BOUGHT WITH THE INCOME FROM THE SAGE ENDOWMENT FUND THE GIFT OF Henrg M. Sage 1891 ft.'&oftUn. ^IMJ/^ 3777 Cornell University Library QE 262.B6U87 1909 The geology of the country around Bodmin 3 1924 004 731 430 Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004731430 MEMOIES OF THE GEOLOGICAL STJEYEY ENGLAND AND WALES. EXPLANATION OP SHEET 347. THE GEOLOGY OF THE COUNTRY AROUND BODMIN AND St. AUSTELL BY W. A. E. USSHEE, G. BAEEOW, AND D. A. MacALISTEE, A.E.S.M, WITH NOTES ON THE PETBOLOGT OF THE IGNEOUS E0CK8 BY J. S. FLETT, M.At D.Sc. . PUBLISHED BY OEDEB OF THE LOBD COMKISSIONEBa OF HIS UAJESTX'S TBEASUBY. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, By DARLING- & SON, Ltd., 34-40, BACON STEBBT, B. And to be purchased from B. STANFORD, 12, 13, and 14, Lo»a Aobb, London ; W. & A. K. JOHNSTON, Ltd., 2, St. Andekw Squaee, EDiuBUBfjH ; HODGBS, FIGGIS, & Co., Gbafton Street, Dublin ; From any Agent for the sale of Ordnance Survey Maps ; or through any Bookseller from T. FISHBR UNWIN, 1, Adelphi Tebbacb, London, W.C, who is the sole Wholesale Agent to the Trade outside the Connly of London. 1909. Price Four Shillings. GEOLOGICAL SURVEY AND MUSEUM. (Ofhcb : 28, Jeemyn Stkeet, London, S.W.) P-UBLIOATIONS RELATING TO THE SURVEY OF CORNWALL AND DEVONSHIRE. MAPS, GENERAL MAP ON THE SCALE OF i INCH = 1 MILE (1 to 253440). Sheet 18 (with part of 17), which includes North Devonshire and large parts of SomersetBhire, Monmouthshire and Glamorganshire, and Sheet 22, which takes in part of East Cornwall, Central and South Devonshire and part of South West Dorsetshire, are published,' price 2s. 6^. each. Sheet 21 (with Sheet 25), which covers nearly all Cornwall, with the exception of a small part in the east of the Gourity, is in course of preparation. ONE-INCH MAPS, NEW SERIES, ON THE SCALE OP 1 INCH =1 MILE (1 to 63360). For prices of these tua,ps, see next page of cover. Sheet 311 (Wellington and Chard) 1906 ; Explanatory Memoir, price Is. M. (1906). Sheet 325 (Exeter) 1899 ; Explanatory Memoir, price 2s. (1902). Sheet 326 with 340 (Sidmouth and Lyme Begis) 1906 ; Explanatory Memoir, price Is. (1906). Sheet 339 (Newton Abbot) 1899 ; Explanatory Memoir in preparation. Sheet 346 (Newquay) 1906 ; Explanatory Memoir, price 3s. (1906). Sheet 347 (Bodmin and St. Austell) 1909 ; Explanatory Memoir (1909). Sheet 348 (FIvmouth and Liskeard) 1907 ; Explanatory Memoir, price 3s. (1907). Sheet 349 (Plymouth and Ivybridge) 1899 ; Explanatory Memoir in preparation. Sheet 350 (Torquay) 1898 ; Explanatory Memoir, price 2s. (1903). Sheet 351 with 358 (Land's End District) 1907 ; Explanatory Memoir, price 3«.6d(1907). Sheet 352 (Falmouth, Truro amd Camborne) 1906 ; Explanatory Memoir, price 7s. 6d. (1906). ' Sheet 353 with 354 (Mevagissey) 1907 ; ExplaJiatoiy Memoir, price 2«. (1907). Sheet 355 (KiUgsbridge) 1898 > Explanatory Memoir, pijcels. 6d. (1904). Sheet 356 f Stait Poinfl 1898 j *" •' '*'*"" "" '■ ="*-'■ Sheet 356 (Stait Point) 1898 Sheet 357 with 360 (Isles o (1906). Sheets 335, 336, 337, 338, 359, with Ex;planatory Memoirs, are in preparation, Sheet 357 with 360 (Isles of Scilly) 1906; Explanatory Memoir, price Is (1906). MEIOIES OE THE GEOLOGICAL SUEVEY ENGLAND AND WALES. EXPLANATION OF SHEET 347. THE GEOLOGY OF THE COUNTRY AROUND BODMIN AND St. AUSTELL BY W. A. E. USSHER, G. BARROW, AND D. A. MacALISTER, A.R.S.M. WITH NOTES ON THE PETROLOGY OF THE IGNEOUS ROCKS BY J. S. FLETT, M.A., D.Sc. PUBLISHED BY OEDEH OP THE LORD COMMISSIOHBKS OF HIS MAJESTY'S TBEASUnY. LONDON : PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, By darling & SON, Ltd., 34-40, BACON STREET, E. And to be purchased from B. STANFORD, 12, 13, and 14, Long Acre, London ; W. & A. K. JOHNSTON, Ltd.. 2, St. Andebw Square, Edinburgh ; HODGES, FIGGIS, & Co., Grafton Street, Dublin ; From any Agent for the sale of Ordnance Survey Maps ; or through any Bookseller from T. FISaER UNWIN, 1, Adelphi Terrace, London, W.C., who is the sole Wholesale Agent to the Trade outside the Couniy of London. 1909. Price Four Shillings. 6 '/ A«'3>6011'] PREFACE. This Memoir deals with the area included in the Bodmin Sheet of the New Series Ordnance Map on the scale of one-inch to one mile. The original geological survey of the district was made by De la Beche on the Old Series one-inch map (Sheets 30 and 31), and the results were published about the year 1839. In the early issues of these Sheets the older sediments were all grouped together and coloured as belonging to the ' Grauwacke Series ' ; for although De la Beche clearly recognised the existence of subdivisions he made no attempt to represent their distribution on his published maps. About the year 1846, when the Devonian System had been definitely established by the researches of Murchison, Sedgwick and Lonsdale, the method of colouring was changed and the term Devonian was introduced. Twenty years later, in 1866, mineral lodes were added by W. W. Smyth. The New Series Map (Sheet 347) is based on a six-inch survey which has been carried out by Messrs. Ussher, Barrow and MacAlister under the superintendence of Mr. Clement Ileid. Mr. Barrow is responsible for a belt of country extending westward from Bodmin, Mr. MacAlister for the northern part of the granite mass of St. Austell with the adjacent sediments, and Mr. Ussher for the rest of the area. Mr. MacAlister has laid down the lodes over the whole of the district. On comparing the earlier with the later versions of the one-inch map it will be seen at once that the most important result of the re-survey, from a stratigraphical point of view, has been the recognition in this area of the subdivisions of the Devonian System established by Mr. Ussher during the years 1888-1891. Amongst the minor results may be mentioned the detection of many new out- crops of igneous ♦ocks and of a peculiar and interesting group of altered calcareous sediments, often quarried for road metal, to which the term ' calc-flinta ' has been given. In this Memoir the field-officers have described their several districts while Dr. Flett has contributed petrographical notes. The part dealing with the metalliferous deposits is due to Mr. MacAlister ; it contains much information, largely compiled from old documents, as to the nature of the lodes, the distribution of ores in the lodes and the yield of individual mines. The two most important economic products, on which the principal mineral-industry of the district depends, are undoubtedly 'china- clay ' and ' china-stone.' The nature and origin of these substances are dealt with in the following pages, but fuller information with regard to the industry will appear in a forthcoming handbook to the collections in the Museum of Practical Geology. J. J. H. TEALL. Director. Geological Survey Office, 28, Jermyn Street, London, 30th September, 1909. (12979—17.) Wt. 267— 60. 500. 11/09, D & S. IV List of the Six-inch Geological Maps included in the area, of which MS. .coloured copies are deposited, for public reference, in the Library of the "-'■ Geological Survey and-Museum of Practical Geology. CORNWALL. 32. NE., by 0. Reid ; 32 SE;, by O. Reid, G.Barrbw; and= D. A. MacAlister ; 32. NW., NE., by C. Reid and G. Barrow ; 32. SW., SE., by G. BarrOw and D. A. MacAlister, ■■ .- '. -■.' ; .. , - ;? > 33. NW., SW., by C. Reid and G. Barrow ; 32. NE., SE., by G. Barrow and D. A. MadAlistei. ' .■.•■.■.,,- . ■ ' ■•. '■ -34. NW., SW., by G. B^rroy^.; 34. IJE., SE., by,W. A. E, IJ^shei;., 35. NW., SW., NE., SE., by W. A. B. Ussher., ..„. .^ „.,•■' '- .40. NE., by C. Reid and D. A. MacAlister ; 40. SE., by C. Reid and W. A. E. Ussher. ^ ■ - - '•'' ''■ '' '■-'■- - -■' ' ■- 41 . NW., SW., NE., SB., by D. A. MapAlister. , 42. NW., by .D. A. MacAlister ; 42. SW., NE., SB., by W. A. E. tJsshOT.' ' 43. NW., SW., NE., SB., by W. A.- E. Fsstei'. ■"' ' - - ' ' '■ '■■• ...;:.. 49. NE., SE., by W. A. E. Ussher and J. R. Scrivenor. , . 50. ' NW., SW., NE., SE., by W. A. E. Ussher. ,51. NW.; SW., NE., SB., by W. A: B. Usslef. ' t ■ • 52. NW., SW., NE., SE., by "V^. :A..'te. Ussher.'''^'' '' "' ' "'■ 6B. NE., by C. Reid, J. B. HUl, and J. B. ScrL-reiipr. ; 59. NW , by 0. Reid ; 59. NE., by C. Reid and W. A. E. Ussher. 60 NW., by W. A. E. Ussher. •;'■'■'' ^^ ^' •' -"■''■ *■'■ '■' ■•'"' -. I ■.'■-:■'■ .■'..-■ .- . . ■ •■ For the information, respecting mines in -the above maps, Mr. "MsLcAlister is mainly responsible. ' '' ' CONTENTS. Page. Preface by the Director iii Chapter I. — Intkoduction. General Description of the District. Table of Strata. Literature. General G-eology 1 Chapter II.