, these terraces are particu- 
 larly well exhibited, as is represented in the following 
 diagram. The thickness of the gravel forming these 
 
 Xo. 28. 
 
 \Ri\Qr} 
 
 G-round-plan of a bifurcating valley in the Cordillera, bordered by smooth, sloping 
 gravel-fringes (A A A), worn along the course of the river into cliffs. 
 
 fringes, on a rude average, may be said to vary from 
 thirty to sixty or eighty feet ; but near the mouths of 
 the valleys it was in several places from 200 to 300 
 feet. The amount of matter removed by the torrents 
 has been immense; yet in the lower parts of the 
 valleys the terraces have seldom been entirely worn 
 away on either side, nor has the solid underlying rock 
 been reached : higher up the valleys, the terraces have 
 frequently been removed on one or the other side, and 
 sometimes on both sides ; but in this latter case they 
 re-appear after a short interval on the line, which they 
 Avould have held had they been unbroken. Where the 
 
 u 2 
 
292 Sloping Terraces of Gravel part n. 
 
 solid rock has been reached, it has been cut into deep 
 and narrow gorges. Still higher up the valleys, the 
 terraces gradually become more and more broken, 
 narrower, and less thick, until, at a height of from 
 7,000 to 9,000 feet, they become lost, and blended with 
 the piles of fallen detritus. 
 
 I carefully examined in many places the state of the 
 gravel, and almost everywhere found the pebbles equally 
 and perfectly rounded, occasionally with great blocks 
 of rock, and generally distinctly stratified, often with 
 parting seams of sand. The pebbles were sometimes 
 coated with a white aluminous, and less frequently with 
 a calcareous, crust. At great heights up the valleys, 
 the pebbles become less rounded; and as the terraces 
 become obliterated, the whole mass passes into the 
 nature of ordinary detritus. I was repeatedly struck 
 with the great difference between this detritus high up 
 the valleys, and the gravel of the terraces low down, 
 namely, in the greater number of the quite angular 
 fragments in the detritus, — in the unequal degree to 
 which the other fragments have been rounded, — in the 
 quantity of associated earth, — in the absence of stratifi- 
 cation, — and in the irregularity of the upper surfaces. 
 This difference was likewise well shown at points low 
 down the valleys, where precipitous ravines, cutting 
 through mountains of highly coloured rock, have thrown 
 down wide, fan-shaped accumulations of detritus on the 
 terraces : in such cases, the line of separation between 
 the detritus and the terrace could be pointed out to 
 within an inch or two ; the detritus consisting entirely 
 of angular and only partially rounded fragments of the 
 adjoining coloured rocks ; the stratified shingle (as I 
 ascertained by close inspection, especially in one case, 
 in the valley of the R. Mendoza) containing only a 
 
CHAP. X. in the Valleys of the Cordillera. 293 
 
 small proportion of these fragments, and those few well 
 rounded. 
 
 I particularly attended to the appearance of the 
 terraces where the valleys made abrupt and considerable 
 bends, but I could perceive no difference in their struc- 
 ture : they followed the bends with their usual nearly 
 equable inclination. I observed, also, in several 
 valleys, that wherever large blocks of any rock became 
 numerous, either on the surface of the terrace or em- 
 bedded in it, this rock soon appeared higher up in situ : 
 thus I have noticed blocks of porphyry, of andesitic 
 syenite, of porphyry and of syenite, alternately becoming 
 numerous, and in each case succeeded by mountains 
 thus constituted. There is, however, one remarkable 
 exception to this rule ; for along the valley of the 
 Cachapual, M. Gay found numerous large blocks of 
 white granite, which does not occur in the neighbour- 
 hood : I observed these blocks, as well as others of 
 andesitic syenite (not occurring here in situ)^ near the 
 baths of Cauquenes at a height of between 200 and 300 
 feet above the river, and therefore quite above the 
 terrace or fringe which borders that river ; some miles 
 higher up the valleys there were other blocks at about 
 the same height : I also noticed, at a less height, just 
 above the terrace, blocks of porphyries (apparently not 
 found in the immediately impending mountains), 
 arranged in rude lines, as on a sea-beach. All these 
 blocks were rounded, and though large, not gigantic, 
 like the true erratic boulders of Patagonia and Fuegia 
 M. Gay ^ states that granite does not occur in situ 
 within a distance of twenty leagues; I suspect, for 
 several reasons, that it will ultimatelv be found at a 
 
 ^ • Annales des Scienc. Nat.' (I. series, torn. 28). M. Gay, as I 
 was informed, penetrated the Cordillera by the great obhque valley 
 of Los Cupressos, and not by the most direct line. 
 
294 Sloping Terraces of Gravel : paet it. 
 
 mucli less distance, though certainly not in the imme- 
 diate neighbourhood. The boulders found by MM. 
 Meyen and Gay on the upper plain of S. Fernando 
 (mentioned in a previous note) probably belong to this 
 same class of phenomena. 
 
 These fringes of stratified gravel occur along all the 
 great valleys of the Cordillera, as well as along their 
 main branches ; they are strikingly developed in the 
 valleys of the Maypti, Mendoza, Aconcagua, Gachapual, 
 and according to Meyen,^ in the Tinguirica. In the 
 valleys, however, of northern Chile, and in some on the 
 eastern flank of the Cordillera, as in the Portillo 
 Valley, where streams have never flowed, or are quite 
 insignificant in volume, the presence of a mass of 
 stratified gravel can be inferred only from the smooth 
 slightly concave form of the bottom. One naturally 
 seeks for some explanation of so general and striking a 
 phenomenon ; that the matter forming the fringes 
 along the valleys, or still filling up their entire beds, 
 has not fallen from the adjoining mountains like 
 common detritus, is evident from the complete con- 
 trast in every respect between the gravel and the piles 
 of detritus, whether seen high up the valleys on their 
 sides, or low down in front of the more precipitous 
 ravines ; that the matter has not been deposited by 
 debacles, even if we could believe in debacles having 
 rushed down Qverij valley, and all their branches, east- 
 ward and westward from the central pinnacles of the 
 Cordillera, we must admit from the following reasons, 
 — from the distinct stratification of the mass, — its 
 smooth upper surface, — the well-rounded and some- 
 times encrusted state of the pebbles, so diff"erent from 
 the loose debris on the mountains, — and especially from 
 the terraces preserving their uniform inclination round 
 » ' Eeise,' &c. Th. I. s. 302. 
 
CHAP. X. their Marine Oidgin. 295 
 
 the most abrupt bends. To suppose that as the land 
 now stands, the rivers deposited the shingle along the 
 course of every valley, and all their main branches, 
 appears to me preposterous, seeing that these same 
 rivers not only are now removing and have removed 
 much of this deposit, but are everywhere tending to cut 
 deep and narrow gorges in the hard underlying rocks. 
 
 I have stated that these fringes of gravel, the origin 
 of which is inexplicable on the notion of debacles or 
 of ordinary alluvial action, are directly continuous with 
 the similarly-composed basin-like plains at the foot of 
 the Cordillera, which, from the several reasons before 
 assigned, I cannot doubt were modelled by the agency 
 of the sea. Now if we suppose that the sea formerly 
 occupied the valleys of the Chilian Cordillera, in pre- 
 cisely the same manner as it now does in the more 
 southern parts of the continent, where deep winding 
 creeks penetrate into the very heart of, and in the case 
 of Obstruction Sound quite through, this great range ; 
 and if we suppose that the mountains were upraised in 
 the same slow manner as the eastern and western coasts 
 have been upraised within the recent period, then the 
 origin and formation of these sloping, terrace-like fringes 
 of gravel can be simply explained. For every part of 
 the bottom of each valley will, on this view, have long 
 stood at the head of a sea-creek, into which the then 
 existing torrents will have delivered fragments of rocks, 
 where, by the action of the tides, they will have been 
 rolled, sometimes encrusted, rudely stratified, and the 
 whole surface levelled by the blending together of the 
 successive beach lines.^ As the land rose, the torrents 
 
 ^ Sloping terraces of precisely similar structure have been de- 
 scribed by me (' Philosoph. Transactions,' 1839, p. 58) in the valleys 
 of Lochaber in Scotland, where, at higher levels, the parallel roads 
 of Glen Eoy show the marks of the long and quiet residence of a 
 glacial lake. I have no doubt that sloping terraces would have been 
 
296 Sloping Terraces of G^^ave I : part n. 
 
 in every valley will liave tended to have removed the 
 matter which jnst before had been arrested on, or near, 
 the beach-lines ; the torrents, also, having continued 
 to gain in force by the continued elevation increasing 
 their total descent from their sources to the sea. This 
 slow rising of the Cordillera, which explains so well the 
 otherwise inexplicable origin and structure of the ter- 
 races, judging from all known analogies, will probably 
 have been interrupted by many periods of rest ; but we 
 ought not to expect to find any evidence of these periods 
 in the structure of the gravel-terraces : for, as the waves 
 at the heads of deep creeks have little erosive power, so 
 the only ejffect of the sea having long remained at the 
 same level will be that the upper parts of the creeks 
 will have become filled up at such periods to the level 
 of the water with gravel and sand ; and that afterwards 
 the rivers will have thrown down on the filled-up parts 
 a talus of similar matter, of which the inclination (as 
 at the head of a partially filled-up lake) will have been 
 determined by the supply of detritus, and the force of 
 the stream.^ Hence, after the final conversion of the 
 creeks into valleys, almost the only difference in the 
 terraces at those points at which the sea stood long, will 
 be a somewhat more gentle inclination, with river-worn 
 instead of sea- worn detritus on the surface. 
 
 I know of only one difficulty on the foregoing view, 
 namely, the far-transported blocks of rock high on the 
 sides of the valley of the Cachapual : I will not attempt 
 any explanation of this phenomenon, but I may state 
 
 present in the vallej's of most of the European ranges, had not 
 every trace of them, and all wrecks of sea-action, been swept away 
 by the glaciers which have since occupied them. I have shown that 
 this is the case with the mountains (' London and Edin. Phil. 
 Journal,' vol. xxi. p. 187) of North Wales. 
 
 ' I have attempted to explain this process in a more detailed 
 manner, in a letter to Mr, Maclaren, published in the ' Edinburgh 
 New Phil. Journal,' vol. xxxv. p. 288. 
 
CHAP. X. their Marine Origin. 297 
 
 my belief that a mountain -ridge near the Baths of Cau- 
 quenes has been upraised long subsequently to all the 
 other ranges in the neighbourhood, and that when this 
 was effected the whole face of the country must have 
 been greatly altered. In the course of ages, moreover, 
 in this and other valleys, events may have occurred like, 
 but even on a grander scale than, that described by 
 Molina,^ when a slip during the earthquake of 1762 
 banked up for ten days the great river Lontue, which 
 then bursting its barrier ' inundated the whole country,' 
 and doubtless transported many great fragments of rock. 
 Finally, notwithstanding this one case of difficulty, I 
 cannot entertain any doubt, that these terrace-like 
 fringes, which are continuously united with the basin- 
 shaped plains at the foot of the Cordillera, have been 
 formed by the arrestment of river-borne detritus at 
 
 1 ' Compendio de la Hist.' &c. &c. t. 1. p. 30. M. Brongniart, in 
 Ms report on M. Gay's labours ('Annales des Sciences,' 1833) con- 
 siders that the boulders in the Cachapual belong- to the same class 
 with the erratic boulders of Europe. As the blocks which I saw are 
 not gigantic, and especially as they are not angular, and as they 
 have not been transported fairly across low spaces or wide valleys, 
 I am unwilling to class them with those, which, both in the northern 
 and southern hemisphere (' Geolog. Transac' vol. vi. p. 415), have 
 been transported by ice. It is to be ho]oed, that when M. Gay's long- 
 continued and admirable labours in Chile are published, more light 
 will be thrown on this subject. However, the boulders may have 
 been primarily transported ; the final position of those of porphyry, 
 which have been described as arranged at the foot of the mountain 
 in rude lines, I cannot doubt, has been due to the action of waves 
 on a beach. The valley of the Cachapual, in the part where the 
 boulders occur, bursts through the high ridge of Cauquenes, which 
 runs parallel to, but at some distance from, the Cordillera. This 
 ridge has been subjected to excessive violence ; trachytic lava has 
 burst from it, and hot springs yet flow at its base. Seeing the 
 enormous amount of denudation of solid rock in the upper and much 
 broader parts of this valley where it enters the Cordillera, and see- 
 ing to what extent the ridge of Cauquenes now protects the great 
 range, I could not help believing (as alluded to in the text) that 
 this ridge with its trachytic eruptions had been thrown up at a much 
 later period than the Cordillera. If this has been the case, the 
 boulders, after having been transported to a low level by the 
 torrents (which exhibit in every valley proofs of their power of 
 moving great fragments), may have been raised up to their present 
 height, with the land on which they rested. 
 
298 Formation of Valleys, part n. 
 
 successive levels, in the same manner as we see now 
 taking place at the heads of all those many, deep, 
 winding fiords intersecting the southern coasts. To my 
 mind, this has been one of the most important con- 
 clusions to which my observations on the geology of 
 South America have led me ; for we thus learn that one 
 of the grandest and most symmetrical mountain-chains 
 in the world, with its several parallel lines,^ have been 
 together uplifted in mass between 7,000 and 9,000 
 feet, in the same gradual manner as have the eastern 
 and western coasts within the recent period. 
 
 Formation of Valleys. 
 
 The bulk of solid rock which has been removed in 
 the lower parts of the valleys of the Cordillera has been 
 enormous ; it is only by reflecting on such cases as that 
 of the gravel beds of Patagonia, covering so many thou- 
 sand square leagues of surface, and which if heaped into 
 a ridge, would form a mountain-range, almost equal to 
 the Cordillera, that the amount of denudation becomes 
 credible. The valleys within this range, often follow 
 
 * I do not wish to affirm that all the lines have been uplifted 
 quite equally ; slight differences in the elevation would leave no 
 perceptible effect on the terraces. It may, however, be inferred, 
 perhaps with one exception, that since the period when the sea 
 occupied these valleys, the several ranges have not been dislocated 
 by great and abrupt faults or upheavals ; for if such had occurred, 
 the terraces of gravel at these points would not have been conti- 
 nuous. The one exception is at the lower end of a plain in the Valle 
 del Yeso (a branch of the Maypu), where, at a great height, the 
 terraces and valley appear to have been broken through by a line of 
 upheaval, of which the evidence is plain in the adjoining mountains ; 
 this dislocation, perhaps, occurred after the elevation of this part of 
 the valley above the level of the sea. The valley here is almost 
 blocked up by a pile above 1,000 feet in thickness, formed, as far as 
 I could judge, from three sides, entirely, or at least in chief part, of 
 gravel and detritus. On the south side, the river has cut quite 
 through this mass ; on the northern side, and on the very summit 
 deep ravines, parallel to the line of the valley, are worn, as if the 
 drainage from the valley above had passed by these two lines before 
 following its present course. 
 
€HAP. X. Formation of Valleys. 299 
 
 anticlinal but rarely synclinal lines ; that is, the strata 
 on the two sides more often dip from the line of valley 
 than towards it. On the flanks of the range, the valleys 
 most frequently run neither along anticlinal nor syn- 
 clinal axes, but along lines of flexure or faults ; that is, 
 the strata on both sides dip in the same direction, but 
 with different, though often only slightly different, 
 inclinations. As most of the nearly parallel ridges 
 which together form the Cordillera run approximately 
 north and south, the east and west valleys cross them 
 in zig-zag lines, bursting through the points where the 
 strata have been least inclined. No doubt the greater 
 part of the denudation was affected at the periods when 
 tidal creeks occupied the valleys, and when the outer 
 flanks of the mountains were exposed to the full force 
 of an open ocean. I have already alluded to the power 
 of the tidal action in the channels connecting great 
 bays ; and I may here mention that one of the surveying 
 vessels in a channel of this kind, though under sail, 
 was whirled round and round by the force of the current. 
 We shall hereafter see, that of the two main ridges 
 forming the Chilian Cordillera, the eastern and loftiest 
 one, owes the greater part of its angular upheaval to a 
 period subsequent to the elevation of the western ridge ; 
 and it is likewise probable that many of the other 
 parallel ridges have been angularly upheaved at different 
 periods ; consequently many parts of the surfaces of 
 these mountains must formerly have been exposed to 
 the full force of the waves, which, if the Cordillera 
 were now sunk into the sea, would be protected by 
 parallel chains of islands. The torrents in the valleys 
 certainly have great power in wearing the rocks ; as 
 could be told by the dull rattling sound of the many 
 fragments night and day hurrying downwards ; and as 
 was attested by the vast size of certain fragments, which 
 
300 Formation of Valleys. paet n. 
 
 I was assured liad been carried onwards during floods ; 
 yet we have seen in the lower parts of the valleys, that 
 the torrents have seldom removed all the sea-checked 
 shingle forming the terraces, and have had time since 
 the last elevation in mass only to cut in the under- 
 lying rocks, gorges, deep and narrow, but quite insigni- 
 ficant in dimensions compared with the entire width 
 and depth of the valleys. 
 
 Along the shores of the Pacific, I never ceased 
 during my many and long excursions to feel astonished 
 at seeing every valley, ravine, and even little inequality 
 of surface, both in the hard granitic and soft tertiary 
 districts, retaining the exact outline, which they had 
 when the sea left their surfaces coated with organic 
 remains. When these remains shall have decayed, 
 there will be scarcely any difference in appearance be- 
 tween this line of coast-land and most other countries, 
 which we are accustomed to believe have assumed their 
 present features chiefly through the agency of the 
 weather and fresh- water streams. In the old granitic 
 districts, no doubt it would be rash to attribute all the 
 modifications of outline exclusively to the sea-action; 
 for who can say how often this lately submerged coast 
 may not previously have existed as land, worn by run- 
 ning streams and washed by rain ? This source of doubt, 
 however, does not apply to the districts superficially 
 formed of the modern tertiary deposits. The valleys 
 worn by the sea, through the softer formations, both on 
 the Atlantic and Pacific sides of the continent, are 
 generally broad, winding, and flat-bottomed : the only 
 district of this nature now penetrated by arms of the 
 sea, is the Island of Chiloe. 
 
 Finally, the conclusion at which I have arrived, 
 with respect to the relative powers of rain and sea water 
 on the land, is, that the latter is far the most efficient 
 
CHAP. X. Formation of Valleys. 301 
 
 agent, and that its chief tendency is to widen the 
 valleys; whilst torrents and rivers tend to deepen them, 
 and to remove the wreck of the sea's destroying action. 
 As the waves have more power, the more open and ex- 
 posed the space may be, so will they always tend to 
 widen more and more the mouths of valleys compared 
 with their upper parts : hence, doubtless, it is, that 
 most valleys expand at their mouths, — that part, at 
 which the rivers flowing in them, generally have the 
 least wearing power. 
 
 When reflecting on the action of the sea on the 
 land at former levels, the eff*ect of the great waves, 
 which generally accompany earthquakes, must not be 
 overlooked : few years pass without a severe earthquake 
 occurring on some part of the west coast of South 
 America ; and the waves thus caused have great power. 
 At Concepcion, after the shock of 1835, I saw large 
 slabs of sandstone, one of which was six feet long, three 
 in breadth, and two in thickness, thrown high up on 
 the beach ; and from the nature of the marine animals 
 still adhering to it, it must have been torn up from a 
 considerable depth. On the other hand, at Callao, the 
 recoil-wave of the earthquake of 1746 carried great 
 masses of brickwork, between three and four feet square, 
 some way out seaward. During the course of ages, the 
 effect thus produced at each successive level, cannot 
 have been small ; and in some of the tertiary deposits 
 on this line of coast, I observed great boulders of 
 granite and other neighbouring rocks, embedded in 
 fine sedimentary layers, the transportal of which, except 
 by the means of earthquake-waves, always appeared to 
 me inexplicable. 
 
302 Stiperficial Saline Deposits. part ir. 
 
 Superficial Saline Deposits. 
 
 This subject may be here conveniently treated of: 
 I will begin with the most interesting case, namely, 
 the superficial saline beds near Iquique in Peru. The 
 porphyritic mountains on the coast rise abruptly to a 
 height of between 1,900 and 3,000 feet: between their 
 summits and an inland plain, on which the celebrated 
 deposit of nitrate of soda lies, there is a high undulatory 
 district, covered by a remarkable superficial saliferous 
 crust, chiefly composed of common salt, either in white, 
 hard, opaque nodules, or mingled with sand, in this 
 latter case forming a compact sandstone. This sali- 
 ferous superficial crust extends from the edge of the 
 coast-escarpment, over the whole face of the country ; 
 but never attains, as I am assured by Mr. Bollaert 
 (long resident here) any great thickness. Although a 
 very slight shower falls only at intervals of many years, 
 yet small funnel-shaped cavities show that the salt has 
 been in some parts dissolved.^ In several places I saw 
 large patches of sand, quite moist, owing to the quan- 
 tity of muriate of lime (as ascertained by Mr. T. Reeks) 
 contained in them. From the compact salt-cemented 
 sand being either red, purplish, or yellow, according 
 to the colour of the rocky strata on which it rested, 
 I imagined that this substance had probably been 
 derived through common alluvial action from the layers 
 of salt which occur interstratified in the surrounding 
 mountains : but from the interesting details given by 
 
 1 It is singular how slowly, according to the observations of M, 
 Cordier on the salt-mountain of Cardona in Spain (' Ann. des Mines, 
 Transl. of Geolog. Mem.' by De la Beche, p. 60), salt is dissolved, 
 where the amount of rain is supposed to be as much as 31-4 of an 
 inch in the jeax. It is calculated that only five feet in thickness is 
 dissolved in the course of a centurv. 
 
CHAP. X. Saline Beds at Iqtdqite. 303 
 
 M. d'Orbigny, and from finding on a fresh examination 
 of this agglomerated sand, that it is not irregularly 
 cemented, but consists of thin layers of sand of different 
 tints of colour, alternating with excessively fine paral- 
 lel layers of salt, I conclude that it is not of alluvial 
 origin. M. d'Orbigny ^ observed analogous saline beds 
 extending from Cobija for five degrees of latitude 
 northward, and at heights varying from 600 to 900 
 feet : from finding recent sea-shells strewed on these 
 saliferous beds, and under them, great, well-rounded 
 blocks, exactly Hke those on the existing beach, he 
 believes that the salt, which is invariably superficial, 
 has been left by the evaporation of the sea-water. This 
 same conclusion must, I now believe, be extended to 
 the superficial saliferous beds of Iquique, though they 
 stand about 3,000 feet above the level of the sea. 
 
 Associated with the salt in the superficial beds, 
 there are numerous, thin, horizontal layers of impure, 
 dirty- white, friable, gypseous and calcareous tuffs. The 
 gypseous beds are very remarkable, from abounding 
 with, so as sometimes to be almost composed of, irregu- 
 lar concretions, from the size of an q^^ to that of a 
 man's head, of very hard, compact, heavy gypsum, in 
 the form of anhydrite. This gypsum contains some 
 foreign particles of stone; it is stained, judging from 
 its action with borax, with iron, and it exhales a strong 
 aluminous odour. The surfaces of the concretions are 
 
 ^ ' Voyage,' &c. p. 102, M. d'Orbigny found this deposit inter- 
 sected, in many places, by deep ravines, in which there was no salt. 
 Streams must once, though historically unknown, have flowed in 
 them ; and M. d'Orbigny argues from the presence of undissolved 
 salt over the whole surrounding country, that the streams must have 
 arisen from rain or snow having fallen, not in the adjoining country, 
 but on the now arid Cordillera. I may remark, that from having 
 observed ruins of Indian buildings in absolutely sterile parts of the 
 Chilian Cordillera (' Journal,' 2nd edit. p. 357), I am led to believe 
 that the climate, at a time when Indian man inhabited this part of 
 the continent, was in some slight degree more humid than it is at 
 present . 
 
304 Nitrate of Soda. part h. 
 
 marked by sharp, radiating, or bifurcating ridges, as if 
 they bad been (but not really) corroded : internally 
 they are penetrated by brandling veins (like those of 
 calcareous spar in tbe septaria of tbe London clay) of 
 pure white anhydrite. These veins might naturally 
 have been thought to have been formed by subsequent 
 infiltration, had not each little embedded fragment of 
 rock, been likewise edged in a very remarkable manner 
 by a narrow border of the same white anhydrite : this 
 shows that the veins must have been formed by a pro- 
 cess of segregation, and not of infiltration. Some of 
 the little included and cracked fragments of foreign 
 rock are penetrated by the anhydrite, and portions have 
 evidently been thus mechanically displaced : at St. 
 Helena, I observed that calcareous matter, deposited by 
 rain-water, also had the power to separate small frag- 
 ments of rock from the larger masses. I believe the 
 superficial gypseous deposit is widely extended : I re- 
 ceived specimens of it from Pisagua, forty miles north 
 of Iquique, and likewise from Arica, where it coats a 
 layer of pure salt. M. d'Orbigny ^ found at Cobija a 
 bed of clay, lying above a mass of upraised recent shells, 
 which was saturated with sulphate of soda, and included 
 thin layers of fibrous gypsum. These widely extended, 
 superficial, beds of salt and gypsum, appear to me an 
 interesting geological phenomenon, which could be pre- 
 sented only under a very dry climate. 
 
 The plain or basin, on the borders of which the 
 famous bed of nitrate of soda lies, is situated at a 
 distance of about thirty miles from the sea, being sepa- 
 rated from it by the saliferous district just described. 
 It stands at a height of 3,300 feet ; its surface is level, 
 and some leagues in width; it extends forty miles 
 northward, and has a total length (as I was informed 
 1 * Voyage Geolog.' &c. p. 95. 
 
CHAP. X. Nitrate of Soda. 305 
 
 by Mr. Belford Wilson, the Oonsul-General at Lima) 
 of 420 miles. In a well near the works, thirty-six 
 yards in depth, sand, earth, and a little gravel were 
 found : in another well, near Almonte, fifty yards deep, 
 the whole consisted, according to Mr. Blake, ^ of clay, 
 including a layer of sand two feet thick, which rested 
 on fine gravel, and this on coarse gravel, with large 
 rounded fragments of rock. In many parts of this now 
 utterly desert plain, rushes and large prostrate trees in 
 a hardened state, apparently Mimosas, are found buried, 
 at a depth from three to six feet; according to Mr. 
 Blake, they have all fallen to the south-west. The bed 
 of nitrate of soda is said to extend for forty or fifty 
 leagues along the western margin of the plain, but is 
 not found in its central parts : it is from two to three 
 feet in thickness, and is so hard that it is generally 
 blasted with gunpowder ; it slopes gently upwards from 
 the edge of the plain to between ten and thirty feet 
 above its level. It rests on sand in which, it is said, 
 vegetable remains and broken shells have been found ; 
 shells have also been found, according to Mr. Blake, 
 both on and in the nitrate of soda. It is covered by 
 a superficial mass of sand, containing nodules of common 
 salt, and, as I was assured by a miner, much soft gyp- 
 seous matter, precisely like that in the superficial crust 
 already described : certainly this crust, with its charac- 
 teristic concretions of anhydrite, comes close down to 
 the edge of the plain. 
 
 The nitrate of soda varies in purity in different 
 parts, and often contains nodules of common salt. 
 According to Mr. Blake, the proportion of nitrate of 
 silver varies from twenty to seventy-five per cent. An 
 
 * See an admirable paper, ' Geolog. and Miscell. Notices of 
 Tarapaca,' in Silliman's 'American Journal,' vol. xliv. p. 1. 
 
3o6 Saline Incrustations. part n. 
 
 analysis by Mr. A. Hayes, of an average specimen, 
 
 gave — 
 
 Nitrate of Soda 64-98 
 
 Sulphate of Soda 3-00 
 
 Chloride of Soda 28-69 
 
 Iodic Salts 0-63 
 
 Shells and Marl 2-60 
 
 99-90 
 
 The ' mother water ' at some of the refineries is very 
 rich in iodic salts, and is supposed ^ to contain much 
 muriate of lime. In an unrefined specimen brought 
 home by myself, Mr. T. Reeks has ascertained that the 
 muriate of lime is very abundant. With respect to the 
 origin of this saline mass, from the manner in which 
 the gently inclined, compact bed follows for so many 
 miles the sinuous margin of the plain, there can be no 
 doubt that it was deposited from a sheet of water : from 
 the fragments of embedded shells, from the abundant 
 iodic salts, from the superficial saliferous crust occur- 
 ring at a higher level and being probably of marine 
 origin, and from the plain resembling in form those ol 
 Chile and that of Uspallata, there can be little doubt 
 that this sheet of water was, at least originally, con- 
 nected with the sea.^ 
 
 TA,m, superficial.^ saline Incrustations. — These 
 saline incrustations are common in many parts of 
 America : Humboldt met with them on the table-land 
 
 1 ' Literary Gazette,' 1841, p. 475. 
 
 2 From an official document, shown me by Mr. Belford Wilson, 
 it appears that the first export of nitrate of soda to Europe was in 
 July 1830, on French account, in a British ship : — 
 
 
 Quintals. 
 
 In 1830, the entire export was . 
 
 . 17,300 
 
 1831, „ „ 
 
 . 40,885 
 
 1832, „ „ 
 
 . 51,400 
 
 1833, „ ,, 
 
 . 91,335 
 
 1834, 
 
 . 149,538 
 
 The Spanish quintal nearly equals 100 English pounds. 
 
CHAP. X. Saline Incrustations. 307 
 
 of Mexico, and the Jesuit Falkner and other authors ^ 
 state that they occur at intervals over the vast plains 
 extending from the mouth of the Plata to Eioja and 
 Catamarca. Hence it is that during droughts, most of 
 the streams in the Pampas are saline. I nowhere met 
 with these incrustations so abundantly as near Bahia 
 Blanca : square miles of the mud-flats, which near that 
 place are raised only a few feet above the sea, just 
 enough to protect them from being overflowed, appear, 
 after dry weather, whiter than the ground after the 
 thickest hoar-frost. After rain the salts disappear, and 
 every puddle of water becomes highly saline ; as the 
 surface dries, the capillary action draws the moisture up 
 pieces of broken earth, dead sticks, and tufts of grass, 
 where the salt effloresces. The incrustation, where 
 thickest, does not exceed a quarter of an inch. M. 
 Parchappe ^ has analysed it ; and finds that the speci- 
 mens collected at the extreme head of the low plain, 
 near the P. Manuelo, consist of ninety-three per cent, 
 of sulphate of soda, and seven of common salt ; whilst 
 the specimens taken close to the coast contain only 
 sixty-three per cent, of the sulphate and thirty-seven 
 of the muriate of soda. This remarkable fact, together 
 with our knowledge that the whole of this low muddy 
 plain has been covered by the sea within the recent 
 period, must lead to the suspicion that the common 
 salt, by some unknown process, becomes in time 
 changed into the sulphate. Friable calcareous matter 
 is here abundant, and the case of the apparent double 
 decomposition of the shells and salt on S. Lorenzo, 
 should not be forgotten. 
 
 The saline incrustations, near Bahia Blanca, are not 
 
 ^ Azara (' Travels,' vol. i. p. 55) considers that the Parana is the 
 eastern boundary of the salif erous region ; but I heard of ' salitrales ' 
 in the Province of Entre Rios. 
 
 2 M. d'Orbig-ny's 'Voyage,' &c. Part. Hist. torn. i. p. 664. 
 
 X 2 
 
3o8 Salt Lakes part n. 
 
 confined to, though most abundant on, the low muddy- 
 flats ; for I noticed some on a calcareous plain between 
 thii'ty and forty feet above the sea, and even a little 
 occurs in still higher valleys. Low alluvial tracts in 
 the valleys of the rivers Negro and Colorado are also 
 encrusted, and in the latter valley such spaces appeared 
 to be occasionally overflowed by the river. I observed 
 saline incrustations in some of the valleys of southern 
 Patagonia. At Port Desire a low, flat, muddy valley 
 was thickly incrusfced by salts, which on analysis by 
 Mr. T. Reeks, are found to consist of a mixture of sul- 
 phate and muriate of soda, with carbonate of lime and 
 earthy matter. On the western side of the continent, 
 the southern coasts are much too humid for this phe- 
 nomenon ; but in northern Chile I again met with 
 similar incrustations. On the hardened mud, in parts 
 of the broad, flat-bottomed valley of Copiapo, the saline 
 matter incrusts the ground to the thickness of some 
 inches : specimens, sent by Mr. Bingley to Apothe- 
 caries' Hall for analysis, were said to consist of car- 
 bonate and sulphate of soda. Much sulphate of soda is 
 found in the desert of Atacama. In all parts of S. 
 America, the saline incrustations occur most frequently 
 on low damp surfaces of mud, where the climate is 
 rather dry ; and these low surfaces have, in almost 
 every case, been upraised above the level of the sea, 
 within the recent period. 
 
 Salt-lakes of Patagonia and La Plata. — Salinas, 
 or natural salt-lakes, occur in various formations on the 
 eastern side of the continent, — in the a.rgillaceo-calca- 
 reous deposit of the Pampas, in the sandstone of the 
 Rio Negro, where they are very numerous, in the pumi- 
 ceous and other beds of the Patagonian tertiary forma- 
 tion, and in small primary districts in the midst of this 
 latter formation. Port S. Julian is the most southerly 
 
CHAP. X. of La Plata and Patagonia, 309 
 
 point (lat. 49° to 50°), at whicli salinas are known to 
 occur.^ The depressions, in wliicli these salt-lakes lie, 
 are from a few feet to sixty metres, as asserted by 
 M. d'Orbigny,^ below the surface of the surrounding 
 plains; and, according to this same author, near the 
 Eio Negro they all trend, either in the NE. and SW. 
 or in E. and W. lines, coincident with the general slope 
 of the plain. These depressions in the plain generally 
 have one side lower than the others, but there are no 
 outlets for drainage. Under a less dry climate, an 
 outlet would soon have been formed, and the salt 
 washed away. The salinas occur at different elevations 
 above the sea ; they ^re often several leagues in dia- 
 meter ; they are generally very shallow, but there is a 
 deep one in a quartz-rock formation near C. Blanco. In 
 the wet season, the whole, or a part, of the salt is dis- 
 solved, being redeposited during the succeeding dry 
 season. At this period the appearance of the snow- 
 white expanse of salt crystallised in great cubes, is very 
 striking. In a large salina, northward of the Rio Negro, 
 the salt at the bottom, during the whole year, is between 
 two and three feet in thickness. 
 
 The salt rests almost always on a thick bed of black 
 muddy sand, which is fetid, probably from the decay 
 of the burrowing worms inhabiting it.^ In a salina, 
 situated about fifteen miles above the town of El Car- 
 men on the Rio Negro, and three or four miles from 
 the banks of that river, I observed that this black mud 
 rested on gravel with a calcareous matrix, similar to 
 that spread over the whole surrounding plains : at Port 
 
 ' According to Azara (' Travels,' vol. i. p. .56) there are salt lakes 
 as far north as Chaco (lat. 25°), on the banks of the Vermejo. The 
 salt lakes of Siberia appear (Pallas's ' Travels,' English Trans, vol. i. 
 p. 284) to occur in very similar depressions to those of Patagonia. 
 
 "- ' Voyage Geolog.' p. 63. 
 
 ^ Prof. Ehrenberg examined some of this muddy sand, but was 
 unable to find in it any infusoria. 
 
3 TO Salt Lakes 
 
 PART IT. 
 
 St. Julian the mud, also, rested on the gravel : hence 
 the depressions must have been formed anteriorly to, 
 or contemporaneously with, the spreading out of the 
 gravel. I was informed that one small salina occurs in 
 an alluvial plain within the valley of the Rio Negro^ 
 and therefore its origin must be subsequent to the exca- 
 vation of that valley. When I visited the salina, fifteen 
 miles above the town, the salt was beginning to crystal- 
 lise, and on the muddy bottom there were lying many 
 crystals, generally placed cross-ways of sulphate of soda 
 (as ascertained by Mr, Reeks), and embedded in the mud, 
 numerous crystals of sulphate of lime, from one to three 
 inches in length : M. d'Orbigny ^ states that some of 
 these crystals are acicular and more than even nine 
 inches in length ; others are macled and of great purity : 
 those I found all contained some sand in their centres. 
 As the black and fetid sand overlies the gravel, and 
 that overlies the regular tertiary strata, I think there 
 can be no doubt that these remarkable crystals of sul- 
 phate of lime have been deposited from the waters of 
 the lake. The inhabitants call the crystals of selenite, 
 the fcidjTQ del sal, and those of the sulphate of soda, 
 the madre del sal ; they assured me that both are found 
 under the same circumstances in several of the neigh- 
 bouring Salinas ; and that the sulphate of soda is an-^ 
 nually dissolved, and is always crystallised before the 
 common salt on the muddy bottom.^ The association, 
 of gypsum and salt in this case, as well as in the super- 
 ficial deposits of Iquique, appears to me interesting, 
 considering how generally these substances are associated 
 in the older stratified formations. 
 
 1 ' Voyage Geolog.' p. 64. 
 
 2 This is what might have been expected ; for M. Ballard asserts 
 ('Acad, des Sciences,' Oct. 7, 1844) that sulphate of soda is precipi- 
 tated from solution more readily from water containing muriate 
 of soda in excess, than from pure water. 
 
CHAP. X. of La Plata and Patagonia. 311 
 
 Mr. Eeeks lias analysed for me some of the salt 
 from tlie salina near the Rio Negro, he finds it com- 
 posed entirely of chloride of sodium, with the exception 
 of 0' 26 of sulphate of lime and of 0-22 of earthy matter 
 there are no traces of iodic salts. Some salts from the 
 salina Chiquitos in the Pampean formation, is equally 
 pure. It is a singular fact, that the salt from these 
 Salinas does not serve so well for preserving meat, as 
 sea-salt from the Cape de Verde Islands ; and a mer- 
 chant at Buenos Ayres told me that he considered it as 
 fifty per cent, less valuable. The purity of the Pata- 
 gonian salt, or absence from it of those other saline 
 bodies found in all sea-water, is the only assignable 
 cause for this inferiority ; a conclusion which is sup- 
 ported by the fact lately ascertained,^ that those salts 
 answer best for preserving cheese which contain most of 
 the deliquescent chlorides.^ 
 
 With respect to the origin of the salt in the salinas, 
 the foregoing analysis seems opposed to the view enter- 
 tained by M. d'Orbigny and others, and which seems 
 so probable considering the recent elevation of this line 
 of coast, namely, that it is due to the evaporation of 
 sea-water and to the drainage from the surrounding 
 strata impregnated with sea-salt. I was informed (I 
 know not whether accurately) that on the northern side 
 of the salina on the Rio Negro, there is a small brine 
 spring which flows at all times of the year : if this be 
 so, the salt in this case at least, probably is of subter- 
 ranean origin. It at first appears very singular that 
 
 * 'Hort. and Agricult. Gazette,' 1845, p. 93. 
 
 ^ It would probably well answer for the merchants of Buenos 
 Ayres (considering the great consumption there of salt for preserving 
 meat) to import the deliquescent chlorides to mix with the salt from 
 the salinas : I may call attention to the fact, that at Iquique, a large 
 quantity of muriate of lime, left in the mother-water during the 
 refinement of the nitrate of soda, is annually thrown away. 
 
312 Salt Lakes. 
 
 PART II. 
 
 fresh-water can often be procured in wells, ^ and is some- 
 times found in small lakes, quite close to tliese salinas. 
 I am not aware that this fact bears particularly on the 
 origin of the salt ; but perhaps it is rather opposed to 
 the view of the salt having been washed out of the 
 surrounding superficial strata, but not to its having 
 been the residue of sea-water, left in depressions as the 
 land was slowly elevated. 
 
 ^ Sir W. Parish states (' Buenos Ayres,' &c. pp. 122 and 170) that 
 this is the case near the great salinas westward of the S. Ventana. 
 I have seen similar statements in an ancient MS. Journal lately 
 published by S. Angelis. At Iquique, where the surface is so thickly 
 encrusted with saline matter, I tasted water only slightly brackish, 
 procured in a well thirty-six yards deep ; but here one feels less sur- 
 prise at its presence, as pure water might percolate under ground 
 from the not very distant Cordillera. 
 
313 
 
 CHAPTER XI. 
 
 ON THE FORMATIONS OF THE PAMPAS. 
 
 Mineralogical constitution — Microscojncal structure — Buenos Ayres, 
 shells enibedded in tosca-roek — Buenos Ayres to the Colorado — S. 
 VentatUL — Bahia Blanca ; H. Jlermoso, ho7ws and infusoria of ; P. 
 Alta, shells, tones and infusoria of ; co-existence of the recent sliells 
 and extinct mammifers — Buenos Ayres to St. Fe — Skeletons of 
 Mastodon — Infusoria — Inferior marine tertiary strata, their age 
 — Horse's tooth. Banda Oeiental — Superficial Pampean forma- 
 tion — Inferior tertiary strata.^ variation of, connected with, volcanic 
 action ; Macrauchenia Patachonica at S. Julian in Patagonia, age 
 of, subsequent to living mollusca and to the erratic tloch ])eriod. 
 Summary — Area of Pa/inpean formation — Theories of origin — 
 Sowrce of sediment — Estuary origin — Contemporaneous with, exist- 
 ing mollusca — Belations to underlying tertiary strata — Ancient 
 deposit of estuary origin — Elevation and successive deposition of 
 the Pampean formation — Numiber and state of the remains of 
 mammifers ; their habitation, food, extinction, and range — Con- 
 clusion — Localities in Pampas at which mammiferous remains 
 have been found. 
 
 The Pampean formation is highly interesting from its 
 vast extent, its disputed origin, and from the number 
 of extinct gigantic mammifers embedded in it. It has 
 upon the whole a very uniform character : consisting of 
 a more or less dull reddish, slightly indurated, argil- 
 laceous earth or mud, often, but not always, including 
 in horizontal lines concretions of marl, and frequently 
 passing into a compact marly rock. The mud, wher- 
 ever I examined it, even close to the concretions, did 
 not contain any carbonate of lime. The concretions are 
 generally nodular, sometimes rough externally, some- 
 
314 Pa77tpean Formation. part it. 
 
 times stalactiformed ; they are of a compact structure, 
 but often penetrated (as well as the mud) by hair-like 
 serpentine cavities, and occasionally with irregular 
 fissures in their centres, lined with minute crystals of 
 carbonate of lime ; they are of white, brown, or pale 
 pinkish tints, often marked by black dendritic man- 
 ganese or iron ; they are either darker or lighter tinted 
 than the surrounding mass ; they contain much car- 
 bonate of lime, but exhale a strong aluminious odour, 
 and leave, when dissolved in acids, a large but varying 
 residue, of which the greater part consists of sand. 
 These concretions often unite into irregular strata ; and 
 over very large tracts of country, the entire mass consists 
 of a hard, but generally cavernous marly rock : some 
 of the varieties might be called calcareous tuffs. 
 
 Dr. Carpenter has kindly examined under the mi- 
 croscope, sliced and polished specimens of these concre- 
 tions, and of the solid marl-rock, collected in various 
 places between the Colorado and St. Fe Bajada. In 
 the greater number, Dr. Carpenter finds that the whole 
 substance presents a tolerably uniform amorphous cha- 
 racter, but with traces of incipient crystalline meta- 
 morphosis ; in other specimens he finds microscopically 
 minute rounded concretions of an amorphous substance 
 (resembling in size those in oolitic rocks, but not having 
 a concentric structure), united by a cement which is 
 often crystalline. In some. Dr. Carpenter can perceive 
 distinct traces of shells, corals, Polythalamia, and rarely 
 of spongoid bodies. For the sake of comparison, I sent 
 Dr. Carpenter specimens of the calcareous rock, formed 
 chiefly of fragments of recent shells, from Coquimbo in 
 Chile : in one of these specimens. Dr. Carpenter finds, 
 besides the larger fragments, microscopical particles of 
 shells, and a varying quantity of opaque amorphous 
 matter; in another specimen from the same bed, he 
 
CHAP. XI. Pampean Forviation. 315 
 
 finds tlie wliole composed of the amorplious matter, 
 with layers showing indications of an incipient crystal- 
 line metamorphosis : hence these latter specimens, both 
 in external appearance and in microscopical structure, 
 closely resemble those of the Pampas. Dr. Carpenter 
 informs me that it is well known that chemical preci- 
 pitation throws down carbonate of lime in the opaque 
 amorphous state ; and he is inclined to believe that the 
 long-continued attrition of a calcareous body in a state 
 of crystalline or semi-crystalline aggregation (as, for 
 instance, in the ordinary shells of Mollusca, which, 
 when sliced, are transparent) may yield the same result. 
 From the intimate relation between all the Coquimbo 
 specimens, I can hardly doubt that the amorphous 
 carbonate of lime in them has resulted from the attri- 
 tion and decay of the larger fragments of shell : whether 
 the amorphous matter in the marly rocks of the Pampas 
 has likewise thus originated, it would be hazardous to 
 conjecture. 
 
 For convenience sake, I will call the marly rock by 
 the name given to it by the inhabitants, namely, Tosca- 
 rock; and the reddish argillaceous earth, Pampean 
 mud. This latter substance, I may mention, has been 
 examined for me by Professor Ehrenberg, and the 
 result of his examination will be given under the proper 
 localities. 
 
 I will commence my descriptions at a central spot, 
 namely, at Buenos Ayres, and thence proceed first south- 
 ward to the extreme limit of the deposit, and afterwards 
 northward. The plain on which Buenos Ayres stands 
 is from thirty to forty feet in height. The Pampean 
 mud is here of a rather pale colour, and includes small 
 nearly white nodules, and other irregular strata of an 
 uu usually arenaceous variety of tosca-rock. In a well at 
 the depth of seventy feet, according to Ignatio Nunez, 
 
3 1 6 Pampean Formation. part h. 
 
 much tosca-rock was met with, and at several points, 
 at 100 feet deep, beds of sand have been found. I have 
 already given a list of the recent marine and estuary 
 shells found in many parts on the surface near Buenos 
 Ayres, as far as three and four leagues from the Plata. 
 Specimens from near Ensenada, given me by Sir W. 
 Parish, where the rock is quarried just beneath the 
 surface of the plain, consist of broken bivalves, cemented 
 by and converted into, white crystalline carbonate of 
 lime. I have already alluded, in the first chapter, to 
 a specimen (also given me by Sir W. Parish) from the 
 A, del Tristan, in which shells, resembling in every 
 respect the Azara lahiata, d'Orbig., as far as their 
 worn condition permits of comparison, are embedded in 
 a reddish, soffcish, somewhat arenaceous marly rock : 
 after careful comparison, with the aid of a microscope 
 and acids, I can perceive no difference between the 
 basis of this rock and the specimens collected by me 
 in many parts of the Pampas. I have also stated, on 
 the authority of Sir W. Parish, that northward of 
 Buenos Ayres, on the highest parts of the plain, about 
 forty feet above the Plata, and two or three miles from 
 it, numerous shells of the Azara labioia (and I believe 
 of Venus sinuosa) occur embedded in a stratified 
 earthy mass, including small marly concretions and said 
 to be precisely like the great Pampean deposit. Hence 
 we may conclude that the mud of the Pampas continued 
 to be deposited to within the period of this existing 
 estuary shell. Although this formation is of such 
 immense extent, I know of no other instance of the 
 presence of shells in it. 
 
 Buenos Ayres to the Rio Colorado. — With the 
 exception of a few metamorphic ridges, the country 
 between these two points, a distance of 400 geographical 
 miles, belongs to the Pampean formation, and in the 
 
CHAP. XI. Sierra Ventana, 317 
 
 soutliern part is generally formed of the harder and 
 more calcareous varieties. I will briefly describe my 
 route : about twenty-five miles SSW. of the capital, 
 in a well forty yards in depth, the upper part, and, as I 
 was assured, the entire thickness, was formed of dark 
 red Pampean mud without concretions. North of the 
 R. Salado, there are many lakes ; and on the banks of 
 one (near the Guardia) there was a little cliff similarly 
 composed, but including many nodular and stalactiform 
 concretions : I found here a large piece of tesselated 
 armour, like that of the Glyptodon, and many fragments 
 of bones. The cliffs on the Salado consist of pale- 
 coloured Pampean mud, including and passing into 
 great masses of tosca-rock : here a skeleton of the 
 Megatherium and the bones of other extinct quadrupeds 
 (see the list at the end of this chapter) were found. 
 Large quantities of crystallized gypsum (of which 
 specimens were given me) occur in the cliffs of this 
 river ; and likewise (as I was assured by Mr. Lumb) in 
 the Pampean mud on the R. Chuelo, seven leagues 
 from Buenos Ayres : I mention this because M. d'Or- 
 bigny lays some stress on the supposed absence of this 
 mineral in the Pampean formation. 
 
 Southward of the Salado the country is low and 
 swampy, with tosca-rock appearing at long intervals at 
 the surface. On the banks, however, of the Tapalguen 
 (sixty miles south of the Salado) there is a large extent 
 of tosca-rock, some highly compact and even semi- 
 crystalline, overlying pale Pampean mud with the usual 
 concretions. Thirty miles further south, the small 
 quartz-ridge of Tapalguen is fringed on its northern 
 and southern flank, by little, narrow, flat-topped hills 
 of tosca-rock, which stand higher than fche surrounding 
 plain. Between this ridge and the Sierra of Guitru- 
 gueyu, a distance of sixty miles, the country is swampy, 
 
3 1 8 Pampean Formation, paet ii. 
 
 with the tosca-rock appearing only in four or five spots : 
 this sierra, precisely like that of Tapalguen, is bordered 
 by horizontal, often cliff-bounded, little hills of tosca- 
 rock, higher than the surrounding plain. Here, also, 
 a new appearance was presented in some extensive and 
 level banks of alluvium or detritus of the neighbouring 
 metam Orphic rocks ; but I neglected to observe whether 
 it was stratified or not. Between Guitru-gueyu and 
 the Sierra Ventana, I crossed a dry plain of tosca-rock 
 higher than the country hitherto passed over, and with 
 small pieces of denuded table-land of the same forma- 
 tion, standing still higher. 
 
 The marly or calcareous beds not only come up 
 nearly horizontally to the northern and southern foot 
 of the great quartzose mountains of the Sierra Ventana, 
 but interfold between the parallel ranges. The super- 
 ficial beds (for I nowhere obtained sections more than 
 twenty feet deep) retain, even close to the mountains, 
 their usual character : the uppermost layer, however, 
 in one place included pebbles of quartz, and rested on 
 a mass of detritus of the same rock. At the very foot 
 of the mountains, there were some few piles of quartz 
 and tosca-rock detritus, including land-shells ; but at 
 the distance of only half a mile from these lofty, jagged, 
 and battered mountains, I could not, to my great sur- 
 prise, find on the boundless surface of the calcareous 
 plain even a single pebble. Quartz-pebbles, however, 
 of considerable size have at some period been trans- 
 ported to a distance of between forty and fifty miles to 
 the shores of Bahia Blanca.^ 
 
 The highest peak of the S. Ventana is, by Captain 
 FitzRoy's measurement, 3,340 feet, and the calcareous 
 plain at its foot (from observations taken by some 
 
 ^ Schmidtmeyer (' Travels in Chile,' p. 150) states that he first 
 noticed on the Pampas, very small bits of red granite, when fifty 
 miles distant from the southern extremity of the mountains of 
 Cordova, which project on the plain, like a reef into the sea. 
 
CHAP. XI. Sierra Ventmta. 319 
 
 Spanish officers ^) 840 feet above tlie sea-level. On the 
 flanks of the mountains, at a height of 300 or 400 feet 
 above the plain, there were a few small patches of con- 
 glomerate and breccia, firmly cemented by ferruginous 
 matter to the abrupt and battered face of the quartz — 
 traces being thus exhibited of ancient sea-action. The 
 high plain round this range sinks quite insensibly to 
 the eye on all sides, except to the north, where its 
 surface is broken into low cliffs. Round the Sierras 
 Tapalguen, Guitru-gueyu, and between the latter 
 and the Yentana we have seen (and shall hereafter 
 see round some hills in Banda Oriental), that the 
 tosca-rock forms low, flat-topped, clifi'-bounded hills, 
 higher than the surrounding plains of similar compo- 
 sition. From the horizontal stratification and from 
 the appearance of the broken cliffs, the greater height 
 of the Pampean formation round these primary hills 
 ought not to be altogether or in chief part attributed 
 to these several points having been uplifted more ener- 
 getically than the surrounding country, but to the 
 argillaceo-calcareous mud having collected round them, 
 when they existed as islets or submarine rocks, at a 
 greater height, than at the bottom of the adjoining 
 open sea ; — the cliffs having been subsequently worn 
 during the elevation of the whole country in mass. 
 
 Southward of the Ventana, the plain extends farther 
 than the eye can range \ its surface is not very level, 
 having slight depressions with no drainage exits ; it is 
 generally covered by a few feet in thickness of sandy 
 earth ; and in some places, according to M. Parchappe,^ 
 by beds of clay two yards thick. On the banks of the 
 Sauce, four leagues SE. of the Ventana, there is an im- 
 perfect section about 200 feet in height, displaying in 
 the upper part tosca-rock and in the lower part red 
 
 1 • La Plata,' &c. by Sir W. Parish, p. 146. 
 
 2 M. d'Orbigny, ' Voyage, Part. Geolog.' pp. 47, 48. 
 
320 Painpean Formaiioii. part n. 
 
 Pampean mud. At the settlement of Bahia Blanca, 
 the uppermost plain is composed of very compact, 
 stratified tosca-rock, containing rounded grains of 
 quartz distinguishable by the naked eye : the lower 
 plain, on which the Fortress stands, is described by 
 M. Parchappe ^ as composed of solid tosca-rock ; but the 
 sections which I examined appeared more like a re- 
 deposited mass of this rock, with small pebbles and frag- 
 ments of quartz. I shall immediately return to the 
 important sections on the shores of Bahia Blanca. 
 Twenty miles southward of this place, there is a re- 
 markable ridge extending W. by N. and E. by S., 
 formed of small, separate, flat-topped, steep-sided hills, 
 rising between 100 and 200 feet above the Pampean 
 plain at its southern base, which plain is a little lower 
 than that to the north. The uppermost stratum in 
 this ridge consists of pale, highly calcareous, compact 
 tosca-rock, resting (as seen in one place) on reddish 
 Pampean mud, and this again on a paler kind : at the 
 foot of the ridge, there is a well in reddish clay or 
 mud. I have seen no other instance of a chain of hills 
 belonging to the Pampean formation ; and as the 
 strata shows no signs of disturbance, and as the direc- 
 tion of the ridge is the same with that common to all 
 the metamorphic lines in this whole area, I suspect 
 that the Pampean sediment has in this instance been 
 accumulated on and over a ridge of hard rocks, instead 
 of, as in the case of the above-mentioned Sierras, round 
 their submarine flanks. South of this little chain of 
 tosca-rock, a plain of Pampean mud declines towards 
 the banks of the Colorado : in the middle a well has been 
 dug in red Pampean mud, covered by two feet of white 
 softish, highly calcareous tosca-rock, over which lies sand 
 with small pebbles three feet in thickness — the first 
 appearance of that vast shingle formation described in 
 1 M. d'Orbigny, ' Voyage, Part. Geologi' pp. 47, 48. 
 
CHAP. XI. Bahia Blanca. 321 
 
 the eiglitii chapter. In the first section after crossing 
 the Colorado, an old tertiary formation, namely, the Rio 
 Negro sandstone (to ibe described in the next chapter), is 
 met with : but from the accounts given me by the Gau- 
 chos, I believe that at the mouth of the Colorado the 
 Pampean formation extends a little farther southwards. 
 Bahia Blanca. — To return to the shores of this 
 bay. At Monte Hermoso. there is a good section, 
 about 100 feet in height, of four distinct strata, appear- 
 ing to the eye horizontal, but thickening a little 
 towards the NW. The uppermost bed, about twenty 
 feet in thickness, consists of obliquely laminated, soft 
 sandstone, including many pebbles of quartz, and fall- 
 ing at the surface into loose sand. The second bed, only 
 six inches thick, is a hard, dark-coloured sandstone. 
 The third bed is pale-coloured Pampean mud; and 
 the fourth is of the same nature, but darker coloured, 
 including in its lower part horizontal layers and lines 
 of concretions of not very compact pinkish tosca-rock. 
 The bottom of the sea, I may remark, to a distance of 
 several miles from the shore, and to a depth of between 
 sixty and one hundred feet, was found by the anchors 
 to be composed of tosca-rock and reddish Pampean 
 mud. Professor Ehrenberg has examined for me speci- 
 mens of the two lower beds, and finds in them three 
 Polygastrica and six Phytolitharia.^ Of these, only 
 one (SpongoUthis Fiistis ?) is a marine form ; five of 
 them are identical with microscopical structures, of 
 
 ^ The following list is given in the ' Monatsberichten der konig. 
 Akad. zu Berlin,' April 1845 : — 
 
 POLTGASTEICA. 
 Fragilaria rhabdosoma. t Pinnularia ? 
 
 Grallionella distans. f 
 
 Phytolithaeia. 
 
 Lithodontium Bursa. 
 
 „ furcatum. 
 
 Lithostylidium exesum. 
 
 Lithostylidium rude 
 „ Serra 
 
 Spongolithis Fustis 
 
 Y 
 
32 2 Pampean Formation. part n. 
 
 brackish- water origin, hereafter to be mentioned, from 
 a central point in the Pampean formation. In these 
 two beds, especially in the lower one, bones of extinct 
 mammifers, some embedded in their proper relative 
 positions and others single, are very numerous in a small 
 extent of the cliffs. These remains consist of, first, 
 the head of Gtenomys antiquus, allied to the living 
 G. Brasiliensis; secondly, a fragment of the remains 
 of a rodent ; thirdly, molar teeth and other bones of a 
 large rodent, closely allied to, but distinct from, the 
 existing species of Hydrochoerus, and therefore probably 
 an inhabitant of fresh water ; fourth and fifthly, portions 
 of vertebra, limbs, ribs, and other bones of two rodents ; 
 sixthly, bones of the extremities of some great mega- 
 theroid quadruped.^ The number of the remains of 
 rodents gives to this collection a peculiar character, 
 compared with those found in any other locality. All 
 these bones are compact and heavy ; many of them are 
 stained red, with their surfaces polished ; some of the 
 smaller ones are as black as jet. 
 
 Monte Hermoso is between fifty and sixty miles 
 distant in a SE. line from the Ventana, with the inter- 
 mediate country gently rising towards it, and all con- 
 sisting of the Pampean formation. What relation, 
 then, do these beds, at the level of the sea and under 
 it, bear to those on the flanks of the Ventana, at the 
 height of 840 feet, and on the flanks of the other 
 neighbouring sierras, which, from the reasons already 
 assigned, do not appear to owe their greater height to 
 unequal elevation ? When the tosca-rock was accumu- 
 lating round the Ventana, and when, with the exception 
 of a few small rugged primary islands, the whole wide 
 
 1 See ' Fossil Mammalia,' (p. 109), by Professor Owen, in the 
 * Zoology of the Voyage of the Beagle ; ' and Catalogue (p. 36) of 
 ' Fossil Remains in Museum of Royal College of Surgeons.' 
 
CHAP. xi. Bakia Blanca. 323 
 
 surrounding plains must liave been under water, were 
 the strata at Monte Hermoso depositing at the bottom 
 of a great open sea, between 800 and 1,000 feet in 
 depth ? I much doubt this ; for if so, the almost per- 
 fect carcasses of the several small rodents, the remains 
 of which are so very numerous in so limited a space, 
 must have been drifted to this spot from the distance 
 of many hundred miles. It appears to me far more 
 probable, that during the Pampean period this whole 
 area had commenced slowly rising (and in the cliffs, at 
 several different heights, we have proofs of the land 
 having been exposed to sea-action at several levels), and 
 that tracts of land had thus been formed of Pampean 
 sediment round the Ventana and the other primary 
 ranges, on which the several rodents and other quadru- 
 peds lived, and that a stream (in which perhaps the 
 extinct aquatic Hydrochcerus lived) drifted their bodies 
 into the adjoining sea, into which the Pampean mud 
 continued to be poured from the north. As the land 
 continued to rise, it appears that this source of sediment 
 was cut off; and in its place sand and pebbles were 
 borne down by stronger currents, and conformably de- 
 posited over the Pampean strata. 
 
 Punta Alta is situated about thirty miles higher up 
 on the northern side of this same bay : it consists of 
 a small plain, between twenty and thirty feet in height, 
 cut off on the shore by a line of low cliffs about a mile 
 in length, represented in the diagram with its vertical 
 scale necessarily exaggerated. The lower bed (A) is 
 more extensive than the upper ones : it consists of 
 stratified gravel or conglomerate, cemented by calcareo- 
 arenaceous matter, and is divided by curvilinear layers 
 of pinkish marl, of which some are precisely like tosca- 
 rock, and some more sandy. The beds are curvilinear, 
 owing to the action of currents, and dip in different 
 
 Y 2 
 
324 Pmnpean Formation. paet ii. 
 
 directions ; they include an extraordinary number of 
 bones of gigantic mammifers and many shells. The 
 pebbles are of considerable size, and are of hard sand- 
 stone, and of quartz, like that of the Ventana : there 
 are also a few well-rounded masses of tosca-rock. 
 
 No. 29. 
 
 Section of Beds with Kecent Shells and Extinct Mammifers, at Punta Alta in 
 
 Bahia Blauca. 
 
 The second bed (B) is about fifteen feet in thickness, 
 but towards both extremities of the cliff (not included 
 in the diagram) it either thins out and dies away, or 
 passes insensibly into an overlying bed of gravel. It 
 consists of red, tough clayey mud, with minute linear 
 cavities; it is marked with faint horizontal shades of 
 colour ; it includes a few pebbles, and rarely a minute 
 particle of shell : in one spot, the dermal armour and a 
 few bones of a Dasypoid quadruped were embedded in 
 it : it fills up furrows in the underlying gravel. With 
 the exception of the few pebbles and pai'ticles of shells, 
 this bed resembles the true Pampean mud ; but it still 
 more closely resembles the clayey flats (mentioned in 
 the eighth chapter) separating the successively rising 
 parallel ranges of sand-dunes. 
 
 The bed (0) is of stratified gravel, like the lowest 
 one ; it fills up furrows in the underlying red mud, and 
 is sometimes interstratified with it, and sometimes in- 
 sensibly passes into it ; as the red mud thins out, this 
 upper gravel thickens. Shells are more numerous in 
 it than in the lower gravel ; but the bones, thougb 
 some are still present, are less numerous. In one part, 
 however, where this gravel and the red mud passed into 
 
CHAP. XI. Bahia Blanca. 325 
 
 each other, I found several bones and a tolerably per- 
 fect head of the Megatherium. Some of the large 
 Volutas, though embedded in the gravel-bed (C), were 
 filled with the red mud, including great numbers of the 
 little recent PaludestriTia australis. These three lower 
 beds are covered by an unconformable mantle (D) of 
 stratified sandy earth, including many pebbles of quartz, 
 pumice and phonolite, land and sea-shells. 
 
 M. d'Orbigny has been so obliging as to name for 
 me the twenty species of Mollusca embedded in the two 
 gravel beds ; they consist of — 
 
 1. Volutella angulata, d'Orbig. 
 
 ' Voyage' Mollusq. and Pal. 
 
 2. Voluta Brasiliana, Sol. 
 
 3. Olicancilleria BrasiUensis, 
 
 [d'Orbig. 
 
 4. „ auricularia, do. 
 
 5. Olivina puelchana, do. 
 
 6. Buccinanopscochlidium,do. 
 
 7. ,, globulosiim, do. 
 
 8. Colombella sertulariarum, do. 
 
 9. Trochus Patagonicus, andvar. 
 
 of ditto, d'Orbig. 
 
 10. Paludestrina australis, 
 
 [d'Orbig. 
 
 11. Fissiirella Patagonica, do. 
 
 12. Crepidula muricata, Lam. 
 
 13. Venus purpurata, do. 
 
 14. „ rostrata, Phillippi. 
 
 15. Mytilus Darwiuianus, 
 
 [d'Orbig. 
 
 16. Nucula semiornata, do. 
 
 17. Cardita Patagonica, do. 
 
 18. Corbula „ (?) do. 
 
 19. Pecten tethuelcbus, do. 
 
 20. Ostrea puelchana, do. 
 
 21. A living species of Balanus. 
 
 22. and 23. An Astr^a and en- 
 
 crusting Flustra, apparently 
 identical with species now 
 living in the Bay. 
 
 All these shells uow live on this coast, and most of them 
 in this same bay. I was also struck with the fact, that 
 the proportional numbers of the different kinds appeared 
 to be the same with those now cast up on the beach : 
 in both cases specimens of Voluta, Crepidula, Venus, 
 and Trochus are the most abundant. Four or five of 
 the species are the same with the upraised shells on 
 the Pampas near Buenos Ayres. All the specimens 
 have a very ancient and bleached appearance,^ and do 
 not emit, when heated, an animal odour ; some of them 
 
 * A Bulinus, mentioned in the Introduction to the ' Fossil Mam- 
 malia in the Zoology of the Voyage of the Beagle,' has so much 
 fresher an appearance, than the marine species, that I suspect it 
 must have fallen amongst the others, and been collected by mistake. 
 
326 Pampeaji Formation. part n. 
 
 are changed thronghout into a white, soft, fibrous sub- 
 stance ; others have the space between the external 
 walls, either hollow, or filled up with crystalline car- 
 bonate of lime. 
 
 The remains of the extinct mammiferous animals, 
 from the two gravel beds have been described by Pro- 
 fessor Owen in the ' Zoology of the Voyage of the Beagle : ' 
 they consist of 1st, one nearly perfect head and three 
 fragments of heads of the Megatherium Guvieriii 2nd, 
 a lower jaw of Megalonyx Jeffersonii ; ord, lower jaw 
 of Mylodon Barwinii', 4th, fragments of a head of 
 some gigantic Edental quadruped ; 5th, an almost entire 
 skeleton of the great Scelidotherium leptocejphalum^ 
 with most of the bones, including the head, vertebrae, 
 ribs, some of the extremities to the claw-bone, and even, 
 as remarked by Professor Ovs^en, the knee-cap, all nearly 
 in their proper relative positions; 6th, fragments of 
 the jaw and a separate tooth of a Toxodon, belonging 
 either to T. Platensis^ or to a second species lately dis- 
 covered near Buenos Ayres ; 7th, a tooth of I]qims 
 curvidens ; 8th, tooth of a Pachyderm, closely allied to 
 Pal?Potherium, of which parts of the head have been 
 lately sent from Buenos Ayres to the British Museum ; 
 in all probability this pachyderm is identical with the 
 Macrauckenia Patachonica from Port S. Julian, here- 
 after to be referred to. Lastly, and 9thly, in a cliff of 
 the red clayey bed (B), there was a double piece, about 
 three feet long and two wide, of the bony armour of a 
 large Dasypoid quadruped, with the two sides pressed 
 nearly close together : as the cliff is now rapidly wash- 
 ing away, this fossil probably was lately much more 
 perfect ; from between its doubled- up sides, I extracted 
 the middle and ungueal phalanges, united together, of 
 one of the feet, and likewise a separate phalang : hence 
 one or more of the limbs must have been attached to 
 
CHAP. XI. Bahia Blanca. 327 
 
 the dermal case, when it was embedded. Besides these 
 several remains in a distinguishable condition, there 
 were very many single bones : the greater number were 
 embedded in a space 200 yards square. The prepon- 
 derance of the Edental quadrupeds is remarkable ; as 
 is, in contrast with the beds of Monte Hermoso, the 
 absence of Rodents. Most of the bones are now in a 
 soft and friable condition, and, like the shells, do not 
 emit when burnt an animal odour. The decayed state 
 of the bones may be partly owing to their late exposure 
 to the air and tidal waves. Barnacles, Serpulae and 
 corallines are attached to many of the bones, but I 
 neglected to observe ^ whether these might not have 
 grown on them since being exposed to the present tidal 
 action ; but I believe that some of the barnacles must 
 have grown on the Scelidotherium, soon after being 
 deposited, and before being vjliolly covered up by the 
 gravel. Besides the remains in the condition here 
 described, I found one single fragment of bone very 
 much rolled, and as black as jet, so as perfectly to re- 
 semble some of the remains from Monte Hermoso. 
 
 Very many of the bones had been broken, abraded, 
 and rolled, before being embedded. Others, even some 
 of those included in the coarsest parts of the now hard 
 conglomerate, still retain all their minutest promi- 
 nences perfectly preserved ; so that I conclude that 
 they probably were protected by skin, flesh, or ligaments, 
 whilst being covered up. In the case of the Scelido- 
 therium, it is quite certain that the whole skeleton 
 was held together by its ligaments, when deposited in 
 the gravel in which I found it. Some cervical vertebras 
 and a humerus of corresponding size lay so close to- 
 
 * After having packed up my specimens at Baliia Blanca, this 
 point occurred to me, and I noted it ; but forgot it on my retm-n, 
 until the remains had been cleaned and oiled : my attention was 
 afterwards recalled to the subject by some remarks by M. d'Orbigny. 
 
328 Pavipean Formation, paet ii. 
 
 gether, as did some ribs and the bones of a leg, that I 
 thought that they must originally have belonged to two 
 skeletons, and not have been washed in single ; but as 
 remains were here very numerous, I will not lay much 
 stress on these two cases. We have just seen that the 
 armour of the Dasypoid quadruped was certainly em- 
 bedded together with some of the bones of the feet. 
 
 Professor Ehrenberg ^ has examined for me speci- 
 mens of the finer matter from in contact with these 
 mammiferous remains : he finds in them two Polygas- 
 trica, decidedly marine forms ; and six Phytolitharia, 
 of which one is probably marine, and the others either 
 of fresh- water or terrestrial origin. Only one of these 
 eight microscopical bodies is common to the nine from 
 Monte Hermoso : but five of them are in common with 
 those from the Pampean mud on the banks of the 
 Parana. The presence of any fresh-water Infusoria, 
 considering the aridity of the surrounding country, is 
 here remarkable : the most probable explanation appears 
 to be, that these microscopical organisms were washed 
 out of the adjoining great Pampean formation during 
 its denudation, and afterwards redeposited. 
 
 We will now see what conclusions may be drawn 
 from the facts above detailed. It is certain that the 
 gravel-beds and intermediate red mud were deposited 
 within the period, when existing species of Mollusca 
 held to each other nearly the same relative proportions 
 
 * ' Monatsberichten der konig. Akad. zu Berlin,' April, 1845. The 
 list consists of, — 
 
 POLYGASTRICA. 
 
 Gallionella sulcata. | Stauropteraaspera? fragm. 
 
 Phytolitharia. 
 Lithasteriscustuberculatus. I Spongolithis acicularis. 
 
 Lithostylidium Clepsammidium. 
 „ quadratum. 
 
 „ rude. 
 
 „ unidentatum. 
 
CHAP. XI. Bahia Blmtca. 329 
 
 as they do on the present coast. These beds, from the 
 number of littoral species, must have been accumulated 
 in shallow water ; but not, judging from the stratifica- 
 tion of the gravel and the layers of marl, on a beach. 
 From the manner in which the red clay fills up furrows 
 in the underlying gravel, and is in some parts itself 
 furrowed by the overlying gravel, whilst in other parts 
 it either insensibly passes into, or alternates with, this 
 upper gravel, we may infer several local changes in the 
 currents, perhaps caused by slight changes, up or down, 
 in the level of the land. By the elevation of these 
 beds, to which period the alluvial mantle with pumice- 
 pebbles, land and sea-shells belongs, the plain of Punta 
 Alta, from twenty to thirty feet in height, was formed. 
 In this neighbourhood there are other and higher sea- 
 formed plains and lines of clifis in the Pampean forma- 
 tion worn by the denuding action of the waves at 
 different levels. Hence we can easily understand the 
 presence of rounded masses of tosca-rock in this lowest 
 plain; and likewise, as the clifi*s at Monte Hermoso 
 with their mammiferous remains stand at a higher level, 
 the presence of the one much-rolled fragment of bone 
 which was as black as jet : possibly some few of the 
 other much-rolled bones may have been similarly de- 
 rived, though I saw only the one fragment, in the same 
 condition with those from Monte Hermoso. M. d'Or- 
 bigny has suggested ^ that all these mammiferous 
 remains may have been washed out of the Pampean 
 formation, and afterwards redeposited together with 
 the recent shells. Undoubtedly it is a marvellous fact 
 that these numerous gigantic quadrupeds, belonging, 
 with the exception of the Equus curvideiis, to seven 
 extinct genera, and one, namely, the Toxodon, not 
 falling into any existing family, should have co-existed 
 ^ ' Voyage, Part. Geolog.' p. 49. 
 
330 Pampean Formation. part n. 
 
 with. Mollusca, all of whicli are still living species ; but 
 analogous facts have been observed in N. America and 
 in Europe. In the first place, it should not be over- 
 looked, that most of the co-embedded shells have a 
 more ancient and altered appearance than the bones. 
 In the second place, is it probable that numerous bones 
 not hardened by silex or any other mineral, could have 
 retained their delicate prominences and surfaces perfect 
 if they had been washed out of one deposit, and re- 
 embedded in another ; — this later deposit being formed 
 of large, hard pebbles, arranged by the action of currents 
 or breakers in shallow water into variously curved and 
 inclined layers ? The bones which are now in so perfect 
 a state of preservation, must, I conceive, have been 
 fresh and sound when embedded, and probably were 
 protected by skin, flesh, or ligaments. The skeleton of 
 the Scelidotherium indisputably was deposited entire : 
 shall we say that when held together by its matrix it 
 was washed out of an old gravel -bed (totally unlike in 
 character to the Pampean formation), and re-embedded 
 in another gravel-bed, composed (I speak after careful 
 comparison) of exactly the same kind of pebbles, in 
 the same kind of cement ? I will lay no stress on the 
 two cases of several ribs and bones of the extremities 
 having apparently been embedded in their proper 
 relative position : but will anyone be so bold as to affirm 
 that it is possible, that a piece of the thin tesselated 
 armour of a DavSypoid quadruped, at least three feet 
 long and two in width, and now so tender that I was 
 unable with the utmost care to extract a fragment more 
 than two or three inches square, could have been washed 
 out of one bed, and re-embedded in another, together 
 with some of the small bones of the feet, without having 
 been dashed into atoms ? We must then wholly reject 
 
CHAP. XI. Buenos Ay res to St, Fd Bajada, 331 
 
 M. d'Orbigny's supposition, and admit as certain, that 
 the Scelidotherium and the large Dasypoid quadruped, 
 and as highly probable, that the Toxodon, Megatherium , 
 &c., some of the bones of which are perfectly preserved, 
 were embedded for the first time, and in a fresh condi- 
 tion, in the strata in which they were found entombed. 
 These gigantic quadrupeds, therefore, though belonging 
 to extinct genera and families, co-existed with the 
 twenty above-enumerated Mollusca, the barnacle and 
 two corals, still living on this coast. From the rolled 
 fragment of black bone, and from the plain of Punta 
 Alta being lower than that of Monte Hermoso, I con- 
 clude that the coarse sub-littoral deposits of Punta Alta, 
 are of subsequent origin to the Pampean mud of Monte 
 Hermoso ; and the beds at this latter place, as we have 
 seen, are probably of subsequent origin to the high 
 tosca-plg-in round the Sierra Ventana : we shall, how- 
 ever, return, at the end of this chapter, to the considera- 
 tion of these several stages in the great Pampean 
 formation. 
 
 Buenos Ayres to St. Fe Bajada in JEntre Rios. — 
 For some distance northward of Buenos Ayres, the 
 escarpment of the Pampean formation does not approach 
 very near to the Plata, and it is concealed by vegeta- 
 tion : but in sections on the banks of the Rios Luxan, 
 Areco, and Arrecifes, I observed both pale and dark 
 reddish Pampean mud, with small, whitish concretions 
 of tosca ; at all these places mammiferous remains have 
 been found. In the cliffs on the Parana, at San Nicolas, 
 the Pampean mud contains but little tosca; here M. 
 d'Orbigny found the remains of two rodents (^Gtenomys 
 Bonariensis and Kerodon antiquus) and the jaw of a 
 Canis : when on the river I could clearly distinguish in 
 this fine line of cliffs, ' horizontal lines of variation 
 
S3^ Pd'^npean Formatio7t. part h. 
 
 both in tint and compactness.'^ The plain northward of 
 this point is very level, but with some depressions and 
 lakes ; I estimated its height at from forty to sixty feet 
 above the Parana. At the A. Medio the bright red 
 Pampean mud contains scarcely any tosca-rock ; whilst 
 at a short distance the stream of the Pabon forms a 
 cascade, about twenty feet in height, over a cavernous 
 mass of two varieties of tosca-rock ; of which one is 
 very compact and semi-crystalline, with seams of crys- 
 tallised carbonate of lime : similar compact varieties 
 are met with on the Salidillo and Seco. The absolute 
 identity (I speak after a comparison of my specimens) 
 between some of these varieties, and those from Tapal- 
 guen, and from the ridge south of Bahia Blanca, a dis- 
 tance of 400 miles of latitude, is very striking. 
 
 At Rosario there is but little tosca-rock : near this 
 place I first noticed at the edge of the river traces of 
 an underlying formation, which, twenty-five miles 
 higher up in the estancia of Gorodona, consists of a 
 pale yellowish clay, abounding with concretionary 
 cylinders of a ferruginous sandstone. This bed, which 
 is probably the equivalent of the older tertiary marine 
 strata, immediately to be described in Entre Rios, only 
 just rises above the level of the Parana when low. The 
 rest of the cliff" at Gorodona, is formed of red Pampean 
 mud, with, in the lower part, many concretions of 
 tosca, some stalactiformed, and with only a few in the 
 upper part : at the height of six feet above the river, 
 two gigantic skeletons of the Mastodon Andiwn were 
 here embedded ; their bones were scattered a few feet 
 apart, but many of them still held their proper relative 
 positions : they were much decayed and as soft as cheese, 
 
 * I quote these words from my note-book, as written down on 
 the spot, on account of the general absence of stratification in the 
 Pampean formation having been insisted on by M. d'Orbigny as a 
 proof of the diluvial origin of this great deposit. 
 
CHAP. XI. S^. F^ Bajada. ^^-^ 
 
 so tliat even one of tlie great molar teeth fell into 
 pieces in my hand. We here see that the Pampean 
 deposit contains mammiferous remains close to its base. 
 On the banks of the Carcarana, a few miles distant, the 
 lowest bed visible was pale Pampean mud, with masses 
 of tosca-rock, in one of which I found a much decayed 
 tooth of the Mastodon : above this bed, there was a 
 thin layer almost composed of small concretions of 
 white tosca, out of which I extracted a well preserved, 
 but slightly broken tooth of Toxodon Platensis : above 
 this there was an unusual bed of very soft impure sand- 
 stone. In this neighbourhood I noticed many single 
 embedded bones, and I heard of others having been 
 found in so perfect a state that they were long used as 
 gate-posts : the Jesuit Falkner found here the dermal 
 armour of some gigantic Edental quadruped. 
 
 In some of the red mud scraped from a tooth of 
 one of the mastodons at Gorodona, Professor Ehrenberg 
 finds seven Polygastrica and thirteen Phytolitharia,* all 
 of them, I believe, with two exceptions, already known 
 species. Of these twenty, the preponderating number 
 are of fresh-water origin ; only two species of Coscino- 
 discus and a Spongolithis show the direct influence of 
 
 ^ ' Monatsberichten der konig. Akad. zu Berlin,' April, 1845. The 
 list consists of : — 
 
 Polygastrica. 
 
 Campylodiscus clypeus. 
 Coscinodiscus subtilis. 
 al. sp. 
 
 Gallionella granulata. 
 Himantidium gracile. 
 Pinnularia borealis. 
 
 Eunotia. 
 
 Phytolitharia. 
 
 Litbasteriscus tuberculatus. I Litbostylidium Hamus. 
 
 Litbodontium bursa. „ polyedrum. 
 
 „ furcatnm. [ „ quadratum. 
 
 rostratnm. 
 Litbostylidium Ampbiodon. 
 „ Clep- 
 
 sammidinm. 
 
 rude. 
 „ vSerra. 
 „ uniden- 
 tatum. 
 Spongolithis Fustis. 
 
334 Panipean Fo7^ination. part u. 
 
 the sea ; therefore Professor Ehrenberg arrives at the 
 important conclusion that the deposit must have been 
 of brackish-water origin. Of the thirteen Phytolitharia, 
 nine are met with in the two deposits in Bahia Blanca, 
 where there is evidence from two other species of 
 Polygastrica that the beds were accumulated in brackish 
 water. The traces of corals, sponges, and Polythalamia, 
 found by Dr. Carpenter in the tosca-rock (of which I 
 must observe the greater number of specimens were 
 from the upper beds in the southern parts of the 
 formation), apparently show a more purely marine 
 origin. 
 
 At 8i. Fe Bajada^ in Entre Rios, the cliffs, esti- 
 mated at between sixty and seventy feet in heigbt, 
 expose an interesting section : the lower half consists 
 of tertiary strata with marine shells, and the upper half 
 of the Pampean formation. The lowest bed is an 
 obliquely laminated, blackish, indurated mud, with 
 distinct traces of vegetable remains.^ Above this there 
 is a thick bed of yellowish sandy clay, with much crys- 
 tallised gypsum and many shells of Ostrese, Pectens, 
 and Areas : above this there generally comes an arena- 
 ceous crystalline limestone, but there is sometimes 
 interposed a bed, about twelve feet thick, of dark green, 
 soapy clay, weathering into small angular fragments. 
 The limestone, where purest, is white, highly crystalline, 
 and full of cavities : it includes small pebbles of quartz, 
 broken shells, teeth of sharks, and sometimes, as I was 
 informed, large bones : it often contains so much sand 
 as to pass into a calcareous sandstone, and in such 
 
 ^ M. d'Orbigny has given (' Voyage, Part. Geolog.' p. 37) a 
 detailed description of this section, but as he does not mention this 
 lowest bed, it may have been concealed when he was there by the 
 river. There is a considerable discrepancy between his description 
 and mine, which I can only account for by the beds themselves 
 varying considerably in short distances. 
 
CHAP. XI. St. Fd Bajada. 335 
 
 parts the great Ostrea Patagonica ^ chiefly abounds. 
 In the upper part, the limestone alternates with layers 
 of fine white sand. The shells included in these beds 
 have been named for me by M. d'Orbigny ; they consist 
 of- 
 
 1. Ostrea Patagonica, d'Orbig. 
 
 ' Voyage,' Part. Pal. 
 
 2. „ Alvarezii, do. 
 
 3. Pecten Paranensis, do. (and 
 . PI. IV. of this work, fig. 30). 
 
 4. „ Darwinianus, do. and PL 
 
 IV. of this work, figs. 28, 29. 
 
 5. Venus Munsterii, d'Orbig. 
 
 'Voyage,' Pal. 
 
 6. Area Bonplandiana, do. 
 7 Cardium Platense, do. 
 
 8. Tellina, probably nov. spec, 
 but too imperfect for de- 
 scription. 
 
 These species are all extinct : the six first were 
 found by M. d'Orbigny and myself in the formations of 
 the Rio Negro, S. Josef, and other parts of Patagonia ; 
 and therefore, as first observed by M. d'Orbigny, these 
 beds certainly belong to the great Patagonian forma- 
 tion, which will be described in the ensuing chapter, 
 and which we shall see must be considered as a very 
 ancient tertiary one. North of the Bajada, M. d'Orbigny 
 found, in beds which he considers as lying beneath the 
 strata here described, remains of a Toxodon, which he 
 has named as a distinct species from the T. Platensis 
 of the Pampean formation. Much silicified wood is 
 found on the banks of the Parana (and likewise on the 
 Uruguay), and I was informed that they come out of 
 these lower beds; four specimens collected by myself 
 are dicotyledonous. 
 
 The upper half of the clifi", to a thickness of about 
 thirty feet, consists of Pampean mud, of which the 
 lower part is pale coloured, and the upper part of a 
 brighter red, with some irregular layers of an arenaceous 
 variety of tosca, and a few small concretions of the 
 ordinary kind. Close above the marine limestone, 
 
 ' Capt, Sulivan E.N., has given me a specimen of this shell, 
 which he found in the cliffs at Point Cerrito, between twenty and 
 thirty miles above the Bajada. 
 
^2,6 Pampean Formation. paet ii. 
 
 tliere is a thin stratum witli a concretionary outline of 
 wMte hard tosca-rock or marl, whicli may be considered 
 either as the uppermost bed of the inferior deposits, 
 or the lowest of the Pampean formation; at one time 
 I considered this bed as marking a passage between 
 the two formations ; but I have since become convinced 
 that I was deceived on this point. In the section on 
 the Parana, I did not find any mammiferous remains ; 
 but at two miles distance on the A. Tapas (a tributary 
 of the Conchitas), they were extremely numerous in a 
 low cliff of red Pampean mud with small concretions, 
 precisely like the upper bed on the Parana. Most of 
 the bones were solitary and much decayed ; but I saw 
 the dermal armour of a gigantic Edental quadruped, 
 forming a cauldron-like hollow, four or five feet in 
 diameter, out of which, as I was informed, the almost 
 entire skeleton had been lately removed. I found single 
 teeth of the Mastodon Andium, Toxodon Platensis, 
 and 'Equus curvidens, near to each other. As this 
 latter tooth approaches closely to that of the common 
 horse, I paid particular attention to its true embedment, 
 for I did not at that time know that there was a similar 
 tooth hidden in the matrix with the other mammiferous 
 remains from Punta Alta. It is an interesting circum- 
 stance, that Prof. Owen finds that the teeth of this 
 horse approach more closely in their peculiar curvature 
 to a fossil specimen brought by Mr. Lyell ^ from North 
 America, than to those of any other species of Equus. 
 
 The underlying marine tertiary strata extend over a 
 wide area : I was assured that they can be traced in 
 ravines in an east and west line across Entre Rios to 
 the Uruguay, a distance of about 135 miles. In a SE. 
 direction I heard of their existence at the head of the 
 
 ' Lyell's ' Travels in North America,' vol. i. p. 164, and ' Proc. of 
 Geolog. Soc' vol. iv. p. 39. 
 
CHAP. XI. Banda Oriental. '^'i>1 
 
 R. Nankay ; and at P. Gorda in Banda Oriental, a 
 distance of 170 miles, I found the same limestone, 
 containing the same fossil shells, lying at about the 
 same level above the river as at St. Fe. In a southerly 
 direction, these beds sink in height, for at another P. 
 Gorda in Entre Rios, the limestone is seen at a much 
 less height; and there can be little doubt that the 
 yellowish sandy clay, on a level with the river, between 
 the Carcarana and S. Nicolas, belongs to this same 
 formation ; as perhaps do the beds of sand at Buenos 
 Ayres, which lie at the bottom of the Pampean forma- 
 tion, about sixty feet beneath the surface of the Plata. 
 The southerly declination of these beds may perhaps be 
 due, not to unequal elevation, but to the original form 
 of the bottom of the sea, sloping from land situated to 
 the north; for that land existed at no great distance, 
 we have evidence in the vegetable remains in the lowest 
 bed at St. Fe ; and in the silicified wood and in the 
 bones of Toxodon Paranensis, found (according to 
 M. d'Orbigny) in still lower strata. 
 