— Devonian. General Structure 6 Chapter III.— Dartmouih Slates 13 Chapter IV. — Meadboot Gsonp. Grampound Grit ... ) j^ Staddon Grits i Chapter V. — Middle Devonian ... 32 Chapter VI.— The Older Igneous Rocks 35 Chapter VII. — Granite and El van 54 Chapter VIIL— The Metamorphic Aureole 80 Chapter IX.— Nature and Origin op China Clay Rock and 'Cornish Stone' in the St. Austell Granite ... ... 105 Chapter X.— Pliocene, Pleistocene and Recent 119 Chapter XL— Economics. Mining • 131 Chapter XIL— Economics. Stream Tin. Building Stone. Road- stone. Bricks and Tiles. Water Supply. Agriculture 170 Appendix.— Bibliography 182 Index 189 13979 ILLUSTRATIONS. Fig. 1. Junction of dark-grey and variegated slates in Broad Cove „ 2. Junction of Grampound grit and slate near Gamas Point, Pentuan „ 3. Contorted grit in Dartmouth Slate „ 4. Beach Stacks at Grribbin Head „ 5. Quartz-veins following bedding ... „ 6. Bedding in Penhellick Quarry „ 7. Pegmatite Vein at St. Dennis Downs „ 8. Elvan dyke in quarry north of Chytane Clay-works „ 9. Quarry in Oalc-flintaa west of Treesmill „ 10. Map to show distribution of Kaolinisod Granite „ 11. Microscopic structure of China stone ,1 12. Blencowe Consols Tin Mine ; ,, 13. Greisen Bands in Bunny Mine „ 14-16. Charlestown United Mines „ 17. Duke of Cornwall Mine „ 18. East Crinnis Mine ... „ 19. Yein at Fowey Consols „ 20. Great Beam Mine ,, 21. Lanescot Mine „ 22-26. Pembroke Mine . „ 27, 28. Polgooth Mine „ 29. Polmear Mine „ 30. Eestormel Mine „ 31-33. St. Austell Consols „ 34. South Polgooth Mine Page. 7 9 13 2^ 33 33 62 72 81 108 113 137 138 140-^2 143 143 145 U5 147 150-1 152 153 155 156 157 Plates I-III.— Photomicrographs to follow p. 188. THE GEOLOGY OF THE COUNTRY AROUND BODMIN AND ST. AUSTELL. OHAPTEflR I. INTRO'DUCTION. The following pages describe the geology of about 200 square miles in Cornwall, including the whole of St. Austell Moor, and about 16 miles of the south coast from St. Austell Bay eastward. Though Bodmin is the principal town in the district, it lies at the extreme north and is perhaps more related to the region surrounding Bodmin Moor than to the country now under con- sideration. St. Austell is more central, and is also the capital of the china-clay industry, which is the principal mineral-industry in Cornwall. Other places of importance are Orampound, St. Columb Major, Lostwithiel, and Fowey. In addition there are Charlestown and Par, ports from which the china-clay is shipped. The most striking physical feature of the district is St. Austell Moor, from which all the streams west of the Fowey radiate. This moor is a granitic upland rising to 1,026 feet at Hensbarrow, but with most of its summits 300 or 400 feet lower. The principal river is the Fowey, which drains about a third of the area ; but the head-waters of the Fal, St. Austell River, and some of those of the Camel lie also in this region. Most of the drainage is southward, toward the English Channel ; but the Camel flows westward and northward to the sea at Padstow. The valley-systems of the area, however, will be best understood by a reference to the map, they are too intricate to be described before the geological structure has be.en discussed. The boundary between the various catchment basins is sometimes very ill defined. This is especially the case in the flattish moorland tracts on which tributaries of the Fowey, Camel, and Par River take their rise. The most extensive of these flats is Goss Moor, which occupies about 2 square miles, but others at the same level (about 400 feet above the sea) are of considerable extent. The principal industries connected with the geology are the preparation of china-clay and the digging of china-stone. Besides this there is a small amount of tin and copper mining, and one mine is now worked for uranium. The tin-mining was formerly of sufficient importance for Lostwithiel to be one of the four Cornish towns empowered to ' coin ' and sell tin. Granite is quarried and occasionally sent out of the district, other building-stones are used for local purposes only. For road- metal the best stone is obtained from the hard splintery calc- 12979 A INTRODUCTION. flinta, and the greenstone-sills; but the quarries are not con- venient for shipping and road-^tone is seldom sent out of the district. The valleys in and descending from the granite have been ' streamed' for. alluvial tin; biit this industry has long ceased. It is noteworthy that nearly all the gold and the largest nuggets found in alluvial deposits in Cornwall were obtained from stream- works in the valleys draining the granite area north-west of St. Austell. The scenery of the district is diversified, and the coast-scenery from Gribhin Head eastward is often bold and imposing. The Fowey Valley and estuary are charming and the scenery east of Doublebois recalls in a measure the wooded valleys of the Ardennes. The appearance of the St. Austell granite-heights has been modified by the great clay-pits opened in them and the huge banks of insoluble waste piled on their slopes and summits. The best natural scenery is met with in the district between L'anlivery, Luxulian, and St. Blazey. The formations represented on Sheet 347 are the following: — Sedimentary. ( Blown Sand. \ Alluvium. r Valley Gravel and Stream- tin Gravel, •< Head, River Terrace Gravel. ( Raised Beach. Grey Slates with silty bands in lower part. Soft sandy rock and silty shales, hard grits, ■■■ \ and slates. 'Grey slates with occasional grit beds, on calcareous slates — with fossiliferous grits (Looe type) in the eastern part of the map. Dark slates with grit intercala- tions are developed at the base of the series near Fowey and Lansallos. 'Purple and greenish and buff- weathered slate, with intercalated grits and gritty shales. Igneous. ... Schalsteins (north of Bury Down). f Probably thin bands in the Meadfoot ...< Group, seen in the cliff at Pol- ( kerris, &c. f Serpentine of Duporth 7 <-, , ] Diabase sills | Greenstones. "■ { Qnartz-felsite siljs. ( Elvans or quartz-porphyry dykes. ■"\ Granite. ■"1 M o s o 1-3 Recent Pleistocene Middle Devonian Staddon Grit Meadfoot Group, includ-- ing Grampound Grits. Dartmouth Slates 2 "3 a o Hi a; ' m M Eh 'Middle Devonian Lower Devonian , Pee-foldinc} pobt-folding Up to the Fowey Valley the Lower Devonian subdivisions have been continuously traced by the writer during the course of the Survey from the Kingswear and Brixham coast, and in that distance of 50 miles, in spite of local modifications, there is no uncertainty as to their general distinctive characters, although these characteristics often change so gradually that precise boun- daries between the subdivisions cannot be drawn. To the west of the Fpwey Valley, however, although the Staddon Grif out- crop persists along the north margin of the map, the Dartmouth INTRODTTCTION. 3 Slates, disappear before reaching the eastern boundary of the St. Austell granite and the calcareous fossiliferous grits of Fowey and Pencarrow Head have also disappeared. Fossils are confined to silty and calcareous intercalations in the slates of the coast section, apparently the same series repeated at intervals from Par to Pentuan. At Pentuaii the slates are succeeded by sand- stones, the Orampound Grits, which enter this map at Nans- ladron in the Pentuan Valley and extend westward through Grampound and Grampound Road to Ladock in the adjacent map on the west. No signs of fossils or of calcareous beds have been detected in the slates south of the St. Austell Granite except on the coast. Literature. Though (Sedgwick, Murchison, and Lonsdale had previously founded the Devonian system, the first attempt to explain the general structure of this particular district is that contained in De la Beche's ' Eeport on the Geology of Cornwall, Devon, &c.' De la Beche's views will be found in pp. 80 to 83, and on p. 86 of his ' Report.' In these pages his insistence on directions of dip appears throughout, and it will be clearly seen that he gives a continuous upward succession from the Looe beds of Fowey and Pencarrow Head to the arenaceous rocks of Bury Down, Bocconoc, Broadoak, &c., although this is more than qualified in a subsequent passage, p. 91. In constructing a geological map of Cornwall in 1890 from the information supplied by De la Beche's Report, this succes- sion was adopted by the writer, and, in consequence, the Dart- mouth Slates were wrongly placed above the Looe beds ; although it should be noted that in an alternative version shown on that map, the Dartmouth Slates of Watergate Bay (in Sheet 346) are shown as an anticline,* a suggestion which has since proved correct. This error of misplacing the Dartmouth Slates was not finally cleared up till 1902, when a direct comparison of all the coast sections between Brixham and Looe was undertaken. t De la Beche specially mentions the important fault at Coombe Hawne near Fowey, shown on the present map. The area is comprised in Mr. J. H. Collins's sketch ™ap of 1878,:j: in which, under the name ' Ladock beds,' he includes the Grampound Grits and the rocks of The Van, Par, and Newquay as probably Upper Silurian, and introduces Lower Silurian rocks on the south margin of the St. Austell granite. In a later paper, § Mr. Collins regarded the Ladock beds as Devonian. In 1843, the Rev. D. Williams traced the 'fish-bearing Killas' from the JBrixham Coast westward to this area.ll Detailed work * Trans. Boy. Geol. Soo. Corn. vol. xx, 1891, p. 273. t See ' Summary of Progress ' for 1902 (Mem. Oeol. Sw/rv."). t Trans. Boy. Oeol, Sac. Corn. vol. x, 1879, p. 3. § Jowrn. Boy. Inst. Corn, part i. vol. vii, 1881, p 18. II Trans. Boy. Oeol. Soc. Corn. vol. vi, 1846, p. 122, X2979 A 3 INTHODTJCTION. has establisliecl the identity of this group of his with the pari> mouth Slates, and has shown the marvellous atjcuiacy ol his description of its termination near Lostwithiel. • it.- None of the fossiliferous localities of the coastline m this map escaped the notice of C. W. Peach.* Especially note- worthy are his discoveries of fish remains in Lantivet Bay and other spots in rocks locally yielding Belterophon and Loxonema. il. Q. Couch also described the occurrence of fish remains on the Polperro and Fowey coast.t ... The discoveries of Peaich led MurchisonJ to alter his opinion respecting the age of the rocks, which on a considerable part of the coast in the neighbourhood of Looe seem to have been re- garded as Upper Silurian, and so coloured on a map which does not appear to have been published. This map is referred to by Sedgwick in his historic paper on the Slate Rocks of Devon ^nd Cornwall, § in which he expresses the opinion that the rocks on this coast were wrongly coloured as Silurian. He alludes to the reported discovery of 'Cfmptolites at the Black Head by Peach, and to their determination by McCoy as a new species of Cladochomts. He- also announces McCoy's determination- of the fish remains of the Lantivet Bay, &c.-, coast as sponges, and remarks " Bellerophon hisulcatus abounds in this part of the series.. It is a trueDevonian shell." Sedgwick here divides the Devonian rocks into three groups ; these do not correspond to the Upper, Middle, and Lower Devonian, and his Middle Division, the Dartmouth group, is by no means synonymous with the Dartmouth Slates of the writer's classification. Many fossils from the district have been figured and described by Mr. J. H. Collins. |j The basic igneous rocks of the district have been described in a classic paper by John Arthur Phillips. H „ There are numerous papers relating to the superficial deposits of the district, contributed by Carne, Rashleigh, and others, but it was not until .1879 that a general classification of -these appeared in a- series of papers by the writer, in which he dis- cussed, the relative age of the Submerged Forests, Stream-tin gravels, and Raised Beaches.** As' regards the economics, a pamphlet by Mr. J. H. Collins on oThp Hensbarrow Granite District,' -Truro, 1878; a 'Treatise Technical and Practical on the Naturci Production and uses of China-Clay,' by David Cock, published in 1880 ; and references to the mineral lodes of the district in W. J. Henwood's ' Metal- liferous Deposits of Devon and Cornwall/ft must be mentioned. * Tram. Roy. Oeol. Soc. Corn. vol. vi, p. 12, &:o., vol. vii. p. 57, vol. ix. pp 31 49 and vol. X, p. 90 (1846-1880). ^ fi- , , f. Ibid. vol. vi, 1846, p. 147. t Ibid. p. 317. § Quart. Jourtt. Qeol. Soc. vol. viii, 1852, p. 1. II J^am. Boy. Geol. Soo. Com. vols. xi. and xii, 1887-1904. See especiallv vol, xi, p. 553. " If Quart. Journ. Oeol. Soe. vol. xxxiv, 1878, p. 471. ** Geol. Mag. 1879, Jan. to July, and ' Post Tertiary Geology of Cornwall ' (privately printed). 1879. *' '™" t-f- lyam. Boy. Geol. Soo. Corn. vol. v, 1843, INTEODTJCTION. General Geology. The detailed mapping of the area brings out the anticlinal structure of the oldest rocks, the Dartmouth Slates. This dominant structure was produced during the later stages of the Armorican movement by the further compression of rocks already cleaved and stiffened by puckering and minor foldings. The intrusion of the granite either accompanied or succeeded this final movement. Its effect has been to deform the anticlinal structure, which, again, becomes manifest in the Newquay map on the west; to deflect the strike of the rocks toward Bodmin, as shown by the outcrop of the Staddon grits; and to produce the structural faulting which accompanies the disappearance of the Dartmouth Slates on the east of the granite. By selective metamorphism, the calcareous rocks in the lower part of the Meadfoot Group have been converted into calc-flintas, which exhibit a considerable development and much repetition by folding on the north of the granite. The proximity of their outcrop to that of the Staddon grits in this part of the map, strongly suggests the presence of a strike fault, or faults, cutting out a considerable part of the Meadfoot Group, although no evidence of this was obtained on the ground. CHAPTER II. DEVONIAN. General STmrcTUEE. The Dartmouth Slates are the oldest rocks recognised in the map. They have been traced from the coast line south of Brixham, westward to the Fowey, almost persistently.* Between Portnadler Bay in Sheet 348, where the Dartmouth Slates are faulted against dark slates belonging to the lower part of the Meadfoot Group, and the faults (extending from Coombe Hawne on the coast in a northerly direction by Penhale and Castle Dora), which accompany their disappearance on the west, the dips of schistosity and consequently the axes of the folds incline northward. On the west of the Castle Dore fault a change of strike takes place, and in the rocks on the east margin of the St. Austell Granite it is practically north and south. From Polmear by Par Sands an E.N.B. fault may be traced which unites with the Castle Dore dislocation near Trenython and brings up on its north side Dartmouth Slates. These are so badly evidenced on the north between Lampetho and Tywardreth that their relations to the overlying beds are unknown. It is possible that this patch may be terminated on the west by a fault running parallel to the Castle Dore dislocation, but no evidence of the existence of such a fault was obtained. Dartmouth Slates are shown on the map near Treverran on the west side of the Castle Dore fault, so that their termination in the Fowey River Valley at three-quarters of a mile south of Lostwithiel may be regarded as an anticline complicated by a strike fault. Their northerly termination is .exceedingly in- definite and unsatisfactory, as the distinctive variegation which characterises the group as a whole gives place to pale-grey, lavender-grey, buff, and other non-distinctive hues, and the slates and grit-shales are such as might be found in them or in the overlying beds of the Meadfoot Group. The basement beds of the Meadfoot Group are fundamentally a dark grey slate series in which grits, grit-shales and arenaceous bands occur in irregular proportion. These beds become cal- careous and fossiliferous when traced upward, presenting in grits and calcareous beds the Looe fossil types. Making every allowance for irregularity in breadth of outcrop produced by folding, the practically unfossiliferous rocks between these cal- careous horizons and the Dartmouth Slates would appear to be of irregular development. This type of lower beds in the Mead- foot Group may develop — upwards through the restriction of the fossiliferous horizons locally to higher positions in the series or to their partial absence — downwards through the local restric- tion of the colours characteristic of the Dartmouth Slates to locally lower limits. * They