 Banda Oriental. — This province lies on the north- 
 ern side of the Plata, and eastward of the Uruguay : it 
 has a gently undulatory surface, with a basis of primary 
 rocks : and is in most parts covered up with an un- 
 stratified mass, of no great thickness, of reddish 
 Pampean mud. In the eastern half, near Maldonado, 
 this deposit is more arenaceous than in the Pampas ; it 
 contains many though small concretions of marl or 
 tosca-rock, and others of highly ferruginous sandstone ; 
 in one section, only a few yards in depth, it rested on 
 stratified sand. Near Monte Video this deposit in some 
 spots appears to be of greater thickness ; and the re- 
 mains of the Glyptodon and other extinct mammifers 
 have been found in it. In the long line of cliffs, between 
 fifty and sixty feet in height, called the Barrancas de 
 
 z 
 
338 Pampean Formation, part h'' 
 
 S. Crregoi'lo, which extend westward of the Rio S. Lucia, 
 the lower half is formed of coarse sand of quartz and 
 feldspar without mica, like that now cast up on the 
 beach near Maldonado ; and the upper half of Pampean 
 mud, varying in colour and containing honey-combed 
 veins of soft calcareous matter and small concretions of 
 tosca-rock arranged in lines, and likewise a few pebbles 
 of quartz. This deposit fills up hollows and furrows in 
 the underlying sand ; appearing as if water charged 
 with mud had invaded a sandy beach. These cliffs 
 extend far westward, and at a distance of sixty miles, 
 near Colonia del Sacramiento, I found the Pampean 
 deposit resting in some places on this sand, and in 
 others on the primary rocks : between the sand and the 
 reddish mud, there appeared to be interposed, but the 
 section was not a very good one, a thin bed of shells of 
 an existing Mytilus, still partially retaining their colour. 
 The Pampean formation in Banda Oriental might readily 
 be mistaken for an alluvial deposit : compared with 
 that of the Pampas, it is often more sandy, and con- 
 tains small fragments of quartz ; the concretions are 
 much smaller, and there are no extensive masses of 
 tosca-rock. 
 
 In the extreme western parts of this province, be- 
 tween the Uruguay and a line drawn from Oolonia to 
 the R. Perdido (a tributary of the R. Negro), the 
 formations are far more complicated. Besides primary 
 rocks, we meet with extensive tracts and many flat- 
 topped, horizontally stratified, cliff-bounded, isolated 
 hills of tertiary strata, varying extraordinarily in 
 mineralogical nature, some identical with the old 
 marine beds of St. Fe Bajada, and some with those of 
 the much more recent Pampean formation. There are, 
 also, extensive Ioid tracts of country covered with a 
 deposit containing mammiferous remains, precisely like 
 
CHAP. XI. Banda Oriental. 339 
 
 that just described in the more eastern parts of the 
 province. Although from the smooth and unbroken 
 state of the country, I never obtained a section of this 
 latter deposit close to the foot of the higher tertiary 
 hills, yet I have not the least doubt that it is of quite 
 subsequent origin ; having been deposited after the sea 
 had worn the tertiary strata into the clifF-bounded hills. 
 This later formation, which is certainly the equivalent 
 of that of the Pampas, is well seen in the valleys in the 
 estancia of Berquelo, near Mercedes ; it here consists of 
 reddish earth, full of rounded grains of quartz, and 
 with some small concretions of tosca-rock arranged in 
 horizontal lines, so as perfectly to resemble, except in 
 containing a little calcareous matter, the formation in 
 the eastern parts of Banda Oriental, in Entre Rios, and 
 at other places : in this estancia the skeleton of a great 
 Edental quadruped was found. In the valley of the 
 Sarandis, at the distance of only a few miles, this de- 
 posit has a somewhat different character, being whiter, 
 softer, finer-grained, and full of little cavities, and con- 
 sequently of little specific gravity ; nor does it contain 
 any concretions or calcareous matter : I here procured 
 a head, which when first discovered must have been 
 quite perfect, of the Toxodon Platensis, another of a 
 Mylodon,^ perhaps M. Darwinii, and a large piece of 
 dermal armour, differing from that of the Glyptodon 
 clavipes. These bones are remarkable from their ex- 
 traordinarily fresh appearance ; when held over a lamp 
 of spirits of wine, they give out a strong odour and 
 burn with a small flame ; Mr. T. Reeks has been so kind 
 as to analyse some of the fragments, and he finds that 
 
 * This head was at first considered by Professor Owen (in the 
 ' Zoology of the Beagle's Voyage ') as belonging to a distinct genus, 
 namely, Grlossotherium. 
 
 z 2 
 
340 Pampean Formation, part h, 
 
 tliey contain about seven per cent, of animal matter, 
 and eight per cent, of water.^ 
 
 Tlie older tertiary strata, forming the higher isolated 
 hills and extensive tracts of country, vary, as I have 
 said, extraordinarily in composition : within the dis- 
 tance of a few miles, I sometimes passed over crystalline 
 limestone with agate, calcareous tuffs, and marly rocks, 
 all passing into each other, — red and pale mud with 
 concretions of tosca-rock, quite like the Pampean for- 
 mation, — calcareous conglomerates and sandstones, — 
 bright red sandstones passing either into red con- 
 glomerate, or into white sandstone, — hard siliceous 
 sandstones, jaspery and chalcedonic rocks, and numerous 
 other subordinate varieties. I was unable to make out 
 the relations of all these strata, and will describe only 
 a few distinct sections : — in the cliffs between P. Gorda 
 on the Uruguay and the A. de Vivoras, the upper bed 
 is crystalline cellular limestone often passing into cal- 
 careous sandstone, with impressions of some of the same 
 shells as at St. Fe Bajada ; at P. Gorda,^ this limestone 
 is interstratified with, and rests on, white sand, which 
 covers a bed about thirty feet thick of pale-coloured 
 clay, with many shells of the great Ostrea Patagonica : 
 beneath this, in the vertical cliff, nearly on a level with 
 the river, there is a bed of red mud absolutely like the 
 Pampean deposit, with numerous often large concre- 
 tions of perfectly characterised white, compact tosca- 
 rock. At the mouth of the Vivoras, the river flows 
 over a pale cavernous tosca-rock, quite like that in the 
 
 * Liebig (' Chemistry of Agriculture,' p. 194) states that fresh 
 dry bones contain from thirty- two to thirty-three per cent, of dry 
 gelatine. See also Dr. Daubeny in ' Edin. New Phil. Journ.' vol. 
 xxxvii. p. 293. 
 
 2 In my 'Journal' (p. 171, 1st edit.), I have hastily and inaccu- 
 rately stated that the Pampean mud, which is found over the eastern 
 part of B. Oriental, lies over the limestone at P. Gorda ; I should 
 have said that there was reason to infer that it was a subsequent or 
 superior deposit. 
 
CHAP. XI. Banda Oriental. 341 
 
 Pampas, and this appeared to underlie the crystalline 
 limestone; but the section was not unequivocal like 
 that at P. Gorda. These beds now form only a narrow 
 and much denuded strip of land ; but they must once 
 have extended much farther ; for on the next stream, 
 south of the S. Juan, Captain Sulivan, R.N., found a 
 little cliff, only just above the surface of the river, with 
 numerous shells of the Venus Mimsterii, d'Orbig.,' — 
 one of the species occurring at St. Fe, and of which 
 there are casts at P. Gorda : the line of cliffs of the 
 subsequently deposited true Pampean mud, extend 
 from Colonia to within half a mile of this spot, and no 
 doubt once covered up this denuded marine stratum. 
 Again at Colonia, a Frenchman found, in digging the 
 foundations of a house, a great mass of the Ostrea Pata- 
 gonica (of which I saw many fragments), packed to- 
 gether just beneath the surface, and directly superim- 
 ]3osed on the gneiss. These sections are important : 
 JVI. d'Orbigny is unwilling to believe that beds of the 
 same nature with the Pampean formation ever underlie 
 the ancient marine tertiary strata ; and I was as much 
 surprised at it as he could have been ; but the vertical 
 cliff at P. Gorda allowed of no mistake, and I must be 
 permitted to affirm, that after having examined the 
 country from the Colorado to St. Fe Bajada, I could not 
 be deceived in the mineralogical character of the Pam- 
 pean deposit. 
 
 Moreover, in a precipitous part of the ravine of 
 Las Bocas, a red sandstone is distinctly seen to overlie 
 a thick bed of pale mud, also quite like the Pampean 
 formation, abounding with concretions of true tosca- 
 rock. This sandstone extends over many miles of 
 country : it is as red as the brightest volcanic scoriae ; 
 it sometimes passes into a coarse red conglomerate 
 composed of the underlying primary rocks ; and often 
 
342 Pmnpeaii Formation. part n. 
 
 passes into a soft white sandstone with red streaks. 
 At the Calera de los Huerfanos, only a quarter of a 
 mile south of where I first met with the red sand- 
 stone, the crystalline white limestone is quarried : as 
 this bed is the uppermost, and as it often passes into 
 calcareous sandstone, interstratified with pure sand ; 
 and as the red sandstone likewise passes into soft white 
 sandstone, and is also the uppermost bed, I believe 
 that these two beds, though so different, are equiva- 
 lents. A few leagues southward of these two places, 
 on each side of the low primary range of S. Juan, 
 there are some flat-topped, cliff-bounded, separate 
 little hills, very similar to those fringing the primary 
 ranges in the great plain south of Buenos Ayres : they 
 are composed — 1st, of calcareous tuff with many par- 
 ticles of quartz, sometimes passing into a coarse con- 
 glomerate; 2nd, of a stone undistinguishable on the 
 closest inspection from the compacter varieties of 
 tosca-rock; and 3rd, of semi-crystalline limestone, 
 including nodules of agate : these three varieties pass 
 insensibly into each other, and as they form the upper- 
 most stratum in this district, I believe that they, also, 
 are the equivalents of the pure crystalline limestone, 
 and of the red and white sandstones and conglomerates. 
 Between these points and Mercedes on the Rio 
 Negro, there are scarcely any good sections, the road 
 passing over limestone, tosca-rock, calcareous and 
 bright red sandstones, and near the source of the S. Sal- 
 vador over a wide extent of jaspery rocks, with much 
 milky agate, like that in the limestone near S. Juan. 
 In the estancia of Berquelo, the separate, flat-topped, 
 cliff-bounded hills are rather higher than in other parts 
 of the country ; they range in a NE. and SW. direc- 
 tion ; their uppermost beds consist of the same bright 
 red sandstone, passing sometimes into a conglomerate, 
 
CHAP. XI. Banda Oriental. 343 
 
 and in the lower part into soft white sandstone, and 
 even into loose sand : beneath this sandstone, I saw 
 in two places layers of calcareous and marly rocks, and 
 in one place red Pampean-like earth ; at the base of 
 these sections, there was a hard, stratified, white sand- 
 stone, with chalcedonic layers. Near Mercedes, beds 
 of the same nature and apparently of the same age, are 
 associated with compact, white, crystalline limestone, 
 including much botryoidal agate, and singular masses, 
 like porcelain, but really composed of a calcareo-sili- 
 ceous paste. In sinking wells in this district the 
 chalcedonic strata seem to be the lowest. Beds, such 
 as here described, occur over the whole of this neigh- 
 bourhood ; but twenty miles further up the R. Negro, 
 in the cliffs of Perika, which are about fifty feet in 
 height, the upper bed is a prettily variegated chalce- 
 dony, mingled with a pure white tallowy limestone ; 
 beneath this there is a conglomerate of quartz and 
 granite ; beneath this many sandstones, some highly 
 calcareous ; and the whole lower two-thirds of the cliff 
 consist of earthy calcareous beds of various degrees of 
 purity, with one layer of reddish Pampean-like mud. 
 
 When examining the agates, the chalcedonic and 
 jaspery rocks, some of the limestones, and even the 
 bright red sandstones, I was forcibly struck with 
 their resemblance to deposits formed in the neigh- 
 bourhood of volcanic action. I now find that M. 
 Isabelle, in his ' Voyage a Buenos Ayres,' has described 
 closely similar beds on Itaquy and Ibicuy (which enter 
 the Uruguay some way north of theR. Negro) and these 
 beds include fragments of red decomposed true scoria 
 hardened by zeolite, and of black retinite : we have 
 then here good evidence of volcanic action during our 
 tertiary period. Still farther north, near S. Anna,^ 
 1 M. d'Orbigny, ' Voyage, Part. Geolog.,' p. 29. 
 
344 Panipean Formation. paet h. 
 
 where the Parana makes a remarkable bend, M. 
 Bonpland found some singular amygdaloidal rocks, 
 which perhaps may belong to this same epoch. 1 may 
 remark that, judging from the size and well-rounded 
 condition of the blocks of rock in the above -de scribed 
 conglomerates, masses of primary formation probably 
 existed at this tertiary period above water : there is, 
 also, according to M. Isabelle, much conglomerate 
 farther north, at Salto. 
 
 From whatever source and through whatever means 
 the great Pampean formation originated, we here have, 
 I must repeat, unequivocal evidence of a similar 
 action at a period before that of the deposition of the 
 marine tertiary strata with extinct shells, at St. Fe and 
 P. Gorda. During also the deposition of these strata, 
 we have in the intercalated layers of red Pampean-like 
 mud and tosca-rock, and in the passage near S. Juan of 
 the semi-crystalline limestones with agate into tosca 
 undistinguishable from that of the Pampas, evidence 
 of the same action, though continued only at intervals 
 and in a feeble manner. We have further seen that in 
 this district, at a period not only subsequent to the de- 
 position of the tertiary strata, but to their upheavement 
 and most extensive denudation, true Pampean mud 
 with its usual characters and including mammiferous 
 remains, were deposited round and between the hills 
 or islets formed of these tertiary strata, and over the 
 whole eastern and low primary districts of Banda 
 Oriental. 
 
 Earthy Qnass, luith extinct mammiferous remains^ 
 over the ^jorphyritic gravel at S. Julian, lat. 49° 14'' 
 8. in Patagonia. — This case, though not coming 
 strictly under the Pampean formation, may be con- 
 veniently given here. On the south side of the 
 harbour, there is a nearly level plain (mentioned in 
 
CHAP. XI. Mammiferotts Remains at S.Julian. 345 
 
 the eighth chapter) about seven miles long, and three or 
 four miles wide, estimated at ninety feet in height, and 
 bordered by perpendicular cliffs, ot which a section is 
 here represented. 
 
 No. 30. 
 Section of the Lowest Plain at Port S. Julian, 
 
 
 Cx-:;^-^ 
 
 
 A A. Superficial bed of reddisli earth, with the remains of the Macrauchenia, and 
 
 with recent sea-shells on the surface. 
 B. Gravel of porphyritic rocks. 
 
 CandD. Pumiceousmudstone. I Ancient tertiary formation. 
 
 E and F. Sandstone and argillaceous beds. ) -^ 
 
 The lower old tertiary strata (to be described in the 
 next chapter) are covered by the usual gravel bed ; 
 and this by an irregular earthy, sometimes sandy mass, 
 seldom more than two or three feet in thickness, except 
 where it fills up furrows or gullies worn not only 
 through the underlying gravel, but even through the 
 upper tertiary beds. This earthy mass is of a pale 
 reddish colour, like the less pure varieties of Pampean 
 mud in Banda Oriental ; it includes small calcareous 
 concretions, like those of tosca-rock but more arena- 
 ceous, and other concretions of a greenish, indurated 
 argillaceous substance : a few pebbles, also, from the 
 underlying gravel-bed are also included in it, and these 
 being occasionally arranged in horizontal lines, show 
 that the mass is of sub-aqueous origin. On the sur- 
 face and embedded in the superficial parts, there are 
 numerous shells, partially retaining their colours, of 
 three or four of the now commonest littoral species. 
 Near the bottom of one deep furrow (represented in 
 the diagram), filled up with this earthy deposit, I 
 found a large part of the skeleton of the Macrauchenia 
 
346 Pmnpean For^nahoji. part it.. 
 
 Patachonica — a gigantic and most extraordinary 
 pachyderm, allied, according to Professor Owen, to 
 the Palseotherium, but with affinities to the Ruminants, 
 especially to the American division of the Camelidae. 
 Several of the vertebree in a chain, and nearly all the 
 bones of one of the limbs, even to the smallest bones of 
 the foot, were embedded in their proper relative posi- 
 tions : hence the skeleton was certainly united by its 
 flesh or ligaments, when enveloped in the mud. This 
 earthy mass, with its concretions and mammiferous 
 remains, filling up furrows in the underlying gravel, 
 certainly presents a very striking resemblance to some 
 of the sections (for instance, at P. Alta in B. Blanca, 
 or at the Barrancas de S. Gregorio) in the Pampean 
 formation ; but I must believe that this resemblance is 
 only accidental. I suspect that the mud which at the 
 present day is accumulating in deep and narrow gullies 
 at the head of the harbour, would, after elevation, pre- 
 sent a very similar appearance. The southernmost 
 part of the true Pampean formation, namely, on the 
 Colorado, lies 560 miles of latitude north of this 
 point. ^ 
 
 With respect to the age of the Macrauchenia, the 
 shells on the surface prove that the mass in which the 
 skeleton was enveloped has been elevated above the 
 sea within the recent period : I did not see any of the 
 shells embedded at a sufficient depth to assure me 
 (though it be highly probable) that the whole thick- 
 ness of the mass was contemporaneous with these indi- 
 vidual specimens. That the Macrauchenia lived sub- 
 sequently to the spreading out of the gravel on this 
 
 ^ In the succeeding chapter I shall have to refer to a great 
 deposit of extinct mammiferous remains, lately discovered by Capt. 
 Sulivan, R.N., at a point still farther south, namely at the R- 
 Gallegos ; their age must at present remain doubtful. 
 
CHAP. XI. Mmnmiferous Remains at S.Julia?i. 2>A7 
 
 plain is certain ; and that this gravel, at the height of 
 ninety feet, was spread out long after the existence of 
 recent shells, is scarcely less certain. For, it was 
 shown in the eighth chapter, that this line of coast has 
 been upheaved with remarkable equability, and that 
 over a vast space both north and south of S. Julian, 
 recent species of shells are strewed on (or embedded in) 
 the surface of the 250 feet plain, and of the 350 feet 
 plain up to a height of 400 feet. These wide step- 
 formed plains have been formed by the denuding action 
 of the coast-waves on the old tertiary strata ; and 
 therefore, when the surface of the 350 feet plain, with 
 the shells on it, first rose above the level of the sea, 
 the 250 feet plain did not exist, and its formation, as 
 well as the spreading out of the gravel on its summit, 
 must have taken place subsequently. So also the 
 denudation and the gravel-covering of the ninety feet 
 plain must have taken place subsequently to the eleva- 
 tion of the 250 feet plain, on which recent shells are 
 also strewed. Hence there cannot be any doubt that 
 the Macrauchenia, which certainly was entombed in a 
 fresh state, and which must have been alive after the 
 spreading out of the gravel on the ninety feet plain, 
 existed, not only subsequently to the upraised shells on 
 the surface of the 250 feet plain, but also to those on 
 the 350 to 400 feet plain : these shells, eight in number 
 (namely, three species of Mytilus, two of Patella, one 
 Fusus, Voluta, and Balanus), are undoubtedly recent 
 species, and are the commonest kinds now living on 
 this coast. At Punta Alta in B. Blanca, I remarked 
 how marvellous it was, that the Toxodon, a mammifer 
 so unlike to all known genera, should have co-existed 
 with twenty-three still living marine animals ; and now 
 we find that the Macrauchenia, a quadruped only a 
 little less anomalous than the Toxodon, also co-existed 
 
34^ PcL^mpean Formation : pakt h. 
 
 with eight other still existing Mollusca : it should, 
 moreover, be borne in mind, that a tooth of a pachy- 
 dermatous animal was found with the other remains at 
 Punta Alta, which Professor Owen thinks almost cer- 
 tainly belonged to the Macrauchenia. 
 
 Mr. Lyell ^ has arrived at a highly important con- 
 clusion with respect to the age of the North American 
 extinct mammifers (many of which are closely allied to, 
 and even identical with, those of the Pampean forma- 
 tion), namely, that they lived subsequently to the period 
 when erratic boulders were transported by the agency 
 of floating ice in temjDerate latitudes. Now in the 
 valley of the San Cruz, only fifty miles of latitude south 
 of the spot where the Macrauchenia was entombed, vast 
 numbers of gigantic, angular boulders, which must 
 have been transported from the Cordillera on icebergs, 
 lie strewed on the plain, at the height of 1,400 feet 
 above the level of the sea. In ascending to this level, 
 several step-formed plains must be crossed, all of which 
 have necessarily required long time for their formation ; 
 hence the lowest or ninety feet plain, with its super- 
 ficial bed containing the remains of the Macrauchenia, 
 must have been formed very long subsequently to the 
 period when the 1 ,400 feet plain was beneath the sea, 
 and boulders were dropped on it from floating masses 
 of ice.^ Mr. Lyell's conclusion, therefore, is thus far 
 confirmed in the southern hemisphere ; and it is the 
 naore important, as one is naturally tempted to admit 
 so simple an explanation, that it was the ice-period 
 that caused the extinction of the numerous great 
 
 ' ' Geological Proceedings,' vol. iv. p. 36. 
 
 2 It must not be inferred from these remarks, that the ice-action 
 oeased in South America at this comparatively ancient period ; for 
 in Tierra del Fuego boulders were probably transported contempo- 
 raneously with, if not subsequently to, the formation of the ninety 
 ieet plain at S. Julian, and at other parts of the coast of Patagonia. 
 
CHAP. XI. concluding Renzarks on. 349 
 
 mammifers which so lately swarmed over the two 
 Americas. 
 
 Summary and concluding remarhs on the Pam- 
 pean Formation. — One of its most striking features is 
 its great extent ; I passed continuously over it from the 
 Colorado to St. Fe Bajada, a distance of 500 geographical 
 miles ; and M. d'Orbigny traced it for 250 miles farther 
 north. In the latitude of the Plata, I examined this 
 formation at intervals over an east and west line of 
 300 miles from Maldonado to the River Carcarana ; and 
 M. d'Orbigny believes it extends 100 miles farther 
 inland : from Mr. Caldcleugh's travels, however, I should 
 have thought that it had extended, south of the Cordo- 
 vese range, to near Mendoza, and I may add that I 
 heard of great bones having been found high up the 
 River Quinto. Hence the area of the Pampean forma- 
 tion, as remarked by M. d'Orbigny, is probably at least 
 equal to that of France, and perhaps twice or thrice 
 as great. In a basin, surrounded by gravel-cliff (at a 
 height of nearly 3,000 feet), south of Mendoza, there 
 is, as described in the tenth chapter, a deposit very like 
 the Pampean, interstratified with other matter ; and 
 again at S. Julian's, in Patagonia, 560 miles south of 
 the Colorado, a small irregular bed of a nearly similar 
 nature contains, as we have just seen, mammiferous 
 remains. In the provinces of Moxos and Chiquitos 
 (1,000 miles northward of the Pampas), and in Bolivia, 
 at a height of 4,000 metres, M. d'Orbigny has described 
 similar deposits, which he believes to have been formed 
 by the same agency contemporaneously with the Pam- 
 pean formation. Considering the immense distances 
 between these several points, and their different heights, 
 it appears to me infinitely more probable, that this 
 similarity has resulted not from contemporaneousness of 
 origin, but from the similarity of the rocky framework 
 
350 Pampean Foinnation, part h. 
 
 of the continent : it is known that in Brazil an immense 
 area consists of gneissic rocks, and we shall hereafter 
 see, over how great a length the plutonic rocks of the 
 Cordillera, the overlying purple porphyries, and the 
 trachytic ejections, are almost identical in nature. 
 
 Three theories on the origin of the Pampean forma- 
 tion have been propounded : — First, that of a great 
 debacle by M. d'Orbigny; this seems founded chiefly 
 on the absence of stratification, and on the number of 
 embedded remains of terrestrial quadrupeds. Although 
 the Pampean formation (like so many argillaceous 
 deposits) is not divided into distinct and separate strata, 
 yet we have seen that in one good section it was striped 
 with horizontal zones of colour, and that in several 
 specified places the upper and lower parts differed, not 
 only considerably in colour, but greatly in constitution. 
 In the southern part of the Pampas the upper mass (to 
 a certain extent stratified) generally consists of hard 
 tosca-rock, and the lower part of red Pampean mud, 
 often itself divided into two or more masses, varying in 
 colour and in the quantity of included calcareous matter. 
 In western Banda Oriental, beds of a similar nature, 
 but of a greater age, conformably underlie and are 
 intercalated with the regularly stratified tertiary forma- 
 tion. As a general rule, the marly concretions are 
 arranged in horizontal lines, sometimes united into 
 irregular strata : surely, if the mud had been tumul- 
 tuously deposited in mass, the included calcareous 
 matter would have segregated itself irregularly, and 
 not into nodules arranged in horizontal lines, one above 
 the other and often far apart : this arrangement appears 
 to me to prove that mud, differing slightly in composi- 
 tion, was successively and quietly deposited. On the 
 theory of a debacle, a prodigious amount of mud, with- 
 out a single pebble, is supposed to have been borne over 
 
CHAP. XI. Theories on its Origin. 351 
 
 the wide surface of tlie Pampas, when under water : on 
 the other hand, over the whole of Patagonia, the same 
 or another debacle is supposed to have borne nothing 
 but gravel, — the gravel and the fine mud in the neigh- 
 bourhood of the Eios Negro and Colorado having been 
 borne to an equal distance from the Cordillera, or 
 imagined line of disturbance : assuredly directly oppo- 
 site effects ought not to be attributed to the same 
 agency. Where, again, could a mass of fine sediment, 
 charged with calcareous matter in a fit state for chemi- 
 cal segregation, and in quantity sufficient to cover an 
 area at least 750 miles long, and 400 miles broad, to a 
 depth of from twenty or thirty feet to a hundred feet, 
 have been accumulated, ready to be transported by the 
 supposed debacle ? To my mind it is little short of 
 demonstration, that a great lapse of time was necessary 
 for the production and deposition of the enormous 
 amount of mud-like matter forming the Pampas ; nor 
 should I have noticed the theory of a debacle, had 
 it not been adduced by a naturalist so eminent as 
 M. d'Orbigny. 
 
 A second theory, first suggested, I believe, by Sir 
 
 . Parish, is that the Pampean formation was thrown 
 
 Idown on low and marshy plains by the rivers of this 
 
 country before they assumed their present courses. 
 
 The appearance and composition of the deposit, the 
 
 [manner in which it slopes up and round the primary 
 
 ranges, the nature of the underlying marine beds, the 
 
 estuary and sea-shells on the surface, the overlying 
 
 sandstone beds at M. Hermoso, are all quite opposed 
 
 [to this view. Nor do I believe that there is a single 
 
 instance of a skeleton of one of the extinct mammifers 
 
 having been found in an upright position, as if it had 
 
 been mired. 
 
 The third theory, of the truth of which I cannot 
 
352 Pampean Formatio7i. paet n. 
 
 entertain the smallest doubt, is that the Pampean for- 
 mation was slowly accmnulated at the mouth of the 
 former estuary of the Plata and in the sea adjoining it. 
 I have come to this conclusion from the reasons assigned 
 against the two foregoing theories, and from simple 
 geographical considerations. From the numerous shells 
 of the AzarcL lahiata lying loose on the surface of the 
 plains, and near Buenos Ayres embedded in the tosca- 
 rock, we know that this formation not only was formerly 
 covered by, but that the uppermost parts were deposited 
 in, the brackish water of the ancient La Plata. South- 
 ward and seaward of Buenos Ayres, the plains were 
 upheaved from under water inhabited by true marine 
 shells. We further know from Professor Ehrenberg's 
 examination of the twenty microscopical organisms in 
 the mud round the tooth of the Mastodon high up the 
 course of the Parana, that the bottom-most part of 
 this formation was of brackish- water origin. A similar 
 conclusion must be extended to the beds of like com- 
 position, at the level of the sea and under it, at 
 M. Hermoso in Bahia Blanca. Dr. Carpenter finds 
 that the harder varieties of tosca-rock, collected chiefly 
 to the south, contain marine spongoid bodies, minute 
 fragments of shells, corals, and Polythalamia ; these 
 perhaps may have been drifted inwards by the tides, 
 from the more open parts of the sea. The absence of 
 shells, throughout this deposit, with the exception of 
 the uppermost layers near Buenos Ayres, is a remark- 
 able fact : can it be explained by the brackish condition 
 of the water, or by the deep mud at the bottom ? I 
 have stated that both the reddish mud and the concre- 
 tions of tosca-rock are often penetrated by minute, 
 linear cavities, such as frequently may be observed in 
 fresh-water calcareous deposits : — were they produced 
 by the burrowing of small worms ? Only on this view 
 
CHAP. XI. Theories on its Origin. 353 
 
 of the Pampean formation having been of estuary 
 origin, can the extraordinary numbers (presently to be 
 alluded to) of the embedded mammiferous remains be 
 explained.^ 
 
 With respect to the first origin of the reddish mud, 
 I will only remark, that the enormous area of Brazil 
 consists in chief part of gneissic and other granitic rocks, 
 which have suffered decomposition, and been converted 
 into a red, gritty, argillaceous mass, to a greater depth 
 than in any other country which I have seen. The 
 mixture of rounded grains, and even of small fragments 
 and pebbles of quartz, in the Pampean mud of Banda 
 Oriental, is evidently due to the neighbouring and 
 underlying primary rocks. The estuary mud was drifted 
 during the Pampean period in a much more southerly 
 source, owing probably to the east and west primary 
 ridges south of the Plata not having been then elevated, 
 than the mud of the Plata at present is ; for it was 
 formerly deposited as far south as the Colorado. The 
 quantity of calcareous matter in this formation, espe- 
 cially in those large districts where the whole mass 
 passes into tosca-rock, is very great : I have already 
 remarked on the close resemblance in external and 
 microscopical appearance between this tosca-rock and 
 the strata at Coquimbo, which have certainly resulted 
 from the decay and attrition of recent shells : ^ I dare 
 
 ^ It is almost superfluous to give the numerous cases (for instance, 
 in Sumatra ; Lyell's ' Principles,' vol. iii. p. 325, sixth edit.) of the 
 carcases of animals having been washed out to sea by swollen rivers : 
 but I may refer to a recent account by Mr. Bettington ('Asiatic Soc' 
 1845, June 21st), of oxen, deer, and bears being carried into the 
 Gulf of Cambray ; see, also, the account in my 'Journal ' (2nd edit, 
 p. 133) of the numbers of animals drowned in the Plata during the 
 great, often recurrent, droughts. 
 
 2 I may add, that there are nearly similar superficial calcareous 
 beds at King Greorge's Sound in Australia ; and these undoubtedly 
 have been found by the disintegration of marine remains (see Chap- 
 ter Vn.). There is, however, something very remarkable 'in the 
 frequency of superficial, thin beds of earthy calcareous matter, in 
 
 A A 
 
354 Panipean Formation part n. 
 
 not, however, extend this conclusion to the calcai'eous 
 rocks of the Pampas, more especially as the underlying 
 tertiary strata in Western Banda Oriental show that at 
 that period there was a copious emission of carbonate 
 of lime in connection with volcanic action. 
 
 The Pampean formation, judging from its similar 
 composition, and from the aj)parent absolute specific 
 identity of some of its mammiferous remains, and from 
 the generic resemblance of others, belongs over its vast 
 area— throughout Banda Oriental, Entre Bios, and the 
 wide extent of the Pampas as far south as the Colorado, 
 — to the same geological epoch. The mammiferous 
 remains occur at all depths from the top to the bottom 
 of the deposit ; and I may add that nowhere in the 
 Pampas is there any appearance of much superficial 
 denudation : some bones which I found near the 
 Guardia del Monte were embedded close to the surface : 
 and this appears to have been the case with many of 
 those discovered in Banda Oriental : on the Matanzas, 
 twenty miles south of Buenos Ayres, a Glyptodon was 
 embedded five feet beneath the surface ; numerous 
 remains were found by S. Muniz, near Luxan, at an 
 average depth of eighteen feet; in Buenos Ayres a 
 skeleton was disinterred at sixty feet depth, and on the 
 Parana I have descried two skeletons of the Mastodon 
 only five or six feet above the very base of the deposit. 
 With respect to the age of this formation, as judged of 
 by the ordinary standard of the existence of Mollusca, 
 
 districts where the surrounding rocks are not calcareous. Major 
 Charters in a Paper read before the Eoyal Geographical Society 
 (April IBth, 1840, and abstracted in the ' Atheneeum,' p. 317), states 
 that this is the case in parts of Mexico, and that he has observed 
 similar appearances in many parts of South Africa. The circum- 
 stance of the uppermost stratum round the rugged Sierra Ventana 
 consisting of calcareous or marly matter, without any covering of 
 alluvial matter, strikes me as very singular, in whatever manner we 
 view the deposition and elevation of the Pampean formation. 
 
cjHAj. XI. of Recent Origin. 355 
 
 the only evidence within the limits of the true Pampas 
 which is at all trustworthy is afforded by the still living 
 Azara labiata being embedded in tosca-rock near 
 Buenos Ayres. At Punta Alta, however, we have seen 
 that several of the extinct mammifers, most character- 
 istic of the Pampean formation, co-existed with twenty 
 species of Mollusca, a barnacle and two corals^ all still 
 living on this same coast ; — for when we remember 
 that the shells have a more ancient appearance than 
 the bones ; that many of the bones, though embedded 
 in a coarse conglomerate, are perfectly preserved ; that 
 almost all the parts of the skeleton of the Scelidothe- 
 rium, even to the knee-cap, were lying in their proper 
 relative positions ; and that a large piece of the fragile 
 dermal armour of a Dasypoid quadruped, connected 
 with some of the bones of the foot, had been entombed 
 in a condition allowing the two sides to be doubled 
 together, it must assuredly be admitted that these 
 mammiferous remains were embedded in a fresh state, 
 and therefore that the living animals co-existed with 
 the co-embedded shells. Moreover, the Macrauchenia 
 Patachonica (of which, according to Professor Owen, 
 remains also occur in the Pampas of Buenos Ayres, and 
 at Punta Alta) has been shown by satisfactory evidence 
 of another kind to have lived on the plains of Pata- 
 gonia long after the period when the adjoining sea was 
 first tenanted by its present commonest molluscous 
 animals. We must, therefore, conclude that the Pam- 
 pean formation belongs, in the ordinary geological 
 sense of the word, to the Recent Period.^ 
 
 At St. Fe Bajada, the Pampean estuary formation, 
 with its mammiferous remains, conformably overlies 
 
 ' M. d'Orbigny believes ('Voyage, Part. G6olog.' p. 81) that this 
 formation, though 'tres voisine de la Dotre, est neanmoins de beau- 
 coup anterieure ^ notre creation.' 
 
 A A 2 
 
356 Pampean Forniation paet ir. 
 
 the marine tertiary strata, wliicli (as first sliowii by 
 M. d'Orbigny) are contemporaneous with those of 
 Patagonia, and which, as we shall hereafter see, belong 
 to a very ancient tertiary stage. When examining the 
 junction between these two formations, I thought that 
 the concretionary layer of marl marked a passage be- 
 tween the marine and estuary stages. M. d'Orbigny 
 disputes this view (as given in my Journal), and I admit 
 that it is erroneous, though in some degree excusable, 
 from their conformability and from both abounding 
 with calcareous matter. It would, indeed, have been a 
 great anomaly if there had been a true passage between 
 a deposit contemporaneous with existing species of 
 Mollusca, and one in which all the Mollusca appear to 
 be extinct. Northward of St. Fe, M. d'Orbigny met 
 with ferruginous sandstones, marly rocks, and other 
 beds, which he considers as a distinct and lower forma- 
 tion ; but the evidence that they are not parts of the 
 same, with an altered mineralogical character, does not 
 appear to me quite satisfactory. 
 
 In Western Banda Oriental, whilst the marine ter- 
 tiary strata were accumulating, there were volcanic 
 eruptions, much silex and lime were precipitated from 
 solution, coarse conglomerates were formed, being de- 
 rived probably from adjoining land, and layers of red 
 mud and marly rocks, like those of the Pampean for- 
 mation, were occasionally deposited. The true Pampean 
 deposit, with mammiferous remains, instead of as at 
 St. Fe overlying conformably the tertiary strata, is 
 here seen at a lower level folding round and between 
 the flat-topped, cliff-bounded hills, formed by the up- 
 heaval and denudation of these same tertiary strata. 
 The upheaval, having occurred here earlier than at 
 St. Fe, may be naturally accounted for by the contem- 
 poraneous volcanic action. At the Barrancas de S. 
 
<3HAP. XI. of Recent Origin. 357 
 
 Gregorio, the Pampean deposit, as we have seen, over- 
 lies and fills up furrows in coarse sand, precisely like 
 that now accumulating on the shores near the mouth of 
 the Plata. I can hardly believe that this loose and 
 coarse sand is contemporaneous with the old tertiary 
 and often crystalline strata of the more western parts 
 of the province ; and am induced to suspect that it is 
 of subsequent origin. If that section near Colonia 
 could be implicitly trusted, in which, at a height of 
 only fifteen feet above the Plata, a bed of fresh-looking 
 mussels, of an existing littoral species, appeared to lie 
 between the sand and the Pampean mud, I should con- 
 clude that Banda Oriental must have stood, when the 
 coarse sand was accumulating, at only a little below its 
 present level, and had then subsided, allowing the 
 estuary Pampean mud to cover far and wide its surface 
 up to a height of some hundred feet ; and that after 
 this subsidence the province had been uplifted to its 
 present level. 
 
 In Western Banda Oriental, we know, from two 
 unequivocal sections, that there is a mass, absolutely 
 un distinguishable from the true Pampean deposit, be- 
 neath the old tertiary strata. This inferior mass must 
 be very much more ancient than the upper deposit with 
 its mammiferous remains, for it lies beneath the ter- 
 tiary strata in which all the shells are extinct. Never- 
 theless, the lower and upper masses, as well as some 
 intermediate layers, are so similar in mineralogical 
 character, that I cannot doubt that they are all of 
 estuary origin, and have been derived from the same 
 great source. At first it appeared to me extremely 
 improbable that mud of the same nature should have 
 been deposited on nearly the same spot, during an 
 immense lapse of time, namely, from a period equiva- 
 lent perhaps to the Eocene of Europe to that of the 
 
358 Pampeaii Formation part n, 
 
 Pampean formation. But as, at tlie very commencement 
 of the Pampean period, if not at a still earlier period, 
 the Sierra Ventana formed a boundary to the south, — 
 the Cordillera or the plains in front of them to th& 
 west, — the whole province of Corrientes probably to 
 the north, for, according to M. d'Orbigny, it is not 
 covered by the Pampean deposit, — and Brazil, as known 
 by the remains in the caves, to the north-east ; and as 
 again, during the older tertiary period, land already 
 existed in Western Banda Oriental and near St. Fe 
 Bajada, as may be inferred from the vegetable debris, 
 from the quantities of silicified wood, and from the 
 remains of a Toxodon found, according to M. d'Orbigny,. 
 in still lower strata, we may conclude that at this an- 
 cient period a great expanse of water was surrounded 
 by the same rocky framework which now bounds the 
 plains of Pampean formation. This having been the 
 case, the circumstance of sediment of the same nature 
 having been deposited in the same area during an im- 
 mense lapse of time, though highly remarkable, does 
 not appear incredible. 
 
 The elevation of the Pampas, at least of the southern 
 parts, has been slow and interrupted by several periods 
 of rest, as may be inferred from the plains, cliffs, and 
 lines of sand-dunes (with shells and pumice-pebbles) 
 standing at different heights. I believe, also, that the 
 Pampean mud continued to be deposited, after parts of 
 this formation had already been elevated, in the same 
 manner as mud would continue to be deposited in the 
 estuary of the Plata, if the mud-banks on its shores 
 were now uplifted and changed into plains : I believe 
 in this from the improbability of so many skeletons 
 and bones having been accumulated at one spot, where 
 M. Hermoso now stands, at a depth of between 800 and 
 1,000 feet, and at a vast distance from any land except 
 
CHAP. XI. of Recent Origin. 359 
 
 small rocky islets, — as must have been the case, if the 
 high tosca-plain round the Yentana and adjoining 
 Sierras, had not been already uplifted and converted 
 into land, supporting mammiferous animals. At Punta 
 Alta we have good evidence that the gravel-strata, 
 which certainly belong to the true Pampean period, 
 were accumulated after the elevation in that neighbour- 
 hood of the main part of the Pampean deposit, whence 
 the rounded masses of tosca-rock were derived, and 
 that rolled fragment of black bone in the same peculiar 
 condition with the remains at Monte Hermoso. 
 
 The number of the mammiferous remains embedded 
 in the Pampas is, as I have remarked, wonderful ; it 
 should be borne in mind that they have almost exclu- 
 sively been found in the cliffs and steep banks of rivers, 
 and that, until lately, they excited no attention amongst 
 the inhabitants ; I am firmly convinced that a deep 
 trench could not be cut in any line across the Pampas, 
 without intersecting the remains of some quadruped. 
 It is difficult to form an opinion in what part of the 
 Pampas they are most numerous ; in a limited spot 
 they could not well have been more numerous than 
 they were at P. Alta ; the number, however, lately found 
 by Seiior F. Muniz, near Luzan, in a central spot in 
 the Pampas, is extraordinarily great : at the end of 
 this chapter I will give a list of all the localities at 
 which I have heard of remains having been discovered. 
 Very frequently the remains consist of almost perfect 
 skeletons ; but there are, also, numerous single bones, 
 as for instance at St. Fe. Their state of preservation 
 varies much, even when embedded near each other : I 
 saw none others so perfectly preserved as the heads of 
 the Toxodon and Mylodon from the white soft earthy 
 bed on the Sarandis in Banda Oriental. It is remarkable 
 
360 Panipean Formation : part n. 
 
 that in two limited sections I found no less tlian five 
 teeth separately embedded, and I heard of teeth having 
 been similarly found in other parts : may we suppose 
 that the skeletons or heads were for a long time gently 
 drifted by currents over the soft muddy bottom, and 
 that the teeth occasionally, here and there, dropped 
 out? 
 
 It may be naturally asked, where did these numerous 
 animals live ? From the remarkable discoveries of 
 MM. Lund and Clausen, it appears that some of the 
 species found in the Pampas inhabited the high-lands 
 of Brazil : the Mastodon Andium is embedded at great 
 heights in the Cordillera from north of the equator ^ to 
 at least as far south as Tarija; and as there is no higher 
 land, there can be little doubt that this Mastodon must 
 have lived on the plains and valleys of that great range. 
 These countries, however, appear too far distant for 
 the habitation of the individuals entombed in the 
 Pampas : we must probably look to nearer points, for 
 instance to the province of Corrientes, which, as already 
 remarked, is said not to be covered by the Pampean 
 formation, and may therefore, at the period of its 
 deposition, have existed as dry land. I have already 
 given my reasons for believing that the animals em- 
 bedded at M. Hermoso and at P. Alta in Bahia Blanca, 
 lived on adjoining land, formed of parts of the already 
 elevated Pampean deposit. With respect to the food 
 of these many great extinct quadrupeds, I will not 
 repeat the facts given in my Journal (second edit. p. 85), 
 showing that there is no correlation between the luxuri- 
 ance of the vegetation of a country and the size of its 
 
 * Humboldt states that the Mastodon has been discovered in 
 New Granada ; it has been found in Quito. When at Lima, I saw a 
 tooth of a Mastodon in the possession of Don M. Kivero, found at 
 Playa Chica on the Maranon, near the Guallaga. Every one has 
 heard of the numerous remains of Mastodon in Bolivia. 
 
CHAP. XI. Mannniferous Remains of. 361 
 
 mammiferous inhabitants. I do not doubt that larg-e 
 animals could now exist, as far as the amount, not kind, 
 of vegetation is concerned, on the sterile plains of Bahia 
 Blanca and of the R. Negro, as well as on the equally, 
 if not more sterile plains of Southern Africa. The 
 climate, however, may perhaps have somewhat deterior- 
 ated since the mammifers embedded at Bahia Blanca 
 lived there ; for we must not infer, from the continued 
 existence of the same shells on the present coasts, that 
 there has been no change in climate ; for several of 
 these shells now range northward along the shores of 
 Brazil, where the most luxuriant vegetation flourishes 
 under a tropical temperature. With respect to the 
 extinction, which at first fills the mind with astonish- 
 ment, of the many great and small mammifers of this 
 period, I may also refer to the work above cited (second 
 edit. p. 173), in which I have endeavoured to show that, 
 however unable we may be to explain the precise cause, 
 we ought not properly to feel more surprised at a species 
 becoming extinct than at one being rare ; and yet we 
 are accustomed to view the rarity of any particular 
 species as an ordinary event, not requiring any extra- 
 ordinary agency. 
 
 The several mammifers embedded in the Pampean 
 formation, which mostly belong to extinct genera, and 
 some even to extinct families or orders, and which differ 
 nearly, if not quite, as much as do the Eocene mammifers 
 of Europe from living quadrupeds having existed con- 
 temporaneously with Mollusca, all still inhabiting the 
 adjoining sea, is certainly a most striking fact. It is, 
 however, far from being an isolated one ; for, during 
 the late tertiary deposits of Britain, an elephant, rhi- 
 noceros, and hippopotamus co-existed with many recent 
 land and fresh- water shells ; and, in North America, 
 we have the best evidence that a mastodon, elephant, 
 
362 Pampean Formation : part n. 
 
 megatlierium, megalonyx, mylodon, an extinct horse 
 and ox, likewise co-existed with numerous land, fresh- 
 water, and marine recent shells.^ The enumeration of 
 these extinct North American animals naturally leads 
 me to refer to the former closer relation of the 
 mammiferous inhabitants of the two Americas, which 
 I have discussed in my Journal, and likewise to the 
 vast extent of country over which some of them ranged : 
 thus the same species of the Megatlierium, Megalonyx, 
 JEquus (as far as the state of their remains permits of 
 identification), extended from the Southern United 
 States of North America to Bahia Blanca, in lat. 39° S., 
 on the coast of Patagonia. The fact of these animals 
 having inhabited tropical and temperate regions does 
 not appear to me any great difficulty, seeing that at 
 the Cape of Good Hope several quadrupeds, such as the 
 elephant and hippopotamus, range from the equator to 
 lat. 35° south. The case of the Mastodon Andium is 
 one of more difficulty, for it is found from lat. 36° S., 
 over, as I have reason to believe, nearly the whole of 
 Brazil, and up the Cordillera, to regions which, according 
 to M. d'Orbigny, border on perpetual snow, and which 
 are almost destitute of vegetation : undoubtedly the 
 climate of the Cordillera must have been different when 
 the mastodon inhabited it ; but we should not forget 
 the case of the Siberian mammoth and rhinoceros, as 
 showing how severe a climate the larger pachyderm ata 
 can endure ; nor overlook the fact of the guanaco rang- 
 ing at the present day over the hot low deserts of Peru, 
 the lofty pinnacles of the Cordillera, and the damp 
 forest-clad land of Southern Tierra del Fuego; the 
 
 * Many original observations, and a summary on this subject, are 
 given in Mr. Lyell's paper in the ' Geolog. Proc' vol. iv. p. 3, and in 
 his ' Travels in North America,' vol. i. p. 164, and vol. ii. p. 60. For 
 the European analogous cases, see Mr. Lyell's ' Principles of Geology' 
 (6th edit.) vol. i. p. 137. 
 
CHAP. XI. MammiferoMS Remams of. 363 
 
 puma, also, is found from tlie equator to the Strait of 
 Magellan, and I have seen its footsteps only a little 
 below the limits of perpetual snow in the Cordillera of 
 Chile. 
 
 At the period, so recent in a geological sense, when 
 these extinct mammifers existed, the two Americas 
 must have swarmed with quadrupeds, many of them 
 of gigantic size ; for, besides those more particularly 
 referred to in this chapter, we must include in this 
 same period those wonderfully numerous remains, some 
 few of them specifically, and others generically related 
 to those of the Pampas, discovered by MM. Lund and 
 Clausen in the caves of Brazil. Finally, the facts here 
 given show how cautious we ought to be in judging of 
 the antiquity of a formation from even a great amount 
 of difference between the extinct and living species in 
 any one class of animals ; — we ought even to be cautious 
 in accepting the general proposition, that change in 
 organic forms and lapse of time are at all, necessarily ,^ 
 correlatives. 
 
 SUPPLEMENT. 
 
 On tJie Thichness of the Pampean Formation, near- 
 Buenos Ay res. 
 
 Eepublished from the ' Proc. of the Geological Soc' Dec. 3, 1862. 
 
 M. Sourdeaux and J. Coghlan, Esq., C.E., have had the 
 kindness to send me, through E. B. Webb, Esq., C.E., 
 some excellent sections of, and specimens from, two 
 artesian wells lately made at Buenos Ayres. I beg 
 permission to present these specimens to the Geological 
 
364 Panipean Formation : paet n. 
 
 Society, as they would be of considerable service to any- 
 one investigating the geology of that country. The 
 Panipean formation is in several respects so interesting, 
 from containing an extraordinary number of the remains 
 of various extinct Mammifers, such as Megatherium^ 
 Mylodon, Mastodon, Toxodon^ &c., and from its great 
 extent, stretching in a north and south line for at least 
 750 geographical miles, and covering an area fully 
 equal to that of France, that, as it appears to me, a 
 record ought to be preserved of these borings. South- 
 ward, at the Rio Colorado, the Pampean formation 
 meets the great Tertiary formation of Patagonia ; and 
 northward, at St. Fe Bajada, it overlies this same for- 
 mation with its several extinct shells. 
 
 In the central region near Buenos Ayres no natural 
 section shows its thickness ; but, by the borings there 
 made in two artesian wells (figs. 31 and 32), the Pampean 
 mud, with tosca-rock, is seen to extend downwards 
 from the level of the Rio Plata to a depth of sixty-one 
 feet, and to this must be added fifty-five feet above 
 the level of the river. These argillaceous beds overlie 
 coarse sand, containing the Azara lahiata (a shell 
 characteristic of the Pampean formation), and attaining 
 a thickness of about ninety-three feet.^ So that the 
 
 ^ The following extract from the Report of the borers relates to 
 this bed : — The bed of yellow, fluid sands between IS^-GO and47'°-20 
 below the ground contains a subterranean ascending current, the 
 level of which has not varied by a centimetre for three years. The 
 level is 0™-60 (2 feet over the level of the wells at Barracas). This bed 
 ('napa')is powerfully absorbent. At&S^-SO a second subterranean cur- 
 rent (' overflowing'), was met, which rose one foot over the surface of 
 the ground at Barracas. The discharge was about 50 pipes daily, but 
 the water was salt and undrinkable. At 73"" "30 was found a third 
 subterranean current ('overflowing'), which reached with difficulty 
 the level of the ground. The discharge might be calculated at 
 100 pipes daily. The water was very salt, and absorbed that of 
 the flrst overflowing current. The great spring was met with at 
 77""65.' 
 
 As regards the quality and abundance of the water, Mr. Coghlan 
 remarks that ' The quantity of water discharged per hour through a 
 tube of about 4| inches in diameter, at a level of 6 feet above high- 
 
CHAP. XI. 
 
 On the Thickness of the. 
 
 Z^'S 
 
 entire thickness of tlie great estuarine or Pampean for- 
 mation near Buenos Ayres is nearly 210 feet. 
 
 I 
 
 No. 31. 
 
 Comparatire sections of the Artesian Wells of Barracas and Buenos Ayres. 
 (Distance, 3| miles.) 
 
 Barracas. Riachuelo. 
 
 Buenos Ayres. 
 
 Level of equi- 
 librium of 
 the princi- 
 pal spring 
 
 \ 
 
 1st. spring 
 
 2nd spring 
 
 3rd spring . 
 4th spring . 
 
 =^ High water 
 level 
 
 'm d 
 1 / 
 
 H B^ 2nd spring 
 "^ n=^ 3rd spring 
 
 ■mm ^ 
 
 SL^^ 4th spring 
 ^ k^ 245 feet 
 
 470 feet 
 
 a. Clays and Tosca . 
 
 6. Sand 
 
 c. Very sandy clay . . . \ 
 
 d. Dark blue plastic clay . . y 
 
 e. Tosca, with calcareous nodules ) 
 /. Yellow sands, very fine and fluid 
 
 Thickness Thickness 
 at Barracas. at Buenos 
 Peet Ayres. Feet 
 — 57 
 
 13 51 
 
 47 
 94 
 
 52 
 45 
 
 water mark, was 2,658 gallons. Its temperature was 21° Cent., and 
 it had a slightly disagreeable taste, from its being impregnated with, 
 salts of lime and magnesia, and a small quantity of sulph ur 
 hydrogen.' 
 
366 
 
 Painpean Formation : 
 
 PAKT II. 
 
 g. G-reen sands . 
 
 h. Tertiary clay and sandstone (for details see fig. 32) . 
 Z;,. Hard sandstone at the bottom of the Barracas well . 
 k^. Very calcareous red clay, becoming more marly 
 beneath ; bored through to a depth of . 
 
 Thickness Thickness 
 
 at Barracas at Buenos 
 
 Feet Ayres. Feet 
 
 66 62 
 
 34 33 
 
 4i - 
 
 225 
 
 This formation rests on various marine beds of in- 
 durated green clay, sand with corals, sandstone, and 
 limestone, altogether 107 feet in thickness. These 
 
 No. 32. 
 Detailed section of the Artesian Well at Barracas 
 
 Thickness 
 in metres 
 
 a. Sand 4*33 
 
 6. Very arenaceous clay 8'02 
 
 J Fine clay 1-05 
 
 I Blue plastic clay 2-90 
 
 d. Tosca, with calcareous nodules .... 2*30 
 
 e. Yellow sand, very fine and fluid, Avith quartz 
 
 pebbles and fluviatile shells .... 28'60 
 /. Green clay, more or less plastic and calcareous, 
 
 with iron pyrites, marine shells, and nodules 
 
 of lithographic stone 20*30 
 
 g. Green sand with shells and quartz pebbles . . '80 
 li. Shelly limestone ....... -45 
 
 i. Calcareous clay 2 '00 
 
 k. Shelly sandstone '25 
 
 I. Green arenaceous clay 2*00 
 
 m. Shelly sandstone "30 
 
 n. Speckled sand -70 
 
 0. Very compact arenaceous clay .... 2"25 
 
 p. Coarse sandstone 1'40 
 
 q. G-reen sand, very fine and fluid, with quartz 
 
 pebbles and shells 2*35 
 
 beds contain fragments of the great Ostrea Patagonica, 
 0. Alvarezii (?), Pecten Paranensis, and other shells, 
 apparently the same (but they have not been rigorously 
 compared) with those enumerated by M. A. d'Orbigny 
 and by myself as found at St. Fe Bajada, as well as at 
 various points on the coast of Patagonia. The already 
 enormous continuous extension of the Patagonian ter- 
 tiary formation is thus largely increased. Beneath 
 
CHAP. XI. 071 the Thickness of the. 367 
 
 these beds a mass of red calcareous clay, becoming in 
 tlie lower part more and more marly, containing layers 
 of sand, and of tlie thickness of 213 feet, was bored 
 through to a depth of 470 feet from the level of the 
 Rio Plata. This lower mass contained no fossils, and 
 its age is of course unknown ; ^ but I may add that I 
 saw at two points in Western Banda Oriental, beneath 
 the marine tertiary strata, beds of red clay with marly 
 'Concretions, which, from their mineralogical resemblance 
 to the overlying Pampean formation, seemed to indicate 
 that at an ancient period the Rio Plata had deposited 
 an estuarine formation, subsequently covered by the 
 marine tertiary beds, and these by the more modern 
 ■estuarine formation, with its remains of numerous 
 gigantic Mammalia; and that, finally, the whole had 
 l3een elevated into the present plains of the Pampas. 
 
 JLocalities loithin the region of the Pampas where great bones have 
 
 been found. 
 
 The following list, which includes every account which I have 
 Mtherto met with of the discovery of fossil mammiferous remains 
 in the Pampas, may be hereafter useful to a geologist investigating 
 this region, and it tends to show their extraordinary abundance. 
 I heard of and saw many fossils, the original position of which I 
 could not ascertain ; and 1 received many statements too vague to 
 be here inserted. Beginning to the south : — we have the two 
 stations in Bahia Blanca, described in this chapter, where, at P. 
 Alta, the Megatherium, Megalonyx, Scelidotherium, Mylodon, 
 Holophractus (or an allied genus), Toxodon, Macrauchenia, and 
 an Equus were collected ; and at M. Hermoso a Ctenomys, Hydro- 
 •chaerus, some other rodents and the bones of a great megatheroid 
 quadruped. Close north-east of the S. Tapalguen, we have the 
 Rio ' Huesos ' (i.e. bones), which probably takes its name from 
 large fossil bones. Near Villa Nuevo, and at Las Averias, not 
 far from the Salado, three nearly perfect skeletons, one of the 
 Megatherium, one of the Glyptodon clavipes, and one of some great 
 Dasypoid quadruped, were found by the agent of Sir W. Parish 
 
 * It was supposed b}' Dr. Burmeister to be Silurian. 
 
368 Pampean Formation : part n, 
 
 (see his work ' Buenos Ayres/ &c. p. 171). I have seen the tooth 
 of a Mastodon from the Salado ; a little northward of this river, 
 on the borders of a lake near the G. del Monte, I saw many hones, 
 and one large piece of dermal armour : higher up the Salado, there 
 is a place called Monte ^ Huesos.' On the Matanzas, about twenty 
 miles south of Buenos Ayres, the skeleton (vide p. 178, of ^ Buenos 
 Ayres,' &c. by Sir W. Parish) of a Glyptodon was found about 
 five feet beneath the surface ; here also (see ' Cat, of Royal College 
 of Surgeons ') remains of Glyptodon clavipes, G. ornafus, and G. 
 reticulatus were found. Signor Angelis, in a letter which I have 
 seen, refers to some great remains found in Buenos Ayres, at a 
 depth of twenty varas from the surface. Seven leagues north of 
 this city the same author found the skeletons of Mylodon robustun 
 and Glyptodon ornatus. From this neighbourhood he has lately 
 sent to the British Museum the following fossils : — Remains of 
 three or four individuals of Megatherium ; of three species of 
 Glyptodon ; of three individuals of the Mastodon Andium ; of 
 Macrauchenia ; of a second species of Toxodon, different from T. 
 Platensis \ and, lastly, of the Machairodus, a wonderful large car- 
 nivorous animal. M. d'Orbigny has lately received from the Reco- 
 late (' Voyage,' Pal. p. 144), near Buenos Ayres, a tooth of Toxodon 
 Platensis. 
 
 Proceeding northward, along the west bank of the Parana, we 
 come to the Rio Luxan, where two skeletons of the Megatherium 
 have been found ; and lately, within eight leagues of the town of 
 Luxan, Dr. F. X. Muniz has collected (' British Packet,' Buenos 
 Ayres, September 25th, 1841), from an average depth of eighteen 
 feet, very numerous remains, of no less than, as he believes, nine 
 distinct species of mammifers. At Areco, large bones have been 
 found, which are believed, by the inhabitants, to have been changed 
 from small bones by the water of the river! At Arrecifes, the 
 Glyptodon, sent to the College of Surgeons, was found ; and I 
 have seen two teeth of a Mastodon from this quarter. At S. 
 Nicolas, M. d'Orbigny found remains of a Canis, Ctenomys, and 
 Kerodon ; and M. Isabelle {' Voyage,' p. 332) refers to a gigantic 
 Armadillo found there. At S, Carlos I heard of great bones. A 
 little below the mouth of the Oarcarana, the two skeletons of 
 Mastodon were found ; on the banks of this river, near S. Miguel, 
 I found teeth of the Mastodon and Toxodon ; and ' Falkner ' 
 (p. 65) describes the osseous armour of some great anima] ; I heard 
 of manv other bones in this neighbourhood. I have seen, I may 
 add, in the possession of Mr. Caldcleugh, the tooth of a Mastodon 
 Andium. said to have been found in Paraguay ; I may here also refer 
 to a statement in this gentleman's travels (vol. i. p. 48), of a great 
 skeleton having been found in the province of Bolivia in Brazil, on 
 the R. de las Contas. The farthest point westward in the Pampas, 
 at which I have heard of fossil bones, was high up on the banks of 
 the R. Quinto. 
 
 In Entre Rios, besides the remains of the Mastodon, Toxodon, 
 
CHAP. XI. Mammiferotis Remains of. 369 
 
 Equus, and a great Dasypoid quadruped near St. F6 Bajada, I 
 received an account of bones having been found a little SE. of 
 P. Gorda (on tlie Parana), and of an entire skeleton at Matanzas^ 
 on the Arroyo del Animal. 
 
 In Banda Oriental, besides the remains of the Toxodon, Mylo- 
 don, and two skeletons of great animals with osseous armour (dis- 
 tinct from that of the Glyptodon), found on the Arroyos Sarandis 
 and Berquelo, M. Isabelle (' Voyage/ p. 322) says, many bones 
 have been found near the B. Negro, and on the R. Arapey, an 
 affluent of the Paraguay, in lat. 30° 40^ south. I heard of bones 
 near the source of the A. Vivoras. I saw the remains of a Dasy- 
 poid quadruped from the Arroyo Seco, close to M. Video ; and 
 M. d'Orbigny refers (' Voyage, Geolog.' p. 24) to another foimd on 
 the Pedernal, an affluent of the St. Lucia ; and Signor Angelis, in 
 a letter, states that a third skeleton of this family has been found 
 near Oanelones. I saw a tooth of the Mastodon from Talas, 
 another affluent of the St. Lucia. The most eastern point at 
 which I heard of great bones having been found, was at Solis 
 Grande, between M. Video and Maldonado. 
 
 B B 
 
370 Teidiary Formations. part h. 
 
 CHAPTER XII. 
 
 ON THE OLDER TERTIARY FORMATIONS OF PATAGONIA AND 
 
 CHILE. 
 
 Rio Negro — S. Josef — Port Desire, white jyumxceous nmdstone with in- 
 fusoria, — Pooi) S. Julicun — Santa Cruz,hasaltic lava of — P. Gallegos 
 — Eastern Tierra del Fuego ; leaves of extinct heech-trees — Sum- 
 mary on the Patagonian tertiary formations — Tertiary formations 
 of the Western Coast — Chonos and Chiloe groups, volca/nio roclis of 
 — ConcejiGion — Navidad — Coquinibo — Summary — Age of the ter- 
 tiary formations — Lines of elevation — Silicified wood — Comjjarative 
 ranges of the extinct and living Mollusca on the West Coast of S. 
 America — Climate of the tertiary period — On the causes of the 
 absence of recent conchiferous deposits on the coasts of S. Aonerica 
 — On the contemporaneous deposition and preservation of sedi- 
 mentary formations. 
 
 Bio Negro. — I can add little to tlie details given by 
 M. d'Orbigny ^ on tlie sandstone formation of this dis- 
 trict. The cliffs to the south of the river are about 
 200 feet in height, and are composed of sandstone of 
 various tints and degrees of hardness. One layer, which 
 thinned out at both ends, consisted of earthy matter, of 
 a pale reddish colour, with some gypsum, and very like 
 (I speak • after comparison of the specimens brought 
 home) Pampean mud : above this was a layer of compact 
 marly rock with dendritic manganese. Many blocks of 
 a conglomerate of pumice-pebbles embedded in hard 
 sandstone were strewed at the foot of the cliff, and had 
 evidently fallen from above. A few miles NE. of the 
 1 ' Voyage, Part. G6olog.' pp. 57-65. 
 
CHAP. xn. Rio Negro. 371 
 
 to WD, I found, low down in the sandstone, a bed, a few 
 inches in thickness, of a white, friable, harsh-feeling 
 sediment, which adheres to the tongue, is of easy fusi- 
 bility, and of little specific gravity; examined under 
 the microscope, it is seen to be pumiceous tuff, formed 
 of broken transparent crystals. In the clifis south of 
 the river there is, also, a thin layer of nearly similar 
 nature, but finer grained, and not so white ; it might 
 easily have been mistaken for a calcareous tufi", but it 
 contains no lime : this substance precisely resembles a 
 most widely extended and thick formation in southern 
 Patagonia, hereafter to be described, and which is re- 
 markable for being partially formed of Infusoria. These 
 beds, conjointly with the conglomerate of pumice, are 
 interesting, as showing the nature of the volcanic action 
 in the Cordillera during this old tertiary period. 
 
 In a bed at the base of the southern cliSs, M. d'Or- 
 bigny found two extinct fresh-water shells, namely, a 
 Unio and Chilina. This bed rested on one with bones 
 of an extinct rodent, namely, the Megamys Patagoni- 
 ensis ; and this again on another with extinct marine 
 shells. The species found by M. d'Orbigny in different 
 parts of this formation consist of: — 
 
 1. Ostrea Patagonica, d'Orbig. j 'Voyage Pal.' (also St. Fe 
 
 ' Voyage Pal.' (also at St. | and S. Josef). 
 
 Fe, and whole coast of Pata- j 4. Pecten Patagoniensis, do. 
 
 gonia). I 5. Venus Munsterii, do. (also St. 
 
 2. Ostrea Ferraris! , do. Fe). 
 
 3. Ostrea Alvarezii, d'Orbig. j 6. Area Bonplandiana, do. (do.) 
 
 According to M. d'Orbigny, the sandstone extends 
 westward along the coast as far as Port S. Antonio, and 
 up the Rio Negro far into the interior : northward I 
 traced it to the southern side of the Rio Colorado, where 
 it forms a low denuded plain. This formation, though 
 contemporaneous with that of the rest of Patagonia, is 
 
 B B 2 
 
372 Tertiary Formations. part n. 
 
 quite different in mineralogical composition, being con- 
 nected with it only by tlie one thin white layer : this 
 difference may be reasonably attributed to the sediment 
 brought down in ancient times by the Rio Negro ; by 
 which agency, also, we can understand the presence of 
 the fresh- water shells, and of the bones of land animals. 
 Judging from the identity of four of the above shells, 
 tbis formation is contemporaneous (as remarked by 
 M. d'Orbigny) with that under the Pampean deposit in 
 Entre Rios and in Banda Oriental. The gravel capping 
 the sandstone plain, with its calcareous cement and 
 nodules of gypsum, is probably, from the reasons given 
 in the eighth chapter, contemporaneous with the upper- 
 most beds of the Pampean formation on the upper plain 
 north of the Colorado. 
 
 Sdn Josef. — My examination here was very short : 
 the cliffs are about 100 feet high; the lower third 
 consists of yellowish-brown, soft, slightly calcareous, 
 muddy sandstone, parts of which when struck emit a 
 fetid smell. In this bed the great Ostrea Patagonica, 
 often marked with dendritic manganese and small coral- 
 lines, were extraordinarily numerous. I found here the 
 following shells : — 
 
 1. Ostrea Patagonica, d'Orbi^. ' Voyage Pal.' (also at St, Fe and 
 
 whole coast of Patagonia). 
 
 2. Ostrea Alvarezii, d'Orbig. ' V. Pal.' (also St. Fe and E. Negro.) 
 
 3. Pecten Paranensis, d'Orbig. 'V. Pal.' and PI. III. f. 30 o^f this 
 
 work (also St. Fe, S. Julian, and Port Desire). 
 
 4. Pecten Darwinianus, d'Orbig. ' V. Pal.' and PL III. f. 28 and 29 
 
 (also St. Fe.) 
 
 5. Pecten actinodes, G. B. Sowerby, PI. III. f. 33. 
 
 6. Terebratula Patagonica, G. B. Sowerby, PI. II. f, 26 and 27 
 
 (also S. Julian). 
 
 7. Casts of a Turritella. 
 
 The four first of these species occur at St. Fe in 
 Entre Rios, and the two first in the sandstone of the 
 Rio Negro. Above this fossiliferous mass, there is a 
 
CHAP. XII. Ntcevo Gtdf and Po7d Desire. 373 
 
 stratum of very fine-grained, pale brown mudstone, 
 including numerous laminae of selenite. All the strata 
 appear horizontal, but when followed by the eye for a 
 long distance, they are seen to have a small easterly 
 dip. On the surface we have the porphyritic gravel, 
 and on it sand with recent shells. 
 
 Nuevo Gulf. — From specimens and notes given me 
 by Lieut. Stokes, it appears that the lower bed consists 
 of soft muddy sandstone, like that of S. Josef, with 
 many imperfect shells, including the Fed en Faranensis^ 
 d'Orbig., casts of a Turritella and Scutella. On this 
 there are two strata of the pale brown mudstone, also, 
 like that of 8. Josef, separated by a darker coloured, 
 more argillaceous variety, including the Osfrea Pata- 
 gonica. Prof. Ehrenberg has examined this mudstone 
 for me : he finds in it three already known microscopic 
 organisms, enveloped in a fine-grained pumiceous tuff", 
 which I shall have immediately to describe in detail. 
 Specimens brought to me from the uppermost bed, 
 north of the Rio Chupat, consist of this same substance, 
 but of a whiter colour. 
 
 Tertiary strata, such as are here described, appear 
 to extend along the whole coast between the Rio Chupat 
 and Port Desire, except where interrupted by the under- 
 lying claystone porphyry, and by some metamorphic 
 rocks ; these hard rocks, I may add, are found at in- 
 tervals over a space of about five degrees of latitude, 
 from Point Union to a point between Port S. Julian 
 and S. Cruz, and will be described in the ensuing chapter. 
 Many gigantic specimens of the Ostrea Patagonica 
 were collected in the Gulf of St. George. 
 
 Po7't Desire. — A good section of the lowest fossili- 
 ferous mass, about forty feet in thickness, resting on 
 claystone porphyry, is exhibited a few miles south of 
 
374 Tertiary Formations. part h. 
 
 tlie harbour. The shells sufficiently perfect to be 
 recognised consist of: — 
 
 1. Ostrea Patagonica, d'Orbig. (also at St. F6 and whole coast of 
 
 Patagonia). 
 
 2. Pecten Paranensis, d'Orbig. ' Voy. Pal.,' and PI. III. f. 30 of this 
 
 work (also at St. Fe, S. Josef, S. Julian). 
 
 3. Pecten centralis, Gr. B. Sowerby, PI. III. f. 31 (also S. Julian 
 
 and S. Cruz). 
 
 4. CucullEea alta, do., PI. II. f. 22, 23 (also S. Cruz). 
 
 5. Nucula ornata, do., PL II. f. 19. 
 
 6. Turritella Patagonica, do., PI. III. f. 48. 
 
 The fossiliferous strata, where not denuded, are 
 conformably covered by a considerable thickness of the 
 fine-grained pumiceous mudstone, divided into two 
 masses : the lower half is very fine-grained, slightly 
 unctuous, and so compact as to break with a semi- 
 conchoidal fracture, though yielding to the nail ; it 
 includes laminae of selenite : the upper half precisely 
 resembles the one layer at the Rio Negro, and, with the 
 exception of being whiter, the upper beds at San Josef 
 and Nuevo Gulf. In neither mass is there any trace to 
 the naked eye of organic forms. Taking the entire 
 deposit, it is generally quite white, or yellowish, or 
 feebly tinted with green; it is either almost friable 
 under the finger, or as hard as chalk ; it is of easy 
 fusibility, of little specific gravity, is not harsh to the 
 touch, adheres to the tongue, and when breathed on 
 exhales a strong aluminous odour ; it sometimes con- 
 tains a very little calcareous matter, and traces (besides 
 the included laminae) of gypsum. Under the microscope, 
 according to Prof. Ehrenberg,^ it consists of minute, 
 triturated, cellular, glassy fragments of pumice, with 
 some broken crystals. In the minute glassy fragments, 
 Prof. Ehrenberg recognises organic structures, which 
 have been afiected by volcanic heat : in the specimens 
 from this place, and from Port S. Julian, he finds six- 
 
 * « Monatsberichten der konig. Akad. zu Berlin vom April, 1845.' 
 
CHAP. XII. Port S.Jtdian. 375 
 
 teen Polygastrica and twelve Phytolitharia. Of these 
 organisms, seven are new forms, the others being pre- 
 viously known : all are of marine, and chiefly of oceanic, 
 origin. This deposit to the naked eye resembles the 
 crust which often appears on weathered surfaces of 
 feldspathic rocks; it likewise resembles those beds of 
 earthy feldspathic matter, sometimes interstratified with 
 porphyritic rocks, as is the case in this very district 
 with the underlying purple claystone porphyry. From 
 ■examining specimens under a common microscope, and 
 comparing them with other specimens undoubtedly of 
 volcanic origin, I had come to the same conclusion with 
 Prof. Ehrenberg, namely, that this great deposit, in its 
 £rst origin, is of volcanic nature. 
 
 Vort S. Julian. — On the south side of the harbour, 
 the following section, which I here repeat, gives the 
 nature of the beds seen in the cliffs of the ninety feet 
 
 No. 33. 
 
 Section of the strata exliibited in the cliffs of the 90-feet plain at Port 
 S. Julian. 
 
 ^_^^^^^^=r^ - I D > 
 
 
 plain. Beginning at the top, — 1st, the earthy mass 
 (A A), including the remains of the Macrauchenia, with 
 recent shells on the surface; 2nd, the porphyritic 
 shingle (B), which in its lower part is interstratified 
 (owing, I believe, to redeposition during denudation) 
 with the white pumiceous mudstone; 3rd, this white 
 mudstone, about twenty feet in thickness, and divided 
 into two varieties (C and D), both closely resembling 
 the lower, fine-graiued, more unctuous and compact 
 kind at Port Desire ; and, as at that place, including 
 much selenite; 4th, a fossiliferous mass, divided into 
 
2^*]^ Te7diary Formations. paet n. 
 
 three main beds, of which the uppermost is thin, and 
 consists of ferruginous sandstone, with many shells of 
 the great oyster and Pecten Paranensis ; the middle 
 bed (E) is a yellowish earthy sandstone abounding with 
 Scutellee; and the lowest bed (F) is an indurated, 
 greenish, sandy clay, including large concretions of 
 calcareous sandstone, many shells of the great oyster, 
 and in parts almost made up of fragments of Balanidge. 
 Out of these three beds, I procured the following twelve 
 species, of which the two first were exceedingly numerous 
 in individuals, as were the Terebratulse and Turritellse- 
 in certain layers : — 
 
 1. Ostrea Patagonica, d'Orb. ' Voyage Pal.' (also at St. Fe and 
 
 whole coast of Patagonia), 
 
 2. Pecten Paranensis, d'Orbig. do,, and PL III. f. 30 of this work 
 
 (St. Fe, S. Josef, Port Desire). 
 
 3. Pecten centralis, Gr. B. Sowerby, PI. III. f. 31 (also P. Desire 
 
 and S. Cruz). 
 
 4. Pecten geminatus, do., PI, II, f , 24, 
 
 5. Terebratula Patagonica, do., PI. II, f , 26 and 27 (also S, Josef). 
 
 6. Struthiolaria ornata, do., PI. IV. f. 62 (also S, Cruz). 
 
 7. Fusus Patagonicus, do., PI. IV. f. 60. 
 
 8. Fusus Noachinus, do., PI. IV. f. 58 and 59. 
 
 9. Scalaria rugulosa, do., PI. III. f, 42 and 43, 
 
 10. Turritella ambulacrum, do., PL III. f . 49 (also S. Cruz). 
 
 11. Pyrula, cast of, like P. ventricosa of Sowerby, Tank Cat. 
 
 12. Balanus varians, Gr. B. Sowerby, PI. II. f. 4, 5, 6. 
 
 13. Scutella, differing from the species from Nuevo Gulf. 
 
 At the head of the inner harbour of Port S. Julian, 
 the fossiliferous mass is not displayed, and the sea-cliffs 
 from the water's edge to a height of between 100 and 
 200 feet are formed of the white pumiceous mudstone, 
 which here includes innumerable, far-extended, some- 
 times horizontal, sometimes inclined or vertical laminae 
 of transparent gypsum, often about an inch in thick- 
 ness. Further inland, with the exception of the 
 superficial gravel, the whole thickness of the truncated 
 hills, which represent a formerly continuous plain 950 
 feet in height, appears to be formed of this white mud- 
 
CHAP. XII. Po74 S. Jtdian and Santa Cruz, ^ill 
 
 stone : here and there, however, at various heights, thin 
 earthy layers, containing the great oyster, Pecten Fara- 
 nensis and Turritella ambulacrum, are interstratified ; 
 thus showing that the whole mass belongs to the same 
 epoch. I nowhere found even a fragment of a shell 
 actually in the white deposit, and only a single cast of 
 a Turritella. Out of the eighteen microscopic organisms 
 discovered by Ehrenberg in the specimens from this 
 place, ten are common to the same deposit at Port 
 Desire. I may add that specimens of this white mud- 
 stone, with the same identical characters, were brought 
 me from two points, — one twenty miles north of S. 
 Julian, where a wide gravel-capped plain, 350 feet in 
 height, is thus composed ; and the other forty miles 
 south of S. Julian, where, on the old charts, the cliffs 
 are marked as ' Glialk Hills' 
 
 Santa Cruz. — The gravel-capped cliffs at the mouth 
 of the river are 355 feet in height : the lower part, to 
 a thickness of fifty or sixty feet, consists of a more or 
 less hardened, darkish, muddy, or argillaceous sandstone 
 (like the lowest bed of Port Desire), containing very 
 many shells, some silicified and some converted into 
 yellow calcareous spar. The great oyster is here 
 numerous in layers ; the Trigonocelia and Turritella 
 are also very numerous : it is remarkable that the 
 Pecten Paranensis, so common in all other parts of 
 the coast, is here absent : the shells consist of: — 
 
 1. Ostrea Patagonica, d'Orbig. ' Voyage Pal.' (also at St. Fe and 
 
 whole coast of Patagonia). 
 
 2. Pecten centralis, G. B. Sowerby, PI. III. f . 31 (also P. Desire 
 
 and S. Julian). 
 
 3. Venus meridionalis of G. B. Sowerby, PI. II. f. 13. 
 
 4. Crassatella Lyellii, do. PL II. f. 10. 
 
 5. Cardium pulchellum, do. PL II. f. 15. 
 
 6. Cardita Patagonica. do. PL II. f. 17. 
 
 7. Mactra rugata, do. PL II. f. 8. 
 
 8. Mactra Darwinii, do. PL II. f. 9. 
 
 9. CucuUsea alta, do. PL II. f. 22, 23 (also P. Desire). 
 
^yS Tertiary Formatio^is. part ii. 
 
 10. Trigonocelia insolita, do. PL II. f. 20, 21. 
 
 11. Nucula (?) glabra, do. PI. II. f. 18. 
 
 12. Crepidula gregaria, do. PI. III. f . 34. 
 
 13. Voluta alta, do. PI. IV. f. 75. 
 
 14. Trochus collaris, do. PL III. f. 44, 45. 
 
 15. Natica solida (?), do. PL III. f. 40, 41. 
 
 16. Struthiolaria ornata, do. PL IV. f. 62 (also P. Desire). 
 
 17. Turritella ambulacrum, do. PL III. f. 49 (also P. S. Julian). 
 Imperfect fragments of the genera Byssoarca, Artemis, and Fusus. 
 
 The upper part of tlie cliff is generally divided into 
 three great strata, differing slightly in composition, but 
 essentially resembling the pumiceous mudstone of the 
 places farther north ; the deposit, however, here is more 
 arenaceous, of greater specific gravity, and not so white : 
 it is interlaced with numerous thin veins, partially or 
 quite filled with transverse fibres of gypsum ; these fibres 
 were too short to reach across the vein, have their extre- 
 mities curved or bent : in the same veins with the gyp- 
 sum, and likewise in separate veins as well as in little 
 nests, there is much powdery sulphate of magnesia (as 
 ascertained by Mr. Reeks) in an uncompressed form : I 
 believe that this salt has not heretofore been found in 
 veins. Of the three beds, the central one is the most com- 
 pact, and more like ordinary sandstone : it includes nu- 
 merous flattened spherical concretions, often united like 
 a necklace, composed of hard calcareous sandstone, con- 
 taining a few shells : some of these concretions were 
 four feet in diameter, and in a horizontal line nine feet 
 apart, showing that the calcareous matter must have 
 been drawn to the centres of attraction from a distance 
 of four feet and a half on both sides. In the upper and 
 lower finer-grained strata, there were other concretions 
 of a grey colour, containing calcareous matter, and so 
 fine-grained and compact as almost to resemble por- 
 celain-rock : I have seen exactly similar concretions in 
 a volcanic tufaceous bed in Ohiloe. Although in this 
 upper fine-grained strata, organic remains were very 
 rare, yet I noticed a few of the great oyster ; and in 
 
CHAP. XII. 
 
 Santa Cruz. 
 
 379 
 
 one included soft ferruginous layer, there were some speci- 
 mens of the Cttcullcea alta (found at Port Desire in the 
 lower fossiliferous mass) and of the Mactra rugata, which 
 latter shell has been partially converted into gypsum. 
 
 In ascending the valley of the S. Cruz, the upper 
 strata of the coast-cliffs are prolonged, with nearly the 
 same characters, for fifty miles : at about this point, 
 they begin in the most gradual and scarcely perceptible 
 manner, to be banded with white lines ; and after as- 
 cending ten miles farther, we meet with distinct thin 
 layers of whitish, greenish, and yellowish fine-grained, 
 fusible sediments. At eighty miles from the coast,^ in 
 a cliff thus composed, there were a few layers of ferru- 
 ginous sandstone, and of an argillaceous sandstone with 
 
 No. 34. 
 Section of the plains of Patagonia, on tlie banks of the S. Cruz, 
 Surface of plain mth erratic boulders; 1,416 ft. above the sea. 
 
 212 ft. thick 
 
 322 ft. thick 
 
 River of S. Cruz ; here 280 ft. above sea. 
 
 a. Gravel and boulders. b. Basaltic lava. 
 
 c. Sedimentary layers. d. Bed of small pebbles. e. Talus. 
 
 concretions of marl like those in the Pampas. At 100 
 miles from the coast, that is at a central point between 
 
 ' At this spot, for a space of three-quarters of a mile along the 
 north side of the river, and for a width of half a mile, there has been 
 
380 Tertiary Formations. paet u, 
 
 the Atlantic and the Cordillera, we have the preceding 
 section. 
 
 The upper half of the sedimentary mass, under the 
 basaltic lava, consists of innumerable zones of perfectly 
 white, bright green, yellowish and brownish, fine-grained, 
 sometimes incoherent, sedimentary matter. The white, 
 pumiceous, trachytic tuff-like varieties are of rather 
 greater specific gravity than the pumiceous mudstone 
 on the coast to the north : some of the layers, especially 
 the browner ones, are coarser, so that the broken crys- 
 tals are distinguishable with a weak lens. The layers 
 vary in character in short distances. With the excep- 
 tion of a few of the Ostrea Patagonica, which appeared 
 to have rolled down from the cliff above, no organic 
 remains were found. The chief difference between 
 these layers taken as a whole, and the upper beds both 
 at the mouth of the river and on the coast northward, 
 seems to lie in the occasional presence of more colouring 
 matter, and in the supply having been intermittent : 
 these characters, as we have seen, very gradually dis- 
 appear in descending the valley, and this fact may 
 perhaps be accounted for by the currents of a more 
 open sea having blended together the sediment from a 
 distant and intermittent source. 
 
 The coloured layers in the foregoing section rest on 
 a mass, apparently of great thickness (but much hidden 
 by the talus), of soft sandstone, almost composed of 
 minute pebbles, from one-tenth to two-tenths of an 
 inch in diameter, of the rocks (with the entire exception 
 
 a great slip, which has formed hills between 60 and 70 feet in height, 
 and has tilted the strata into highly inclined and even vertical posi- 
 tions. The strata generally dipped at an angle of 45° towards the 
 cliff from which they had slided. I have observed in slips, both on 
 a small and large scale, that this inward dip is very general. Is it 
 due to the hydrostatic pressure of water percolating with difficulty 
 tlirough the strata acting with greater force at the base of the 
 mass than against tlie upper part ? 
 
€HAP. XII. Santa Cruz. 381 
 
 of the basaltic lava) composing tlie great boulders on 
 the surface of the plain, and probably composing the 
 neighbouring Cordillera. Five miles higher up the 
 valley, and again thirty miles higher up,^ (that is twenty 
 miles from the nearest range of the Cordillera) the lower 
 plain included within the upper escarpments is formed, 
 as seen on the banks of the river, of a nearly similar 
 but finer-grained, more earthy, laminated sandstone, 
 alternating with argillaceous beds, and containing nu- 
 merous moderately sized pebbles of the same rocks, and 
 some shells of the great Ostrea Patagonica. As most 
 of these shells had been rolled before being here em- 
 bedded, their presence does not prove that the sand- 
 stone belongs to the great Patagonian tertiary formation, 
 for they might have been redeposited in it when the 
 valley existed as a sea-strait ; but as amongst the 
 pebbles there were none of basalt, although the cliffs on 
 both sides of the valley are composed of this rock, I 
 believe that the sandstone does belong to this formation. 
 At the highest point to which we ascended, twenty 
 miles distant from the nearest slope of the Cordillera, I 
 could see the horizontally zoned white beds, stretching 
 under the black basaltic lava, close up to the mountains ; 
 ^so that the valley of the S. Cruz gives a fair idea of the 
 constitution of the whole width of Patagonia. 
 
 Basaltic Lava of the S. Cruz. — This formation is 
 first met with sixty-seven miles from the mouth of the 
 river ; thence it extends uninterruptedly, generally but 
 not exclusively on the northern side of the valley, close 
 up to the Cordillera. The basalt is generally black 
 and fine-grained, but sometimes gray and laminated ; 
 it contains some olivine, and high up the valley much 
 
 ^ I found at both places, but not i7i situ, quantities of coniferous 
 and ordinary dicotyledonous silicified wood, which was examined 
 for me by Mr. K. Brown. 
 
382 Tertiary Foi^mations. part h. 
 
 glassy feldspar, where, also, it is often amygdaloidal ; 
 it is never highly vesicular, except on the sides of rents 
 and on the upper and lower, spherically laminated sur- 
 faces. It is often columnar ; and in one place I saw 
 magnificent columns, each face twelve feet in width, 
 with their interstices filled up with calcareous tufi*. 
 The streams rest conformably on the white sedimentary 
 beds, but I nowhere saw the actual junction ; nor did I 
 anywhere see the white beds actually superimposed on 
 the lava ; but some way up the valley, at the foot of 
 the uppermost escarpments, they must be thus super- 
 imposed. Moreover, at the lowest point down the 
 valley, where the streams thin out and terminate in 
 irregular projections, the spaces or intervals between 
 these projections are filled up to the level of the now 
 denuded and gravel-capped surfaces of the plains, with 
 the white-zoned sedimentary beds; proving that this 
 matter continued to be deposited after the streams had 
 flowed. Hence we may conclude that the basalt is 
 contemporaneous with the upper parts of the great 
 tertiary formation. 
 
 The lava where first met with is 130 feet in thick- 
 ness : it there consists of two, three, or perhaps more 
 streams, divided from each other by vesicular spheroids, 
 like those on the surface. From the streams having, 
 as it appears, extended to different distances, the terminal 
 points are of unequal heights. Generally the surface 
 of the basalt is smooth ; but in one part high up the 
 valley it was so uneven and hummocky, that until I 
 afterwards saw the streams extending continuously on 
 both sides of the valley up to a height of about 3,000 
 feet close to the Cordillera, I thought that the craters of 
 eruption were probably close at hand. This hummocky 
 surface I believe to have been caused by the crossing 
 and heaping up of different streams. In one place, 
 
CHAP. XII. Santa Crttz. ^y^^y 
 
 there were several rounded ridges about twenty feet in 
 heiglit, some of tliem as broad as high, and some broader ,. 
 which certainly had been formed whilst the lava was 
 fluid, for in transverse sections each ridge was seen to 
 be concentrically laminated, and to be composed of im- 
 perfect columns radiating from common centres, like 
 the spokes of wheels. 
 