are partially absent or hardly represented near East AUington see Man in Proc. Oeol. Assoc, vol. xvii., 1901, p. 121, and where their outcrop lies south of the coastline on the Tregantle and Looe Bay coasts. GENEEAL STEUCTUEE. An instance of the nonoonf ormity of colour distinctions in the iJartmoTith Slates to stratigraphical horizons was figured in the Plymouth Memoir, p. 23. In PenpoU Creek the Dartmouth Slates are often dull grey and weather a drab grey-green, purple tints come on without definite stratigraphical significance. The appearance presented by the junction of the Dartmouth Slates with the lower beds of the Meadfoot Group, near East Coombe, east of Lanivet Bay, is figured here (Fig. 1) as seen Pig. 1. Junction of dark-grey and variegated slates in Broad Cove. looking eastward toward the Day Mark. The dark slates form the coast line from here toward Polperro, and contain beds, lenticles, and films of quartzite, grit, and arenaceous materials. Similar rocks occur on the north side of the Dartmouth Slate anticline around Kite's Nest and Penkelly. The arenaceous banding sometimes present in these slates is traversed by cleavage planes, exactly similar to interlaminated material found at the coming on of the Grampound type west of Pentuan. Dark slates with similar grit intercalations separate the fossiliferous rocks of Pencarrow Head from the Dartmouth Slates which come on north of the Watch House on the west coast of Lanivet Bay, where, as Peach noticed, the rocks are much contorted. The Dartmouth slates are often more or less siliceous, and contain beds and masses of hard grit or quartzite, as in Penpoll Creek. Thick beds of quartzite occur in them south-east of Bodinnick, where they seem to be due to the welding, together of siliceous slate with bands and beds of quartzite, as in the Kings- wear promontory. , In Pont Pill Creek and Fowey the Dartmouth Slate boundary is faulted, the dark slates in the lower part of the Meadfoot Group, as in other parts of the inland and creek sections, being weathered buff or pale-grey, and mottled in places with straw- coloured tints, with ratlier soapy feel and pulverulent weathering. This type is met with on the east of Par Sands and near Tywardreath; near Couchsmill, south of Boconnoc; here and there in the cliffs between Par and. the Black Head. Dark 8 DEVONIAN. slates with hard grit beds wliicli have been taken as a syncline of basement beds of the Meadfoot Group cross the river near Mixtow Pill, and a mass of green sheared diabase is visible in them on the west bank. Between Fowey and Penhale, near the Castle Dore fault, the relations of the Dartmouth Slates are not clear, and it is probable that the basement beds of the Mead- foot Group are partly cut out by the westerly prolongation of the Pont Pill Creek fault. There is a faulted patch of Dart- mouth Slates near Lanreath, to which reference will be made further on. On the north and east side of the Dartmouth Slate anticline fossiliferous horizons often marked by decomposed materials after calcareous bands may be traced more or less continuously, but when we approach Lostwithiel, to the north of Treweather, they are absent or not conspicuous. The prolongation, however, of the presumable horizon northward through Polscoe presents us, just on the borders of the granite contact zone, with imper- sistent hard bands approaching calc-flintas in Trap Wood oppo- site Restormel, at Eestormel, and near Brownqueen. These are the commencement of the hornstones mentioned in 1904* as occurring at Lostwithiel, south of Lanhydrock; at Rosevanion, east of St. Columb Major; and at FraddOn. Since then they have been traced almost continuously from Landydrock west- ward by Messrs. Barrow and MacAlister. The Fraddon bands having been traced by the latter at Ruthvoes and south of Roche. At and east of Lanivet they are associated with green- stone sills. These bands, repeated by plication, form conspicuous features, as pointed out by Mr. Barrow, on the north of the St. Austell Granite, toward St. Columb Major, and are apparently repre- sented in the Newquay Map by the calcareous rocks of Beacon Cove and Mawgan on the north side of the Dartmouth Slate anti- cline of Watergate Bay; the Ruthvoes band and that south of Roche, with which the Fraddon Rock is connected, being, per- haps, represented by the calcareous rocks of Newquay and St. Columb Porth on the south of the anticline, f Retracing our steps to Restormel, we find a develop- ment of calc-flintas between Sweetshouse and Lost- withiel. From Lostwithiel southward to Par no con- tinuous horizon even approaching to calc-flintas can be traced, but there are hard bands of this nature between Castle and Pelyn ; in the tips from Polharmon Copper Mine and from an old shaft on the west side of the railway, between Pelean and Trenadling; by the road from Lostwithiel to St. Blazey, between Penpillick and Porcupine. Th« only place where they are distinctly recognisable is in a small section in the corner of a field west of Treesmill, where over 20 feet of banded calc-flintas was exposed. Between this and Par Sands occasional fragments of calc-flintas have been found on the sur- face, south of the section mentioned, and west of Tywardreath near the alluvium. * 'Summary of Progress' for 1903 (Mem. Geol. Surv.), p. 21. + Ibid., 1905, p. 26 ; and 1906, p. 34. GENERAL STRtJCTTTEE. 9 Within, or on the outskirts of, the aureole on the south of the St. Austell Granite not a sign of this type of alteration has been met with, although the rocks altered are similar to the slates and variously interlaminated shale and silt- stones which accompany this type. Calcareo-siliceous beds and seams are, however, associated with the slates of Polkerris on thj east of St. Austell Bay, and the same horizons appear in the beach reefs and lower part of the cliffs here and there from Par Harbour to the Black Head. Between the Van and a point in the clifi due east of Pentewan Church (on the north side of Gamas Point), where the sandstones of the Grampound type emerge, appar- ently from underneath the slate and interlaminated beds, the latter are generally represented by slates or shales with quartz eyes, seams, and films. A series in which quartz seems to have largely replaced the more siliceous interlaminations, and where these had been sheared out or dismembered, had taken the place of the dismembered portions. These quartz-eyed slates are more or less prevalent between the outcrop of the Ladock and Gram- pound arenaceous rocks on the south and the limits of contact- alteration on the north, up to the west margin of the map. These slates give place to hard and more even slates with fine sandy grit beds (in places resembling Portscatho types), in which we encounter, in a somewhat irregular and impersistent manner, the grey and buff-weathered greywackes, or gritty masses, which characterise the Grampound type. Owing to the local development of this type in the upper part of the even slates, at Pentewan and between Grampound Road and Ladock the boundary can be fixed with precision at these places, but in the intervening district it is often extremely indefinite. In the Commerce Mine, now, worked, rather fine-grained rock of the Grampound and Ladock type occurs in the slates, but to so small an extent that, were it not for stones in the mine tip or burrow, and the evidence furnished by the shafts, it could not be detected by surface indications. Near Gamas Point (Pentewan) the quartz-eyed slates overlie about p^^_ ^.-i^ea. Gamas Point, Pentuan. 60 feet of shales, with hard siliceo-caleareous beds interca- lated, which rest on a mass of hard grit, the top of the Gram- pound horizon, the whole being cut off on the south against similar hard massive grits with' quartz veins by a fault with 1,. northerly hade of ^^° 3^^^^iou oi (iv^mvoxyn^ QrA 2.nA A^\^. (Fig. 2). A specimen of the hard beds above the grit was sent to Dr. Pollard for examination, together with specimens from Polrud- den Cove; Polgwyn Beach and the Cove between Black Head and Drennick; and a specimen from Polkerris, on the east side of St. Austell Bay, as these, as well as the calcareous inter- laminations between the Black Head and Par, appeared to occupy the same general stratigraphical position. 10 DEVONIAN. There were three speeimens from the Cove between Black Head and Drennick; one each from the other localities. He describes them as follows : " All are impure carbonates of iron, lime, and magnesia, with some phosphate and organic matter. In No. 2 (the specimen from Polgwyn Beach, south of the Van) the portion soluble in hot dilute acid consists mainly of, iron and some magnesia with a little phosphate anfl very little lime." Mr. J. B. Hill recognised the fine-grained conglomerate of Grampound and Probus in 1902 as the equivalent of the coarser conglomerate of his Manaocan Beds on the south of the Helford River, and Dr. Flett's microscopical determinations confirmed this inference. Mr. Hill notes the variation of the coarser beds according to the strata from which they were derived, and the presence in the associated or overlying beds of more calcareous material than is met with in the Portscatho, Falmouth, and Mylor Rocks.* Speaking generally, the Grampound Grit Series consists of a variable association of quartz and argillaceous materials, pro- ducing a rock varying from a fine conglomerate or coarse grit with occasional small pebbles and pieces of dark slate to a fine grained sandstone or a softish rock with more or less scattered quartz grains. XJnweathered it is of a grey or greenish-grey colour, in which the slate fragments are conspicuously dark. In the weathered State, in which these rocks are more .often found, they are stained pale brown, bufE, or greenish-brown, and the dark slate fragments have been bleached. Besides these, the grits seem to contain felspar in variable proportion. They are sometimes associated with dense grey and greenish-grey mudstone, as in quarries south and south-west of Nantellan. The types do not resemble the Staddon Grits. The strati- graphical evidence is entirely in favour of their representing the marginal conditions of lower beds in the Meadfoot Group, apparently below the strata on their northern boundary. Whether this representation extends to the upper horizons of the .Dartmouth Slate or not it is impossible for me to say. Mr. Reid, who mapped the Staddon and Grampound 'Grits in the Newquay and Mevagissey areas, considers on the other hand, " that they probably represent the same deposit repeated on the two sides of an anticline. On the south the Dartmouth Slate has been completely overlapped by sandy and conglomeratic beds (the Grampound 'Grit) which abut against a shore-line of Lower Palteozoic rocks. He thinks that this grit represents the higher, sandy, portion of the Lower Devonian rocks, which in the southern area have overlapped the Meadfoot Beds also. In the absence, of fossils this question must remain for the present un- settled." Sandy, practically unfosssiliferous, beds occur west of Looe; which seem locally to represent the fossiliferous beds. These fossiliferous beds have not been detected west of the Fowey Valley, unless, as there is every reason to ' think, they are re- placed by the Newquay type. The very unequal representation of the calc-flintas on the north side, as compared with the east * Cfeol. Mag., 1906, p. 212. GENEEAL STKUCTUEE. 11 side of the St. Austell Granite and their absence on the south of it may therefore be due to original or secondary differences in the materials of the same horizons rendering them locally, or altogether, proof against this type of contact metamorphism, as well as to their occurrence outside the limits of the contact zone in the south part of the Map. In the Plymouth Memoir (p. 20) the Portnadler Bay fault is specially referred to as being instrumental in shifting the Staddon Grit outcrop in the east part of this map northward from latitude 50° 24' 40" to latitude 50° 28', near Bodmin. This fault enters the east margin of the map at latitude 50° 21' 23*. If it follows the W.N.W. direction pursued from Portnadler Bay to the map junction, it would run from Cartole on the north of Lerryn to Lostwithiel, but in this direction no direct proof of its occurrence has been obtained. There is, however, proof of a con- siderable fault on the north, which throws the Staddon Grits of Buckabarrow Downs against the Middle Devonian north of Pelyne, and shifts their outcrop southward to Bury Down. It- is therefore practically certain that the Portnadler fault either splits on entering Sheet 347 or deflects north by Tregarrick to a point east of Tremain, where it shifts a strike fault, which in Sheet 348 bounds the mass of Dartmouth Slates north of Con- gorlan on the north. From the point where it meets this strike fault the Portnadler main fault runs N".N.W. to Pelyne, shifting the strike fault nearly a mile and a quarter northward. At its shifted continuation the strike fault bounds a patch of Dartnaouth Slates on the north, but beyond this its direction toward Lerryn is unknown. Near Trevecca, south-east of St. Veep, the Dartmouth Slate boundary runs across the strike of schistosity, and this seems to be due to a W.N.W. fault which cannot be traced in the Meadfoot Group. Again, it is possible that a fault may run westward from Tregarrick on the east border of the map toward St. Veep, as there seems to be an obscure indication of Dartmouth Slates at about a quarter of a mile west of the Camp. If we draw a line from Trevalfry (west of Lanreath) to Colwood, and thence by Beacon Hill to Eestormel or Brownqueen, tihis line divides fossiliferous beds of the Meadfoot Group (including Taunusian or representatives of the Looe Beds) from unfossiliferous, and apparently higher, horizons in the group on the east. North and east of Boconnoc the Staddon Grits and Meadfoot Group are in natural junction relation, but from Fairy Cross to Halgavor Moor the junction is very indefinite. As pointed out in the introductory notes, if the folded repetitions of the ealc-flintas represent the lower cal- careous horizons of the Meadfoot Group, Newquay type, of which there can be no reasonable doubt, a strike fault of some magni- tude is necessary to cut out the greater part of the Meadfoot Group, and thus account for the proximity of the calc-flintas to the outcrop of the Staddon Grits. It seems, therefore, highly probable that the Castle Dore fault may continue northward along the Fowey Valley, and uniting with a fault or faults traversing the district between Boconnoc 12 , DEVONIAN. atid Lerryn in a north-westerly direction, may deflect westward on or near the Staddon Grit boundary, cutting out a large part of the Meadfoot Group. From its shifted continuation from Bury Down to the north of Buckabarrow Down, the north boundary of the Staddon Grits runs north-west for four miles, but the difficulty in distinguishing the boundary between slates with siliceous interlaminations belonging to this series and the base- ment beds of the Middle Devonian makes this line very indefi- nite, especially on the north and. east of Trewindle, and between Hollycoombe and Glynn. It is probable that the north-westerly "trend of the boundary from Buckabarrow Downs to Bodmin is rather due to deflected strike than to faulting. The evidences of faulting in the Bodmin area are thus described by Mr. Barrow : — The tracing of faults in the intensely folded killas is very difficult, as unless they have a great throw it is difficult to feel sure that a broadening of the outcrop may not be due to pitch or an inclination of the axis of folding, rather than to the effects of a normal fauh. This difficulty is well shown by the ■ ontorops about Lanivet ; it is impossible to prove there is not a fault north and south there, though there must be a sudden westerly pitch of the folding, and the latter alone would explain all the phenomena seen. On the other hand, there is an undoubted north and south fault, as shown on the map, to the south of Bodmin, for the mode of ending off of the outcrops cannot in this case be explained by " pitch " alone. The fault, possibly, has a considerable throw, and there seems good reason to believe that it passes along the east side of the Bodmin Monument Hill, but its exact course could not be traced clearly, as the ground is built over where it crosses the boundary of the Staddon Grits. The latter line cannot be shifted far, however, and the fault is clearly dying out in this direction. The north and south iron-bearing lodes appear to be mostly faults, and in several cases they can be clearly seen to shift the outcrops of the belts of the calc-flintas to some extent ; their effects are best seen on the great ridge about Withiel and St. Wenn, where they