 The basaltic mass where first met with is, as I have 
 said, 130 feet in thickness, and, thirty-five miles higher 
 up the valley, it increases to 322 feet. In the first 
 fourteen and a half miles of this distance, the upper 
 surface of the lava, judging from three measurements 
 taken above the level of the river (of which the appa- 
 rently very uniform inclination has been calculated 
 from its total height at a point 135 miles from the 
 mouth) slopes towards the Atlantic at an angle of only 
 0° 7' 20" : this must be considered only as an approxi- 
 mate measurement, but it cannot be far wrong. Taking 
 the whole thirty-five miles, the upper surface slopes at 
 an angle of 0° 10' 53" ; but this result is of no value in 
 showing the inclination of any one stream, for half-way 
 between the two points of measurement, the surface 
 suddenly rises between 100 and 200 feet, apparently 
 caused by some of the uppermost streams having 
 extended thus far and no farther. From the measure- 
 ments made at these two points, thirty-five miles aparty 
 the mean inclination of the sedimentary beds, over 
 which the lava has flowed, is now (after elevation from 
 under the sea) only 0° 7^ 52" : for the sake of compari- 
 son, it may be mentioned that the bottom of the present 
 sea in a line from the mouth of the S. Cruz to the 
 Falkland Islands, from a depth of seventeen fathoms to 
 a depth of eighty-five fathoms, declines at an angle of 
 0° 1' 22" ; between the beach and the depth of seven- 
 teen fathoms, the slope is greater. From a point about 
 
384 Tertiary Formations. part n. 
 
 half-way up the valley, the basaltic mass rises more 
 abruptly towards the foot of the Cordillera, namely, 
 from a height of 1,204 feet, to about 3,000 feet above 
 the sea. 
 
 This great deluge of lava is worthy, in its dimensions, 
 of the great continent to which it belongs. The aggre- 
 gate streams have flowed from the Cordillera to a dis- 
 tance (unparalleled, 1 believe, in any case yet known) 
 of about 100 geographical miles. Near their furthest 
 extremity their total thickness is 130 feet, which increase 
 thirty-fi.ve miles farther inland, as we have just seen, 
 to 322 feet. The least inclination given by M. E. de 
 Beaumont of the upper surface of a lava stream, namely, 
 0° 30^, is that of the great subaerial eruption in 1783 
 from Skaptar Jukul in Iceland ; and M. E. de Beaumont 
 shows^ that it must have flowed down a mean inclination 
 of less than 0° 20'. But we now see that under the 
 pressure of the sea successive streams have flowed over 
 a smooth bottom with a mean inclination not more 
 than 0° 7' 52" ; and that the upper surface of the 
 terminal portion (over a space of fourteen and a half 
 miles) has an inclination of not more than 0° 1' 20^'. 
 If the elevation of Patagonia has been greater nearer 
 the Cordillera than near the Atlantic (as is probable), 
 then these angles are now all too large. I must repeat, 
 that although the foregoing measurements, which were 
 all carefully taken with the barometer, may not be 
 absolutely correct, they cannot be widely erroneous. 
 
 Southward of the S. Cruz, the clifis of the 840 feet 
 plain extend to Coy Inlet, and, owing to the naked 
 patches of the white sediment, they are said on the 
 charts to be ' like the coast of Kent.' At Coy Inlet 
 the high plain trends inland, leaving flat-topped outliers. 
 At Port Gallegos (lat. 51° 35', and ninety miles south 
 
 ^ ' Memoires pour servir,' &c., pp. 178 and 217. 
 
CHAP. xn. Tier r a del Ftiego. 385 
 
 of S. Cruz), I am informed by Captain Sulivan, R.N., 
 
 that there is a gravel-capped plain from 200 to 300 feet 
 
 in height, formed of numerous strata, some fine-grained 
 
 and pale-coloured, like the upper beds at the mouth of 
 
 the S. Cruz, others rather darker and coarser, so as to 
 
 resemble gritstones or tuffs ; these latter include rather 
 
 large fragments of apparently decomposed volcanic 
 
 rocks ; there are, also, included layers of gravel. This 
 
 formation is highly remarkable, from abounding with 
 
 mammiferous remains, which have not as yet been 
 
 examined by Professor Owen, but which include some 
 
 large, but mostly small, species of Pachydermata, 
 
 Edentata, and Podentia. From the appearance of the 
 
 pale-coloured, fine-grained beds, I was inclined to 
 
 believe that they corresponded with the upper beds of 
 
 the S. Cruz; but Professor Ehrenberg, who has examined 
 
 some of the specimens, informs me that the included 
 
 microscopical organisms are wholly different, being 
 
 fresh and brackish water forms. Hence the 200 to 
 
 300 feet plain at Port Gallegos is of unknown age, but 
 
 probably of subsequent origin to the great Patagonian 
 
 tertiary formation. 
 
 JE astern Tierra del Fuego. — Judging from the 
 
 height, the general appearance, and the white colour 
 
 of the patches visible on the hill sides, the uppermost 
 
 plain, both on the north and western side of the Strait 
 
 of Magellan, and along the eastern coast of Tierra del 
 
 Fuego as far south as near Port St. Polycarp, probably 
 
 belongs to the great Patagonian tertiary formation. 
 
 These higher table-ranges are fringed by low, irregular, 
 
 extensive plains, belonging to the boulder formation,^ 
 
 and composed of coarse unstratified masses, sometimes 
 
 associated (as north of C. Virgin's) with fine, laminated, 
 
 muddy sandstones. The cliffs in Sebastian Bay are 
 
 * Described in the ' Geological Transactions,' vol. vi. p. 415. 
 
 C C 
 
386 Sttmmary on the Patagonian part h. 
 
 200 feet in height, and are composed of fine sandstones, 
 often in curvilinear layers, including hard concretions 
 of calcareous sandstone, and layers of gravel. In these 
 beds there are fragments of wood, legs of crabs, barnacles 
 encrusted with corallines still partially retaining their 
 colour, imperfect fragments of a Pholas distinct from 
 any known species, and of a Venus, approaching very 
 closely to, but slightly different in form from, the 
 V. lenticularis^ a species living on the coast of Chile. 
 Leaves of trees are numerous between the laminae of 
 the muddy sandstone ; they belong, as I am informed 
 by Dr. J. D. Hooker,^ to three species of deciduous 
 beech, different from the two species which compose 
 the great proportion of trees in this forest-clad land. 
 From these facts it is difficult to conjecture, whether 
 we here see the basal part of the great Patagonian 
 formation, or some later deposit. 
 
 Summary on the Patagonian Tertiary Formation. 
 — Four out of the seven fossil shells, from St. Fe in 
 Entre Rios, were found by M. d'Orbigny in the sand- 
 stone of the Rio Negro, and by me at San Josef. Three 
 out of the six from San Josef are identical with those 
 from Port Desire and S. Julian, which two places have 
 together fifteen species, out of which three are common 
 to both. Santa Cruz has seventeen species, out of 
 which five are common to Port Desire and S. Julian. 
 Considering the difference in latitude between these 
 several places, and the small number of species altogether 
 collected, namely thirty-six, I conceive the above pro- 
 portional number of species in common, is sufficient to 
 show that the lower fossiliferous mass belongs nearly, 
 I do not say absolutely, to the same epoch. What this 
 epoch may be, compared with the European tertiary 
 stages, M. d'Orbigny will not pretend to determine. 
 ' Botany of the Antarctic Voyage,' p. 212. 
 
CHAP. XII. Tertia7y Foj'-mation. 387 
 
 The thirty-six species (including those collected by 
 myself and by M. d'Orbigny) are all extinct, or at least 
 unknown ; but it should be borne in mind, that the 
 present coast consists of shingle, and that no one, I 
 believe, has dredged here for shells; hence it is not 
 improbable that some of the species may hereafter be 
 found living. Some few of the species are closely related 
 with existing ones ; this is especially the case, according 
 to M. d'Orbigny and Mr. Sowerby, with the Fusus 
 Patagonicus ; and, according to Mr. Sowerby, with 
 the Pyrula^ the Venus meridionalis, the Crepidula 
 gregaria, and the Turritella amhtdacrum, and T. 
 Patagonica. At least three of the genera, namely, 
 Cucullsea, Crassatella, and (as determined by Mr. 
 Sowerby) Struthiolaria, are not found in this quarter 
 of the world ; and Trigonocelia is extinct. The evidence 
 taken altogether indicates that this great tertiary 
 formation is of considerable antiquity ; but when treat- 
 ing of the Chilian beds, I shall have to refer again to 
 this subject. 
 
 The white pumiceous mudstone, with its abundant 
 gypsum, belongs to the same general epoch with the 
 underlying fossiliferous mass, as may be inferred from 
 the shells included in the intercalated layers at JSTeuvo 
 Gulf, S. Julian, and S. Cruz. Out of the twenty-seven 
 marine microscopic structures found by Prof. Ehrenberg 
 in the specimens from S. Julian and Port Desire, ten 
 are common to these two places : the three found at 
 Neuvo Gulf are distinct. I have minutely described 
 this deposit, from its remarkable characters and its 
 wide extension. From Coy Inlet to Port Desire, a dis- 
 tance of 230 miles, it is certainly continuous ; and I 
 have reason to believe that it likewise extends to the 
 Rio Chupat, Neuvo Gulf and San Josef, a distance of 
 570 miles : we have, also, seen that a single layer occurs 
 
 c c 2 
 
o 
 
 88 Summary on the Patagonian part h. 
 
 at the Rio Negro. At Port S. Julian it is from 800 to 
 900 feet in thickness ; and at S. Cruz it extends, with 
 a slightly altered character, up to the Cordillera. From 
 its microscopic structure, and from its analogy with 
 other formations in volcanic districts, it must be con- 
 sidered as originally of volcanic origin : it may have 
 been formed by the long-continued attrition of vast 
 quantities of pumice, or, judging from the manner in 
 which the mass becomes, in ascending the valley of S. 
 Cruz, divided into variously coloured layers, from the 
 long-continued eruption of clouds of fine ashes. In 
 either case, we must conclude, that the southern volcanic 
 orifices of the Cordillera, now in a dormant state, were 
 at about this period over a wide space, and for a great 
 length of time, in action. We have evidence of this 
 fact, in the latitude of the Rio Negro in the sandstone- 
 conglomerate with pumice, and demonstrative proof of 
 it, at S. Cruz, in the vast deluges of basaltic lava : at 
 this same tertiary period, also, there is distinct evidence 
 of volcanic action in Western Banda Oriental. 
 
 The Patagonian tertiary formation extends continu- 
 ously, judging from fossils alone, from S. Cruz to 
 near the Rio Colorado, a distance of above 600 miles, 
 and reappears over a wide area in Entre Rios and Banda 
 Oriental, making a total distance of 1,100 miles; but 
 this formation undoubtedly extends (though no fossils 
 were collected) far south of the S. Cruz, and, accord- 
 ing to M. d'Orbigny, 120 miles north of St. Fe. At 
 S. Cruz we have seen that it extends across the con- 
 tinent ; being on the coast about 800 feet in thickness 
 (and rather more at S. Julian), and rising with the 
 contemporaneous lava-streams to a height of about 
 3,000 feet at the base of the Cordillera. It rests, 
 wherever any underlying formation can be seen, on 
 plutonic and metamorphic rocks. Including the newer 
 
CHAP. XII. Tertiary Formation. 389 
 
 Pampean deposit, and tliose strata in eastern Tierra del 
 Fuego of doubtful age, as well as the boulder formation, 
 we have a line of more than twenty-seven degrees of 
 latitude, equal to that from the Straits of Gibraltar to 
 the south of Iceland, continuously composed of tertiary 
 formations. Throughout this great space the land has 
 been upraised, without the strata having been in a 
 single instance, as far as my means of observation went, 
 unequally tilted or dislocated by a fault. 
 
 Tertiary Formations on the West Coast. 
 
 Glionos Archijpelago. — The numerous islands of this 
 group, with the exception of Lemus, Ypun, consist 
 of metamorphic schists ; these two islands are formed of 
 softish grey and brown, fusible, often laminated sand- 
 stones, containing a few pebbles, fragments of black 
 lignite, and numerous mammillated concretions of hard 
 calcareous sandstone. Out of these concretions at Ypun 
 (lat. 40° 30' S.), I extracted the four following extinct 
 species of shells : — 
 
 1. Turritella suturalis, Gr. B. Sowerby, PL III. f. 50 (also Navidad). 
 
 2. Sigaretus subglobosTSs, do. PI. III. f. 36, 37. (do.) 
 
 3. Cythersea (?) sulciilosa (?), do. PI. II. f. 14 (also Chiloe and 
 
 Huafo ?). 
 
 4. Yoluta, fragments of. 
 
 In the northern parts of this group there are some 
 cliffs of gravel and of the boulder formation. In the 
 southern part (at P. Andres in Tres Montes), there is 
 a volcanic formation, probably of tertiary origin. The 
 lavas attain a thickness of from 200 to 300 feet ; they 
 are extremely variable in colour and nature, being 
 compact, or brecciated, or cellular, or amygdaloidal 
 with zeolite, agate and bole, or porphyritic with glassy 
 albitic feldspar. There is also much imperfect rubbly 
 
390 Tertiary Formations. part ti. 
 
 pitchstone, with tlie interstices charged with powdery 
 carbonate of lime apparently of contemporaneous origin. 
 These lavas are conformably associated with strata of 
 breccia and of brown tnff containing lignite. The 
 whole mass has been broken up and tilted at an angle 
 of 45°, by a series of great volcanic dikes, one of which 
 was thirty yards in breadth. This volcanic formation 
 resembles one, presently to be described, in Chiloe. 
 
 Huafo. — This island lies between the Chonos and 
 Chiloe groups: it is about 800 feet high, and perhaps 
 has a nucleus of metamorphic rocks. The strata which 
 I examined consisted of fine-grained muddy sandstones, 
 with fragments of lignite and concretions of calcareous 
 sandstone. I collected the following extinct shells, of 
 which the Turritella was in great numbers : — 
 
 1. BuHa cosmopMla, G. B. Sowerby, PI. III. f. 35. 
 
 2. Pleurotoma subeequalis, do. PI. IV. f. 52. 
 
 3. Fnsus cleryanus, d'Orbig. ' Voy. Pal.' PI. XII. f. 6, 7 (also at 
 
 Coquimbo). 
 
 4. Triton leucostomoides, G. B. Sowerbj'-, PI. IV. f. 64. 
 
 5. Turritella Chilensis, do. PL IV. f. 51 (also Mocha). 
 
 6. Venus, probably a distinct species, but very imperfect. 
 
 7. Cyther^a (?) sulculosa (?), do. PI. II. f . 14. 
 
 8. Dentalium majus, G. B. Sowerby, PI. II. f. 3. 
 
 Ghiloe. — This fine island is about 100 miles in 
 length. The entire southern part, and the whole 
 western coast, consists of mica-schist, which likewise is 
 seen in the ravines of the interior. The central moun- 
 tains rise to a height of 3,000 feet, and are said to be 
 partly formed of granite and greenstone : there are 
 two small volcanic districts. The eastern coast, and 
 large parts of the northern extremity of the island are 
 composed of gravel, the boulder formation, and under- 
 lying horizontal strata. The latter are well displayed 
 for twenty miles north and south of Castro ; they vary 
 in character from common sandstone to fine-grained, 
 laminated mudstones : all the specimens which I ex- 
 
CHAP. XII. 
 
 Chiloe. 391 
 
 amined are easily fusible, and some of tlie beds might 
 be called volcanic grit-stones. These latter strata are 
 perhaps related to a mass of columnar trachyte which 
 occurs behind Castro. The sandstone occasionally in- 
 cludes pebbles, and many fragments and layers of lignite ; 
 of the latter, some are apparently formed of wood and 
 others of leaves : one layer on the N W. side of Lemuy 
 is nearly two feet in thickness. There is also much 
 silicified wood, both common dicotyledonous and coni- 
 ferous : a section of one specimen in the direction of the 
 medullary rays has, as I am informed by Mr. R. Brown, 
 the discs in a double row placed alternately, and not 
 opposite as in the true Araucaria. I found marine 
 remains only in one spot, in some concretions of hard 
 calcareous sandstone : in several other districts I have 
 observed that organic remains were exclusively confined 
 to such concretions; are we to account for this fact, by 
 the supposition that the shells lived only at these points, 
 or is it not more probable that their remains were pre- 
 served only where concretions were formed ? The shells 
 here are in a bad state, they consist of: — 
 
 1. Tellinides (?) oblonga, G. B. Sowerby, PL n. f. 12 (a solenella 
 
 in M. d'Orbigny's opinion). 
 
 2. Natica striolata, Gr. B. Sowerby, PL III. f. 39. 
 
 3. Natica (?) pumila, do. PL III. f. 38. 
 
 4. CytherEea (?) suloulosa, do. PL II. f . 14 (also Ypun and Huafo ?) 
 
 At the northern extremity of the island, near S. 
 Carlos, there is a large volcanic formation, between 600 
 and 700 feet in thickness. The commonest lava is 
 blackish-grey or brown, either vesicular, or amygda- 
 loidal with calcareous spar and bole : most even of the 
 darkest varieties fuse into a pale-coloured glass. The 
 next commonest variety is a rubbly, rarely well charac- 
 terised pitchstone (fusing into a white glass) which 
 passes in the most irregular manner into stony gray 
 
392 Tertiary Formations. paet n. 
 
 lavas. This pitchstone, as well as some purple clay- 
 stone porphyry, certainly flowed in the form of streams. 
 These various lavas often pass, at a considerable depth 
 from the surface, in the most abrupt and singular 
 manner into wacke. Great masses of the solid rock are 
 brecciated, and it was generally impossible to discover 
 whether the recementing process had been an igneous 
 or aqueous action.^ The beds are obscurely separated 
 from each other ; they are sometimes parted by seams 
 of tuff and layers of pebbles. In one place they rested 
 on, and in another place were capped by, tuffs and grit- 
 stones, apparently of submarine origin. 
 
 The neighbouring peninsula of Lacuy is almost 
 wholly formed of tufaceous deposits, connected probably 
 in their origin with the volcanic hills just described. 
 The tuffs are pale-coloured, alternating with laminated 
 mudstones and sandstones (all easily fusible) and passing 
 sometimes into fine grained white beds strikingly re- 
 sembling the great upper infusorial deposit of Patagonia, 
 and sometimes into brecciolas with pieces of pumice in 
 the last stage of decay ; these again pass into ordinary 
 coarse breccias and conglomerates of hard rocks. With- 
 in very short distances, some of the finer tuffs often 
 passed into each other in a peculiar manner, namely, 
 by irregular polygonal concretions of one variety in- 
 creasing so much and so suddenly in size, that the 
 second variety, instead of any longer forming the entire 
 mass, was left merely in thin veins between the concre- 
 
 * Iq a clifE of the hardest fragmentary mass, I found several 
 tortuous, vertical veins, varying in thickness from a few tenths of an 
 inch to one inch and a half, of a substance which I have not seen 
 described. It is glossy, and of a brown colour ; it is thinly laminated, 
 with the laminae transparent and elastic ; it is a little harder than 
 calcareous spar ; it is infusible under the blowjaipe, sometimes decre- 
 pitates, gives out water, curls up, blackens and becomes magnetic. 
 Borax easily dissolves a considerable quantity of it, and gives a 
 glass tinged with green. I have no idea what its true nature is. 
 On first seeing it, I mistook it for lignite ! 
 
CHAP. XTI. 
 
 Chiloe. 
 
 393 
 
 tions. In a straight line of cliffs, at Point Tenuy, I 
 examined the following remarkable section : — 
 
 No. 35 
 
 Level of sea. 
 
 On the left hand, the lower part (A A) consists of regular 5. 
 alternating strata of brown tuffs and greenish laminated 
 mudstone, gently inclined to the right, and conformably 
 covered by a mass (B left^ of a white, tufaceous and 
 brecciolated deposit. On the right hand, the whole 
 cliff (BB riglii) consists of the same white tufaceous 
 matter, which on this side presents scarcely a trace of 
 stratification, but to the left becomes very gradually 
 and rather indistinctly divided into strata quite con- 
 formable with the underlying beds (A A) : moreover, a 
 few hundred yards farther to the left, where the surface 
 has been less denuded, the tufaceous strata (B lef^ are 
 conformably covered by another set of strata, like the 
 underlying ones (A A) of this section. In the middle 
 of the diagram, the beds (A A) are seen to be abruptly 
 cut off, and to abut against the tufaceous non-stratified 
 mass ; but the line of junction has been accidentally 
 
394 Tertiary Formations. part n. 
 
 not represented steep enough, for I particularly noticed 
 that before the beds had been tilted to the right, this 
 line must have been nearly vertical. It appears that a 
 current of water cut for itself a deep and steep sub- 
 marine channel, and at the same time or afterwards 
 filled it up with the tufaceous and brecciolated matter, 
 and spread the same over the surrounding submarine 
 beds ; the matter becoming stratified in these more 
 distant and less troubled parts, and being moreover 
 subsequently covered up by other strata (like A A) not 
 shown in the diagram. It is singular that three of the 
 beds (of A A) are prolonged in their proper direction, 
 as represented, beyond the line of junction into the 
 white tufaceous matter : the prolonged portions of two 
 of the beds are rounded; in the third, the terminal 
 fragment has been pushed upwards : how these beds 
 could have been left thus prolonged, I will not pretend 
 to explain. In another section on the opposite side of 
 a promontory, there was at the foot of this same line 
 of junction, that is at the bottom of the old submarine 
 channel, a pile of fragments of the strata (A A), with 
 their interstices filled up with the white tufaceous 
 matter : this is exactly what might have been antici- 
 pated under such circumstances. 
 
 The various tufaceous and other beds at this northern 
 end of Chiloe probably belong to about the same age 
 with those near Castro, and they contain, as there, many 
 fragments of black lignite and of silicified and pyritous 
 wood, often embedded close together. They also con- 
 tain many and singular concretions ; some are of hard 
 calcareous sandstone, in which it would appear that 
 broken volcanic crystals and scales of mica have been 
 better preserved (as in the case of the organic remains 
 near Castro) than in the surrounding mass. Other 
 concretions in the white brecciola, are of a hard fer- 
 
CHAP. XII. 
 
 Chiloe. 
 
 395 
 
 ruginous, yet fusible, nature; they are as round as 
 cannon-balls, and vary from two or three inches to two 
 feet in diameter ; their insides generally consist either 
 of fine, scarcely coherent volcanic sand,^ or of an argil- 
 laceous tuff; in this latter case^ the external crust was 
 quite thin and hard. Some of the spherical balls were 
 encircled, in the line of their equators, by a necklace- 
 like row of smaller concretions. Again there were other 
 concretions, irregularly formed, and composed of a hard, 
 compact, ash-coloured stone, with an almost porcelain- 
 ous fracture, adhesive to the tongue, and without any 
 calcareous matter. These beds are, also, interlaced by 
 many veins, containing gypsum, ferruginous matter, 
 calcareous spar, and agate. It was here seen with re- 
 markable distinctness, how intimately concretionary 
 action and the production of fissures and veins are re- 
 lated together. The following diagram is an accurate 
 
 No. 36. 
 
 Ground plan showing the relation between veins and concretionary zones 
 in a mass of tuff. 
 
 representation of a horizontal space of tuflP, about four 
 * The frequent tendency in iron to form hollow concretions or shell. 
 
\g6 Tertiary Formations. part h. 
 
 feet long by two and a half in width : the double lines 
 represent the fissures partially filled with oxide of iron 
 and agate : the curvilinear lines show the course of the 
 innumerable, concentric, concretionary zones of different 
 shades of colour and of coarseness in the particles of 
 tuflf. The symmetry and complexity of the arrangement 
 gave the surface an elegant aj)pearance. It may be 
 seen how obviously the fissures determine (or have been 
 determined by) the shape, sometimes of the whole con- 
 cretion, and sometimes only of its central parts. The 
 fissures also determine the curvatures of the long undu- 
 lating zones of concretionary action. From the varying 
 composition of the veins and concretions, the amount 
 of chemical action which the mass has undergone is 
 surprisingly great ; and it would likewise appear from 
 the difference in size in the particles of the concretionary 
 zones, that the mass, also, has been subjected to internal 
 mechanical movements. 
 
 In the peninsula of Lacuy, the strata over a width 
 of four miles have been upheaved by three distinct, and 
 some other indistinct, lines of elevation, ranging with- 
 in a point of north and south. One line, about 200 
 feet in height, is regularly anticlinal, with the strata 
 dipping away on both sides, at an angle of 15°, from a 
 central ' valley of elevation,' about 300 yards in width. 
 A second narrow steep ridge, only sixty feet high, is 
 uniclinal, the strata throughout dipping westward; 
 those on both flanks being inclined at an angle of from 
 ten to fifteen degrees ; whilst those on the ridge dip in 
 the same direction at an angle of between thirty and 
 forty degrees. This ridge, traced northwards, dies away ; 
 and the beds at its terminal point, instead of dijDping 
 westward, are inclined 12° to the north. This case 
 
 containing incoherent matter is singular ; D'Aubuisson (' Traite de 
 Geogn.' torn. i. p. 318) remarks on this circumstance. 
 
CHAP. XII. Valdivia. Concepcion. 397 
 
 interested me, as being the first in wliicli I found in 
 South America, formations perhaps of tertiary origin, 
 broken by lines of elevation. 
 
 Valdivia: Island of Mocha. — The formations of 
 Chiloe seem to extend with nearly the same character 
 to Valdivia, and for some leagues northward of it : the 
 underlying rocks are micaceous schists, and are covered 
 up with sandstone and other sedimentary beds, including, 
 as I was assm-ed, in many places layers of lignite. I 
 did not land on Mocha (lat. 38° 20'), but Mr. Stokes 
 brought me specimens of the gray, fine-grained, slightly 
 calcareous sandstone, precisely like that of Huafo, con- 
 taining lignite and numerous Turritella3. The island is 
 flat topped, 1,240 feet in height, and appears like an 
 outlier of the sedimentary beds on the mainland. The 
 few shells collected consist of: — 
 
 1. Turritella Chilensis, G. B. Sowerby, PL IV. f . 51 (also at Huafo). 
 
 2. FusiTS, very imperfect, somewhat resembling F, snbreflexus of 
 
 Navidad (PL IV. f . 57), but probably different. 
 
 3. Venus, fragments of. 
 
 Concepcion. — Sailing northward from Valdivia, the 
 coast-clifis are seen, first to assume near the R. Tolten, 
 and thence for 150 miles northward, to be continued 
 with the same mineralogical characters, immediately to 
 be described at Concepcion. I heard in many places 
 of bed sof lignite, some of it fine and glossy, and likewise 
 of silicified wood ; near the Tolten the cliffs are low, 
 but they soon rise in height ; and the horizontal strata 
 are prolonged, with a nearly level surface, until coming 
 to a more lofty tract between points Rumena and 
 Lavapie. Here the beds have been broken up by at 
 least eight or nine parallel lines of elevation, ranging 
 E. or ENE., and W. or WSW. These lines can be 
 followed with the eye many miles into the interior ; 
 they are all uniclinal, the strata in each dipping to a 
 
398 Tertiary Formations. part h. 
 
 point between S. and SSE. with an inclination in 
 the central lines of about forty degrees, and in the 
 outer ones of under twenty degrees. This band of 
 symmetrically troubled country is about eight miles in 
 width. 
 
 The island of Quiriquina, in the Bay of Concepcion, 
 is formed of various soft and often ferruginous sand- 
 stones, with bands of pebbles, and with the lower strata 
 sometimes passing into a conglomerate resting on the 
 underlying metamorphic schists. These beds include 
 subordinate layers of greenish impure clay, soft mica- 
 ceous and calcareous sandstones, and reddish friable 
 earthy matter with white specks like decomposed crystals 
 of feldspar ; they include, also, hard concretions, frag- 
 ments of shells, lignite, and silicified wood. In the 
 upper part they pass into white, soft sediments and 
 brecciolas, very like those described at Chiloe ; as in- 
 deed is the whole formation. At Lirguen and other 
 places on the eastern side of the bay, there are good 
 sections of the lower sandstones, which are generally 
 ferruginous, but which vary in character, and even pass 
 into an argillaceous nature; they contain hard concre- 
 tions, fragments of lignite, silicified wood, and pebbles 
 (of the same rocks with the pebbles in the sandstones 
 of Quiriquina), and they alternate with numerous, often 
 very thin layers of imperfect coal, generally of little 
 specific gravity. The main bed here is three feet thick ; 
 and only the coal of this one bed has a glossy fracture. 
 Another irregular, curvilinear bed of brown, compact 
 lignite, is remarkable for being included in a mass of 
 coarse gravel. These imperfect coals, when placed in a 
 heap, ignite spontaneously. The cliffs on this side of 
 the bay, as well as on the island of Quiriquina, are 
 capped with red friable earth, which, as stated in the 
 ninth chapter, is of recent formation. The stratifica- 
 
CHAP. XII. 
 
 Concepcion, 
 
 399 
 
 tion in this neiglibourliood is generally horizontal ; but 
 near Lirguen the beds dip NW. at an angle of 23° ; 
 near Ooncepcion they are also inclined : at the northern 
 end of Quiriquina they have been tilted at an angle of 
 30° and at the southern end at angles varying from 15° 
 to 40° : these dislocations must have taken place under 
 the sea. 
 
 A collection of shells, from the island of Quiriquina, 
 has been described by M. d'Orbigny : they are all extinct, 
 and from their generic character, M. d'Orbigny inferred 
 that they were of tertiary origin : they consist of : — 
 
 1. Scalaria Chilensis, d'Orbig. 
 
 ' Voyage, Part. Pal.' 
 
 2. Natica A ran can a, clc. 
 
 3. Natica australis, do. 
 
 4. Fusus dijQELcilis, do. 
 
 5. Pyrula longirostra, do. 
 
 6. Pleurotoma Araucana, do. 
 
 7. Cardium auca, do. 
 
 8. Cardium acuticostatum. 
 
 d'Orbig. ' Voyages, Pal.' 
 
 9. Venus auca, do. 
 
 10. Mactra cecileana, do. 
 
 11. Mactra Araucana, do. 
 
 12. Area Araucana, do. 
 
 13. Nucula Largillierti, do. 
 
 14. Trigonia Hanetiana, do. 
 
 During a second visit of the Beagle to Ooncepcion,, 
 Mr. Kent collected for me some silicified wood and 
 shells out of the concretions in the sandstone from Tome, 
 situated a short distance north of Lirguen ; they consist 
 of:— 
 
 1. Natica australis, d'Orbig. 
 
 ' Voyage, Pal.' 
 
 2. Mactra Araucana, do. 
 
 3. Trigonia Hanetiana, do. 
 
 4. Pecten, fragments of, pro- 
 
 bably two species, but too 
 
 imperfect for description. 
 
 5. Baculites vagina, E. Forbes, 
 
 PI. V. f. 3. 
 
 6. Nautilus d'Orbignyanus, E. 
 
 Forbes, PI. V. f . 1 (a) and 
 1(b). 
 
 Besides these shells, Oaptain Belcher^ found here an 
 Ammonite, nearly three feet in diameter, and so heavy 
 that he could not bring it away ; fragments are deposited 
 at Haslar Hospital : he also found the silicified vertebrae 
 of some very large animal. From the identity in 
 
 ' ' Zoology of Capt. Belcher's Voyage,' p. 163. 
 
400 Tertiary Formations. paet n. 
 
 miner alogical nature of the rocks, and from Captain 
 Belcher's minute description of the coast between Lirguen 
 and Tome, the fossiliferous concretions at this latter 
 place certainly belong to the same formation with the 
 beds examined by myself at Lirguen ; and these again 
 are undoubtedly the same with the strata of Quiriquina ; 
 moreover, the three first of the shells from Tome, though 
 associated in the same concretions with the Baculite, 
 are identical with the species from Quiriquina. Hence 
 all the sandstone and lignitiferous beds in this neigh- 
 bourhood certainly belong to the same formation. Al- 
 though the generic character of the Quiriquina fossils 
 naturally led M. d'Orbigny to conceive that they were 
 of tertiary origin, yet as we now find them associated 
 with the Baculites vagina and with an Ammonite, we 
 must, in the opinion of M. d'Orbigny, and if we are 
 guided by the analogy of the Northern Hemisphere, rank 
 them in the Cretaceous system. Moreover, the Baculites 
 vagina, which is in a tolerable state of preservation, 
 appears to Professor E. Forbes certainly to be identical 
 with a species, so named by him, from Pondicherry in 
 India ; where it is associated with numerous decidedly 
 cretaceous species, which approach most nearly to Lower 
 Greensand or Neocomian forms : this fact, considering 
 the vast distance between Chile and India, is truly sur- 
 prising. Again, the Nautilus d'Orbigny aivus, as far 
 as its imperfect state allows of comparison, resembles, 
 as I am informed by Professor Forbes, both in its general 
 form and in^that of its chambers, two species from the 
 Upper Greensand. It may be added that every one of 
 the above-named genera from Quiriquina, which have 
 an apparently tertiary character, are found in the Pon- 
 dicherry strata. There are, however, some difiiculties 
 on this view of the formations at Concepcion being cre- 
 taceous, which I shall afterwards allude to ; and I will 
 
CHAP. XII. Navidad. 401 
 
 here only state tliat tlie Gardium cmca is found also at 
 Coquimbo, tlie beds at wliich place, there can be no 
 doubt, are tertiary. 
 
 Navidad} — The Concepcion formation extends some 
 distance northward, but how far I know not ; for the 
 next point at which I landed was at Navidad, 160 miles 
 north of Concepcion, and 60 miles south of Valparaiso. 
 The cliffs here are about 800 feet in height ; they 
 consist, wherever I could examine them, of fine-grained, 
 yellowish, earthy sandstones, with ferruginous veins, and 
 with concretions of hard calcareous sandstone. In one 
 part, there were many pebbles of the common meta- 
 morphic porphyries of the Cordillera : and near the 
 base of the -cliff, I observed a single rounded boulder of 
 greenstone, nearly a yard in diameter. I traced this 
 sandstone formation beneath the superficial covering of 
 gravel, for some distance inland : the strata are slightly 
 inclined from the sea towards the Cordillera, which 
 apparently has been caused by their having been accu- 
 mulated against or round, outlying masses of granite, 
 of which some points project near the coast. The sand- 
 stone contains fragments of wood, either in the state of 
 lignite or partially silicified, sharks' teeth, and shells in 
 great abundance, both high up and low down the sea- 
 cliffs. Pectunculus and Oliva were most numerous in 
 individuals, and next to them Turritella and Fusus. I 
 collected in a short time, though suffering from illness, 
 the following thirty-one species, all of which are extinct, 
 and several of the genera do not now range (as we shall 
 hereafter show) nearly so far south : — 
 
 1. Gastridium cepa, G. B. Sowerby, PI. IV. f . 68, 69. 
 
 2. Monoceros, fragments of, considered by M. d'Orbigny as a new- 
 
 species. 
 
 ' I was guided to this locality by the Eeport on M. Gay's ' Geolo- 
 gical Kesearches,' in the ' Annales des Scienc. Nat.' (1st series)tom. 28. 
 
 DD 
 
402 Tertiary Formations. paet h. 
 
 3. Voluta alta, G. B. Sowerby, PI. IV. f. 75 (considered by M. 
 
 d'Orbig-iiy as distinct from the V. alta of S. Craz). 
 
 4. Voluta triplicata, G. B. Sowerby, PI. IV. f. 74. 
 
 5. Oliva dimidiata, do. PI. IV. f. 76, 77. 
 
 6. Pleurotoma discors^ do. PI. IV. f. 54. 
 
 7. Pleurotoma turbinelloides, do. PL IV. f. 53. 
 
 8. Fusus subrefiexus, do. PL IV. f. 57. 
 
 9. Fusus pyruliformis, do. PL IV. f. 56. 
 
 10. Fusus, allied to F. regularis, PL IV. f . 55 (considered by M. 
 
 d'Orbigny as a distinct species). 
 
 11. Turritella suturalis, G. B. Sowerby, PL III. f. 50. 
 
 12. Turritella Patagonica (do.), PL III. f. 48 (fragments of). 
 
 13. Trochus Isevis, G. B. Sowerby, PL III. f. 46, 47. 
 
 14. Trochus collaris, do., PL III. f. 44, 45 (considered by M. 
 
 d'Orbigny as the young of the T. laevis). 
 
 15. Cassis monilifer, G. B. Sowerby, PL IV. f. 65. 
 
 16. Pyrula distans, do., PL IV. f. 61. 
 
 17. Triton verruculosus, do., PL IV. f. 63. 
 
 18. Sigaretus subglobosus, G. B. Sowerby, PL III, f. 36, 37. 
 
 19. Natica solida, do., PL III. f. 40, 41 (it is doubtful whether the 
 
 N. solida of S. Cruz is the same species with this). 
 
 20. Terebra undulifera, G. B. Sowerby, PL IV. f. 72, 73. 
 
 21. Terebra costellata, do., PL IV. f. 70, 71. 
 
 22. Bulla (fragments of). 
 
 23. Dentalium giganteum, do., PL II. f. 1. 
 
 24. Dentalium sulcosum, do., PL II. f. 2. 
 
 25. Corbis (?) Igevigata, do., PL IL f. 11. 
 
 26. Cardium multiradiatum, do., PL II. f. 16. 
 
 27. Venus meridionalis, do., PL IE. f. 13. 
 
 28. Pectunculus dispar, (?) Desh. (considered by M. d'Orbigny as a 
 
 distinct species). 
 
 29. 30. Cythera3a and Mactra, fragments of (considered by M. 
 
 d'Orbigny as new species). 
 31. Pecten, fragments of. 
 
 Coquimbo. — For more than 200 miles northward of 
 Navidad, the coast consists of plutonic and metamorphic 
 rocks, with the exception of some quite insignificant 
 superficial beds of recent origin. At Tonguay, twenty- 
 five miles south of Coquimbo, tertiary beds recommence. 
 I have already minutely described in the ninth chapter, 
 the step-formed plains of Coquimbo, and the upper 
 calcareous beds (from twenty to thirty feet in thickness) 
 containing shells of recent species, but in different 
 proportions from those on the beach. There remains 
 to be described only the underlying ancient tertiary 
 
CHAP. xn. Coquimbo. 403 
 
 beds, represented in the following diagram (here given 
 again) by the letters F and E : — 
 
 No. 37. 
 
 Section of the Tertiary Formation at Coquimbo. 
 Surface of plain, 252 feet above sea. 
 
 D -— ^^= — 
 
 
 
 
 Level of Sea. 
 
 F — Lower Sandstone, with concretions and silicified bones, 1 with fossil shells, all, or 
 E — Upper ferruginous sandstone, with numerous Balani, I nearly all, extinct. 
 C and D — Calcareous beds with recent shells. A — Stratified sand in a ravine, also 
 with recent shells. 
 
 I obtained good sections of bed (F) only in Herra- 
 dura Bay : it consists of soft whitish sandstone, with 
 ferruginous veins, some pebbles of granite, and concre- 
 tionary layers of hard calcareous sandstone. These 
 concretions are remarkable from the great number of 
 large silicified bones, apparently of cetaceous animals, 
 which they contain 5 and likewise of a shark's teeth, 
 closely resembling those of the Garcharias megcdodon. 
 Shells of the following species, of which the gigantic 
 Oyster and Perna are the most conspicuous, are nume- 
 rously embedded in the concretions : — 
 
 1. Bulla ambigua, d'Orbig. ' Voyage Pal.' 
 
 2. Monoceros Blainvillii, do. 
 
 3. Cardium atica, do. 
 
 4. Panopgea Coquimbensis, do. 
 
 5. Perna Gaudichaudi, do. 
 
 6. Artemis ponderosa ; Mr. Sowerby can find no distinguishing 
 
 character between this fossil and the recent A. ponderosa ; it 
 is certainly an Artemis, as shown by the pallial impression. 
 
 7. Ostrea Patagonica (?) Mr. Sowerby can point out no distin- 
 
 guishing character between this species and that so eminently 
 characteristic of the great Patagonian formation ; but he will 
 not pretend to afl&rm that they are identical. 
 
 8. Fragments of a Venus and Natica. 
 
 The cliffs on one side of Herradura Bay are capped 
 by a mass of stratified shingle, containing a little calca- 
 
 D D 2 
 
404 Tertiary Formations. part h. 
 
 reous matter, and I did not doubt that it belonged to 
 tlie same recent formation with the gravel on the sur- 
 rounding plains, also cemented by calcareous matter, 
 until to my surprise, I found in the midst of it, a single 
 thin layer almost entirely composed of the above gigantic 
 oyster. 
 
 At a little distance inland, I obtained several sections 
 of the bed (E), which, though different in appearance 
 from the lower bed (F), belongs to the same formation : 
 it consists of a highly ferruginous sandy mass, almost 
 composed, like the lowest bed at Port [S. Julian, of 
 fragments of Balanidse ; it includes some pebbles, and 
 layers of yellowish-brown mudstone. The embedded 
 shells consist of: — 
 
 1. Monoceros Blainvillii, d'Orbig. ' Voyage Pal.' 
 
 2. ambiguus, G. B. Sowerby, PL lY. f. 66, 67. 
 
 8. Anomia alternans, do., PI, II. f. 25. 
 
 4. Pecten rudis, do., PL III. f . 32. 
 
 5. Perna Gaudichaudi, d'Orbig. ' Voyage PaL' 
 
 6. Ostrea Patagonica (?) do. 
 
 7. Ostrea, small species, in imperfect state ; it appeared to me 
 
 like a small kind now living in, but very rare in the bay. 
 
 8. Mytilus Chiloensis ; Mr. Sowerby can find no distinguisMng 
 
 character between this fossil, as far as its not very perfect 
 condition allows of comparison, and the recent species. 
 
 9. Balanus Coquimbensis, G. B. Sowerby, PL II. f. 7. 
 
 10. Balanus psittacus ? King. This appears to Mr. Sowerby and 
 myself identical with a very large and common species now 
 living on the coast. 
 
 The uppermost layers of this ferrugino-sandy mass 
 are conformably covered by, and impregnated to the 
 depth of several inches with, the calcareous matter of 
 the bed (D) called losa : hence I at one time imagined 
 that there was a gradual passage between them ; but as 
 all the species are recent in the bed (D), whilst the 
 most characteristic shells of the uppermost layers of (E) 
 are the extinct Perna, Pecten, and Monoceros, I agree 
 with M. d'Orbigny, that this view is erroneous, and that 
 there is only a mineralogical passage between them. 
 
CHAP. XII. Coquimbo to Copiapo. 405 
 
 and no gradual transition in the nature of their organic 
 remains. Besides the fourteen species enumerated from 
 these two lower beds, M. d'Orbigny has described ten 
 other species given to him from this locality ; namely, 
 
 1. Fusus Cleryanus, d'Orbig. 
 
 ' Voyage Pal.' 
 
 2. petitianus, do. 
 
 3. Venus hanetiana, do. 
 
 4. incerta (?) do. 
 
 5. Cleryanaj do. 
 
 6. Venus petitiana, d'Orbig. 
 
 'Voyage Pal.' 
 
 7. Chilensis, do. 
 
 8. Solecurtus hanetianus, do. 
 
 9. Mactra auca, do. 
 10. Oliva serena, do. 
 
 Of these twenty-four shells, all are extinct, except^ 
 according to Mr. Sowerby, the Artemis fonderosa, 
 Mytilus Chiloe7isis, and probably the great Balanus. 
 
 Coquimho to Copiapo. — A few miles north of Co- 
 quimbo, I met with the ferruginous, balaniferous mass 
 (E) with many silicified bones; I was informed that 
 these silicified bones occur also at Tonguay, south of 
 Coquimbo : their number is certainly remarkable, and 
 they seem to take the place of the silicified wood, so 
 common on the coast- formations of southern Chile. In 
 the valley of Chaneral, I again saw this same formation, 
 capped with the recent calcareous beds. I here left 
 the coast, and did not see any more of the tertiary 
 formations, until descending to the sea at Copiapo : 
 here in one place I found variously coloured layers of 
 sand and soft sandstone, with seams of gypsum, and in 
 another place, a comminuted shelly mass, with layers 
 of rotten-stone and seams of gypsum, including many 
 of the extinct gigantic oyster : beds with these oysters 
 are said to occur at English Harbor, a few miles north 
 of Copiapo. 
 
 Coast of Peru. — With the exception of deposits 
 containing recent shells and of quite insignificant 
 dimensions, no tertiary formations have been observed 
 on this coast, for a space of twenty-two degrees of lati- 
 tude north of Copiapo, until coming to Payta, where 
 
4o6 Tertiary Formations : part h. 
 
 there is said to be a considerable calcareous deposit : a 
 few fossils have been described by M. d'Orbigny from 
 this place, namely : — 
 
 1. Rostellaria Gaudichaudi, d'Orbig. ' Voyage Pal.' 
 
 2. Pectunculus Paytensis, do. 
 
 3. Venus petitiana, do. 
 
 4. Ostrea Patagonica 1 This great oyster (of which specimens 
 
 have been given me) cannot be distinguished by Mr. Sowerby 
 from some of the varieties from Patagonia ; though it would 
 be hazardous to assert it is the same with that species, or 
 with that from Coquimbo. 
 
 Goncluding Remarks. — The formations described 
 in this chapter, have, in the case of Chiloe and probably 
 in that of Concepcion and Navidad, apparently been 
 accumulated in troughs formed by submarine ridges 
 extending parallel to the ancient shores of the continent ; 
 in the case of the islands of Mocha and Huafo it is 
 highly probable, and in that of Ypun and Lemus almost 
 certain, that they were accumulated round isolated 
 rocky centres or nuclei, in the same manner as mud 
 and sand is now collecting round the outlying islets 
 and reefs in the West Indian archipelago. Hence, I 
 may remark, it does not follow that the outlying ter- 
 tiary masses of Mocha and Huafo were ever continuously 
 united at the same level with the formations on the 
 mainland, though they may have been of contempora- 
 neous origin, and been subsequently upraised to the 
 same height. In the more northern parts of Chile, the 
 tertiary strata seem to have been separately accumu- 
 lated in bays, now forming the mouths of valleys. 
 
 The relation between these several deposits on the 
 shores of the Pacific, is not nearly so clear as in the 
 case of the tertiary formations on the Atlantic. Judging 
 from the form and height of the land (evidence which 
 I feel sure is here much more trustworthy than it can 
 be in such broken continents as that of Europe), from 
 
CHAP. XII. Conchiding Remarks on. 407 
 
 the identity of mineralogical composition, from tlie 
 presence of fragments of lignite and of silicified wood, 
 and from tlie intercalated layers of imperfect coal, I 
 must believe that the coast-formations from central 
 Chiloe to Concepcion, a distance of 400 miles, are of 
 the same age : from nearly similar reasons, I suspect 
 that the beds of Mocha, Huafo, and Ypun, belong also 
 to the same period. The commonest shell in Mocha 
 and Huafo is the same species of Turritella ; and I 
 believe the same Cyther^ea is found on the islands of 
 Huafo, Chiloe, and Ypun ; but with these trifling ex- 
 ceptions, the few organic remains found at these places 
 are distinct. The numerous shells from Navidad, with 
 the exception of two, namely, the Sigaretus and Tur- 
 ritella found at Ypun, are likewise distinct from those 
 found in any other part of this coast. Coquimbo has 
 Cardium auca in common with Concepcion, and Fusus 
 Cleryanus with Huafo ; I may add, that Coquimbo has 
 Venus petitiana^ and a gigantic oyster (said by 
 M. d'Orbigny also to be found a little south of Concep- 
 cion) in common with Payta, though this latter place 
 is situated twenty-two degrees northward of lat. 27°, to 
 which point the Coquimbo formation extends. 
 
 From these facts, and from the generic resemblance 
 of the fossils from the different localities, I cannot avoid 
 the suspicion that they all belong to nearly the same 
 epoch, which epoch, as we shall immediately see, must 
 be a very ancient tertiary one. But as the Baculite, 
 especially considering its apparent identity with the 
 Cretaceous Pondicherry species, and the presence of an 
 Ammonite, and the resemblance of the Nautilus to two 
 upper greensand species, together afford very strong 
 evidence that the formation at Concepcion is a Secondary 
 one ; I will, in my remarks on the fossils from the other 
 localities, put on one side those from Concepcion and 
 
4o8 Tertiary Formations : part u. 
 
 from Eastern Ohiloe, whicli, whatever tlieir age may be, 
 appear to me to belong to one group. I must, however, 
 as'ain call attention to the fact that the Cardium auca 
 is found both at Concepcion and in the undoubtedly 
 tertiary strata of Coquimbo : nor should the possibility 
 be overlooked, that as Trigonia, though known in the 
 Northern Hemisphere only as a Secondary genus, has 
 living representatives in the Australian seas, so a Bacu- 
 lite, Ammonite, and Trigonia may have survived in this 
 remote part of the Southern Ocean to a somewhat later 
 period than to the north of the equator. 
 
 Before passing in review the fossils from the other 
 localities, there are two points, with respect to the for- 
 mations between Concepcion and Chiloe, which deserve 
 some notice. First, that though the strata are generally 
 horizontal, they have been upheaved in Chiloe, in a set 
 of parallel anticlinal and uniclinal lines ranging north 
 and south, — in the district near P. Rumena by eight 
 or nine far-extended, most symmetrical, uniclinal lines 
 ranging nearly east and west, — and in the neighbourhood 
 of Concepcion by less regular single lines, directed both 
 NE. and SW., andNW. and SE. This fact is of some 
 interest, as showing that within a period which cannot 
 be considered as very ancient in relation to the history 
 of the continent, the strata between the Cordillera and 
 the Pacific have been broken up in the same variously- 
 directed manner as have the old plutonic and meta- 
 morphic rocks in this same district. The second point 
 is, that the sandstone between Concepcion and Southern 
 Ohiloe is everywhere lignitiferous, and includes much 
 silicified wood ; whereas the formations in Northern 
 Chile do not include beds of lignite or coal, and in place 
 of the fragments of silicified wood there are silicified 
 bones. Now, at the present day, from Cape Horn to 
 near Concepcion, the land is entirely concealed by forests, 
 
CHAP. XTT. 
 
 Age of. 409 
 
 wMch thill out at Concepcion, and in central and 
 Northern Chile entirely disappear. This coincidence in 
 the distribution of the fossil wood and the living forests 
 may be quite accidental ; but I incline to take a diffe- 
 rent view of it; for, as the difference in climate, on 
 which the presence of forests depends, is here obviously 
 in chief part due to the form of the land, and as the 
 Cordillera undoubtedly existed when the lignitiferous 
 beds were accumulating, I conceive it is not improbable 
 that the climate, during the lignitiferous period, varied 
 on different parts of the coast in a somewhat similar 
 manner as it now does. Looking to an earlier epoch, 
 when the strata of the Cordillera were depositing, there 
 were islands which even in the latitude of Northern 
 Chile, where now all is irreclaimably desert, supported 
 large coniferous forests. 
 
 Seventy-nine species of fossil shells, in a tolerably 
 recognisable condition, from the coast of Chile and Peru, 
 are described in this volume, and in the Palgeontological 
 part of M. d'Orbigny's ' Voyage ' : if we put on one side 
 the twenty species exclusively found at Concepcion and 
 Chiloe, fifty-nine species from Navidad and the other 
 specified localities remain. Of these fifty-nine species 
 only an Artemis, a Mytilus, and Balanus, all from 
 Coquimbo, are (in the opinion of Mr. Sowerby, but not 
 in that of M. d'Orbigny) identical with living shells ; 
 and it would certainly require a better series of speci- 
 mens to render this conclusion certain. Only the 
 TuTTitella Ghilensis from Huafo and Mocha, the T. 
 Patagonica and Venus meridionalis from Navidad, 
 come very near to recent South American shells, namely, 
 the two Turritellas to T. cingulata, and the Venus to 
 V. exalhida : some few other species come rather less 
 near ; and some few resemble forms in the older Euro- 
 pean tertiary deposits : none of the species resemble 
 
4IO 
 
 Tertiary Formations : 
 
 PAET II. 
 
 secondary forms. Hence I conceive there can be no 
 doubt that these formations are tertiary, — a point ne- 
 cessary to consider, after the case of Ooncepcion. The 
 fifty-nine species belong to thirty-two genera ; of these, 
 Gastridium is extinct, and three or four of the genera 
 (viz. Panopaea, Rostellaria, Corbis ?, and I believe 
 Solecurtus) are not now found on the west coast of South 
 America. Fifteen of the genera have on this coast 
 living representatives in about the same latitudes with 
 the fossil species ; but twelve genera now range very 
 differently to what they formerly did. The idea of the 
 
 Genera, witli living and 
 
 Latitudes, in which found 
 
 Southernmost latitude, in 
 
 tertiary species on the 
 
 fossil on the coasts of 
 
 which found living on the 
 
 west coast of S. America ^ 
 
 Chile and Peru 
 
 west coast of S. America 
 
 Bulla . 
 
 30° to 43° 30' 
 
 12° near Lima 
 
 Cassis . . . 
 
 34° 
 
 1° 37' 
 
 Pyrula . 
 
 34° (and 36° 30' at 
 Ooncepcion) 
 
 6° Payta 
 
 Fusus . . . 
 
 30° to 43° 30' 
 
 23° Mexillones ; re- 
 appears at the St. 
 of Magellan 
 
 Pleurotoma . 
 
 34° to 43° 30' 
 
 2° 18' St. Elena 
 
 Terebra . . . 
 
 34° 
 
 5° Payta 
 
 Sigaretus 
 
 34° to 44° 30' 
 
 12° Lima 
 
 Anomia . . . 
 
 30° 
 
 7° 48' 
 
 Perna . 
 
 30° 
 
 1° 23' Xixappa 
 
 Cardium . . . 
 
 30° to 34° (and 36° 
 30' at Concepcion) 
 
 5° Payta 
 
 Artemis 
 
 30° 
 
 5° Payta 
 
 Voluta . . . 
 
 34° to 44° 30' 
 
 Mr. Cuming does 
 not know of any 
 species living on 
 the west coast, 
 between the equa- 
 tor and lat. 43° 
 south; from this 
 latitude a species 
 is found as far 
 south as Tierra 
 del Fuego. 
 
 ^ M. d'Orbigny states that the genus Natica is not found on the 
 coast of Chile ; but Mr. Cuming found it at Valparaiso. Scalaria 
 was found at Valparaiso ; Area, at Iquique, in lat. 20°, by Mr. 
 Cuming ; Area, also, was found by Capt. King, at Juan Fernandez, 
 in lat. 33° 30'. 
 
C5HAP. XIT. 
 
 Age of. 411 
 
 table on the previous page, in whicli tlie difference 
 between tbe extension in latitude of tbe fossil and existing 
 species is shown, is taken from M. d'Orbigny's work ; but 
 the range of the living shells is given on the authority 
 of Mr. Cuming, whose long-continued researches on the 
 conchology of South America are well known. 
 
 When we consider that very few, if any, of the fifty- 
 nine fossil shells are identical with, or make any close 
 approach to, living species ; when we consider that some 
 of the genera do not now exist on the west coast of 
 South America, and that no less than twelve genera out 
 of the thirty-two formerly ranged very differently from 
 the existing species of the same genera, we must admit 
 that these deposits are of considerable antiquity, and 
 that they probably verge on the commencement of the 
 tertiary era. May we not venture to believe, that they 
 are of nearly contemporaneous origin with the Eocene 
 formations of the Northern Hemisphere ? 
 
 Comparing the fossil remains from the coast of Chile 
 (leaving out, as before, Concepcion and Chiloe) with 
 those from Patagonia, we may conclude, from their 
 generic resemblance, and from the small number of the 
 species which from either coast approach closely to 
 living forms, that the formations of both belong to 
 nearly the same epoch ; and this is the opinion of M. 
 d'Orbigny. Had not a single fossil shell been common 
 to the two coasts, it could not have been argued that 
 the formations belonged to different ages ; for Messrs. 
 Cuming and Hinds have found, on the comparison of 
 nearly 2,000 living species from the opposite sides of 
 South America, only one in common, namely, the Tur- 
 jpura lapillus from both sides of the Isthmus of Panama : 
 even the shells collected by myself amongst the Chonos 
 Islands and on the coast of Patagonia, are dissimilar, 
 and we must descend to the apex of the continent, to 
 
412 Tertiary Forinations : part h. 
 
 Tierra del Fuego, to find these two great conchological 
 provinces united into one. Hence it is remarkable tliat 
 four or five of the fossil shells from Navidad, namely, 
 Valuta alta, Turritella Patagonica, Trochits collarisj 
 Venus meridionalis, perhaps Natica solida^ and per- 
 haps the large oyster from Ooquimbo, are considered by 
 Mr. Sowerby as identical with species from Santa Cruz 
 and Port Desire. M. d'Orbigny, however, admits the 
 perfect identity only of the Trochus. 
 
 On the TemiJerature of the Tertiary Period. — As 
 the number of the fossil species and genera from the 
 western and eastern coasts is considerable, it will be 
 interesting to consider the probable nature of the 
 climate under which they lived. We will first take the 
 case of Navidad, in lat. 34", where thirty-one species 
 were collected, and which, as we shall presently see, 
 must have inhabited shallow water, and therefore will 
 necessarily well exhibit the effects of temperature. 
 Referring to the Table given in the previous page, we 
 find that the existing species of the genera Cassis, 
 Pyrula, Pleurotoma, Terebra, and Sigaretus, which are 
 generally (though by no means invariably) characteristic 
 of warmer latitudes, do not at the present day range 
 nearly so far south on this line of coast as the fossil 
 species formerly did. Including Coquimbo, we have 
 Perna in the same predicament. The first impression 
 from this fact is, that the climate must formerly have 
 been warmer than it now is ; but we must be very 
 cautious in admitting this, for Cardium, Bulla, and 
 Pusus (and, if we include Coquimbo, Anomia and 
 Artemis) likewise formerly ranged farther south than 
 they now do ; and as these genera are far from being 
 characteristic of hot climates, their former greater 
 southern range may well have been owing to causes 
 quite distinct from climate : Voluta, again, though 
 
CHAP. xn. Temperature of Tertiary Period. 413 
 
 generally so tropical a genus, is at present confined on 
 the west coast to colder or more southern latitudes than 
 it was during the tertiary period. The Troclius colla/risj 
 moreover, and, as we have just seen according to Mr. 
 Sowerby, two or three other species, formerly ranged 
 from Navidad as far south as Santa Cruz in lat. 50°. If, 
 instead of comparing the fossils of Navidad,. as we have 
 hitherto done, with the shells now living on the west 
 coast of South America, we compare them with those 
 found in other parts of the world, under nearly similar 
 latitudes ; for instance, in the southern parts of the 
 Mediterranean or of Australia, there is no evidence 
 that the sea off Navidad was formerly hotter than what 
 might have been expected from its latitude, even if it 
 was somewhat warmer than it now is when cooled by 
 the great southern polar current. Several of the most 
 tropical genera have no representative fossils at Navi- 
 dad ; and there are only single species of Cassis, Pyrula, 
 and Sigaretus, two of Pleurotoma and two of Terebra, 
 but none of these species are of conspicuous size. In 
 Patagonia, there is even still less evidence in the 
 character of the fossils, of the climate having been 
 formerly warmer.^ As from the various reasons already 
 assigned, there can be little doubt that the formations 
 of Patagonia and at least of Navidad and Coquimbo in 
 Chile, are the equivalents of an ancient stage in the 
 tertiary formations of the northern hemisphere, the 
 conclusion that the climate of the southern seas at this 
 period was not hotter than what might have been ex- 
 pected from the latitude of each place, appears to me 
 highly important ; for we must believe, in accordance 
 
 * It may be worth while to mention that the shells living at the 
 present day on this eastern side of S. America, in lat. 40°, have 
 perhaps a more tropical character than those in corresponding 
 latitudes on the shores of Europe : for at Bahia Blanca and S. Bias, 
 there are two fine species of Voluta and four of Oliva. 
 
414 On the Absence of part n. 
 
 with tlie views of Mr. Lyell, that the causes which gave 
 to the older tertiary productions of the quite temperate 
 zones of Europe a tropical character, ivere of a local 
 character and did not affect the entire glohe. On the 
 other hand, I have endeavoured to show, in the ' Geo- 
 logical Transactions/ that, at a much later period, Europe 
 and North and South America were nearly contempora- 
 neously subjected to ice-action, and consequently to a 
 colder, or at least, more equable climate than that now 
 characteristic of the same latitudes. 
 
 On the Absence of extensive modern Gonchiferous 
 Deposits in South A merica ; and on the Contempo- 
 raneousness of the older Tertiary Deposits at distant 
 points heing due to contemporaneous movements of 
 subsidence. — Knowing from the researches of Professor 
 E. Forbes, that molluscous animals chiefly abound 
 within a depth of 100 fathoms and under, and bearing 
 in mind how many thousand miles of both coasts of 
 South America have been upraised within the recent 
 period by a slow, long- continued, intermittent move- 
 ment, — seeing the diversity in nature of the shores and 
 the number of shells now living on them, — seeing also 
 that the sea off Patagonia and off many parts of Chile, 
 was during the tertiary period highly favourable to the 
 accumulation of sediment, — the absence of extensive 
 deposits including recent shells over these vast spaces 
 of coast is highly remarkable. The conchiferous cal- 
 careous beds at Coquimbo, and at a few isolated points 
 northward, offer the most marked exception to this 
 statement ; for these beds are from twenty to thirty 
 feet in thickness, and they stretch for some miles along 
 shore, attaining, however, only a very trifling breadth. 
 At Yaldivia there is some sandstone with imperfect casts 
 of shells, which possiblij may belong to the recent period : 
 parts of the boulder formation and the shingle-beds on 
 
CHAP. xn. Conchiferous Deposits. 415 
 
 the lower plains of Patagonia probably belong to this 
 same period, but neither are fossiliferous : it also so 
 happens that the great Pampean formation does not in- 
 clude, with the exception of the Azara, any mollusca. 
 There cannot be the smallest doubt that the upraised 
 shells along the shores of the Atlantic and Pacific, 
 whether lying on the bare surface, or embedded in mould 
 or in sand-hillocks, will in the course of ages be destroyed 
 by alluvial action : this probably will be the case even 
 with the calcareous beds of Coquimbo, so liable to dis- 
 solution by rain-water. If we take into consideration 
 the probability of oscillations of level and the conse- 
 quent action of the tidal waves at different heights, 
 their destruction will appear almost certain. Looking 
 to an epoch as far distant in futurity as we now are 
 from the past Miocene period, there seems to me scarcely 
 a chance, under existing conditions, of the numerous 
 shells now living in those zones of depths most fertile 
 in life, and found exclusively on the western and south- 
 eastern coasts of South America, being preserved to this 
 imaginary distant epoch. A whole conchological series 
 will in time be swept away, with no memorials of their 
 existence preserved in the earth's crust. 
 
 Can any light be thrown on this remarkable absence 
 of recent conchiferous deposits on these coasts, on which, 
 at an ancient tertiary epoch, strata abounding with 
 organic remains were extensively accumulated ? I think 
 there can, namely, by considering the conditions neces- 
 sary for the preservation of a formation to a distant 
 age. Looking to the enormous amount of denudation 
 which on all sides of us has been effected, — as evi- 
 denced by the lofty cliffs cutting off on so many coasts 
 horizontal and once far-extended strata of no great 
 antiquity (as in the case of Patagonia), — as evidenced 
 by the level surface of the ground on both sides of great 
 
41 6 On the Absence of paet u. 
 
 faults and dislocations, — by inland lines of escarpments, 
 by outliers, and numberless other facts, and by that 
 argument of high generality advanced by Mr. Lyell, 
 namely, that every sedimentary formation, whatever its 
 thickness may be, and over however many hundred 
 square miles it may extend, is the result and the measure 
 of an equal amount of wear and tear of pre-existing 
 form8.tions ; considering these facts, we must conclude 
 that, as an ordinary rule, a formation to resist such vast 
 destroying powers, and to last to a distant epoch, must 
 be of wide extent, and either in itself, or together with 
 superincumbent strata, be of great thickness. In this 
 discussion, we are considering only formations contain- 
 ing the remains of marine animals, which, as before 
 mentioned, live, with some exceptions, within (most of 
 them much within) depths of a hundred fathoms. How, 
 then, can a thick and widely extended formation be 
 accumulated, which shall include such organic remains ? 
 First, let us take the case of the bed of the sea long re- 
 maining at a stationary level : under these circumstances 
 it is evident that conchiferoiis strata can accumulate 
 only to the same thickness with the depth at which 
 the shells can live ; on gently inclined coasts alone can 
 they accumulate to any considerable width ; and from 
 the want of superincumbent pressure, it is probable 
 that the sedimentary matter will seldom be much con- 
 solidated : such formations have no very good chance, 
 when in the course of time they are upraised, of long 
 resisting the powers of denudation. The chance will 
 be less if the submarine surface, instead of having re- 
 mained stationary, shall have gone on slowly rising 
 during the deposition of the strata, for in this case their 
 total darkness must be less, and each part, before being 
 consolidated or thickly covered up by superincumbent 
 matter, will have had successively to pass through the 
 
CHAP. XII. Recent Conchiferotts Formations. 417 
 
 ordeal of the beacli ; and on most coasts, the waves on 
 the beach tend to wear down and disperse every object 
 exposed to their action. Now, both on the south-eastern 
 and western shores of South America, we have had clear 
 proofs that the land has been slowly rising, and in the 
 long lines of lofty cliffs, we have seen that the tendency 
 of the sea is almost everywhere to eat into the land. 
 Considering these facts, it ceases, I think, to be sur- 
 prising, that extensive recent conchiferous deposits are 
 entirely absent on the southern and western shores of 
 America. 
 
 Let us take the one remaining case, of the bed of 
 the sea slowly subsiding during a length of time, whilst 
 sediment has gone on being deposited. It is evident 
 that strata might thus accumulate to any thickness, each 
 stratum being deposited in shallow water, and conse- 
 quently abounding with those shells which cannot live 
 at great depths : the pressure, also, I may observe, of 
 each fresh bed would aid in consolidating all the lower 
 ones. Even on a rather steep coast, though such must 
 ever be unfavourable to widely extended deposits, the 
 formations would always tend to increase in breadth 
 from the water encroaching on the land. Hence we 
 may admit that periods of slow subsidence will com- 
 monly be most favourable to the accumulation of 
 concliiferoiis deposits, of sufficient thickness, extension, 
 and hardness, to resist the average powers of denudation. 
 
 We have seen that at an ancient tertiary epoch, 
 fossiliferous deposits were extensively deposited on the 
 coasts of South America ; and it is a very interesting 
 fact, that there is evidence that these ancient tertiary 
 beds were deposited during a period of subsidence. 
 Thus, at Navidad, the strata are about 800 feet in thick- 
 ness, and the fossil shells are abundant both at the level 
 of the sea and some way up the cliffs ; having sent a 
 
 E E 
 
41 8 Formation du^dng Subsidence pakt n. 
 
 list of these fossils to Professor B. Forbes, he thinks 
 they must have lived in water between one and ten 
 fathoms in depth : hence the bottom of the sea on 
 which these shells once lived must have subsided at 
 least 700 feet to allow of the superincumbent matter 
 being deposited. I must here remark, that, as all these 
 and the following fossil shells are extinct species. Pro- 
 fessor Forbes necessarily judges of the depths at which 
 they lived only from their generic character, and from 
 the analogical distribution of shells in the Northern 
 Hemisphere ; but there is no just cause from this to 
 doubt the general results. At Huafo the strata are 
 about the same thickness, namely, 800 feet, and Pro- 
 fessor Forbes thinks the fossils found there cannot have 
 lived at a greater depth than fifty fathoms, or 300 feet. 
 These two points, namely, Navidad and Huafo, are 570 
 miles apart, but nearly half-way between them lies 
 Mocha, an island 1,200 feet in height, apparently formed 
 of tertiary strata up to its level summit, and with many 
 shells, including the same Turritella with that found 
 at Huafo, embedded close to the level of the sea. In 
 Patagonia, shells are numerous at St. Cruz, at the foot 
 of the 350 feet plain, which has certainly been formed 
 by the denudation of the 840 feet plain, and therefore 
 was originally covered by strata that number of feet in 
 thickness, and these shells, according to Professor 
 Forbes, probably lived at a depth of between seven and 
 fifteen fathoms : at Port St. Julian, sixty miles to the 
 north, shells are numerous at the foot of the ninety feet 
 plain (formed by the denudation of the 950 feet plain), 
 and likewise occasionally at the height of several hundred 
 feet in the upper strata ; these shells must have lived in 
 water somewhere between five and fifty fathoms in depth. 
 Although in other parts of Patagonia I have no direct 
 evidence of shoal-water shells having been buried under 
 
CHAP. XII. of ConchiferoMs Deposits, 419 
 
 a great thickness of superincumbent submarine strata, 
 yet it should be borne in mind that the lower fossili- 
 ferous strata with several of the same species of Mollusca, 
 the upper tufaceous beds, and the high summit-plain, 
 stretch for a considerable distance southward, and for 
 hundreds of miles northward ; seeing this uniformity 
 of structure, I conceive it may be fairly concluded that 
 the subsidence by which the shells at Santa Cruz and 
 St. Julian were carried down and covered up, was not 
 confined to these two points, but was co-extensive with 
 a considerable portion of the Patagonian tertiary forma- 
 tion. In a succeeding chapter it will be seen, that we 
 are led to a similar conclusion with respect to the 
 secondary fossiliferous strata of the Cordillera, namely, 
 that they also were deposited during a long-continued 
 and great period of subsidence. 
 
 From the foregoing reasoning, and from the facts 
 just given, I think we must admit the probability of 
 the following proposition : namely, that when the bed 
 of the sea is either stationary or rising, circumstances 
 are far less favourable, than when the level is sinking, 
 to the accumulation of conchiferous deposits of suflBcient 
 thickness and extension to resist, when upheaved, the 
 average vast amount of denudation. This result appears 
 to me, in several respects, very interesting : everyone is 
 at first inclined to believe that at innumerable points, 
 wherever there is a supply of sediment, fossiliferous 
 strata are now forming, which at some future distant 
 epoch will be upheaved and preserved ; but on the views 
 above given, we must conclude that this is far from 
 being the case ; on the contrary, we require (1st), a 
 long-continued supply of sediment ; (2nd), an extensive 
 shallow area ; and (3rd), that this area shall slowly 
 subside to a great depth, so as to admit the accumula- 
 tion of a widely-extended thick mass of superincumbent 
 
 E E 2 
 
42 o Formation dttring Sttbsidence paet n. 
 
 strata. In how few parts of tiie world, probably, do 
 tbese conditions at the present day concur ! We can 
 thus, also, understand the general want of that close 
 sequence in fossiliferous formations which we might 
 theoretically have anticipated ; for, without we supjDose 
 a subsiding movement to go on at the same spot during 
 an enormous period, from one geological era to another, 
 and during the whole of this period sediment to accu- 
 mulate at the proper rate, so that the depth should not 
 become too great for the continued existence of mollus- 
 cous animals, it is scarcely possible that there should be 
 a perfect sequence at the same spot in the fossil shells 
 of the two geological formations.^ So far from a very 
 long-continued subsidence being probable, many facts 
 lead to the belief that the earth's surface oscillates up 
 and down ; and we have seen that during the elevatory 
 movements there is but a small chance of durable fos- 
 siliferous deposits accumulating. 
 
 Lastly, these same considerations appear to throw 
 some light on the fact that certain periods appear to 
 have been favourable to the deposition, or at least to 
 the preservation, of contemporaneous formations at very 
 distant points. We have seen that in South America 
 an enormous area has been rising within the recent 
 period ; and in other quarters of the globe immense 
 spaces appear to have risen contemporaneously. From 
 my examination of the coral-reefs of the great oceans, 
 
 'Professor H. D. Eogers, in his excellent address to the Associa- 
 tion of American Geologists (Silliman's * Journal,' vol. xlvii. p. 277), 
 makes the following remark : ' I question if we are at all aware how 
 completely the whole history of all departed time lies indelibly re- 
 corded with the amplest minuteness of detail in the successive 
 sediments of the globe, how effectually, in other words, every 
 period of time has written its own history, carefully preserving every 
 created form and every trace of action.' I think the correctness of 
 such remarks is more than doubtful, even if we except (as I suppose 
 he would) all those numerous organic forms which contain no hard 
 parts. 
 
CHAP. XII. of Conckifero^t^s Deposits. 421 
 
 I have been led to conclude tliat the bed of the sea has 
 gone on slowly sinking within the present era, over truly 
 vast areas : this, indeed, is in itself probable, from the 
 simple fact of the rising areas having been so large. In 
 South America we have distinct evidence that at nearly 
 the same tertiary period, the bed of the sea off parts of 
 the coast of Chile and off Patagonia was sinking, though 
 these regions are very remote from each other. If, 
 then, it holds good, as a general rule, that in the same 
 quarter of the globe the earth's crust tends to sink and 
 rise contemporaneously over vast spaces, we can at 
 once see, that we have at distant points, at the same 
 period, those very conditions which appear to be re- 
 quisite for the accumulation of fossiliferous masses of 
 sufficient extension, thickness, and hardness, to resist 
 denudation, and consequently to last iinto an epoch 
 distant in futurity.^ 
 
 1 Professor Forbes has some admirable remarks on this subject, 
 in his ' Report on the Shells of the iEgean Sea.' In a letter to Mr. 
 Maclaren (' Edinburgh New Phil. Journal,' January 1843), I partially- 
 entered into this discussion, and endeavoured to show that it was 
 highly improbable, that upraised stolls or barrier-reefs, though of 
 great thickness, should, owing to their small extension or breadth, 
 be preserved to a distant future period. 
 
42 2 Bakia, Brazil : part ii. 
 
 CHAPTER XIII. 
 
 PLUTONIC AND METAMOKPHIC ROCKS I — CLEAVAGE AND 
 
 FOLIATION. 
 
 Brazil, Bahia, gneiss with disjointed metamorplwsed dikes — Strihe 
 of foliation — Rio de Janeiro, gneiss-granite, emhedded fragment 
 in, decomposition of — La Plata, metamorphic and old volcanic roclts 
 of — S. Veiitana — Clay stone porphyry formation of Patagonia ; 
 singular metamorpJiic roclts; speudo-diTies — Falkland Islands, 
 lpal(Sozoic fossils of — Tierra del Fuego, clay-slate formation, 
 cretaceous fossils of ; cleavage and foliation ; form of land — Chonos 
 ArcTiipelago, mica schists, foliation disturbed ty granitic axis ; 
 dihes — Chiloe — Concepcion, dikes, successive formation of — Central 
 and Northern Chile— Concluding remarks on cleavage and folia- 
 tion — Their close analogy and similar origin- — Stratification of 
 metamorphic schists — Foliation of intrusive rocks — Relation of 
 cleavage and foliation to the lines of tension during metamorphosis. 
 
 The metamorphic and plutonic formations of the several 
 districts visited by the Beagle will be here chiefly 
 treated of, but only such cases as appear to me new, or 
 of some special interest, will be described in detail ; at 
 the end of the chapter I will sum up all the facts 
 on cleavage and foliation, — to which I particularly 
 attended. 
 
 Bahia, Brazil: lat. 13° south. — The prevailing 
 rock is gneiss, often passing, by the disappearance of 
 the quartz and mica, and by the feldspar losing its 
 red colour, into a brilliantly grey primitive green- 
 stone. Not unfrequently quartz and hornblende are 
 arranged in layers in almost amorphous feldspar. 
 
CHAP, xni. 
 
 Rocks of. 423 
 
 There is some fine-grained syenitic granite, orbicularly 
 marked by ferruginous lines, and weathering into 
 vertical, cylindrical holes, almost touching each other. 
 In the gneiss, concretions of granular feldspar and 
 others of garnets with mica occur. The gneiss is 
 traversed by numerous dikes composed of black, finely 
 crystallised, hornblendic rock, containing a little glassy 
 feldspar and sometimes mica, and varying in thickness 
 from mere threads to ten feet : these threads, which 
 are often curvilinear, could sometimes be traced running 
 into the larger dikes. One of these dikes was remark- 
 able from having been in two or three places laterally 
 disjointed, with unbroken gneiss interposed between 
 the broken ends, and in one part with a portion of the 
 gneiss driven, apparently whilst in a softened state, 
 into its side or wall. In several neighbouring places, 
 the gneiss included angular, well-defined, sometimes 
 bent, masses of hornblende rock, quite like, except in 
 being more perfectly crystallised, that forming the 
 dikes, and, at least in one instance, containing (as 
 determined by Professor Miller) augite as well as 
 hornblende. In one or two cases these angular masses, 
 though now quite separate from each other by the solid 
 gneiss, had, from their exact correspondence in size 
 and shape, evidently once been united ; hence I cannot 
 doubt that most or all of the fraofments have been 
 derived from the breaking up of the dikes, of which we 
 see the first stage in the above-mentioned laterally 
 disjointed one. The gneiss close to the fragments 
 generally contained many large crystals of hornblende, 
 which are entirely absent or rare in other parts : its 
 folia or laminae were gently bent round the fragments, 
 in the same manner as they sometimes are round concre- 
 tions. Hence the gneiss has certainly been softened, 
 its composition modified, and its folia arranged, sub- 
 
424 Bakia, Brazil. part n. 
 
 sequently to the breaking up of the dikes/ these latter 
 also having been at the same time bent and softened. 
 
 I must here take the opportunity of premising, 
 that by the term cleavage^ I imply those planes of 
 division which render a rock, appearing to the eye 
 quite or nearly homogeneous, fissile. By the term folia- 
 tion, I refer to the layers or plates of different minera- 
 logical nature of which most metamorphic schists are 
 composed; there are, also, often included in such 
 masses, alternating, homogeneous, fissile layers or folia^ 
 and in this case the rock is both foliated and has a 
 cleavage. By stratification^ as applied to these forma- 
 tions, I mean those alternate, parallel, large masses of 
 different composition, which are themselves frequently 
 either foliated or fissile, — such as the alternating so- 
 called strata of mica-slate, gneiss, glossy clay-slate, and 
 marble. 
 
 The folia of the gneiss within a few miles round 
 Bahia generally strike irregularly, and are often cur- 
 vilinear, dipping in all directions at various angles : 
 but where best defined, they extended most frequently 
 in a NE. by N. (or East 50° N.) and SW. by S. line, 
 corresponding nearly with the coast-line northwards 
 of the bay. I may add that Mr. Gardner ^ found in 
 several parts of the province of Ceara, which lies 
 between 4U0 and 500 miles north of Bahia, gneiss with 
 the folia extending E. 45° N. ; and in Guyana, accord- 
 ing to Sir K. Schomburgk, the same rock strikes E. 
 57° N. Again, Humboldt describes the gneiss-gra.nite 
 over an immense area in Venezuela and even in Colombia, 
 as striking E. 50° N., and dipping to the NW. at an 
 
 ^ Professor Hitchcock (' Geolog. of Massachusetts,' vol, ii. p. 673) 
 gives a closely similar case of a greenstone dike in syenite. 
 
 2 ' Geological Section of the Brit. Assoc' 1840. For Sir R. Schom- 
 burgk's observations, see ' Geograph. Journal,' 1842, p. 190. See 
 also Humboldt's discussion on Loxodrismin the ' Personal Narrative. 
 
CHAP. XIII. Rio de Janeiro. 425 
 
 angle of fifty degrees. Hence all tlie observations, 
 hitherto made tend to show that the gneissic rocks 
 over the whole of this part of the continent have their 
 folia extending generally within almost a point of the 
 compass of the same direction.^ 
 
 Uio de Janeiro. — This whole district is almost 
 exclusively formed of gneiss, abounding with garnets,, 
 and porphyritic with large crystals, even three and four 
 inches in length, of orthoclase feldspar: in these 
 crystals mica and garnets are often enclosed. At the 
 western base of the Corcovado, there is some ferruginous 
 carious quartz-rock; and in the Tijeuka range, much 
 fine-grained granite. I observed boulders of greenstone 
 in several places ; and on the islet of Yillegagnon, and 
 likewise on the coast some miles northward, two large 
 trappean dikes. The porphyritic gneiss, or gneiss- 
 granite as it has been called by Humboldt, is only so 
 far foliated that the constituent minerals are arranged 
 with a certain degree of regularity, and may be said to 
 have a ' grain,' but they are not separated into distinct 
 folia or laminse. There are, however, several other 
 
 ^ I landed at only one place north of Bahia, namely, at Pernam- 
 buco. I found there only soft, horizontally stratified matter, 
 formed from disintegrated granitic rocks, and some yellowish im- 
 pure limestone, probably of a tertiary epoch. I have described a 
 most singular natural bar of hard sandstone, which protects the 
 harbour, in the Appendix to my work, ' The Structure and Distribution 
 of Coral Eeef s,' 2nd edit. p. 265. 
 
 Abrolhos Islets, lat. 18° S. of tJie coast of Brazil. — Although 
 not strictly in place, I do not know where I can more conveniently 
 describe this httle group of small islands. The lowest bed is a 
 sandstone with ferruginous veins ; it weathers into an extraordinary 
 honey-combed mass ; above it there is a dark- coloured argillaceous 
 shale ; above this a coarser sandstone — making a total thickness of 
 about sixty feet ; and lastly, above these sedimentary beds, there is 
 a fine conformable mass of greenstone, in some parts having a 
 columnar structure. All the sttata, as well as the surface of the 
 land, dip at an angle of about 12° to N. by W. Some of the islets 
 are composed entirely of the sedimentary, others of the trappean 
 rocks, generally, however, with the sandstones cropping out on the 
 southern shores. 
 
426 Rio de J aneiro : paet n. 
 
 varieties of gneiss regularly foliated, and alternating 
 with eacli other in so-called strata. The stratification 
 and foliation of the ordinary gneisses, and the folia- 
 tion or ^ grain' of the gneiss-granite, are parallel to 
 each other, and generally strike within a point of NE. 
 and SW. dipping at a high angle (between 50° and 60°) 
 generally to SE. : so that here again we meet with the 
 strike so prevalent over the more northern parts of this 
 continent. The mountains of gneiss-granite are to a 
 remarkable degree abruptly conical, which seems caused 
 by the rock tending to exfoliate in thick, conically 
 concentric layers : these peaks resemble in shape those 
 of phonolite and other injected rocks on volcanic 
 islands ; nor is the grain or foliation (as we shall after- 
 wards see) any difficulty on the idea of the gneiss- 
 granite having been an intrusive rather than a meta- 
 morphic formation. The lines of mountains, but not 
 always each separate hill, range nearly in the same 
 direction with the foliation and so-called stratification, 
 but rather more easterly. 
 
 On a bare gently inclined surface of the porphyritic 
 gneiss in Botofogo Bay, I observed the appearance here 
 represented. 
 
 A fragment seven yards long and two in width, 
 with angular and distinctly defined edges, composed of 
 a peculiar variety of gneiss with dark layers of mica 
 and garnets, is surrounded on all sides by the ordinary 
 gneiss-granite ; both having been dislocated by a 
 granitic vein. The folia in the fragment and in the 
 surrounding rock strike in the same NNE. and SSW. 
 line; but in the fragment they are vertical, whereas 
 in the gneiss-granite they" dip at a small angle, as 
 shown by the arrows, to SSE. This fragment, con- 
 sidering its great size, its solitary position, and its 
 foliated structure parallel to that of the surrounding 
 
CHAP. XIII. 
 
 Granitic Rocks of. 
 
 427 
 
 rock, is, as far as I know, a unique case : and I will 
 not attempt any explanation of its origin. 
 
 No. 38. 
 Fragment of Gneiss embedded in another variety of the same rock. 
 
 The numerous travellers ^ in this country, have all 
 been greatly surprised at the depth to which the gneiss 
 and other granitic rocks, as well as the talcose slates of 
 the interior, have been decomposed. Near Rio, every 
 mineral except the quartz has been completely softened, 
 in some places to a depth little less than one hundred feet.^ 
 The minerals retain their positions in folia ranging in 
 the usual direction ; and fractured quartz veins may be 
 traced from the solid rock, running for some distance 
 into the softened, mottled, highly coloured, argillaceous 
 mass. It is said that these decomposed rocks abound 
 
 igpix and Martins have collected, in an Appendix to their 
 ' Travels,' the largest body of facts on this subject. See, also, some 
 remarks by M. Lund, in his communications to the Academy at 
 Copenhagen ; and others by M. Gaudichaud, in Freycinet's ' Voyage.' 
 
 2 Dr. Benza describes granitic rock (' Madras Journal of Lit.' &c. 
 Oct. 1836, p. 246), in the Neelgherries, decomposed to a depth of 
 forty feet. 
 
428 La Plata : 
 
 PART II. 
 
 with gems of various kinds, often in a fractured state, 
 owing, as some have supposed, to the collapse of geodes, 
 and that they contain gold and diamonds. At Rio, it 
 appeared to me that the gneiss had been softened before 
 the excavation (no doubt by the sea) of the existing, 
 broad, flat-bottomed valleys; for the depth of decom- 
 position did not appear at all conformable with the 
 present undulations of the surface. The porphyritic 
 gneiss, where now exposed to the air, seems to with- 
 stand decomposition remarkably well ; and I could see 
 no signs of any tendency to the production of argilla- 
 ceous masses like those here described. I was also 
 struck with the fact, that where a bare surface of this 
 rock sloped into one of the quiet bays, there were no 
 marks of erosion at the level of the water, and the 
 parts both beneath and above it preserved a uniform 
 curve. At Bahia, the gneiss rocks are similarly decom- 
 posed, with the upper parts insensibly losing their 
 foliation, and passing, without any distinct line of 
 separation, into a bright red argillaceous earth, includ- 
 ing partially rounded fragments of quartz and granite. 
 From this circumstance, and from the rocks appearing 
 to have suffered decomposition before the excavation of 
 the valleys, I suspect that here, as at Rio, the decom- 
 position took place under the sea. The subject 
 appeared to me a curious one, and would probably well 
 repay careful examination by an able mineralogist. 
 
 T]iG Northern Provinces of La Plata. — According 
 to some observations communicated to me by Mr. Fox, 
 the coast from Rio de Janeiro to the mouth of the 
 Plata seems everywhere to be granitic, with a few 
 trappean dikes. At Port Alegre, near the boundary of 
 Brazil, there are porphyries and diorites.^ At the 
 mouth of the Plata, I examined the country for twenty- 
 ' M. Isabelle, ' Voyage k Buenos Ayres,' p. 479. 
 
CHAP. XIII. Crystalline Rocks of. 429 
 
 five miles west, and for about seventy miles north of 
 Maldonado : near this town, there is some common 
 gneiss, and much, in all parts of the country, of a 
 coarse-grained mixture of quartz and reddish feldspar, 
 often, however, assuming a little dark-green imperfect 
 hornblende, and then immediately becoming foliated. 
 The abrupt hillocks thus composed, as well as the 
 highly inclined folia of the common varieties of gneiss, 
 strike NNE. or a little more easterly, and SSW. Olay- 
 slate is occasionally met with, and near the L. del 
 Potrero, there is white marble, rendered fissile from the 
 presence of hornblende, mica, and asbestus ; the cleavage 
 of these rocks and their stratification, that is the alter- 
 nating masses thus composed, strike NNE. and SSW. 
 like the foliated gneisses, and have an almost vertical 
 dip. The Sierra Larga, a low range five miles west 
 of Maldonado, consists of quartzite, often ferruginous, 
 having an arenaceous feel, and divided into excessively 
 thin, almost vertical laminse or folia by microscopically 
 minute scales, apparently of mica, and striking in the 
 usual NNE. and SSW. direction. The range itself is 
 formed of one principal line with some subordinate 
 ones ; and it extends with remarkable uniformity far 
 northward (it is said even to the confines of Brazil), in 
 the same line with the vertically ribboned quartz rock 
 of which it is composed. The S. de las Animas is the 
 highest range in the country; I estimated it at 1,000 
 feet ; it runs north and south, and is formed of feld- 
 spathic porphyry ; near its base there is a NNW. and 
 SSE. ridge of a conglomerate in a highly porphyritic 
 basis. 
 
 Northward of Maldonado, and south of Las Minas, 
 there is an E. and W. hilly band of country, some miles 
 in width, formed of siliceous clay-slate, with some quartz, 
 rock and limestone, having a tortuous irregular cleav- 
 
430 La Plata : 
 
 PAET II. 
 
 age, generally ranging east and west. E. and SE. of 
 Las Minas there is a confused district of imperfect 
 gneiss and laminated quartz, witli the hills ranging in 
 various directions, but with each separate hill generally 
 running in the same line with the folia of the rocks of 
 which it is composed : this confusion appears to have 
 been caused by the intersection of the [E. and W.] and 
 [NNE. and SSW.] strikes. Northward of Las Minas, 
 the more regular northerly ranges predominate : from 
 this place to near Polanco, we meet with the coarse- 
 grained mixture of quartz and feldspar, often with the 
 imperfect hornblende, and then becoming foliated in 
 a N. and S. line — with imperfect clay-slate, including 
 laminae of red crystallised feldspar — with white or black 
 marble, sometimes containing asbestus and crystals of 
 gypsum — with quartz-rock — with syenite — and lastly, 
 with much granite. The marble and granite alternate 
 repeatedly in apparently vertical masses : some miles 
 northward of the Polanco, a wide district is said to be 
 entirely composed of marble. It is remarkable, how 
 rare mica is in the whole range of country north and 
 westward of Maldonado. Throughout this district, the 
 cleavage of the clay-slate and marble — the foliation of 
 the gneiss and the quartz — the stratification or alter- 
 nating masses of these several rocks — and the range 
 of the hills, all coincide in direction ; and although the 
 country is only hilly, the planes of division are almost 
 everywhere very highly inclined or vertical. 
 
 Some ancient submarine volcanic rocks are worth 
 mentioning, from their rarity on this eastern side of 
 the continent. In the valley of the Tapas (fifty or 
 sixty miles N. of Maldonado) there is a tract three 
 or four miles in length, composed of various trappean 
 rocks with glassy feldspar — of apparently metamorphosed 
 grit-stones — of purplish amygdaloid s with large kernels 
 
CHAP. XIII. Crystalline Rocks of. 431 
 
 of carbonate of lime ^ — and mucli of a harshisli rock 
 with, glassy feldspar intermediate in character between 
 claystone porphyry and trachyte. This latter rock was 
 in one spot remarkable from being full of drnsy cavities, 
 lined with quartz crystals, and arranged in planes, 
 dipping at an angle of 50° to the east, and striking 
 parallel to the foliation of an adjoining hill composed 
 of the common mixture of quartz, feldspar, and im- 
 perfect hornblende : this fact perhaps indicates that 
 these volcanic rocks have been metamorphosed, and 
 their constituent parts re-arranged, at the same time 
 and according to the same laws, with the granitic and 
 metam Orphic formations of this whole region. In the 
 valley of the Marmaraya, a few miles south of the 
 Tapas, a band of trappean and amygdaloidal rock is 
 interposed between a hill of granite and an extensive 
 surrounding formation of red conglomerate, which (like 
 that at the foot of the S. Animas) has its basis porphy- 
 ritic with crystals of feldspar, and which hence has 
 certainly suffered metamorphosis. 
 
 Monte Video. — The rocks here consist of several 
 varieties of gneiss, with the feldspar often yellowish, 
 granular and imperfectly crystallised, alternating with, 
 and passing insensibly into, beds, from a few yards to 
 nearly a mile in thickness, of fine or coarse grained, 
 dark-green hornblendic slate ; this again often passing 
 into chloritic schist. These passages seem chiefly due 
 to changes in the mica, and its replacement by other 
 minerals. At Rat Island I examined a mass of chloritic 
 schist, only a few yards square, irregularly surrounded 
 on all sides by the gneiss, and intricately penetrated 
 by many curvilinear veins of quartz, which gradually 
 hlend into the gneiss : the cleavage of the chloritic 
 
 * Near the Pan de Azucar there is some greenish porphyry, in one 
 place amygdaloidal with agate. 
 
432 La Plata : 
 
 PART II. 
 
 schist and the foliation of the gneiss were exactly 
 parallel. Eastward of the city there is much fine- 
 grained dark-coloured gneiss, almost assuming the 
 character of hornblende-slate, which alternates in thin 
 laminge with laminse of quartz, the whole mass being 
 transversely intersected by numerous large veins of 
 quartz : I particularly observed that these veins were 
 absolutely continuous with the alternating laminas of 
 quartz. In this case and at Rat Island, the passage of 
 the gneiss into imperfect hornblendic or into chloritic 
 slate, seemed to be connected with the segregation of 
 the veins of quartz.^ 
 
 The Mount, a hill believed to be 450 feet in height, 
 from which the place takes its name, is much the 
 highest land in this neighbourhood : it consists of horn- 
 blendic slate, which (except on the eastern and disturbed 
 base) has an east and west nearly vertical cleavage ; 
 the longer axis of the hill also ranges in this same line. 
 Near the summit the hornblende-slate gradually be- 
 comes more and more coarsely crystallised, and less 
 plainly laminated, until it passes into a heavy, sonorous 
 greenstone, with a slaty conchoidal fracture ; the 
 laminge on the north and south sides near the summit 
 dip inwards, as if this upper part had expanded or 
 bulged outwards. This greenstone must, I conceive, be 
 considered as metamorphosed hornblende-slate. The 
 Cerrito, the next highest, but much less elevated 
 point, is almost similarly composed. In the more 
 western parts of the province, besides gneiss, there is 
 quartz-rock, syenite, and granite ; and at Oolla, I heard 
 of marble. 
 
 ^ Mr. Grreenough (p. 78, ' Critical Examination,' &c.) observes that 
 quartz in mica-slate sometimes appears in beds and sometimes in 
 veins. Von Bucb also, in his ' Travels in Norway ' (p. 236), remarks 
 on alternating laminae of quartz and hornblende-slate replacing mica- 
 schist. 
 
CHAP. XIII. Crystalline Rocks of. 433 
 
 Near M. Video, tlie space which I more accurately 
 examined was about fifteen miles in an east and west 
 line, and here I found the foliation of the gneiss and the 
 cleavage of the slates generally well developed, and ex- 
 tending parallel to the alternating strata composed of the 
 gneiss, hornblendic and chloritic schists. These planes 
 of division all range within one point of east and west, 
 frequently east by south and west by north ; their dip 
 is generally almost vertical, and scarcely anywhere 
 under 45° : this fact, considering how slightly undula- 
 tory the surface of the country is, deserves attention. 
 Westward of M. Video, towards the Uruguay, wherever 
 the gneiss is exposed, the highly inclined folia are 
 seen striking in the same direction ; I must except one 
 spot where the strike was NW. by W. The little 
 Sierra de S. Juan, formed of gneiss and laminated 
 quartz, must also be excepted, for it ranges between 
 [N. to NE.] and [S. to SW.] and seems to belong to 
 the same system with the hills in the Maldonado 
 district. Finally, we have seen that, for many miles 
 northward of Maldonado and for twenty-five miles 
 westward of it, as far as the S. de las Animas, the folia- 
 tion, cleavage, so-called stratification and lines of hills, 
 all ranges NNE. and SSW., which is nearly coincident 
 with the adjoining coast of the Atlantic. Westward of 
 the S. de las Animas, as far as even the Uruguay, the 
 foliation, cleavage, and stratification (but not lines of 
 hills, for there are no defined ones) all range about E. 
 by S. and W. by N., which is nearly coincident with 
 the direction of the northern shore of the Plata : in the 
 confused country near Las Minas, where these two great 
 systems appear to intersect each other, the cleavage, 
 foliation, and stratification run in various directions, 
 but generally coincide with the line of each separate 
 hill. 
 
 FF 
 
434 ^^ Plata. 
 
 PAET II. 
 
 Southern La Plata. — -The first ridge, south of the 
 Plata, which projects through the Pampean formation, 
 is the Sierra Tapalguen and Vulcan, situated 200 miles 
 southward of the district just described. This ridge is 
 only a few hundred feet in height, and runs from C. 
 Oorrientes in a WNW. line for at least 150 miles into 
 the interior : at Tapalguen, it is composed of unstrati- 
 fied granular quartz, remarkable from forming tabular 
 masses and small plains, surrounded by precipitous cliffs : 
 other parts of the range are said to consist of granite : 
 and marble is found at the S. Tinta. It appears from 
 M. Parchappe's ^ observations, that at Tandil there is a 
 range of quartzose gneiss, very like the rocks of the S. 
 Larga near Maldonado, running in the same NNE. and 
 SSW. direction ; so that the framework of the country 
 here is very similar to that on the northern shore of 
 the Plata. 
 
 The Sierra Guitru-gueyu is situated sixty miles 
 south of the S. Tapalguen : it consists of numerous 
 parallel, sometimes blended together ridges, about 
 twenty-three miles in width, and 500 feet in height 
 above the plain, and extending in a WW. and SE. 
 direction. Skirting round the extreme SE. termination, 
 I ascended only a few points, which were composed of 
 a fine-grained gneiss, almost composed of feldspar with 
 a little mica, and passing in the upper parts of the 
 hills into a rather compact purplish-clay state. The 
 cleavage was nearly vertical, striking in a NW. by W. 
 and SE. by E. line, nearly, though not quite, coinci- 
 dent with the direction of the parallel ridges. 
 
 The Sierra Ventana lies close south of that of Guitru- 
 gueyu ; it is remarkable from attaining a height, very 
 
 1 M. d'Orbigny's 'Voyage, Part. Geolog.' p. 46. I have given a 
 short account of the peculiar forms of the quartz hills of Tapalguen, 
 so unusual in a metamorphic formation, in my ' Journal of Re- 
 searches ' (2nd edit.), p. 116. 
 
CHAP. XIII. Patagonia. 435 
 
 unusual on this side of tlie continent, of 3,340 feet. It 
 consists up to its summit, of quartz, generally pure and 
 white, but sometimes reddish, and divided into thick 
 laminae or strata : in one part there is a little glossy 
 clay-slate with a tortuous cleavage. The thick layers 
 of quartz strike in a W. 30° N. line, dipping southerly 
 at an angle of 45° and upwards. The principal line of 
 mountains, with some quite subordinate parallel ridges, 
 range about W. 45° N. : but at their SE. termination, 
 only W. 25° N. This Sierra is said to extend between 
 twenty and thirty leagues into the interior. 
 
 Patagonia. — With the exception perhaps of the 
 hill of S. Antonio (600 feet high) in the Gulf of S. 
 Matias, which has never been visited by a geologist, 
 crystalline rocks are not met with on the coast of Pata- 
 gonia for a space of 380 miles south of the S. Yentana. 
 At this point (lat. 43° 50^), at Points Union and Tombo, 
 plutonic rocks are said to appear, and are found, at 
 rather wide intervals, beneath the Patagonian tertiary 
 formation for a space of about 300 miles southward, to 
 near Bird Island, in lat. 48° 56'. Judging from speci- 
 mens kindly collected for me by Mr. Stokes, the pre- 
 vailing rock at Ports St. Elena, Camerones, Malaspina, 
 and as far south as the Paps of Pineda, is a purplish- 
 pink or brownish claystone porphyry, sometimes la- 
 minated, sometimes slightly vesicular, with crystals of 
 opaque feldspar and with a few grains of quartz ; hence 
 these porphyries resemble those immediately to be de- 
 scribed at Port Desire, and likewise a series which I have 
 seen from P. Alegre on the southern confines of Brazil. 
 This porphyritic formation further resembles in a 
 singularly close manner the lowest stratified formation 
 of the Cordillera of Chile, which, as we shall hereafter 
 see has a vast range, and attains a great thickness. 
 At the bottom of the Gulf of St. George only tertiary 
 
 2 F P 
 
43 6 Patagonia : part n. 
 
 deposits appear to be present. At Cape Blanco, there 
 is quartz rock, very like that of the Falkland Islands, 
 and some hard, blue, siliceous clay-slate. 
 
 At Port Desire there is an extensive formation of 
 the claystone porphyry, stretching at least twenty-five 
 miles into the interior : it has been denuded and deeply 
 worn into gullies before being covered up by the ter- 
 tiary deposits, through which it here and there ]3rojects 
 in hills ; those north of the bay being 440 feet in 
 height. The strata have in several places been tilted 
 at small angles, generally either to NNW. or SSE. 
 By gradual passages and alternations, the porphyries 
 change incessantly in nature. I will describe only 
 some of the principal mineralogical changes, which are 
 highly instructive, and which I carefully examined. 
 The prevailing rock has a compact purplish base, with 
 crystals of earthy or opaque feldspar, and often with grains 
 of quartz. There are other varieties, with an almost truly 
 trachytic base, full of little angular vesicles and crystals 
 of glassy feldspar ; and there -are beds of black perfect 
 pitchstone, as well as of a concretionary imperfect 
 variety. On a casual inspection, the whole series would 
 be thought to be of the same plutonic or volcanic 
 nature with the trachytic varieties and pitchstone ; but 
 this is far from being the case, as much of the porphyry 
 is certainly of metamorphic origin. Besides the true 
 porphyries, there are many beds of earthy, quite white 
 or yellowish, friable, easily fusible matter, resembling 
 chalk, which under the microscope is seen to consist of 
 minute broken crystals, and which, as remarked in a 
 former chapter, singularly resembles the upper tufaceous 
 beds of the Patagonian tertiary formation. This earthy 
 substance often becomes coarser, and contains minute 
 rounded fragments of porphyries and rounded grains of 
 quartz, and in one case so many of the latter as to 
 
CHAP. XIII. Porphyritic Rocks of. 437 
 
 resemble a common sandstone. These beds are sometimes 
 marked with true lines of aqueous deposition, separat- 
 ing particles of different degrees of coarseness ; in other 
 cases there are parallel ferruginous lines not of true 
 deposition, as shown by the arrangement of the par- 
 ticles, though singularly resembling them. The more 
 indurated varieties often include many small and some 
 larger angular cavities, which appear due to the re- 
 moval of earthy matter : some varieties contain mica. 
 All these earthy and generally white stones insensibly 
 pass into more indurated sonorous varieties, breaking 
 with a conchoidal fracture, yet of small specific gravity ; 
 many of these latter varieties assume a pale purple tint, 
 being singularly banded and veined with different shades, 
 and often become plainly porphyritic with crystals of 
 feldspar. The formation of these crystals could be 
 most clearly traced by minute angular and often par- 
 tially hollow patches of earthy matter, first assuming a 
 fibrous structure, then passing into opaque imperfectly 
 shaped crystals, and lastly, into perfect glassy crystals. 
 When these crystals have appeared, and when the 
 basis has become compact, the rock in many places 
 could not be distinguished from a true claystone por- 
 phyry without a trace of mechanical structure. 
 
 In some parts, these earthy or tufaceous beds pass 
 into jaspery and into beautifully mottled and banded 
 porcelain rocks, which break into splinters, translucent 
 at their edges, hard enough to scratch glass, and fusible 
 into white transparent beads : grains of quartz included 
 in the porcelainous varieties can be seen melting into 
 the surrounding paste. In other parts, the earthy or 
 tufaceous beds either insensibly pass into, or alternate 
 with, breccias composed of large and small fragments 
 of various purplish porphyries, with the matrix gene- 
 rally porphyritic : these breccias, though their sub- 
 
43 8 Patagonia. part n. 
 
 aqueous origin is in many places shown both by the 
 arrangement of their smaller particles and by an oblique 
 or current lamination, also pass into porphyries, in 
 which every trace of mechanical origin and stratifica- 
 tion has been obliterated. 
 
 Some highly porphyritic though coarse-grained 
 masses, evidently of sedimentary origin, and divided 
 into thin layers, differing from each other chiefly in 
 •the number of embedded grains of quartz, interested 
 me much from the peculiar manner in which here and 
 there some of the layers terminated in abrupt points, 
 quite unlike those produced by a layer of sediment 
 naturally thinning out, and a]3parently the result of a 
 subsequent process of metamorphic aggregation. In 
 another common variety of a finer texture, the aggre- 
 gating process had gone further, for the whole mass 
 consisted of quite short, parallel, often slightly curved 
 layers or patches, of whitish or reddish finely granule- 
 crystalline feldspathic matter, generally terminating at 
 both ends in blunt points ; these layers or patches fur- 
 ther tended to pass into wedge or almond shaped little 
 masses, and these finally into true crystals of feldspar, 
 with their centres often slightly drusy. The series was 
 so perfect that I could not doubt that these large 
 crystals, which had their longer axes placed parallel to 
 each other, had primarily originated in the metamor- 
 phosis and aggregation of alternating layers of tufi"; 
 and hence their parallel position must be attributed 
 (unexpected though the conclusion may be), not to 
 laws of chemical action, but to the original planes of 
 deposition. I am tempted briefly to describe three 
 other singular allied varieties of rock; the first with- 
 out examination would have passed for a stratified 
 porphyritic breccia, but all the included angular frag- 
 ments consisted of a border of pinkish crystalline feld- 
 
CHAP. XIII. PsettdO' Dikes, 
 
 439 
 
 spathic matter, surrounding a dark translucent siliceous 
 centre, in whicli grains of quartz not quite blended 
 into the paste could be distinguished : this uniformity 
 in the nature of the fragments shows that they are not 
 of mechanical, but of concretionary origin, having re- 
 sulted perhaps from the self- breaking up and aggrega- 
 tion of layers of indurated tuff containing numerous 
 grains of quartz, — into which, indeed, the whole mass 
 in one part passed. The second variety is a reddish 
 non-porphyritic clay stone, quite full of spherical 
 cavities, about half an inch in diameter, each lined with 
 a collapsed crust formed of crystals of quartz. The 
 third variety also consists of a pale purple non-porphy- 
 ritic claystone, almost wholly formed of concretionary 
 balls,, obscurely arranged in layers, of a less compact 
 and paler coloured claystone; each ball being on one 
 side partly hollow and lined with crystals of quartz. 
 
 Pseudo-Bikes. — Some miles up the harbour, in a 
 line of cliffs formed of slightly metamorphosed tuface- 
 ous and porphyritic claystone beds, I observed three 
 vertical dikes, so closely resembling in general appear- 
 ance ordinary volcanic dikes, that I did not doubt, 
 until closely examining their composition, that they 
 had been injected from below. The first is straight, 
 with parallel sides, and about four feet wide; it con- 
 sists of whitish, indurated tufaceous matter, precisely 
 like some of the beds intersected by it. The second 
 dike is more remarkable ; it is slightly tortuous, about 
 eighteen inches thick, and can be traced for a con- 
 siderable distance along the beach ; it is of a purplish- 
 red or brown colour, and is formed chiefly of rounded 
 grains of quartz, with broken crystals of earthy feld- 
 spar, scales of black mica, and minute fragments of 
 claystone porphyry, all firmly united together in a hard 
 sparing base. The structure of this dike shows obviously 
 
440 Falkland Islands, paet n. 
 
 that it is of meclianical and sedimentary origin ; yet 
 it thinned out upwards, and did not cut through the 
 uppermost strata in the cliffs. This fact at first appears 
 to indicate that the matter could not have been washed 
 in from above ; ^ but if we reflect on the suction which 
 would result from a deep-seated fissure being formed, 
 we may admit that if the fissure were in any part open 
 to the surface, mud and water might well be drawn 
 into it along its whole course. The third dike consisted 
 of a hard, rough, white rock, almost composed of broken 
 crystals of glassy feldspar, with numerous scales of black 
 mica, cemented in a scanty base ; there was little in 
 the appearance of this rock, to preclude the idea of its 
 having been a true injected feld spathic dike. The 
 matter composing these three pseudo-dikes, especially 
 the second one, appears to have suffered, like the sur- 
 rounding strata, a certain degree of metamorphic 
 action ; and this has much aided the deceptive appear- 
 ance. At Bahia, in Brazil, we have seen that a true 
 injected hornblendic dike, not only has suffered meta- 
 morphosis, but has been dislocated and even diffused 
 in the surrounding gneiss, under the form of separate 
 crystals and of fragments. 
 
 Falkland Islands. — I have described these islands 
 in a paper published in the third volume of the ' Geo- 
 logical Journal.' The mountain-ridges consist of quartz, 
 and the lower country of clay-slate and sandstone, the 
 latter containing palaeozoic fossils. These fossils have 
 been separately described by Messrs. Morris and Sharpe : 
 some of them resemble Silurian, and others Devonian 
 forms. In the eastern part of the group the several 
 parallel ridges of quartz extend in a west and east line ; 
 
 ' UpfiUed fissures are known to occur both in volcanic and in 
 ordinary sedimentary formations. At the Galapagos Archipelago 
 (see Chapter V. of this work), there are some striking examples of 
 pseudo-dikes composed of hard tufE. 
 
CHAP. XIII. Tierra del Fuego. 441 
 
 but farther westward the line becomes WNW. and ESE., 
 and even still more northerly. The cleavage-planes of 
 the clay-slate are highly inclined, generally at an angle 
 of above 50°, and often vertical; they strike almost 
 invariably in the same direction with the quartz ranges. 
 The outline of the indented shores of the two main 
 islands, and the relative positions of the smaller islets, 
 accord with the strike both of the main axes of elevation 
 and of the cleavage of the clay-slate. 
 
 Tierra del Fitego. — My notes on the geology of 
 this country are copious, but as they are unimportant, 
 and as fossils were found only in one district, a brief 
 sketch will be here sufficient. The east coast from the 
 Straits of Magellan (where the boulder formation is 
 largely developed) to St. Polycarp's Bay is formed of 
 horizontal tertiary strata, bounded some way towards 
 the interior by a broad mountainous band of clay-slate. 
 This great clay-slate formation extends from St. Le 
 Maire westward for 140 miles, along both sides of the 
 Beagle Channel to near its bifurcation. South of this 
 channel, it forms all Navarin Island, and the eastern 
 half of Hoste Island and of Hardy Peninsula ; north of 
 the Beagle Channel it extends in a north-west line on 
 both sides of Admiralty Sound to Brunswick Peninsula 
 in the Straits of Magellan, and I have reason to believe, 
 stretches far up the eastern side of the Cordillera. The 
 western and broken side of Tierra del Fuego towards 
 the Pacific is formed of metamorphic schists, granite 
 and various trappean rocks : the line of separation be- 
 tween the crystalline and clay-slate formations can 
 generally be distinguished, as remarked by Captain 
 King,^ by the parallelism in the clay-slate districts of 
 the shores and channels, ranging in a line between 
 [W. 20° to 40° K] and [E. 20° to 40° S.]. 
 
 ^ 'Geographical Journal,' vol. i. p. 155. 
 
442 Tierra del Fuego : part h. 
 
 The clay-slate is generally fissile, sometimes siliceous 
 or ferruginous, with veins of quartz and calcareous 
 spar ; it often assumes, especially on the loftier moun- 
 tains, an altered feldspathic character, jD^ssing into 
 feldspathic porphyry : occasionally it is associated with 
 breccia and grauwacke. At Good Success Bay, there 
 is a little intercalated black crystalline limestone. At 
 Port Famine much of the clay-slate is calcareous, and 
 passes either into a mudstone or into grauwacke, in- 
 cluding odd-shaped concretions of dark argillaceous 
 limestone. Here alone, on the shore a few miles north 
 of Port Famine, and on the summit of Mount Tarn 
 (2,600 feet high), I found organic remains ; they con- 
 sist of: — 
 
 1. Ancyloceras simplex, d'Orbig. 'Pal. Franc' (PI. V. f. 2) Mount Tarn. 
 
 2. Fusus (in imperfect state) do. 
 
 3. Natica do. do. 
 
 4. Pentacrimus do. do. 
 
 5. Lucina excentrica, G. B. Sowerby (PL V. fig. 21), Port Famine. 
 
 6. Venus (in imperfect state) do, 
 
 7. Turbinolia? do. do. 
 
 8. Hamites elatior, G. B. Sowerby, do. 
 
 M. d'Orbigny states ^ that MM. Hombron and 
 Grange found in this neighbourhood an Ancyloceras, 
 perhaps A. simjplex^ an Ammonite, a Plicatula and 
 Modiola. M. d'Orbigny believes from the general 
 character of these fossils, and from the Ancyloceras 
 being identical (as far as its imperfect condition allows 
 of comparison) with the A. simiolex of Europe, that 
 the formation belongs to an early stage of the Cretaceous 
 system. Professor E. Forbes, judging only from my 
 specimens, concurs in the probability of this conclusion. 
 The Hamites elatior of the above list, of which a de- 
 scription is given by Mr. Sowerby in the Appendix, and 
 which is remarkable from its large size, has not been 
 
 » ' Voyage, Part. Geolog.' p. 242. 
 
CHAP. XIII. Crystalline Rocks of. 443 
 
 seen either by M. d'Orbigny or Professor E. Forbes, as, 
 since my return to England, tlie specimens have been 
 lost. The great clay-slate formation of Tierra del Fiiego 
 being cretaceous, is certainly a very interesting fact, — 
 whether we consider the appearance of the country, 
 which, without the evidence afforded by the fossils, 
 would form the analogy of most known districts, pro- 
 bably have been considered as belonging to the Palaso- 
 zoic series, — or whether we view it as showing that the 
 age of this terminal portion of the great axis of South 
 America, is the same (as will hereafter be seen) with 
 the Cordillera of Chile and Peru. 
 
 The clay-slate in many parts of Tierra del Fuego, 
 is broken by dikes ^ and by great masses of greenstone, 
 often highly hornblendic : almost all the small islets 
 within the clay-slate districts are thus composed. The 
 slate near the dikes generally becomes paler- coloured, 
 harder, less fissile, of a feldspathic nature, and passes 
 into a porphyry or greenstone : in one case, however, 
 it became more fissile, of a red colour, and contained 
 minute scales of mica, which were absent in the un- 
 altered rock. On the east side of Ponsonby Sound, 
 some dikes com]30sed of a pale sonorous feldspathic 
 rock, porphyritic with a little feldspar, were remarkable 
 from their number, — there being within the space of a 
 mile at least one hundred, — from their nearly equalling 
 in bulk the intermediate slate, — and more especially 
 from the excessive fineness (like the finest inlaid car- 
 pentry) and perfect parallelism of their junctions with 
 the almost vertical laminaB of clay-slate. I was unable 
 to persuade myself that these great parallel masses had 
 been injected, until I found one dike which abruptly 
 
 ^ In a greenstone-dike in the Magdalen Channel, the feldspar 
 cleaved with the angle of albite. This dike was crossed, as well as 
 the surrounding slate, by a large vein of quartz, a circumstance of 
 unusual occurrence. 
 
444 Tie7'ra del Fuego. part n. 
 
 thinned out to half its thickness, and had one of its 
 walls jagged, with fragments of the slate embedded 
 in it. 
 
 In southern T. del Fuego, the clay- slate towards 
 its SW. boundary, becomes much altered and feld- 
 spathic. Thus on Wollaston Island slate and grauwacke 
 can be distinctly traced passing into feldspathic rocks 
 and greenstones, including iron pyrites and epidote, 
 but still retaining traces of cleavage with the usual 
 strike and dip. One such metamorphosed mass was 
 traversed by large vein-like masses of a beautiful 
 mixture (as ascertained by Professor Miller) of green 
 epidote, garnets, and white calcareous spar. On the 
 northern point of this same island, there were various 
 ancient submarine volcanic rocks, consisting of amyg- 
 daloids with dark bole and agate, — of basalt with 
 decomposed olivine, — of compact lava with glassy 
 feldspar, — and of a coarse conglomerate of red scorise, 
 parts being amygdaloidal with carbonate of lime. The 
 southern part of Wollaston Island and the whole of 
 Hermite and Horn Islands, seem formed of cones of 
 greenstone : the outlying islets of II Defenso and D. 
 Raminez are said ^ to consist of porphyritic lava. In 
 crossing Hardy Peninsula, the slate still retaining 
 traces of its usual cleavage, passes into columnar feld- 
 spathic rocks, which are succeeded by an irregular tract 
 of trappean and basaltic rocks, containing glassy feld- 
 spar and much iron pyrites : there is, also, some harsh 
 red claystone porphyry, and an almost true trachyte, 
 with needles of hornblend, and in one spot a curious 
 slaty rock divided into quadrangular columns, having 
 a base almost like trachyte, with drusy cavities lined 
 by crystals, too imperfect, according to Professor Miller, 
 
 ^ Delsermined by Professor Jameson. Weddell's ' Voyage,' p. 169. 
 
CHAP. XIII. Cleavage of Clay -Slate. 445 
 
 to be measured, but resembling Zeagonite.^ In the 
 midst of these singular rocks, no doubt of ancient sub- 
 marine volcanic origin, a high hill of feldspathic clay- 
 slate projected, retaining its usual cleavage. Near this 
 point, there was a small hillock, having the aspect of 
 granite, but formed of white albite, brilliant crystals of 
 hornblende (both ascertained by the reflecting gonio- 
 meter) and mica ; but with no quartz. No recent 
 volcanic district has been observed in any part of Tierra 
 del Fuego. 
 
 Five miles west of the bifurcation of the Beagle 
 Channel, the slate-formation, instead of becoming, as 
 in the more southern parts of Tierra del Fuego, feld- 
 spathic, and associated with trappean or old volcanic 
 rocks, passes by alternations into a great underlying 
 mass of fine gneiss and glossy clay-slate, which at no 
 great distance is succeeded by a grand formation of 
 mica-slate containing garnets. The folia of these 
 metamorphic schists strike parallel to the cleavage- 
 planes of the clay-slate, which have a very uniform 
 direction over the whole of this part of the country : 
 the folia, however, are undulatory and tortuous, whilst 
 the cleavage-laminge of the slate are straight. These 
 schists compose the chief mountain-chain of southern 
 T. del Fuego, ranging along the north side of the north- 
 ern arm of the Beagle Channel, in a short WNW. 
 and ESE. line, with two points (Mounts Sarmiento and 
 Darwin) rising to heights of 6,800 and 6,900 feet. 
 On the south-western side of this northern arm of the 
 Beagle Channel, the clay-slate is seen with its strata 
 dipping from the great chain, so that the metamorphic 
 schists here form a ridge bordered on each side by clay- 
 slate. Farther north, however, to the west of this 
 
 ^ See Mr. Brooke's Paper in the 'London Phil, Mag.' vol. x. 
 This mineral occurs in an ancient volcanic rock near Rome. 
 
446 Tierra del Ftiego. paet n, 
 
 great range, there is no clay-slate, but only gneiss, mica, 
 and hornblendic slates, resting on great barren liills of 
 true granite, and forming a tract about sixty miles in 
 widtli. Again, westward of tbese rocks, the outermost 
 islands are of trappean formation, which, from infor- 
 mation obtained during the voyages of the Adventure 
 and Beagle,^ seem, together with granite, chiefly to 
 prevail along the western coast as far north as the en- 
 trance of the St. of Magellan : a little more inland, on 
 the eastern side of Clarence Island and S. Desolation, 
 granite, greenstone, mica-slate, and gneiss appear to 
 predominate. I am tempted to believe, that where the 
 clay-slate has been metamorphosed at great depths 
 beneath the surface, gneiss, mica-slate, and other allied 
 rocks have been formed, but where the action has taken 
 place nearer the surface, feldspathic porphyries, green- 
 stones, etc., have resulted, often accompanied by sub- 
 marine volcanic eruptions. 
 
 Only one other rock, met with in both arms of the 
 Beagle Channel, deserves any notice, namely a granulo- 
 crystalline mixture of white albite, black hornblende 
 (ascertained by measurement of the crystals, and con- 
 firmed by Professor Miller), and more or less of brown 
 mica, but without any quartz. This rock occurs in 
 large masses, closely resembling in external form 
 granite or syenite : in the southern arm of the Channel, 
 one such mass underlies the mica- slate, on which clay- 
 slate was superimposed : this peculiar plutonic rock 
 which, as we have seen, occurs also in Hardy Peninsula, 
 is interesting, from its perfect similarity with that 
 (hereafter often to be referred to under the name of 
 
 1 See the Paper by Gapt. King, in the ' Geograph. Journal ; ' also 
 a Letter to Dr. Fitton in ' Geolog. Proc' vol. i. p. 29 ; also some ob- 
 servations by Capt. FitzRoy, 'Voyages,' vol. i. p. 375. I am indebted 
 also to Mr. Lyell for a series of specimens collected by Lieut. 
 Graves, 
 
CHAP. XIII. Cleavage of Clay -Slate. 447 
 
 andesite) forming tlie great injected axes of the Cordil- 
 lera of Chile. 
 
 The stratification of the clay-slate is generally very 
 obscure, whereas the cleavage is remarkably well defined : 
 to begin with the extreme eastern parts of T. del Fuego ; 
 the cleavage -planes near the St. of Le Maire strike 
 either W. and E. or WSW. and ENE., and are highly 
 inclined ; the form of the land, including Staten Island, 
 indicates that the axes of elevation have run in this 
 same line, though I was unable to distinguish the planes 
 of stratification. Proceeding westward, I accurately 
 examined the cleavage of the clay-slate on the northern, 
 eastern, and western sides (thirty-five miles apart) of 
 Navarin Island, and everywhere found the laminas 
 ranging with extreme regularity, WNW. and ESE., 
 seldom varying more than one point of the compass 
 from this direction.^ Both on the east and west coasts, 
 I crossed at right-angles the cleavage-planes for a space 
 of about eight miles, and found them dipping at an 
 angle of between 45° and 90°, generally to SSW., 
 sometimes to NNE., and often quite vertically. The 
 SSW. dip was occasionally succeeded abruptly by a 
 NNE. dip, and this by a vertical cleavage, or again by 
 the SSW. dip ; as in a lofty clifi" on the eastern end of 
 the island the laminse of slate were seen to be folded 
 into very large steep curves, ranging in the usual WNW. 
 line, I suspect that the varying and opposite dips may 
 possibly be accounted for by the cleavage-laminas, 
 though to the eye appearing straight, being parts 
 of large abrupt curves, with their summits cut ofi" and 
 worn down. 
 
 In several places I was particularly struck with the 
 
 ^ The clay-slate in this island was in many places crossed by 
 parallel smooth joints. Out of five cases, the angle of intersection 
 between the strike of these joints and that of the cleavage-laminse 
 was in two cases 45° and in two others 79°. 
 
44^ Tierra del Fttego. paet ii 
 
 fact, that the fine laminae of the clay-slate, where cut- 
 ting straight through the bands of stratification, and 
 therefore indisputably true cleavage-planes, differed 
 slightly in their greyish and greenish tints of colour, in 
 compactness, and in some of the laminse having a rather 
 more jaspery appearance than others. I have not seen 
 this fact recorded, and it appears to me important, for 
 it shows that the same cause which has produced the 
 highly fissile structure, has altered in a slight degree 
 the mineralogical character of the rock in the same 
 planes. The bands of stratification, just alluded to, 
 can be distinguished in many places, especially in 
 Navarin Island, but only on the weathered surfaces of 
 the slate ; they consist of slightly undulatory zones of 
 different shades of colour and of thicknesses, and re- 
 semble the marks (more closely than anything else 
 to which I can compare them) left on the inside of a 
 vessel by the draining away of some dirty slightly 
 agitated liquor : no difference in composition, corre- 
 sponding with these zones, could be seen in freshly 
 fractured surfaces. In the more level parts of 
 Navarin Island, these bands of stratification were 
 nearly horizontal ; but on the flanks of the mountains 
 they were inclined from them, but in no instance that 
 I saw at a very high angle. There can, I think, be no 
 doubt that these zones, which appear only on the 
 weathered surfaces, are the last vestiges of the ori- 
 ginal planes of stratification, now almost obliterated 
 by the highly fissile and altered structure which the 
 mass has assumed. 
 
 The clay-slate cleaves in the same WNW. and ESE. 
 direction, as on Navarin Island, on both sides of the 
 Beagle Channel, on the eastern side of Hoste Island, on 
 the NE. side of Hardy Peninsula, and on the northern 
 point of WoUaston Island; although in these two 
 
CHAP. xTTi. Cleavage of Clay-Slate. 449 
 
 latter localities the cleavage has been much obscured 
 by the metamorphosed and feldspathic condition of the 
 slate. "Within the area of these several islands, in- 
 cluding Kavarin Island, the direction of the stratifica- 
 tion and of the mountain-chains is very obscure ; though 
 the mountains in several places appeared to range in 
 the same WNW. line with the cleavage : the outline 
 of the coast, however, does not correspond with this 
 line. Near the bifurcation of the Beagle Channel, 
 where the underlying metamorphic schists are first seen, 
 they are foliated (with some irregularities) in this same 
 WNW. line, and parallel, as before stated, to the main 
 mountain-axis of this part of the country. Westward 
 of this main range the metamorphic schists are foliated, 
 though less plainly, in the same direction, which is 
 likewise common to the zone of old erupted trappean 
 rocks forming the outermost islets. Hence the area, 
 over which the cleavage of the slate and the foliation of 
 the metamorphic schists extends with an average WNW. 
 and ESE. strike, is about forty miles in a north and 
 south line, and ninety miles in an east and west line. 
 
 Further northward, near Port Famine, the stratifi- 
 cation of the clay-slate and of the associated rocks is 
 well defined, and there alone the cleavage and strata- 
 planes are parallel. A little north of this port there is 
 an anticlinal axis ranging NW. (or a little more westerly) 
 and SE. : south of the port, as far as Admiralty Sound 
 and Gabriel Channel, the outline of the land clearly 
 indicates the existence of several lines of elevation in 
 this same NW. direction, which, I may add, is so uni- 
 form in the western half of the St. of Magellan, that, 
 as Captain King ^ has remarked, ' a parallel ruler placed 
 on the map upon the projecting points of the south 
 shore, and extended across the strait, will also touch 
 ^ ' Geograph. Journal,' vol. i. p. 170.,' 
 
 G G 
 
450 Clionos Archipelago. part n. 
 
 the headlands on the opposite coast.' It would appear, 
 from Captain King's observations, that over all this 
 area the cleavage extends in the same line. Deep-water 
 channels, however, in all parts of Tierra del Fuego 
 have burst through the trammels both of stratification 
 and cleavage ; most of them may have been formed during 
 the elevation of the land by long-continued erosion, 
 but others, for instance, the Beagle Channel, which 
 stretches like a narrow canal for 120 miles obliquely 
 through the mountains, can hardly have thus originated. 
 
 Finally, we have seen that in the extreme eastern 
 point of Tierra del Fuego, the cleavage and coast-lines 
 extend W. and E. and even WSW. and ENE. : over a 
 large area westward, the cleavage, the main range of 
 mountains, and some subordinate ranges, but not the 
 outlines of the coast, strike WNW. and ESE. ; in the 
 central and western parts of the Strait of Magellan, the 
 stratification, the mountain-ranges, the outlines of the 
 coast, and the cleavage all strike nearly NW. and SE. 
 North of the strait, the outline of the coast, and the 
 mountains on the mainland, run nearly north and 
 south. Hence we see, at this southern point of the 
 continent, how gradually the Cordillera bend, from 
 their north and south course of so many thousand miles 
 in length, into an E. and even ENE. direction. 
 
 West Coast^ from the Southern Ghonos Islands to 
 Northern Chile. — The first place at which we landed 
 north of the St. of Magellan was near Cape Tres Montes, 
 in lat. 47° S. Between this point and the northern 
 Chonos Islands, a distance of 200 miles, the ' Beagle ' 
 visited several points, and specimens were collected for 
 me from the intermediate spaces by Lieut. Stokes. 
 The predominant rock is mica-slate, with thick folia 
 of quartz, very frequently alternating with and passing 
 into a chloritic, or into a black, glossy, often striated, 
 
«HAP. XIII. Chonos Archipelago, 451 
 
 sliglitly antliracitic schist, wliicli soils paper, and be- 
 comes white under a great heat, and then fuses. Thin 
 layers of feldspar, swelling at intervals into well crystal- 
 lised kernels, are sometimes included in these black 
 schists ; and I observed one mass of the ordinary black 
 variety insensibly lose its fissile structure, and pass into a 
 singular mixture of chlorite, epidote, feldspar, and mica. 
 Great veins of quartz are numerous in the mica-schist ; 
 wherever these occur the folia are much convoluted. 
 In the southern part of the Peninsula of Tres Montes, 
 a compact altered feldspathic rock with crystals of 
 feldspar and grains of quartz is the commonest variety ; 
 this rock ^ exhibits occasionally traces of an original 
 brecciated structure, and often presents (like the altered 
 state of Tierra del Fuego) traces of cleavage-planes, 
 which strike in the same direction with the folia of 
 mica-schist farther northward. At Inchemo Island, a 
 similar rock gradually becomes granulo-crystalline and 
 acquires scales of mica ; and this variety at S. Estevan 
 becomes highly laminated, and though still exhibiting 
 some rounded grains of quartz, passes into the black, 
 glossy, slightly anthracitic schist which, as we have 
 seen, repeatedly alternates with and passes into the 
 micaceous and chloritic schists. Hence all the rocks 
 on this line of coast belong to one series, and insensibly 
 vary from an altered feldspathic clay-slate into largely 
 foliated, true mica- schist. 
 
 The cleavage of the homogeneous schists, the folia- 
 tion of those composed of more or less distinct minerals 
 in layers, and the planes of alternation of the different 
 varieties or so-called stratification are all parallel, and 
 preserve over this 200 miles of coast a remarkable 
 
 ^ The peculiar, abruptly conical form of the hills in this neigh- 
 bourhood, would have led any one at first to have supposed that they 
 had been formed of injected or intrusive rocks. 
 
 G G 2 
 
452 
 
 Chonos Archipelago. 
 
 PAET II.. 
 
 degree of uniformity in direction. At the northern 
 end of the group, at Low's Harbour, the well-defined 
 folia of mica-schist everywhere ranged within eight 
 degrees (or less than one point of the compass) of 
 N. 19° W. and S. 19° B. ; and even the point of dip 
 varied very little, being always directed to the west and 
 generally at an angle of forty degrees : I should mention 
 that I had here good opportunities of observation, for I 
 followed the naked rock on the beach, transversely to 
 the strike, for a distance of four miles and a half, and 
 all the way attended to the dip. Along the outer islands 
 for 100 miles south of Low's Harbour, Lieutenant Stokes, 
 during his boat-survey, kindly observed for me the strike^ 
 of the foliation, and he assures me that it was invariably 
 northerly, and the dip with one single exception to the 
 west. Farther south, at Yallenar Bay, the strike was 
 almost universally N. 25° W., and the dip, generally at 
 an angle of about 40° to W. 25° S., but in some places 
 almost vertical. Still farther south, in the neighbour- 
 hood of the harbours of Anna Pink, S. Estevan, and S . 
 Andres, and (judging from a distance) along the southern 
 part of Tres Montes, the foliation and cleavage extended 
 in a line between [N. 11° to 22° W.] and [S. 11° to 
 22° E.] ; and the planes dipped generally westerly, but 
 often easterly, at angles varying from a gentle inclina- 
 tion to vertical. At A. Pink's Harbour, where the 
 schists generally dipped easterly, wherever the angle 
 became high, the strike changed from N. 11° W. to 
 even as much as N. 45° W. : in an analogous manner 
 at Yallenar Bay, where the dip was westerly (viz. on an 
 average directed to W. 25° S.), as soon as the angle 
 became very high, the planes struck in a line more 
 than 25° west of north. The average result from all 
 the observations on this 200 miles of coast, is a strike 
 of N. 19° W. and S. 19° E. : considering that in each 
 
■CHAP. XIII. Foliation of Mica-Schist. 453 
 
 specified place my examination extended over an area 
 of several miles, and that Lieut. Stokes' observations 
 apply to a length of 100 miles, I think this remarkable 
 uniformity is pretty well established. The prevalence, 
 throughout the northern half of this line of coast, of a 
 dip in one direction, that is, to the west, instead of being 
 sometimes west and sometimes east, is, judging from 
 what I have elsewhere seen, an unusual circumstance. 
 In Brazil, La Plata, the Falkland Islands, and Tierra 
 del Fuego, there is generally an obvious relation be- 
 tween the axes of elevation, the outline of the coast, 
 and the strike of the cleavage or foliation : in the 
 Chonos Archipelago, however, neither the minor details 
 of the coast-line nor the chain of the Cordillera, nor 
 the subordinate transverse mountain-axes, accord with 
 the strike of the foliation and cleavage : the seaward 
 face of the numerous islands composing this archi- 
 pelago, and apparently the line of the Cordillera, range 
 N. 11° E., whereas, as we have just seen, the average 
 strike of the foliation is IST. 19° W. 
 
 There is one interesting exception to the uniformity 
 in the strike of the foliation. At the northern point 
 of Tres Montes (lat. 45° 52') a bold chain of granite, 
 between 2,000 and 3,000 feet in height, runs from the 
 coast far into the interior,^ in a ESE. line, or more 
 strictly E. 28° S. and W. 28° N. In a bay, at the north- 
 ern foot of this range, there are a few islets of mica- 
 slate, with the folia in some parts, horizontal, but mostly 
 inclined at an average angle of 20° to the north. On 
 the northern steep flank of the range, there are a few 
 patches (some quite isolated, and not larger than half-a- 
 
 * In the distance, other mountains could be seen apparently 
 ranging NNE. and SSW. at right angles to this one. I may add, 
 that not far from Vallenar Bay there is a fine range, apparently of 
 granite, which has burst through the mica-slate in a NE. by E. and 
 SW. by S. line. 
 
454 Chonos Ai^chipeiago. paet n. 
 
 crown !) of the mica-schist, foliated with the same 
 northerly dip. On the broad summit, as far as the 
 southern crest, there is much mica- slate, in some places 
 even 400 feet in thickness, with the folia all dipping 
 north, at angles varying from 5° to 20°, but sometimes 
 mounting up to 30°. The southern flank consists of 
 bare granite. The mica-slate is penetrated by small 
 veins ^ of granite, branching from the main body. 
 Leaving out of view the prevalent strike of the folia in 
 other parts of this archipelago, it might have been 
 expected that here they would have dipped N. 28° E., 
 that is, directly from the ridge, and, considering its 
 abruptness, at a high inclination ; but the real dip, as 
 we have just seen, both at the foot and on the northern 
 flank, and over the entire summit, is at a small angle, 
 and directed nearly due north. From these considera- 
 tions it occurred to me, that perhaps we here had the 
 novel and curious case of already inclined laminae 
 obliquely tilted at a subsequent period by the granitic 
 axis. Mr. Hopkins, so well known from his mathe- 
 matical investigations, has most kindly calculated the 
 problem : the proposition sent was, — take a district 
 composed of lamina, dipping at an angle of 40° to 
 W. 19° S., and let an axis of elevation traverse it in an 
 E. 28° S. line, what will the position of the laminae be 
 on the northern flank after a tilt, we will first suppose, 
 of 45° ? Mr. Hopkins informs me, that the angle of 
 the dip will be 28° 31', and its direction to north 
 30° 33' west.^ By varying the supposed angle of the 
 
 ^ The granite within these veins, as well as generally at the 
 junction with the mica-slate, is more quartzose than elsewhere. The 
 granite, I may add, is traversed by dikes running for a very great 
 length in the line of the mountains ; they are composed of a some- 
 what laminated eurite, containing crystals of feldspar, hornblende, 
 and octagons of quartz. 
 
 - On the south side of the axis (where, however, I did not see any 
 mica-slate) the dip of the folia would be at an angle of 77° 55',. 
 
CHAP. XIII. Foliation of Mica-Schist. 455 
 
 tilt, our previously inclined folia can be thrown into 
 any angle between 26°, wliicH is the least possible angle, 
 and 90° ; but if a small inclination be thus given to 
 them, their point of dip will depart far from the north, 
 and therefore not accord with the actual position of the 
 folia of mica-schist on our granitic range. Hence it ap- 
 pears very difficult, without varying considerably the ele- 
 ments of the problem, fchus to explain the anomalous strike 
 and dip of the foliated mica-schist, especially in those 
 jDarts, namely, at the base of the range, where the folia 
 are almost horizontal. Mr. Hopkins, however, adds, 
 that great irregularities and lateral thrusts might be 
 expected in every great line of elevation, and that these 
 would account for considerable deviations from the 
 calculated results : considering that the granitic axis, 
 as shown by the veins, has indisputably been injected 
 after the perfect formation of the mica-slate, and con- 
 sidering the uniformity of the strike of the folia through- 
 out the rest of the archipelago, I cannot but still think 
 that their anomalous position at this one point is 
 someway directly and mechanically related to the in- 
 trusion of this WNW. and ESE. mountain-chain of 
 granite. 
 
 Dikes are frequent in the metamorphic schists of the 
 Chonos Islands, and seem feebly to represent that great 
 band of trappean and ancient volcanic rocks on the 
 south-western coast of T. del Fuego. At S. Andres I 
 observed in the space of half a mile, seven broad, parallel 
 dikes, composed of three varieties of trap, running in a 
 NW. aud SE. line, parallel to the neighbouring moun- 
 tain-ranges of altered clay-slate ; but they must be of 
 long subsequent origin to these mountains; for they 
 
 directed to the west 35° 33' south. Hence the two points of dip on 
 the opposite sides of the range, instead of being as in ordinary cases 
 directly opposed to each other at an ano-le of 180°, would here be 
 only 86° 50' apart. 
 
45^ Chiloe and Concepcioii. taut ir. 
 
 intersected the volcanic formation described in tlie last 
 cliapter. North of Tres Montes, I noticed three dikes 
 differing from each other in composition, one of them 
 having an euritic base including large octagons of 
 quartz ; these dikes, as well as several of porphyritic 
 greenstone at Vallenar Bay, extended NE. and SW., 
 nearly at right angles to the foliation of the schists, 
 but in the line of their joints. At Low's Harbour, 
 however, a set of great parallel dikes, one ninety yards 
 and another sixty yards in width, have been guided by 
 the foliation of the mica-schist, and hence are inclined 
 westward at an angle of 45° : these dikes are formed of 
 various porphyritic traps, some of which are remarkable 
 from containing numerous rounded grains of quartz. 
 A porphyritic trap of this latter kind, passed in one of 
 the dikes into a most curious hornstone, perfectly white, 
 with a waxy fracture and pellucid edges, fusible, and 
 containing many grains of quartz and specks of iron 
 pyrites. In the ninety yard dike several large, appa- 
 rently now quite isolated fragments of mica-slate were 
 embedded ; but as their foliation was exactly parallel 
 to that of the surrounding solid rock, no doubt these 
 now separate fragments originally formed wedge-shaped 
 depending portions of a continuous vault or crust, 
 once extending over the dike, but since worn down and 
 denuded. 
 
 Gliiloe Valdivia, Goncefcion. — In Chiloe, a great 
 formation of mica-schist strikingly resembles that of 
 the Ohonos Islands. For a space of eleven miles on 
 the SE. coast, the folia were very distinct, though 
 slightly convoluted, and ranged within a point of NNW. 
 and SSE., dipping either ENE. or more commonly 
 WSW., at an average angle of 22° (in one spot, however, 
 at 60°), and therefore decidedly at a lesser inclination 
 than amongst the Chonos Islands. On the west and 
 north-western shores, the foliation was often obscure, 
 
CHAP. XIII. Cliiloe and Concepcion. 457 
 
 thougli, where best defined, it ranged within a point of 
 N. by W. and S. by E., dipping either easterly or 
 westerly, at varying and generally very small angles. 
 Hence, from the southern part of Tres Montes to the 
 northern end of Chiloe, a distance of 300 miles, we 
 have closely allied rocks with their folia striking on an 
 average in the same direction, namely, between N. 11° 
 and 22° W. Again, at Valdivia, we meet with the 
 same mica-schist, exhibiting nearly the same minera- 
 logical passages as in the Chonos Archipelago, often, 
 however, becoming more ferruginous, and containing 
 so much feldspar as to pass into gneiss. The folia were 
 generally well defined ; but nowhere else in South 
 America did I see them varying so much in direction : 
 this seemed chiefly caused by their forming parts, as I 
 could sometimes distinctly trace, of large flat curves : 
 nevertheless, both near the settlement and towards the 
 interior, a NW. and SE. strike seemed more frequent 
 than any other direction; the angle of the dip was 
 generally small. At Concepcion, a highly glossy clay- 
 slate had its cleavage often slightly curvilinear, and 
 inclined, seldom at a high angle, towards various points 
 of the compass ; ^ but here, as at Valdivia, a NW. and 
 
 * I observed in some parts that the tops of the laminje of the 
 clay-slate {h of the diagram) under the superficial detritus and soil 
 {a) were bent, sometimes without be- -j^ on 
 
 ing broken, as represented in the 
 accompanying diagram, which is 
 copied from one given by Sir. H. De 
 la Beche (p. 42, ' Geological Manual') 
 •of an exactly similar phenomenon in 
 Devonshire. Mr. E. A. C. Austen, also, 
 in his excellent paper on S.E. Devon 
 
 (' Geolog. Transact.' vol. vi. p. 4.87), has described this phenomenon ; 
 he attributes it to the action of frosts, but at the same time doubts 
 whether the frosts of the present day penetrate to a sufficient depth. 
 As it is known that earthquakes particularly affect the surface of the 
 ground, it occurred to me that this appearance might perhaps be due, 
 •at least at Concepcion, to their frequent occurrence ; the superficial 
 layers of detritus being either jerked in one direction, or, where the 
 
458 
 
 Chiloe and Concepcion. 
 
 PAET II „ 
 
 SE. strike seemed to be the most frequent one. In 
 certain spots large quartz veins were numerous, and 
 near tliem the cleavage, as was the case with the folia- 
 tion of the schists in the Ohonos Archipelago, became 
 extremely tortuous. 
 
 At the northern end of Quiriquina Island, in the 
 Bay of Concepcion, at least eight rudely parallel dikes, 
 which have been guided to a certain extent by the 
 cleavage of the slate, occur within the space of a quarter 
 of a mile. They vary much in composition, resembling 
 in many respects the dikes at Low's Harbour : the 
 greater number consist of feldspathic j)orphyries, some- 
 times containing grains of quartz : one, however, was 
 black and brilliant, like an augitic rock, but really 
 formed of feldspar ; others of a feldspathic nature were 
 perfectly white, with either an earthly or crystalline 
 fracture, and including grains and regular octagons of 
 quartz ; these white varieties passed into ordinary green- 
 stones. Although, both here and at Low's Harbour, 
 the nature of the rock varied considerably in the same 
 dike, yet I cannot but think, that at these two places 
 and in other parts of the Chonos group, where the dikes, 
 though close to each other and running parallel, are of 
 different composition, that they must have been formed 
 at different periods. In the case of Quiriquina this is a 
 rather interesting conclusion, for these eight parallel 
 dikes cut through the metamorphic schists in a NW. 
 and SE. line, and since their injection the overlying 
 cretaceous or tertiary strata have been tilted (whilst 
 still under the sea) from a NW. by N. and SE. by 
 
 surface was inclined, pushed a little downwards during- each strong- 
 vibration. In North Wales I have seen a somewhat analogous but 
 less regular appearance, though on a greater scale (' London Phil. 
 Mag.' vol. xxi. p. 1S4), and produced by a quite different cause, 
 namely, by the stranding of great icebergs ; this latter appearance 
 has also been observed in North America. 
 
CHAP. XIII. Ceittral and Northern Chile. 459 
 
 S. line; and again, during the great earthquake of 
 February 1835, the ground in this neighbourhood was 
 fissured in NW. and SB. lines ; and from the manner in 
 which buildings were thrown down, it was evident that 
 the surface undulated in this same direction.^ 
 
 Central and Northern Chile. — Northward of Con- 
 cepcion, as far as Copiapo, the shores of the Pacific 
 consist, with the exception of some small tertiary basins, 
 of gneiss, mica-schist, altered clay-slate, granite, green- 
 stone and syenite : hence the coast from Tres Montes 
 to Copiapo, a distance of 1,200 miles, and I have reason 
 to believe for a much greater space, is almost similarly 
 constituted. 
 
 Near Valparaiso the prevailing rock is gneiss,, 
 generally including much hornblende : concretionary 
 balls formed of feldspar, hornblende and mica, from 
 two to three feet in diameter, are in very many places 
 conformably enfolded by the foliated gneiss : veins 
 of quartz and feldspar, including black schorl and well- 
 crystallised epidote, are numerous. Epidote likewise 
 occurs in the gneiss in thin layers, parallel to the folia- 
 tion of the mass. One large vein of a coarse granitic 
 character was remarkable from in one part quite 
 changing its character, and insensibly passing into a 
 blackish porphyry, including acicular crystals of glassy 
 feldspar and of hornblende : I have never seen any other 
 such case.^ 
 
 I shall in the few following remarks on the rocks of 
 Chile allude exclusively to their foliation and cleavage. 
 In the gneiss round Valparaiso the strike of the foliation 
 is very variable, but I think about N. by W. and S. by 
 
 * 'Greolog. Trans.' vol. vi. pp. 602 and 617. 'Journal of Ee- 
 searches ' (2nd edit.), p, 307. 
 
 - Humboldt (' Personal Narrative,' vol. iv. p. 60) has described 
 with much surprise, concretionary balls, with concentric divisions,, 
 composed of partially vitreous feldspar, hornblende, and garnets, 
 included within great veins of gneiss, which cut across the mica- 
 slate near Venezuela. 
 
460 Cleavage and Foliation. part n. 
 
 E. is the commonest direction ; this likewise holds good 
 with the cleavage of the altered feldspathic clay-slates, 
 occasionally met with on the coast for ninety miles north 
 of Valparaiso. Some feldspathic slate, alternating with 
 strata of clay-stone porphyry in the Bell of Quillota 
 and at Jajuel, and therefore, perhaps, belonging to a 
 later period than the metamorphic schists on the coast, 
 cleaved in this same direction. In the eastern Cordillera, 
 in the Portillo Pass, there is a grand mass of mica- 
 slate, foliated in a north and south line, and with a 
 high westerly dip : in the TJspallata range, clay-slate 
 and grauwacke have a highly inclined, nearly north and 
 south cleavage, though in some parts the strike is irreg- 
 ular : in the main or Cumbre range, the direction of the 
 cleavage in the feldspathic clay-slate is NW. and SE. 
 
 Between Coquimbo and Guasco there are two con- 
 siderable formations of mica- slate, in one of which the 
 rock passed sometimes into common clay-slate and some- 
 times into a glossy black variety, very like that in the 
 Chonos Archipelago. The folia and cleavage of these 
 rocks ranged between [N. and NW. by N.] and [S. and 
 SW. by S.] Near the Port of Guasco several varieties 
 of altered clay-slate have a quite irregular cleavage. 
 Between Guasco and Copiapo, there are some siliceous 
 and talcaceous slates cleaving in a north and south line, 
 with an easterly dip of between 60° and 70° : high up, 
 also, the main valley of Copiapo, there is mica-slate 
 with a high easterly dip. In the whole space between 
 Valparaiso and Copiapo an easterly dip is much more 
 ■common than an opposite or westerly one. 
 
 Concluding Rema/rks on Cleavage and Foliation. 
 
 In this southern part of the Southern Hemisphere, 
 we have seen that the cleavage-lam inge range over wide 
 
CHAP. xni. Cleavage and Foliation. 461 
 
 areas with remarkable uniformity, cutting straight 
 through the planes of stratification/ but yet being 
 parallel in strike to the main axes of elevation, and 
 generally to the outlines of the coast. The dip, how- 
 ever, is as variable, both in angle and in direction (that 
 is, sometimes being inclined to the one side and some- 
 times to the directly opposite side), as the strike is 
 uniform. In all these respects there is a close agree- 
 ment with the facts given by Professor Sedgwick in his 
 celebrated memoir in the ' Geological Transactions,' and 
 by Sir R. I. Murchison in his various excellent dis- 
 cussions on this subject. The Falkland Islands, and 
 more especially Tierra del Fuego, offer striking instances 
 of the lines of cleavage, the principal axes of elevation, 
 and the outlines of the coast, gradually changing 
 together their courses. The direction which prevails 
 throughout Tierra del Faego and the Falkland Islands, 
 namely, from west with some northing to east with 
 some southing, is also common to the several ridges in 
 northern Patagonia and in the western parts of Banda 
 Oriental : in this latter province, in the Sierra Tapalguen, 
 and in the western Falkland Island, the W. by N., or 
 WNW. and ESE., ridges, are crossed at right angles by 
 others ranging NNE. and SSW. 
 
 The fact of the cleavage-laminae in the clay-slate of 
 Tierra del Fuego, where seen cutting straight through 
 the planes of stratification, and where consequently 
 there could be no doubt about their nature, differing 
 slightly in colour, texture, and hardness, appears to me 
 very interesting. In a thick mass of laminated, feld- 
 spathic and altered clay-slate, interposed between two 
 
 ^ In ray paper on the Falkland Islands (vol. iii. p. 267 ' Geolog- 
 ical Journal'), I have given a curious case on the authority of Capt. 
 Sulivan, E.N"., of much folded beds of clay-slate, in some of which the 
 cleavage is perpendicular to the horizon, and in others it is perpen- 
 dicular to each curvature or fold of the bed ; this appears a new case 
 
462 Cleavage and Foliatiojt. part h. 
 
 great strata of porphyritic conglomerate in central 
 Chile, and where there could be but little doubt about 
 the bedding, I observed similar slight diflferences in com- 
 position, and likewise some distinct thin layers of 
 epidote, parallel to the highly inclined cleavage of the 
 mass. Again, I incidentally noticed in North Wales,^ 
 where glaciers had passed over the truncated edges of 
 the highly inclined laminae of clay-slate, that the surface, 
 though smooth, was worn into small parallel undula- 
 tions, caused by the component lamina being of slightly 
 different degrees of hardness. With reference to the 
 slates of North Wales, Professor Sedgwick describes the 
 planes of cleavage, as ' coated over with chlorite and 
 semi-crystalline matter, which not only merely define the 
 planes in question, but strike in parallel flakes through 
 the whole mass of the rock.'^ In some of those glossy 
 and hard varieties of clay-slate which may often be 
 seen passing into mica-schist, it has appeared to me that 
 the cleavage-planes were formed of excessively thin, 
 generally slightly convoluted, folia, composed of micro- 
 scopically minute scales of mica. From these several 
 facts, and more especially from the case of the clay- 
 slate in Tierra del Fuego, it must, I think, be con- 
 cluded, that the same power which has impressed on 
 the slate its fissile structure or cleavage has tended 
 to modify its raineralogical character in parallel 
 planes. 
 
 Let us now turn to the foliation of the meta- 
 morphic schists, a subject which has been much less 
 attended to. As in the case of cleavage-laminae^ the 
 folia preserve over very large areas a uniform strike : 
 thus Humboldt^ found for a distance of 300 miles in 
 
 ' ' London Phil. Mag.' vol. xxi. p. 182. 
 
 - ' Geological Trans.' vol. iii. p. 471. 
 
 3 ' Personal Narrative,' vol. vi. p. 591, et seq. 
 
€HAP. xiTi. Cleavage and Foliation. 463 
 
 Venezuela, and indeed over a mucli larger space, gneiss, 
 granite, mica, and clay-slate, striking very uniformly 
 NE. and SW., and dipping at an angle of between 60^ 
 and 70° to NW. : it would even appear from tlie facts 
 given in this chapter,' that the metamorphic rocks 
 throughout the north-eastern part of S. America are 
 generally foliated within two points of NE. and SW. 
 Over the eastern parts of Banda Oriental, the foliation 
 strikes with a high inclination, very uniformly NNE. to 
 SSW., and over the western parts, in a W. by N. and 
 E. by S. line. For a space of 300 miles on the shores 
 of the Chonos and Chiloe Islands, we have seen that the 
 foliation seldom deviates more than a point of the com- 
 pass from a N. 19° W. and S. 19° E. strike. As in the 
 case of cleavage, the angle of the dip in foliated rocks 
 is generally high but variable, and alternates from one 
 side of the line of strike to the other side, sometimes 
 being vertical : in the northern Chonos Islands, however 
 the folia are inclined almost always to the west • in 
 nearly the same manner, the cleavage- laminge in 
 southern Tierra del Fuego certainly dip much more 
 frequently to SSW. than to the opposite point. In 
 eastern Banda Oriental, in parts of Brazil, and in some 
 other districts, the foliation runs in the same direction 
 with the mountain-ranges and adjoining coast-lines : 
 amongst the Chonos Islands, however, this coincidence 
 fails, and I have given my reasons for suspecting 
 that one granitic axis has burst through and tilted the 
 already inclined folia of mica-schist : in the case of 
 cleavage,^ the coincidence between its strike and that 
 of the main stratification seems sometimes to fail. 
 Foliation and cleavage resemble each other in the planes 
 winding round concretions, and in becoming tortuous 
 
 ^ Cases are given by Mr. Jukes, in his 'Geology of Newfoundland ' 
 p, 130. 
 
464 Cleavage and Foliation. pakt n. 
 
 where veins of quartz abound.^ On the flanks of the- 
 mountains both in Tierra del Fuego and in other 
 countries, I have observed that the cleavage-planes fre- 
 quently dip at a high angle inwards ; and this was long- 
 ago observed by Von Buch to be the case in Norway : 
 this fact is perhaps analogous to the folded, fan-like or 
 radiating structure in the metamorphic schists of th& 
 Alps,^ in which the folia in the central crests are vertical 
 and on the two flanks inclined inwards. Where masses 
 of flssile and foliated rocks alternate together, the cleav- 
 age and foliation, in all cases which I have seen, are- 
 parallel. Where in one district the rocks are fissile, 
 and in another adjoining district they are foliated, the 
 planes of cleavage and foliation are likewise generally 
 parallel : this is the case with the feldspathic homo- 
 geneous slates in the southern part of the Chonos group, 
 compared with the fine foliated mica-schists of the- 
 northern part ; so again the clay-slate of the whole 
 eastern side of Tierra del Fuego cleaves in exactly the 
 same line with the foliated gneiss and mica-slate of the 
 western coast; other analogous instances might have 
 been adduced.^ 
 
 With respect to the origin of the folia of quartz, 
 mica, feldspar, and other minerals composing the meta- 
 morphic schists, Professor Sedgwick, Mr. Lyell and 
 most authors believe, that the constituent parts of each 
 layer were separately deposited as sediment, and then 
 
 1 I have seen in Brazil and Chile concretions thus enfolded by 
 foliated gneiss; and Macculloch ('Highlands,' vol. i. p. 64) has 
 described a similar case. For analogous cases in clay-slate, see 
 Prof. Henslow's Memoir in ' Cambridge Phil. Trans.' vol. i. p. 379, 
 and Macculloch's 'Class, of Rocks,' p. 351. With respect to both 
 foliation and cleavage becoming tortuous where quartz-veins abound, 
 I have seen instances near Monte Video, at Concepcion, and in the 
 Chonos Islands. See also Mr. Greenough's ' Critical Examination,'' 
 p. 78. 
 
 2 Studer in ' Edin. New Phil. Journal,' vol. xxiii. p. 144. 
 
 3 I have given a case in Australia. See Chapter VII. of this 
 work. 
 
CHAP. XIII. Cleavage and Foliation. 465 
 
 metamorphosed. This view, in the majority of cases, I 
 believe to be quite untenable. In those not uncommon 
 instances, where a mass of clay-slate, in approaching 
 granite, gradually passes into gneiss,^ we clearly see 
 that folia of distinct minerals can originate through the 
 metamorphosis of a homogeneous fissile rock. The de- 
 position, it may be remarked, of numberless alternations 
 of pure quartz, and of the elements of mica or feldspar, 
 does not appear a probable event.^ In those districts 
 in which the metamorphic schists are foliated in planes 
 parallel to the cleavage of the rocks in an adjoining 
 district ; are we to believe that the folia are due to 
 sedimentary layers, whilst the cleavage-laminee, though 
 parallel, have no relation whatever to such planes of 
 deposition ? On this view, how can we reconcile the 
 vastness of the areas over which the strike of the folia- 
 tion is uniform, with what we see in disturbed districts 
 composed of true strata : and especially, how can we 
 understand the high and even vertical dip throughout 
 many wide districts, which are not mountainous, and 
 throughout some, as in western Banda Oriental, which 
 are not even hilly ? Are we to admit that in the 
 northern part of the Chonos Archipelago, mica-slate was 
 first accumulated in parallel horizontal folia to a thick- 
 ness of about four geographical miles, and then upturned 
 at an angle of forty degrees; whilst, in the southern 
 part of this same archipelago, the cleavage-laminae 
 of closely allied rocks, which none would imagine had 
 ever been horizontal, dip at nearly the same angle, to 
 nearly the same point ? 
 
 Seeing, then, that foliated schists indisputably are 
 
 ^ I have described (in Chapter VII. of this work) a good instance 
 of such a passage at the Cape of Good Hope. 
 
 ^ See some excellent remarks on this subject, in D'Aubuisson's 
 ' Traite de Geog.' torn, i, p. 297. Also, some remarks by Mr, Dana 
 in Silliman's ' American Journ.' vol. xlv. p. 108. 
 
 H H 
 
466 Cleavage aiid Foliation. part h. 
 
 sometimes produced by the metamorphosis of homo- 
 geneous fissile rocks ; seeing that foliation and cleavage 
 are so closely analogous in the several above-enumerated 
 respects; seeing that some fissile and almost homo- 
 geneous rocks show incipient miner alogical changes 
 along the planes of their cleavage, and that other rocks 
 with a fissile structure alternate with, and pass into 
 varieties with a foliated structure, I cannot doubt that 
 in most cases foliation and cleavage are parts of the 
 same process : in cleavage there being only an incipient 
 separation of the constituent minerals ; in foliation a 
 much more complete separation and crystallisation. 
 
 The fact, often referred to in this chapter, of the 
 foliation and the so-called strata in the metamorphic 
 series — that is, the alternating masses of different 
 varieties of gneiss, mica-schist, and hornblende-slate, 
 &c. — being parallel to each other, at first appears quite 
 opposed to the view that the folia have no relation to 
 the planes of original deposition. Where the so-called 
 beds are not very thick and of widely different minera- 
 logical composition from each other, I do not think that 
 there is any difficulty in supposing that they have 
 originated in an analogous manner with the separate 
 folia. We should bear in mind what thick strata, 
 in ordinary sedimentary masses, have obviously been 
 formed by a concretionary process. In a pile of volcanic 
 rocks on the Island of Ascension, there are strata, dif- 
 fering quite as much in appearance as the ordinary 
 varieties of the metamorphic schists, which undoubtedly 
 have been produced, not by successive flowings of lava, 
 but by internal molecular changes. Near Monte Video, 
 where the stratification, as it would be called, of the 
 metamorphic series is, in most parts, particularly well 
 developed, being as usual, parallel to the foliation, we 
 have seen that a mass of chloritic schist, netted with 
 
CHAP. XIII. Cleavage and Foliatioji. 467 
 
 quartz-veins, is entangled in gneiss, in sucli a manner as 
 to sliow tliat it liad certainly originated in some pro- 
 cess of segregation : again, in another spot, the gneiss 
 tended to pass into hornblendic schist by alternating 
 with layers of quartz ; but these layers of quartz almost 
 certainly had never been separately deposited, for they 
 were absolutely continuous with the numerous intersect- 
 ing veins of quartz. I have never had an opportunity of 
 tracing for any distance, along the line both of strike 
 and of dip, the so-called beds in the metamorphic 
 schists, but I strongly suspect that they would not be 
 found to extend with the same character, very far in the 
 line either of their dip or strike. Hence I am led to 
 believe, that most of the so-called beds are of the nature 
 of complex folia, and have not been separately de- 
 posited. Of course, this view cannot be extended to 
 iliick masses included in the metamorphic series, which 
 are of totally different composition from the adjoining 
 schists, and which are far extended, as is sometimes the 
 case with quartz and marble ; these must generally be 
 of the nature of true strata.^ Such strata, however, 
 will almost always strike in the same direction with the 
 folia, owing to the axes of elevation being in most 
 countries parallel to the strike of the foliation; but 
 they will generally dip at a different angle from that of 
 the foliation ; and the angle of the foliation in itself 
 almost always varies much : hence, in crossing a meta- 
 morphosed schistose district, it would require especial 
 attention to discriminate between true strata of depo- 
 sition and complex foliated masses. The mere presence 
 of true strata in the midst of a set of metamorphic 
 schists, is no argument that the foliation is of sedimen- 
 
 ' MaccuUocli states (' Classification of Eocks,' p. 364) that prim- 
 ary limestones are often found in irregular masses or great nodules, 
 ' which can scarcely be said to possess a stratified shape.' 
 
 H H 2 
 
468 Cleavage and Foliation. paet n. 
 
 tary origin, without it be furtlier shown in each case, 
 that the folia not only strike, but dip throughout in 
 parallel planes with those of the true stratification. 
 
 As in some cases it appears that where a fissile rock 
 has been exposed to partial metamorphic action — for 
 instance, from the irruption of granite — the foliation 
 has supervened on the already existing cleavage-planes ; 
 so perhaps, in some instances, the foliation of a rock may 
 have been determined by the original planes of deposi- 
 tion or of oblique current-lamina : I have, however, 
 myself, never seen such a case, and I must maintain that 
 in most extensive metamorphic areas, the foliation is 
 the extreme result of that process, of which cleavage 
 is the first effect. That foliation may arise without any 
 previous structural arrangement in the mass, we may 
 infer from injected, and therefore once liquefied, rocks, 
 both of volcanic and plutonic origin, sometimes having 
 a ' grain ' (as expressed by Professor Sedgwick), and 
 sometimes being composed of distinct folia or laminse of 
 different compositions. In the earlier chapters of the 
 present work, I have given several instances of this struc- 
 ture in volcanic rocks, and it is not uncommonly seen in 
 plutonic masses — thus, in the Cordillera of Chile, there 
 are gigantic mountain-like masses of red granite, which 
 have been injected whilst liquefied, and which neverthe- 
 less, display in parts a decidedly laminar structure.^ 
 
 Finally, we have seen that the planes of cleavage 
 and of foliation — that is, of the incipient process and of 
 the final result — generally strike parallel to the principal 
 
 ^ As remarked in a former part of tliis chapter, I suspect that 
 the boldly conical mountains of gneiss-granite, near Rio de Janeiro, 
 in which the constituent minerals are arranged in parallel planes, 
 are of intrusive origin. We must not, however, forget the lesson of 
 caution taught by the curious clay-stone porphyries of Port Desire, 
 in which we have seen that the breaking up and aggregation of a 
 thinly stratified tufaceous mass, has yielded a rock semi-porphyritic 
 with crystals of feldspar, arranged in the planes of original deposition. 
 
CHAP. XIII. Cleavage and Foliation. 469 
 
 axes of elevation, and to the outline of the land : the 
 strike of the axes of elevation (that is, of the lines of 
 fissures with the strata on their edges upturned), ac- 
 cording to the reasoning of Mr. Hopkins, is determined 
 by the form of the area undergoing changes of level, 
 and the consequent direction of the lines of tension and 
 fissure. Now, in that remarkable pile of volcanic rocks ' 
 at Ascension, which has several times been alluded to 
 (and in some other cases), I have endeavoured to show,^ 
 that the lamination of the several varieties, and their 
 alternations, have been caused by the moving mass, ju^t 
 before its final consolidation, having been subjected (as 
 in a glacier) to planes of different tension, this differ- 
 ence in the tension affecting the crystalline and concre- 
 tionary processes. One of the varieties of rock thus 
 produced, at Ascension, at first sight, singularly resembles 
 a fine-grained gneiss ; it consists of quite straight and 
 parallel zones of excessive tenuity, of more and less 
 coloured crystallised feldspar, of distinct crystals of 
 quartz, diopside, and oxide of iron. These considera- 
 tions, notwithstanding the experiments made by Mr. 
 Fox, showing the influence of electrical currents in pro- 
 ducing a structure like that of cleavage, and notwith- 
 standing the apparently inexplicable variation, both in 
 the inclination of the cleavage -laminse and in their dip- 
 ping first to one side and then to the other side of the line 
 of strike, lead me to suspect that the planes of cleavage 
 and foliation are intimately connected with the planes 
 of different tension, to which the area was long sub- 
 jected, after the main fissures or axes of upheavement 
 had been formed, but hefore the final consolidation of 
 the mass and the total cessation of all molecular move- 
 ment. 
 
 ^ See Chapter III. of the present work. 
 
470 Central Chile, paet n. 
 
 CHAPTER XIV. 
 
 CENTEAL CHILE; STRUCTURE OF THE CORDILLERA. 
 
 Central Chile — Basal formations of tl\e Cordillera — Origin of the 
 jporphyritic clay-stone conglomerate — Andesite — Volcanic rocJcs — 
 Section of the Cordillera l)y the Peuquenes or Portillo Pass — Great 
 gypseous formation — Peuqueiies line; thichness of strata, fossils of 
 — Portillo line, conglomerate, orthitic granite, mica-schist, and 
 volcanic rochs of — Concluding remarks on the denudation and eleva- 
 tion of the Portillo line — Section iy the Cmiibre or TJspallata Pass 
 — Porphyries — Gypseous strata — Section near Puente del Inca ; 
 fossils of — Great subsidence — Intrusive porphyries — Plain of Us- 
 pallata — Section of the TJspallata chain — Structure and nature of 
 the strata — Silicified vertical trees — Great subsidence — Granitic 
 rocTis of axis — Concluding remarks on tlie JJspallata range ; origin 
 subsequent to that of the main Cordillera ; two periods of subsid- 
 ence ; comparison with the Portillo chain. 
 
 The district between tlie Cordillera and the Pacific, on 
 a rude average, is from about eighty to one hundred 
 miles in width. It is crossed by many chains of moun- 
 tains, of which the principal ones, in the latitude of 
 Valparaiso and southward of it, range nearly north and 
 south ; but in the more northern parts of the province, 
 they run in almost every possible direction. Near the 
 Pacific, the mountain-ranges are generally formed of 
 syenite or granite, or of an allied euritic porphyry ; in 
 the low country, besides these granitic rocks and green- 
 stone, and much gneiss, there are, especially northward 
 of Valparaiso, some considerable districts of true clay- 
 slate with quartz veins, passing into a feldspathic and 
 porphyritic slate; there is also some grauwacke and 
 
CHAP. xiY. Central Chile. 471 
 
 quartzose and jaspery rocks, the latter occasionally 
 assuming tlie character of the basis of clay-stone por- 
 phyry : trap-dikes are numerous. Nearer the Cordillera 
 the ranges (such as those of S. Fernando, the Prado,^ 
 and Aconcagua) are formed parfcly of granitic rocks, 
 and partly of purple porphyritic conglomerates, clay- 
 stone porphyry, greenstone porphyry, and other rocks, 
 such as we shall immediately see form the basal strata 
 of the main Cordillera. In the more northern parts of 
 Chile, this porphyritic series extends over large tracts 
 of country far from the Cordillera ; and even in Central 
 Chile such occasionally occur in outlying positions. 
 
 I will describe the Campana of Quillota, which 
 stands only fifteen miles from the Pacific, as an instance 
 of one of these outlying masses. This hill is conspicuous 
 from rising to the height of 6,400 feet : its summit 
 shows a nucleus, uncovered for a height of 800 feet, of 
 fine greenstone, including epidote and octahedral mag- 
 netic iron ore ; its flanks are formed of great strata 
 of porphyritic clay-stone conglomerate, associated with 
 various true porphyries and amygdaloids, alternating 
 with thick masses of a highly feldspathic, sometimes 
 porphyritic, pale-coloured slaty rock, with its cleavage- 
 lamina dipping inwards at a high angle. At the base 
 of the hill there are syenites, a granular mixture of 
 quartz and feldspar, and harsh quartzose rocks, all be- 
 longing to the basal metamorphic series. I may ob- 
 serve that at the foot of several hills of this class, where 
 the porphyries are first seen (as near S. Fernando, the 
 Prado, Las Vacas, &c.), similar harsh quartzose rocks 
 and granular mixtures of quartz and feldspar occur, as 
 if the more fusible constituent parts of the granitic 
 series had been drawn off to form the overlying por- 
 phyries. 
 
 1 Meyen, ' Eeise urn Erde,' Th. 1, S. 235. 
 
472 Basal Strata of the Cordillera, paeth. 
 
 In Central Cliilej tlie flanks of the 'main Cordillera, 
 into wliicli I penetrated by four different valleys, gene- 
 rally consist of distinctly stratified rocks. Tke strata 
 are inclined at angles varying from sometimes even 
 under ten, to twenty degrees, very rarely exceeding 
 forty degrees : in some, however, of the quite small, 
 exterior, spur-like ridges, the inclination was not unfre- 
 quently greater. The dip of the strata in the main 
 outer lines was usuallv outwards or from the Cordillera, 
 but in Northern Chile frequently inwards, — that is, 
 their basset-edges fronted the Pacific. Dikes occur in 
 extraordinary numbers. In the great, central, loftiest 
 ridges, the strata, as we shall presently see, are almost 
 always highly inclined and often vertical. Before giving 
 a detailed account of my two sections across the Cor- 
 dillera, it will, I think, be convenient to describe the 
 basal strata as seen, often to a thickness of 4,000 or 
 5,000 feet, on the flanks of the outer lines. 
 
 Sascd 8trata of the Cordillera. — ^The prevailing 
 rock is a purplish or greenish, porphyritic clay-stone 
 conglomerate. The embedded fragments vary in size 
 from mere particles to blocks as much as six or eight 
 inches (rarely more) in diameter ; in many places, where 
 the fragments were minute, the signs of aqueous depo- 
 sition were unequivocally distinct; where they were 
 large, such evidence could rarely be detected. The 
 basis is generally porphyritic with perfect crystals of 
 feldspar, and resembles that of a true injected clay- 
 stone porphyry : often, however, it has a mechanical 
 or sedimentary aspect, and sometimes (as at Jajuel) is 
 jaspery. The included fragments are either angular, 
 or partially or quite rounded ; ^ in some parts the 
 
 ^ Some of the rounded fragments in the porphyritic conglomerate 
 near the Baths of Cauquenes, were marked with radii and concentric 
 zones of different shades of colour : any one who did not know that 
 
cHAP.xiY. Porphyritic Clay stone Conglomerate. 473; 
 
 rounded, in others tlie angularj fragments prevail, and 
 usually both kinds are mixed together : hence the word 
 hrecda ought strictly to be appended to the term por- 
 plvyritic conglomerate. The fragments consist of many 
 varieties of clay-stone porphyry, usually of nearly 
 the same colour with the surrounding basis, namely^ 
 purplish-reddish, brownish, mottled or bright green; 
 occasionally fragments of a laminated, pale-coloured, 
 feldspathic rock, like altered clay-slate, are included; 
 as are sometimes grains of quartz ; but only in one in- 
 stance in Central Chile (namely, at the mines of Jajuel) 
 a few pebbles of quartz. I nowhere observed mica in 
 this formation, and rarely hornblende ; where the latter 
 mineral did occur, I was generally in doubt whether 
 the mass really belonged to this formation, or was of 
 intrusive origin. Calcareous spar occasionally occurs 
 in small cavities ; and nests and layers of epidote are 
 common. In some few places in the finer-grained 
 varieties (for instance, at Quillota), there were shorty 
 interrupted layers of earthy feldspar, which could be 
 traced, exactly as at Port Desire, passing into large 
 crystals of feldspar : I doubt, however, whether in thi& 
 instance the layers had ever been separately deposited 
 as tufaceous sediment. 
 
 All the varieties of porphyritic conglomerates and 
 breccias pass into each other, and by innumerable 
 gradations into porphyries no longer retaining the least 
 trace of mechanical origin : the transition appears to 
 have been effected much more easily in the finer-grained, 
 than in the coarser-grained varieties. In one instance, 
 T;^3ar Cauquenes, I noticed that a porphyritic conglo- 
 
 pebbles — for instance, flint pebbles from the chalk — are sometimes 
 zoned concentrically with their worn and rounded surfaces, might 
 have been led to infer that these balls of porphyry were not true 
 pebbles, but had originated in concretionary action. 
 
474 Basal Strata of the Cordillera, paet ii. 
 
 merate assumed a spheroidal structure, and tended to 
 become columnar. Besides ttie porphyritic conglomerates 
 and the perfectly characterised porphyries of meta- 
 morphic origin, there are other porphyries which, 
 though differing not at all or only slightly in composi- 
 tion, certainly have had a different origin : these consist 
 of pink or purple clay-stone porphyries, sometimes 
 including grains of quartz, — of greenstone porphyry, 
 and of other dusky rocks, all generally porphyritic with 
 fine, large, tabular, opaque crystals, often placed cross- 
 wise, of feldspar cleaving like albite (judging from 
 several measurements), and often amygdaloidal with 
 silex, agate, carbonate of lime, green and brown bole.^ 
 These several porphyritic and amygdaloidal varieties 
 
 ^ This bole is a very common mineral in the amygdaloidal rocks ; 
 it is generally of a greenish-brown colour, with a radiating structure; 
 externally it is black with an almost metallic lustre, but often 
 coated by a bright green film. It is soft and can be scratched by a 
 quill ; under the blowpipe swells greatly and becomes scaly, then 
 fuses easily into a black magnetic bead. This substance is evidently 
 similar to that which often occurs in submarine volcanic rocks. 
 An examination of some very curious specimens of a fine porphyry 
 (from Jajuel) leads me to suspect that some of these amygdaloidal 
 balls, instead of having been deposited in pre-existing air-vesicles, 
 are of concretionary origin ; for in these specimens, some of the 
 pea- shaped little masses (often externally marked with minute pits) 
 are formed of a mixture of green earth with stony matter, like the 
 basis of the porphyry, including minute imperfect crystals of feldspar ; 
 and these pea-shaped little masses are themselves amygdaloidal with 
 minute spheres of the green earth, each enveloped by a film of white, 
 apparently feldspathic, earthy matter : so that the porphyry is doubly 
 amygdaloidal. It should not, however, be overlooked, that all the 
 strata here have undergone metamorphic action, which may have 
 caused crystals of feldspar to appear, and other changes to be 
 effected, in the originally simple amygdaloidal balls. Mr. J. D. 
 Dana, in an excellent paper on Trap rocks (' Edin. New Phil. Journ.' 
 vol. xli. p. 198), has argued, with great force, that all amygdaloidal 
 minerals have been deposited by aqueous infiltration. I may take 
 this opportunity of alluding to a curious case, described in Chapter 
 II. of the present work, of an amygdaloidal rock, with many of the 
 cells only half filled up with a mesotypic mineral. 
 
 M. Rose has described an amygdaloid, brought by Dr. Meyen 
 (' Reise um Erde,' Th. 1, S. 316) from Chile, as consisting of crystall- 
 ised quartz, with crystals of stilbite within, and lined externally by 
 green earth. 
 
Q^Ks.TiN.Porphyritic Clay stone Conglomei^ate. 475 
 
 never show any signs of passing into masses of sedi- 
 mentary origin : they occur both in great and small 
 intrusive masses, and likewise in strata alternating with 
 those of the porphyritic conglomerate, and with the 
 planes of junction often quite distinct, yet not seldom 
 blended together. In some of these intrusive masses, 
 the porphyries exhibit, more or less plainly, a brecciated 
 structure, like that often seen in volcanic masses. These 
 brecciated porphyries could generally be distinguished 
 at once from the metamorphosed, porphyritic breccia- 
 conglomerates, by all the fragments being angular and 
 being formed of the same variety, and by the absence 
 of every trace of aqueous deposition. One of the por- 
 phyries above specified, namely, the greenstone porphyry 
 with large tabular crystals of albite, is particularly 
 abundant, and in some parts of the Cordillera (as near 
 St. Jago) seemed more common even than the purplish 
 porphyritic conglomerate. Numerous dikes likewise 
 consist of this greenstone porphyry ; others are formed 
 of various fine-grained trappean rocks ; but very few 
 of clay- stone porphyry : I saw no true basaltic dikes. 
 