are always accompanied by the formation of a quartz reef. The north-east corner of the map is presumably composed of Middle Devonian Slates, as we have no proof whatever of higher beds being troughed in. 13 Fig. 3. CHAPTIER HI. DARTMOUTH SLATES. Erom the Day (or Land) Mark near Lizzen, where their junction with thfe dark slates and grits included in the Meadfoot Group has been already referred to, the Dartmouth Slates form the clifE6 for a distance of more than a mile and a half, to a point south- east of Triggabrowne, midway between Lantivet Beach and the Watch House, where they give place to dark slates "with grit beds in a manner that leaves the precise' division between the groups very indefinite. All along this coast the dips of schistosity are to the north, and also, with few exceptions, the limbs of the folds. The folds are often very clearly shown by intercalated grit beds. The grit beds vary in thickness, some, as in the cliffs south of Lansallos, attaining to 4 feet, others being thin, even, and shaly. The slates are usually mottled greenish or pale-grey and purple, or vice versa, but dark, almost black, slates occur locally in them as in Parsons Cove on the east of West Coombe. Faults and thrusts are of frequent occurrence, but none of these proved of sufiS- cient magnitude to be re- cognisable inland. In a stack on the east side of Par- son's Cove, and above Lanti- vet Beach, good instances of grit beds crossing the cleav- age of the slates may be seen. The instance selected for illustration (Fig 3) is on th^ west side of West Coombe. There is an Contorted grit in Dartmouth slate, admirable detailed description of this part of the coast by C. W. Peach.* He seems to have considered the thin-bedded grits as indications of the ' Tilestones.' On the west of West Coombe Peach noticed veins of limestone containing fish remains; he describes the structure known as the honeycomb layers of Pteraspis. The calcareous veins are said to become trappean, though containing fish remains. OnchuS and scales were found in dark-brown arenaceous-looking rocks. " Underlying these calcareous and trappean veins about 30 feet of slates occur in which are abundance of (probably) Bdlerophon and a few Loxonema. The original matter is generally completely destroyed, and its place filled with a brown powder, which, I think, might be used. as a pigment." In Palace Cove, a little further on, he noticed calcareous nodules, as well as the brown earthy residual matter in " the Bellerophon beds." He figured the fish remains obtained from Lantivet Bay.t He noticed the change in type of organic remains on the coast passing the Watch House toward Pencarrow Head, and anticlinal structures in the rocks. * Trans. Boy. (feol. 8oc. Com., vol. vii. (1847), p. 19. t Jbid. Plate 1, figs, 1 and 2, Plate 2, and Plate 3, figs. 1 and 2, 14 DEVONIAN. The calcareous and earthy material, probably denoting the presence of Bellerophon referred to by Peach, has been noticed m Parsons Cove, where it is associated with pinkish or salmon- coloTired limestone JjcUets. In the adjacent map (348)* and m all the Dartmouth Slate coast-sections similar materials are pre- sent. The dark-brown arenaceous material, apparently regarded as trappean by Peaph, is the Fish Grit, a type described at Portwrinkle. Some of Peach's fossils from Lantivet Bay were submitted in 1899 to Dr. A. Smith Woodward, who identified them as Pterasfis comubica.f Pteraspis corrtubica (M'Coy) was also found in comparative abundance by the Survey in Parson's Cove, and also in fragments on the surface near Tregue, east of Lansallos. In the Jermyn Street Museum there are two specimens from the Pengelly Col- lection (Nos. 5724, 5,735) of finely-laminated pale-grey or greenish-grey slate with Pteraspis, labelled iSt. Veep. In a quarry behind Coombe, the farm on the map in the Coombe Hawne valley, east of Ready Money, blue-grey calcareous slates or shales, with much brown friable material, dip N.N.E., at 60°. In the residues films were encountered showing the sculpture of Pteraspis, possibly P cornubica. The range of Pteraspis into the Taunusian or lower part of the Meadfoot group has been already proved in Devon,! and by Drevermann in the Rhine district.! Mr. J. H. Collins in his ' Working List of Cornish Palaeozoic Fossils ' ascribes some of the specimens of Eukeraspis pustuliferus figured by Ray Lankester, Plate XIII., Figs. 9-14 to Polruan, but the memoir says expressly that all belong to the Downton Sandstone.il To the north of the coast-section the Dartmouth Slates are easily identifiable by surface-fragments, lane-cuttings, and quarries, but to the north of Treweere and Tremeer, around Trigamelling and Trenewan, grey, buff, drab, and greenish tints prevail, almost to the entire extinction of the red, and this renders their boundary rather uncertain. Decomposed brown patches and pellets have been noticed in the purple and green slates east of 'Tregue ; in a quarry north- east of Tregavithick and south of Trenewan, where there appears to be a buff band in the slate ; and north of Lanteglos, between Watergate and Pont. East of Kite's Nest and around Penkelly the dark slates are variously blended with arenaceous materials of buff or dull-green tins occurring in tough dense beds with white mica flakes. Beds of fine grit or.quartzite are also present. The arenaceous bands are sometimes distorted and broken into lozenges by the cleavage. In the valley east of Kite's Nest, for about 10 chains from north * ' Geology of Plymouth and Liskeard ' (Mem. Oeol. Surv.'), 1907, p. 24. + Trans. Roy. Geol. Sob. Corn., vol xii., 1899, p. 229. j ' Summary of Progress,' for 1902 QMem. Geol. Surv."), pp. 161, 164, 165. § Zeifsehr. d. B. Oeol. Gesell., Band. lvi„ 1904, p. 275. II ' The Fishes of the Old Red Sandstone of Britain,' by James Powrie & E, Ray Lankeater,^ Pal. Soa,^ vol. xxiii,, 1870, p. 59, ' DAHTMOtlTH SLATES. 16 to south, the dips of schistosity are to the south ; this is excep- tional. Some hard grit beds show an anticline with N., dip of 715° and S., dip of 80° by the tributary valley about three-eighths of a mile south-east of Cartole. Although we include this dark, apparently unfossiliferous, slate and grit series in the Meadfoot group, the probability that it may in part pass horizontally into the variegated Dartmouth Slates cannot be too strongly enforced, as it is to phenomena of this sort that I attribute the difficulty in correlating the strata on the opposite sides of anticlines of variegated slates, and ascribe the variation constantly met with in the beds in unfaulted contact with the Dartmouth Slates. In other words, the colour distinc- tions have a general, not a particular stratigraphical value. When the above is considered in connection with the varying manner and proportion in which the grits and silty beds occur in the slates, and the different aspect locally produced by weathering, it will be apparent that the boundaries of the Dart- mouth Slates may be uncertain even where sections are procurable. This lincertainty attaches to the northern termination of the anticline and to the boundary taken at Milltown, east of Tre- verran and east of Trenadling. About Milltown pale-grey tints predominate, and the rocks are partly evenly interlaminated beds and grit-shales. The quarry on the north side of the Milltown Valley at its junction with the Fowey Yalley is in rather siliceous pale-grey slates with silty inter-banding. The grey tint gives place to greenish and purplish hues in the lower part. The planes of schistosity dip S.E., at about 33°. The Castle Dore fault cannot be traced for more than a quarter of a mile to the north of iCastle Dore. East of Trenadling there are signs of Dartmouth Slates on the slope between the 200 and 300 feet con- tours. The rocks in the cutting at the Tunnel mouth near Treverran might possibly be a grey phase of the Dartmouth Slates. At Restormel and south of Lostwithiel there are pale-buff, grey, and greenish very finely-laminated shales, or fine silty beds. These are seen in the railway cutting south of Lostwithiel, where they are altered, as also in the quarries south, west, and north- west of Lostwithiel, in the road near Castle, north-east of Mill- town, near Striokstenton, and outside the contact zone between Castle and Treverran. Apart from colour, these types are in- distinguishable from beds in the Dartmouth Slates. Dartmouth Slates are shown on the south of the railway near Polmear, just north of their fault boundary which joins the Castle Dore fault near Trenython. They were also exposed by the path- road to Lampetho. Fragments of purple and green slate were noticed on the surface at about three-eighths of a mile W.S.W. -of Tywardreath Church. Near the east end of this faulted inlier of Dartmouth Slates there is a quarry in grey and greenish-buff grit-shale with coherent laminae, which has .been included in the lower beds of the iMeadfoot Group. Beyond this there is very little evidence on the north till we come to Kilgogue, where there is a quarry in grey argillaceous slates and shales, weathering reddish-grey and 16 DEVONIAN buff. The planes, are coherent, have a southerly dip, and are broken by more or less horizontal joints in places, yielding a local building stone. There is not sufficient evidence to tell the nature of the western termination of this patch of Dartmouth Slates ; it may be a fault running north from 'Polmear. 