 In several places in the lower part of the series, but 
 not everywhere, thick masses of a highly feldspathic, 
 often porphyritic, slaty rock occur inter stratified with 
 the porphyritic conglomerate : I believe in one or two 
 cases blackish limestone has been found in a similar 
 position. The feldspathic rock is of a pale grey or 
 greenish colour ; it is easily fasible ; where porphyritic, 
 the crystals of feldspar are generally small and vitreous ; 
 it is distinctly laminated, and sometimes includes 
 parallel layers of epidote ; ^ the lamination appears to 
 
 ^ This mineral is extremely common in all the formations of Chile ; 
 in the gneiss near Valparaiso and in the granitic veins crossing it, in 
 the injected greenstone crowning the C.of Quillota, in some granitic 
 porphyries, in the porphyritic conglomerate, and in the feldspathic 
 clay-slates. 
 
47 6 Basal Strata of the Coi^dillera. paetii. 
 
 be distinct from stratification. Occasionally this rock 
 is somewhat carious ; and at one spot, namely, at the 
 0. of Quillota, it had a brecciated structure. Near the 
 mines of Jajuel, in a thick stratum of this feldspathic, 
 porphyritic slate, there was a layer of hard, blackish, 
 siliceous, infusible, compact clay-slate, such as I saw 
 nowhere else : at the same place I was able to follow 
 for a considerable distance the junction between the slate 
 and the conformably underlying porphyritic conglo- 
 merate, and they certainly passed gradually into each- 
 other. Wherever these slaty feldspathic rocks abound^ 
 greenstone seems common ; at the C. of Quillota a bed 
 of well-crystallised greenstone lay conformably in the- 
 midst of the feldspathic slate, with the upper and lower 
 junctions passing insensibly into it. From this fact, 
 and from the frequently porphyritic condition of the 
 slate, I should perhaps have considered this rock as an 
 erupted one (like certain laminated feldspathic lavas- 
 in the trachytic series), had I not seen in T. del Fuega 
 how readily true clay-slate becomes feldspathic and 
 porphyritic, and had I not seen at Jajuel the included 
 layer of black, siliceous clay-slate, which no one could 
 have thought of igneous origin. The gentle passage 
 of the feldspathic slate, at Jajuel, into the porphyritic 
 conglomerate, which is certainly of aqueous origin^ 
 should also be taken into account. 
 
 The alternating strata of porphyries and porphyritic 
 conglomerate, and with the occasionally included beds 
 of feldspathic slate, together make a grand formation ; 
 in several places within the Cordillera I estimated its 
 thickness at from 6,000 to 7,000 feet. It extends for 
 many hundred miles, forming the western flank of the 
 Chilian Cordillera ; and even at Iquique in Peru, 850 
 miles north of the southernmost point examined by me 
 in Chile, the coast-escarpment, which rises to a height 
 
<jHAP. xiY. Porphyritic Clay stone Conglomerate, a^"]*] 
 
 of between 2,000 and 3,000 feet, is thus composed. In 
 several parts of Northern Chile this formation extends 
 much farther towards the Pacific, over the granitic and 
 metamorphic lower rocks, than it does in Central Chile ; 
 but the main Cordillera may be considered as its cen- 
 tral line, and its breadth in an east and west direction 
 is never great. At first the origin of this thick, mass- 
 ive, long but narrow formation, appeared to me very 
 anomalous : whence were derived, and how were dis- 
 persed the innumerable fragments, often of large size, 
 sometimes angular and sometimes rounded, and almost 
 invariably composed of porphyritic rocks ? Seeing that 
 the interstratified porphyries are never vesicular and 
 often not even amygdaloidal, we must conclude that the 
 pile was formed in deep water ; how then came so many 
 fragments to be well rounded and so many to remain 
 angular, sometimes the two kinds being equally mingled, 
 sometimes one and sometimes the other preponder- 
 ating? That the clay-stone, greenstone, and other 
 porphyries and amygdaloids, which lie conformably be- 
 tween the beds of conglomerate, are ancient submarine 
 lavas, I think there can be no doubt ; and I believe we 
 must look to the craters whence these streams were 
 erupted, as the source of the breccia-conglomerate : 
 after a great explosion, we may fairly imagine that 
 the water in the heated and scarcely quiescent crater 
 would remain for a considerable time ^ sufficiently 
 agitated to triturate and round the loose fragments 
 lying within it : these rounded fragments, few or many 
 in number, would be shot forth at the next eruption, 
 associated with a few or many angular fragments, ac- 
 cording to the strength of the explosion. The porphyr- 
 
 ^ This certainly seems to have taken place in some recent volcanic 
 archipelagos, as at the Galapagos, where numerous craters are exclus- 
 ively formed of tuff and fragments of lava. 
 
47 S Plutonic Rocks of the Cordillera, part n. 
 
 itic conglomerate being purple or reddish, even when 
 alternating with dusky-coloured or bright green por~ 
 phyries and amygdaloids, is probably an analogous 
 circumstance to the scoriae of the blackish basalts be- 
 ing often bright red. The ancient submarine orifices 
 whence the porphyries and their fragments were ejected 
 having been arranged in a band, like most still active 
 volcanos, accounts for the thickness, the narrowness, and 
 linear extension of this formation. 
 
 This whole great pile of rock has suffered much 
 metamorphic action, as is very obvious in the gradual 
 formation and appearance of the crystals of albitic 
 feldspar and of epidote — in the blending together 
 of the fragments — in the appearance of a lami- 
 nated structure in the feldspathic slate — and, lastly, 
 in the disappearance of the planes of stratification, 
 which could sometimes be seen on the same mountain, 
 quite distinct in the upper part, less and less plain on 
 the flanks, and quite obliterated at the base. Partly 
 owing to this metamorphic action, and partly to the 
 close relationship in origin, I have seen fragments of 
 porphyries — taken from a metamorphosed conglomerate 
 — from a neighbouring stream of lava — from the nucleus 
 or centre (as it appeared to me) of the whole submarine 
 volcano — and lastly from an intrusive mass of quite 
 subsequent origin, all of which were absolutely undis- 
 tinguishable in external characters. 
 
 One other rock, of plutonic origin, and highly im- 
 portant in the history of the Cordillera, from having 
 been injected in most of the great axes of elevation, and 
 from having apparently been instrumental in meta- 
 morphosing the superincumbent strata, may be con- 
 veniently described in this preliminary discussion. It 
 has been called by some authors Andesite : it mainly 
 
CHAP. XIV. Andesitic and Volca^iic Rocks. 479 
 
 consists of well-crystallised wliite albite ^ (as determined 
 with tlie goniometer in numerous specimens botli by 
 Professor Miller and myself), of less perfectly crystall- 
 ised green hornblende, often associated with much 
 mica, with chlorite and epidote, and occasionally ^dth 
 a few grains of quartz : in one instance in Northern 
 Chile, I found crystals of orthitic or potash feldspar, 
 mingled with those of albite. Where the mica and 
 quartz are abundant, the rock cannot be distinguished 
 from granite ; and it may be called andesitic granite. 
 Where these two minerals are quite absent, and when, 
 as often then happens, the crystals of albite are imper- 
 fect and blend together, the rock may be called andes- 
 itic porphpy, which bears nearly the same relation to 
 andesitic granite that euritic porphyry does to common 
 granite. These andesitic rocks form mountain masses 
 of a white colour, which, in their general outline and 
 appearance — in their joints — in their occasionally in- 
 cluding dark-coloured, angular fragments, apparently of 
 some pre-existing rock — and in the great dikes branch- 
 ing from them into the superincumbent strata, manifest 
 a close and striking resemblance to masses of common 
 granite and syenite : I never, however, saw in these 
 andesitic rocks, those granitic veins of segregation 
 which are so common in true granites. We have seen 
 that andesite occurs in three places in Tierra del Fuego ; 
 in Chile, from St, Fernando to Copiapo, a distance of 
 
 1 I here, and elsewhere, call by this name, those feldspathic mine- 
 rals which cleave like albite : but it now appears (' Edin. New Phil. 
 Journ.' vol. xxiv. p. 181) that Abichhas analysed a mineral from the 
 Cordillera, associated with hornblende and quartz (probably the same 
 rock with that here under discussion), which cleaves like albite, but 
 which is a new and distinct kind, called by him Andesine. It is 
 allied to leucite, with the greater proportion of its potash replaced by 
 lime and soda. This mineral seems scarcely distinguishable from 
 albite, except by analysis. 
 
480 Plutonic Rocks of the Cordillera, paet ii. 
 
 450 miles, I found it under most of the axes of elevation ; 
 in a collection of specimens from the Cordillera of Lima 
 in Peru, I immediately recognised it ; and Erman ^ 
 states that it occurs in eastern Kamtschatka. From 
 its wide range, and from the important part it has 
 played in the history of the Cordillera, I think this 
 rock has well deserved its distinct name of andesite. 
 
 The few still active volcanos in Chile are confined 
 to the central and loftiest ranges of the Cordillera ; and 
 volcanic matter, such as appears to have been of sub- 
 .aerial eruption, is everywhere rare. According to 
 Meyen,- there is a hill of pumice high up the valley 
 of the Maypu, and likewise a tr achy tic formation at 
 Colina, a village situated north of St. Jago. Close to 
 this latter city, there are two hills formed of a pale 
 feldspathic porphyry, remarkable from being doubly 
 columnar, great cylindrical columns being subdivided 
 into smaller four or five sided ones ; and a third hillock 
 (Cerro Blanco) is formed of a fragmentary mass of 
 rock, which I believe to be of volcanic origin, inter- 
 mediate in character between the above feldspathic 
 porphyry and common trachyte, and containing needles 
 of hornblende and granular oxide of iron. Near the 
 Baths of Cauquenes, between two short parallel lines of 
 elevation, where they are intersected by the valley, there 
 is a small, though distinct volcanic district; the rock 
 is a dark grey (andesitic) trachyte, which fuses into a 
 o-reenish-grey bead, and is formed of long crystals of 
 fractured glassy albite (judging from one measurement) 
 mingled with well-formed crystals, often twin, of augite. 
 The whole mass is vesicular, but the surface is darker 
 coloured and much more vesicular than any other part. 
 This trachyte forms a cliff-bounded, horizontal, narrow 
 
 ^ Geograph. Journal,' vol ix. p. 510. 
 
 2 Keise urn Erde,' Th. 1, SS. 338 und 362. 
 
CHAP. xiY. Section by the Portillo Pass. 481 
 
 strip on the steep southern side of the valley, at the 
 height of 400 or 500 feet above the river-bed ; judging 
 from an apparently corresponding line of cliff on the 
 northern side, the valley must once have been filled up 
 to this height by a field of lava. On the summit of a 
 lofty mountain some leagues higher up this same valley 
 of the Cachapual, I found columnar pitchstone porphy- 
 ritic with feldspar ; I do not suppose this rock to be 
 of volcanic origin, and only mention it here, from its 
 being intersected by masses and dikes of a vesicular 
 rock, approaching in character to trachyte ; in no other 
 part of Chile did I observe vesicular or amygdaloidal 
 dikes, though these are so common in ordinary volcanic 
 districts. 
 
 Passage of the Andes hij the Portillo or Peuquenes 
 
 Pass. 
 
 Although I crossed the Cordillera only once by this 
 pass, and only once by that of the Cumbre or Uspallata 
 (presently to be described), riding slowly and halting 
 occasionally to ascend the mountains, there are many 
 circumstances favourable to obtaining a more faithful 
 sketch of their structure than would at first be thought 
 possible from so short an examination. The mountains 
 are steep and absolutely bare of vegetation ; the atmo- 
 sphere is resplendently clear ; the stratification distinct ; 
 and the rocks brightly and variously coloured : some of 
 the natural sections might be truly compared for dis- 
 tinctness to those coloured ones in geological works. 
 Considering how little is known of the structure of this 
 gigantic range, to which I particularly attended, most 
 travellers having collected only specimens of the rocks, 
 I think my sketch-sections, though necessarily imper- 
 fect, possess some interest. The section given in Plate I. 
 
 I I 
 
482 Section by the Portillo Pass. part h. 
 
 fig. 1, wliich 1 will now describe in detail, is on a 
 horizontal scale of a third of an inch to a nautical mile, 
 and on a vertical scale of one inch to a mile or 6,000 
 feet. The width of the range (excluding a few out- 
 lying hillocks), from the plain on which St. Jago the 
 capital of Chile stands, to the Pampas, is sixty miles, as 
 far as I can judge from the maps, which differ from each 
 other and are all exceedingly imperfect. The St. Jago 
 plain at the mouth of the Maypu, I estimate from ad- 
 joining known points at 2,300 feet, and the Pampas at 
 3,500 feet, both above the level of the sea. The height 
 of the Peuquenes line, according to Dr. Gillies,^ is 
 13,210 feet; and that of the Portillo line (both in the 
 gaps where the road crosses them) is 14,345 feet ; the 
 lowest part of the intermediate valley of Tenuyan is 
 7,530 feet — all above the level of the sea. 
 
 The Cordillera here, and indeed I believe throughout 
 Chile, consist of several parallel, anticlinal and uniclinal 
 mountain-lines, ranging north, or north with a little 
 westing, and south. Some exterior and much lower 
 ridges often vary considerably from this course, pro- 
 jecting like oblique spurs from the main ranges : in 
 the district towards the Pacific, the mountains, as be- 
 fore remarked, extend in various directions, even east 
 and west. In the main exterior lines, the strata, as also 
 before remarked, are seldom inclined at a high angle ; 
 but in the central lofty ridges they are almost always 
 highly inclined, broken by many great faults, and often 
 vertical. As far as I could judge, few of the ranges are 
 of great length : and in the central parts of the Cor- 
 dillera, I was frequently able to follow with my eye a 
 ridge gradually becoming higher and higher, as the 
 stratification increased in inclination, from one end 
 where its height was trifling and its strata gently inclined 
 ^ ' Journal of Nat. and Geograph. Science,' August, 1830. 
 
CHAP. xiY. Section by the Portillo Pass. 483 
 
 to tlie other end where vertical strata formed snow-clad 
 pinnacles. Even outside the main Cordillera, near the 
 baths of Cauquenes, I observed one such case, where a 
 north and south ridge had its strata in the valley in- 
 clined at 37°, and less than a mile south of it at 67° : 
 another parallel and similarly inclined ridge rose at the 
 distance of about five miles, into a lofty mountain with 
 absolutely vertical strata. Within the Cordillera, the 
 height of the ridges and the inclination of the strata 
 often became doubled and trebled in much shorter dis- 
 tances than five miles : this peculiar form of upheaval 
 probably indicates that the stratified crust was thin, 
 and hence yielded to the underlying intrusive masses 
 unequally, at certain points on the lines of fissure. 
 
 The valleys, by which the Cordillera are drained, 
 follow the anticlinal or rarely synclinal troughs, which 
 deviate most from the usual north and south course ; or 
 still more commonly those lines of faults or of unequal 
 curvature (that is, lines with the strata on both hands 
 dipping in the same direction, but at a somewhat 
 different angle) which deviate most from a northerly 
 course. Occasionally the torrents run for some distance 
 in the north and south valleys, and then recover their 
 eastern or western course by bursting through the ranges 
 at those points where the strata have been least inclined 
 and the height consequently is less. Hence the valleys, 
 along which the roads run, are generally zigzag ; and, 
 in drawing an east and west section, it is necessary to 
 contract greatly that which is actually seen on the road. 
 
 Commencing at the western end of the coloured 
 section [Plate I.] where the R. Maypu debouches on the 
 plain of St. Jago, we immediately enter on the por- 
 phyritic conglomerate formation, and in the midst of 
 it find some hummocks [A] of granite and syenite, 
 which probably (for I neglected to collect specimens) 
 
 I I 2 
 
484 Section by the Portillo Pass. part h. 
 
 belong to the anclesitic class. These are succeeded by 
 some rugged hills [B] of dark-green, crystalline, feld- 
 spathic and in some parts slaty rocks, which I be- 
 lieve belong to the altered clay-slate formation. From 
 this point, great mountains of purplish and greenish, 
 generally thinly stratified, highly porphyritic conglo- 
 merates, including many strata of amygdaloidal and 
 greenstone porphyries, extend up the valley to the 
 junction of the rivers Yeso and Volcan. As the valley 
 here runs in a very southerly course, the width of the 
 porphyritic conglomerate formation is quite conjectural ; 
 and from the same cause, I was unable to make out 
 much about the stratification. In most of the exterior 
 mountains the dip was gentle and directed inwards ; 
 and at only one spot I observed an inclination as high 
 as 50°. Near the junction of the R. Colorado with the 
 main stream, there is a hill of whitish, brecciated, 
 partially decomposed feldspathic porphyry, having a 
 volcanic aspect but not being really of that nature : at 
 ToUa, however, in this valley, Dr. Meyen ^ met with a 
 hill of pumice containing mica. At the junction of 
 the Yeso and Volcan [D] there is an extensive mass, in 
 white conical hillocks, of andesite, containing some 
 mica, and passing either into andesitic granite, or into 
 a spotted, semi-granular mixture of albitic (?) feldspar 
 and hornblende : in the midst of this formation Dr. 
 Meyen found true trachyte. The andesite is covered 
 by strata of dark-coloured, crystalline, obscurely por- 
 phyritic rocks, and above them by the ordinary por- 
 phyritic conglomerates, — the strata all dipping away at 
 a small angle from the underlying mass. The surround- 
 ing lofty mountains appear to be entirely comj)osed 
 of the porphyritic conglomerate, and I estimated its 
 thickness here at between 6,000 and 7,000 feet. 
 1 ' Eeise urn Erde,' Tli. 1. sp. 338, 341. 
 
CHAP. XIV. Section by the Portillo Pass. 485 
 
 Beyond the junction of tlie Yeso and Volcan, ttie 
 porpiiyritic strata appear to dip towards tbe hillocks of 
 andesite at an angle of 40° ; but at some distant points 
 on the same ridge they are bent up and vertical. 
 Following the valley of the Yeso, trending ISTE. (and 
 therefore still unfavourable for our transverse section), 
 the same porphyritic conglomerate formation is pro- 
 longed to near the Cuestadel Indio, situated at the 
 western end of the basin (like a drained lake) of Yeso. 
 Some way before arriving at this point, distant lofty 
 pinnacles capped by coloured strata belonging to the 
 great gypseous formation could first be seen. From 
 the summit of the Cuesta, looking southward, there is 
 a magnificent sectional view of a mountain -mass, at 
 least 2,000 feet in thickness [E], of fine andesitic 
 granite (containing much black mica, a little chlorite 
 and quartz), which sends great white dikes far into the 
 superincumbent, dark-coloured, porphyritic conglome- 
 rates. At the line of junction the two formations are 
 wonderfully interlaced together : in the lower part of 
 the porphyritic conglomerate, the stratification has 
 been quite obliterated, whilst in the upper part it is 
 very distinct, the beds composing the crests of the 
 surrounding mountains being inclined at angles of 
 between 70° and 80°, and some being even vertical. 
 On the northern side of the valley, there is a great 
 corresponding mass of andesitic granite, which is 
 encased by porphyritic conglomerate, dipping both 
 on the western and eastern sides, at about 80° to west, 
 but on the eastern side with the tips of the strata bent 
 in such a manner, as to render it probable that the 
 whole mass had been on that side thrown over and 
 inverted. 
 
 In the valley-basin of the Yeso, which I estimated 
 at 7,000 feet above the level of the sea, we first reach 
 
486 Section by the Portillo Pass. paet h. 
 
 at [F] the gypseous formation. Its thickness is very 
 great. It consists in most parts of snow-white, hard, 
 compact gypsum, which breaks with a saccharine frac- 
 ture, having translucent edges ; under the blowpipe 
 gives out much vapour; it frequently includes nests- 
 and exceedingly thin layers of crystallised, blackish 
 carbonate of lime. Large, irregularly shaped concre- 
 tions (externally still exhibiting lines of aqueous 
 deposition) of blackish-gray, but sometimes white, 
 coarsely and brilliantly crystallised, hard anhydrite, 
 abound within the common gypsum. Hillocks, formed 
 of the hardest and purest varieties of the white gypsum, 
 stand up above the surrounding parts, and have their 
 surfaces cracked and marked, just like newly baked 
 bread. There is much pale brown, soft, argillaceous 
 gypsum ; and there were some intercalated green beds 
 which I had not time to reach. I saw only one frag- 
 ment of selenite or transparent gypsum, and that 
 perhaps may have come from some subsequently formed 
 vein. From the miner alogical characters here given, 
 it is probable that these gypseous beds have undergone 
 some metamorphic action. The strata are much hidden 
 by detritus, but they appeared in most parts to be 
 highly inclined ; and in an adjoining lofty pinnacle they 
 could be distinctly seen bending up, and becoming 
 vertical, conformably with the underlying porphyritic 
 conglomerate. In very many parts of the great moun- 
 tain-face [F], composed of thin gypseous beds, there 
 were innumerable masses, irregularly shaped and not 
 like dikes, yet with well-defined edges, of an imperfectly 
 granular, pale greenish or yellowish- white rock, essen- 
 tially composed of feldspar, with a little chlorite or 
 hornblende, epidote, iron-pyrites, and ferruginous pow- 
 der : I believe that these curious trappean masses have 
 been injected from the not far distant mountain-mass 
 
CHAP. xiT. Gypseous Formation. 487 
 
 [E] of andesite whilst still fluid, and that owing to the 
 softness of the gypseous strata they have not acquired 
 the ordinary forms of dikes. Subsequently to the 
 injection of these feldspathic rocks, a great dislocation 
 has taken place ; and the much shattered gypseous 
 strata here overlie a hillock [G], composed of vertical 
 strata of impure limestone and of black highly calcare- 
 ous shale including threads of gypsum : these rocks, as 
 we shall presently see, belong to the upper parts of the 
 gypseous series, and hence must here have been thrown 
 down by a vast fault. 
 
 Proceeding up the valley-basin of the Yeso, and 
 taking our section sometimes on one hand and some- 
 times on the other, we come to a great hill of stratified 
 porphyritic conglomerate [H] dipping at 45° to the 
 west ; and a few hundred yards farther on, we have a 
 bed between 300 or 400 feet thick of gypsum [I] dip- 
 ping eastward at a very high angle : here then we have 
 a fault and anticlinal axis. On the opposite side of 
 the valley, a vertical mass of red conglomerate, con- 
 formably underlying the gypsum, appears gradually to 
 lose its stratification and passes into a mountain of 
 porphyry. The gypsum [I] is covered by a bed [K], 
 at least 1,000 feet in thickness, of a purplish-red, 
 compact, heavy, fine-grained sandstone or mudstone, 
 which fuses easily into a white enamel, and is seen 
 under a lens to contain triturated crystals. This is 
 succeeded by a bed [L], 1,000 feet thick (I believe I 
 understate the thickness) of gypsum, exactly like the 
 beds before described ; and this again is capped by 
 another great bed [M] of purplish-red sandstone. All 
 these strata dip eastward ; but the inclination becomes 
 less and less, as we leave the first and almost vertical 
 bed [I] of gypsum. 
 
 Leaving the basin-plain of Yeso, the road rapidly 
 
488 Section by the For til to Pass. part h. 
 
 ascends, passing by mountains com^oosed of the gypseous 
 and associated beds, with their stratification greatly 
 disturbed and therefore not easily intelligible : hence 
 this part of the section has been left uncoloured. 
 Shortly before reaching the great Peuquenes ridge, the 
 lowest stratum visible [N] is a red sandstone or mud- 
 stone, capped by a vast thickness of black, compact, 
 calcareous, shaly rock [0], which has been thrown 
 into four lofty, though small ridges : looking northward, 
 the strata in these ridges are seen gradually to rise in 
 inclination, becoming in some distant pinnacles abso- 
 lutely vertical. 
 
 The ridge of Peuquenes, which divides the waters 
 flowing into the Pacific and Atlantic Oceans, extends in 
 a nearly NNW. and SSE. line ; its strata dip eastward 
 at an angle of between 30° and 45°, but in the higher 
 peaks bending up and becoming almost vertical. Where 
 the road crosses this range, the height is 13,210 feet 
 above the sea-level, and I estimated the neighbouring 
 pinnacles at from 14,000 to 15,000 feet. The lowest 
 stratum visible in this ridge is a red stratified sandstone 
 [P] ; on it are superimposed two great masses [Q and 
 S] of black, hard, compact, even having a conch oidal 
 fracture, calcareous, more or less laminated shale, pass- 
 ing into limestone : this rock contains organic remains, 
 presently to be enumerated. The compacter varieties 
 fuse easily in a white glass ; and this I may add is a 
 very general character with all the sedimentary beds in 
 the Cordillera : although this rock when broken is 
 generally quite black, it everywhere weathers into an 
 ash-gray tint. Between these two great masses [Q and 
 S], a bed [E] of gypsum is interposed, about 300 feet 
 in thickness, and having the same characters as hereto- 
 fore described. 1 estimated the total thickness of these 
 three beds [Q, P, S] at nearly 3,000 feet ; and to this 
 
CHAP. xiT. Gypseotis Formation. 489 
 
 must be added, as will be immediately seen, a great 
 overlying mass of red sandstone. 
 
 In descending the eastern slope of this great central 
 range, the strata, which in the upper part dip eastward 
 at about an angle of 40°, become more and more cm-ved, 
 till they are nearly vertical; and a little farther onwards 
 there is seen on the farther side of a ravine, a thick 
 mass of strata of bright red sandstone [T], with their 
 upper extremities slightly curved, showing that they 
 were once conformably prolonged over the beds [S] : 
 on the southern and opposite side of the road, this red 
 sandstone and the underlying black shaly rocks stand 
 vertical, and in actual juxtaposition. Continuing to 
 descend, we come to .a synclinal valley filled with 
 rubbish, beyond which we have the red sandstone [T 2] 
 corresponding with [T], and now dipping, as is seen 
 both north and south of the road, at 45° to the west ; 
 and under it, the beds [S ^, R 2, Q ^, and I believe P 2] 
 in corresponding order and of similar composition, with 
 those on the western flank of the Peuquenes range, but 
 dipping westward. Close to the synclinal valley the 
 dip of these strata is 45°, but at the eastern or farther 
 end of the series it increases to 60°. Here the great 
 gypseous formation abruptly terminates, and is suc- 
 ceeded eastward by a pile of more modern strata. 
 Considering how violently these central ranges have 
 been dislocated, and how very numerous dikes are in 
 the exterior and lower parts of the Cordillera, it is 
 remarkable that I did not here notice a single dike. 
 The prevailing rock in this neighbourhood is the black, 
 calcareous, compact shale, whilst in the valley-basin of 
 the Yeso the purplish-red sandstone or mudstone pre- 
 dominates, — both being associated with gypseous strata 
 of exactly the same nature. It would be very difficult 
 to ascertain the relative superposition of these several 
 
490 Section by the PoiHillo Pass. paet h. 
 
 masses, for we shall afterwards see in the Cuinbre Pass 
 that the gypseous and intercalated beds are lens-shaped, 
 and that they thin out, even where very thick, and 
 disappear in short horizontal distances : it is quite 
 possible that the black shales and red sandstones may 
 be contemporaneous, but it is more probable that the 
 former compose the uppermost parts of the series. 
 
 The fossils above alluded to in the black calcareous 
 shales are few in number, and are in an imperfect 
 condition ; they consist, as named for me by M. d'Or- 
 bigny, of— 
 
 1. Ammonite, indeterminable, near to A. recticostattis, D'Orbig. 
 
 'Pal. Franc' (Neocomian formation". 
 
 2. Gryphsea, near to G. Couloni (Neocomian formations of France 
 
 and Neufchatel). 
 
 3. Natica, indeterminable. 
 
 4. Cyprinarostrata, D'Orbig. 'Pal. Franc' (Neocomian formation). 
 
 5. Eostellaria angulosa(?) D'Orbig. 'Pal. de I'Amer. Mer.'|g 
 
 6. Terebratula ? 
 
 Some of the fragments of Ammonites were as thick 
 as a man's arm : the Gryphgea is much the most 
 abundant shell. These fossils M. d'Orbigny considers 
 as belonging to the Neocomian stage of the Cretaceous 
 system. Dr. Meyen,^ who ascended the valley of the 
 Rio Yolcan, a branch of the Yeso, found a nearly 
 similar, but ap^Darently more calcareous formation, with 
 much gypsum, and no doubt the equivalent of that 
 here described : the beds were vertical, and were pro- 
 longed up to the limits of perpetual snow : at the height 
 of 9,000 feet above the sea, they abounded with fossils, 
 consisting, according to Von Buch,^ of — 
 
 1. Exogyra (Gryphsea) Couloni, absolutely identical witb specimens 
 
 from the Jura and South of France. 
 
 2. Trigonia costata, 1 identical with those found in the upper 
 
 3. Pecten striatus, J Jurassic beds at Hildesheim. 
 
 1 ' Keise urn Erde,' Th. 1. s. 355. 
 
 ^ ' Descript. Phys. des lies Canaries,' p. 471. 
 
CHAP. xiY. Neocomimi Fossils. 491 
 
 4. Cucullgea, corresponding in form to C. longirostris, so frequent 
 
 in the upper Jurassic beds of Westphalia. 
 
 5. Ammonites, resembling A. M^ylex. 
 
 Von Buch. concludes that this formation is intermediate 
 between the limestone of the Jura and the chalk, and 
 that it is analogous with the uppermost Jurassic beds 
 forming the plains of Switzerland. Hence M. d'Orbigny 
 and Yon Buch, under different terms, compare these 
 fossils to those from the same late stage in the Secondary 
 formations of Europe. 
 
 Some of the fossils which I collected were found a 
 good way down the western slope of the main ridge, 
 and hence must originally have been covered up by a 
 great thickness of the black slialy rock, independently 
 of the now denuded, thick, overlying masses of red 
 sandstone. I neglected at the time to estimate how 
 many hundred or rather thousand feet thick the 
 superincumbent strata must have been : and I will 
 not now attempt to do so. This, however, would have 
 been a highly interesting point, as indicative of a great 
 amount of subsidence, of which we shall hereafter find 
 in other parts of the Cordillera analogous evidence 
 during this same period. The altitude of the Peu- 
 quenes range, considering its not great antiquity, is 
 very remarkable ; many of the fossils were embedded at 
 the height of 13,210 feet, and the same beds are pro- 
 longed up to at least from 14,000 to 15,000 above the 
 level of the sea. 
 
 The Portillo or JEastern Chain. — The valley of 
 Tenuyan, separating the Peuquenes and Portillo lines, 
 is, as estimated by Dr. Gillies and myself, about twenty 
 miles in width ; the lowest part, where the road crosses 
 the river, being 7,500 feet above the sea-level. The 
 pass on the Portillo line is 14,365 feet high (1,100 feet 
 higher than that on the Peuquenes), and the neigh- 
 
492 Section of the Portillo Chain, paet n. 
 
 bom-ing pinnacles must, I conceive, rise to nearly 16,000 
 feet above tlie sea. The river draining the intermediate 
 valley of Tenuyan, passes through the Portillo line. 
 To return to our section : — shortly after leaving the 
 lower beds [P 2] of the gypseous formation, we come to 
 grand masses of a coarse, red conglomerate [V], totally 
 unlike any strata hitherto seen in the Cordillera. This 
 conglomerate is distinctly stratified, some of the beds 
 being well defined by the greater size of the pebbles : the 
 cement is calcareous and sometimes crystalline, though 
 the mass shows no signs of having been metamorphosed. 
 The included pebbles are either perfectly or only par- 
 tially rounded : they consist of purplish sandstones, of 
 various porphyries, of brownish limestone, of black 
 calcareous, compact shale precisely like that in situ in 
 the Peuquenes range, and containing some of the same 
 fossil shells ; also very many pebbles of quartz, some of 
 micaceous schist, and numerous, broken, rounded crys- 
 tals of a reddish orthitic or potash feldspar (as deter- 
 mined by Professor Miller), and these from their size 
 must have been derived from a coarse-grained rock, 
 probably granite. From this feldspar being orthitic, 
 and even from its external appearance, I venture posi- 
 tively to affirm that it has not been derived from the 
 rocks of the western ranges ; but, on the other hand, 
 it may well have come, together with the quartz and 
 metamorphic schists, from the eastern or Portillo line, 
 for this line mainly consists of coarse orthitic granite. 
 The pebbles of the fossiliferous slate and of the purple 
 sandstone, certainly have been dei'ived from the Peu- 
 quenes or western ranges. 
 
 The road crosses the valley of Tenuyan in a nearly 
 east and west line, and for several miles we have on 
 both hands the conglomerate, everywhere dipping west 
 and forming separate great mountains. The strata, 
 
CHAP. XIV. Section of the Portillo Chain. 491^ 
 
 where first met with, after leaving the gypseous forma- 
 tion, are inclined westward at an angle of only 20° 
 which farther on increases to about 45°. The gypseous 
 strata, as we have seen, are also inclined westward : 
 hence, when looking from the eastern side of the valley 
 towards the Peuquenes range, a most deceptive appear- 
 ance is presented, as if the newer beds of conglomerate 
 dipped directly under the much older beds of the 
 gypseous formation. In the middle of the valley, a 
 bold mountain of unstratified lilac-coloured porphyry 
 (with crystals of hornblende) projects ; and farther on, 
 a little south of the road, there is another mountain, 
 with its strata inclined at a small angle eastwards, which 
 in its general aspect and colour, resembles the porphy- 
 ritic conglomerate formation, so rare on this side of the 
 Peuquenes line and so grandly developed throughout 
 the western ranges. 
 
 The conglomerate is of great thickness : I do not 
 suppose that the strata forming the separate mountain- 
 masses [V, V, V] have ever been prolonged over each 
 other, but that one mass has been broken up by several, 
 distinct, parallel, uniclinal lines of elevation. Judging 
 therefore of the thickness of the conglomerate, as seen 
 in the separate mountain-masses, I estimated it at least 
 from 1,500 to 2,000 feet. The lower beds rest con- 
 formably on some singularly coloured, soft strata [W], 
 which I could not reach to examine ; and these again 
 rest comformably on a thick mass of micaceous, thinly 
 laminated, siliceous sandstone [X], associated with a 
 little black clay-slate. These lower beds are traversed 
 by several dikes of decomposing porphyry. The lami- 
 nated sandstone is directly superimposed on the vast 
 masses of granite [Y, Y] which mainly compose the 
 Portillo range. The line of junction between this 
 latter rock, which is of a bright red colour, and the 
 
494 Section of the Portillo Chain. paet h. 
 
 whitish sandstone was beautifully distinct; the sand- 
 stone being penetrated by numerous, great, tortuous 
 dikes branching from the granite, and having been 
 converted into a granular quartz rock (singularly like 
 that of the Falkland Islands), containing specks of an 
 ochery powder, and black crystalline atoms, apparently 
 of imperfect mica. The quartzose strata in one spot 
 were folded into a regular dome. 
 
 The granite which composes the magnificent bare 
 pinnacles and the steep western flank of the Portillo 
 chain, is of a brick-red colour, coarsely crystallized, and 
 composed of orthitic or potash feldspar, quartz, and im- 
 perfect mica in small quantity, sometimes passing into 
 chlorite. These minerals occasionally assume a laminar 
 or foliated arrangement. The fact of the feldspar being 
 orithic in this range, is very remarkable, considering 
 how rare, or rather, as I believe, entirely absent, this 
 mineral is throughout the western ranges, in which 
 soda-feldspar, or at least a variety cleaving like albite, 
 is so extremely abundant. In one spot on the western 
 flank, and on the eastern flank near Los Manantiales 
 and near the crest, I noticed some great masses of a 
 whitish granite, parts of it fine-grained, and parts con- 
 taining large crystals of feldspar ; I neglected to collect 
 specimens, so I do not know whether this feldspar is 
 also orthitic, though I am inclined to think so from its 
 general appearance. I saw also some syenite and one 
 mass which resembled andesite, but of which I likewise 
 neglected to collect specimens. From the manner in 
 which the whitish granites formed separate irountain- 
 masses in the midst of the brick-red variety, and from 
 one such mass near the crest being traversed by nume- 
 rous veins of flesh-coloured and greenish earite (into 
 which I occasionally observed the brick-red granite 
 insensibly passing), I conclude that the white granites 
 
CHAP. xiY. Section of the Portillo Chain. 495 
 
 probably belong to an older formation, almost over- 
 ivlielmed and penetrated by the red granite. 
 
 On tbe crest I saw also, at a short distance, some 
 coloured stratified beds, apparently like those [W] at 
 the western base, but was prevented examining them 
 by a snow-storm : Mr. Caldcleugh,^ however, collected 
 here specimens of ribboned jas]3er, raagnesian lime- 
 •stone, and other minerals. A little way down the 
 eastern slope a few fragments of quartz and mica-slate 
 are met with ; but the great formation of this latter 
 rock [Z], which covers up much of the eastern flank 
 and base of the Portillo range, cannot be conveniently 
 examined until much lower down at a place called Mai 
 Paso. The mica-schist here consists of thick layers 
 of quartz, with intervening folia of finely-scaly mica, 
 often passing into a substance like black glossy clay- 
 slate : in one spot, the layers of quartz having disap- 
 peared, the whole mass became converted into glossv 
 €lay-slate. Where the folia were best defined, they 
 were inclined at a high angle westward, that is, towards 
 the range. The line of junction between the dark 
 mica-slate and the coarse red granite was most clearly 
 distinguishable from a vast distance : the granite sent 
 many small veins into the mica-slate, and included 
 some angular fragments of it. As the sandstone on the 
 western base has been converted by the red granite into 
 a granular quartz-rock, so this great formation of mica- 
 schist may possibly have been metamorphosed at the 
 same time and by the same means; but I think it 
 more probable, considering its more perfect metamor- 
 phic character and its well-pronounced foliation, that it 
 belongs to an anterior epoch, connected with the white 
 granites : I am the more inclined to this view, from 
 having found at the foot of the range the mica-schist 
 ' 'Travels,' &c., vol. p. 308. 
 
49^ Section of the Portillo Chain. paet n. 
 
 surrounding a hummock [Y 2], exclusively composed of 
 wliite granite. Near Los Arenales, tlie mountains on 
 all sides are composed of tlie mica-slate ; and looking 
 backwards from this point up to the bare gigantic 
 peaks above, the view was eminently interesting. The 
 colours of the red granite and the black mica-slate are 
 so distinct, that with a bright light these rocks could 
 be readily distinguished even from the Pampas, at a 
 level of at least 9,000 feet below. The red granite, 
 from being divided by parallel joints, has weathered 
 into sharp pinnacles, on some of which, even on some 
 of the loftiest, little caps of mica-schist could be clearly 
 seen : here and there isolated patches of this rock 
 adhered to the mountain-flanks, and these often corre- 
 sponded in height and position on the opposite sides of 
 the immense valleys. Lower down the schist prevailed 
 more and more, with only a few quite small points of 
 granite projecting through. Looking at the entire 
 eastern face of the Portillo range, the red colour far 
 exceeds in area the black ; yet it was scarcely possible 
 to doubt that the granite had once been almost wholly 
 encased by the mica-schist. 
 
 At Los Arenales, low down on the eastern flank, the 
 mica-slate is traversed by several closely adjoining, 
 broad dikes, parallel to each other and to the foliation 
 of the schist. The dikes are formed of three different 
 varieties of rock, of which a pale brown feldspathic 
 porphyry with grains of quartz was much the most 
 abundant. These dikes with their granules of quartz, 
 as well as the mica-schist itself, strikingly resemble the 
 rocks of the Ohonos Archipelago. At a height of about 
 1,200 feet above the dikes, and perhaps connected with 
 them, there is a range of cliffs formed of successive 
 lava-streams [AA], between 300 and 400 feet in thick- 
 ness, and in places finely columnar, The lava consists 
 
CHAP. XIV, Section of the Portillo Chain. 497 
 
 of dark-grayisli, liarsli rocks, intermediate in character 
 between trachyte and basalt, containing glassy feldspar, 
 olivine, and a little mica, and sometimes amygdaloidal 
 with zeolite : the basis is either quite compact, or crenu- 
 lated with air-vesicles arranged in laminae. The 
 streams are separated from each other by beds of frag- 
 mentary brown scoriae, firmly cemented together, and 
 including a few well-rounded pebbles of lava. From 
 their general appearance, I suspect that these lava- 
 streams flowed at an ancient period under the pressure 
 of the sea, when the Atlantic covered the Pampas and 
 washed the eastern foot of the Cordillera.^ On the 
 opposite and northern side of the valley there is another 
 line of lava-cliffs at a corresponding height ; the valley 
 between being of considerable breadth, and as nearly as 
 I could estimate 1,500 feet in depth. This field of 
 lava is confined on both sides by the mountains of 
 mica-schist, and slopes down rapidly but irregularly to 
 the edge of the Pampas, where, having a thickness of 
 about 200 feet, it terminates against a little range of 
 clay-stone porphyry. The valley in this lower part 
 expands into a bay-like, gentle slope, bordered by the 
 cliffs of lava, which must certainly once have extended 
 across this wide expanse. The inclination of the 
 streams from Los Arenales to the mouth of the valley is 
 so great, that at the time (though ignorant of M. Elie 
 de Beaumont's researches on the extremely small slope 
 over which lava can flow, and yet retain a compact 
 structure and considerable thickness) I concluded that 
 they must subsequently to their flowing have been 
 
 ^ This conclusion mig-lit, perhaps, even have been anticipated, 
 from the general rarity of volcanic action, except near the sea or 
 large bodies of water. Comformably with this rule, at the present 
 day, there are no active volcanos on this eastern side of the Cordillera ; 
 nor are severe earthquakes experienced here. 
 
 K K 
 
49^ Section of the Portillo Chain, part n. 
 
 upheaved and tilted from the mountaiDS : of this con- 
 clusion I can now entertain not the smallest doubt. 
 
 At the mouth of the valley, within the cliffs of the 
 above lava-field, there are remnants, in the form of 
 separate small hillocks and of lines of low cliffs, of a 
 considerable deposit of compact white tuff (quarried for 
 filtering-stones), composed of broken pumice, volcanic 
 crystals, scales of mica, and fragments of lava. This 
 mass has suffered much denudation, and the hard mica- 
 schist has been deeply worn, since the period of its 
 deposition ; and this period must have been subsequent 
 to the denudation of the basaltic lava-streams, as at- 
 tested by their encircling cliffs standing at a higher 
 level. At the present day, under the existing arid 
 climate, ages might roll past without a square yard of 
 rock of any kind being denuded, except perhaps in the 
 rarely moistened drainage-channel of the valley. Must 
 we then look back to that ancient period, when the 
 waves of the sea beat against the eastern foot of the 
 Cordillera, for a power sufiicient to denude extensively, 
 though superficially, this tufaceous deposit, soft al- 
 though it be ? 
 
 There remains only to mention some little water- 
 worn hillocks [B B], a few hundred feet in height, and 
 mere mole-hills compared with the gigantic mountains 
 behind them, which rise out of the sloping, shingle- 
 covered margin of the Pampas. The first little range 
 is composed of a brecciated purple porphyritic clay- 
 stone, with obscurely marked strata dipping at 70° to 
 the SW. ; the other ranges consist of — a pale-coloured 
 feldspathic porphyry, — a purple clay-stone porphyry 
 with grains of quartz, — and a rock almost exclusively 
 comj)Osed of brick-red crystals- of feldspar. These 
 outermost small lines of elevation extend in a NW. by 
 W. and SE. by S. direction. 
 
CHAP. xiT. The Portillo Range. 499 
 
 Concluding Remarlis on the Portillo Range. — When 
 on tlie Pampas and looking southward, and whilst travel- 
 ling northward, I could see for very many leagues the 
 red granite and dark mica- schist forming the crest and 
 eastern flank of the Portillo line. This great range, 
 according to Dr. Gillies, can be traced with little inter- 
 ruption for 140 miles southward to the P. Diamante, 
 where it unites with the western ranges : northward, 
 according to this same author, it terminates where the 
 R. Mendoza debouches from the mountains ; but a 
 little farther north in the eastern part of the Cumbre 
 section, there are, as we shall hereafter see, some 
 mouu tain-masses of a brick-red porphyry, the last in- 
 jected amidst many other porphyries, and having so 
 close an analogy with the coarse red granite of the Por- 
 tillo line, that I am tempted to believe that they belong 
 to the same axis of injection ; if so, the Portillo line is 
 at least 200 miles in leng-th. Its height, even in the 
 lowest gap on the road, is 14,365 feet, and some of the 
 pinnacles apparently attain an elevation of about 
 16,000 feet above the sea. The geological history of 
 this grand chain appears to me eminently interesting. 
 We may safely conclude, that at a former period the 
 valley of Tenuyan existed as an arm of the sea, about 
 twenty miles in width, bordered on one hand by a ridge 
 or chain of islets of the black calcareous shales and 
 purple sandstones of the Gypseous formation ; and on 
 the other hand, by a ridge or chain of islets composed 
 of mica-slate, white granite, and perhaps to a partial 
 extent of red granite. These two chains, whilst thus 
 bordering the old sea-channel, must have been exposed 
 for a vast lapse of time to alluvial and littoral action, 
 during which the rocks were shattered, the fragments 
 rounded, and the strata of conglomerate accumulated 
 to a thickness of at least 1,500 or 2,000 feet. The 
 
 K K 2 
 
500 Conchtding Remarks on part h. 
 
 red ortliitic granite now forms, as we have seen, tlie 
 main part of tlie Portillo cliain : it is injected in dikes 
 not only into the mica- schist and white granites, but 
 into the laminated sandstone, which it has metamor- 
 phosed, and which it has thrown off, together with the 
 conformably overlying coloured beds and stratified 
 conglomerate, at an angle of forty-five degrees. To 
 have thrown off so vast a pile of strata at this angle, 
 is a proof that the main part of the red granite 
 (whether or not portions, as perhaps is probable, 
 previously existed) was injected in a liquified state after 
 the accumulation both of the laminated sandstone and 
 of the conglomerate ; this conglomerate, we know, was 
 accumulated, not only after the deposition of the fos- 
 siliferous strata of the Peuquenes line, but after their 
 elevation and long-continued denudation : and these 
 fossiliferous strata belong to the early part of the 
 Cretaceous system. Late, therefore, in a geological 
 sense, as must be the age of the main part of the red 
 granite, I can conceive nothing more impressive than 
 the eastern view of this great range, as forcing the mind 
 to grapple with the idea of the thousands of thousands 
 of years requisite for the denudation of the strata 
 which originally encased it, — for that the fluidified 
 granite was once encased, its mineralogical composition 
 and structure, and the bold conical shape of the moun- 
 tain-masses, yield sufficient evidence. Of the encasing 
 strata we see the last vestiges in the coloured beds on 
 the crest, in the little caps of mica- schist on some of 
 the loftiest pinnacles, and in the isolated patches of this 
 same rock at corresponding heights on the now bare and 
 steep flanks. 
 
 The lava-streams at the eastern foot of the Portillo 
 are interesting, not so much from the great denudation 
 which they have suffered at a comparatively late period 
 
CHAP. xiY. the Portillo Range. 501 
 
 as from tke evidence they afford by their inclination 
 taken conjointly with their thickness and compactness, 
 that after the great range had assnmed its present 
 general outline, it continued to rise as an axis of eleva- 
 tion. The plains extending from the base of the 
 Cordillera to the Atlantic show that the continent has 
 been upraised in mass to a height of 3,500 feet, and 
 probably to a much greater height, for the smooth 
 shingle-covered margin of the Pampas is prolonged in a 
 gentle unbroken slope far up many of the great valleys. 
 Nor let it be assumed that the Peuquenes and Portillo 
 ranges have undergone only movements of elevation ; 
 for we shall hereafter see, that the bottom of the sea 
 subsided several thousand feet during the deposition of 
 strata, occupying the same relative place in the Cor- 
 dillera, with those of the Peuquenes ridge ; moreover, 
 we shall see from the unequivocal evidence of buried 
 upright trees, that at a somewhat later period, during 
 the formation of the Uspallata chain, which corresponds 
 geographically with that of the Portillo, there was 
 another subsidence of many thousand feet : here, in- 
 deed, in the valley of Tenuyan, the accumulation of the 
 coarse stratified conglomerate to a thickness of 1,500 
 or 2,000 feet, offers strong presumptive evidence of 
 subsidence ; for all existing analogies lead to the belief 
 that large pebbles can be transported only in shallow 
 water, liable to be affected by currents and movements 
 of undulation — and if so, the shallow bed of the sea on 
 which the pebbles were first deposited must necessarily 
 have sunk to allow of the accumulation of the super- 
 incumbent strata. What a history of changes of level, 
 and of wear and tear, all since the age of the latter 
 Secondary formations of Europe, does the structure of 
 this one great mountain-chain reveal ! 
 
502 Section by the Ctunbre Pass, paet n. 
 
 Passage of the Andes hy the Ciimhre or IJsiJallata 
 
 Pass. 
 
 This Pass crosses tlie Andes about sixty miles nortli 
 of that just described : the section given in Plate I. 
 fig. 2, is on the same scale as before, namely, at one- 
 third of an inch to a mile in distance, and one inch to 
 a mile (or 6,000 feet) in height. Like the last section, it 
 is a mere sketch, and cannot pretend to accuracy, though 
 made under favourable circumstances. We will com- 
 mence as before, with the western half, of which the 
 main range bears the name of the Cumbre (that is the 
 Ridge), and corresponds to the Peuquenes line in the 
 former section ; as does the Uspallata range, though on 
 a much smaller scale, to that of the Portillo. Near the 
 point where the river Aconcagua debouches on the basin 
 plain of the same name, at a height of about 2,300 feet 
 above the sea, we meet with the usual purple and 
 greenish porphyritic clay-stone conglomerate. Beds of 
 this nature, alternating with numerous compact and 
 amygdaloidal porphyries, which have flowed as sub- 
 marine lavas, and associated with great mountain- 
 masses of various, injected, non-stratified porphyries, 
 are prolonged the whole distance up to the Cumbre or 
 central ridge. One of the commonest stratified por- 
 phyries is of a green colour, highly amygdaloidal with 
 the various minerals described in the preliminary dis- 
 cussion, and including fine tabular crystals of albite. 
 The mountain-range north (often with a little westing) 
 and south. The stratification, wherever I could clearly 
 distinguish it, was inclined westward or towards the 
 Pacific, and, except near the Cumbre, seldom at angles 
 above 25°. Only at one spot on this western side, on a 
 lofty pinnacle not far from the Cumbre, I saw strata 
 apparently belonging to the Gypseous formation, and 
 
CHAP. xiY. Section by the Ctmibre Pass. 503 
 
 conformably capping a pile of stratified porphyries. 
 Hence, both in composition and in stratification, the 
 structure of the mountains on this western side of 
 the divortiium cuiuarimi^ is far more simple than in the 
 corresponding part of the Peuquenes section. In the 
 porphyritic clay-stone conglomerate, the mechanical 
 structure and the planes of stratification have generally 
 been much obscured and even quite obliterated towards 
 the base of the series, whilst in the upper parts, near 
 the summits of the mountains, both are distinctly dis- 
 played. In these upper portions the porphyries are 
 generally lighter coloured. In three places [X, Y, Z] 
 masses of andesite are exposed : at [Y], this rock con- 
 tained some quartz, but the greater part consisted of 
 andesitic porphyry, with only a few well-developed crys- 
 tals of albite, and forming a great white mass, having 
 the external aspect of granite, capped by much dark 
 unstratified porphyry. In many parts of the moun- 
 tains, there are dikes of a green colour, and other white 
 ones, which latter probably spring from underlying 
 masses of andesite. 
 
 The Cumbre, where the road crosses it, is, according 
 to Mr. Pentland, 12,454 feet above the sea ; and the 
 neighbouring peaks, composed of dark purple and 
 whitish porphyries, some obscurely stratified with a 
 westerly dip, and others without a trace of stratification, 
 must exceed 13,000 feet in height. Descending the 
 eastern slope of the Cumbre, the structure becomes very 
 complicated, and generally difiers on the two sides of 
 the east and west line of road and section. First we 
 come to a great mass [A] of nearly vertical, singularly 
 contorted strata, composed of highly compact red sand- 
 stones, and of often calcareous conglomerates, and pene- 
 trated by green, yellow, and reddish dikes ; but I shall 
 presently have an opportunity of describing in some 
 
504 Section by the Ctwibre Pass, pakt ii, 
 
 detail an analogous pile of strata. These vertical beds 
 are abruptly succeeded by others [B], of apparently 
 nearly the same nature but more metamorphosed, alter- 
 nating with porphyries and limestones ; these dip for a 
 short space westward, but there has been here an extra- 
 ordinary dislocation, which, on the north side of the 
 road, appears to have determined the excavation of the 
 north and south valley of the R. de las Cuevas. On 
 this northern side of the road, the strata [B] are pro- 
 longed till they come in close contact with a jagged 
 lofty mountain [D] of dark-coloured, unstratified, in- 
 trusive porphyry, where the beds have been more highly 
 inclined and still more metamorphosed. This moun- 
 tain of porphyry seems to form a short axis,of elevation, 
 for south of the road in its line, there is a hill [C] 
 of porphyritic conglomerate with absolutely vertical 
 strata. 
 
 We now come to the Gypseous formation : I will 
 first describe the structure of the several mountains, and 
 then give in one section a detailed account of the nature 
 of the rocks. On the north side of the road, which here 
 runs in an east and west valle}^, the mountain of por- 
 phyry [D] is succeeded by a hill [E] formed of the 
 upper gypseous strata tilted, at an angle of between 
 70° and 80° to the west, by an uniclinal axis of elevation 
 which does not run parallel to the other neighbouring 
 ranges, and which is of short length ; for on the south 
 side of the valley its prolongation is marked only by a 
 small flexure in a pile of strata inclined by a quite 
 separate axis. A little farther on the north and south 
 valley of Horcones enters at right angles our line of 
 section; its western side is bounded by a hill of 
 gypseous strata [F], dipping westward at about 45°, 
 and its eastern side by a mountain of similar strata 
 [G] inclined westward at 70°, and superimposed by an 
 
CHAP. XIV. Gypseous Formation. 505 
 
 oblique fault on anotlier mass of the same strata [H], 
 also inclined westward, but at an angle of only about 
 30° : tbe complicated relation of tliese three masses 
 [F, G, H] is explained by the structure of a great 
 mountain-range lying some way to the north, in which 
 a regular anticlinal axis (represented in the section by 
 dotted lines) is seen, with the strata on its eastern side 
 again bending up and forming a distinct uniclinal axis, 
 of which the beds marked [H] form the lower part. 
 This great uniclinal line is intersected, near the Puente 
 del Inca, by the valley along which the road runs, and 
 the strata composing it will be immediately described. 
 On the south side of the road, in the space correspond- 
 ing with the mountains [E, F and G], the strata every- 
 where dip westward generally at an angle of 30°, occa- 
 sionally mounting up to 45°, but not in an unbroken 
 line, for there are several vertical faults, forming 
 separate uniclinal masses, all dipping in the same 
 direction, — a form of elevation common in the Cordil- 
 lera. We thus see that within a narrow space, the 
 gypseous strata have been upheaved and crushed to- 
 gether by a great uniclinal, anticlinal, and one lesser 
 uniclinal line [E] of elevation ; and that between these 
 three lines and the Cumbre, in the sandstones, con- 
 glomerates and porphyritic formation, there have been 
 at least two or three other great elevatory axes. 
 
 The uniclinal axis [I] intersected near the Puente 
 del Inca ^ (of which the strata at [H] form a part) 
 
 ^ At this place, there are some hot and cold springs, the warmest 
 having- a temperature, according to Lieut. Brand (' Travels,' jd. 240), 
 of 91° ; they emit much gas. According to Mr. Brande, of the Eoyal 
 Institution, ten cubical inches contain forty-five grains of solid 
 matter, consisting chiefly of salt, gypsum, carbonate of lime, and 
 oxide of iron, The water is charged with carbonic acid and 
 sulphuretted hydrogen. These springs deposit much tufa in the 
 form of spherical balls. They burst forth, as do those of Cauquenes, 
 and probably those of Villa Vicencio, on a line of elevation. 
 
5o6 Section by the Cumbre Pass, pakt ii. 
 
 ranges N. by W. and S. by E., forming a chain of 
 mountains, apparently little inferior in height to the 
 Cumbre : the strata, as we have seen, dip at an average 
 angle of 30° to the west. The flanks of the mountains 
 are here quite bare and steep, affording an excellent 
 section ; so that I was able to inspect the strata to a 
 thickness of about 4,000 feet, and could clearly dis- 
 tinguish their general nature for 1,000 feet higher, 
 making a total thickness of 5,000 feet, to which must 
 be added about 1,000 feet of the inferior strata seen a 
 little lower down the valley. I will describe this one 
 section in detail, beginning at the bottom. 
 
 1st. The lowest mass is the altered clay-slate de- 
 scribed in the preliminary discussion, and which in this 
 line of section was here first met with. Lower down 
 the valley, at the R. de las Vacas, I had a better oppor- 
 tunity of examining it ; it is there in some parts well 
 characterised, having a distinct, nearly vertical, tortuous 
 cleavage, ranging NW. and SE., and intersected by 
 quartz veins : in most parts, however, it is crystalline 
 and feldspathic, and passes into a true greenstone often 
 including grains of quartz. The clay-slate, in its upper 
 half, is frequently brecciated, the embedded angular 
 fragments being of nearly the same nature with the 
 paste. 
 
 2nd. Several strata of purplish porphyritic con- 
 glomerate, of no very great thickness, rest conformably 
 upon the feldspathic slate. A thick bed of fine, purple, 
 clay-stone porphyry, obscurely brecciated (but not 
 of metamorphosed sedimentary origin), and capped 
 by porphyritic conglomerate, was the lowest bed 
 actually examined in this section at the Puente del 
 Inca. 
 
 3rd. A stratum, eighty feet thick, of hard and very 
 •compact impure whitish limestone, weathering bright 
 
€HAP. XIV. Gypseous Formation. 507 
 
 red, with included layers brecciated and re-cemented. 
 Obscure marks of sliell are distinguishable in it. 
 
 4th. A red, quartzose, fine-grained conglomerate, 
 with grains of quartz, and with patches of white earthy 
 feldspar, apparently due to some process of concretionary 
 crystalline action : this bed is more compact and 
 metamorphosed than any of the overlying conglome- 
 rates. 
 
 5th. A whitish cherty limestone, with nodules of 
 blueish argillaceous limestone. 
 
 6th. A white conglomerate, with many particles of 
 quartz, almost blending into the paste. 
 
 7th. Highly siliceous, fine-grained white sand- 
 stone. 8th and 9th. Eed and white beds not ex- 
 amined. 
 
 10th. Yellow, fine-grained, thinly stratified, mag- 
 nesian (judging from its slow dissolution in acids) lime- 
 stone : it includes some white quartz pebbles, and little 
 <3avities, lined with calcareous spar, some retaining the 
 form of shells. 
 
 11th. A bed between twenty and thirty feet thick, 
 quite conformable with the underlying ones, composed 
 of a hard basis, tinged lilac-gray porphyritic with 
 numeivus crystals of whitish feldspar, with black mica 
 and little spots of soft ferruginous matter : evidently a 
 submarine lava. 
 
 12th. Yellow magnesian limestone, as before, part- 
 stained purple. 
 
 13th. A most singular rock; basis purplish gray, 
 obscurely crystalline, easily fusible into a dark green 
 glass, not hard, thickly speckled with crystals more or 
 less perfect of white carbonate of lime, of red hydrous 
 oxide of iron, of a white and transparent mineral like 
 analcime, and of a green opaque mineral like soap-stone ; 
 the basis is moreover amygdaloidal with many spherical 
 
5o8 Section by the Cwnbre Pass, part ii. 
 
 balls of white crystallised carbonate of lime, of whicli 
 some are coated with the red oxide of iron. I have no 
 doubt, from the examination of a superincumbent 
 stratum (19), that this is a submarine lava; though in 
 Northern Chile, some of the metamorphosed sedimentary 
 beds are almost as crystalline, and of as varied com- 
 position. 
 
 14th. Red sandstone, passing in the upper part into 
 a coarse, hard, red conglomerate, 300 feet thick, having 
 a calcareous cement, and including grains of quartz and 
 broken crystals of feldspar ; basis infusible ; the pebbles 
 consist of dull purplish porphyries, with some of quartz, 
 from the size of a nut to a man's head. This is the 
 coarsest conglomerate in this part of the Cordillera : in 
 the middle there was a white layer not examined. 
 
 15th. Grand thick bed, of a very hard, yellowish- 
 white rock, with a crystalline feldspathic base, including 
 large crystals of white feldspar, many little cavities 
 mostly full of soft ferruginous matter, and numerous 
 hexagonal plates of black mica. The upper part of 
 this great bed is slightly cellular ; the lower part 
 compact : the thickness varied a little in different parts. 
 Manifestly a submarine lava; and is allied to bed ll. 
 
 16th and 17th. Dull purplish, calcareous, fine- 
 grained, compact sandstones, which pass into coarse 
 white conglomerates with numerous particles of quartz. 
 
 18th. Several alternations of red conglomerate, 
 purplish sandstone, and submarine lava, like that singu- 
 lar rock forming bed 13. 
 
 19th. A very heavy, compact, greenish-black stone, 
 with a fine-grained obviously crystalline basis, contain- 
 ing a few specks of white calcareous spar, many specks 
 of the crystallised hydrous red oxide of iron, and some 
 specks of a green mineral ; there are veins and nests 
 filled with epidote : certainly a submarine lava. 
 
CHAP. XIV. Gypseous Formation. 509 
 
 20tli. Many thin strata of compact, fine-grained, 
 pale purple sandstone. 
 
 21st. Gypsum in a nearly pure state, about 300 feet 
 in thickness : this bed, in its concretions of anhydrite 
 and layers of small blackish crystals of carbonate of 
 lime, exactly resembles the great gypseous beds in the 
 Peuquenes range. 
 
 22nd. Pale purple and reddish sandstone, as in bed 
 20 : about 300 feet in thickness. 
 
 23rd. A thick mass composed of layers, often as 
 thin as paper and convoluted, of pure gypsum with 
 others very impure, of a purplish colour. 
 
 24th. Pure gypsum, thick mass. 
 
 25th. Red sandstones, of great thickness. 
 
 26th. Pure gypsum, of great thickness. 
 
 27th. Alternating layers of pure and impure gypsum, 
 of great thickness. 
 
 I was not able to ascend to these few last great 
 strata, which compose the neighbouring loftiest pin- 
 nacles. The thickness, from the lowest to the uppermost 
 bed of gypsum, cannot be less than 2,000 feet : the beds 
 beneath I estimated at 3,000 feet, and this does not 
 include either the lower parts of the porphyritic conglo- 
 merate, or the altered clay-slate ; I conceive the total 
 thickness must be about 6,000 feet. I distinctly 
 observed that not only the gypsum, but the alternating 
 sandstones and conglomerates were lens-shaped, and 
 repeatedly thinned out and replaced each other : thus 
 in the distance of about a mile, a bed 300 feet thick of 
 sandstone between two beds of gypsum, thinned out to 
 nothing and disappeared. The lower part of this section 
 differs remarkably, — in the much greater diversity of 
 its mineralogical composition, — in the abundance of 
 calcareous matter, — in the greater coarseness of some 
 of the conglomerates, — and in the numerous particles 
 
5IO Sectio7i by the Cumbre Pass, part ii. 
 
 and well rounded pebbles, sometimes of large size, of 
 quartz, — from any other section hitherto described in 
 Chile. From these peculiarities, and from the lens- 
 form of the strata, it is probable that this great pile of 
 strata was accumulated on a shallow and very uneven 
 bottom, near some pre-existing land formed of various 
 porphyiies and quartz-rock. The formation of por- 
 phyritic clay-stone conglomerate does not in this section 
 attain nearly its ordinary thickness ; this may be fartly 
 attributed to the metamorphic action having been here 
 much less energetic than usual, though the lower beds 
 have been affected to a certain degree. If it had been 
 as energetic as in most other parts of Chile, many of 
 the beds of sandstone and conglomerate, containing 
 rounded masses of porphyry, would doubtless have been 
 converted into porphyritic conglomerate ; and these 
 would have alternated with, and even blended into, 
 crystalline and porphyritic strata without a trace of 
 mechanical structure, — namely, into those which, in the 
 present state of the section, we see are unquestionably 
 submarine lavas. 
 
 The beds of gypsum, together with the red alternat- 
 ing sandstones and conglomerates, present so perfect 
 and curious a resemblance with those seen in our former 
 section in the basin- valley of Yeso, that I cannot doubt 
 the identity of the two formations : I may add, that a 
 little westward of the P. del Inca, a mass of gypsum 
 passed into a fine-grained, harb , drown sandstone, which 
 contained some layers of black, calcareous, compact, 
 shaly rock, precisely like that seen in such vast masses- 
 on the Peuquenes range. 
 
 Near the Puente del Inca, numerous fragments of 
 limestone, containing some fossil remains, were scattered 
 on the ground : these fragments so perfectly resemble 
 the limestone of bed No. 3, in which I saw impressions 
 
CHAP. xiT. Neoco77iian Fossils. 511 
 
 of sliells, tliat I have no doubt they have fallen from it. 
 The yellow magnesian limestone of bed No. 10, which 
 also includes traces of shells, has a different appearance. 
 These fossils (as named by M. d'Orbigny) consist of — 
 
 Gryphasa, near to G. Couloni (Neocomian formation). 
 Area, perhaps A. Gahrielis, d'Orbig. ' Pal. Franc' (Neocomian for- 
 mation). 
 
 Mr. Pentland made a collection of shells from this 
 
 same spot, and Von Buch ^ considers them as consisting 
 
 of— 
 
 Trigonia, resembling in form T. costata. 
 
 Pholadomya, like one found by M. Dufresnoy near Alengon. 
 
 Isocardiaexcentrica, Voltz., identical with that from the Jura, 
 
 Two of these shells, namely, the Grypheea and 
 Trigonia, appear to be identical with species collected 
 by Meyen and myself on the Penquenes range ; and in 
 the opinion of Von Buch and M. d'Orbigny, the two 
 formations belong to the same age. I must here add, 
 that Professor E. Forbes, who has examined my speci 
 mens from this place and from the Peuquenes range, 
 has likewise a strong impression that they indicate the 
 Cretaceous period, and probably an early epoch in it : 
 so that all the palasontologists who have seen these 
 fossils nearly coincide in oi3inion regarding their age. 
 The limestone, however, with these fossils here lies at 
 the very base of the formation, just above the porphyritic 
 conglomerate, and certainly several thousand feet lower 
 in the series, than the equivalent, fossiliferous, blacky 
 shaly rocks high up on the Peuquenes range. 
 
 It is well worthy of remark that these shells, or at 
 least those of which I saw impressions in the limestone 
 (bed ISTo. 3), must have been covered up, on the least 
 computation, by 4,000 feet of strata : now we know 
 
 * ' Descript. Phys. des lies Can.' p. 472. 
 
512 Section by the Cumbre Pass. paet h. 
 
 from Professor E. Forbes's researclies, that the sea at 
 greater depths than 600 feet becomes exceedingly 
 barren of organic beings, — a result quite in accordance 
 with what little I have seen of deep-sea soundings. 
 Hence, after this limestone with its shells was deposited, 
 the bottom of the sea where the main line of the 
 Cordillera now stands, must have subsided some thou- 
 sand feet to allow of the deposition of the superincum- 
 bent submarine strata. Without supposing a movement 
 of this kind, it would, moreover, be impossible to 
 understand the accumulation of the several lower strata 
 of coarse, well-rounded conglomerates, which it is 
 scarcely possible to believe were spread out in profoundly 
 deep water, and which, especially those containing 
 pebbles of quartz, could hardly have been rounded in 
 submarine craters and afterwards ejected from them, as 
 I believe to have been the case with much of the 
 porphyritic conglomerate formation. I may add that, 
 in Professor Forbes's opinion, the above-enumerated 
 species of Mollusca probably did not live at a much 
 greater depth than twenty fathoms, that is only 120 
 feet. 
 
 To return to our section down the valley : standing 
 on the great N. by W. and S. by E. uniclinal axis of 
 the Puente del Inca, of which a section has just been 
 given, and looking north-east, great tabular masses of 
 the Gypseous formation [K K] could be seen in the 
 distance, very slightly inclined towards the east. Lower 
 down the valley, the mountains are almost exclusively 
 composed of porphja'ies, many of them of intrusive 
 origin and non-stratified, others stratified, but with the 
 stratification seldom distinguishable except in the 
 upper parts. Disregarding local disturbances, the beds 
 are either horizontal or inclined at a small angle east- 
 wards : hence, when standing on the plain of Uspallata 
 
^TTAP. XIV. Section by the Ctimbre Pass. 513 
 
 -and looking to tlie west or backwards, tlie Cordillera 
 appear composed of liuge, square, nearly horizontal, 
 tabular masses : so wide a space, with such lofty moun- 
 tains so equably elevated, is rarely met with within the 
 Cordillera. In this line of section, the interval between 
 the Puente del Inca and the neighbourhood of the 
 Cumbre, includes all the chief axes of dislocation. 
 
 The altered clay- slate formation, already described, 
 is seen in several parts of the valley as far down as Las 
 Vacas, underlying the porphyritic conglomerate. At 
 the Casa de Pujios [L], there is a hummock of (ande- 
 sitic ?) granite ; and the stratification of the surrounding 
 mountains here changes from W. by S. to SW. Again, 
 near the R. Vacas there is a larger formation of (ande- 
 sitic ?) granite [M], which sends a mesh-work of veins 
 into the superincumbent clay-slate, and which locally 
 1:hrows off the strata, on one side to NW. and on the 
 other to SE. but not at a high angle : at the junction, 
 the clay-slate is altered into fine-grained greenstone. 
 This granitic axis is intersected by a green dike, which 
 I mention, because I do not remember having elsewhere 
 seen dikes in this lowest and latest intrusive rock. 
 From the E,. Vacas to the plain of Uspallata, the valley 
 Tuns NE., so that I have had to contract my section; 
 it runs exclusively through porphyritic rocks. As far 
 -as the Pass of Jaula, the clay-stone conglomerate forma- 
 tion, in most parts highly porphyritic, and crossed by 
 numerous dikes of greenstone-porphyry, attains a great 
 thickness : there is also much intrusive porphyry. From 
 the Jaula to the plain, the stratification has been in 
 most places obliterated, except near the tops of some of 
 the mountains ; and the metamorphic action has been 
 extremely great. In this space, the number and bulk 
 of the intrusive masses of differently coloured porphyries, 
 injected one into another and intersected by dikes, is 
 
 L L 
 
5 1 4 Section by the Cumbre Pass, paet h. 
 
 truly extraordinary. I saw one mountain of whitish, 
 porphyry, from which two huge dikes, thinning out, 
 branched doiumuards into an adjoining blackish por- 
 phyry. Another hill of white porphyry, which had 
 burst through dark-coloured strata, was itself injected 
 by a purple, brecciated, and recemented porphyry, both 
 being crossed by a green dike, and both having been 
 upheaved and injected by a granitic dome. One brick- 
 red porphyry, which above the Jaula forms an isolated 
 mass in the midst of the porphyritic conglomerate 
 formation, and lower down the valley a magnificent 
 group of peaked mountains, differs remarkably from 
 all the other porphyries. It consists of a red feldspathic 
 base, including some rather large crystals of red feldspar, 
 numerous large angular grains of quartz, and little bits 
 of a soft green mineral answering in most of its charac- 
 ters to soap-stone. The crystals of red feldspar resemble 
 in external appearance those of orthite, though, from 
 being partially decomposed, I was unable to measure 
 them ; and they certainly are quite unlike the variety, 
 so abundantly met with in almost all the other rocks of 
 this line of section, and which, wherever I tried it, 
 cleaved like albite. This brick-red porphyry appears 
 to have burst through all the other porphyries, and 
 numerous red dikes traversing the neighbouring moun- 
 tains have proceeded from it : in some few places, 
 however, it was intersected by white dikes. From this 
 posteriority of intrusive origin, — from the close general 
 resemblance between this red porphyry and the fed 
 granite of the Portillo line, the only difference being 
 that the feldspar here is less perfectly granular, and 
 that soap-stone replaces the mica, which is there im- 
 perfect and passes into chlorite, — and from the Portillo 
 line a little southward of this point appearing to blend 
 (according to Dr. Gillies) into the western ranges, — I 
 
CHAP. XIV. Plain of Uspallata. 5 « 5 
 
 am strongly urged to believe (as formerly remarked) 
 that tlie grand mountain-masses composed of this brick- 
 red porphyry belong to the same axis of injection with 
 the granite of the Portillo line : if so, the injection of 
 this porphyry probably took place, as long subsequently 
 to the several axes of elevation in the gypseous forma- 
 tion near the Cumbre, as the injection of the Portillo 
 granite has been shown to have been subsequent to the 
 elevation of the gypseous strata composing the Peu- 
 quenes range ; and this interval, we have seen, must 
 have been a very long one. 
 
 The Plain of Uspallata has been briefly described 
 in Chap. X. ; it resembles the basin-plains of Chile ; 
 it is ten or fifteen miles wide, and is said to extend for 
 180 miles northward; its surface is nearly 6,000 feet 
 above the sea ; it is composed, to a thickness of some 
 hundred feet of loosely aggregated, stratified shingle, 
 which is prolonged with a gently sloping surface up the 
 valleys in the mountains on both sides. One section 
 in this plain [Z] is interesting, from the unusual ^ cir- 
 cumstance of alternating layers of almost loose red and 
 white sand with lines of pebbles (from the size of a nut 
 to that of an apple), and beds of gravel, being inclined 
 at an angle of 45°, and in some spots even at a higher 
 angle. These beds are dislocated by small faults : and 
 are capped by a thick mass of horizontally stratified 
 gravel, evidently of subaqueous origin. Having been 
 accustonied to observe the irregularities of beds accu- 
 mulated under currents, I feel sure that the inclination 
 here has not been thus produced. The pebbles consist 
 chiefly of the brick-red porphyry just described and of 
 white granite, both probably derived from the ranges 
 to the west, and of altered clay- slate and of certain 
 
 1 I find that Mr, Smith, of Jordanhill, has described (' Edinburgh 
 New Phil. Journ.' voL xxv. p. 392) beds of sand and gravel, near Edin- 
 burgh, tilted at an angle of 60°, and dislocated by miniature faults, 
 
 L L 2 
 
5 1 6 Section of the Uspallata Range, part h. 
 
 porphyries, apparently belonging to tlie rocks of the 
 TJspallata chain. This plain corresponds geographically 
 with the valley of Tenuyan between the Portillo and 
 Peuquenes ranges ; but in that valley the shingle, 
 which likewise has been derived both from the eastern 
 and western ranges, has been cemented into a hard con- 
 glomerate, and has been throughout tilted at a con- 
 siderable inclination ; the gravel there apparently attains 
 a much greater thickness, and is probably of higher 
 antiquity. 
 
 The TJsioallcda Range. — The road by the Villa 
 Vicencio Pass does not strike directly across the range, 
 but runs for some leagues northward along its western 
 base : and I must briefly describe the rocks here seen, 
 before continuing with the coloured east and west section. 
 At the mouth of the valley of Canota, and at several 
 points northwards, there is an extensive formation of a 
 glossy and harsh, and of a feldspathic clay-slate, includ- 
 ing strata of grauwacke, and having a tortuous, nearly 
 vertical cleavage, traversed by numerous metalliferous 
 veins and others of quartz. The clay-slate is in many 
 parts capped by a thick mass of fragments of the same 
 rock, firmly recemented ; and both together have been 
 injected and broken up by very numerous hillocks, 
 ranging north and south, of lilac, white, dark and 
 salmon-coloured porphyries : one steep, now denuded, 
 hillock of porphyry had its face as distinctly impressed 
 with the angles of a fragmentary mass of the slate, with 
 some of the points still remaining embedded, as sealing- 
 wax could be by a seal. At the mouth of this same 
 valley of Canota, in a fine escarpment having the strata 
 dipping from 50° to 60° to the NE.,^ the clay-slate 
 
 1 Nearly opposite to this escarpment, there is another correspond- 
 ing one, with the strata dipping not to the exactly opposite point, or 
 SW., but to SSW. : consequently the two escarpments trend towards 
 
CHAP. xiY. Section of the Uspallata Range. 517 
 
 formation is seen to be covered by (1st), a purple clay- 
 stone porphyry resting unconformably in some parts 
 on the solid slate, and in others on a thick fragmentary 
 mass : (2nd), a conformable stratum of compact blackish 
 rock, having a spheroidal structure, full of minute 
 acicular crystals of glassy feldspar, with red sj)ots of 
 oxide of iron : (3rd), a great stratum of purplish-red 
 clay-stone porphyry, abounding with crystals of opaque 
 feldspar, and laminated with thin, j)arallel, often short, 
 layers, and likewise with great irregular patches of 
 white, earthy, semi-crystalline feldspar ; this rock 
 (which I noticed in other neighbouring places) per- 
 fectly resembles a curious variety described at Port 
 Desire, and occasionally occurs in the great porphyritic 
 conglomerate formation of Chile : (4th), a thin stratum 
 of greenish-white, indurated tuff, fusible and containing 
 broken crystals and particles of porphyries : (5th), a 
 grand mass, imperfectly columnar and divided into 
 three parallel and closely joined strata, of cream- 
 coloured claystone porphyry : (6th), a thick stratum of 
 lilac-coloured porphyry, which I could see was capped 
 by another bed of the cream-coloured variety : I was 
 unable to examine the still higher parts of the escarp- 
 ment. These conformably stratified porphyries, though 
 none are either vesicular or amygdaloidal, have evi- 
 dently flowed as submarine lavas : some of them are 
 separated from each other by seams of indurated tuff, 
 which, however, are quite insignificant in thickness 
 compared with the porphyries. This whole pile 
 resembles, but not very closely, some of the less 
 brecciated parts of the great porphyritic conglomerate 
 formation of Chile ; but it does not probably belong to 
 the same age, as the porphyries here rest unconformably 
 
 each other, and some miles southward they become actually united : 
 this is a form of elevation which I have not elsewhere seen. 
 
5 1 8 Stratification of part ti. 
 
 on the altered feldspathic clay-slate, whereas the por- 
 phyritic conglomerate formation alternates with and 
 rests conformably on it. These porphyries, moreover, 
 with the exception of the one blackish stratum, and of 
 the one indurated, white tufaceous bed, differ from the 
 beds composing the Uspallata range in the line of the 
 Villa Vicencio Pass. 
 
 I will now give, first, a sketch of the structure of the 
 range, as represented in the coloured section, and will 
 then describe its composition and interesting history. 
 At its western foot, a hillock [N] is seen to rise out of 
 the plain, with its strata dipping at 70° to the west, 
 fronted by strata [0] inclined at 45° to the east, thus 
 forming a little north and south anticlinal axis. Some 
 other little hillocks of similar composition, with their 
 strata highly inclined, range NE. and SW., obliquely 
 to the main Uspallata line. The cause of these dislo- 
 cations, which, though on a small scale, have been vio- 
 lent and complicated, is seen to lie in hummocks of 
 lilac, purple and red porphyries, which have been in- 
 jected in a liquefied state through and into the under- 
 lying clay-slate formation. Several dikes were exposed 
 here, but in no other part, that I saw of this range. 
 As the strata consist of black, white, greenish, and 
 brown coloured rocks, and as the intrusive porphyries 
 are so brightly tinted, a most extraordinary view was 
 presented, like a coloured geological drawing. On the 
 gently inclined main western slope [P P], above the 
 little anticlinal ridges just mentioned, the strata dip at 
 an average angle of 25° to the west ; the inclination in 
 some places being only 10°, in some few others as much 
 as 45°. The masses having these different inclinations, 
 are separated from each other by parallel vertical faults 
 [as represented at P a], often giving rise to separate, 
 parallel, uniclinal ridges. The summit of the main 
 
CHAP. XIV. the Uspallata Range, 519 
 
 range is broad and undulatory, witli tlie stratification 
 undulatory and irregular : in a few places granitic and 
 porpliyritic masses [Q] protrude, wliicii, from the small 
 effect tliey have locally produced in deranging the 
 strata, probably form the upper points of a regular, 
 great underlying dome. These denuded granitic points, 
 I estimated at about 9,000 feet in height above the sea. 
 On the eastern slope, the strata in the upper part are 
 regularly inclined at about 25° to the east, so that the 
 summit of this chain, neglecting small irregularities, 
 forms a broad anticlinal axis. Lower down, however, 
 near Los Hornillos [R], there is a well-marked synclinal 
 axis, beyond which the strata are inclined at nearly the 
 same angle, namely from 20° to 30°, inwards or west- 
 ward. Owing to the amount of denudation which this 
 chain has suffered, the outline of the gently inclined 
 eastern flank scarcely offers the slightest indication of 
 this synclinal axis. The stratified beds, which we have 
 hitherto followed across the range, a little farther down 
 are seen to lie, I believe unconformably, on a broad 
 mountainous band of clay-slate and grauwacke. The 
 strata and laminae of this latter formation, on the ex- 
 treme eastern flank, are generally nearly vertical; 
 further inwards they become inclined from 45° to 80° 
 to the west : near Villa Vicencio [S] there is apparently 
 an anticlinal axis, but the structure of this outer part 
 of the clay-slate formation is so obscure, that I have not 
 marked the planes of stratification in the coloured sec- 
 tion. On the margin of the Pampas, some low, much 
 dislocated spurs of this same formation, project in a 
 north-easterly line, in the same oblique manner as do 
 the ridges on the western foot, and as is so frequently 
 the case with those at the base of the main Cordillera. 
 
 I will now describe the nature of the beds, begin- 
 ning at the base on the eastern side. First, for the 
 
520 Section of the Uspallata Range, pakt n.. 
 
 clay-slate formation : the slate is generally hard and 
 bluish, with the laminas coated by minute micaceous 
 scales ; it alternates many times with a coarse-grained, 
 greenish grauwacke, containing rounded fragments of 
 quartz and bits of slate in a slightly calcareous basis. 
 The slate in the upper part generally becomes purplish, 
 and the cleavage so irregular that the whole consists 
 of mere splinters. Transverse veins of quartz are 
 numerous. At the Oalera, some leagues distant, there 
 is a dark crystalline limestone, apparently included in 
 this formation. With the exception of the grauwacka 
 being here more abundant, and the clay-slate less altered, 
 this formation closely resembles that unconformably 
 underlying the porphyries at the western foot of this 
 same range ; and likewise that alternating with the 
 porphyritic conglomerate in the main Cordillera. This 
 formation is a considerable one, and extends several 
 leagues southward to near Mendoza : the mountains 
 composed of it rise to a height of about 2,000 feet 
 above the edge of the Pampas, or about 7,000 feet 
 above the sea.^ 
 
 Secondly : the most usual bed on the clay-slate is 
 a coarse, white, slightly calcareous conglomerate, of no 
 great thickness, including broken crystals of feldspar, 
 grains of quartz, and numerous pebbles of brecciated 
 clay-stone porphyry, but without any pebbles of the 
 underlying clay -slate. I nowhere saw the actual junc- 
 tion between this bed and the clay-slate, though I spent 
 a whole day in endeavouring to discover their relations. 
 In some places I distinctly saw the white conglomerate 
 and overlying beds inclined at from 25° to 30° to the 
 west, and at the bottom of the same mountain, the 
 clay-slate and grauwacke inclined to the same point, but 
 
 ^ I infer this from the height of V. Vicencio, which was ascer- 
 tained by Mr. Miers to be 5,328 feet above the sea. 
 
CHAP. xiY. Sectio7t of the Uspallata Range. 521 
 
 at an angle from 70° to 80° : in one instance, the clay- 
 slate dipped not only at a different angle, but to a 
 different point from the overlying formation. In these 
 cases the two formations certainly appeared quite un- 
 conformable : moreover, I found in the clay-slate one 
 great, vertical, dike-like jfissure, filled up with an in- 
 durated wLitish tuff, quite similar to some of the upper 
 beds presently to be described ; and this shows that the 
 clay-slate must have been consolidated and dislocated 
 before their deposition. On the other hand, the strati- 
 fication of the slate and grauwacke,^ in some cases gra- 
 dually and entirely disappeared in approaching the 
 overlying white conglomerate ; in other cases the 
 stratification of the two formations became strictly con- 
 formable; and again in other cases, there was some 
 tolerably well characterised clay-slate lying above the 
 conglomerate. The most probable conclusion appears 
 to be, that after the clay-slate formation had been dis- 
 located and tilted, but whilst under the sea, a fresh and 
 more recent deposition of clay-slate took place, on which 
 the white conglomerate was conformably deposited, with 
 here and there a thin intercalated bed of clay-slate. On 
 this view the white conglomerates and the presently to 
 be described ' tuffs and lavas are really unconformable 
 to the main part of the clay-slate ; and this, as we hav& 
 seen, certainly is the case with the clay-stone lavas in 
 the valley of Canota, at the western and opposite base 
 of the range. 
 
 Thirdly : on the white conglomerate, strata several 
 
 ^ The coarse, mechanical structure of many grauwackes has always 
 appeared to me a difficulty ; for the texture of the associated clay- 
 slate and the nature of the embedded organic remains where present, 
 indicate that the whole has been a deep-water deposit. Whence have 
 the sometimes included angular fragments of clay-slate, and the- 
 rounded masses of quartz and other rocks, been derived ? Many 
 deep-water limestones, it is well known, have been brecciated, and 
 then firmly recemented. 
 
522 Section of the Uspallata Range. paet n. 
 
 hundred feet in thickness are superimposed, varying 
 much in nature in short distances : the commonest 
 variety is a white, much indurated tuff, sometimes 
 slightly calcareous, with ferruginous spots and water- 
 lines, often passing into whitish or purplish compact, 
 fine-grained grit or sandstones ; other varieties become 
 semi-porcellanic, and tinted faint green or blue ; others 
 pass into an indurated shale : most of these varieties 
 are easily fusible. 
 
 Fourthly : a bed, about 100 feet thick, of a compact, 
 partially columnar, pale-gray, feldspathic lava, stained 
 with iron, including very numerous crystals of opaque 
 feldspar, and with some crystallised and disseminated 
 calcareous matter. The tufaceous stratum on which 
 this feldspathic lava rests is much hardened, stained 
 purple, and has a spherico-concretionary structure; 
 it here contains a good many pebbles of clay-stone 
 porphyry. 
 
 Fifthly : thin beds, 400 feet in thickness, varying 
 much in nature, consisting of white and ferruginous 
 tuffs, in some parts having a concretionary structure, in 
 others containing rounded grains and a few pebbles of 
 quartz; also passing into hard gritstones and into 
 greenish mudstones : there is, also, much * of a bluish- 
 gray and green semi-porcellanic stone. 
 
 Sixthly : a volcanic stratum, 250 feet in thickness, 
 of so varying a nature that I do not believe a score of 
 specimens would show all the varieties ; much is highly 
 amygdaloidal, much compact; there are greenish, 
 blackish, purplish, and gray varieties, rarely including 
 crystals of green augite and minute acicular ones of 
 feldspar, but often crystals and amygdaloidal masses of 
 white, red, and black carbonate of lime. Some of the 
 blackish varieties of this rock have a conchoidal fracture 
 and resemble basalt : others have an irregular fracture. 
 