'Between Treverran and Tywardreath the slates are often stained reddish, and contain occasional grit or sandy bands. At Penhale, between Polmear and Fowey, purple and green slates were seen in situ. They are probably cut off on the west by the Coombe Hawne fault. On the north dark and dull-grey slates, resembling in places the junction beds on the Newquay coast, are imperfectly exposed. Brown arenaceous rocks seem to be associated with, or be in junction with, the Dartmouth Slates between Newtown and Lawhire. The faulted Dartmouth Slates near Lanreath are exposed in a quarry a quarter of a mile north of the 'Eectory, apparently near their western termination. They consist of purple, green, and grey slates intersected by strike faults, which probably denote sheared-out contortions. At a quarter of a mile north- west of Lanreath Church fragments of purple and green slates were seen, but they may have been brought from the above- mentioned quarry. As the Dartmouth Slates may be faulted on the south as well as on the north, their relation to the Meadfoot Group, which is evidenced by surface stones more than by exposures, is some- what doubtful, but they appear to be overlaid by, and to terminate westward in, dark-grey slates. Instances of the occurrence of igneous rocks in the Dartmouth Slates, in most cases too small to be shown on the map, will be found in a sub- sequent chapter. 17 CHAPTER IV. MEADFOOT GROITP. The almost abrupt change in character from the fossiliferous types of Polruan and Fowey to the grey slates with calcareous and silty bands and interlaminations which prevail from Gribbin Head to Par and thence to the Black Head and Pentewan suggests a very considerable downthrow on the west in the Coombe Hawne fault. But if this is the case we should expect to find some- where on the west of this dislocation, or of its northern prolonga- tion in the Castle Dore fault, similar fossiliferous types among the lower beds of the group. The relations of the rocks seem to be analogous to those of the Kingsbridge district,* where the Ringmore Beds, which correspond to those of Fowey and Polruan, seem to be locally replaced by the Torcross and Tinsey Head types, which are those of the coast between the Coombe Hawne fault and the Pentuan grits (Gram- pound Grit). Pteraspis has been recognised in brown fossiliferous materials in decomposed calcareous shales dipping N.N.E. at about- 60° in a quarry behind Coombe. On the coast these beds consist of dark- grey calcareous shales and interlaminated beds, probably repre- senting the Monticuliporoid Limestone horizons, and belonging to the calcareous slate group of Polruan and Pencarrow Head. Between these beds and the fault there is a wedge of grey slates, containing igneous rock on either side of Coombe Hawne Beach, dipping northward. The fault is in these slates with igneous rocks which correspond to those of the Torcross' section. There can hardly be any doubt that their junction, on the north-east side of the fault is an inverted one, which would make the beds with Pteraspis in Coombe Quarry the top of the fossiliferous beds of Fowey and Pencarrow Head. The calcareous and interbanded rocks which appear' near Pol- kerris and between Par and Pentuan are taken as partly repre- senting the fossiliferous beds. The Grampound and Manaccan Grits may well be, as already suggested, the shore deposits of the lower part of the Meadfoot Group. At any rate the rocks which surround the St. Aiistell Granite are slates and interlaminated beds in which calcareous material is unequally distributed, judging by the calc-flintas, and there is no reason to think that these beds are anywhere higher than the middle of the Meadfoot Group. The coast-section commences on the east with the basement beds of the group, a mass of dark-grey slates, with arenaceous films in places, and lenticles and beds of grit, often hard, compact, and evenly-bedded. South of Raphael there is an appearance of sharp anticlinal plication near the top of the cliff, suggested by northerly dips of 65° and 80°. All the schistosity dips taken are north or north by west. * See ' Summary of Progress ' for 1902 {Mem. Oeol. Surv,} Appendix iii. pp. 160-162. 12979 B 18 ' DEVONIAN. Passing over the Dartmoutt Slate coastline of Lantivet Bay, we again encounter the dark slates and grits as we approach the Watch House. The grits show sharp anticlines, as noticed by- Peach. Although faults and thrusts are seen on either side of Lantivet Bay, there is no proof that they have any serious effect on the relations of these beds to the Dartmouth Slates, and, indeed, the junction-line from the coast to Lanteglos is very uncer- tain ; nor can we prove that it is along, the line of the Pont Pill Creek fault, presently to be described. As we approach Pen- carrow Headland the rocks become fossiliferous, partially cal- careous and very distinctly cleaved, there are baiids of limestone and the bedding is distinctly shown. On the south cliff of Pen- carrow Head the dip is north about 40°, whilst the cleavage dips north at 10°. The cleavage planes are uneven through traversing silty, partly calcareous and argillaceous interbanding, which gives their surfaces a knubbly appearance. This type is a locally characteristic one in the Meadfoot Group, on the Torquay and Plymouth coasts. The beds from Pencarrow Head to the Dart- mouth Slate boundary correspond to the beds of the Meadfoot Group on the Tregantle coast* between Portwrinkle and Sharrow Point, and to those of the Plymouth coast between Crownhill Bay and Andurn Point, t These knubbly slates, with fossiliferous material in places, extend west from the inner shore of Lantic Bay to Polruan and Punch's Cross Quarry (at the mouth of Pont Pill Creek, a quarter of a mile from Polruan), and, on crossing the estuary, continue from the Ferry westward to the Coombe Hawne fault. Their distinctive character is, however, chiefly confined to the craggy coastline between Polruan and Pencarrow Head, where the cleavage and bedding are rarely coincident. East of Polruan the varying angles of dip prove the constant repetition of the slates by plication. Where the calcareous silty mud prevails, the beds often weather or rot to a yellowish or buff colour, and the series loses its distinctive characters as we approach the Coombe Hawne fault. At Punch's Cross Quarry very fossiliferous decomposed calcareous beds are overlain by thick beds of yellowish-brown grit. The beds dip north or N.N.E. between this quarry and the bend in the creek 600. to 700 yards east ; they belong to the underlying dark-slates and grits ; the slates here exhibit buff and straw-coloured variegation, and the beds of grit show numerous contortions. From here to the fault, which is a quarter of a mile further on and due west of the north end of Lanteglos Churchyard, the slates are weathered greenish-buff and drab and contain silty beds and hard grits, one mass being similar in character to large grit boulders noticed on the surface near Essa on the south. These beds are intersected by two faults, 56 amd 124 yards from the junction fault, respec- tively. The junction fault is marked by 5 feet of crushed rock ; it has a northerly hade of 65°, separating grey and buff- mottled slates, partly siliceous, with grit and occasional red * ' Geology, of Plyna^utli and Llskeard,' (^Menn. Geol. SurvO, 1907, p. 35, t ' Summary of Progress' for 1901 ^Mem. Oeol. Surv.), p. 29.. MEADFOOT REOFP. 