CHAP. XIV. Section of the Uspallata Range. 523 
 
 Some of tlie gray and purplish varieties are thickly 
 speckled with green earth and with white crystalline 
 carbonate of lime ; others are largely amygdaloidal with 
 green earth and calcareous spar. Again, other earthy 
 varieties of greenish, purplish and gray tints, contain 
 much iron, and are almost half-composed of amygdaloidal 
 balls of dark brown bole, of a whitish indurated feld- 
 spathic matter, of bright green earth, of agate, and of 
 black and white crystallised carbonate of lime. All these 
 varieties are easily fusible. Viewed from a distance, 
 the line of junction with the underlying semi-porcel- 
 lanic strata was distinct ; but when examined closely, 
 it was impossible to point out within a foot where the 
 lava ended and where the sedimentary mass began : the 
 rock at the time of junction was in most places hard, of 
 a bright green colour, and abounded with irregular 
 amygdaloidal masses of ferruginous and pure calcareous 
 spar, and of agate. 
 
 Seventhly : strata, eighty feet in thickness, of various 
 indurated tuffs, as before ; many of the varieties have a 
 fine basis including rather coarse extraneous particles ; 
 some of them are compact and semi-porcellanic, and 
 include vegetable impressions. 
 
 Eighthly : a bed, about fifty feet thick, of greenish- 
 gray, compact, feldspathic lava, with numerous small 
 crystals of opaque feldspar, black augite, and oxide of 
 iron. The junction with the bed on which it rested, 
 was ill defined; balls and masses of the feldspathic 
 rock being enclosed in much altered tuff. 
 
 Ninthly : indurated tuffs, as before. 
 
 Tenthly : a conformable layer, less than two feet 
 in thickness, of pitchstone, generally brecciated, and 
 traversed by veins of agate and of carbonate of lime : 
 parts are composed of ap]oarently concretionary frag- 
 ments of a more perfect variety, arranged in horizontal 
 
524 Section 0/ the Uspallata Range. part n, 
 
 lines in a less perfectly characterised variety. I have 
 much difficulty in believing that this thin layer of 
 pitchstone flowed as lava. 
 
 Eleventhly : sedimentary and tufaceous beds as 
 before, passing into sandstone, including some con- 
 glomerate : the pebbles in the latter are of clay-stone 
 porphyry, well rounded, and some as large as cricket- 
 balls. 
 
 Twelfthly : a bed of compact, sonorous, feldspathic 
 lava, like that of bed No. 8, divided by numerous joints 
 into large angular blocks. 
 
 Thirteenthly : sedimentary beds as before. Four- 
 teenthly : a thick bed of greenish or grayish black, 
 compact basalt (fusing into a black enamel), with small 
 crystals, occasionally distinguishable, of feldspar and 
 augite : the junction with the underlying sedimentary 
 bed, differently from that in most of the foregoing 
 streams, here was quite distinct : — the lava and tufaceous 
 matter preserving their perfect characters within two 
 inches of each other. This rock closely resembles 
 certain parts of that varied and singular lava-stream 
 No. 6 ; it likewise resembles, as we shall immediately 
 see, many of the great upper beds on the western flank 
 and on the summit of this range. 
 
 The pile of strata here described attains a great 
 thickness ; and above the last-mentioned volcanic stra- 
 tum, there were several other great tufaceous beds 
 alternating with submarine lavas, which I had not time 
 to examine ; but a corresponding series, several thou- 
 sand feet in thickness, is well exhibited on the crest 
 and western flank of the range. Most of the lava- 
 streams on the western side are of a jet-black colour 
 and basaltic nature ; they are either compact and 
 fine-grained, including minute crystals of augite and 
 feldspar, or they are coarse-grained and abound with 
 
CHAP. XIV. Section of the Uspallata Range. 525 
 
 rather large coppery-brown crystals of aD augitic mine- 
 ral. ^ Another variety was of a dull-red colour, having 
 a clay-stone brecciated basis, including specks of oxide 
 of iron and of calcareous spar, and amygdaloidal with 
 green earth : there were apparently several other 
 varieties. These submarine lavas often exhibit a sphe- 
 roidal, and sometimes an imperfect columnar structure : 
 their upper junctions are much more clearly defined 
 than their lower junctions ; but the latter are not so 
 much blended into the underlying sedimentary beds as 
 is the case in the eastern flank. On the crest and west- 
 >ern flank of the range, the streams, viewed as a whole, 
 -are mostly basaltic ; whilst those on the eastern side, 
 which stand lower in the series, are, as we have seen, 
 mostly feldspathic. 
 
 The sedimentary strata alternating with the lavas 
 on the crest and western side, are of an almost infinitely 
 varying nature ; but a large proportion of them closely 
 resemble those already described on the eastern flank : 
 there are white and brown, indurated, easily fusible 
 tuffs, — some passing into pale blue and green semi- 
 porcellanic rocks, — others into brownish and purplish 
 sandstones and gritstones, often including grains of 
 quartz, — others into mudstone containing broken crys- 
 tals and particles of rock, and occasionally single large 
 pebbles. There was one stratum of a bright red, coarse, 
 volcanic gritstone ; another of conglomerate ; another 
 of a black, indurated, carbonaceous shale marked with 
 imperfect vegetable impressions ; this latter bed, which 
 was thin, rested on a submarine lava, and followed all 
 the considerable inequalities of its upper surface. Mr. 
 Miers states that coal has been found in this range. 
 Lastly, there was abed (like No. 10 on the eastern flank) 
 
 * Very easily fusible into a jet black bead, attracted b}^ the magnet : 
 the crystals are too much tarnished to be measured by the goniometer. 
 
526 Section of the Uspallata Range. paet it. 
 
 evidently of sedimentary origin, and remarkable from 
 closely approaching in character to an imperfect pitch- 
 stone, and from including extremely thin layers of perfect 
 pitchstone, as well as nodules and irregular fragments 
 (but not resembling extraneous fragments) of this same 
 rock arranged in horizontal lines : I conceive that this 
 bed, which is only a few feet in thickness, must have 
 assumed its present state through metamorphic and 
 concretionary action. Most of these sedimentary strata 
 are much indurated, and no doubt have been partially 
 metamorphosed : many of them are extraordinarily 
 heavy and compact ; others have agate and crystalline 
 carbonate of lime disseminated throughout them. 
 Some of the beds exhibit a singular concretionary ar- 
 rangement, with the curves determined by the lines of 
 fissure. There are many veins of agate and calcareous 
 spar, and innumerable ones of iron and other metals, 
 which have blackened and curiously affected the strata 
 to considerable distances on both sides. 
 
 Many of these tufaceous beds resemble, with the 
 exception of being more indurated, the upper beds of 
 the great Patagonian Tertiary formation, especially 
 those variously coloured layers high up the river Santa 
 Cruz, and in a remarkable degree the tufaceous forma- 
 tion at the northern end of Ohiloe. I was so much 
 struck with this resemblance, that I particularly looked 
 out for silicified wood, and found it under the following 
 extraordinary circumstances. High up on this western 
 flank,^ at a height ' estimated at 7,000 feet above the 
 
 ^ For the information of any future traveller, I will describe the 
 spot in detail. Proceeding eastward from the Agua del Zcrro, and 
 afterwards leaving on the north side of the road a rancho attached 
 to some old gold-mines, you pass through a gully with low but steej^ 
 rocks on each hand : the road then bends, and the ascent becomes 
 steeper. A few hundred yards farther on, a stone's throw on the 
 south side of the road, the white calcareous stumps may be seen. 
 The spot is about half a mile east of the Agua del Zorro. 
 
CHAP. XIV. Upright Silicified Trees. 527 
 
 sea, in a broken escarpment of thin strata, composed of 
 compact green gritstone passing into a fine mudstone, 
 and alternating with layers of coarser, brownish, very 
 heavy mudstone including broken crystals and particles 
 of rock almost blended together, I counted the stumps 
 of fifty-two trees. They projected between two and 
 five feet above the ground, and stood at exactly right 
 angles to the strata, which were here inclined at an 
 angle of about 25° to the west. Eleven of these trees 
 were silicified and well preserved : Mr. E. Brown has 
 been so kind as to examine the wood when sliced and 
 polished; he says it is coniferous, partaking of the 
 characters of the Araucarian tribe, with some curious 
 points of affinity with the Yew. The bark round the 
 trunks must have been circularly furrowed with irregu- 
 lar lines, for the mudstone round them is thus plainly 
 marked. One cast consisted of dark argillaceous lime- 
 stone ; and forty of them of coarsely crystallised car- 
 bonate of lime, with cavities lined by quartz crystals : 
 these latter white calcareous columns do not retain any 
 internal structure, but their external form plainly shows 
 their origin. All the stumps have nearly the same 
 diameter, varying from one foot to eighteen inches ; 
 some of them stand within a yard of each other ; they 
 are grouped in a clump within a space of about sixtv 
 yards across, with a few scattered round at the distance 
 of 150 yards. They all stand at about the same level. 
 The longest stump stood seven feet out of the ground : 
 the roots, if they are still preserved, are buried and 
 concealed. No one layer of the miidstone appeared 
 much darker than the others, as if it had formerly ex- 
 isted as soil, nor could this be expected, for the same 
 agents which replaced with silex and lime the wood of 
 the trees, would naturally have removed all vegetable 
 matter from the soil. Besides the fifty-two upright 
 
528 Section of the Uspallata Range, paet n. 
 
 trees, there were a few fragments, like broken branches, 
 horizontally embedded. The surrounding strata are 
 crossed by veins of carbonate of lime, agate, and oxide 
 of iron ; and a poor gold- vein has been worked not far 
 from the trees. 
 
 The gTeen and brown mudstone beds including the 
 trees, are conformably covered by much indurated, 
 compact, white or ferruginous tujffs, which pass upwards 
 into a fine-grained, purplish sedimentary rock : these 
 strata, which, together, are from 400 to 500 feet in 
 thickness, rest on a thick bed of submarine-lava, and 
 are conformably covered by another great mass of fine- 
 grained basalt,^ which I estimated at 1,000 feet in thick- 
 ness, and which probably has been formed by more than 
 one stream. Above this mass I could clearly distin- 
 guish five conformable alternations, each several hun- 
 dred feet in thickness, of stratified sedimentary rocks 
 and lavas, such as have been previously described. 
 Certainly the upright trees have been buried under 
 several thousand feet in thickness of matter, accumu- 
 lated under the sea. As the trees obviously must once 
 have grown on dry land, what an enormous amount of 
 subsidence is thus indicated ! Nevertheless, had it not 
 been for the trees there was no appearance which would 
 have led any one even to have conjectured that these 
 strata had subsided. As the land, moreover, on which 
 the trees grew, is formed of subaqueous deposits, of 
 nearly if not quite equal thickness with the superin- 
 cumbent strata, and as these deposits are regularly 
 stratified and fine-grained, not like the matter thrown 
 up on a sea-beach, a previous upward movement, aided 
 
 1 This rock is quite black, and fuses into a black bead, attracted 
 strongly by the magnet ; it breaks with a conchoidal fracture ; the 
 included crystals of augite are distinguishable by the naked eye, but 
 are not perfect enough to be measured : there are many minute 
 acioalar crystals of glassy feldspar. 
 
CHA.P. xiY. Section of the Uspallata Range. 529 
 
 no doubt by tbe great accumulation of lavas and sedi- 
 ment, is also indicated.^ 
 
 In nearly tbe middle of tlie range, there are some 
 hills [Q], before alluded to, formed of a kind of gra'nite 
 externally resembling andesite, and consisting of a 
 white, imperfectly granular, feldspathic basis, including 
 some perfect crystals apparently of albite (but I was 
 unable to measure them), much black mica, epidote in 
 veins, and very little or no quartz. Numerous small 
 veins branch from this rock into the surrounding 
 strata ; and it is a singular fact that these veins, though 
 composed of the same kind of feldspar and small scales 
 of mica as in the solid rock, abound with innumerable 
 minute rounded grains of quartz : in the veins or dikes 
 also, branching from the great granitic axis in the pen- 
 insula of Tres Montes, I observed thab quartz was more 
 abundant in them than in the main rock : I have heard 
 of other analogous cases : can we account for this fact, 
 by the long-continued vicinity of quartz ^ when cooling, 
 
 ^ At first I imagined, that the strata with the trees might Iiave 
 been accumulated in a lake : but this seems highly improbable ; for, 
 first, a very deep lake was necessary to receive the matter below the 
 trees, then it must have been drained for their growth, and afterwards 
 re-formed and made profoundly deep, so as to receive a subsequent 
 accumulation of matter several thousand feet in thickness. And all 
 this must have taken place necessarily before the formation of the 
 Uspallata range, and therefore on the margin of the wide level expanse 
 of the Pampas ! Hence I conclude, that it is infinitely more probable 
 that the strata were accumulated under the sea : the vast amount of 
 denudation, moreover, which this range has suffered, as shown by the 
 wide valleys, by the exposure of the very trees and by other appear- 
 ances, could have been effected, I conceive, only by the long-continued 
 action of the sea ; and this shows that the range was either upheaved 
 from under the sea, or subsequently let down into it. From the 
 natural manner in which the stumps (fifty-two in number) 2.r% grouped 
 in a clumi)^ and from their all standing vertically to the strata, it is 
 superfluous to speculate on the chance of the trees having been drifted 
 from adjoining land, and deposited upright : I may, however, mention 
 that the late Dr. Malcolmson assured me, that he once met in the 
 Indian Ocean, fifty miles from land, several cocoa-nut trees floating 
 upright, owing to their roots being loaded with earth. 
 
 - See a paper bv M. Elie de Beaumont, ' Soc. Philomath.' May, 
 1839 (' L'Institut,' 1839, p. 161). 
 
 M M 
 
530 Cone hiding Remarks on the paet h. 
 
 and by its having been thus more easily sucked into 
 fissures than the other constituent minerals of granite. 
 The strata encasing the flanks of these granitic or 
 andesitic masses, and forming a thick cap on one of 
 their summits, appear originally to have been of the 
 same tufaceous nature with the beds already described, 
 but they are now changed into porcellanic, jaspery, and 
 crystalline rocks, and into others of a white colour with. 
 a harsh texture, and having a siliceous aspect, though 
 really of a feldspathic nature and fusible. Both the 
 granitic intrusive masses and the encasing strata are 
 penetrated by innumerable metallic veins, mostly ferru- 
 ginous and auriferous, but some containing copper- 
 pyrites and a few silver : near the veius, the rocks are 
 blackened as if blasted by gunpowder. The strata are 
 only slightly dislocated close round these hills, and 
 hence, perhaps, it may be inferred that the granitic 
 masses form only the projecting points of a broad 
 continuous axis-dome, which has given to the upper 
 parts of this range its anticlinal structure. 
 
 Concluding BemarJcs on the TJspcdlata Range. — I 
 will not attempt to estimate the total thickness of the 
 pile of strata forming this range, but it must amount 
 to many thousand feet. The sedimentary and tufaceous 
 beds have throughout a general similarity, though with, 
 infinite variations. The submarine lavas in the lower 
 part of the series are mostly feldspathic, whilst in the 
 upper part, on the summit and western flank, they are 
 mostly basaltic. We are thus reminded of the relative 
 position in most recent volcanic districts of the trachy- 
 tic and basaltic lavas, — the latter from their greater 
 weight having sunk to a lower level in the earth's 
 crust, arid having consequently been erupted at a later 
 period over the lighter and upper lavas of the trachytic 
 series.^ Both the basaltic and feldspathic submarine 
 * See on this subject, Chapter YI. 
 
€HAp. XIV. Uspallata Range. 531 
 
 streams are very compact; none being vesicular, and 
 only a few amygdaloidal : the effects wliich some of 
 them, especially those low in the series, have produced 
 on the tufaceous beds over which they have flowed is 
 highly curious. Independently of this local meta- 
 morphic action, all the strata undoubtedly display an 
 indurated and altered character ; and all the rocks of 
 this range — the lavas, the alternating sediments, the 
 intrusive granite and porphyries, and the underlying 
 clay-slate — are intersected by metalliferous veins. The 
 lava-strata can often be seen extending for great dis- 
 tances, conformably with the under- and over-lying 
 beds ; and it was obvious that they thickened towards 
 the west. Hence the points of eruption must have been 
 situated westward of the present range, in the direction 
 of the main Cordillera : as, however, the flanks of the 
 Cordillera are entirely composed of various porphyries, 
 chiefly claystone and greenstone, some intrusive, and 
 others belonging to the porphyritic conglomerate for- 
 mation, but all quite unlike these submarine lava- 
 streams, we must in all probability look to the plain of 
 Uspallata for the now deeply buried points of eruption. 
 Comparing our section of the Uspallata range with 
 that of the Cumbre, we see, with the exception of the 
 underlying clay- slate, and perhaps of the intrusive rocks 
 of the axes, a striking dissimilarity in the strata com- 
 posing them. The great porphyritic conglomerate 
 formation has not extended as far as this range ; nor 
 have we here any of the gypseous strata, the magnesian 
 and other limestones, the red sandstones, the siliceous 
 beds with pebbles of quartz, and comparatively little of 
 the conglomerates, all of which form such vast masses 
 over the basal series in the main Cordillera. On the 
 other hand, in the Cordillera, we do not find those end- 
 less varieties of indurated tuffs, with their numerous 
 
 M 31 2 
 
532 Concluding Remarks on the paet n. 
 
 veins and concretionary arrangement, and those grit 
 and mud stones, and singular semi-porcellanic rocks, 
 so abundant in the Uspallata range. The submarine 
 lavas, also, differ considerably ; the feldspathic streams 
 of the Cordillera contain much mica, which is absent in 
 those of the Uspallata range : in this latter range we 
 have seen on how grand a scale, basaltic lava has been 
 poured forth, of which there is not a trace in the 
 Cordillera. This dissimilarity is the more striking, 
 considering that these two parallel chains are separated 
 by a plain only between ten and fifteen miles in width ; 
 and that the Uspallata lavas, as well as no doubt the 
 alternating tufaceous beds, have proceeded from the 
 west, from points apparently between the two ranges. 
 To imagine that these two piles of strata were con- 
 temporaneously deposited in two closely adjoining, very 
 deep, submarine areas, separated from each other by 
 a lofty ridge, where a plain now extends, would be a 
 gratuitous hypothesis. And had they been contempo- 
 raneously deposited, without any such dividing ridge, 
 surely some of the gypseous and other sedimentary^ 
 matter forming such immensely thick masses in the 
 Cordillera, would have extended this short distance 
 eastwards ; and surely some of the Uspallata tuffs and 
 basalts also accumulated to so great a thickness, would 
 have extended a little westward. Hence I conclude, 
 that it is far more probable that these two series are 
 not contemporaneous ; but that the strata of one of the 
 chains were deposited, and even the chain itself uplifted, 
 before the formation of the other : — which chain, then, 
 is the oldest ? Considering that in the Uspallata range 
 the lowest strata on the western flank lie unconforma- 
 bly on the clay-slate, as probably is the case with those 
 on the eastern flank, whereas in the Cordillera all the 
 overlying strata lie conformably on this formation : — 
 
oHAjp. XIV. Uspallata Range. 533 
 
 considering tliat in tlie Uspallata range some of tlie 
 beds, both low down and high up in the series, are 
 marked with vegetable impressions, showing the con- 
 tinued existence of neighbouring land; — considering 
 the close general resemblance between the deposits of 
 this range and those of tertiary origin in several parts 
 of the continent; — and lastly, even considering the 
 lesser height and outlying position of the Uspallata 
 range, — I conclude that the strata composing it are in 
 all probability of subsequent origin, and that they were 
 accumulated at a period when a deep sea studded with 
 submarine volcanos washed the eastern base of the 
 already partially elevated Cordillera. 
 
 This conclusion is of much importance, for we have 
 seen that in the Cordillera, during the deposition of 
 the Neocomian strata, the bed of the sea must have 
 subsided many thousand feet : we now learn that at a 
 later period an adjoining area first received a great 
 accumulation of strata, and was upheaved into land on 
 which coniferous trees grew, and that this area then 
 subsided several thousand feet to receive the superin- 
 cumbent submarine strata, afterwards being broken up, 
 denuded, and elevated in mass to its present height. I 
 am strengthened in this conclusion of there having 
 been two distinct, great periods of subsidence, by 
 reflecting on the thick mass of coarse stratified conglo- 
 merate in the valley of Tenuyan, between the Peuquenes 
 and Portillo lines ; for the accumulation of this mass 
 seems to me, as previously remarked, almost necessarily 
 to have required a prolonged subsidence ; and this 
 subsidence, from the pebbles in the conglomerate having 
 been to a great extent derived from the gypseous or 
 Neocomian strata of the Peuquenes line, we know must 
 have been quite distinct from, and subsequent to, that 
 sinking movement which probably accompanied the 
 
534 ^^^^ Uspallata Range. paut ii. 
 
 deposition of the Peuquenes strata, and which certainly 
 accompanied the deposition of the equivalent beds near 
 the Puente del Inca, in this line of section. 
 
 The Uspallata chain corresponds in geographical 
 position, though on a small scale, with the Portillo line ; 
 and its clay-slate formation is probably the equivalent 
 of the mica-schist of the Portillo, there metamorphosed 
 by the old white granites and syenites. The coloured 
 beds under the conglomerate in the valley of Tenuyan, 
 of which traces are seen on the crest of the Portillo, 
 and even the conglomerate itself, may perhaps be 
 synchronous with the tufaceous beds and submarine 
 lavas of the Uspallata range ; an open sea and volcanic 
 action in the latter case, and a confined channel between 
 two bordering chains of islets in the former case, having* 
 been sufficient to account for the mineralogical dissimi- 
 larity of the two series. From this correspondence 
 between the Uspallata and Portillo ranges, perhaps in 
 age and certainly in geographical position, one is 
 tempted to consider the one range as the prolongation 
 of the other ; but their axes are formed of totally diffe- 
 rent intrusive rocks ; and we have traced the apparent 
 continuation of the red granite of the Portillo in the 
 red porphyries diverging into the main Cordillera. 
 Whether the axis of the Uspallata range was injected 
 before, or, as perhaps is more probable, after that of 
 the Portillo line, I will not pretend to decide ; but it 
 is well to remember that the highly inclined lava- 
 streams on the eastern flank of the Portillo line, prove 
 that its angular upheavement was not a single and 
 sudden event ; and therefore that the anticlinal eleva- 
 tion of the Uspallata range may have been contempo- 
 raneous with some of the later angular movements by 
 which the gigantic Portillo range gained its present 
 height above the adjoining p)lain. 
 
CHAP. XT. Valparaiso to Coqtdmbo. 535 
 
 CHAPTER XY. 
 
 NORTHEEN CHILE. — CONCLUSION. 
 
 Section from Illajjel to Com'barhala ; Gyjjseous formation with sili- 
 cified wood — Panuncillo — Coquimho ; mines of Arqueros ; section 
 up valley ; fossils — Guasco, fossils of — Coinapo section up valley ; 
 Las Amolanas silicified wood, conglomerates, nature of former land, 
 fossils, thicTioiess of strata, great subsidence — Valley of Desjjoblado, 
 fossils, tufaceous dejjosit, complicated dislocations of — Relations 
 between ancient orifices of eruption and subsequent axes of infection 
 — Iquique, Peru, fossils of salt-deposits — Metalliferous veins — Sum- 
 mary on the Porpliyritic conglomerate and Gypseous formations — 
 Great siibsidence with partial elevations during the Cretaceo- 
 oolitic period — On the elevation and stomcture of the Cordillera — • 
 Recapitulation on the Tertiary series — Relation between move- 
 ments of siibsidence and volcanic action — Pampean formation — 
 Recent elevatory movements — Long -continued volcanic action in the 
 Cordillera. Conclusion. 
 
 Valparaiso to Goquimbo. — I have already described 
 tlie general nature of tlie rocks in the low country north 
 of Valparaiso, consisting of granites, syenites, green- 
 stones, and altered feldspathic clay-slate. Near Coquimbo 
 there is much hornblendic rock and various dusky- 
 coloured porphyries. I will describe only one section 
 in this district, namely, from near Illapel in a NE. line 
 to the mines of Los Hornos, and thence in a north by 
 east direction to Combarbala, at the foot of the main 
 Cordillera. 
 
 Near Illapel, after passing for some distance over 
 granite, andesite, and andesitic porphyry, we come to 
 a greenish stratified feldspathic rock, which I believe 
 is altered clay-slate, conformably capped by porphyries 
 
536 Section fro7n part ii. 
 
 and porpliyritic conglomerate of great thicknesSj dip- 
 ping at an average angle of 20° to NE. by N. The 
 uppermost beds consist of conglomerates and sandstone 
 only a little metamorphosed, and conformably covered 
 by a gypseous formation of very great thickness, but 
 much denuded. This gypseous formation, where first 
 met with, lies in a broad valley or basin, a little south- 
 ward of the mines of Los Hornos : the lower half alone 
 contains gypsum, not in great masses as in the Cordillera, 
 but in innumerable thin layers, seldom more than an 
 inch or two in thickness. The gypsum is either opaque 
 or transparent, and is associated with carbonate of lime. 
 The layers alternate with numerous varying ones of a 
 calcareous clay-shale (with strong aluminous odour, 
 adhering to the tongue, easily fusible into a pale green 
 glass), more or less indurated, either earthy and cream 
 coloured, or greenish and hard. The more indurated 
 varieties have a compact, homogeneous almost crystal- 
 line fracture, and contain granules of crystallised oxide 
 of iron. Some of the varieties almost resemble hone- 
 stones. There is also a little black, hardly fusible, 
 siliceo-calcareous clay-slate, like some of the varieties 
 alternating with gypsum on the Peuquenes range. 
 
 The upper half of this gypseous formation is mainly 
 formed of the same calcareous clay-shale rock, but 
 without any gypsum, and varying extremely in nature : 
 it passes from a soft, coarse, earthy, ferruginous state, 
 including particles of quartz, into compact clay-stones 
 with crystallised oxide of iron, — into porcellanic layers, 
 alternating with seams of calcareous matter,— and into 
 green porcelain-jasper excessively hard, but easily 
 fusible. Strata of this nature alternate with much 
 black and brown siliceo-calcareous slate, remarkable 
 from the wonderful number of huge embedded logs of 
 silicified wood. This wood, according to Mr. E. Brown, 
 
CHAP. XY. Illapel to Los Homos, 537 
 
 is (judging from several specimens) all coniferous. 
 Some of the layers of the black siliceous slate contained 
 irregular angular fragments of imperfect pitchstone, 
 which I believe, as in the Uspallata range, has origin- 
 ated in a metamorphic process. There was one bed of 
 a marly tufaceous nature, and of little specific gravity. 
 Veins of agate and calcareous spar are numerous. The 
 ivhole of this gypseous formation, especially the upper 
 lialf, has been injected, metamorphosed, and locally 
 contorted by numerous hillocks of intrusive porphyries 
 crowded together in an extraordinary manner. These 
 hillocks consist of purple clay-stone and of various other 
 porphyries, and of much white feldspathic greenstone 
 passing into andesite ; this latter variety included in 
 one case crystals of orthitic and albitic feldspar touch- 
 ing each other, and others of hornblende, chlorite, and 
 epidote. The strata surrounding these intrusive hil- 
 locks at the mines of Los Hornos, are intersected by 
 many veins of copper-pyrites, associated with much 
 micaceous iron-ore, and by some of gold : in the neigh- 
 bourhood of these veins the rocks are blackened and 
 much altered. The gypsum near the intrusive masses 
 is always opaque. One of these hillocks of porphyry 
 was capped by some stratified porphyritic conglomerate, 
 which must have been brought up from below, through 
 the whole immense thickness of the overlying gypseous 
 formation. The lower beds of the gypseous formation 
 resemble the corresponding and probably contempora- 
 neous strata of the main Cordillera ; whilst the upper 
 beds in several respects resemble those of the Uspallata 
 chain, and possibly may be contemporaneous with 
 them ; for I have endeavoured to show that the Uspal- 
 lata beds were accumulated subsequently to the gyp- 
 seous or Neocomian formations of the Cordillera. 
 
 This pile of strata dips at an angle of about 20° to 
 
538 Mines of Paiiuncillo. part n. 
 
 NE. by N., close up to the very foot of the Cuesta de 
 Los Hornos, a crooked range of mountains formed of 
 intrusive rocks of the same nature with the above de- 
 scribed hillocks. Only in one or two places, on this 
 south-eastern side of the range, I noticed a narrow 
 fringe of the upper gypseous strata brushed up and 
 inclined south-eastward from it. On its north-eastern 
 flank, and likewise on a few of the summits, the strati- 
 fied porphyritic conglomerate is inclined NE. : so that, 
 if we disregard the very narrow anticlinal fringe of 
 gypseous strata at its 8E. foot, this range forms a 
 second uniclinal axis of elevation. Proceeding in a 
 north by east direction to the village of Combarbala, 
 we come to a third escarpment of the porphyritic con- 
 glomerate, dipping eastwards, and forming the outer 
 range of the main Cordillera. The lower beds were 
 here more jaspery than usual, and they included some 
 white cherty strata and red sandstones, alternating with 
 purple claystone porphyry. Higher up in the Cordillera 
 there appeared to be a line of andesitic rocks ; and 
 beyond them, a fourth escarpment of the porphyritic 
 conglomerate, again dipping eastwards or inwards. 
 The overlying gypseous strata, if they ever existed here, 
 have been entirely removed. 
 
 Gofper Mines of Panuncillo. — From Combarbala 
 to Coquimbo, I traversed the country in a zig-zag 
 direction, crossing and recrossing the porphyritic con- 
 glomerate and finding in the granitic districts an un- 
 usual number of mountain-masses composed of various 
 intrusive, porphyritic rocks, many of them andesitic. 
 One common variety was greenish-black, with large 
 crystals of blackish albite. At Panuncillo a short 
 NNW. and SSE. ridge, with a nucleus formed of 
 greenstone and of a slate-coloured porphyry including 
 crystals of glassy feldspar, deserves notice, from the 
 
CHAP. XV. Coquimbo, Arqtieros. 539 
 
 very singular nature of tlie almost vertical strata com- 
 posing it. These consist chiefly of a finer or coarser 
 granular mixture, not very compact, of wliite carbonate 
 of lime, of protoxide of iron and of yellowish garnets 
 (ascertained by Prof. Miller), each grain being an 
 almost perfect crystal. Some of the varieties consist 
 exclusively of granules of the calcareous spar; and 
 some contain grains of copper ore, and, I believe, of 
 quartz. These strata alternate with a bluish, compact, 
 fusible, feldspathic rock. Much of the above granular 
 mixture has, also, a pseudo-brecciated structure, in 
 which fragments are obscurely arranged in planes 
 parallel to those of the stratification, and are con- 
 spicuous on the weathered surfaces. The fragments 
 are angular or rounded, small or large, and consist of 
 bluish or reddish compact feldspathic matter, in which 
 a few acicular crystals of feldspar can sometimes be 
 seen. The fragments often blend at their edges into 
 the surrounding granular mass, and seem due to a kind 
 of concretionary action. 
 
 These singular rocks are traversed by many copper 
 veins, and appear to rest conformably on a granular 
 mixture (in parts as fine-grained as a sandstone) of 
 quartz, mica, hornblende, and feldspar ; and this on 
 fine-grained, common gneiss ; and this on a laminated 
 mass, composed of pinkish orthitic feldspar, including 
 a few specks of hornblende ; and lastly, this on granite, 
 which together with andesitic rocks, form the surround- 
 ing district. 
 
 Coquimho : Mining District of Arqueros. — At 
 Coquimbo the porphyritic conglomerate formation ap- 
 proaches nearer to the Pacific than in any other part 
 of Chile visited by me, being separated from the coast 
 by a tract only a few miles broad of the usual plutonic 
 rocks, with the addition of a porphyry having a red 
 
540 Coquimbo, Arqtceros. paet n. 
 
 euritic base. In proceeding to the mines of Arqueros, 
 the strata of porphyritic conglomerate are at first nearly 
 horizontal, an unusual circumstance, and afterwards 
 they dip gently to SSE. After having ascended to a 
 considerable height, we come to an undulatory district 
 in which the famous silver mines are situated : my 
 examination was chiefly confined to those of S. Rosa. 
 Most of the rocks in this district are stratified, dipping 
 in various directions, and many of them are of so 
 singular a nature, that at the risk of being tedious I 
 must briefly describe them. The commonest variety is 
 a dull-red, compact, finely-brecciated stone, containing 
 much iron and innumerable white crystallised particles 
 of carbonate of lime and minute extraneous fragments. 
 Another variety is almost equally common near S. Rosa ; 
 it has a bright green, scanty basis, including distinct 
 crystals and patches of white carbonate of lime, and 
 grains of red, semi-micaceous oxide of iron : in parts 
 the basis becomes dark green, and assumes an obscure 
 crystalline arrangement, and occasionally in parts it 
 becomes soft and slightly translucent like soapstone. 
 These red and green rocks are often quite distinct, and 
 often pass into each other : the passage being sometimes 
 afiected by a fine brecciated structure, particles of the 
 red and green matter being mingled together. Some 
 of the varieties appear gradually to become porphyritic 
 with feldspar ; and all of them are easily fusible into 
 pale or dark-coloured beads, strongly attracted by the 
 magnet. I should perhaps have mistaken several of 
 these stratified rocks for submarine lavas, like some of 
 those described at the Puente del Inca, had I not ex- 
 amined, a few leagues eastward of this point, a fine series 
 of analogous but less metamorphosed, sedimentary beds 
 belonging to the gypseous formation, and probably de- 
 rived from a volcanic source. 
 
CHAP. XY. Section up the Valley. 541 
 
 This formation is intersected by numerous metal- 
 liferous veins, running, tliougli irregularly, NW. and 
 SE., and generally at right angles to the many dikes. 
 The veins consist of native silver, of muriate of silver, 
 an amalgam of silver, cobalt, antimony, and arsenic,^ 
 generally embedded in sulphate of barytes. I was 
 assured by Mr. Lambert, that native copper without a 
 trace of silver has been found in the same vein with 
 native silver without a trace of copper. At the mines 
 of Aristeas, the silver veins are said to be unproductive 
 as soon as they pass into the green strata, whereas at 
 S. Rosa, only two or three miles distant, the reverse 
 happens ; and at the time of my visit, the miners were 
 working through a red stratum, in the hopes of the 
 vein becoming productive in the underlying green sedi- 
 mentary mass. I have a specimen of one of these green 
 rocks, with the usual granules of white calcareous spar 
 and red oxide of iron, abounding with disseminated 
 particles of glittering native and muriate of silver, 
 yet taken at the distance of one yard from any 
 vein, — a circumstance, as I was assured, of very rare 
 occurrence. 
 
 Section J^astward^ up the Valley of Goquimho. — 
 After passing for a few miles over the coast granitic 
 series, we come to the porphyritic conglomerate, with 
 its usual characters, and with some of the beds dis- 
 tinctly displaying their mechanical origin. The strata, 
 where first met with, are, as before stated, only slightly 
 inclined ; but near the Hacienda of Pluclaro, we come 
 to an anticlinal axis, with the beds much dislocated and 
 shifted by a great fault, of which not a trace is ex- 
 ternally seen in the outline of the hill. I believe that 
 this anticlinal axis can be traced northwards, into the 
 
 ^ See the Eeport on IM. Domeyko's account of these mines, in 
 the 'Comptes Eendus,' t. xiv. p. 560. 
 
542 Coquivibo. 
 
 PART II. 
 
 district of Arqueros, where a conspicuous hill called 
 Oerro Blanco, formed of a liarsh, cream-coloured euritic 
 rock, including a few crystals of reddish feldspar, and 
 associated with some purplish claystone porphyry, seems 
 to fall on a line of elevation. In descending from the 
 Arqueros district, I crossed on the northern border of the 
 valley, strata inclined eastward from the Pluclaro axis : 
 on the porphyritic conglomerate there rested a mass, 
 some hundred feet thick, of brown argillaceous limestone, 
 in parts crystalline, and in parts almost composed of 
 Hif'pujrites Ghilensis, d'Orbig. ; above this came a black 
 calcareous shale, and on it a red conglomerate. In the 
 brown limestone, with the Hippurites, there was an 
 impression of a Pecten and a coral, and great numbers 
 of a large Gryphaea, very like, and, according to Prof. 
 E. Forbes, probably identical with G. Orientalisj Forbes 
 MS., — a cretaceous species (probably upper greensand) 
 from Verdachellum, in Southern India. These fossils 
 seem to occupy nearly the same position with those at 
 the Puente del Inca, — namely, at the top of the por- 
 phyritic conglomerate, and at the base of the gypseous 
 formation. 
 
 A little above the Hacienda of Pluclaro, I made a 
 detour on the northern side of the valley, to examine 
 the superincumbent gypseous strata, which I estimated 
 at 6,000 feet in thickness. The uppermost beds of the 
 porphyritic conglomerate, on which the gypseous strata 
 conformably rest, are variously coloured, with one very 
 singular and beautiful stratum composed of purple 
 pebbles of various kinds of porphyry, embedded in 
 white calcareous spar, including cavities lined with 
 bright-green crystallised epidote. The whole pile of 
 strata belonging to both formations is inclined, ap- 
 parently from the above-mentioned axis of Pluclaro, 
 at an angle of between 20° and 30° to the east. I will 
 
CHAP. XT. Section tLp the Valley. 543 
 
 here give a section of tlie principal beds met with in 
 crossing the entire thickness of the gypseous strata. 
 
 First : above the jDoiT^^y^'itic conglomerate for- 
 mation, there is a fine-grained, red, crystalline sand- 
 stone. 
 
 Secondly : a thick mass of smooth-grained, calcareo- 
 aluminous, shaly rock, often marked with dendritic 
 manganese, and having, where most compact, the ex- 
 ternal appearance of honestone. It is easily fusible. 
 I shall for the future, for convenience sake, call this 
 variety pseudo-honestone. Some of the varieties are 
 quite black when freshly broken, but all weather into 
 a yellowish-ash coloured, soft, earthy substance, pre- 
 cisely as is the case with the compact shaly rocks of 
 the Peuquenes range. This stratum is of the same 
 general nature with many of the beds near Los Hornos 
 in the Illapel section. In this second bed, or in the 
 underlying red sandstone (for the surface was partially 
 concealed by detritus), there was a thick mass of 
 gypsum, having the same mineralogical characters with 
 the great beds described in our sections across the 
 Cordillera. 
 
 Thirdly : a thick stratum of fine-grained, red, 
 sedimentary matter, easily fusible into a white glass, 
 like the basis of claystone porphyry ; but in parts 
 jaspery, in parts brecciated, and including crystalline 
 specks of carbonate of lime. In some of the jaspery 
 layers, and in some of the black siliceous slaty bands, 
 there were irregular seams of imperfect pitchstone, 
 undoubtedly of metamorphic origin, and other seams of 
 brown, crystalline limestone. Here, also, were masses, 
 externally resembling ill-preserved silicified wood. 
 
 Fourthly and fifthly : calcareous pseudo-honestone ; 
 and a thick stratum concealed by detritus. 
 
 Sixthly : a thinly stratified mass of bright green, 
 
544 Coqttimbo. part n. 
 
 compact, smootli-grained, calcareo-argillaceous stone, 
 easily fusible, and emitting a strong aluminous odour : 
 the whole has a highly angulo-concretionary structure ; 
 and it resembles, to a certain extent, some of the upper 
 tufaceo-infusorial deposits of the Patagonian Tertiary 
 formation. It is in its nature allied to our pseudo- 
 honestone, and it includes well characterised layers of 
 that variety ; and other layers of a pale green, harder, 
 and brecciated variety ; and others of red sedimentary 
 matter, like that of bed Three. Some pebbles of por- 
 phyries are embedded in the upper part. 
 
 Seventhly : red sedimentary matter or sandstone 
 like that of bed One, several hundred feet in thickness, 
 and including jaspery layers, often having a finely 
 brecciated structure. 
 
 Eighthly : white, much indurated, almost crystalline 
 tuff, several hundred feet in thickness, including 
 rounded grains of quartz and particles of green matter 
 like that of bed Six. Parts pass into a very pale green, 
 semi-porcellanic stone. 
 
 Ninthly : red or brown coarse conglomerate, 300 to 
 400 feet thick, formed chiefly of pebbles of porphyries, 
 with volcanic particles, in an arenaceous, non-calcareous, 
 fusible basis : the upper two feet are arenaceous without 
 any pebbles. 
 
 Tenthly : the last and uppermost stratum here 
 exhibited, is a compact, slate-coloured porphyry, with 
 numerous elongated crystals of glassy feldspar, from 
 150 to 200 feet in thickness : it lies strictly conformably 
 on the underlying conglomerate, and is undoubtedly a 
 submarine lava. 
 
 This great pile of strata has been broken up in 
 several places by intrusive hillocks of purple claystone 
 porphyry, and by dikes of porphyritic greenstone : it is 
 said that a few poor metalliferous veins have been 
 
CHAP. XT. Section up the Valley. 545 
 
 discovered here. From the fusible nature and general 
 appearance of the finer-grained strata, they probably 
 owe their origin (like the allied beds of the Uspallata 
 range, and of the upper Patagonian Tertiary formations), 
 to gentle volcanic eruptions, and to the abrasion of 
 volcanic rocks. Comparing these beds with those in 
 the mining district of Arqueros, we see at both places 
 rocks easily fusible, of the same peculiar bright green 
 and red colours, containing calcareous matter, often 
 having a finely brecciated structure, often passing into 
 each other and often alternating together : hence I 
 cannot doubt that the onlv difference between them, 
 lies in the Arqueros beds having been more metamor- 
 phosed (in conformity with their more dislocated and 
 injected condition), and consequently in the calcareous 
 matter, oxide of iron and green colouring matter, having 
 been segregated under a more crystalline form. 
 
 The strata are inclined, as before stated, from 20° to 
 30° eastward, towards an irregular north and south 
 chain of andesitic porphyry and of porphyritic green- 
 stone, where they are abruptly cut offl In the valley 
 of Coquimbo, near to the H. of Gualliguaca, similar 
 plutonic rocks are met with, apparently a southern 
 prolongation of the above chain ; and eastward of it we 
 have an escarpment of the porphyritic conglomerate, 
 with the strata inclined at a small angle eastward, 
 which makes the third escarpment, including that 
 nearest the coast. Proceeding up the valley we come 
 to another north and south line of granite, andesite, 
 and blackish porphyry, which seem to lie in an irregular 
 trough of the porphyritic conglomerate. Again, on the 
 south side of the R. Claro, there are some irregular 
 granitic hills, which have thrown ofi" the strata of porphy- 
 ritic conglomerate to the NW. by W. ; but the stratifica- 
 tion here has been much disturbed. I did not proceed 
 
 N N 
 
546 Coqtmnbo. paet it. 
 
 any farther up tlie valley, and tliis point is about two- 
 thirds of tlie distance between the Pacific and the 
 main Cordillera. 
 
 I will describe only one other section, namely, on 
 the north side of the H. Claro, which is interesting 
 from containing fossils : the strata are much dislocated 
 by faults and dikes, and are inclined to the north, 
 towards a mountain of andesite and porphyry, into 
 which they appear to become almost blended. As the 
 beds approach this mountain, their inclination increases 
 up to an angle of 70°, and in the upper part, the rocks 
 become highly metamorphosed. The lowest bed visible 
 in this section, is a purplish hard sandstone. Secondly, 
 a bed 200 or 300 feet thick, of a white siliceous sand- 
 stone, with a calcareous cement, containing seams of 
 slaty sandstone, and of hard yellowish-brown (dolomitic ?) 
 limestone; numerous, well-rounded, little pebbles of 
 quartz are included in the sandstone. Thirdly, a dark 
 coloured limestone with some quartz pebbles, from fifty 
 to sixty feet in thickness, containing numerous silicified 
 shells, presently to be enumerated. Fourthly, very 
 compact, calcareous, jaspery sandstone, passing into 
 (fifthly) a great bed, several hundred feet thick, of 
 conglomerate, composed of pebbles of white, red, and 
 purple porphyries, of sandstone and quartz, cemented 
 by calcareous matter. I observed that some of the 
 finer parts of this conglomerate were much indurated 
 within a foot of a dike eight feet in width, and were 
 rendered of a paler colour with the calcareous matter 
 segregated into white crystallised particles ; some parts 
 were stained green from the colouring matter of the 
 dike. Sixthly, a thick mass, obscurely stratified, of a 
 red sedimentary stone or sandstone, full of crystalline 
 calcareous matter, imperfect crystals of oxide of iron, 
 and I believe of feldspar, and therefore closely resem- 
 
CHAP. XV. Section ttp the Valley. 547 
 
 bling some of the liiglily metamorpliosed beds at Ar- 
 queros : this bed was capped by, and appeared to pass 
 in its upper part into, rocks similarly coloured, con- 
 taining calcareous matter, and abounding with minute 
 crystals, mostly elongated and glassy, of reddish albite. 
 Seventhly, a conformable stratum of fine reddish por- 
 phyry with large crystals of (albitic ?) feldspar ; pro- 
 bably a submarine lava. Eighthly, another conformable 
 bed of green porphyry, with specks of green earth and 
 cream-coloured crystals of feldspar. I believe that 
 there are other superincumbent crystalline strata and 
 submarine lavas, but I had not time to examine them. 
 
 The upper beds in this section probably correspond 
 with parts of the great gypseous formation ; and the 
 4ower beds of red sandstone conglomerate and fossili- 
 ferous limestone no doubt are the equivalents of the 
 Hippurite stratum, seen in descending from Arqueros 
 to Pluclaro, which there lies conformably upon the 
 porphyritic conglomerate formation. The fossils found 
 in the third bed, consist of — 
 
 Pecten Dufreynoyi, d'Orbig. ' Voyage, Part. Pal.' 
 
 This species, which occurs here in vast numbers, according to 
 M. d'Orbigny, resembles certain cretaceous forms. 
 
 Ostrea hemispherica, d'Orbig. ' Voyage, &c.' 
 Also resembles, according to the same author, cretaceous forms. 
 
 Terebratula aenigma, d'Orbig. ' Voyage, &c.' (PL 
 XXII. figs. 10-12), and PI. V. figs. 10, 11, 12 of this 
 work. 
 
 Is allied, according to M. d'Orbigny, to T. concinna from the 
 Forest Marble. A series of this species, collected in several localities 
 hereafter to be referred to, has been laid before Prof. E. Forbes ; and 
 he informs me that many of the specimens are almost undistinguish- 
 ablefrom our oolitic T. tetraedra, and that the varieties amongst them 
 are such as are found in that variable species. Grenerally speaking, 
 the American specimens of T. jenigmamay be distinguished from the 
 
 N N 2 
 
54^ Coquimbo. 
 
 PAET II. 
 
 British T. tetraeclra, by the surface having the ribs sharp and well 
 defined to the beak, whilst in the British species they become obsolete 
 and smoothed down ; but this difference is not constant. Prof. Forbes 
 adds, that, possibly, internal characters may exist, which would 
 distinguish the American species from its European allies. 
 
 Spirifer linguiferoides, E. Forbes, PL V. figs. 17, 18. 
 
 Professor Forbes states (see Appendix) that this species is very 
 near to S. linguifera of Phillips (a carboniferous limestone fossil), 
 but probably distinct. M. d'Orbigny considers it as perhaps in- 
 dicating the Jurassic period. 
 
 Ammonites, imperfect impression of. 
 
 M. Domeyko has sent to France a collection of 
 fossils, whicli, I presume, from the description given, 
 must have come from the neighbourhood of Arqueros ; 
 they consist of — 
 
 Pecten Dufreynoyi, d'Orbig. ' Voyage, Part. Pal.' 
 
 Ostrea hemispherica, do. do. 
 
 Turritella Andii, do. do. (Pleurotomaria Humboldtii 
 
 of Von Buch). 
 
 Hippurites Chilensis, do. do. 
 
 The specimens of this Hippurite, as well as those I collected in my 
 descent from Arqueros, are very imperfect ; but in M. d'Orbigny's 
 opinion they resemble, as does the Turritella Andii, cretaceous 
 (upper greensand) forms. 
 
 Nautilus Domeykus, d'Orbig. do. do. 
 
 Terebratula senigma, do. do. 
 
 Terebratula ignaciana, do. do. 
 
 This latter species was found by M. Domeyko in the same block of 
 limestone with the T. genigma. According to M. d'Orbigny, it comes 
 near to T. ornithocephala from the Lias. A series of this species 
 collected at Guasco, has been examined by Professor E. Forbes, and he 
 states that it is difficult to distinguish between some of the specimens 
 andthe T. hastata from the mountain limestone ; and that it is equally 
 difficult to draw a line between them and someMarlstoneTerebratulae. 
 Without a knowledge of the internal structure, it is impossible at 
 present to decide on their identity with analogous European forms. 
 
 The remarks given on the several foregoing shells, 
 show that, in M. d'Orbigny's opinion, the Pecten, 
 
CHAP. XV. Section up the Valley. 549 
 
 Ostrea, Turritella, and Hippurite indicate the creta- 
 ceous period ; and the Gryphsea appears to Prof. 
 Forbes to be identical with a species, associated in 
 Southern India with unquestionably cretaceous forms. 
 On the other hand, the two Terebratul^ and the Spirifer 
 point, in the opinion both of M. d'Orbigny and Prof. 
 Forbes, to the oolitic series. Hence M. d'Orbigny, not 
 having himself examined this country, has concluded 
 that there are here two distinct formations ; but the 
 Spirifer and T. genigma were certainly included in 
 the same bed with the Pecten and Ostrea, whence I 
 extracted them ; and the geologist M. Domeyko sent 
 home the two Terebratulse with the other-named shells, 
 from the same locality, without specifying that they 
 came from different beds. Again, as we shall presently 
 see, in a collection of shells given me from Guasco, the 
 same species, and others presenting analogous differences 
 are mingled together, and are in the same condition ; 
 and lastly, in three places in the valley of Copiapo, I 
 found some of these same species similarly grouped. 
 Hence there cannot be any doubt, highly curious 
 though the fact be, that these several fossils, namely, 
 the Hippurites, Gryphasa, Ostrea, Pecten, Turritella, 
 Nautilus, two Terebratulas, and Spirifer all belong to 
 the same formation, which would appear to form a 
 passage between the oolitic and cretaceous systems of 
 Europe. Although aware how unusual the term must 
 sound, I shall, for convenience sake, call this formation 
 cretaceo-oolitic. Comparing the sections in this valley 
 of Coquimbo with those in the Cordillera described in 
 the last chapter, and bearing in mind the character of 
 the beds in the intermediate district of Los Hornos, 
 there is certainly a close general mineralogical resem- 
 blance between them, both in the underlying porphy- 
 ritic conglomerate, and in the overlying gypseous 
 
550 Coquimbo to Gtiasco. paet ii, 
 
 formation. Considering this resemblance, and that the 
 fossils from the Puente del Inca at the base of the 
 gypseous formation, and throughout the greater part of 
 its entire thickness on the Peuquenes range, indicate 
 the Neocomian period, — that is, the dawn of the cre- 
 taceous system, or, as some have believed, a passage be- 
 tween this latter and the oolitic series — I conclude that 
 probably the gypseous and associated beds in all the 
 sections hitherto described, belong to the same great 
 formation, which I have denominated — cretaceo-oolitic. 
 I may add, before leaving Coquimbo, that M. Gay found 
 in the neighbouring Cordillera, at the height of 14,000 
 feet above the sea, a fossiliferous formation, including a 
 Trigonia and Pholadomya ; ^ — both of which genera 
 occur at the Puente del Inca. 
 
 Goquimho to Guasco. — The rocks near the coast, 
 and some way inland, do not differ from those described 
 northwards of Valparaiso : we have much greenstone, 
 syenite, feldspathic and jaspery slate, and grauwackes 
 having a basis like that of claystone ; there are some 
 large tracts of granite, in which the constituent 
 minerals are sometimes arranged in folia, thus compos- 
 ing an imperfect gneiss. There are two large districts 
 of mica-schist, passing into glossy clay-slate, and re- 
 sembling the great formation in the Chonos Archipelago. 
 In the valley of Guasco, an escarpment of porphyritic 
 conglomerate is first seen high up the valley, about two 
 leagues eastward of the town of Ballenar, I heard of a 
 great gypseous formation in the Cordillera ; and a col- 
 lection of shells made there was given me. These 
 shells are all in the same condition, and appear to have 
 come from the same bed : they consist of — 
 
 1 D'Orbigny, ' Voyage, Part. Geolog,' p. 242. 
 
CHAP. XV. Valley of Copiapo. 551 
 
 Turritella Andii, d'Orbig. ' Voyage, Part. Pal.' 
 Pecten Dufreynoyi, do. 
 Terebratula ignaciana, do. 
 
 The relations of these species have been given under the head, of 
 Coqnimbo. 
 
 Terebratula genigma, d'Orbig. ' Voyage, Part. Pal.' 
 (var. E. Forbes, PI. V. figs. 13, 14). 
 
 This shell M. d'Orbigny does not consider identical with his T. 
 enigma, but near to T. obsoleta. Professor Forbes thinks that it is 
 certainly a variety of T. asnigma, and his observations on this species 
 are given in the list of fossils from Coquimbo : we shall meet with 
 this variety again at Copiapo. 
 
 Spirifer Cliilensis, E, Forbes, PL V. figs. 15, 16. 
 
 Professor Forbes remarks that this fossil resembles several car- 
 boniferous limestone Spirifers ; and that it is also related to some 
 liassic species, as S. Wolcotii. 
 
 If these shells had been examined independently of 
 the other collections, they would probably have been 
 considered, from the characters of the two Terebratul^e 
 and from the Spirifer, as oolitic ; but considering that 
 the three first species, and according to Professor Forbes, 
 the four first, are identical with those from Coquimbo, 
 the two formations no doubt are the same, and may, 
 as I have said, be provisionally called cretaceo-oolitic. 
 
 Valley of Copiapo. — The journey from Guasco to 
 Copiapo, owing to the utterly desert nature of the 
 country, was necessarily so hurried, that I do not con- 
 sider my notes worth giving. In the valley of Copiapo 
 some of the sections are very interesting. From the 
 sea to the town of Copiapo, a distance estimated at 
 thirty miles, the mountains are composed of greenstone, 
 granite, andesite, and blackish porphyry, together with 
 some dusky-green feldspathic rocks, which I believe to 
 be altered clay-slate : these mountains are crossed by 
 
552 Valley of Copiapo. pakt ii- 
 
 many brown- coloured dikes, running north and south. 
 Above the town, the main valley runs in a south-east 
 and even more southerly course towards the Cordillera, 
 where it is divided into three great ravines, by the 
 northern one of which, call Jolquera, I penetrated for a 
 short distance. The coloured section, fig. 3 in Plate I., 
 gives an eye- sketch of the structure and composition 
 of the mountains on both sides of this valley : a straight 
 east and west line from the town to the Cordillera is 
 perhaps not more than thirty miles, but along the 
 valley the distance is much greater. Wherever the 
 valley trended very southerly, I have endeavoured to 
 contract the section into its true proportion. This 
 valley, I may add, rises much more gently than any 
 other valley which I saw in Chile. 
 
 To commence with our section, for a short distance 
 above the town we have hills of the granitic series, 
 together with some of that rock [A], which I suspect to 
 be altered clay-slate, but which Prof. G. Rose, judg- 
 ing from specimens collected by Meyen at P. Negro, 
 states is serpentine passing into greenstone. We then 
 come suddenly to the great Gypseous formation [B] 
 without having passed over, differently from in all the 
 sections hitherto described, any of the porphyritic con- 
 glomerate. The strata are at first either horizontal or 
 gently inclined westward ; then highly inclined in 
 various directions, and contorted by underlying masses 
 of intrusive rocks ; and lastly, they have a regular east- 
 ward dip, and form a tolerably well pronounced north 
 and south line of hills. This formation consists of 
 thin strata, with innumerable alternations, of black, 
 calcareous slate-rock, of calcareo-aluminous stones like 
 those at Coquimbo, which I have called pseudo-hone- 
 stones, of green jaspery layers, and of pale-purplish 
 calcareous, soft rottenstone, including seams and veins 
 
CHAP. XV. Porphyritic Formation. 55^ 
 
 of gypsum. These strata are conformably overlaid by a 
 great thickness of thinly stratified, compact limestone 
 with included crystals of carbonate of lime. At a place 
 called Tierra Amarilla, at the foot of a mountain thus 
 composed, there is a broad vein, or perhaps stratum, of 
 a beautiful and curious crystallised mixture, composed, 
 according to Prof. G. Eose,^ of sulphate of iron under 
 two forms, and of the sulphates of copper and alumina : 
 the section is so obscure that I could not make out 
 whether this vein or stratum occurred in the gypseous 
 formation, or more probably in some underlying masses 
 £A], which I believe are altered clay-slate. 
 
 Second Axis of Mevation. — After the gypseous 
 masses [B], we come to a line of hills of unstratified 
 porphyry [C], which on their eastern side blend into 
 strata of great thickness of porphyritic conglomerate, 
 dipping eastward. This latter formation, however, here 
 has not been nearly so much metamorphosed as in most 
 parts of central Chile ; it is composed of beds of true 
 purple claystone porphyry, repeatedly alternating with 
 thick' beds of purplish-red conglomerate with the well- 
 rounded, large pebbles of various porphyries, not blended 
 together. 
 
 Third Axis of Elevation. — Near the ravine of Los 
 Hornitos, there is a well-marked line of elevation, 
 extending for many miles in a NNE. and SSW. direc- 
 tion, with the strata dipping in most parts (as in the 
 second axis) only in one direction, namely, eastward at 
 an average angle of between 30° and 40°. Close to the 
 mouth of the valley, however, there is, as represented 
 in the section, a steep and high mountain [D], composed 
 of various green and brown intrusive porphyries en- 
 veloped wibh strata, apparently belonging to the upper 
 parts of the porphyritic conglomerate, and dipping 
 ^ Meyen's 'Eeise,' &c. Th. 1. s. 394. 
 
554 Valley of Copiapo. part m 
 
 both eastward and westward. I will describe tbe 
 section seen on tbe eastern side of this mountain [D], 
 beginning at the base with the lowest bed visible in 
 the porphyritic conglomerate, and proceeding upwards 
 through the gypseous formation. Bed (1) consists of 
 reddish and brownish j^orphyry varying in character, 
 and in many parts highly amygdaloidal with carbonate 
 of lime, and with bright green and brown bole. Its 
 upper surface is throughout clearly defined, but the 
 lower surface is in most parts indistinct, and towards 
 the summit of the mountain [D] quite blended into 
 the intrusive porphyries. Bed (2), a pale lilac, hard 
 but not heavy stone, slightly laminated, including small 
 extraneous fragments, and imperfect as well as some 
 perfect and glassy crystals of feldspar; from 150 to 
 200 feet in thickness. When examining it in situ^ 
 I thought it was certainly a true porphyry, but my 
 specimens now lead me to suspect that it possibly may 
 be a metamorphosed tuff. From its colour it could be 
 traced for a long distance, overlying in one part, quite 
 conformably to the porphyry of bed 1, and in another 
 not distant part, a very thick mass of conglomerate, 
 composed of pebbles of a porphyry chiefly like that of 
 bed 1 : this fact shows how the nature of the bottom 
 formerly varied in short horizontal distances. Bed (3), 
 white, much indurated tuff, containing minute pebbles, 
 broken crystals, and scales of mica, varies much in 
 thickness. This bed is remarkable from containing 
 many globular and pear-shaped, externally rusty balls,, 
 from the size of an apple to a man's head, of very 
 tough, slate-coloured porphyry, with imperfect crystals 
 of feldspar : in shape these balls do not resemble pebbles, 
 a/iid I believe that they are suhaqueoiis volcanic bombs ; 
 they differ from subaerial bombs only in not being 
 vesicular. Bed (4), a dull purplish-red, hard conglo- 
 
CHAP. XV. Gypseous Formation. 555 
 
 merate, with crystallised particles and veins of carbonate 
 of lime, from 300 to 400 feet in thickness. The 
 pebbles are of claystone porphyries of many varieties ; 
 they are tolerably well rounded, and vary in size from 
 a large apple to a man's head. This bed includes 
 three layers of coarse, black, calcareous, somewhat 
 slaty rock : the upper part passes into a compact red 
 sandstone. 
 
 In a formation so highly variable in mineralogical 
 nature, any division not founded on fossil remains, 
 must be extremely arbitrary : nevertheless, the beds 
 below the last conglomerate may, in accordance with 
 all the sections hitherto described, be considered as 
 belonging to the porphyritic conglomerate, and those 
 above it to the gypseous formation, marked [E] in the 
 section. The part of the valley in which the following 
 beds are seen is near Potrero Seco. Bed (5), compact, 
 fine-grained, pale greenish-gray, non-calcareous, indu- 
 rated mudstone, easily fusible into a pale green and 
 white glass. Bed (6), purplish, coarse-grained, hard 
 sandstone, with broken crystals of feldspar and crystal- 
 lised particles of carbonate of lime ; it possesses a 
 slightly nodular structure. Bed (7), blackish-gray, 
 much indurated, calcareous mudstone, with extraneous 
 particles of unequal size ; the whole being in parts 
 finely brecciated. In this mass there is a stratum, twenty 
 feet in thickness, of impure gypsum. Bed (8), a 
 greenish mudstone, with several layers of gypsum . Bed 
 (9), a highly indurated, easily fusible, white tufi", thickly 
 mottled with ferruginous matter, and including some 
 white semi-porcellanic layers, which are interlaced with 
 ferruginous veins. This stone closely resembles some 
 of the commonest varieties in the Uspallata chain. 
 Bed (10), a thick bed of rather bright green, indurated 
 mudstone or tuff", with a concretionary nodular structure 
 
55^ Valley of Copiapo, part u. 
 
 so strongly developed that the whole mass consists of 
 balls. I will not attempt to estimate the thickness of 
 the strata in the gypseous formation hitherto described, 
 but it must certainly be very many hundred feet. Bed 
 (11) is at least 800 feet in thickness: it consists of thin 
 layers of whitish, greenish, or more commonly brown, 
 fine-grained indurated tuffs, which crumble into angular 
 fragments : some of the layers are semi-porcellanic, 
 many of them highly ferruginous, and some are almost 
 composed of carbonate of lime and iron with drusy 
 cavities lined with quartz-crystals. Bed (12), dull pur- 
 plish or greenish or dark-gray, very compact and much 
 indurated mudstone : estimated at 1,500 feet in thick- 
 ness : in some parts this rock assumes the character of 
 an imperfect coarse claj^-slate ; but viewed under a lens, 
 the basis always has a mottled appearance, with the 
 edges of the minute component particles blending to- 
 gether. Parts are calcareous, and there are numerous 
 veins of highly crystalline carbonate of lime charged 
 with iron. The mass has a nodular structure, and is 
 divided by only a few planes of stratification : there 
 are, however, two layers, each about eighteen inches 
 thick, of a dark brown, finer-grained stone, having a 
 conchoidal, semi-porcellanic fracture, which can be 
 followed with the eye for some miles across the country. 
 I believe this last great bed is covered by other 
 nearly similar alternations ; but the section is here 
 obscured by a tilt from the next porphyritic chain, 
 presently to be described. I have given this section in 
 detail, as being illustrative of the general character of 
 the mountains in this neighbourhood ; but it must not 
 be supposed that any one stratum long preserves the 
 same character. At a distance of between only two and 
 three miles, the green mudstones and white indurated 
 tuff's are to a great extent replaced by red sandstone 
 
CHAP. XY. Gypseous Formation. 557 
 
 and black calcareous slialy rocks, alternating togetlier. 
 The white indurated tuff, bed (11), here contains little 
 or no gypsum, whereas on the northern and opposite 
 side of the valley, it is of much greater thickness and 
 abounds with layers of gypsum, some of them alterna- 
 ting with thin seams of crystalline carbonate of lime. 
 The uppermost, dark coloured, hard mudstone (bed 12) 
 is in this neighbourhood the most constant stratum. 
 The whole series differs to a considerable extent, 
 especially in its upper part, from that met with at 
 fBB], in the lower part of the valley; nevertheless, I 
 do not doubt that they are equivalents. 
 
 Fourth Axis of Mevation (Valley of Copiajpo). — 
 This axis is formed of a chain of mountains [F], of 
 which the central masses (near La Punta) consist of 
 andesite containing green hornblende and coppery mica, 
 and the outer masses of greenish and black porphyries, 
 together with some fine lilac-coloured clay-stone por- 
 phyry ; all these porphyries being injected and broken 
 up by small hummocks of andesite. The central great 
 mass of this latter rock, is covered on the eastern side 
 by a black, fine-grained, highly micaceous slate, which, 
 together with the succeeding mountains of porphyry, 
 are traversed by numerous white dikes, branching from 
 the andesite, and some of them extending in straight 
 lines, to a distance of at least two miles. The mountains 
 of porphyry eastward of the micaceous schist soon, but 
 gradually, assume (as observed in so many other cases) 
 a stratified structure, and can then be recognised as a 
 part of the porphyritic conglomerate formation. These 
 strata [G] are inclined at a high angle to the SE., and 
 form a mass from 1,500 to 2,000 feet in thickness. 
 The gypseous masses to the west already described, dip 
 directly towards this axis, with the strata only in a few 
 places (one of which is represented in the section) 
 
55^ Valley of Copiapo. paet n. 
 
 thrown from it ; hence this fourth axis is mainly 
 nniclinal towards the SE., and just like our third axis, 
 only locally anticlinal. 
 
 The above strata of porphyritic conglomerate [G] 
 with their south-eastward dip, come abruptly up against 
 beds of the gypseous formation [H], which are gently, 
 but irregularly, inclined westward : so that there is 
 here a synclinal axis and great fault. Farther up the 
 valley, here running nearly north and south, the gypse- 
 ous formation is prolonged for some distance ; but the 
 stratification is unintelligible, the whole being broken 
 up by faults, dikes, and metalliferous veins. The strata 
 consist chiefly of red calcareous sandstones, with nume- 
 rous veins, in the place of layers, of gypsum ; the sand- 
 stone is associated with some black calcareous slate-rock, 
 and with green pseudo-honestones, passing into porce- 
 lain-jasper. Still farther up the valley, near Las Amo- 
 lanas [I], the gypseous strata become more regular, 
 dipping at an angle of between 30° and 40° to WSW., 
 and conformably overlying, near the mouth of the ravine 
 of Jolquera, strata [K] of porphyritic conglomerate. The 
 whole series has been tilted by a partially concealed 
 axis [L], of granite, andesite, and a granitic mixture 
 of white feldspar, quartz, and oxide of iron. 
 
 'Fifili Axis of 'Elevation (Valley of Cojoiajpo, near 
 Las Amolanas). — I will describe in some detail the 
 beds [I] seen here, which, as just stated, dip to WSW., 
 at an angle of from 30° to 40°. I had not time to 
 examine the underlying porphyritic conglomerate, of 
 which the lowest beds, as seen at the mouth of the 
 Jolquera, are highly compact, with crystals of red oxide 
 of iron ; and I am not prepared to say whether they 
 are chiefly of volcanic or metamorphic origin. On 
 these beds there rests a coarse purplish conglomerate, 
 very little metamorphosed, composed of pebbles of 
 
CHAP. xY. Porphyritic Formation. 559 
 
 porphyry, but remarkable from containing one pebble 
 of granite ; — of wbicli fact no instance has occurred in 
 the sections hitherto described. Above this conglome- 
 rate, there is a black siliceous clay-stone, and above it 
 numerous alternations of dark-purplish and green por- 
 phyries, which may be considered as the uppermost 
 limit of the porphyritic conglomerate formation. 
 
 Above these porphyries comes a coarse, arenaceous 
 conglomerate, the lower half white and the upper half 
 of a pink colour, composed chiefly of pebbles of various 
 porphyries, but with some of red sandstone and jaspery 
 rocks. In some of the more arenaceous parts of the 
 conglomerate, there was an oblique or current lamina- 
 tion ; a circumstance which I did not elsewhere observe. 
 Above this conglomerate, there is a vast thickness of 
 thinly stratified, pale-yellowish, siliceous sandstone, 
 passing into a granular quartz-rock, used for grindstones 
 (hence the name of the place Ijcls Amolcvnas)^ and 
 certainly belonging to the gypseous formation, as does 
 probably the immediately underlying conglomerate. 
 In this yellowish sandstone there are layers of white 
 and pale-red siliceous conglomerate ; other layers with 
 small, well-rounded pebbles of white quartz, like the 
 bed at the R. Claro at Coquimbo ; others of a greenish, 
 fine-grained, less siliceous stone, somewhat resembling 
 the pseudo-honestones lower down the valley ; and 
 lastly, others of a black calcareous shale-rock. In one 
 of the layers of conglomerate, there was embedded a 
 fragment of mica-slate, of which this is the first instance ; 
 hence, perhaps, it is from a formation of mica-slate, 
 that the numerous small pebbles of quartz, both here 
 and at Coquimbo, have been derived. Not only does 
 the siliceous sandstone include layers of the black, 
 thinly stratified, not fissile, calcareous shale-rock, but 
 in one place the whole mass, especially the upper part. 
 
^6o Valley of Copiapo. part n. 
 
 was, in a marvellously short horizontal distance, after 
 frequent alternations, replaced by it. When this 
 occurred, a mountain-mass, several thousand feet in 
 thickness, was thus composed ; the black calcareous 
 shale-rock, however, always included some layers of the 
 pale-yellowish siliceous sandstone, of the red conglome- 
 rate, and of the greenish jaspery and pseudo-honestone 
 varieties. It likewise included three or four widely 
 separated layers of a brown limestone, abounding with 
 shells immediately to be described. This pile of strata 
 was in parts traversed by many veins of gypsum. The 
 calcareous shale-rock, though when freshly broken quite 
 black, weathers into an ash-colour; in which respect 
 and in general appearance, it perfectly resembles those 
 great fossiliferous beds of the Peuquenes range, alterna- 
 ting with gypsum and red sandstone, described in the 
 last chapter. 
 
 The shells out of the layers of brown limestone, in- 
 cluded in the black calcareous shale-rock, which latter, 
 as just stated, replaces the white siliceous sandstone, 
 consist of — 
 
 Pecten Dufreynoyi, d'Orbig. ' Voyage, Part. Pal.' 
 Turritella Andii, do. 
 
 Eelations given in the list from Coquimbo. 
 
 Astarte Darwinii, E. Forbes, PI. V. figs. 22, 23. 
 Grypheea Darwinii, do. PL V. fig. 7. 
 
 An intermediate form between G. gigantea and G. incurva. 
 
 Gryphaea, nov. spec. ? do. PI. V. figs. 8 and 9. 
 Perna Americana, do. PL V. figs. 4, 5, 6. 
 Avicula, nov. spec. 
 
 Considered by Mr. G. B. Sowerby as the A. echinata, by M. 
 d'Orbigny as certainly a new and distinct species, having a Jurassic 
 aspect. The specimen has been unfortunately lost. 
 
CHAP. XY. Fossil Shells. 561 
 
 Terebratula senigma, d'Orbig. (var. of do. E. Forbes, 
 PI. V. figs. 13, 14). 
 
 This is the same variety, with that from Guasco, considered bj^ 
 M. d'Orbigny to be a distinct species from his T. ^enigma, and related 
 to T. obsoleta. 
 
 Plagiostoma and Ammonites, fragments of. 
 
 Tbe lower layers of tlie limestone contained thou- 
 sands of the Gryplisea ; and tlie upper ones as many 
 of the Turritella, with the Gryphsea (nov. spec.) and 
 Serpulee adhering to them ; in all the layers, the Tere- 
 bratula and fragments of the Pecten were included. 
 It was evident, from the manner in which the species 
 were grouped together, that they had lived where now 
 embedded. Before making any further remarks, I may 
 state, that higher up this same valley we shall again 
 meet with a similar association of shells ; and in the 
 great Despoblado Valley, which branches off near the 
 town from that of Copiapo, the Pecten Dufreynoyi, 
 some Gryphites (I believe G. Darwinii), and the irue 
 Terebratula senigma of d'Orbigny were found together 
 in an equivalent formation as will be hereafter seen. 
 A specimen also, I may add, of the true T. genigma, 
 was given me from the neighbourhood of the famous 
 silver mines of Chanuncillo, a little south of the valley 
 of Copiapo, and these mines, from their position, I have 
 no doubt, lie within the great gypseous formation : the 
 rocks close to one of the silver veins, judging from 
 fragments shown me, resemble those singular meta- 
 morphosed deposits from the mining district of Arqueros 
 near Coquimbo. 
 
 I will reiterate the evidence on the association of 
 these several shells in the several localities. 
 
 o o 
 
562 
 
 Valley of Copiapo. 
 
 PART II. 
 
 Goqtdmho. 
 
 Pecten Dufreynoyi ^ 
 Ostrea hemispherica [ 
 Terebratula enigma i 
 Spirifer linguiferoidesj 
 
 Hippnrites Chilensis 
 Gryphtea orientalis 
 
 Terebratula ffinig-ma 
 
 — ignaciana 
 
 Pecten Dufreynoyi 
 Ostrea hemispherica 
 Hippnrites Chilensis 
 Turritella Andii 
 Nautilus Domeykus 
 
 Pecten Dufreynoyi 
 Turritella Andii 
 Terebratula ignaciana 
 
 fenigma, i'ar. 
 
 in the same bed, llio Claro. 
 
 same bed, near Arqueros. 
 
 in same block 
 of limestone. 
 
 Collected by M . Domeyko 
 from the same locality, 
 apparently near Arque- 
 ros. 
 
 Spirifer Chilensis. 
 
 Giiasco. 
 
 In a collection from the Cordillera, 
 given me : the specimens all in the 
 same condition. 
 
 Goinwpo. 
 
 Pecten Dufreynoyi n 
 
 Turritella Andii 
 
 Terebratula ^enigma, var. as at Guasco 
 
 Astarte Darwinii 
 
 Gryphsea Darwinii 
 
 nov. spec. ? 
 
 Perna Americana 
 Avicala, nov. spec. 
 
 Mingled together in alter- 
 nating beds in the main 
 valley of Copiapo near 
 Las Amolanas, and like- 
 wise higher up the valley. 
 
 Terebratula senigma (true) 
 
 Terebratula asnigma 
 Pecten Dufreynoyi 
 Gryphtea Darwinii ? 
 
 (true) 
 
 [ Main valley of Copiapo, apparently 
 \ same formation with that of 
 ( Amolanas. 
 
 In the same bed, high up the great 
 lateral valley of the Despoblado, 
 in the ravine of Maricongo. 
 
 Considering this table, I tliink it is impossible to 
 clonbt that all these fossils belong to the same formation. 
 If, however, the species from Las Amolanas, in the 
 Valley of Copiapo, had, as in the case of those from 
 Guasco, been separately examined, they would probably 
 have been ranked as oolitic ; for, although no Spirifers 
 
CHAP. XV. Conglomerate with Silicified Wood. 563 
 
 were found here, all tlie other species, with the excep- 
 tion of the Pecten, Turritella, and Astarte, have a more 
 ancient aspect than cretaceous forms. On the other 
 hand, taking into account the evidence derived from 
 the cretaceous character of these three shells, and of 
 the Hippurites, Gryph^a orientalis, and Ostrea, from 
 Coquimbo, we are driven back to the provisional name 
 already used of cretaceo- oolitic. From geological 
 evidence, I believe this formation to be the equiva- 
 lent of the Neocomian beds of the Cordillera of Central 
 Chile. 
 
 To return to our section near Las Amolanas : — 
 Above the yellow siliceous sandstone, or the equivalent 
 calcareous slate-rock, with its bands of fossil-shells, 
 according as the one or the other prevails, there is 
 a pile of strata, which cannot be less than from 2,000 
 to 3,000 feet in thickness, in main part composed of 
 a coarse, bright, red conglomerate, with many inter- 
 calated beds of red sandstone, and some of green and 
 other coloured porcelain-jaspery layers. The included 
 pebbles are well rounded, varying from the size of an 
 egg to that of a cricket-ball, with a few larger ; and 
 they consist chiefly of porphyries. The basis of the 
 conglomerate, as well as some of the alternating thin 
 beds, are formed of a red, rather harsh, easily fusible 
 sandstone, with crystalline calcareous particles. This 
 whole great pile is remarkable from the thousands of 
 huge, embedded, silicified trunks of trees, one of which 
 was eight feet long, and another eighteen feet in cir- 
 cumference : how marvellous it is, that every vessel in 
 so thick a mass of wood should have been converted 
 into silex ! I brought home many specimens, and all of 
 them, according to Mr. R. Brown, present a coniferous 
 structure. 
 
 Above this great conglomerate, we have from 200 to 
 
 002 
 
564 Valley of Copiapo. paet n. 
 
 300 feet in thickness of red sandstone ; and above this, 
 a stratum of black calcareous slate-rock, like that 
 which alternates with and replaces the underlying 
 yellowish white, siliceous sandstone. Close to the 
 junction between this upper black slate-rock and the 
 upper red sandstone, I found the GrypluBa Darwinii, 
 the Turritella Andii, and vast numbers of a bivalve, 
 too imperfect to be recognised. Hence we see that, as 
 far as the evidence of these two shells serves — and the 
 Turritella is an eminently characteristic species — the 
 whole thickness of this vast pile of strata belongs to 
 the same age. Again, above the last-mentioned upper 
 red sandstone, there were several alternations of the 
 black, calcareous slate-rock ; but I was unable to ascend 
 to them. All these uppermost strata, like the lower ones, 
 vary extremely in character in short horizontal distances. 
 The gypseous formation, as here seen, has a coarser, 
 more mechanical texture, and contains much more 
 siliceous matter than the corresponding beds lower 
 down the valley. Its total thickness, together with the 
 upper beds of the porphyritic conglomerate, I estimated 
 at least at 8,000 feet ; and only a small portion of the 
 porphyritic conglomerate, which on the eastern flank of 
 the fourth axis of elevation appeared to be from 1,500 
 to 2,000 feet thick, is here included. As corroborative 
 of the great thickness of the gypseous formation, I 
 may mention that in the Despoblado Yalley (which 
 branches from the main valley a little above the town 
 of Copiapo) I found a corresponding pile of red and 
 white sandstones, and of dark, calcareous, semi-jaspery 
 mudstones, rising from a nearly level surface and 
 thrown into an absolutely vertical position ; so that, by 
 pacing, I ascertained their thickness to be nearly 2,700 
 feet ; taking this as a standard of comparison, I esti- 
 
CHAP. xy. Conglomerate with Silicified Wood. 565 
 
 mated the tHckness of the strata cihove the porphyritic 
 conglomerate at 7,000 feet. 
 
 The fossils before enumerated, from the limestone- 
 layers in the whitish siliceous sandstone, are now 
 covered, on the least computation, by strata from 5,000 
 to 6,000 feet in thickness. Professor E. Forbes thinks 
 that these shells probably lived at a depth of from about 
 thirty to forty fathoms, that is from 180 to 240 feet; 
 anyhow, it is impossible that they could have lived at 
 the depth of from 6,000 to 6,000 feet. Hence in this 
 case, as in that of the Puente del Inca, we may safely 
 conclude that the bottom of the sea on which the shells 
 lived, subsided, so as to receive the superincumbent 
 submarine strata : and this subsidence must have taken 
 place during the existence of these shells ; for, as I 
 have shown, some of them occur high up as well as low 
 ■down in the series. That the bottom of the sea sub- 
 sided, is in harmony with the presence of the layers of 
 coarse well-rounded pebbles included throughout this 
 whole pile of strata, as well as of the great upper mass 
 of conglomerate from 2,000 to 3,000 feet thick ; for 
 coarse gravel could hardly have been formed or spread 
 out at the profound depths indicated by the thickness 
 of the strata. The subsidence, also, must have been 
 slow to have allowed of this often-recurrent spreading 
 out of the pebbles. Moreover, we shall presently see 
 that the surfaces of some of the streams of porphyritic 
 lava beneath the gypseous formation, are so highly 
 amygdaloidal that it is scarcely possible to believe that 
 they flowed under the vast pressure of a deep ocean. 
 The conclusion of a great subsidence during the exist- 
 ence of these cretaceo-oolitic fossils, may, I believe, 
 be extended to the district of Coquimbo, although 
 owing to the fossiliferous beds there not being directly 
 
566 Valley of Copiapo. part n. 
 
 covered by the upper gypseous strata, wMcli in the 
 section north of the valley are about 6,000 feet in thick- 
 ness, I did not there insist on this conclusion. 
 
 The pebbles in the above conglomerates, both in 
 the upper and lower beds, are all well rounded, and, 
 though chiefly composed of various porphyries, there 
 are some of red sandstone and of a jaspery stone, both 
 like the rocks intercalated in layers in this same 
 gypseous formation ; there was one pebble of mica- slate 
 and some of quartz, together with many particles of 
 quartz. In these respects there is a wide difference 
 between the gypseous conglomerates and those of the 
 porphyritic- conglomerate formation, in which latter, 
 angular and rounded fragments, almost exclusively 
 composed of porphyries, are mingled together, and 
 which, as already often remarked, probably were ejected 
 from craters deep under the sea. From these facts I 
 conclude, that during the formation of the conglome- 
 rates, land existed in the neighbourhood, on the shores 
 of which the innumerable pebbles were rounded and 
 thence dispersed, and on which the coniferous forests 
 flourished — for it is improbable that so many thousand 
 logs of wood should have been drifted from any great 
 distance. This land, probably islands, must have been 
 mainly formed of porphyries, with some mica-slate, 
 whence the quartz was derived, and with some red sand- 
 stone and jaspery rocks. This latter fact is important, 
 as it shows that in this district, even previously to the 
 deposition of the lower gypseous or cretaceo-oolitic beds, 
 strata of an analogous nature had elsewhere, no doubt 
 in the more central ranges of the Cordillera, been 
 elevated; thus recalling to our minds the relations of 
 the Cumbre and Uspallata chains. Having already 
 referred to the great lateral valley of the Despoblado, 
 I may mention that above the 2,700 feet of red and 
 
CHAP. XT. Ravine of Jolquera. 567 
 
 white sandstone and dark mudstone, tliere is a vast 
 mass of coarse, hard, red conglomerate, some thousand 
 feet in thickness, which contains mnch silicified wood, 
 and evidently corresponds with the great upper con- 
 glomerate at Las Amolanas : here, however, the con- 
 glomerate consists almost exclusively of pebbles of 
 granite, and of disintegrated crystals of reddish feldspar 
 and quartz firmly recemented together. In this case, 
 we may conclude that the land whence the pebbles were 
 derived, and on which the now silicified trees once 
 flourished, was formed of granite. 
 
 The mountains near Las Amolanas, composed of 
 the cretaceo-oolitic strata, are interlaced with dikes like 
 a spider's web, to an extent which I have never seen 
 equalled, except in the denuded interior of a volcanic 
 crater : north and south lines, however, predominate. 
 These dikes are composed of green, white, and blackish 
 rocks, all porphyritic with feldspar, and often with 
 large crystals of hornblende. The white varieties 
 approach closely in character to andesite, which com- 
 poses, as we have seen, the injected axes of so many of 
 the lines of elevation. Some of the green varieties are 
 finely laminated, parallel to the walls of the dikes. 
 
 Sixili Axis of JEleuation (Valley of Goinajpo). — 
 This axis consists of a broad mountainous mass [0] of 
 andesite, composed of albite, brown mica, and chlorite, 
 passing into andesitic granite, with quartz : on its 
 western side it has thrown ofi", at a considerable angle, 
 a thick mass of stratified porphyries, including much 
 epidote [NN], and remarkable only from being divided 
 into very thin beds, as highly amygdaloidal on their 
 surfaces as sub-aerial lava-streams are often vesicular. 
 This porphyritic formation is conformably covered, as 
 seen some way up the ravine of Jolquera, by a mere 
 remnant of the lower part of the cretaceo-oolitic 
 
568 Valley of Cop lap : part n. 
 
 formation [M M], which in one part encases, as repre- 
 sented in the coloured section, the foot of the andesitic 
 axis [L], of the already described fifth line, and in 
 another part entirely conceals it : in this latter case, 
 the gypseous or cretaceo-oolitic strata falsely appeared 
 to dip under the porphyritic conglomerate of the fifth 
 axis. The lowest bed of the gypseous formation, as 
 seen here [M], is of yellowish siliceous sandstone, pre- 
 cisely like that of Amolanas, interlaced in parts with 
 veins of gypsum, and including layers of the black, 
 calcareous, non-fissile slate-rock : the Turritella Andii^ 
 Pecten Dufreynoyi, Terehrakda cenigma, var. and 
 some Gryphites were embedded in these layers. The 
 sandstone varies in thickness from only twenty to eighty 
 feet ; and this variation is caused by the inequalities in 
 the upper surface of an underlying stream of purple 
 clay-stone porphyry. Hence the above fossils here lie 
 at the very base of the gypseous or cretaceo-oolitic 
 formation, and hence they were probably once covered 
 up by strata about 7,000 feet in thickness : it is, how- 
 ever, possible, though from the nature of all the other 
 sections in this district not probable, that the por- 
 phyritic clay-stone lava may in this case have invaded a 
 higher level in the series. Above the sandstone there 
 is a considerable mass of much indurated, purplish- 
 black, calcareous clay-stone, allied in nature to the 
 often-mentioned black calcareous slate-rock. 
 
 Eastward of the broad andesitic axis of this sixth 
 line, and penetrated by many dikes from it, there is 
 a great formation [P] of mica-schist, with its usual 
 variations, and passing in one part into a ferruginous 
 quartz-rock. The folio are curved and highly inclined, 
 generally dipping eastward. It is probable that this 
 mica-schist is an old formation, connected with the 
 granitic rocks and metamorphic schists near the coast ; 
 
CHAP. xy. near Castano. 569 
 
 and that the one fragment of mica- slate, and the pebbles 
 of quartz low down in the gypseous formation at Las 
 Amolanas, have been derived from it. The mica-schist 
 is succeeded by stratified porphyritic conglomerate [Q] 
 of great thickness, dipping eastward with a high in- 
 clination : I have included this latter mountain-mass 
 in the same anticlinal axis with the jDorphyritic streams 
 [N N] ; but I am far from sure that the two masses 
 may not have been independently upheaved. 
 
 Seventh' Axis of JElevation. — Proceeding up the 
 ravine, we come to another mass [R] of andesite ; and 
 beyond this, we again have a very thick, stratified por- 
 phyritic formation [S], dipping at a small angle east- 
 ward, and forming the basal part of the main Cordillera. 
 I did not ascend the ravine any higher; but here, 
 near Castano, I examined several sections, of which I 
 will not give the details, only observing, that the por- 
 phyritic beds, or submarine lavas, preponderate greatly 
 in bulk over the alternating sedimentary layers, which 
 have been but little metamorphosed : these latter con- 
 sist of fine-grained red tuffs and of whitish volcanic 
 grit-stones, together with much of a singular, compact 
 rock, having an almost crystalline basis, finely brec- 
 ciated with red and green fragments, and occasionally 
 including a few large pebbles. The porphyritic lavas 
 are highly amygdaloidal, both on their upper and 
 lower surfaces ; they consist chiefly of clay-stone por- 
 phyry, but with one common variety, like some of the 
 streams at the Puente del Inca, having a gray mottled 
 basis, abounding with crystals of red hydrous oxide of 
 iron, green ones apparently of epidote, and a few glassy 
 ones of feldspar. This pile of strata differs consider- 
 ably from the basal strata of the Cordillera in Central 
 Chile, and may possibly belong to the upper and 
 gypseous series : I saw, however, in the bed of the 
 
570 Valley of Copiapo. part n. 
 
 valley, one fragment of porphyritic breccia-conglome- 
 rate, exactly like those great masses met witli in the 
 more southern parts of Chile. 
 
 linally, I must observe, that though I have de- 
 scribed between the town of Copiapo and the western 
 flank of the main Cordillera seven or eight axes of 
 elevation, extending nearly north and south, it must 
 not be supposed that they all run continuously for 
 great distances. As was stated to be the case in our 
 sections across the Cordillera of Central Chile, so here 
 most of the lines of elevation, with the exception of 
 the first, third, and fifth, are very short. The stratifi- 
 cation is everywhere disturbed and intricate ; nowhere 
 have I seen more numerous faults and dikes. The 
 whole district, from the sea to the Cordillera, is more 
 or less metalliferous ; and I heard of gold, silver, 
 copper, lead, mercury, and iron veins. The metamor- 
 phic action, even in the lower strata, has certainly 
 been far less here than in Central Chile. 
 
 Valley of the BesiJohlado. — This great barren valley, 
 which has already been alluded to, enters the main 
 valley of Copiapo a little above the town : it runs at 
 first northerly, then NE , and more easterly into the 
 Cordillera ; I followed its dreary course to the foot of 
 the first main ridge. I will not give a detailed section, 
 because it would be essentially similar to that already 
 given, and because the stratification is exceedingly 
 complicated. After leaving the plutonic hills near the 
 town, I met first, as in the main valley, with the gypseous 
 formation, having the same diversified character as be- 
 fore, and soon afterwards with masses of porphyritic 
 conglomerate, about 1,000 feet in thickness. In the 
 lower part of this formation there were very thick beds 
 composed of fragments of clay-stone porphyries, both 
 angular and rounded, with the smaller ones partially 
 
CHAP. XV. Valley of the Despoblado. 571 
 
 blended together and the basis rendered porphyritic ; 
 these beds separated distinct streams, from sixty to 
 eighty feet in thickness, of clay-stone lavas. Near 
 Paipote, also, there was much true porphyritic breccia- 
 conglomerate : nevertheless, few of these masses were 
 metamorphosed to the same degree with the corre- 
 sponding formation in Central Chile. I did not meet in 
 this valley with any true andesite, but only with im- 
 perfect andesitic porphyry, including large crystals of 
 hornblende : numerous as have been the varieties of 
 intrusive porphyries already mentioned, there were here 
 mountains composed of a new kind, having a compact, 
 smooth, cream-coloured basis, including only a few 
 crystals of feldspar, and mottled with dendritic spots of 
 oxide of iron. There were also some mountains of a 
 porphyry with a brick-red basis, containing irregular, 
 often lens-shaped, patches of compact feldspar, and 
 crystals of feldspar, which latter to my surprise I find 
 to be orthite. 
 
 At the foot of the first ridge of the main Cordillera, 
 in the ravine of Maricongo, and at an elevation which, 
 from the extreme coldness and appearance of the vege- 
 tation, I estimated at about 10,000 feet, I found beds of 
 white sandstone and of limestone including the Peden 
 I)ufrey7ioyi, Terehrahda cenigma, and some Gryphites. 
 This ridge throws the water on the one hand into the 
 Pacific, and on the other, as I was informed, into a 
 great gravel-covered, basin-like plain, including a salt- 
 lake, and without any drainage-exit. In crossing the 
 Cordillera by this Pass, it is said that three principal 
 ridges must be traversed, instead of two, or only one as 
 in Central Chile. 
 
 The crest of this first main ridge and the surround- 
 ing mountains, with the exception of a few lofty 
 pinnacles, are capped by a great thickness of a hori- 
 
572 Coptapo. PAET II. 
 
 zontally stratified, tufaceous deposit. The lowest bed 
 is of a pale purple colour, hard, fine-grained, and full 
 of broken crystals of feldspar and scales of mica. The 
 middle bed is coarser, and less hard, and hence weathers 
 into very sharp pinnacles ; it includes very small frag 
 ments of granite, and innumerable ones of all sizes Ox 
 gray vesicular trachyte, some of which were distinctly 
 rounded. The uppermost bed is about 200 feet in 
 thickness, of a darker colour and apparently hard ; but 
 I had not time to ascend to it. These three horizontal 
 beds may be seen for the distance of many leagues, 
 especially westward or in the direction of the Pacific, 
 capping the summits of the mountains, and standing on 
 the opposite sides of the immense valleys at exactly 
 corresponding heights. If united they would form a 
 plain, inclined very slightly towards the Pacific ; the 
 beds become thinner in this direction, and the tuff 
 (judging from one point to which I ascended, some 
 way down the valley) finer-grained and of less specific 
 gravity, though still compact and sonorous under the 
 hammer. The gently inclined, almost horizontal 
 stratification, the presence of some rounded pebbles, 
 and the compactness of the lowest bed, though render- 
 ing it probable, would not have convinced me that this 
 mass had been of subaqueous origin, for it is known 
 that volcanic ashes falling on land and moistened by 
 rain often become hard and stratified ; but beds thus 
 originating, and owing their consolidation to atmo- 
 spheric moisture, would have covered almost equally 
 every neighbouring summit, high and low, and would 
 not have left those above a certain exact level abso- 
 lutely bare; this circumstance seems to me to prove 
 that the volcanic ejections were arrested at their pre- 
 sent, widely extended, equable level, and there con- 
 solidated by some other means than simple atmospheric 
 
CHAP. XY. Valley of the Despoblado. 573 
 
 moisture ; and this no doubt must liave been a sheet of 
 water. A lake at this great height, and without a 
 barrier on any one side, is out of the question ; conse- 
 quently we must conclude that the tufaceous matter 
 was anciently deposited beneath the sea. It was cer- 
 tainly deposited before the excavation of the valleys, or 
 at least before their final enlargement ; ^ and I may 
 add, thab Mr. Lambert, a gentleman well acquainted 
 with this country, informs me, that in ascending the 
 ravine of Santandres (which branches off from the Des- 
 poblado) he met with streams of lava and much erupted 
 matter capping all the hills of granite and porphyry, 
 with the exception of some projecting points ; he also 
 remarked that the valleys had been excavated subse- 
 quently to these eruptions. 
 
 This volcanic formation, which I am informed by 
 Mr. Lambert extends far northward, is of interest, as 
 typifying what has taken place on a grander scale on 
 the corresponding western side of the Cordillera of 
 Peru. Under another point of view, however, it pos- 
 sesses a far higher interest, as confirming that conclu- 
 sion drawn from the structure of the fringes of stratified 
 shingle which are prolonged from the plains at the foot 
 of the Cordillera far up the valleys, — namely, that this 
 great range has been elevated in mass to a height ot 
 between 8,000 and 9,000 feet ;^ and now, judging from 
 this tufaceous deposit, we may conclude that the hori- 
 
 * I have endeavoured to show in my 'Journal,' &c. (2nd edit.) 
 p. 355, that this arid valley was left by the retreating sea, as the 
 land slowly rose, in the state in which we now see it. 
 
 2 I may here mention that on the south side of the main valley 
 of Copiapo, near Potrero Seco, the mountains are capped by a thick 
 mass of horizontally stratified shingle, at a height which I estimated 
 at between 1,500 and 2,000 feet above the bed of the valley. This 
 shingle, I believe, forms the edge of a wide plain, which stretches 
 southwards between two mountain ranges. 
 
574 
 
 Copiapo. 
 
 PART II. 
 
 zontal elevation has been in the district of Copiapo 
 about 10,000 feet. 
 
 In the valley of the Despoblado, the stratification, 
 as before remarked, has been much disturbed, and in 
 some points to a greater degree than I have anywhere 
 else seen. I will give two cases : a very thick mass of 
 thinly stratified red sandstone, including beds of con- 
 glomerate, has been crushed together (as represented 
 in the woodcut) into a yoke or urn-formed trough, so 
 that the strata on both sides have been folded inwards : 
 on the right hand the properly underlying porphyritic 
 clay stone conglomerate is seen overlying the sandstone, 
 but it soon becomes vertical, and then is inclined to- 
 wards the trough, so that the beds radiate like the 
 
 No. 40. 
 
 spokes of a wheel : on the left hand, the inverted por- 
 phyritic conglomerate also assumes a dip towards the 
 trough, not gradually, as on the right hand, but by 
 means of a vertical fault and synclinal break ; and a 
 little still farther on towards the left, there is a second 
 great oblique fault (both shown by the arrow-lines), 
 with the strata dipping to a directly opposite point : 
 these mountains are intersected by infinitely numerous 
 dikes, some of which can be seen to rise from hummocks 
 of greenstone, and can be traced for thousands of feet. 
 In the second case, two low ridges trend together and 
 unite at the head of a little wedge-shaped valley; 
 
CHAP. XT. Iquique, Peru. 575 
 
 througliout the right-hand ridge, the strata dip at 45° 
 to the east : in the left-hand ridge, we have the very 
 same strata and at first with exactly the same dip ; but 
 in following this ridge up the valley, the strata are 
 seen very regularly to become more and more inclined 
 xintil they stand vertical, they then gradually fall over, 
 {the basset edges forming symmetrical serpentine lines 
 along the crest) till at the very head of the valley they 
 are reversed at an angle of 45° : so that at this point 
 the beds have been turned through an angle of 135°; 
 and here there is a kind of anticlinal axis, with the 
 strata on both sides dipping to opposite points at an 
 angle of 4 5°, but with those on the left hand upside- 
 down. 
 
 On the Eruptive Sources of the Porphyritic Clay- 
 stone and Greenstone Lavas. — In Central Chile, from 
 the extreme metamorphic action, it is in most parts 
 difficult to distinguish between the streams of porphyritic 
 lava and the porphyritic breccia-conglomerate, but 
 here, at Copiapo, they are generally perfectly distinct, 
 and in the Despoblado, I saw for the first time, two 
 great strata of purple clay-stone porphyry, after having 
 been for a considerable space closely united together, 
 one above the other, become separated by a mass of 
 fragmentary matter, and then both thin out ; — the 
 lower one more rapidly than the upper and greater 
 stream. Considering the number and thickness of the 
 streams of porphyritic lava, and the great thickness of 
 the beds of breccia-conglomerate, there can be little 
 doubt that the sources of eruption must originally have 
 been numerous : nevertheless, it is now most difficult 
 aven to conjecture the precise point of any one of the 
 ancient submarine craters. I have repeatedly observed 
 mountains of porphyries, more or less distinctly strati- 
 fied towards their summits or on their flanks, without a 
 
576 Iquiqtie, Peru. part ii. 
 
 trace of stratification in their central and basal parts : 
 in most cases, I believe this is simply due either to the 
 obliterating effects of metamorphic action, or to such 
 parts having been mainly formed of intrusive por- 
 phyries, or to both causes conjoined ; in some instances^ 
 however, it appeared to me very probable that the 
 great central unstratified masses of porphyry were the 
 now partially denuded nuclei of the old submarine 
 volcanos, and that the stratified parts marked the 
 points whence the streams flowed. In one case alone, 
 and it was in this Valley of the Despoblado, I was able 
 actually to trace a thick stratum of purplish porphyry, 
 which for a space of some miles conformably overlay 
 the usual alternating beds of breccia-conglomerates and 
 clay-stone lavas, until it became united with, and blended 
 into, a mountainous mass of various unstratified por- 
 phyries. 
 
 The difficulty of tracing the streams of porphyries- 
 to their ancient and doubtless numerous eruptive 
 sources, may be partly explained by the very general 
 disturbance which the Cordillera in most parts has 
 suffered ; but I strongly suspect that there is a more 
 specific cause, namely, iliat the original points of 
 eruption tend to become the points of injection. This 
 in itself does not seem improbable ; for where the earth's, 
 crust has once yielded, it would be liable to yield 
 again, though the liquefied intrusive matter might not 
 be any longer enabled to reach the submarine surface 
 and flow as lava. I have been led to this conclusion, 
 from having so frequently observed that, where part of 
 an unstratified mountain-mass resembled in mineralo- 
 gical character the adjoining streams or strata, there 
 were several other kinds of intrusive porphyries and 
 andesitic rocks injected into the same point. As these 
 intrusive mountain-masses form most of the axes-lines 
 
CHAP. XV. Iqtnque, Peru. 577 
 
 in the Cordillera, whether anticlinal, uniclinal, or syn- 
 clinal, and as the main valleys have generally been 
 hollowed out along these lines, the intrusive masses 
 have generally suffered much denudation. Hence they 
 are apt to stand in some degree isolated, and to be 
 situated at the points where the valleys abruptly bend, 
 or where the main tributaries enter. On this view of 
 there being a tendency in the old points of eruption to 
 become the points of subsequent injection and dis- 
 turbance, and consequently of denudation, it ceases to 
 be surprising that the streams of lava in the porphyritic 
 clay stone conglomerate formation, and in other analo- 
 gous cases, should most rarely be traceable to their 
 actual sources. 
 
 Iquique, Southern Peru. — Differently from what we 
 have seen throughout Chile, the coast here is formed 
 not by the granitic series, but by an escarpment of the 
 porphyritic conglomerate formation, between 2,000 and 
 3,000 feet in height.^ I had time only for a very short 
 examination ; the chief part of the escarpment appears 
 to be composed of various reddish and purple, some- 
 times laminated, porphyries, resembling those of Chile ; 
 and I saw some of the porphyritic breccia-conglomerate ; 
 the stratification appeared but little inclined. The 
 uppermost part, judging from the rocks near the famous 
 silver mine of Huantajaya,^ consists of laminated, im- 
 pure, argillaceous, purplish-gray limestone, associated, 
 I believe, with some purple sandstone. In the lime- 
 stone shells are found : the three following species were 
 given me : — 
 
 * The lowest point, where the road crosses the coast-escarpment, 
 is 1,900 feet by the barometer above the level of the sea. 
 
 "^ Mr. BoUaert has described (' Geolog. Proceedings,' vol. ii. p. 
 598) a sing'ular mass of stratified detritus, gravel, and sand, eighty-one 
 yards in thickness, overlying the limestone, and abounding with loose 
 masses of silver ore. The miners believe that they can attribute 
 these masses to their proper veins. 
 
 PP 
 
57^ . IqtnqiLe, Pertt. part ii. 
 
 Lucina Americana, E. Forbes, PL V. fig. 24., 
 Terebratula inca, do. PL Y, figs. 19, 20. 
 senigma, D'Orbig. PL V. figs. 10, 11, 12. 
 
 Tliis latter species we have seen associated with the 
 fossils of which lists have been given in this chapter, in 
 two places in the valley of Coquimbo, and in the ravine 
 of Maricongo at Copiapo. Considering this fact, and 
 the superposition of these beds on the porphyritic con- 
 glomerate formation ; and, as we shall immediately see, 
 from their containing much gypsum, and from their 
 otherwise close general resemblance in mineralogical 
 nature with the strata described in the valley of Copiapo, 
 I have little doubt that these fossiliferous beds of Iquique 
 belong to the great cretaceo-oolitic formation of Northern 
 Chile. Iquique is situated seven degrees latitude north 
 of Copiapo ; and I may here mention, that an Ammon- 
 ites, nov. spec, and Astarte, nov. spec, were given me 
 from the Cerro Pasco, about ten degrees of latitude north 
 of Iquique, and M. d'Orbigny thinks that they probably 
 indicate a Neocomian formation. Again, fifteen degrees 
 of latitude northward, in Colombia, there is a grand 
 fossiliferous deposit, now well known from the labours 
 of Yon Buch, Lea, d'Orbigny, and Forbes, which be- 
 longs to the earlier stages of the cretaceous system. 
 Hence, bearing in mind the character of the few fossils 
 from Tierra del Fuego, there is some evidence that a 
 great portion of the stratified deposits of the whole vast 
 range of the South American Cordillera belongs to 
 about the same geological epoch. 
 
 Proceeding from the coast escarpment inwards, I 
 crossed, in a space of about thirty miles, an elevated 
 undulatory district, with the beds dipping in various 
 directions. The rocks are of many kinds, — white 
 laminated, sometimes siliceous sandstone, — purple and 
 
CHAP. XV. Iquique, Peru. 579 
 
 red sandstone, sometimes so highly calcareous as to 
 have a crystalline fracture, — argillaceous limestone, — 
 black calcareous slate-rock, like that so often described 
 at Copiapo and other places, — thinly laminated, fine- 
 grained, greenish, indurated, sedimentary, fusible rocks, 
 approaching in character to the so-called pseudo-hone- 
 stone of Chile, including thin contemporaneous veins of 
 gypsum, — and lastly, much calcareous, laminated por- 
 celain j asper, of a green colour, with red spots, and of 
 extremely easy fusibility : I noticed one conformable 
 stratum of a freckled-brown, feldspathic lava. I may 
 here mention that I heard of great beds of gypsum in 
 the Cordillera. The only novel point in this formation, is 
 the presence of innumerable thin layers of rock-salt, 
 alternating with the laminated and hard, but sometimes 
 earthy, yellowish, or bright red and ferruginous sand- 
 stones. The thickest layer of salt was only two inches, 
 and it thinned out at both ends. On one of these 
 saliferous masses I noticed a stratum about twelve feet 
 thick, of dark-brown, hard brecciated, easily fusible 
 rock, containing grains of quartz and of black oxide of 
 iron, together with numerous imperfect fragments of 
 shells. The problem of the origin of salt is so obscure, 
 that every fact, even geographical position, is worth 
 recording.^ With the exception of these saliferous 
 
 ^ It is well known that stratified salt is found in several places on 
 the shores of Peru. The island of San Lorenzo, off Lima, is composed 
 of a pile of thin strata, about 800 feet in thickness, composed of 
 yellowish and purplish, hard siliceous, or earthy sandstones, alter- 
 nating with thin layers of shale, which in places passes into a 
 greenish, semi-porcellanic, fusible rock. There are some thin beds of 
 reddish mudstone, and soft ferruginous rotten-stones, with layers of 
 gypsum. In nearly all these varieties, especially in the softer sand- 
 stones, there are numerous thin seams of rock-salt : I was informed 
 that one layer has been found two inches in thickness. The manner 
 in which the minutest fissures of the dislocated beds have been 
 penetrated by the salt, apparently by subsequent infiltration, is very 
 curious. On the south side of the island, layers of coal and of 
 impure limestone have been discovered. Hence we here have salt, 
 
 p p 2 
 
580 Metalliferous Veins. part ii. 
 
 beds, most of the rocks, as already remarked, present 
 a striking general resemblance with the upper parts of 
 the gypseous or cretaceo-oolitic formation of Chile. 
 
 Metalliferotts Veins. 
 
 I have only a few remarks to make on this subject :: 
 in nine mining districts, some of them of considerable 
 extent, which I visited in Central Chile, I found the 
 principal veins running from between [N. and NW.] 
 to [S. and SE.] : ^ in some other places, however, their 
 course appeared quite irregular, as is said to be gene- 
 rally the case in the whole valley of Copiapo : at Tam- 
 billos, south of Coquimbo, I saw one large copper vein 
 extending east and west. It is worthy of notice, that 
 the foliation of the gneiss and mica -slate, and the 
 cleavage of the altered clay-slate, where such rocks 
 occur, certainly tend to run like the metalliferous 
 veins, though often irregularly, in a direction a little 
 westward of north. At Yaquil, I observed that the prin- 
 cipal auriferous veins ran nearly parallel to the grain or 
 imperfect cleavage of the sui rounding granitic rocks. 
 
 gypsum, and coal associated together. The strata include veins of 
 quartz, carbonate of lime, and iron pyrites ; they have been dislocated 
 by an injected mass of greenish-brown feldspathic trap. 
 
 Not only is salt abundant on the extreme western limits of the 
 district between the Cordillera and the Pacific, but, according to 
 Helms, it is found in the outlying low hills on the eastern flank of the 
 Cordillera. These facts appear to me opposed to the theory, that 
 rock-salt is due to the sinking of water, charged with salt, in medi- 
 terranean spaces of the ocean. The general character of the geology 
 of these countries would rather lead to the opinion, that its origin 
 is in some way connected with volcanic heat at the bottom of the 
 sea : see on this subject, Sir E. Murchison's Anniversary Address to 
 Geolog. Soc. 1843, p. 65. 
 
 ^ These mining districts are Yaquil near Nancagua, where the 
 direction of the chief veins, to which only in all cases I refer, is 
 north and south ; in the Uspallata range, the prevailing line is NNW. 
 and SSE. ; in the C. de Prado, it is NNW. and SSE. ; near Illapel, it 
 is N. by W. and S. by E. ; at Los Hornos, the direction varies from 
 between [N. and NW.] to [S. and SE]. ; at the C. de los Hornos 
 (farther northward), it is NNW. and SSE. ; at Panuncillo, it is NNW. 
 and SSE. : and, lastly, at Arqueros, the direction is NW. and SE. 
 
-CHAP. XV. Metalliferous Veins. 581 
 
 Witli respect to the distribution of the diflferent metals, 
 copper, gold, and iron are generally associated together, 
 and are most frequently found (but with many ex- 
 <jeptions, as we shall presently see) in the rocks of the 
 lower series, between the Cordillera and the Pacific, 
 namely, in granite, syenite, altered feldspathic clay- 
 slate, gneiss, and as near Guasco mica-schist. The 
 copper- ores consist of sulphurets, oxides, and carbon- 
 ates, sometimes with lamina3 of native metal : I was 
 assured that in some cases (as at Panuncillo SE. of Co- 
 quimbo) the upper part of the same vein contains oxides, 
 and the lower part sulphurets of copper.^ Gold occurs 
 in its native form ; it is believed that, in many cases, 
 the upper part of the vein is the most productive part : 
 this fact probably is connected with the abundance of 
 this metal in the stratified detritus of Chile, which 
 must have been chiefly derived from the degradation of 
 the upper portions of the rocks. These superficial beds 
 of well-rounded gravel and sand, containing gold, 
 appeared to me to have been formed under the sea 
 close to the beach, during the slow elevation of the 
 land : Schmidtmeyer ^ remarks that in Chile gold is 
 sought for in shelving banks at the height of some feet 
 on the sides of the streams, and not in their beds, as 
 would have been the case had this metal been deposited 
 by common alluvial action. Very frequently the 
 copper-ores, including some gold, are associated with 
 abundant micaceous specular iron. Gold is often 
 found in iron-pyrites: at two gold mines at Yaquil 
 (near Nancagua), I was informed by the proprietor 
 that in one the gold was always associated with copper- 
 pyrites, and in the other with iron-pyrites: in this 
 
 ^ The same fact has been observed by Mr. Taylor in Cuba; 
 ^ London Phil. Journ.' vol. xi. p. 21. 
 2 ' Travels in Chile,' p. 29. 
 
582 Metalliferotis Veins. part n. 
 
 latter case, it is said tliat if tlie vein ceases to contain 
 iron-pyrites, it is yet worth wMle to continue the 
 search, but if the iron-pyrites, when it reappears, is not 
 auriferous, it is better at once to give up working the 
 vein. Although I believe copper and gold are most 
 frequently found in the lower granitic and metamorphic 
 schistose series, yet these metals occur both in the 
 porphyritic conglomerate formation (as on the flanks of 
 the Bell of Quillota and at Jajuel), and in the superin- 
 cumbent strata. At Jajuel I was informed that the 
 copper-ore, with some gold, is found only in the green- 
 stones and altered feldspathic clay-slate, which alternate 
 with the purple porphyritic conglomerate. Several 
 gold veins and some of copper-ore are worked in several 
 parts of the Uspallata range, both in the metamor- 
 phosed strata, which have been shown to have been of 
 probably subsequent origin to the Neocomian or gyp- 
 seous formation of the main Cordillera, and in the 
 intrusive andesitic rocks of that range. At Los Hornos 
 (NE. of Illapel), likewise, there are numerous veins of 
 copper-pyrites and of gold, both in the strata of the 
 gypseous formation and in the injected hills of andesite 
 and various porphyries. 
 
 Silver, in the form of a chloride, sulphuret, or an 
 amalgam, or in its native state, and associated with 
 lead and other metals, and at Arqueros with pure 
 native copper, occurs chiefly in the upper great gyp- 
 seous or cretaceo-oolitic formation, which forms pro- 
 bably the richest mass in Chile. We may instance 
 the mining districts of Arqueros near Coquimbo, 
 and of nearly the whole valley of Copiapo, and of 
 Iquique (where the principal veins run NE. by E. and 
 SW. by W.), in Peru. Hence comes Molina's remark, 
 that silver is born in the cold and solitary deserts of 
 the upper Cordillera. There are, however, exceptions 
 
CHAP. XT. Metal iifei'oiis Veins. 583 
 
 to tHs rule : at Paral (SE. of Ooquimbo) silver is found 
 in the porphyritic conglomerate formation ; as I suspect 
 is likewise tlie case at S. Pedro de ISTolasko in the 
 Peuquenes Pass. Rich argentiferous lead is found in 
 the clay-slate of the Uspallata range ; and I saw an old 
 silver mine in a hill of syenite at the foot of the Bell of 
 Quillota : I was also assured that silver has been found 
 in the andesitic and porphyritic region between the 
 town of Copiapo and the Pacific. I have stated in a 
 previous part of this chapter, that in two neighbouring 
 mines at Arqueros the veins in one were productive 
 when they traversed the singular green sedimentary 
 beds, and unproductive when crossing the reddish beds ; 
 whereas at the other mine exactly the reverse takes 
 place ; I have also described the singular and rare case 
 of numerous particles of native silver and of the chloride 
 being disseminated in the green rock at the distance of 
 a yard from the vein. Mercury occurs with silver both 
 at Arqueros and at Copiapo : at the base of C. de los 
 Hornos (SE. of Ooquimbo, a different place from Los 
 Hornos, before mentioned) I saw in a syenitic rock 
 numerous quartzose veins, containing a little cinnabar 
 in nests : there were here other parallel veins of copper 
 and of a ferrugino-auriferous ore. I believe tin has 
 never been found in Chile. 
 
 From information given me by Mr. Nixon of Yaquil,^ 
 and by others, it appears that in Chile those veins are 
 generally most permanently productive, which consist- 
 ing of various minerals (sometimes differing but slightly 
 from the surrounding rocks), include parallel strings 
 ridi in metals ; such a vein is called a veta real. More 
 commonly the mines are worked only where one, two, 
 
 ^ At the Durazno mine, the gold is associated with copper-pyrites, 
 and the veins contain large prisms of plumbago. Crystallised car- 
 bonate of lime is one of the commonest minerals in the matrix of 
 the Chilian veins. 
 
584 Metalliferotts Veins. paet h. 
 
 or more thin veins or strings running in a different 
 direction, intersect a 'poor ' veta real : ' it is unanimously 
 believed that at such points of intersection (cruceros), 
 the quantity of metal is much greater than that con- 
 tained in other parts of the intersecting veins. In some 
 criiceros or points of intersection, the metals extend 
 even beyond the walls of the main, broad, stony vein. 
 It is said that the greater the angle of intersection, the 
 greater the produce; and that nearly parallel strings 
 attract each other ; in the Uspallata range, I observed 
 that numerous thin auri-ferruginous veins repeatedly 
 ran into knots, and then branched out again. I have 
 already described the remarkable manner in which rocks 
 of the Uspallata range are indurated and blackened (as 
 if by a blast of gunpowder) to a considerable distance 
 from the metallic veins. 
 
 Finally, I may observe, that the presence of metallic 
 veins seems obviously connected with the presence of 
 intrusive rocks, and with the degree of metamorphic 
 action which the different districts of Chile have 
 undergone.^ Such metamorphosed areas are generally 
 accompanied by numerous dikes and injected masses 
 of andesite and various porphyries : I have in several 
 places traced the metalliferous veins from the in- 
 trusive masses into the encasing strata. Knowing 
 that the porphyritic conglomerate formation consists of 
 alternate streams of submarine lavas and of the debris 
 of anciently erupted rocks, and that the strata of the 
 upper gypseous formation sometimes include submarine 
 lavas, and are composed of tuffs, mudstones, and mineral 
 substances, probably due to volcanic exhalations, — the 
 richness of these strata is highly remarkable when com- 
 
 * Sir E. Murchison and his fellow travellers have given some 
 striking facts on this subject in their account of the Ural Mountains. 
 ' Geolog. Proc' vol. iii. p. 748. 
 
•CHAP. XY. The Chilian Cordillera, 585 
 
 pared with the erupted beds, often of submarine origin, 
 but not metamoTjpliosed^ whicli compose the numerous 
 islands in the Pacific, Indian, and Atlantic Oceans ; for 
 in these islands metals are entirely absent, and their 
 rnature even unknown to the aborigines. 
 
 ■Summary on the Geological History of the Chilian 
 Cordillera J and of the Southern Parts of South 
 America. 
 
 We have seen that the shores of the Pacific, for a 
 ;space of 1,200 miles from Tres Montes to Copiapo, and 
 I believe for a very much greater distance, are com- 
 posed, with the exception of the tertiary basins, of meta- 
 morphic schists, plutonic rocks, and more or less altered 
 •clay-slate. On the floor of the ocean thus constituted, 
 vast streams of various purplish clay-stone and green- 
 stone porphyries were poured forth, together with great 
 ■alternating piles of angular and rounded fragments of 
 similar rocks ejected from the submarine craters. From 
 the compactness of the streams and fragments, it is 
 probable that, with the exception of some districts in 
 Northern Chile, the eruptions took place in profoundly 
 deep water. The orifices of eruption appear to have 
 been studded over a breadth, with some outliers, of 
 irom 50 to 100 miles : and closely enough together, 
 both north and south, and east and west, for the ejected 
 matter to form a continuous mass, which in Central 
 Chile is more than a mile in thickness. I traced this 
 mould-like mass, for only 450 miles ; but judging from 
 what I saw at Iquique, from specimens, and from 
 published accounts, it appears to have a manifold 
 greater length. In the basal parts of the series, and 
 especially towards the flanks of the range, mud, since 
 converted into a feldspathic slaty rock, and sometimes 
 
586 StLinmary of the StructtLre paet n. 
 
 into green-stone, was occasionally deposited between 
 the beds of erupted matter : with this exception the 
 uniformity of the porphyritic rocks is very remarkable. 
 
 At the period when the clay-stone and green-stone 
 porphyries nearly or quite ceased being erupted, that 
 great pile of strata which, from often abounding with 
 gypsum, I have generally called the Gypseous formation 
 was deposited, and feldspathic lavas, together with 
 other singular volcanic rocks, were occasionally poured 
 forth : I am far from pretending that any distinct line 
 of demarkation can be drawn between this formation 
 and the underlying porphyries and porphyritic con- 
 glomerate, but in a mass of such great thickness, and 
 between beds of such widely different mineralogical 
 nature, some division was necessary. At about the 
 commencement of the gypseous period, the bottom of 
 the sea here seems first to have been peopled by shells, 
 not many in kind, but abounding in individuals. At 
 the P. del Inca the fossils are embedded near the base 
 of the formation ; in the Peuquenes range, at different 
 levels, half-way up, and even higher in the series ; 
 hence, in these sections, the whole great pile of strata 
 belongs to the same period : the same remark is appli- 
 cable to the beds at Copiapo, which attain a thickness of 
 between 7,000 and 8,000 feet. The fossil shells in the 
 Cordillera of Central Chile, in the opinion of all the 
 paleeontologists who have examined them, belong to 
 the earlier stages of the cretaceous system; whilst in 
 Northern Chile there is a most singular mixture of cre- 
 taceous and oolitic forms : from the geological relations, 
 however, of these two districts, I cannot but think that 
 they all belong to nearly the same epoch, which I have 
 provisionally called cretaceo-oolitic. 
 
 The strata in this formation, composed of black 
 calcareous shaly-rocks of red and white, and sometimes 
 
CHAP. XY. of the Cordillera. 587 
 
 siliceous sandstones, of coarse conglomerates, lime- 
 stones, tuffs, dark mud-stones, and those singular fine- 
 grained rocks which I have called pseudo-honestones, 
 vast beds of gypsum, and many other jaspery and 
 scarcely describable varieties, vary and replace each 
 other in short horizontal distances, to an extent, I 
 believe, unequalled even in any tertiary basin. Most 
 of these substances are easily fusible, and have appa- 
 rently been derived either from volcanos still in quiet 
 action, or from the attrition of volcanic products. If 
 we picture to ourselves the bottom of the sea, rendered 
 uneven in an extreme degree, with numerous craters, 
 some few occasionally in eruption, but the greater 
 number in the state of solfataras, discharging calcareous, 
 siliceous, ferruginous matters, and gypsum or sulphuric 
 acid to an amount surpassing, perhaps, even the exist- 
 ing sulphureous volcanos of Java,^ we shall probably 
 understand the circumstances under which this singular 
 pile of varying strata was accumulated. The shells 
 appear to have lived at the quiescent periods when only 
 limestone or calcareo-argillaceous matter was deposit- 
 ing. From Dr. Gillies's account, this gypseous or 
 cretaceo-oolitic formation extends as far south as the 
 Pass of Planchon, and I followed it northward at in- 
 tervals for 500 miles : judging from the character of the 
 beds with the Terehratida cenigma^ at Iquique, it 
 extends from 400 to 500 miles farther; and perhaps 
 even for ten degrees of latitude north of Iquique to the 
 Cerro Pasco, not far from Lima : again, we know that 
 a cretaceous formation, abounding with fossils, is largely 
 developed north of the equator, in Columbia : in Tierra 
 del Fuego, at about this same period, a wide district of 
 clay-slate was deposited, which in its mineralogical 
 
 ' Von Buch's ' Descript. Physique des lies Canaries,' p. 428. 
 
588 Summary of the Structure part n. 
 
 characters and external features, miglit be compared to 
 tlie Silurian regions of North Wales. The gypseous 
 formation, like that of the porphyritic breccia-conglo- 
 merate on which it rests, is of inconsiderable breadth ; 
 though of greater breadth in Northern than in Central 
 Chile. 
 
 As the fossil shells in this formation are covered, in 
 the Peuquenes ridge by a great thickness of strata, at 
 the Puente del Inca by at least 5,000 feet ; at Coquimbo, 
 though the superposition there is less plainly seen, by 
 -about 6,000 feet; and at Copiapo certainly by 5,000 
 or 6,000, and probably by 7,000 feet (the same species 
 there recurring in the upper and lower parts of the 
 series) we may feel confident that the bottom of the 
 sea subsided during this cretaceo-oolitic period, so as 
 to allow of the accumulation of the superincumbent 
 submarine strata. This conclusion is confirmed by, or 
 perhaps rather explains, the presence of the many beds 
 at many levels of coarse conglomerate, the well-rounded 
 pebbles in which we cannot believe were transported in 
 very deep water. Even the underlying porphyries at 
 Copiapo, with their highly amygdaloidal surfaces, do 
 not appear to have flowed under great pressure. The 
 great sinking movement thus plainly indicated, must 
 have extended in a north and south line for at least 
 400 miles, and probably was co-extensive with the 
 ^gypseous formation. 
 
 The beds of conglomerate just referred to, and the 
 extraordinarily numerous silicified trunks of fir-trees 
 at Los Hornos, perhaps at Coquimbo and at two dis- 
 tant points in the valley of Copiapo, indicate that land 
 existed at this period in the neighbourhood. This land, 
 or islands, in the northern part of the district of 
 Copiapo, must have been almost exclusively composed, 
 judging from the nature of the pebbles, of granite ; in 
 
CHAP. XV. of the Cordillera. 589 
 
 tlie southern parts of Copiapo, it must iiave been 
 mainly formed of clay-stone porphyries, with some 
 mica-schist, and with much sand-stone and jaspery 
 rocks exactly like the rocks in the gypseous formation, 
 and no doubt belonging to its basal series. In several 
 other places also, during the accumulation of the 
 gypseous formation, its basal parts and the underlying 
 porphyritic conglomerate must likewise have been 
 already partially upheaved and exposed to wear and 
 tear ; near the Puente del Inca and at Ooquimbo, there 
 must have existed masses of mica-schist or some such 
 rock, whence were derived the many small pebbles of 
 opaque quartz. It follows from these facts, that in 
 some parts of the Cordillera the upper beds of the 
 gypseous formation must lie unconformably on the 
 lower beds ; and the whole gypseous formation, in 
 parts, unconformably on the porphyritic conglomerate ; 
 although I saw no such cases, yet in many places the 
 gypseous formation is entirely absent ; and this, although 
 no doubt generally caused by quite subsequent denuda- 
 tion, may in others be due to the underlying porphy- 
 ritic conglomerate having been locally uj)heaved before 
 the deposition of the gypseous strata, and thus having 
 become the source of the pebbles of porphyry embedded 
 in them. In the porphyritic conglomerate formation, 
 in its lower and middle parts, there is very rarely any 
 evidence, with the exception of the small quartz pebbles 
 at Jajuel, near Aconcagua, and of the single pebble of 
 granite at Copiapo, of the existence of neighbouring- 
 land : in the upper parts, however, and especially in the 
 district of Copiapo, the number of thoroughly well- 
 rounded pebbles of compact porphyries make me be- 
 lieve, that, as during the prolonged accumulation of 
 the gypseous formation the lower beds had already been 
 locally upheaved and exposed to wear and tear, so it 
 
590 Sttmniary of the Strttchtre paet n. 
 
 was with the porphyritic conglomerate. Hence in 
 following thus far the geological history of the Cor- 
 dillera, it may be inferred that the bed of a deep and 
 open, or nearly open, ocean was filled up by porphyritic 
 eruptions, aided probably by some general and some 
 local elevations, so that comparatively shallow level at 
 which the cretaceo-oolitic shells first lived. At this 
 period, the submarine craters yielded at intervals a 
 prodigious supply of gypsum and other mineral exhala- 
 tions, and occasionally, in certain places poured forth 
 lavas, chiefly of a feldspathic nature : at this period, 
 islands clothed with fir-trees and composed of porphy- 
 ries, primary rocks, and the lower gypseous strata had 
 already been locally upheaved, and exposed to the 
 action of the waves ; — the general movement, however, 
 at this time having been over a very wide area, one ot 
 slow subsidence, prolonged till the bed of the sea sank 
 several thousand feet. 
 
 In Central Chile, after the deposition of a great 
 thickness of the gypseous strata, and after their up- 
 heaval, by which the Cumbre and adjoining ranges were 
 formed, a vast pile of tufaceous matter and submarine 
 lava was accumulated, where the Uspallata chain now 
 stands ; also after the deposition and upheaval of the 
 equivalent gypseous strata of the Peuquenes range, the 
 great thick mass of conglomerate in the valley of 
 Tenuyan was accumulated: during the deposition of 
 the Uspallata strata, we know absolutely, from the 
 buried vertical trees, that there was a subsidence of 
 some thousand feet ; and we may infer from the nature 
 of the conglomerate in the valley of Tenuyan, that a 
 similar and perhaps contemporaneous movement there 
 took place. We have, then, evidence of a second great 
 period of subsidence ; and, as in the case of the sub- 
 sidence which accompanied the accumulation of the 
 
€HVP. XT. of the Cordillera. 591 
 
 cretaceo-oolitic strata, so tliis later subsidence appears 
 to have been complicated by alternate or local elevatory 
 movement — for tlie vertical trees, buried in the midst 
 of the Uspallata strata, must have grown on dry land, 
 formed by the upheaval of the lower submarine beds. 
 Presently I shall have to recapitulate the facts, showing 
 that at a still later period, namely, at nearly the com- 
 mencement of the old Tertiary deposits of Patagonia and 
 of Chile, the continent stood at nearly its present level, 
 and then for the third time, slowly subsided to the 
 amount of several hundred feet, and was afterwards 
 slowly re-uplifted to its present level. 
 
 The highest peaks of the Cordillera appear to con- 
 sist of active or more commonly dormant volcanos, — 
 such as Tupungato, Maypu, and Aconcagua, which 
 latter stands 23,000 feet above the level of the sea, and 
 many others. The next highest peaks are formed of 
 the gypseous and porphyritic strata, thrown into vertical 
 or highly inclined positions. Besides the elevation thus 
 gained by angular displacements, I infer, without any hesi- 
 tation — from the stratified gravel-fringes which gently 
 slope up the valleys of the Cordillera from the gravel- 
 capped plains at their base, which latter are connected 
 with the plains, still covered with recent shells on the 
 €oast — that this great range has been upheaved in mass 
 by a slow movement, to an amount of at least 8,000 
 feet. In the Despoblado Valley, north of Copiapo, the 
 horizontal elevation, judging from the compact, stra- 
 tified tufaceous deposit, capping the distant mountains 
 at corresponding heights, was about 10,000 feet. It is 
 very possible, or rather probable, that this elevation in 
 mass may not have been strictly horizontal, but more 
 energetic under the Cordillera, than towards the coast 
 on either side ; nevertheless, movements of this kind 
 may be conveniently distinguished from those by which 
 
592 Summary of the Strticture part h. 
 
 strata have been abruptly broken and upturned. When 
 viewing the Cordillera, before having read Mr. Hopkins's 
 profound ' Eesearches on Physical Geology,' the convic- 
 tion was impressed on me, that the angular dislocations, 
 however violent, were quite subordinate in importance 
 to the great upward movement in mass, and that they 
 had been caused by the edges of the wide fissures, 
 which necessarily resulted from the tension of the 
 elevated area, having yielded to the inward rush of 
 fluidified rock, and having thus been upturned. 
 
 The ridges formed by the angularly upheaved strata 
 are seldom of great length : in the central parts of the 
 Cordillera they are generally parallel to each other, 
 and run in north and south lines ; but towards the- 
 flanks they often extend more or less obliquely. The- 
 angular displacement has been much more violent in 
 the central than in the exterior 'main lines ; but it has 
 likewise been violent in some of the minor lines on the 
 extreme flanks. The violence has been very unequal 
 on the same short lines ; the crust having apparently 
 tended to yield on certain points along the lines of 
 fissures. These points, I have endeavoured to show, 
 were probably first foci of eruption, and afterwards of 
 injected masses of porphyry and andesite.^ The close 
 similarity of the andesitic granites and porphyries, 
 throughout Chile, Tierra del Fuego, and even in Peru, 
 is very remarkable. The prevalence of feldspar cleav- 
 ing like albite, is common not only to the andesites, 
 but (as I infer from the high authority of Prof. G. 
 Rose, as well as from my own measurements) to the 
 various clay-stone and green-stone porphyries, and to 
 
 ^ Sir E.. Murchison, and his companions state (' Geolog. Proc' 
 vol. iii. 13. 747), that no true granite ajDpears in the higher Ural 
 Mountains ; but that syenitic greenstone — a rock closely analogous 
 to our anclesite — is by far the most abundant of the intrusive masses. 
 
CHAP. XV. of the Cordillera. 593 
 
 tlie trachytic lavas of the Cordillera. The andesitic 
 rocks have in most cases been the last injected ones, 
 and they probably form a continuous dome under this 
 great range : they stand in intimate relationship with 
 the modern lavas ; and they seem to have been the 
 immediate agent in metamorphosing the porphyritic 
 conglomerate formation, and often likewise the gypseous 
 strata, to the extraordinary extent to which they have 
 suffered. 
 
 With respect to the age at which the several parallel 
 ridges composing the Cordillera were upthrown, I have 
 little evidence. Many of them may have been con- 
 temporaneously elevated and injected in the same 
 manner ^ as in volcanic archipelagoes lavas are contem- 
 poraneously ejected on the parallel lines of fissure. 
 But the pebbles apparently derived from the wear and 
 tear of the porphyritic conglomerate formation, which 
 are occasionally present in the upper parts of this same 
 formation, and are often present in the gypseous for- 
 mation, together with the pebbles from the basal parts 
 of the latter formation in its upper strata, render it 
 almost certain that portions, we may infer ridges, of 
 these two formations were successively upheaved. In 
 the case of the gigantic Portillo range, we may feel 
 almost certain that a pre-existing granitic line was up- 
 raised (not by a single blow, as shown by the highly 
 inclined basaltic streams in the valley on its eastern 
 flank) at a period long subsequent to the upheavement 
 of the parallel Peuquenes range. ^ Again, subsequently 
 
 * See the latter part of Chapter VI. 
 
 2 I have endeavoured to show in my 'Journal ' (2nd edit. p. 321), 
 that the singular fact of the river, which drains the valley between 
 these two ranges, passing through the Portillo and higher line, is 
 explained by its slow and subsequent elevation. There are many 
 analogous cases in the drainage of rivers : see ' Edinburgh New Phil. 
 Journal,' vol. xxviii. pp. 33 and 44. 
 
 Q Q 
 
594 Structure of the Cordillera. paet ir. 
 
 to the uplieavement of the Cumbre chain, that of 
 Uspallata was formed and elevated ; and afterwards, I 
 may add, in the plain of Uspallata, beds of sand and 
 gravel were violently upthrown. The manner in which 
 the various kinds of porphyries and andesites have been 
 injected one into the other, and in which the infinitely 
 numerous dikes of various composition intersect each 
 other, plainly show that the stratified crust has been 
 stretched and yielded many times over the same points. 
 With respect to the age of the axes of elevation between 
 the Pacific and the Cordillera, I know little : but there 
 are some lines which must — namely, those running 
 north and south in Chiloe, those eight or nine east and 
 west, parallel, far-extended, most symmetrical uniclinal 
 lines at P. Kumena, and the short NW.-SE. and NE.- 
 SW. lines at Ooncepcion — have been upheaved long 
 after the formation of the Cordillera. Even during the 
 earthquake of 1835, when the linear north and south 
 islet of St. Mary was uplifted several feet above the 
 surrounding area, we perhaps see one feeble step in the 
 formation of a subordinate mountain-axis. In some 
 cases, moreover, for instance, near the baths of Cauquenes, 
 I was forcibly struck with the small size of the breaches 
 cut through the exterior mountain-ranges, compared 
 with the size of the same valleys higher up where enter- 
 ing the Cordillera ; and this circumstance appeared 
 to me scarcely explicable, except on the idea of the 
 exterior lines having been subsequently upthrown, and 
 therefore having been exposed to a less amount of denu- 
 dation. From the manner in which the fringes of 
 gravel are prolonged m unbroken slopes up the valleys 
 of the Cordillera, I infer that most of the greater dis- 
 locations took place during the earlier parts of the great 
 elevation in mass : I have, however, elsewhere given a 
 case, and M. de Tschudi * has given another, of a ridge 
 * ' Keise in Peru,' Band 2. s. 8 :— Author's Journal, 2nd edit. p. 359. 
 
CHAP. XT. Sottth America, 595 
 
 thrown up in Peru across the bed of a river, and conse- 
 quently after the final elevation of the country above 
 the level of the sea. 
 
 Ascending to the older Tertiary formations, I will 
 not again recapitulate the remarks already given at the 
 end of the Twelfth Chapter, — on their great extent, es- 
 pecially along the shores of the Atlantic — on their anti- 
 quity, perhaps corresponding with that of the Eocene 
 deposits of Europe, — on the almost entire dissimilarity, 
 though the formations are apparently contemporaneous, 
 of the fossils from the eastern and western coasts, as is 
 likewise the case, even in a still more marked degree, 
 with the shells now living in these opposite though 
 approximate seas, — on the climate of this period not 
 having been more tropical than what might have been 
 expected from the latitudes of the places under which 
 the deposits occur ; a circumstance rendered well 
 worthy of notice, from the contrast with what is known 
 to have been the case during the older Tertiary periods 
 of Europe, and likewise from the fact of the Southern 
 Hemisphere having suffered at a much later period, 
 apparently at the same time with fche Northern Hemi- 
 sphere, a colder or more equable temperature, as shown 
 by the zones formerly affected by ice-action. Nor will 
 I recapitulate the proofs of the bottom of the sea, both 
 on the eastern and western coast, having subsided 700 
 or 800 feet during this Tertiary period ; the movement 
 having apparently been co-extensive, or nearly co-ex- 
 tensive, with the deposits of this age. Nor will I again 
 give the facts and reasoning on which the proposition 
 was founded, that when the bed of the sea is either 
 stationary or rising, circumstances are far less favour- 
 able than when its level is sinking, to the accumulation 
 of conchiferous deposits of sufficient thickness, exten- 
 sion, and hardness to resist, when upheaved, the 
 
 a Q 2 
 
596 Stimmary of Tertiary Formations pakt n. 
 
 ordinary vast amount of denudation. We liave seen 
 that the highly remarkable fact of the absence of any 
 extensive formations containing recent shells, either on 
 the eastern or western coasts of the continentj — though 
 these coasts now abound with living Mollusca, — though 
 they are, and apparently have always been, as favour- 
 able for the deposition of sediment as they were when 
 the Tertiary formations were copiously deposited, — and 
 though they have been upheaved to an amount quite 
 sufficient to bring up strata from the depths the most 
 fertile for' animal life, — can be explained in accordance 
 with the above proposition. As a deduction, it was also 
 attempted to be shown, first, that the want of close 
 sequence in the fossils of successive formations, and of 
 successive stages in the same formation, would follow 
 from the improbability of the same area continuing 
 slowly to subside from one whole period to another, or 
 even during a single entire period ; and secondly, that 
 certain epochs having been favourable at distant points, 
 in the same quarter of the world for the synchronous 
 accumulation of fossiliferous strata, would follow from 
 movements of subsidence having apparently, like those 
 of elevation, contemporaneously affected very large 
 areas. 
 
 There is another point which deserves some notice, 
 namely, the analogy between the upper parts of the 
 Patagonian Tertiary formation, as well as of the upper 
 possibly contemporaneous beds at Ohiloe and Concep- 
 cion, with the great gypseous formation of Cordillera ; 
 for in both formations, the rocks, in their fusible nature, 
 in their containing gypsum, and in many other cha- 
 racters, show a connection, either intimate or remote, 
 with volcanic action; and as the strata in both were 
 accumulated during subsidence, it appears at first 
 natural to connect this sinjiing movement with a state 
 
CHAP. XV. of South America. 597 
 
 of higli activity in the neiglibouring volcanos. During 
 the cretaceo-oolitic period this certainly appears to have 
 been the case at the Puente del Inca, judging from the 
 number of intercalated 'lava-streams in the lower 3,000 
 feet of strata ; but generally, the volcanic orifices seem 
 at this time to have existed as submarine solfataras, and 
 were certainly quiescent compared with their state 
 during the accumulation of the porphyritic conglomerate 
 formation. During the deposition of the tertiary strata 
 we know that at S. Cruz, deluges of basaltic lava were 
 poured forth ; but as these lie in the upper part of the 
 series, it is possible that the subsidence may at that 
 time have ceased : at Chiloe, I was unable to ascertain 
 to what part of the series the pile of lavas belonged. 
 The Uspallata tufis and great streams of submarine 
 lavas, were probably intermediate in age between the 
 cretaceo-oolitic and older Tertiary formations, and we 
 know from the buried trees that there was a great sub- 
 sidence during their accumulation ; but even in this 
 case, the subsidence may not have been strictly con- 
 temporaneous with the great volcanic eruptions, for we 
 must believe in at least one intercalated period of eleva- 
 tion, during which the ground was upraised on which 
 the now buried trees grew. I have been led to make 
 these remarks, and to throw some doubt on the strict 
 contemporaneousness of high volcanic activity and 
 movements of subsidence, from the conviction impressed 
 on my mind by the study of coral formations,^ that 
 these two actions do not generally go on synchronously ; 
 — on the contrary, that in volcanic districts, subsidence 
 ceases as soon as the orifices burst forth into renewed 
 action, and only recommences when they again have 
 become dormant. 
 
 1 The Structure, &c. of Coral Eeefs, 1st ed. p. 140 ; 2nd ed. p. 180. 
 
598 Summary of Recent Elevatory paut n. 
 
 At a later period, tlie Pampean mud, of estuary 
 origin, was deposited over a wide area, — in one district 
 conformably on tlie underlying old tertiary strata, and 
 in another district unconformably on them, after their 
 upheaval and denudation. During and before the 
 accumulation, however, of these old Tertiary strata, 
 and, therefore, at a very remote period, sediment, 
 strikingly resembling that of the Pampas, was depo- 
 sited ; showing during how long a time in this case the 
 same agencies were at work in the same area. The 
 deposition of the Pampean estuary mud was accom- 
 panied, at least in the southern parts of the Pampas, 
 by^an elevatory movement, so that the M. Hermoso 
 beds probably were accumulated after the upheaval of 
 those round the S. Ventana ; and those at P. Alta after 
 the upheaval of the Monte Hermoso strata ; but there 
 is some reason to suspect that one period of subsidence 
 intervened, during which mud was deposited over the 
 coarse sand of the Barrancas de S. Gregorio, and on the 
 higher parts of Banda Oriental. The mammiferous 
 animals characteristic of this formation, many of which 
 differ as much from the present inhabitants of South 
 America, as do the eocene mammals of Europe from 
 the present ones of that quarter of the globe, certainly 
 co-existed at B. Blanca with twenty species of mollusca, 
 one balanus, and two corals, all now living in the 
 adjoining sea : this is likewise the case in Patagonia 
 with the Macrauchenia, which co-existed with eight 
 shells, still the commonest kinds on that coast. I will 
 not repeat what I have elsewhere said, on the place of 
 habitation, food, wide range, and extinction of the 
 numerous gigantic mammifers, which at this late 
 period inhabited the two Americas. 
 
 The nature and grouping of the shells embedded in 
 the old Tertiary formations of Patagonia and Chile, 
 
CHAP. XV. Movements of South America. 599 
 
 show us, tliat the continent at that period must have 
 stood only a few fathoms below its present level, and 
 that afterwards it subsided over a wide area, 700 or 
 800 feet. The manner in which it has since been re- 
 brought up to its actual level, was described in detail 
 in the Eighth and Ninth Chapters. It was there shown 
 that recent shells are found on the shores of the Atlan- 
 tic, from Tierra del Euego northward for a space of at 
 least 1,180 nautical miles, and at the height of about 
 100 feet in La Plata, and of 400 feet in Patagonia. 
 The elevatory movements on this side of the continent 
 have been slow \ and the coast of Patagonia, up to the 
 height in one part of 950 feet and in another of 1,200 
 feet, is modelled into eight great, step-like, gravel- 
 capped plains, extending for hundreds of miles with the 
 same heights ; this fact shows that the periods of denu- 
 dation (which, judging from the amount of matter 
 removed, must have been long-continued) and of eleva- 
 tion were synchronous over surprisingly great lengths 
 of coasts. On the shores of the Pacific, upraised shells 
 of recent species, generally, though not always, in the 
 same proportional numbers as in the adjoining sea, 
 have actualh^ been found over a north and south space 
 of 2,075 miles, and there is reason to believe that they 
 occur over a space of 2,480 miles. The elevation on 
 this western side of the continent has not been equable ; 
 at Valparaiso, within the period during which upraised 
 shells have remained undecayed on the surface, it has 
 been 1,300 feet, whilst at Coquimbo, 200 miles north- 
 ward, it has been within this same period only 252 
 feet. At Lima, the land has been uplifted at least 
 eighty- feet since Indian man inhabited that district; 
 but the level within historical times apparently has 
 subsided. At Coquimbo, in a height of 364 feet, the 
 elevation has been interrupted by five periods of com- 
 
6oo Sum7nary of Recent Elevatory part ir. 
 
 parative rest. At several places the land has been 
 lately, or still is, rising both insensibly and by sudden 
 starts of a few feet during earthquake-shocks ; this 
 shows that these two kinds of upward movement are 
 intimately connected together. For a space of 775 
 miles, upraised recent shells are found on the two op- 
 posite sides of the continent ; and in the southern half 
 of this space, it may be safely inferred from the slope 
 of the land up to the Cordillera, and from the shells 
 found in the central part of Tierra del Fuego, and high 
 up the river Santa Cruz, that the entire breadth of the 
 continent has been uplifted. From the general oc- 
 currence on both coasts of successive lines of escarp- 
 ments, of sandunes and marks of erosion, we must 
 conclude that the elevatory movement has been nor- 
 mally interrupted by periods, when the land either was 
 stationary, or when it rose at so slow a rate as not to 
 resist the average denuding power of the waves, or 
 when it subsided. In the case of the present high sea- 
 cliffs of Patagonia and in other analogous instances, we 
 have seen that the difficulty in understanding how 
 strata can be removed at those depths under the sea, at 
 which the currents and oscillations of the water are 
 depositing a smooth surface of mud, sand, and sifted 
 pebbles, leads to the suspicion that the formation or 
 denudation of such cliffs has been accompanied by a 
 sinking movement. 
 
 In South America, everything has taken place on a 
 grand scale, and all geological phenomena are still in 
 active operation. We know how violent at the present 
 day the earthquakes are, we have seen how great an 
 area is now rising, and the plains of tertiary origin are 
 of vast dimensions ; an almost straight line can be 
 drawn from Tierra del Fuego for 1,600 miles northward, 
 and probably for a much greater distance, which shall 
 
CHAP XV. Movements of South America. 60 1 
 
 intersect no formation older than the Patagonian 
 deposits ; so equable has been the upheaval of the beds, 
 that throughout this long line, not a fault in the strati- 
 fication or abrupt dislocation was anywhere observable. 
 Looking to the basal, metamorphic, and plutonic rocks 
 of the continent, the areas formed of them are likewise 
 vast ; and their planes of cleavage and foliation strike 
 over surprisingly great spaces in uniform directions. 
 The Cordillera, with its pinnacles here and there rising 
 upwards of 20,000 feet above the level of the sea, 
 ranges in an unbroken line from Tierra del Fuego,. 
 apparently to the Arctic circle. This grand range has 
 suffered both the most violent dislocations, and slow, 
 though grand, upward, aud downward movements in 
 mass : I know not whether the sj)ectacle of its immense 
 valleys, with mountain-masses of once-liquefied and 
 intrusive rocks now bared and intersected, or whether 
 the view of those plains, composed of shingle and sedi- 
 ment hence derived, which stretch to the borders of the 
 Atlantic Ocean, is best adapted to excite our astonish- 
 ment at the amount of wear and tear which these 
 mountains have undergone. 
 
 The Cordillera from Tierra del Fuego to Mexico, is 
 penetrated by volcanic orifices, and those now in action 
 are connected in great trains. The intimate relation 
 between their recent eruptions and the slow elevation 
 of the continent in mass,^ appears to me highly impor- 
 tant, for no explanation of the one phenomenon can be 
 considered as satisfactory which is not applicable to 
 the other. The permanence of the volcanic action on 
 this chain of mountains is, also, a striking fact ; first, 
 we have the deluges of submarine lavas alternating 
 with the porphyritic conglomerate strata, then occa- 
 
 * On the connection of certain Volcanic Phenomena in South 
 America. ' Geolog. Transact.,' vol. v. p. 609. 
 
6o2 Summary and Conclusion. part h. 
 
 sionally feldspabMc streams and abundant mineral 
 exhalations during tlie gypseous or cretaceo-oolitic 
 period ; then the eruptions of the Uspallata range, and 
 at an ancient but unknown period, when the sea came 
 up to the eastern foot of the Cordillera, streams of ba- 
 saltic lava at the foot of the Portillo range ; then the 
 old Tertiary eruptions ; and lastly, there are here and 
 there amongst the mountains much worn and appa- 
 rently very ancient volcanic formations without any 
 craters ; there are, also, craters quite extinct, and others 
 in the condition of solfataras, and others occasionally 
 or habitually in fierce action. Hence it would appear 
 that the Cordillera has been, probably with some 
 quiescent periods, a source of volcanic matter from an 
 epoch anterior to our cretaceo-oolitic formation to the 
 present day ; and now the earthquakes, daily recurrent 
 on some part of the western coast, give little hope 
 that the subterranean energy is expended. 
 
 Recurring to the evidence by which it was shown 
 that some at least of the parallel ridges, which together 
 compose the Cordillera, were successively and slowly 
 upthrown at widely different periods; and that the 
 whole range certainly once, and almost certainly twice, 
 subsided some thousand feet, and being then brought 
 up by a slow movement in mass, again, during the old 
 Tertiary formations, subsided several hundred feet, and 
 again was brought up to its present level by a slow and 
 often interrupted movement; we see how opposed is 
 this complicated history of changes slowly effected, to 
 the views of those geologists who believe that this 
 great mountain-chain was formed in late times by a 
 single blow. I have endeavoured elsewhere to show,^ 
 that the excessively disturbed condition of the strata 
 in the Cordillera, so far from indicating single periods 
 
 * ' Geolog. Transact.,' vol. v. p. 626. 
 
CHAP. XY. Stimmary and Conchision. 603 
 
 of extreme violence, presents insuperable difficulties, 
 except on the admission that the masses of once lique- 
 fied rocks of the axes were repeatedly injected with 
 intervals sufficiently long for their successive cooling 
 and consolidation. Finally, if we look to the analogies 
 drawn from the changes now in progress in the earth's 
 crust, whether to the manner in which volcanic matter 
 is erupted, or to the manner in which the land is histo- 
 rically known to have risen and sunk : or again, if we 
 look to the vast amount of denudation which every part 
 of the Cordillera has obviously suffered, the changes 
 through which it has been brought into its present con- 
 dition, will appear neither to have been too slowly 
 effected, nor to have been too complicated. 
 
 Note. — As, both in France and England, translations of a passage 
 in Prof. Ehrenberg's Memoir, often referred to in the Eleventh 
 Chapter of this volume, have appeared, implying that Prof. Ehrenberg 
 believes, from the character of the Infusoria, that the Pampean for- 
 mation was deposited by a sea-debacle rushing over the land, 1 may 
 state, on the authority of a letter to me, that these translations are 
 incorrect. The following is the passage in question : — ' Durch 
 Beachtung der mikroscopischen Formen hat sich nun f eststellenlassen, 
 dass die Mastodonten-Lager am La Plata und die Knochen-Lager 
 am Monte Hermoso, so wie die der Eiesen-Giirtelthiere in den 
 DiineDhiigeln bei Bahia Blanca, beides in Patagonien, unveranderte 
 brakische Siisswasserbildungen sind, die einst wohl sammtlich 
 zum obersten Fluthgebiethe des Meeres im tieferen Festlande 
 gehorten.' — Monais'beric'hte der konigl. Akad. etc., zu Berlin vom 
 April 1845. 
 
APPENDIX TO PART 11. 
 
 DESCRIPTIONS OF TERTIARY FOSSIL SHELLS 
 FROM SOUTH AMERICA. 
 
 By G. B. SOWERBY, Esq., F.L.S., &c. 
 
 MaCTRA ? EUGATA. — PI. II. fig. 8. 
 
 Mactra ? testa oblongd, tenui, turgidd, latere antico altiore, rotun- 
 dato, postico longiore, acuminato ; lineis incrementi rugas con- 
 centricas efformantihus. 
 
 The shell itself is changed into Gypsum. 
 Santa Cruz, Patagonia. 
 
 Mactea Daewinii. — PI. II. fig. 9. 
 
 Mactra testa ovali, subcsquilateralt, subveritricosd, tenuiusculd, Icevi, 
 concentrice striata, mitice rotundatd, postice ohsoletissime suh- 
 quadratd. 
 
 It is impossible to get at the hinge, wherefore it cannot be 
 ascertained positively to be a Mactra. 
 
 Santa Cruz, Patagonia. 
 
 Ceassatella Ltellii. — PI. II. fig. 10. 
 
 Crassatella testa oblongd, planiusculd, tenuiusculd^ postice angulatd, 
 margine postico dorsali declivi, superjicie sulcis obtusis, remotis, 
 longitudinalibus ornatd. 
 
 This species most nearly resembles Crassatella lamellosa of 
 
6o6 Appendix to Part II. 
 
 Lam. ; it is, however, destitute of the erect lamellse which orna- 
 ment the surface of that species. 
 
 Santa Cruz, Patagonia. 
 
 OOKBIS ? L^VIGATA. — PI. II. fig. 11. 
 
 Corhis testa ovato-7'otundatd, ventricosd, IcBvigatd, margine intus 
 leevi: long. 3'2 ; lat. 2' ; alt. '2'7, poll. 
 
 It is not without some hesitation that I have placed this in the 
 genus Corhis, although it is of the same general form as most of the 
 known species of that genus. It is quite free from external rugosity 
 or lameUae. There are two specimens, both of them so imperfect 
 that it is impossible to ascertain with certainty the character of 
 the hinge and muscular impressions. 
 
 Navidad, Chile. 
 
 TeLLIKIDES ? OBLONGA. — PI. II. fig. 12. 
 
 Tellinides ? testd ohlongd, subcBquilatej'oli, anterius altiore, pos~ 
 terius acwninatiore, utrdque rotundatd ; disco glabro, lineis 
 incrementi solummodo signato : long. 1'3 ; alt. 0'7, poll. 
 
 This shell is very thin, and being embedded in a hard compact 
 stone, all attempts to get at the hinge have proved abortive : it is 
 therefore placed in Tellinides as the genus to which it approaches 
 most nearly in external characters. M. d'Orbigny considers it a 
 Solenella. 
 
 Chiloe, eastern coast. 
 
 VeN^US MEEIDIOFALIS. — PI. II. fig. 13. 
 
 Venus testd ovali, plano-convexd, concenti'ice striatd, striis acutis, 
 distantibus, suh-elevatis, interstitiis radiatim obsolete striatis ; 
 margine minutissime crenulato. 
 
 This so closely resembles V. exalbida, Lam. in shape, as not to 
 be distinguishable, except by the radiating striae and the finely 
 crenulated margin. 
 
 Santa Cruz, Patagonia ; and Navidad, Chile. ^ 
 
 Cxtherea stjlculosa. — PI. II. fig. 14. 
 
 Cytherea testd sid)ovatdj antich rotundatiorefpostice longiore, acumi- 
 natiusciddf obtiisd ; sulcis concentricis, confertiusculis, medio 
 
 1 "Wherever a fossil has been found at two localities, the name 
 first given implies that the best specimens came from that place. 
 
Appendix to Part II. 607 
 
 obtusis, antice posticbque acutiot'ibics ornatd: long. 1* ; alt, 0*7 ; 
 lat. 0-4, poll. 
 
 I have compared the single valve of this with numerous recent 
 and fossil Veneres and Cytherece, without being able to identify it 
 with any. As I have not been able to see the hinge, 1 have only- 
 judged it to be a Cytherea from analogy. 
 
 Ohiloe, eastern coast : islands of Huafo and Ypun ? 
 
 Caedittm: PTJELCHina:, — PL II. fig. 15. 
 
 Cardium testa subylobosd, tenui, Icemusculd, latere postico subcari- 
 nato, superjicie striis radiantibus, numerosissimis, confertissimi s 
 instructd. 
 
 The radiating striae and the interstices are nearly equal. Nearly 
 the whole outer surface is gone from both specimens. 
 
 Santa Cruz, Patagonia. 
 
 Cardittm mtjltieadiatfm. — PI. II. fig. 16. 
 
 Cardium testd subglobosd, costellis radiantibus postieis 13, rotundatis, 
 medianis plurimis planulatis, interstitiis rotundatis ; margine 
 denticulato. 
 
 These are all the characters that can be given, as there is only 
 the posterior portion of one valve ; of course the general form is 
 only surmised, and the proportions cannot be ascertained. 
 
 Navidad, Chile. 
 
 Cardita Pata&onica. — PL II. fig. 17. 
 
 Cardita testd subtrapeziformi-rotundd, tumidd, subcordiformi, subob- 
 liqud, costis radiantibus 24, angustis, angulatis, squamosa -serr a- 
 tis, interstitiis latioribus. 
 
 Nearly related to C. acuticostata, and may be distinguished by 
 having fewer and more distant ribs. 
 
 Santa Cruz, Patagonia. 
 
 Ntjcula? glabea. — PL II. fig. 18. 
 
 Nucula testd ovato-oblongdf glabra, nitidd, latere antico breviore, 
 postico magis acuminato ; marginihus dorsalibus declivis. 
 
 I have referred this to Nucula, because there is no external ful- 
 crum for the attachment of the cartilage and ligament ; the nature 
 
6o8 Appendix to Part II. 
 
 of tlie stone in whicli it is imbedded has rendered it impossible to 
 expose any part of the inside. 
 
 Santa Cruz, Patagonia. 
 
 NUCIJLA OEISTATA. — PI. II. fig. 19. 
 
 Nucula testa postice truncatd emai'ginatd, superficie lineis elevatis 
 undatis concentricis ornatd. 
 
 A. beautiful species which apparently resembles N. Tliradce- 
 formis in general shape, but inasmuch as a fragment alone has been 
 found, we cannot give a more complete character. 
 
 Port Desire, Patagonia. 
 
 Teigonocelia iivrsoLiTA. — PI. II. figs. 20, 21. 
 
 Trigonocelia testa suhovali, crassiusculd, valdh ohliqud, Icevi ; area 
 ligamenti trigond, lateribus elevatis ; dentibus paucis, magnis. 
 
 This species is more unlike the typical form of Pectunculus 
 than any which has come under my observation, being even more 
 oblique than the P. obliquus of De France, from which it difiers 
 moreover in being smooth on the outside, and destitute of radia- 
 i;ing ridges. 
 
 Santa Cruz, Patagonia. 
 
 Ctjcull^a alta. — PI. II. figs. 22, 23. 
 
 Cucullcea testd ovato-trapeziformi, suhohliqud, suh'ugosd, umbonibus 
 distantibus, area ligamenti profundi svlcatd, impressionis mus- 
 cularis posticce margine ventrali elevatd. 
 
 There is a considerable primd facie resemblance between this 
 species and Cucullcea decussata, ^ Min. Con.' This from S. Cruz 
 may, however, be easily distinguished from the British, by its 
 greater height, its more oblique form, and by the greater number 
 of impressed lines on the ligamental area. 
 
 Santa Cruz and Port Desire, Patagonia. 
 
 ANOMIA ALTEKIfANS. — PI. II. fig. 26. 
 
 jinomia testd suborbiculari, costellis radiantibus plurimis, subsqua- 
 miferis, alternis minoribus. 
 
 There is only a single valve of this species. 
 Coquimbo, Chile. 
 
Appendix to Part II. 609 
 
 Tekebeatitla Patagonica. — PI. II. figs. 2% 27. 
 
 Terebratula testa ovali, l(svi, valvis fere cequaliter convexis, dorsali 
 product a, incur vd, for amine magno, ad marginem valvarumfere 
 parallelo ; deltidiis, mediocribus; area cardinoli concavd, g longi- 
 tudinis testce ; margine antico integro. 
 
 Slightly different from the T. variabilis of the British Crag,. 
 {vide ' Min. Con.' t. 67Q, ff". 2 to 5) to which however it is very 
 nearly related, as it is also to the T. bisinuata, Lam., of th& 
 Paris basin. It may be distinguished from both by its having no 
 sinus in the anterior margin. 
 
 San Josef and San Julian, Patagonia. 
 
 PeCTEN GEMHiTATFS, — PI. II. fig. 24. 
 
 Pecten testa cequivalvi, ovatd, auriculis incequalibus, costis radianti- 
 bus squamuliferis 22, geminatis ; interstitiis alternis latioribus, 
 nonnunquam costd minore instructd ; auricula altera magna 
 radiatim costatd. 
 
 In general form this species resembles Pecten textorius (Schlot.) 
 Goldf. Tab. XC. f. 9, but it has very few more than half the num- 
 ber of ribs, which in the present species are disposed in pairs. The 
 P. textorius, moreover, belongs to the Lias and inferior Oolite^ ac- 
 cording to Goldfuss. 
 
 San Julian, Patagonia. 
 
 Pecten" Darwinianus. — D'Orbig. '• Voyage, Part. Pal.^ 
 
 (PL III. figs. 28, 29, of this work.) 
 
 Pecten testa fere orbiculari, subcequivalvi, tenui, utrinque convexius- 
 culd; extils Icevi, intus costis radiantibus, per paria dispositis, 
 prope centrum miniis conspicuis ; auriculis parvis. 
 
 Like Pect. Pleuronectes, P. Joponicus, and P. obliteratus in 
 general characters, but easily distinguished from all three by the 
 circumstance of its internal radiating ribs being disposed in pairs. 
 This species has been named and described by M. d'Orbigny, but as 
 his description is very brief, owing to the condition of his speci- 
 mens, and is unaccompanied by any figure, I have thought it 
 advisable to append the above specific character. 
 
 San Josef, Patagonia ; and St. Fe, Entre Rios. 
 
 E R 
 
6 TO Appendix to Part II. 
 
 Pecten Paeanensis. — D'Orbig. ' Voyage, Part. Pal.' (PI. III. 
 fig. 30 of this work.) 
 
 This species has been figured and fully described by M. d'Or- 
 bigny, and has been accidentally refigured here. 
 
 San Josef, San Julian, Port Desire, Patagonia ; and St. Fe, 
 Entre Rios. 
 
 Pecten centealis. — PI. III. fig. 31. 
 
 Fecten testa subcirculari, depi'essd, radiis quinque squamvliferis cen- 
 trali eminentiore,lineis radiantibus asperis numerosisque ornatd; 
 auriculis 'magnis, subeequalibus ? 
 
 A single fragment of this remarkable species was found at 
 Port S. Julian : two others were brought from Port Desire. These 
 fragments are all of the same side, so that we are as yet but very 
 imperfectly acquainted with the species. 
 
 San Julian, Port Desire, Santa Cruz, Patagonia, 
 
 PeCTEN ACTLSrODES. — PL III. fig. 33. 
 
 Pecfen testa suborbiculari, convexiusculd, tenui, vnlvis subcequalibus, 
 radiis pj'incipalibus subeJevatis circa 36, intermediis 3-7 
 minoribus, omnibus squamuliferis ; auriculis incequalibus, 
 radiatim squamuliferis, altera magna, porrectd, alterd parvd, 
 declivi. 
 
 Remarkable for its principal ribs being numerous and only 
 slightly elevated, and for its intermediate ribs being very nu- 
 merous. 
 
 San Josef, Patagonia. 
 
 Pecten efdis. — PI. III. fig. 32. 
 
 '^!pjedten^W^i^ suborbiculari, suhincequivalvi, crassiusculd, rudi, costis 
 '-iiifj'aWd'ntibzis 22, rotundatis, inter stitiis angustioribus ; intermediis 
 ^f^'^'''>^(yii'ifmriq4dmfe7'eobsoletis; Tnargine valide undulato. 
 
 di -trTbe specimefn is only a fragment ; another fragment accompanies 
 it, which may possibly be the opposite valve. 
 
 Coquimbo, Chiloe. 
 
Appendix to Part II. 6 1 1 
 
 Oeepidtjla gkegaeea, — PI. III. fig. 34. 
 
 Crepidula testa oblongd, intortd, crassd, subrugosd ; septo elongato, 
 subspirali, Icevi; vertice suhmarginali. 
 
 This species is remarkable for its lengthened form : it is found 
 grouped together in an argillaceous sandstone of a grayish colour. 
 It bears a strong general resemblance to Crepidula fornicata, 
 which is found, similarly gi'ouped, on the coast of New York, 
 Isew England, and generally on the Atlantic coasts of North 
 America. 
 
 Santa Cruz, Patagonia. 
 
 Bulla cosmophila. — PI. III. fig. 35. 
 
 Sulla testd subcylindraced ; extremitatibus obtusis, rotundatis, 
 anticd paululwn latiore; striu numerosis, confertis, trans- 
 versis, interstitiis angustioribus planiusculis : long. 0'9; lat. 0*4. 
 
 I do not find any character to distinguish this from the fossil 
 which abounds in the neighbourhood of Bordeaux, and which is 
 also found near Paris and in Normandy, and which Deshayes has 
 regarded as merely a variety of Bulla lignaria, Auct., from which 
 however it may easily be distinguished by its much more cylindri- 
 cal form. 
 
 Huafo Island, Chile. 
 
 SlGAEETTTS StTBGLOBOSUS. — PI. III. figs. 36, 37, 
 
 Sigaretus testd subglobosd, anfractibus quatuor, spiraliter concinne 
 sulcatis : long. 0"9; lat. 6'8 ; alt. 0'55,poll. 
 
 The spiral grooves and intermediate ridges are very nearly 
 equal in general, though sometimes rather hregular. This is the 
 most concave species of Adanson's Sigaretus that I have ever seen 
 the position of its aperture being much less inclined to the longi- 
 tudinal axis than it is even in the >S'. concavus, Lam., a recent 
 species common at Valparaiso. 
 
 Navidad, Chile ; and Ypun Island, Chonos Archipelago. 
 
 Natica pttmila.— pi. III. fig. 38. 
 
 Natica testd ovato-subglobosd, glabrd, anfractibus quatuor, umbilico 
 magno, patulo. 
 
 A single individual of this small species, which appears as far 
 .tis I can judge to be distinct from any of the recent species, occurs 
 
 K R 2 
 
6i2 Appendix to Part II. 
 
 in the same sort of rock, namely, a very hard and very dark olive 
 green sandstone, with the following species. The difficulty of 
 detaching the stone from the shells has prevented me from ascer- 
 taining with certainty whether or not there be an umbilical 
 callus. 
 
 Chiloe, eastern coast. 
 
 Natica steiolata. — PI. III. fig. 39. 
 
 Natica testa depi'essiusculo-subglobosd, crasdusculd, glabra, anfrac- 
 tibus quatuor ad quinque, ultimo maximo, spiraliter substriato, 
 striis subdistantibus ; callo umbilicali tnagno, umbilicum om- 
 ninb obtegente, ad labium internum incrassatum antice con- 
 juncto. 
 
 This species resembles Swainson's Natica melastoma in general 
 form, as well as in the umbilical callus : it is however rather more 
 circular and the umbilical callus is rounder. Judging from the 
 apparent general form, I at first sight, when I only saw the upper 
 surface, had taken it for Sigaretus concavus, which it also resembles ; 
 and I was not undeceived until by clearing away the stone I dis- 
 covered the umbilical callus. There are two specimens of this 
 species. r 
 
 Chiloe, eastern coast. 
 
 Natica solida. — PI. III. figs. 40, 41. 
 
 Natica testa subglobosd, crassd, Icevi, spird brevi, anfractibus quin- 
 que, suturd subinconspicud, aperturd ovali, labio columellari 
 postice crassissimo, umbilico jnediocri, callo parvo : long. 1 "8 ; lat. 
 1-5, poll. 
 
 This most nearly resembles a very common recent species^ 
 which has generally been confounded with N. mamilla, but which 
 I have lately received from D'Orbigny under the name of N. Tiber 
 of Valenciennes, it may be distinguished from that species by being 
 almost destitute of the umbilical callosity. The only specimen is 
 very much worn, particularly about the spire, so that the true 
 character of the suture is only discernible in one part, and the 
 general appearance of the specimens conveys the deceptive notion 
 of a deep and broad channelled suture. 
 
 Several specimens of a Natica, closely resembling, but possibly 
 distinct from this species, were procured at Santa Cruz ; they are 
 in a much disguised state, and only a small portion of the shell 
 itself remains, particularly of the outer coats about the suture, 
 which consequently appears very deep and distinct, whereas when 
 
Appendix to Part II. 613 
 
 well preserved the suture is scarcely distinguishalDle ; M. d'Orbigny 
 considers the S. Cruz species are certainly distinct. 
 
 Navidad, Chile ; Santa Cruz, Patagonia ? 
 
 SCALAPvIA EUGTJLOSA. — PI. III. %S. 42, 43. 
 
 Scalaria testa acuminato-pyramidali, crassiusculd,o')nnino rugulosd, 
 varicibus numerosis, crassis, rotiindatis ; interstitiis spiraliter 
 obsolete sulcatis. 
 
 Volutions about eleven or twelve, increasing very gradually 
 in size ; with fourteen or fifteen rounded and thickish varices on 
 «aeh. 
 
 San Julian, Patagonia. 
 
 Teoohus collaeis. — PI. III. figs. 44, 45. 
 
 Trochus testa conicd, Icevi, anfractibus subiequalibus, tenuissime 
 transvershn striatis, postice prope suturas tuberculis minutis 
 seriatiTYh cinctis, infra suheonvexis, spiraliter tenuiter striatis ; 
 apertures angulo externo acuto : lomg. 0*45 ; lat. 0*65, poll. 
 
 A very small portion of the outer surface remains, the inner 
 coat is wholly covered with a yellowish green and reddish irides- 
 cence. Umbilicus as far as I can judge the same as in the following 
 species, TV. Icevis. This may possibly be only a young shell of that 
 species, (and is so considered by M. d'Orbigny) as it is only distin- 
 guished by a row of very small tubercles placed immediately under 
 the suture, which may have existed in that species when yoimg ; 
 and it must be observed that the first volutions are broken from 
 both the specimens of Tr. Icevis. 
 
 Navidad, Chile, Santa Cruz, Patagonia. 
 
 Trochus l^vis. — PL III. figs, 46, 47. 
 
 Trochus testa conicd, Icevi, anfractibus subceqaalibus, postice turgi- 
 diusculis, antice tenuissime transversini striatis, infra subcon- 
 cavis, spiraliter tenuiter striatis ; aperturd rhoniboided, angulo 
 externo acuto ; umbilico mediocri, intus IcBvissimo, labio interno 
 subincrassato ; long. 1'3; lat. 2', poll. 
 
 The remains of the pearly inner coats are beautifully iridescent 
 in this species ; the outer surface is dull. 
 
 Navidad, Chile. 
 
6i4 Appendix to Part II. 
 
 Tfrritella Patagonica. — PI. III. fig. 48. 
 
 Turritella testa elongato-conicd, anfractibus decern, 3 ad 4: costatis,. 
 costis, intermedia anticdque subobsoletd minoribus, posticd sub- 
 acutd, suhgranosd majoiH, tertid carinam efformante ; sutura 
 indistinctd. 
 
 This Turritella is probably only a variety of T. cingulata, and 
 it more closely resembles this species, even than the following 
 ones, inasmuch as its volutions increase in size more rapidly than 
 in either the T. Chilensis or T. ambulacrum. In some respects 
 this resembles T. carinifera of Deshayes ; it is not however nearly 
 so loug in proportion to its width. I have adopted a name sug- 
 gested by D'Orbigny. 
 
 Port Desire, Patagonia ; and fragments at Navidad, Chile. 
 
 Turritella ambulacefm. — PL III. fig. 49. 
 
 Turritella testd elongato-turritd, anfractibus decem, spiraliter tri- 
 costatis, posteriorum costis eequalibus, antei^iorum costd anticd 
 posticdque majoribus, intermedid minori; suturdin sulcumpro- 
 fundum positd. 
 
 A very remarkable species, which somewhat resembles a re- 
 cent one in my possession ; the two may however be easily distin- 
 guished. In the recent species the two spiral ridges are much 
 nearer to each other than they are in the fossil ; and the spiral 
 groove at the suture is much deeper and narrower in the fossil 
 than in the recent. 
 
 Santa Cruz and San Julian, Patagonia. 
 
 Turritella Chilejstsis. — PI. IV. fig. 51. 
 
 Turritella testd elongato-turritd, anfractibus decem, ventricosis^ 
 spiraliter tricostatis, costis granulosis, intermedid majori, suturd 
 in sulcum positd. 
 
 Nearly related to Turritella cingulata (So*wb. ^Tank. Cat.') ; it 
 is even questionable whether it might not be regarded as a variety 
 of that species, along with T. Patagonica and T. ambulacrum. 
 In deference to the opinion of D'Orbigny, who has suggested the 
 name, I have been induced to describe it. The principal differ- 
 ence between this and T. cingulata are, the form of the volutions, 
 which in this are ventricose ; the absence of narrow intermediate 
 ridges ; and the greater depth of the groove in which the suture 
 is placed. From T. ambulacrum it differs principally in the cir- 
 cumstances of the central rib being the most prominent, while in 
 
Appendix to Part II. 615 
 
 T. ambulacrum it is the least prominent. The rihs in the latter 
 species are but slightly granose, and the groove at the suture is 
 deeper. 
 
 Huafo and Mocha Islands, coast of Chile. 
 
 TlJEEITBLlA SUTTJKALIS. — PI. III. fig. 50. 
 
 TuiTitella testa tvrritd, tenuiter transversim striata, anfractihwi 
 9-10, suturd validd divisis, antice posticeque tumidiusculis,post%ch- 
 eminentiore. 
 
 Fragments alone can he separated from the hard stone in which, 
 they are imbedded ; it has therefore been impossible to give the- 
 proportions. 
 
 Navidad, Chile ; and Ypun Island, Ohonos Archipelago. 
 
 PlETJEOTOMA STJBiEQ,TJALIS. — PI. IV. fig. 52. 
 
 Pleurotoma testa oblongd, turritd, utrdque extremitate acuminata^ 
 anticd hreviori; anfractibus senis, medio cariniferis, carina 
 tuberculiferd ; ultimo anfractu carinis quinque, posticali tuber- 
 culiferd : long, 6 ; lat. 0*25. 
 
 The species which most nearly resembles this is an undescribed 
 recent species from S. America : this fossil species differs however 
 from the recent one in the position of the notch in the outer Up, 
 which in the fossil corresponds with the posterior tuberculiferous 
 carina, while in the recent one the notch is placed half way between 
 the posterior tuberculiferous carina and the suture. There are 
 other marks of difference, but this may be considered sufficient, as. 
 forming at once a distiact criterion. 
 
 Huafo Island, coast of Chile. 
 
 PlEIIEOTOMA TtrEBI]!irELLOIDES. — PL IV. fig. 53. 
 
 Pleurotoma testd oblongd, subventricosd, transversim tenuissimh 
 muricato-striatd, anfractibus quinis, ventricosis, infra mediam 
 tuberculatis, tuberculis acuminatis, ultimo antice lineis quatuor 
 vel quinque obsolete tuberculatis ; canali brevi : long. 1"85; lat. 
 0-82, poll. 
 
 Very different from any other known Pleurotoma, either recent 
 or fossil ; but most nearly allied, in shape particularly, to the recent 
 species named PI. imperialis by Lamarck. 
 
 Navidad, Chile. 
 
6i6 Appendix to Part II. 
 
 Pletjeotoma discoks. — PL IV. fig. 64. 
 
 Pleurotoma testa fusiformi-turritdj spird acuminatd, anfractibus 
 octo, jjostice tenuissime transversim striatis, medio tuherculatis, 
 ultimo antice striis crassis subtuberculatis instructo ; canali 
 elongato, tenuiter transversim striata ; columelld rectd : long. 
 1-8; kit. 0-62, poll. 
 
 A species which appears to be nearly related to PL catenata, 
 Lam. Desh. II. t. 62, f. 11, 12, 13 (a fossil of the Paris Basin), 
 and which may perhaps be merely a variety of that species. In 
 stature and general characters it resembles it very closely ; its strise 
 are however very different. 
 
 FUSUS EEGTJLAHIS ? — PI. IV. fig. 55. 
 
 A single very imperfect specimen which may probably be a 
 "variety of this species. It is not sufiiciently complete to allow of 
 its being decided, or of its characters being given. It is not even 
 certain that it belongs to the genus. M. d'Orbigny considers it as 
 a distinct species. 
 
 Navidad, Chile. 
 
 FUSUS PTEULITOEMIS. — PI. IV. fig. 56. 
 
 Fusus testd turbinatd, antice spiraliter sulcatd, spird subdepresso- 
 conicd, rudi; anfractibus .3-4, medio tuberculatis, tuberculis 
 t7'ansve?'sim sulcatis, in castas subdecurrentibus ; canali elongato, 
 transversim sulcata. 
 
 This somewhat resembles the Triton clavator. Lam. (a recent 
 species), in form; its spire is however more elevated, and its 
 canal shorter in proportion, I judge it to be a Fusus horn the 
 general external appearance, but cannot be quite certain, for the 
 stone about the mouth is so much indurated that it cannot be 
 cleared away. 
 
 Navidad, Chile. 
 
 FuStrS SUBEEELEXUS. — PI. IV. fig. b7 . 
 
 Fusus testd fusiformi-turritd, transversim striatd, striis irregu- 
 
 laribus, anfractibus novem, medio tuberculatis, props suturas 
 
 subadpressis ; canali mediocri subrefle.vo : long. 2-1, lat. I', 
 poll. 
 
Appendix to Part II. 617 
 
 The shell to which this bears the greatest resemblance is a fossil 
 named Fasciolaria Burdigalensis, Defr. by De Bastoret in the 
 ' Memoires de la Soc. d'Hist. Nat. de Paris ; ' in our shell there is, 
 however, no appearance of oblique folds on the anterior part of the 
 columella, consequently it is generically distinct ; while in other 
 respects it is sufficiently different, as may be seen by comparison. 
 Its spire is longer in proportion to the last volution, and its canal 
 shorter. 
 
 Navidad, Chile. 
 
 FusTJS NoACHiXFS. — PL IV. figs. 58, 59. 
 
 Fusus testa ovato-fusiformi, utrdque subacuminatd, cequali, an- 
 Jractihus quinque spivalitev sulcatis, sulcis plerumque seriatim 
 pertusis ; postids longitudinaliter obtuse costatis ; canali me- 
 diocri, subascendente ; suticrd distinctd. 
 
 A species which bears some resemblance to Fusus No(S, Lam. ; 
 still it is not nearly related to that species. In shape it resembles 
 F. lamellosus, to which it is really related, but it is quite destitute 
 of the lamellar varices, so that it may easily be distinguished. 
 
 San Julian, Patagonia. 
 
 Ftjstjs Patagoxicus. — PL IV. fig. 60. 
 
 Fusus testa ovato-oblongd, tenuiusculd, multifandm varicosd, an- 
 fractibus postice cmgit'atis; varicibus lamelliformibus^ antice 
 deflexis, postice acuminatis, interstitiis ti'ansversim sulcatis ; 
 aperturd subcirculari, canali breviusculo, umbilico valido. 
 
 Nearly related to Fusus lamellosus and F. Magellanicus, and 
 apparently connecting the two. 
 
 Ptetjla DisTAJsrs. — PL IV. fig. 61. 
 
 Pyrula testd Jiciformi, tenuiusculd, spird hrevissimd obtusd, anfrac- 
 tibus quatuor, ultimo onaximo, decussatim striato, et carinato, 
 carinis 11-12, distantibus, nonnulUs interstitialibus miniis 
 elevatis : long. 1'8 ; lat. 1-2, poll. 
 
 A very elegant species of true Pyrula, somewhat resembling 
 P. nexilis (a tertiary fossil) in general appearance, but differing 
 from that species in its proportions, being much wider in com- 
 parison with its length, and having a much shorter spire. 
 
 Navidad, Chile. 
 
6i8 Appendix to Part II. 
 
 Stetjthiolaeia oknata. — PL lY. fif?. 62. 
 
 o* 
 
 Struthiolaria testa ovatd, apice acuminato, anfractibus senis, 
 spiraliter striatis, prope suturam canaliculatis, longitudinaliter 
 costatis, costis obtusis, antico costis duabus spiralibus, elevatis, 
 ante mediam positis ; suturd profunda : long. 0*7 ; lat. 0*45, 
 lyoll. 
 
 This is the only fossil species of this rare genus I have ever 
 seen. Casts of a large variety are found in a loose clayey sand- 
 stone at Port San Julian. M. d'Orbigny entertains some doubt 
 about this being a Struthiolaria. 
 
 Santa Cruz and San Julian, Patagonia. 
 
 Tkiton veebtjculostjs. — PL IV. fig. 63. 
 
 Triton testa ovato~conicd, transversini tenuiter striata, anfractibus 
 senis, posticis serie unicd mediand tuberculoruni cinctis, ultimo 
 costis trihus subobsoletis tuberculiferis, tuber culis costce posticce 
 majoribus, reliquiarum obsoletis ; varicibus validis, trituberculi- 
 feris: long. 1-6; lat. 1'05, poll. 
 
 This may be distinguished from Trito7i leucostoma {Ranella 
 leucostoma, Lam.), to which recent species it is most nearly 
 related, by the paucity of tubercles forming the posterior row, as 
 well as by the strongly tuberculated varices, and by its being 
 destitute of the pits which are so distinct behind the varices in that 
 species. 
 
 Navidad, Chile. 
 
 Triton" letjcostomoides. — PL IV. fig. 64. 
 
 Triton testd ovato -oblong d, spird obtusd ; anfractibus senis, sub-^ 
 ventmcosis spiraliter sulcatis, et longitudinaliter costatis; vari- 
 cibus sub-irregularibus, rotundatis, transversini sulcatis. 
 
 This species resembles Triton leucostoma {Ranella leucostoma, 
 Lam.) more nearly than any other species : it diifers, however, in 
 the following particulars, viz., in its general form, which is more 
 oblong ; in its longitudinal ribs, which are smaller and rnore 
 numerous, and extend nearly the whole length of each volution ; 
 whereas in T. leucostoma, they are little more than elongated 
 tubercles near the middle of the whorls. 
 
 Huafo Island, coast of Chile. 
 
Appendix to Part II. 619 
 
 Cassis mois^ilifee. — PI. IV. fig. 65. 
 
 Cassis testa subglohosd, transversim tenuite?' striata, spird eleva- 
 tiusculd, anfractihus senis, ultimo gibhoso, serie unicd tuber- 
 culoi'um postice instructo ; labio externo tenuiusculo, rejlexo, 
 intils IcBvi ; labio columellari expanso, Icevi: long. 1*5; lot. 1"1, 
 'poll. 
 
 A second row of small tubercles may be observed occasionally- 
 I know of no species to wHch this is nearly related. 
 
 Na\ddad, Chile. 
 
 MoiSrOCEIlGS AMBIGUUS. — PI. IV. figs. ^'o, 67. 
 
 Monoceros testa subglobosd, crassiusculd, lceviusculd,spiraliter obsolete 
 costellatd, aperturd magnd^ labio externo intus incrassato,, 
 umbilico parvo, angusto. 
 
 A single specimen in very bad condition ; considered by 
 M. d'Orbigny as closely related to, but not identical with, the 
 M. crassilabrum of Lamarck. 
 
 Coquimbo, Chile. 
 
 Gasteidifm.^ — Novum Genus. 
 
 1 have thought it necessary to designate this singular shell by 
 a new generic name, because its characters are such as will not 
 permit its union with any hitherto established genus. The shells 
 to which it appears to be most nearly allied have hitherto been 
 arranged with Buccinum, Eburna, and Fusus. ISuch is the Bucc. 
 plumbeum of Chemnitz (which Swainson has designated by the 
 generic name of Pseudoliva'^) , and which, to avoid the necessity of 
 adding to the number of generic names, I had united to the 
 Eburnce.^ Such also are two fossil shells described and figured by 
 Deshayes, under the names oi Buccinum Tiara and B . Jissuratum. 
 One shell resembles this somewhat in form, but in other respects 
 is very different, and this has been placed with the Buccina in 
 Wood's ' Suppt.,' and with the Fusi by Gray. The characters by 
 
 ^ From ya(TTp'i^i.ov, venirictilus. 
 
 2 This name of Pseudoliva, by which Swainson has designated the 
 Buccinum plumbeum of Chemnitz, and which has been adopted by 
 Grray, is evidently untenable and absurd, because employed to describe 
 an iTnaginary affinity to Oliva, which does not exist. To Eburna and 
 Buccinum, Lam., the genus is nearly related. 
 
 ^ Deshayes, ' Coquilles fossiles des environs de Paris,' torn. ii. pp. 
 655, 656. 
 
620 Appendix to Part II. 
 
 whicli this new genus may be known and distinguislied from its 
 allied genera are as follow : — 
 
 Testa ventricosd, subglobosd, spird hrevi, anfractibus postice ad 
 suturas adpressis ; aperturd magna, ovali ; canali postico 
 angusto ; antico Into, reflexo ; lahio externo postice incrassato, 
 antice tenuiore, dente hrevi, sulco dorsali idoneo, prope anticam 
 partem posito ; lahio columellari inc7'assato, expanse, postice apud 
 canalem crassio7'e. 
 
 Gasteidium Cepa.— pi. IV. figs. 68, 69. 
 
 Gastridium testa cepcsforini, Icevigatd, aTitice spiraliter sulcata, lahii 
 externi margine antico crenato : long. 2*3 ; lat. V7 , poll. 
 
 Navidad, Chile. 
 
 TeeebPvA costellata. — PI. l\. figs. 70, 71. 
 
 Terebra testa turritd, Iceviusculd, anfractibus medio twnidiuscidis, 
 postice lined impressd obsoletd notatis, costellis numerosis longitu- 
 dinalibus, elevatis ; aperturd columelldque Icsvibus. 
 
 The number of volutions and the proportions cannot be given, 
 for there is only a single fragment of this species. 
 
 Navidad, Chile. 
 
 Teeebea tjxdulifeea. — PL IV. figs. 72, 73. 
 
 Terebra testa elongato-turritd, Iceviusculd, lineolis undulatis longi- 
 tudinalibus confertis, posticis fortiorihus, tectd ; anfractibus 
 j)lurimis, postice tumidiuscuUs, lined impressd subobsoletd, medio 
 subconcavis ; aperturd subrhomboided, columella Icevi. 
 
 There are only two fragments of this species, it is obviously 
 impossible to ascertain the number of volutions or the propor- 
 tions. 
 
 Navidad, Chile. 
 
 VOLUTA TEIPLICATA. — PI. IV. fig. 74. 
 
 Valuta testd elong at o- oblong d, spird attenuatd, anfractibus senis 
 spiraliter confertim sti'iatis, ad suturas adpressis, deinde 
 tuberculatis, tuberculis in costas antice decurrentibus ; aperturd 
 oblongd, longitudinem spine cequante ; columelld triplicatd,plicis 
 obliquis, submqualibu^ : long. 2'25; lat. 0-9, jyoll. 
 
 This species is placed among the Volutes, because the posterior 
 or upper folds on the columella are rather smaller than the 
 
Appendix to Part II. 621 
 
 anterior; it nearly resembles in general appearance the fossil 
 VolutcB, muricina, Lam., and angusta, Desh., tkough easily distin- 
 guishable from both, by the circumstance of the three folds on the 
 columella being very nearly equal in our species, whereas in the 
 two above mentioned the posterior folds are more numerous and 
 all very much smaller than the anterior : moreover, the posterior 
 part of the volutions is not adpressed in either of those species^ 
 and the proportions are also different. 
 
 Navidad, Chile. 
 
 VOLUTA ALTA. — PI. IV. fig. 76. 
 
 Valuta testa elongato-oblongd, spird attenuatd, anfraetihus senis 
 gracilibus, spiraliter confertim striatis, prope suturas adpi'essis, 
 deinde suhventricosis ; aperturd oblongd, lahio externo crassiori, 
 subre/lexo ; columelld lcevi,plicis duabus acutiusculis,perobliquis: 
 long. 7'5 ; lat. 2-76, poll, circa. 
 
 There is only one specimen of this very remarkable shell, of 
 which the anterior part is so imperfect, that no part of the inner 
 lip or of the canal is to be seen, consequently the proportions 
 given above may be liable to a slight error. The species is nearer 
 to V. Magellanica, than to any other known species ; it may, 
 however, easily be distinguished from that species by the 
 characters above stated. At Santa Cruz, there are two casts,, 
 apparently belonging to this species, but considered by M. 
 d'Orbigny as different. 
 
 Navidad, Chile ; Santa Cruz, Patagonia ? 
 
 Oliva dimidiata. — PL IV. figs. 7Q, 77. 
 
 Oliva testa oblongo-ovatd, spird acuminatd, apice ohtuso; anfractibus 
 senis, ultimo lined tenuissimd transversim dimidiato ; columelld 
 antice plicis quinque obliquis, posticd majori : long. 0'9 • lat 
 0-^7, poll. 
 
 This species varies in its proportions ; it differs from all other 
 recent or fossil species with which I am acquainted, in the remark- 
 able circumstance of its having a broad band of enamel covering 
 the anterior half of the last volution above or behind the 
 columellar band, which is distinguished from the posterior part of 
 the volution by a very fine line, behind which may be seen the 
 longitudinal lines of growth, these lines being hidden on the 
 anterior part by this last covering of enamel. This species bears 
 a general resemblance to O. ispidula, a common recent species. 
 Navidad, Chile. 
 
62 2 Appendix to Part II. 
 
 DeISTTALIUM GIGANTETJM. — PI. II. fig. 1. 
 
 Dentalium testa tereti, rectiusculd, sulcis longitudinalibus numerosift, 
 interstitiis rotundatis : long. ^'^ ; lat. 0*5, poll. 
 
 This species appears occasionally to grow to a very large size, 
 for one fragment tliat is one inch and a third in length, is half an 
 inch in width at its smaller extremity, and six-tenths of an inch at 
 its larger ; while in its thickest part the shell itself is 0*13 of an 
 inch thick. 
 
 Navidad, Chile. 
 
 Deisttalittm sflcosum. — PI. II. fig. 2. 
 
 Dentalium testa tereti, rectiusculd, costellis longitudinalibus 
 elevatiusculis, subdistantihus 14, interstitiis planulatis. 
 
 The proportions cannot be given ; for there is only one frag- 
 ment, which has been broken and the two pieces conferruminated 
 by the sandstone in which it occurs. 
 
 Navidad, Chile. 
 
 Dentalium majus, — PL II. fig. 3. 
 
 Dentalium testa tereti, rectiuscidd, costis longitudinalibus 24, alternis 
 majoribus, interstitiis rotundatis. 
 
 The proportions of this species cannot be given, because there 
 are only some fragments ; it appears to be one of the larger 
 species of the genus, probably reaching the dimensions of 
 D. sexangulcn-e of Deshayes, tab. 3, fig. 4. It differs from that 
 species in the circumstance of its never having only six angles ; 
 and it differs from D. elephantinum of Deshayes (which I have 
 elsewhere proved not to be the D. elephantinum of Linnseus) in 
 being less rapidly attenuated, and in being straighter. 
 
 Huafo Island, coast of Chile. 
 
 BaLANTJS VAEIAUfS. — PI. II. figs. 4, 5, 6. 
 
 JBalanus testa polymorphd, valvis plerumque Icevibus, nonnunquam 
 radiatim obtusd costatis, apicibus subacuminatis ; valvd basalt 
 modb concavd, modo cyathiformi, basi acuminata. 
 
 This is a very remarkable as well as a very variable species. 
 Its parietal valves are sometimes smooth, only showing the lines 
 •of growth, and sometimes covered with obtuse radiating ribs ; and 
 
Appendix to Part II. 623 
 
 the species belongs to tliat section of the genus which has 
 acuminated and solid parietal valves. But the most variable part, 
 in form, is the basal valve. It is to be observed that in most, if 
 not in all, the species of this genus which have been brought from 
 the Southern Hemisphere, it is the base that becomes tubular 
 whenever any accidental circumstance causes the shell to be 
 elongated ; whereas in the elongated and clavate varieties of our 
 common species, it is the parietal valves that are lengthened and 
 not the basal. Thus, with respect to the present species, we find 
 that when any number of individuals are placed close together 
 when very young, as they increase they form a group, of which 
 the basal valves grow up side by side and become tubular, without 
 the parietpJ valves changing in form ; hence in some specimens 
 this valve is concave in consequence of its having been placed upon 
 a convex substance, and at a distance from each other ; while, in 
 others, which have been placed very closely together when very 
 young, this basal valve has taken a more or less deep cup shape, 
 being very small at its lower extremity and increasing in dimen- 
 sions with age. 
 
 San Julian, Patagonia. 
 
 Balanus CoQUiMBEisrsis. — PI. II. fig. 7. 
 
 £alanus testa polymorphd, valvis Imvibus, nonnunqumn radiatim 
 striatis, later alibus posticis angustiorihus ; apicibus svhtruncatis ; 
 ajjerturd parvuld. 
 
 A remarkable fact is observable in the specimens, both from 
 the upper and lower parts of the formation ; I have selected one 
 from the upper bed as showing it most distinctly. In consequence 
 of numerous individuals being closely grouped together, each one 
 has been compelled to lengthen the basal valve, so as to form a 
 nearly cylindrical tube, closed at the lower part, and gradually 
 increasing as it ascends until it joins the base of the six parietal 
 valves: this increase in the length of the base seems to have 
 taken place more rapidly than the gTOwth of the animal would 
 permit. A portion of the lower part of this basal tube has, there- 
 fore, been filled up with cells or vesicles separated by calcareous 
 septa, very irregular indeed, but which would, nevertheless, 
 answer the purpose of supporting the base of the animal in 
 the tube, so as to enable the animal to continue its vital 
 functions, 
 
 Coquimbo, Chile. 
 
624 Appendix to Part II. 
 
 DESCRIPTIONS OF SECONDARY FOSSIL SHELLS 
 FROM SOUTH AMERICA. 
 
 By Pbofessor E. FOEBES, F.R.S., &c., &c. 
 
 Nautilus d'Orbignyanus. — PL V. fig. L {a) L (^). 
 
 Shell ventricose {^prohahly smooth and slightly wnhilicatedf). Mouth 
 very broad, reniform. Slack rounded. Sutures bend, suddenly 
 towards, and near to, the umbilicus ; on the bach they are very 
 slightly sinuated. 
 
 This specimen is very imperfect. The form of the chambers 
 resembles that seen in Nautilus Sowerbyanus, a species described 
 from the upper greensand by D'Orbigny. The general form more 
 nearly resembles Nautilus Icevigatus of the same author, a species 
 also from the Craie chloritee. 
 
 Concepcion, Chile. 
 
 Hamites elatioPw — G. B, Sower by. 
 
 Testa magna, crassiusculd, Icsvi, subcylindricd, annulis elevatis, 
 conspicuis, subconfertis, ornatd ; extremitatibus invicem prope 
 admotis. 
 
 This is the largest Hamite I have seen ; it is nearly cylindrical, 
 and its largest diameter is 2^ inches, its smaller being 2\. There 
 are two specimens, one of which is much larger than the other. 
 The smaller shows clearly the near approximation of the two 
 extremities. The specimens have been lost since Mr. Darwin's 
 return to England, and so cannot be figured. 
 
 Port Famine, Tierra del Fuego. 
 
 Perna Americana. — PI. V. figs. 4, 5, 6. 
 
 Shell lanceolate f ventricose, carinated, compressed in the cardinal 
 region, abruptly truncate, concave at the opposite side, so that the 
 section of the two valves is triangular and somewhat cordate. 
 The sulcations of the hinge are large, numerous, and regular. 
 
Appendix to Part II. 625 
 
 The surface of the shell appears to have been concenti'ically , 
 though irregularly, striated. 
 
 The specimen consists of the cardinal and apical portions of 
 two united valves. 
 
 CopiapO; Chile. 
 
 AsTAETE Dakwinii. — PI. V. figs. 22, 23. 
 
 &hell hroadly ovate, much compressed, marked loith rather distant 
 regular concentric ridges ; the interstices broad and concentri- 
 cally striate ; anal and oral extremities nearly equally broad ; 
 breaks very obtus. 
 
 Breadth, 1 ^^ ; length, ^^ ; thickness, j^ of an inch, 
 
 Copiapo, ChUe. 
 
 Gktphjea Daewinii. — PI. V. fig. 7. 
 
 Lower valves very tumid, elongated, arcuated, laterally compressed, 
 and much incurved at the rostral extreinity ; its surface undu- 
 lated by distant distinct sinuous furrows, marked loith lesser 
 svlcations or striations. Upper valve concave, spatulate, and 
 concentrically furrowed. 
 
 Length, 3^ ; breadth, 2 ; distance from summit of beak to 
 loivej'most and central part of lower valve, 2~ inches. 
 
 Copiapo, Chile. 
 
 Getphjea Nov. Sp. ?— PI. V. figs. 8, 9. 
 
 Lower valve not very convex, rugged, angulated; upper valve concave 
 orbicular, furrowed with deep concentric sulcations. Apparently 
 a young specimen. 
 
 Length, 1|; breadth, 2~ ; thickness, ^ of an inch. 
 
 Copiapo, Chile. 
 
 Lfcina Ameeicana. — PI. V. fig. 24. 
 
 Shell orbicular, much depressed, the surface rough, with sharp, re- 
 gular, elevated, distant, concentric ridges (about tiuenty-Jive on 
 specimen examined) ; the interstices are striated conceritrically. 
 Length, \~ ; breadth, the same ; thickness, ~ of an inch. 
 
 In shape this species resembles the recent Lucina radula, 
 Iquique, Southern Peru. 
 
 S S 
 
626 Appendix to Part II. 
 
 Ltjcina. excenteica. — G. B. Soweebt, PI. V. fig. 21. 
 
 Testa subovali, leviter ineequiealvi, IcBvi, umbone adunco, postich 
 sulco prof undo ab umbone ad marginem inferam posticam de- 
 currente in altera valvd, minus profunda in altera: long. 1*9; 
 lat. 1* ; alt. '2' poll. 
 
 Like Lucina Childreni, the two valves are somewliat unequal, 
 and sometimes the right, sometimes the left, valve is the larger. 
 The posterior dorsal groove is nearer the edge and deeper than 
 in Lucina Peimsylvanica, and the whole shell is much less 
 orhicular. The present species may be regarded as obliquely sub- 
 oval. 
 
 Port Famine, Tierra del Fuego. 
 
 Spieipee Chilexsts. — PI. V. figs. 15, 16. 
 
 Shell suborbicidar, tumid. Dorsal valve deeper than the ventral ; 
 cardinal area shorter than the transverse diameter of the valve, 
 triangxdar, concave^ bound by angulated margins. Perforation 
 lanceolato-triangular . Centre of the dorsal valve with a rathe)' 
 deep and broad sinus, which, as well as the side, is furrowed and 
 ribbed. Ribs simple {about twenty-six, of vohich four belong to 
 the sinus), becoming obsolete towards the angles of the cardinal 
 area, crossed by strongly marked sinuous lines of groivth. Beak 
 very prominent and somewhat incurved. Dorsal valve ribbed 
 like the ventral, four of the ribs being upon the rounded but 
 loell-dejtned mesial ridge. Frontal margin of both valves slightly 
 linguiform. 
 
 There are two varieties of this shell, the one much more 
 tumid than the other. 
 
 Dimensions of largest specimen : breadth, 1— ; breadth of 
 cardinal line, Ij^ ; length of dorsal valve, 1-^^ ; of ventral valve, 
 1 inch ; thickness of united valves, ~ of an inch. 
 
 This shell nearly resembles several carboniferous limestone 
 spirifers. It is also related to some liassic species, as Spirifer 
 Wolcotii. 
 
 Cordillera of Guasco, Chile. 
 
 Spieifee lijtguifeegides. — PI. V. figs. 17, 18. 
 
 Shell orbicular, globose, surface smooth, undulated toivards the ma?'- 
 gin, where there are also a few strong t7'ansverse furrows of 
 growth. Valves nearly equal. Frontal margin not projecting, 
 bisinuated. Mesial furrow of dorsal valve shallow, lanceolate. 
 
Appendix to Part II. 62 7 
 
 hut well defined, as is also the mesial ridge of the ventral. Area 
 not visible in specimens examined. 
 
 Breadth, 1| ; length nearly the same ; thickness, \^^ of an 
 inch. 
 
 Very near Spirifer linguifera of Phillips (a carboniferous lime 
 stone fossil), but probably distinct. 
 
 Bio Claro, Valley of Coquimbo, Cbile. 
 
 Teeebratfla ii^ca. — PL V. figs. 19, 20. 
 
 8hell orbicular, depressed, surface ohsoletely striated concentrically ; 
 the furroiDs of growth becoming more strongly mjarhed towards 
 the margin. Dorsal valve most convex. Frontal margi7i oh- 
 soletely bisinuated, and in young specimens slightly truncate. 
 Beak of dorsal valve very prominent and incurved, obtusely 
 angled at the sides, terminating in a {small ^) perforation. Area 
 very s'inall but distinct. 
 
 Length of dorsal valve, 1~ ; breadth, Ij- of an inch ; thick- 
 ness, 1 inch. 
 
 Iquique, Southern Peru. 
 
 s s 3 
 
(3) SKETCH -SECTION UP THE VALLEY OF COPIAPOTOTHE BASE OF THE MAIN CORDILLERA. 
 
•f-S.A (i Balanus yarians. i 
 
 22 FtUuiuUj 0tUn^a 
 
 D FemL mtruiwruihs 
 J'iOtiuifa fuh-uh a 
 
 lo . mtUU'culialu/n 
 
 J& Viiatla iflabtXL. 
 
 \ Z^ 2^ iucuUo-a a/fa 
 2S Anwnia alivnan 
 
 30 21 rrt^tmc^lia insolita': \2<^.27 rereimtula fatti^mua 
 
Index. 
 
 631 
 
 BRODERIP 
 
 Broderip, Mr., on elevated shells 
 from Concepcion, 238 
 
 Brown, Mr. E., on sphsrulitic bo- 
 dies in silicified wood, 70 
 
 — on extinct plants from Van 
 Diemen's Land, 157 
 
 — on silicified wood of Uspallata 
 range, 527 
 
 — on silicified wood, 563 
 Bucalema, elevated shells near, 239 
 Buch, Yon, on obsidian streams, 73 
 
 — on laminated lava, 75 
 
 — on superficial calcareous beds 
 in the Canary Islands, 100 
 
 — on cavernous lava, 116 
 
 — on olivine in basalt, 118 
 
 — on crystals sinking in obsidian, 
 132 
 
 — on central volcano, 143 
 
 — on cleavage, 464 
 
 — on cretaceous fossils of the Cor- 
 dillera, 491, 511 
 
 — on the sulphureous volcanos of 
 Java, 587 
 
 Buenos Ayres, 315 
 
 Burchell, Mr., on elevated shells of 
 
 Brazil, 193 
 Byron on elevated shells, 232 
 
 OACHAPUAL, boulders in valley 
 of, 293,296 
 Caldcleugh, Mr., on elevation of 
 Coquimbo, 251 
 
 — on rocks of the Portillo range, 
 495 
 
 Callao, elevation near, 266 
 
 — old town of, 272 
 Calcareous deposit at St. Jago, af- 
 fected by heat, 5-9 
 
 — fibrous matter, entangled in 
 streaks in scorige, 15 
 
 — freestone at Ascension, 56 
 
 ^ — incrustations at Ascension, 58 
 
 — sandstone at St. Helena. 98 
 
 — superficial beds at KingGeorge's 
 Sound, 161 
 
 Cape of Good Hope, 166 
 
 — metamorphic rocks of, 465 
 Carbonic acid, expulsion of, by 
 
 heat, 9, 18 
 
 CLAYSLATE 
 
 Carcliarias megalodon, 403 
 Carmichael, Capt., on glossy coat- 
 ings to dikes, 87 
 Carpenter, Dr., on microscopic or- 
 ganisms, 314 
 Castro (Chiloe), beds near, 390 
 Casts, calcareous, of branches, 163 
 Cauquenes Baths, boulders near, 
 293, 297 
 
 — pebbles in porphyry near, 472 
 — volcanic formation near, 480 
 
 — stratification near, 483 
 
 Caves above sea-level, 233, 239, 
 264 
 
 Cerithium (fossil), 171 
 
 Cervus pumilis, fossil horns of, 235 
 
 Chalcedonic nodules, 157 
 
 Chalcedony in basalt and in silici- 
 fied wood, 54 
 
 Chatham Island, 111, 119, 130, 141, 
 160 
 
 Chevalier, M., on elevation near 
 Lima, 266 
 
 Chile, elevation of coast, 235 
 
 — structure of countiy betweea 
 the Cordillera and the Pacific, 
 283 
 
 — tertiary formations of, 390 
 
 — crystalline rocks in, 459 
 
 — central, geology of, 471 
 
 — northern, geology of, 535 
 Chiloe, gravel on coast, 217 
 
 — elevation of, 233 
 
 — tertiary formation of, 390, 407 
 
 — crystalline rocks of, 456 
 
 . Chlorite-schist, near M. Video, 431 
 Chlorophgeite, 156 
 Chonos Archipelago, tertiary for- 
 mations of, 389 
 
 — crystalline rocks of, 450 
 Chupat Eio, scoriae transported by, 
 
 194 
 Clarke, Eev. W., on the Cape of 
 
 Good Hope, 159, 166 
 Claro Eio, fossiliferous beds of, 546 
 Clay shale of Los Hornos, 537 
 Clayslate, its decomposition and 
 
 junction with granite, at the 
 
 Cape of Good Hope, 167 
 
 — formation of, T. del Fuego, 441 
 
 — of Concepcion, 457 
 
6^2 
 
 Index. 
 
 CLAYSALTE 
 
 Clayslate, feldspathic, of Chile, 
 471, 475, 482 
 
 — feldspathic, of the Uspallata 
 range, 517, 520 
 
 — black siliceous, band of, in por- 
 phyritic formations of Chile, 
 477 
 
 Claystone-porphyry, formation of, 
 in Chile, 472 
 
 — origin of, 477 
 
 — eruptive sources of, 575 
 Cleavage, of clayslate in Austra- 
 lia, 147 
 
 — definition of, 424 
 
 — at Bahia, 425 
 
 — Rio de Janeiro, 245 
 
 — Maldonado, 429 
 
 — Monte Video, 433 
 
 — S. Guitru-gueyu, 434 
 
 — Falkland I., 440 
 
 — T. del Fuego, 447 
 
 — Chonos I., 459 
 
 — Chiloe, 459 
 
 — Concepcion, 458 
 
 — Chile, 459 
 
 — discussion on, 460 
 Cleavage-cross, in sandstone, 134 
 Cleavage -laminee sup er fi cially bent , 
 
 457 
 Cliffs, formation of, 228 
 Climate, late changes in, 303 
 
 — of Chile during tertiary period, 
 412 
 
 Coal, of Concepcion, 398 
 
 — S. Lorenzo, 579 
 Coast-denudation of St. Helena, 
 
 104 
 Cobija, elevation of, 264 
 Coclilicopa (fossil), 174 
 Cochlogena auris vtilpina, 101, 
 
 171 
 Colombia, cretaceous formation of, 
 
 578 
 Colonia del Sacramiento, elevation 
 
 of, 190 
 
 — Pampean formation near, 338 
 Colorado, Rio, gravel of, 219 
 
 — sand-dunes of, 195, 216 
 
 — Pampean formation near, 321 
 Columnar basalt, 13 
 Combarbala, 535, 538 
 
 CORDILLERA 
 
 Comptes Rendus, account of vol- 
 canic phenomena in the Atlan- 
 tic, 105 
 
 Concepcion, earthquake of, 145 
 
 — elevation of, 236 
 
 — deposits of, 398, 407 
 
 — crystalline rocks of, 457 
 Conchalee, gravel-terraces of, 247 
 Concretions in tuff, 54 
 
 — in aqueous and igneous rocks 
 compared, 69 
 
 — of obsidian, 69, 73 
 
 — of gypsum, at Iquique, 303 
 
 — in sandstone at S. Cruz, 378 
 
 — in tufaceous tuff of Chiloe, 
 378 
 
 — in gneiss, 423 
 
 — in claystone-porphyry at Port 
 Desire, 437 
 
 — in gneiss at Valparaiso, 
 460 
 
 — in metam Orphic rocks, 462 
 
 — of anhydrite, 486 
 
 — relations of, to veins, 526 
 Conglomerate, recent, at St. Jago, 
 
 26 
 
 — claystone of Chile, 472, 477 
 
 — of Tenuyan, 492, 499, 533 
 
 — of the Cumbre Pass, 506, 513 
 
 — of Rio Claro, 545 
 
 — of Copiapo, 564, 567 
 
 Cook, Capt., on form of sea-bottom, 
 
 227 
 Copiapo, elevation of, 263 
 
 — tertiary formations of, 405 
 
 — secondary formations of, 553 
 Copper, sulphate of, 553 
 
 — native, at Arqueros, 541 
 
 — mines of, at Panuncillo, 538 
 
 — veins, distribution of, 580 
 Coquimbo, curious rock of, 162 
 
 — elevation and terraces of, 248 
 
 — tertiary formations of, 402 
 
 — secondary formations of, 540 
 Corallines living on pebbles, 
 
 226 
 Corals, fossil, from Van Diemen's 
 
 Land, 155, 178 
 Cordillera, valleys bordered by 
 
 gravel fringes, 289 
 
 — basil, strata of, 472 
 
Index. 
 
 ^ZZ 
 
 CORDILLERA 
 
 Cordillera, fossils of, 491, 512, 547, 
 550, 560, 578 
 
 — elevation of, 472, 501, 528, 531, 
 571, 576, 589, 593, 602 
 
 — gypseous formations of, 485, 
 489, 504, 509, 536, 548, 552, 
 557, 577 
 
 — claystone-porphyries of, 471 
 
 — andesitic rocks of, 478 
 
 — volcanos of, 480, 591, 601 
 Coste, M., on elevation of Lemus, 
 
 232 
 Coy inlet, tertiary formation of, 
 
 384 
 Crater, great central one at St. 
 
 Helena, 92 
 
 — internal ledges round, and para- 
 pet on, 93 
 
 — segment of, at the Galapagos, 
 123 
 
 Craters, basaltic, small, at St, 
 Jago, 20 
 
 — of tuff at Terceira, 28 
 
 — at Ascension, 41 
 
 — form of, affected by the trade- 
 wind, 41 
 
 — of elevation, 105 
 
 — of tuff at the Galapagos Archi- 
 pelago, 111, 113, 119, 121 
 
 — small, at the Galapagos Archi- 
 pelago, 115 
 
 — their breached state, 127 
 Crassatella Lyellii, 387 
 Cruickshanks, Mr., on elevation 
 
 near Lima, 273 
 
 Crystallisation favoured by space, 
 78 
 
 Crystals of feldspar, gradual for- 
 mation of, at Port Desire, 437 
 
 CuGullcea, 387 
 
 Cumbre, Pass of, in Cordillera, 502 
 
 Cuming, Mr., on habits of the 
 Mesodesma, 244 
 
 — on range of living shells on west 
 coast, 410, 411 
 
 DANA, Mr,, on foliated rocks, 
 465 
 — on amygdaloids, 474 
 Dartigues, Mr,, on sphsrulites, 71 
 
 DIKES 
 
 Darwin, Mount, 445 
 Daubeny, Dr., on a basin-formed 
 island, 122 
 
 — on fragments in trachyte, 50 
 D'Aubuisson, on the composition 
 
 of obsidian, 70 
 
 — on the lamination of clayslate, 
 75 
 
 • — on hills of phonolite, 98 
 
 — on concretions, 395 
 
 — on foliated rocks, 465 
 Decay, gradual, of upraised shells, 
 
 265, 267, 273 
 Decomposition of granite rocks, 
 
 428 
 De la Beche, Sir H., on magnesia 
 
 in eruptive lime, 14 
 
 — on specific gravity of lime- 
 stones, 57 
 
 — his theoretical researches on 
 geology, 225 
 
 — on the action of salt on calca- 
 reous rocks, 273 
 
 — on bent cleavage-laminae, 457 
 Denudation of coast at St. Helena, 
 
 104 
 
 — on coast of Patagonia, 214, 228, 
 415 
 
 — great powers of , 415 
 
 — of the Portillo range, 495, 500 
 Deposits, saline, 802 
 Despoblado,valley of, 564, 566, 570 
 Detritus, nature of, in Cordillera, 
 
 292 
 Devonshire, bent cleavage in, 457 
 Diana's Peak, St. Helena, 93 
 Dieffenbach, Dr,, on the Chatham 
 
 Islands, 160 
 Dikes, truncated on central crateri- 
 
 fprm ridge of St. Helena, 93 
 
 — ait St. Helena; number of ; 
 coated by a glossy layer; uni- 
 form thickness of, 87 
 
 — great parallel ones at St.Helena, 
 97 
 
 — remnants of, extending far into 
 sea round St. Helena, 104 
 
 — not observed at Ascension, 105 
 
 — of tuff, 114 
 
 — of trap, in the plutonic series, 
 139 
 
634 
 
 Index. 
 
 DIKES 
 
 Dikes in gneiss of Brazil, 423, 429 
 
 — near Rio de Janeiro, 428 
 
 — pseudo-, at Port Desire, 439 
 
 — in T. del Fuego, 443 
 
 — in Chonos Archipelago, con- 
 taining quartz, 455 
 
 — near Concepcion, with quartz, 
 458 
 
 — granitic porphyritic, at Valpa- 
 raiso, 459 
 
 — rarely vesicular in Cordillera, 
 480 
 
 — absent in the central ridges of 
 the Portillo Pass, 489 
 
 — of the Portillo range, with 
 grains of quartz, 496 
 
 — intersecting each other often, 
 513 
 
 — numerous at Copiapo, 567 
 Dislocations at Ascension, 46 
 
 — at St. Helena, 89 
 Distribution of volcanic islands, 
 
 140 
 Dolimieu on decomposed trachyte, 
 29 
 
 — on obsidian, 72, 73 
 
 — on laminated lava, 75, 77 
 Domeyko, M., on the silver mines 
 
 of Ooquimbo, 541 
 
 — on the fossils of Coquimbo, 548 
 D'Orbigny, M.A., on upraised shells 
 
 of Monte Video, 190 
 
 — on elevated shells at St. Pedro, 
 191 
 
 — on elevated shells near B. Ayres, 
 193 
 
 — on elevation of S. Bias, 196 
 
 — on the sudden elevation of La 
 Plata, 215 
 
 — on elevated shells near Cobija, 
 264 
 
 — on elevated shells near Arica, 
 265 
 
 — on the climate of Peru, 268 
 
 — on salt deposits of Cobija, 302 
 
 — on crystals of gypsum in salt- 
 lakes, 310 
 
 — on absence of gypsum in the 
 Pampean formation, 317 
 
 — on fossil remains from Bahia 
 Blanca, 327, 329 
 
 EDMONSTON 
 
 D'Orbigny, M.A., on fossil remains 
 from the banks of the Parana, 
 332 
 
 — on the geology of St. Fe, 334 
 
 — on the age of Pampean forma- 
 tion, 341, 356 
 
 — on the Mastodon Andium,, 362 
 
 — on the geology of the Hio Negro, 
 370 
 
 — on the character of Patagonian 
 fossils, 386 
 
 — on fossils from Concepcion, 400 
 
 — on fossils from Coquimbo, 405 
 
 — on fossils from Payta, 406 
 
 — on fossil tertiary shells of Chile, 
 409 
 
 — on cretaceous fossils of T. del 
 Fuego, 443 
 
 — on cretaceous fossils from the 
 Cordillera of Chile, 490, 511, 548, 
 551, 560, 578 
 
 Dree, M., on crystals sinking in 
 lava, 133 
 
 Dufrenoy, M., on the composition 
 of the surface of certain lava- 
 streams, 73, 133 
 
 — on the inclination of tuflE-strata, 
 121 
 
 EARTH, marine origin of, 234, 
 241 
 Earthenware, fossil, 270 
 Earthquake, effect of, at S. Maria, 
 216 
 
 — elevation during, at Lemus, 232 
 
 — of 1822, at Valparaiso, 244 
 
 — effects of, in shattering sur- 
 face, 269 
 
 — fissures made by, 269 
 
 — probable effects on cleavage, 
 269 
 
 Earthquakes in Pampas, 211 
 Earthquake-waves, power of, in 
 throwing up shells, 244 
 
 — effects of, near Lima, 273 
 
 — power of, in transporting boul- 
 ders, 301 
 
 Edmonston, Mr., on depths at 
 which shells live at Valparaiso, 
 244 
 
Index. 
 
 635 
 
 EGGS 
 
 Eggs of turtle at Ascension, 57 
 
 — of birds embedded at St. Helena, 
 100 
 
 Ehrenberg, Prof., on infusoria in 
 the Pampean formation, 321, 
 328, 333 
 
 — on infusoria in the Patagonian 
 formation, 373, 374, 377, 385, 
 387 
 
 Ejected fragments at Ascension, 47 
 
 — at the Galapagos Archipelago, 
 125 
 
 Elevation of St. Helena, 103 
 
 — the Gralapagos Archipelago, 130 
 
 — of volcanic islands, 144 
 
 — Van Diemen's Land, Cape of 
 Grood Hope, New Zealand, Aus- 
 tralia, and Chatham Island, 158 
 
 — La Plata, 189 
 
 — Brazil, 193 
 
 — Bahia Blanca, 193, 324 
 
 — San Bias, 196 
 
 — Patagonia, 196, 213, 215 
 
 — Tierra del Fuego, 208 
 
 — Falkland Islands, 210 
 
 — Pampas, 211, 358 
 
 — Chonos Archipelago, 232 
 
 — Chiloe, 233 
 
 — Chile, 235 
 
 — Valparaiso, 239, 245 
 
 — Coquimbo, 247, 261 
 
 — Guasco, 261 
 
 — Iquique, 265 
 
 — Cobija, 264 
 
 — Lima, 266 
 
 — sudden, at S. Maria, 216 
 
 — at Lemus, 232 
 
 — insensible, at Chiloe, 234 
 
 — insensible, at Valparaiso, 246 
 
 — insensible, at Coquimbo, 251 
 
 — axes of, at Chiloe, 397, 407 
 
 — axes of, at P. Rumena, 397, 
 408 
 
 — axes of, at Concepcion, 399, 407 
 
 — unfavourable for the accumu- 
 lation of permanent deposits, 
 415 
 
 — lines of, parallel to cleavage and 
 foliation, 426, 429, 433, 434, 441, 
 447, 453, 458, 464 
 
 — lines of, oblique to foliation, 453 
 
 FELDSPAR 
 
 Elevation, areas of, causing lines 
 of elevation and cleavage, 469 
 
 — lines of, in the Cordillera, 472 
 
 — slow, in the Portillo range, 498 
 
 — two periods of, in Cordillera o- 
 Central Chile, 499 
 
 — of the Cspallata range, 528 
 
 — two periods of, in Cumbre Pass, 
 531 
 
 — horizontal, in the Cordillera of 
 Copiapo, 572 
 
 — axes of, coincident with vol- 
 canic orifices, 577 
 
 — of the Cordillera, summary on, 
 589, 593, 601 
 
 Elliott, Capt., on human remains, 
 
 193 
 Ellis, Rev. W,, on marine remains 
 
 at Otaheite, 32 
 
 — on ledges within the great cra- 
 ter at Hawaii, 94 
 
 Ensenada, elevated shells of, 191 
 Entre Rios, geology of, 334j 
 .Equus curvidens, 336, 362 
 Epidote in T. del Fuego, 444 
 
 — in gneiss, 459 
 
 — frequent in Chile, 475 
 
 — in the Uspallata range, 529 
 
 — in porphyry of Coquimbo, 541 
 Erman, M., on andesite, 480 
 Eruption, fissures of, 131, 142, 145 
 Escarpments, recent, of Patagonia, 
 
 228 
 Extinction of land shells at St. 
 Helena, 102 
 
 — of fossil mammifers, 346 
 
 FALKLAND Islands, elevation 
 of, 210 
 
 — pebbles on coast, 223, 225 
 
 — geology of, 440 
 
 Falkner on saline incrustations, 
 
 306 
 Faraday, Mr., on the expulsion of 
 
 carbonic acid gas, 9 
 Faults, great, in Cordillera, 487, 
 
 574 
 Feldspar, Labrador, ejected, 47 
 
 — fusibility of, 138 
 
 — in radiating crystals 166 
 
e-KG 
 
 Index. 
 
 FELDSPAR 
 
 Feldspar, earthy, metamorphosis 
 of, at Port Desire, 438 
 
 — albitic, 478 
 
 — crystals of, with albite, 478 
 
 — orthitic, in conglomerate of 
 Tenuyan, 492 
 
 — in granite of PortiUo range, 494 
 ■ — in porphyries in the Cumbre 
 
 Pass, 514 
 Feldspathic lavas, 24 
 
 — rocks, alternating with obsi- 
 dian, 70 
 
 — lamination, and origin of, 74 
 
 — at St. Helena, 91 
 Fenestella (fossil), 180 
 Fernando Noronha, 27, 75 
 Ferruginous superficial beds, 160 
 Feuillee on sea level at Coquimbo, 
 
 252 
 Fibrous calcareous matter at St. 
 
 Jago, 15 
 Fissures of eruption, 131, 142, 145 
 
 — relations of, to concretions, 
 395 
 
 — upfilled, at Port Desire, 440 
 — - in clayslate, 521 
 
 Fitton, Dr., on calcareous breccia, 
 165 
 
 — on the geology of T. del Fuego, 
 446- 
 
 FitzRoy, Capt., on the elevation of 
 the Falkland Islands, 210 
 
 — on the elevation of Concepcion, 
 236 
 
 Flagstaff-hill, St. Helena, 86 
 Fleurian de Belle vue on spheeru- 
 
 lites, 71 
 Fluidity of lavas, 117, 119 
 Foliation, definition of, 424 
 
 — of rocks at Bahia, 424 
 
 — Rio de Janeiro, 425 
 
 — Maldonado, 429 
 
 — Monte Video, 433 
 
 — S. Guitru-gueyu, 434 
 
 — Falkland I., 440 
 
 — T. del Fuego, 446 
 
 — Chonos Archipelago, 451 
 
 — Chiloe, 456 
 
 — Concepcion, 458 
 
 — Chile, 459 
 
 — discussion on, 460 
 
 FORMATION 
 
 Forbes, Prof. E., on the structure 
 of glaciers, 80 
 
 — on cretaceous fossils of Con- 
 cepcion, 400 
 
 — on cretaceous fossils and sub- 
 sidence in Cumbre Pass, 512 
 
 — on fossils from Guasco, 551 
 
 — on fossils from Coquimbo, 542, 
 548 
 
 — on fossils from Copiapo, 560 
 
 — on depths at which shells live, 
 414, 565 
 
 Formation, Pampean, 315 
 
 area of, 349 
 
 estuary origin, 352 
 
 — tertiary, of Entre Rios, 335 
 
 of Banda Oriental, 337 
 
 of Patagonia, 370 
 
 — summary on, 386 
 
 of T. del Fuego, 385 
 
 of the Chonos Archipe]ago, 
 
 389 
 
 of Chiloe, 390 
 
 of Chile, 390 
 
 of Concepcion, 397, 407 
 
 — — of Navidad, 401 
 
 of Coquimbo, 402 
 
 of Peru, 405 
 
 subsidence during, 419 
 
 — volcanic, of Tres Montes, 389 
 of Chiloe, 391 
 
 of Cumbre Pass, 511 
 
 in Banda Oriental, 341 
 
 old, near Maldonado, 430 
 
 with laminar structure, 468 
 
 ancient, in T. del Fuego, 444 
 
 — recent, absent on S. American 
 coast, 414 
 
 — metamorphic, of claystone por- 
 phyry of Patagonia, 435, 468 
 
 foliation of, 462 
 
 — plutonic, with laminar struc- 
 ture, 468 
 
 — palseozoic, of the Falkland I. ,440 
 
 — claystone, at Concepcion, 457 
 
 — Jurassic, of Cordillera, 491, 512 
 
 — Neocomian, of the Portillo 
 Pass, 491 
 
 — gypseous, of Los Hornos, 535, 
 549, 550 
 
 of Coquimbo, 542 
 
Index. 
 
 ^Zl 
 
 FORMATION 
 
 Formation, gypseous, of Guasco, 
 550 
 
 of Copiapo, 551 
 
 of Iquique, 577 
 
 — cretaceo-oolitic, of Coquimbo, 
 548, 563 
 
 of Guasco, 551, 562 
 
 of Copiapo, 561 
 
 of Iquique, 578 
 
 Fossils, Neocomian, of Portillo 
 
 Pass, 490 
 of Cumbre Pass, 511 
 
 — secondary, of Coquimbo, 547 
 of Guasco, 550 
 
 of Copiapo, 561 
 
 of Iquique, 578 
 
 — palseozoic, from the Falklands, 
 440 
 
 Fragments ejected at Ascension, 
 47 
 
 — at the Galapagos Archipelago, 
 125 
 
 — of hornblende-rock in gneiss, 
 423 
 
 — of gneiss in gneiss, 427 
 Fresh-water Bay, 123, 132 
 Freyer, Lieut., on elevated shells 
 
 of Arica, 266 
 Frezier on sea-level at Coquimbo, 
 
 252 
 Fuerteventura, calcareous beds of, 
 
 100 
 
 GALAPAGOS Archipelago, 110 
 — parapets round craters, 94 
 
 — pseudo-dikes of, 440 
 Gallegos, Port, tertiary formation 
 
 of, 385 
 Garnets in gneiss, 426 
 
 — in mica slate, 445 
 
 — at Panuncillo, 539 
 Gaudichaud, M., on granites of 
 
 Brazil, 427 
 Gay-Lussac on the expulsion of 
 
 carbonic acid gas, 9 
 Gay, M., on elevated shells, 239 
 
 — on boulders in the Cordillera, 
 293, 297 
 
 — on fossils from Cordillera of 
 Coquimbo, 550 
 
 GRYPH^A 
 
 Gill, Mr., on brickwork transported 
 by an earthquake- wave, 272 
 
 Gillies, Dr., on heights in the Cor- 
 dillera, 482 
 
 — on extension of the Portillo 
 range, 499 
 
 Glaciers, their structure, 80 
 Classiness of texture, origin of, 70 
 Glen Eoy, parallel roads of, 260 
 
 — sloping terraces of, 295 
 GlossojJteris Browni% 147 
 Gneiss, with a great embedded 
 
 fragment, 149 
 
 — derived from clayslate, 168 
 
 — near Bahia, 422 
 
 — of Eio de Janeiro, 425 
 
 — decomposition of, 427 
 Gneiss-granite, forms of hills of, 
 
 160 
 Gold, distribution of, 581 
 Good Hope, Cape of, 1(56 
 Gorges, narrow at St. Helena, 103 
 Gorodona, formations near, 332 
 Granite, junction with clayslate, 
 
 at the Cape of Good Hope, 167 
 
 — axis of, oblique to foliation, 453 
 
 — andesitic, 478 
 
 — of Portillo range, 494 
 
 — veins of, quartzose, 454. 529 
 
 — pebble of, in porphyritic con- 
 glomerate, 559 
 
 — conglomerate, 567 
 Granitic, ejected fragments, 47, 
 
 125 
 Grauwacke of Uspallata range, 516 
 Gravity, specific, of lavas, 132-140 
 Gravel at bottom of sea, 214, 225 
 
 — formation of, in Patagonia, 219 
 
 — means of transportation of, 224 
 
 — strata of, inclined, 515 
 Gravel-terraces in Cordillera, 290 
 Greenough, Mr., on quartz veins, 
 
 464 
 Greenstone, resulting from meta- 
 morphosed hornblende-rock, 432 
 
 — of T. del Fuego, 444 
 
 — on the summit of the Campana 
 of Quillota, 471 
 
 — porphyry, 473 
 
 — relation of, to clayslate, 473 
 Gry^hcea orientalis, 542 
 
638 
 
 Index. 
 
 GUASCO 
 
 Guasco, elevation of, 261 
 
 — secondary formation of, 550 
 Guitru-gneyu, Sierra, 434 
 Guyana, gneissic rocks of, 424 
 Gypsum at Ascension, 61 
 
 — in volcanic strata, at St. Helena, 
 86 
 
 — on surface of the ground at St. 
 Helena, 98 
 
 — nodules of, in gravel at Eio 
 Negro, 219 
 
 — deposited from sea-water, 273 
 
 — deposits of, at Iquique, 303 
 
 — crystals of, in salt lakes, 304 
 
 — in Pampean formation, 317 
 
 — in tertiary formation of Pata- 
 gonia, 371, 373, 377, 378 
 
 — great formation of, in the Por- 
 tillo Pass, 487, 489 
 
 in the Cumbre Pass, 504, 
 
 509 
 
 near Los Hornos, 536 
 
 at Coquimbo, 542 
 
 at Copiapo, 553, 557 
 
 near Iquique, 578 
 
 — of San Lorenzo, 579 
 
 HALL, Capt., on terraces at 
 Coquimbo, 255 
 Hall, Sir J., on the expulsion of 
 
 carbonic acid gas, 9 
 Hamilton, Mr., on elevation near 
 
 Tacna, 266 
 Harlan, Dr., on human remains, 
 
 193 
 Haves, Mr. A., on nitrate of soda, 
 
 305 
 Heat, action of, on calcareous 
 
 matter, 8 
 Helix (fossil), 174 
 Helix melo, 163 
 HemitryiJCb (fossil), 183 
 Hennah, Mr., on ashes at Ascen- 
 sion, 42 
 Henslow, Prof., on chalcedony, 54 
 — on concretions, 464 
 Herbert, Capt., on valleys in the 
 
 Himalaya, 286 
 Herradura Bay, elevated shells of, 
 
 250 
 
 INCRUSTATIONS 
 
 Herradura Bay, tertiary forma- 
 tions of, 403 
 Himalaya, valleys in, 286 
 Hippurites Chilensis, 542, 548 
 Hitchcock, Prof., on dikes, 424 
 Hoffman, on decomposed trachyte, 
 
 29 
 Holland, Dr., on Iceland, 108 
 Honestones, pseudo, of Coquimbo, 
 543 
 
 of Copiapo, 552 
 
 Hooker, Dr. J. D., on fossil beech 
 
 leaves, 386 
 Hopkins, Mr., on axes of elevation 
 oblique to foliation, 454 
 
 — on origin of lines of elevation, 
 469,592 
 
 Hornblende-rock, fragments of, in 
 
 gneiss, 423 
 Hornblende-schist, near M. Video, 
 
 433 
 Horner, Mr., on a calcareo-animal 
 
 substance, 62 
 
 — on fusibility of feldspar, 138 
 Hornos, Los, section near, 536 
 Hornstone, dike of, 456, 458 
 Horse, fossil tooth of, 326, 336 
 Huafo Island, 390, 406 
 
 — subsidence at, 418 
 Huantajaya, mines of, 577 
 Hubbard, Dr., on dikes, 139 
 Humboldt, on ejected fragments, 
 
 48 
 
 — on obsidian formations, 72, 74 
 
 — on spheerulites, 76 
 
 — on parapets round craters, 94 
 
 — on saline incrustations, 306 
 
 — on foliations of gneiss, 424 
 
 - — on concretions in gneiss, 459 
 Hutton on amygdaloids, 18 
 Hyalite in decomposed trachyte, 29 
 
 ICEBERGS, action on cleavage, 
 458, 462 
 Iceland, stratification of the cir- 
 cumferential hills, 108 
 Illapele, section near, 535 
 Imperial, beds of shells near, 236 
 Incrustations, on St. Paul's rock, 
 38 
 
Index. 
 
 639 
 
 INCRUSTATIONS 
 
 Incrustations, calcareous, at As- 
 cension, 58 
 
 — saline, 306 
 
 Infusoria in Pampean formation, 
 315, 321, 328, 333 
 
 — in Patagonian formation, 371, 
 373, 374, 385, 386 
 
 Iodine, salts of, 307, 309 
 Iquique, elevation of, 265 
 
 — saliferous deposits of, 302 
 
 — cretaceo-oolitic formation of, 
 ^ 577 
 
 Iron, oxide of, in lavas, 508, 569 
 
 — in sedimentary beds, 536, 540 
 
 — tendency in, to produce hollow 
 concretions, 396 
 
 — sulphate of, 553 
 
 Isabelle, M., on volcanic rocks of 
 
 Banda Oriental, 343 
 Islands, volcanic, distribution of, 
 
 140 
 
 — their elevation, 144 
 
 J AGO, St., 3 
 James Island, 119, 122, 131 
 Jasper, origin of, 52 
 Joints in clayslate, 447 
 Jonnes, M. Moreau de, on craters 
 
 affected by wind, 42 
 Juan Fernandez, 144 
 Jukes, Mr., on cleavage in New- 
 foundland, 463 
 
 XAMTSCHATKA, andesite of, 
 480 
 Kane, Dr., on the production of 
 
 carbonate of soda, 274 
 Keilhau, M., on granite, 167 
 Kicker Ptock, 114 
 King George's Sound, 160 
 — calcareous beds of, 248 
 
 LABRADOR feldspar, ejected, 47 
 Lakes, origin of, 227 
 — fresh-water, near salt lakes, 311 
 Lamination of volcanic rocks, 74 
 Land-shells, extinct at St. Helena, 
 101 
 
 LONSDALE 
 
 Lanzarote, calcareous beds of, 100 
 Lava, adhesion to sides of a gorge, 
 20 
 
 — feldspathic, 24 
 
 — with cells semi-amygdaloidal, 
 31 
 
 — basaltic, of S. Cruz, 381 
 
 — claystone porphyry, at Chiloe, 
 392 
 
 — claystone, ancient submarine, 
 477 
 
 — basaltic, of the Portillo range, 
 497 
 
 — feldspathic, of the Cumbre 
 Pass, 508 
 
 — submarine, of the Uspallata 
 range, 522, 525, 531 
 
 — basaltic, of the Uspallata 
 range, 528 
 
 — submarine, of Coquimbo, 544, 
 547 
 
 — of Copiapo, 554, 565, 569 
 Lavas, specific gravity of, 132, 140 
 Lava-streams, blending together 
 
 at St. Jago, 20 
 
 — composition of surface of, 73 
 
 — with irregular hummocks at 
 Ascension, 111 
 
 — heaved up into hillocks at the 
 Galapagos Archipelago, 116 
 
 — their fluidity, 117, 119 
 
 — extreme thinness of, 125 
 
 — differences in the state of their 
 surfaces, 133 
 
 Lead, separation from silver, 134 
 Lemus Island, 389, 406 
 Lemuy Islet, 391 
 
 Lesson, M., on craters at Ascen- 
 sion, 42 
 Leucite, 118 
 Lignite of Chiloe, 392 
 
 — of Concepcion, 397 
 Lima, elevation of, 266 
 
 Lime, sulphate of, at Ascension, 59 
 
 — muriate of, 275, 302, 306 
 Limestone of Cumbre Pass, 506 
 
 — of Coquimbo, 542, 546 
 
 — of Copiapo, 560 
 LittoTina (fossil), 171 
 Lonsdale, Mr., on fossil corals from 
 
 Van Diemen's Land, 155, 178 
 
640 
 
 Index. 
 
 LOT 
 
 Lot, St. Helena, 96 
 
 Lund and Clausen on remains of 
 
 caves in Brazil, 360, 363 
 Lund, M., on granites of Brazil, 
 
 427 
 Lyell, M., on embedded turtles' 
 
 eggs, 57 
 • — on glossy coating to dikes, 87 
 
 — on craters of elevation, 107 
 
 — on upraised shells retaining 
 their colours, 219 
 
 — on terraces at Coquimbo, 252 
 
 — on elevation near Lima, 273 
 
 — on fossil horse's tooth, 336 
 
 — on the boulder-formation being 
 anterior to the extinction of 
 North American mammif ers, 348 
 
 — on quadrupeds washed down by- 
 floods, 353 
 
 — on age of American fossil mam- 
 mif ers, 362 
 
 — on changes of climate, 414 
 
 — on denudation, 416 
 
 — on foliation, 464 
 
 MACAULAY, Dr., on calcareous 
 casts at Madeira, 164 
 Mac Culloch, Dr., on an amygda- 
 loid, 31 
 
 — on laminated pitchstone, 74 
 
 — on chlorophgeite, 156 
 
 — on concretions, 464 
 
 — on beds of marble, 467 
 Mackenzie, Sir G., on obsidian 
 
 streams, 73 
 
 — on glossy coatings to dikes, 87 
 
 — on stratification in Iceland, 109 
 
 — on cavernous lava-streams, 116 
 Maclaren, Mr., letter to, on coral 
 
 formations, 421 
 Macrauchenia Pataohonica, 326, 
 
 345 
 Madeira, calcareous casts at, 163 
 
 — subsidence of, 230 
 Magazine, Nautical, account of 
 
 volcanic phenomena in the At- 
 lantic, 105 
 
 Magellan, Straits, elevation near, 
 208 
 
 Magnesia, sulphate of, in veins, 378 
 
 MONTE 
 
 Malcolmson, Dr., on trees carried 
 
 out to sea, 529 
 Maldonado, elevation of, 190 
 
 — Pampean formation of, 337 
 
 — crystalline rocks of, 429 
 Mammalia, fossil, of Bahia Blanca, 
 
 321, 336 
 
 near St. F6, 334 
 
 of Banda Oriental, 339 
 
 of St. Julian, 344 
 
 at Port Gallegos, 385 
 
 — washed down by floods, 352 
 
 — number of remains of, and 
 range of, in Pampas, 357, 367 
 
 Man, skeletons of (Brazil), 193 
 
 — remains of, near Lima, 268 
 
 — Indian, antiquity of, 269 
 Marble, beds of, 430 
 Marekanite, 69 
 Maricongo, ravine of, 571 
 Marsden on elevation of Sumatra, 
 
 235 
 Mastodon Andium, remains of, 332 
 
 — range of, 360 
 Mauritius, 33 
 
 — crater of elevation of, 105 
 Maypu Eio, mouth of, with up- 
 raised shells, 239 
 
 — gravel fringes of, 294 
 
 — debouchement from the Cordil- 
 lera, 483 
 
 Megalonyx, range of, 362 
 Megatherium, range of, 362 
 Miers, Mr., on elevated shells, 246 
 
 — on the height of the Uspallata 
 plain, 286 
 
 Miller, Prof., on ejected Labrador 
 feldspar, 47 
 
 — on quartz crystals in obsidian 
 beds, 63 
 
 Minas, Las, 429 
 
 Mitchell, Sir T., on bombs, 44 
 
 — on the Australian valleys, 152 
 Mocha Island, elevation of, 236 
 
 — tertiary form of, 337 
 
 — subsidence at, 418 
 Molina on a great flood, 297 
 Monte Hermoso, elevation of, 194 
 
 — fossils of, 321 
 
 Monte Video, elevation of, 190 
 
 — PamDean formation of, 337 
 
Index. 
 
 641 
 
 MONTE 
 
 Monte Video, crystalline rocks of, 
 
 431 
 Morris and Sharpe, Messrs., on the 
 
 palgeozoic fossils of the Falk- 
 
 lands, 440 
 Mud, Pampean, 315 
 
 — long deposited on the same 
 area, 357 
 
 Mud streams at the Galapagos 
 
 Archipelago, 120 
 Murchison, Sir K., on cleavage, 461 
 
 — on waves transporting gravel, 
 226 
 
 — on origin of salt formations, 
 580 
 
 — on the relations of metalliferous 
 veins and intrusive rocks, 584 
 
 — on the absence of granite in the 
 Ural, 692 
 
 NAEBOKOUGH Island, 117 
 Nautilus d' Orhigny anus, 400, 
 407 
 Navidad, tertiary formations of, 
 401 
 
 — subsidence of, 418 
 
 Negro, Kio, pumice of pebbles of, 
 194 
 
 — gravel of, 219 
 
 — salt lakes of, 219 
 
 — tertiary strata of, 370 
 Nelson, Lieut., on the Bermuda 
 
 Islands, 162, 165 
 
 New Caledonia, 141 
 
 New Eed Sandstone, cross cleavage 
 of, 151 
 
 New South Wales, 146 
 
 New Zealand, 160 
 
 North America, fossil remains of, 
 362 
 
 North Wales, sloping terraces ab- 
 sent in, 295 
 
 — bent cleavage of, 457 
 Nuevo Gulf, plains of, 197 
 
 — tertiary formation of, 374 
 Nulliporce (fossil), resembling 
 
 concretions, 6 
 
 
 
 BSIDIAN, bombs of, 44 
 — passage of beds into, 62, 66 
 
 PATAGONIA 
 
 Obsidian, composition and origin 
 of, 69, 73 
 
 — streams of, 73 
 
 — absent at the Galapagos Archi- 
 pelago, 129 
 
 — crystals of feldspar sink in, 1 32 
 
 — specific gravity of, 133, 137 
 
 — its eruption from lofty craters, 
 137 
 
 Olivine decomposed at St. Jago, 
 23 
 
 — in the lavas at the Galapagos 
 Archipelago, 118 
 
 — at Van Diemen's Land, 156 
 Oolitic structures of recent calca- 
 reous beds at St. Helena, 99 
 
 Otaheite, 30 
 
 Owen, Prof., on fossil mammif erous 
 remains, 322, 326, 336, 339, 346 
 
 PALMEK, Mr., on transportation 
 of gravel, 227 
 Pampas, elevation of, 211 
 
 — earthquakes of, 211 
 
 — formation of, 219, 313 
 
 — localities in which fossil mam- 
 mifers have been found, 367 
 
 Panuncillo, mines of, 538 
 
 Panza Island, laminated trachyte 
 
 of, 74 
 Parana, Eio, elevation near, 191 
 
 — on saline incrustations, 307 
 
 — Pampean formation near, 331 
 
 — on the S. Tandil, 434 
 
 Parish, Sir W., on elevated shells 
 near Buenos Ayres, 191, 192 
 
 — on earthquakes in the Pampas, 
 211 
 
 — on fresh-water near salt lakes, 
 312 
 
 — on origin of Pampean forma- 
 tion, 351 
 
 Patagonia, elevation and plains of, 
 196 
 
 — denudation of, 213 
 
 — gravel formation of, 219 
 
 — sea-clifEs of, 228 
 
 — subsidence during tertiary pe- 
 riod, 418 
 
 — crystalline rocks of, 435 
 
 T T 
 
642 
 
 Index. 
 
 PATTINSON 
 
 Pattinson, Mr., on the separation 
 
 of lead and silver, 134 
 Paul's, St., rocks of, 36 
 Payta, tertiary formations of, 405 
 Pearlstone, 68 
 Pebbles of pumice, 194 
 
 — decrease in size on the coast of 
 Patagonia, 215 
 
 — means of transportation, 225 
 
 — encrusted with living corallines, 
 226 
 
 — distribution of, at the eastern 
 foot of Cordillera, 289 
 
 — dispersal of, in the Pampas, 318 
 
 — zoned with colour, 472 
 Pentland, Mr., on heights in the 
 
 Cordillera, 503 
 
 — on fossils of the Cordillera, 511 
 Peperino, 113 
 
 Pernambuco, 193, 425 
 
 Peron, M., on calcareous rocks of 
 Australia, 164, 165 
 
 Peru, tertiary formations of, 405 
 
 Peuquenes, Pass of, in the Cor- 
 dillera, 481 
 
 — ridge of, 488 
 
 Pholas, elevated shells of, 233 
 Phonolite, hills of, 24, 27, 96 
 
 — laminated, 75 
 
 — with more fusible hornblende, 
 137 
 
 Pitchstone, 66 
 
 — dikes of, 75 
 
 — of Chiloe, 391 
 
 — of Port Desire, 435 
 
 — near Cauquenes, 480 
 
 — layers of, in the Uspallata range, 
 523, 524 
 
 — of Los Hornos, 538 
 
 — of Coquimbo, 543 
 Plains of Patagonia, 197, 211 
 
 — of Chiloe, 235 
 
 — of Chile, 283 
 
 — of Uspallata, 286 
 
 — on eastern foot of Cordillera, 
 288 
 
 — of Iquique, 304 
 Plants extinct, 157 
 Plata, La, elevation of, 190 
 
 — tertiary formation of, 218, 316 
 
 — crystalline rocks of, 428 
 
 PUNTA 
 
 Playfair, Prof., on the transporta- 
 tion of gravel, 226 
 
 Pluclaro, axis of, 542 
 
 Plutonic rocks, separation of con- 
 stituent parts of, by gravity, 137 
 
 Pondichery, fossils of, 400 
 
 Porcelain rocks of Port Desire, 
 437 
 
 — of the Uspallata range, 522, 
 525, 530 
 
 Porphyry, pebbles of, strewed over 
 
 Patagonia, 221 
 Porphyry- claystone of Chiloe, 392 
 
 of Patagonia, 435 
 
 of Chile, 471, 476 
 
 — greenstone, of Chile, 475 
 
 — doubly columnar, 481 
 
 — claystone rare, on the eastern 
 side of the Portillo Pass, 493 
 
 — brick-red and orthitic, of Cum- 
 bre Pass, 499, 514 
 
 — intrusive, repeatedly injected, 
 514 
 
 — claystone of the Uspallata range, 
 516 
 
 of Copiapo, 553, 570 
 
 — — eruptive sources of, 575 
 Port Desire, elevation and plains 
 
 of, 198 
 
 — tertiary formation of, 373 
 
 — porphyries of, 436 
 
 Portillo Pass in the Cordillera, 481 
 Portillo chain, 491, 499 
 
 — compared with that of the Us- 
 pallata, 534 
 
 Porto Praya, 3 
 
 Prefil or sea-wall of Valparaiso, 
 
 245 
 Pr6vost, M, C, on rarity of great 
 
 dislocations in volcanic islands, 
 
 89 
 Producta, 176 
 
 Prosperous Hill, St. Helena, 90 
 Puente del Inca, section of, 505 
 Pumice, laminated, 74, 75, 77 
 
 — absent at the Galapagos Archi- 
 pelago, 129 
 
 — pebbles of, 195 
 
 — conglomerate of, K. Negro, 370 
 
 — hills of, in the Cordillera, 480 
 Punta Alta, elevation of, 193 
 
Index 
 
 643 
 
 PUNTA 
 
 Punta Alta, beds of, 323 
 Puy de Dome, trachyte of, 50 
 
 AUAIL Island, St. Jago, 5, 11 
 
 Quartz-rock, mottled from meta- 
 morphic action with earthy 
 matter, 8 
 
 — crystals of, in beds alternating 
 with obsidian, ^S 
 
 — fusibility of, 188 
 
 — crystallised in sandstone, 148 
 
 — of the S. Ventana, 434 
 
 — C. Blanco, 436 
 
 — Falkland Islands, 440 
 
 — Portillo range, 494 
 
 — viscidity of, 529 
 
 — grains of, in mica-slate, 450 
 
 — grains of, in dikes, 454, 458 
 
 — veins of, near Monte Video, 433 
 
 — veins of, in dike of greenstone, 
 4^8 
 
 — V eins of, relations to cleavage, 
 
 463 
 Quillota, Campana of, 471 
 Quintero, elevation of, 246 
 Quiriquina, elevation of, 237 
 
 — deposits of, 398 
 
 RANCAGUA, plain of, 285 
 Eapel, E., elevation near, 239 
 Eed Hill, 12, 13 
 
 Eeeks, Mr. T., his analysis of de- 
 composed shells, 274 
 
 — his analysis of salts, 302 
 Eemains, human, 268 
 Eesin-like altered scoriee, 10 
 Eio de Janeiro, gneiss of, 149 
 
 — elevation near, 193 
 
 — crystalline rocks of, 425 
 Elvers, small power of transport- 
 ing pebbles, 224 
 
 — small power of, in forming val- 
 leys, 300 
 
 — drainage of, in the Cordillera, 
 483, 593 
 
 Eoads, parallel, of Glen Eoy, 260 
 Eobert, M., on strata of Iceland, 108 
 Eocks, volcanic, of B. Oriental, 341 
 
 — Tres Montes, 389 
 
 SALSES 
 
 Eocks, Chiloe, 391 
 
 — T. del Fuego, 444 
 
 — with laminar structure, 468 
 Eodents, fossil, remains of, 322, 
 
 371 
 Eogers, Prof., on curved lines of 
 elevation, 142 
 
 — address to Assoc, of American 
 Geologists, 420 
 
 Eose, Prof. G., on sulphate of iron 
 at Copiapo, 558 
 
 SBLAS, elevation of, 196 
 • S. Cruz, elevation and plains 
 of, 201 
 
 — valley of, 202 
 
 — nature of gravel in valley of, 221 
 
 — boulder formation of, 348 
 
 — tertiary formation of, 377 
 
 — subsidence at, 419 
 
 S. Fe Bajada, formations of, 334 
 S. George's Bay, plains of, 198 
 S. Helena, 83 
 
 — crater of elevation of, 105 
 
 S. Helena Island, sea-cliffs, and 
 
 subsidence of, 229 
 S. Jago, Chile, 283 
 
 — crater of, elevation of, 105 
 
 — effects of calcareous matter on 
 lava, 13 
 
 S. Josef, elevation of, 196 
 
 — tertiary formation of, 372 
 S. Juan, elevation near, 190 
 
 S. Julian, elevation and plains of, 
 200 
 
 — salt lake of, 308 
 
 — earthy deposits with mammi- 
 ferous remains, 345 
 
 — tertiary formation of, 875 
 
 — subsidence at, 418 
 
 S. Lorenzo, elevation of, 266 
 
 — old salt formation of, 579 
 
 S. Mary, island of, elevation of, 237 
 S. Paul's Eocks, 36, 141 
 S. Pedro, elevation of, 191 
 Salado, E., elevated shells of, 192 
 
 — Pampean formation of, 317 
 Salines, 308 
 
 Salses, compared with tuff craters, 
 127 
 
644 
 
 Index. 
 
 SALT 
 
 Salt deposited by the sea, 61 
 
 — in volcanic strata, 61, 86 
 
 — lakes of, in craters, 127 
 
 — with upraised shell, 267, 273 
 
 — lakes of, 308 
 
 — purity of, in salt lakes, 811 
 
 — deliquescent, necessary for the 
 preservation of meat, 311 
 
 — ancient formation of, at Iqui- 
 que, 579 
 
 — ancient formation of, at S. Lo- 
 renzo, 579 
 
 — strata of, origin of, 580 
 Salts, superficial deposits of, 302 
 Sand-dunes of the Uruguay, 191 
 
 — of the Pampas, 193 
 
 — near Bahia Blanca, 194, 215 
 
 — of the Colorado, 195, 216 
 
 — of S. Cruz, 204 
 
 — of Arica, 265 
 Sandstone of Brazil, 169 
 
 — of the Cape of Good Hope, 169 
 
 — platforms of, in New South 
 Wales, 147, 169 
 
 Sarmiento, Mount, 445 
 
 Schmidtmeyer on auriferous detri- 
 tus, 581 
 
 Schomburghk, Sir E., on sea- 
 bottom, 226 
 
 — on the rocks of Guyana, 424 
 School, radiating, 166 
 Scotland, sloping terraces of, 295 
 Scrope, Mr. P., on silex in trachyte, 
 
 18 
 
 — on obsidian, 72 
 
 — on laminated trachyte, 74, 76, 80 
 
 — on sphserulites, 76 
 
 — on separation of trachyte and 
 basalt, 183 
 
 Sea, nature of bottom off Pata- 
 gonia, 214 
 
 — power of, in forming valleys, 
 300 
 
 Sea cliffs, formation of, 228 
 Seal, Mr., model of St. Helena, 
 
 229 
 Scale, Mr., geognosy of St. Helena, 
 
 85 
 
 — on embedded birds' bones, 102 
 
 — on extinct shells of St. Helena, 
 102 
 
 SILICA 
 
 Scale, Mr., on dikes, 103, 104 
 Sebastian Bay, tertiary formation 
 
 of, 385 
 Sedgwick, Prof., on concretions, 69 
 
 — on cleavage, 462 
 
 Septaria in concreti ons in tuff, 56 
 Serpentine of Copiapo, 552 
 Serpulee, on upraised rocks, 269 
 Seychelles, 141 
 
 Shale-rock, of the Portillo Pass, 
 489 
 
 — of Copiapo, 559 
 
 Shells, particles of, colours of, 
 affected by light, 61 
 
 — particles of, drifted by the wind 
 at St. Helena, 99 
 
 — land, extinct at St. Helena, 101 
 
 — from Van Diemen's Land, 154, 
 176 
 
 — from St. Jago, 171 
 
 — fossil, from St. Helena, 173 
 
 — upraised, state of, in Patagonia, 
 208 
 
 — elevated, too small for human 
 food, 241 
 
 — transported far inland, for food, 
 242 
 
 — upraised, proportional numbers 
 varying, 249, 267 
 
 — upraised, gradual decay of, 265, 
 267, 273 
 
 — upraised, absent on high plains 
 of Chile, 287 
 
 — upraised, near Bahia Blanca, 
 325 
 
 — preserved in concretions, 391, 
 395 
 
 — living and fossil, range of, on 
 west coast, 410, 413 
 
 — living, different on the east and 
 west coast, 219 
 
 Shelly matter deposited by the 
 
 waves, 60 
 Shingle of Patagonia, 219 
 Siau, M., on ripples, 151 
 
 — on sea bottom, 225 
 Signal Post Hill, 11, 17, 18 
 Silica deposited by steam, 29 
 
 — large proportion of, in obsi- 
 dian, 69, 73 
 
 — specific gravity of, 1 37 
 
Index. 
 
 645 
 
 SILICEOUS 
 
 Siliceous sinter, 52 
 
 Silver mines of Arqueros, 540 
 
 of Chanuncillo, 561 
 
 -" — of Iquique, 577 
 
 — distribution of, 582 
 Slip, great, at S. Cruz, 379 
 Smith, Dr. A., on junction of gran- 
 ite and clayslate, 167 
 
 Smith, Mr., of Jordan Hill, on up- 
 raised shells retaining their 
 colours, 209 
 
 — on Madeira, 231 
 
 — on elevated seaweed, 268 
 
 — on inclined gravel beds, 515 
 Soda, nitrate of, 305 
 
 — sulphate of, near Bahia Blanca, 
 307, 310 
 
 — carbonate of, 308 
 Soundings off Patagonia, 215, 225 
 
 — in T. del Fuego, 227 
 
 Sowerby, Mr. G. B., his descrip- 
 tions of fossil shells (in Appen- 
 dix), 171 
 
 — on fossil shells from St. Jago, 6 
 
 — on land shells from St. Helena, 
 101 
 
 — from Van Diemen's Land, 155 
 Spallanzani, on decomposed tra- 
 chyte, 29 
 
 Specific gravity of recent calca- 
 reous rocks and of limestone, 
 57 
 
 — of lavas, 135 
 Sphjerulites in obsidian, 67, 76 
 
 — - in glass and in silicified wood, 
 
 71 
 Spirifera, 176 
 Spirifers, 548, 551 
 Spix and Martins on Brazil, 427 
 Sprengel on the production of 
 
 carbonate of soda, 274 
 Springs, mineral, in the Cumbre 
 
 Pass, 505 
 Stenopora (fossil), 178 
 Stokes, Mr., his collection of 
 
 Sphasrulites and of obsidians, 
 
 71,79 
 Stony-top, Little, 89, 97 
 
 — Great, 91 
 
 Stratification of sandstone in New 
 South Wales, 149, 154 
 
 SUMMAEY 
 
 stratification in metamorphic 
 rocks, 424 
 
 — of clayslate in T. del Fuego, 445 
 
 — of the Cordillera of Central 
 Chile, 472, 482, 504 
 
 — little disturbed in Cumbre Pass, 
 503, 512 
 
 — disturbance of, near Copiapo, 
 574 
 
 Streams of obsidian, 73 
 
 — of lava at S. Cruz, inclination 
 of, 384 
 
 — in the Portillo range, 497 
 String of cotton with fossil shells, 
 
 268 
 
 StrutMolaria ornata, 387 
 
 Studer, M., on metamorphic rocks, 
 464 
 
 Stutchbury, Mr., on marine re- 
 mains at Otaheite, 32 
 
 Subsided space at Ascension, 46 
 
 Subsidence during formation of 
 sea-clifEs, 228 
 
 — near Lima, 272 
 
 — probable, during Pampean for- 
 mation, 357 
 
 — necessary for the accumulation 
 of permanent deposits, 417 
 
 — during the tertiary formations 
 of Chile and Patagonia, 421 
 
 — probable during the Neocomian 
 formation of the Portillo Pass, 
 491 
 
 — probable during the formation 
 of conglomerate of Tenuyan, 501 
 
 — during the Neocomian forma- 
 tion of the Cumbre Pass, 512 
 
 — of the Uspallata range, 528, 533 
 
 — great, at Copiapo, 565 
 
 — great, during the formation of 
 the CordiUera, 588 
 
 Sulphur, volcanic exhalations of, 
 
 587 
 Sumatra, promontories of, 235 
 Summary on the recent elevatory 
 
 movements, 218, 275, 598 
 
 — on the Pampean formation, 349, 
 598 
 
 — on the tertiary formations of 
 Patagonia and Chile, 386, 406,595 
 
 — on the Chilian Cordillera, 585 
 
646 
 
 Index. 
 
 SUMMAKY 
 
 Summary on the cretaceo-oolitic 
 formation, 586 
 
 — on the subsidences of the Cor- 
 dillera, 588 
 
 — on the elevation of the Cordil- 
 lera, 590, 601 
 
 TACNA, elevation of, 265 
 Tahiti, 30 
 Talus, stratified,withintuif craters, 
 
 121 
 Tampico, elevated shells near, 275 
 Tandil, crystalline rocks of, 434 
 Tapalguen, Pampean formation 
 of, 317 
 
 — crystalline rocks of, 434 
 Taylor, Mr., on copper veins of 
 
 Cuba, 581 
 Temperature of Chile during the 
 
 tertiary period, 412 
 Tension, lines of, origin of axes of 
 
 elevation and of cleavage, 469 
 Tenuy Point, singular section of ,393 
 Tenuyan, valley of, 492, 533 
 Terceira, 28 
 Terraces of the valley of S. Cruz, 204 
 
 — of equable heights throughout 
 Patagonia, 210 
 
 — of Patagonia, formation of, 216 
 
 — of Chiloe, 235 
 
 — at Conchalee, 247 
 
 — of Coquimbo, 252 
 
 — not horizontal at Coquimbo, 255 
 
 — of Guasco, 261 
 
 — of S. Lorenzo, 266 
 
 — of gravel within the Cordillera, 
 290 
 
 Tertiary deposit at St. Jago, 7 
 
 Theories on the origin of the Pam- 
 pean formation, 350 
 
 Tierra amarilla, 553 
 
 Tierra del Fuego, form of sea- 
 bottom, 227 
 
 — tertiary formations of, 385 
 
 — clay slate formation of, 441 
 
 — cretaceous formation of, 443 
 
 — crystalline rocks of, 443 
 
 — cleavage of clayslate, 446, 461 
 Tosca rock, 315 
 
 Trachyte at Terceira, 28 
 
 TUFF 
 
 Trachyte, decomposition of, 
 steam, 28 
 
 — at Ascension, 48 
 
 — softened at Ascension, 48 
 
 — with singular veins, 51 
 
 — absent at the Galapagos Arch| 
 pelago, 129 
 
 — its separation from basalt, 13^ 
 
 — specific gravity of, 136 
 
 — of Chiloe, 390 
 
 — of Port Desire, 436 
 
 — in the Cordillera, 480 
 Traditions of promontories havinj 
 
 been islands, 235 
 
 — on changes of level near Lim? 
 272 
 
 Trap-dikes in the plutonic series| 
 139 
 
 — at King George's Sound, 161 
 Travertin at Van Diemen's Lane 
 
 157 
 
 Trees buried in plain of Iquiquc 
 304 
 
 — silicified, vertical, of the Us 
 pallata range, 527 
 
 Tres Montes, elevation of, 232 
 
 — volcanic rocks of, 389 
 Trigonocelid insolita, 387 
 Tristan Arroyo, elevated shells 0^ 
 
 191 
 Tropic - bird, now rare, at St 
 
 Helena, 103 
 Tschudi, Mr., on subsidence ne^ 
 
 Lima, 272 
 Tuff, craters of, 111, 113, 119, 121 
 
 — peculiar kind of, 112, 113 
 
 — their breached state, 1 27 
 
 — calcareous, at Coquimbo, 250 
 
 — on basin-plain near St. Jagc 
 284 
 
 — structure of, in Pampas, 315 
 
 — origin of, in Pampas, 353 
 
 — pumiceous, of R. Negro, 371 
 
 — Nuevo Gulf, 373 
 
 — Port Desire, 374 
 
 — S. Cruz, 378 
 
 — Patagonia, summary on, 386 
 
 — Chiloe, 392 
 
 — formation of, in Portillo chair 
 498 
 
 — great deposit of, at Copiapo, 57^ 
 
Inde. 
 
 'X. 
 
 647 
 
 TUFFS 
 
 ts, volcanic, metamorphic of 
 [| Uspallata, 521 
 
 of Coquimbo, 544 
 fimier, Mr., on the separation of 
 
 molten metals, 134 
 ['yerman and Bennett on marine 
 remains at Huaheine, 32 
 
 XLOA, on rain in Peru, 268 
 
 — on elevation near Lima, 273 
 Jruguay, Eio, elevation of country 
 near, 190 
 Fspallata, plain of, 286, 515 
 
 pass of, 502 
 
 range of, 516 
 
 concluding remarks on, 531 
 
 ''ALDIVIA, tertiary beds of, 397 
 - mica-slate of, 457 
 ^alley of S. Cruz, structure of, 202 
 
 Coquimbo, 252 
 
 Guasco, structure of, 261 
 
 Copiapo, structure of, 263 
 
 S. Cruz, tertiary formations of. 
 
 378 
 
 Coquimbo, geology of, 541 
 
 Guasco, secondary formations 
 
 of, 550 
 
 Copiapo, secondary formations 
 
 of, 551 
 
 Despoblado, 564, 566, 570 
 ['alleys, in St. Jago, 25 
 
 gorge-like at St. Helena, 103 
 
 in New South Wales, 151 
 
 in the Cordillera bordered by 
 
 gravel fringes, 290 
 
 formation of, 292 
 
 in the Cordillera, 483 
 [alparaiso, elevation of, 239 
 
 gneiss of, 459 
 tan Diemen's Land, 154 
 lein of quartz near Monte Video, 
 
 432 
 
 in mica-slate, 451 
 
 relations of, to cleavage, 463 
 
 in a trap dike, 443 
 
 of granite, quartzose, 454, 529 
 
 remarkable, in gneiss, near Val- 
 [paraiso, 460 
 
 WOOD 
 
 Veins in trachyte, 51 
 
 — of jasper, 52 
 
 — relations of, to concretions, 395 
 
 — metalliferous, of the Uspallata 
 range, 529 
 
 — metalliferous, discussion on, 580 
 Venezuela, gneissic rocks of, 424 
 Ventana, Sierra, Pampean forma- 
 tion near, 318 
 
 — quartz-rock of, 434 
 Venus (fossil), 172 
 Villa Vincencio Pass, 516 
 Vincent, Bory St., on bombs, 44 
 Volcan Kio, mouth of, 485 
 
 — fossils of, 490 
 Volcanic bombs, 42 
 
 — island in process of formation 
 in the Atlantic, 105 
 
 — islands, their distribution, 140 
 Volcanos of the Cordillera, 388, 
 
 480, 591 
 
 — absent, except near bodies of 
 water, 497 
 
 — ancient submarine, in Cordil- 
 lera, 576 
 
 — action of, in relation to changes 
 of level, 596 
 
 — long action of, in the Cordillera, 
 601 
 
 TTTACKE, its passage into lava, 
 VV 31, 156 
 
 Wackes, argillaceous, 5, 22 
 Wafer on elevated shells, 264 
 Waves caused by earthquakes, 
 power of, in transporting boul- 
 ders, 271, 301 
 
 — power of, in throwing up shells, 
 244 
 
 Weaver, Mr., on elevated shells, 
 
 275 
 Webster, Dr., on a basin-formed 
 
 island, 122 
 
 — on gypsum at Ascension, 60 
 White, Martin, on soundings, 150 
 
 — on sea-bottom, 225 
 
 Wind, effects of, on the form of 
 
 craters, 41 
 Wood buried at Iquique, 304 
 
 — silicified, of Entre Eios, 335 
 
648 
 
 Index, 
 
 WOOD 
 
 Wood, S. Cruz, 381 
 
 — Chiloe, 391, 394 
 
 — Uspallata range, 527 
 
 — Los Hornos, 536 
 
 — Copiapo, 563, 567 
 
 ZEAGONITE 
 
 TESO, Eio, and plain of, 485 
 Ypun Island, tertiary foi 
 tion of, 389 
 
 FTEAGONITB, 444 
 
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