19 splotches, fi-om purple-green and yellowish Dartmouth Slates. This junction-fault seems to cross the estuary at about 170 yards north of Pont Pill Oreek, hut its further course westward is very uncertain. The fossiliferous beds occur near Trenant in the vicinity of the Coorabe Hawne fault and south of Lankelly. It is difficult to obtain specifically identifiable fossils in the decom- posed calcareous rocks between the Ferry and St. Catherine's Castle. The following fossils from Fowey were presented to the Survey by Mr. TJpfield Green : — Rhynchonella pengelUana Dav., Hipparionyx, and from Lantic [Bay] a fossil in grit referred by him to (Orthis circularis), Sow, Spirifer primrevus Stein, and OHhotetes (Stropheodonta) gigasl (M'Coy) from Fowey, are in the Survey Collection. Those mentioned in the following list were collected by the Survey from the district south of the Dartmouth Slate anticline and east of the Coombe Hawne fault : — •Favosites? of. Pachypora oristata (Blumenb.). Punch's Cross.* Petraia ? Pencarrow Head. . Pleurpdictyum sp. Punch's Cross and S.W. of Lankelly. Crinoidal remains [pinnulse and oolumnals]. Punch's Cross. ? Atrypa desquamata J. de 0. Sow. Punch's Cross. Hipparionyx ? Punch's Cross. cf. Leptsena ? looiensis Dav. Punch's Cross. Orthis sp. Punch's Cross. Rensselaeria ? i mile S.W. of Lanteglos Church and Pencarrow Head. V " Khynchonella " pengelliana Dav. Punch's Cross. Rhynchonellid. Punch's Cross and E. of. Spirifer hystericus ? {Schloth.). 1 mile E. of Polruan Quay. „ primsevus? Stein, Punch's Cross. „ solitarius ? Krantz. Punch's Cross. „ sp. Punch's Cross and' B. of. Stropheodonta ? Punch's Cross. Tropidoleptus ? Punch's Cross. ? Pterinea costata Goldf. Punch's Cross. Pleurotomaria ? Pencarrow Head. Homalonotus ? Punch's Cross. Pterapis sp. Quarry behind Coombe Farm. Punch's Cross is a fossiliferous locality mentioned by Peach, but the name is not found on the maps. On the north of the Dartmouth Slate Anticline and east of the Castle Dore fault, though fossiliferous localities are numerous in the country around Lerryn and south of Lanreath, well- preserved fossils are almost unprocurable. The more calcareous beds, bands, and seams in the slates have been decomposed to friable or earthy brown residues, and the grit beds, though to judge from surface stones not unf ossilif eroug, are seldom well exposed. The fossiliferous horizons can seldom be continuously traced so that their presence or absence forms no certain guide to the occurrence of dislocations which must traverse the district in which they are found. * In the list, Quarry on S, side of mouth of Pont Pill Creek, Polruan. 12979 B 2 20 DEVONIAN. The following is a list of the fossils collected by the Survey in the Meadfoot Group on the north of the Dartmouth Slate anti- cline : — Petraia? 350 yards S. of Colwood (2 J miles B.8.E. of Lostwithiel). Crinoidal oolumnals. 350 yards S. of Colwood and lane on N. side of Tawell (B.S.E. of Lostwithiel), and quarry IJ miles S.E. of Lerryn. FenestelM. Lane N. of Tawell. Atrypa ? Quarry IJ miles S.E. of Lerryn. Orthis sp. Quarry 14 miles S.E. of Lerryn. Eensselaeria ? Quarry U miles S.E. of Lerryn. In a stone heap S. of Downend (f mile E. by S. of Lostwithiel). Spirifer primsevus ? Stein. Lane N. of Tawell and near Court Wood S. of Lanreath in surface stones. Spirifer sp. Quarry H miles S.E. of Lerryn. Tropidoleptus carinatus (_Conr.) var. rhenanua? Freeh. Lane N. of Tawell. In the lane on the north side of Tawell Farm the fossils were found in a mass of pale-buff sandy grit, allied in appearance and texture to varieties in the fossiliferous beds of Looe. The grit seems to be impersistent. The exposure south of Colwood is east of this and exhibits very fossiliferous tough grey and brown shales (Ringmore type in Kingsbridge area, &c.). Between these localities and the line taten as the south boundary of the Staddon Grits on the north and north-east the rocks chiefly consist of grey slates; sometimes, as in the road-cutting east of Couchsmill, exhibiting the pulverulent weathering of the slates on the east of Par Sands ; sometimes with arenaceous bands and interbanded occasionally with hard beds of grit. Where their planes are suffi- ciently coherent to yield large fragments these rocks have been quarried for local building purposes in Boconnoc Park. No fossils have been found in these beds. The fossiliferous localities lie south of a line from Colwood to Trevalfry. West and north-west of Tawell signs of fossils are occasionally met with, as: — north of Treweather, where there are numerous indications of fossils in irregular slates, grits, and grit-shales; at Silvervein Mine, where reddish-grey and brown, obscurely- fossiliferous, grit-shales or sheared grits occur; at half a mile north of Polscoe, where pale buff-grey glossy grit-shales contain obscure fossil cavities; on the south of Bosmaugan, where grit and siliceous bands interlaminated with hard brown, more or less friable material suggest decomposed fossiliferous calcareous grit bands; about three-quarters of a mile W.S.W. of Bosmaugan, where a grey quartzite, with cavities, gives place to hard brown gritj- with obscure traces of crinoids. Greatwood Plantation is the wood on the map between Bosmaugan and Restormel Castle. Bosmaugan Wood is the adjoining wood, separated by a stream valley on the south-east. There are hard rocks in these woods, specimens of which were sent to Dr. Plett under the impression that they were of igneous origin. He reports on them as follows : — " Three of these rocks have been sliced and examined micro- scopicallr (3688-3690); they are all quartose grits or greywackes with pebbles of quartz m a finer argillaceous matrix. The rocks have been subjected to. crashing, and the pebbles, though often entire, may be broken down or granulitised, wholly or in part MfiADFOOT GaOUf . 21 Tlie argillaceous matrix consists mainly of finely-divided quartz with green chlorite and possibly some mica ; it sliows a puckered cleavage, crossed often by a well-marked slip-cleavage. Some parts of these sections look as if the rock had been originally a banded sediment with coarser and finer layers of deposit, and, during crushing, there had been some brecciation producing ellip- tical or rounded phacoids which simulate pebbles. Pyrites and iron oxides (titaniferous) are common, but there is nothing to indicate that they contain ashy material or are derived to any extent from the degradation of igneous rocks." Trap Wood is the wood by the railway east of Restormel. The dark slates in it occasionally incline to the calc-flinta type, as further north, east of Brownqueen. It appears therefore that the rocks from Treweather to Bosmaugan overlie those exhibiting the calc-flinta type, or pass into them. There is no evidence for drawing a boundary for Staddon Grits, north of Bosmaugan. On the west of Ethy (south of Tawell) there are quarries and crags of blue-grey siliceo-calcareous shales with fossiliferous seams and patches mostly sheared. The dip appears to be north-east, but near the 'House there is a quarry also containing grit of Looe type, apparently dipping north. These blue cal- careous shales and slates with occasional friable seams prevail at Lerryn, and south of Ethy. Orit-shales, slates, and grit, more or less fossiliferous, occupy the summit north-east of "Wooda Cross, and sirailaf materials were recognised east of CoUon. The same types with- decomposed films, beds, or bands of brown fos- siliferous arenaceous material are present near Tencreek, Kingole, and Willake, north and south of Castlemawgan, south of Trevalfry, south and east of Lower Treire. , The quarry .1^ miles south-east of Lerryn is among the fossiliferous beds on the east and north-east of St. Veep, which strike eastward by Tregun- nick and Trefrawl to Lancare and Cartole. It is in whitish- weathered silty shales penetrated by diabase, and as Highgate is east of this, it may be the Highgate quarry, St. Veep, in which Peach found many fossils, but badly preserved, and also as he thought, rain drops and ripple marks.* South of Lanreath the same types appear, and near Court Wood there are stones of quartzite and brown grit with fossil impressions similar to those of Polscoe and other places in the district east of Lostwithiel. The evidence afforded by the country north of the Dartmouth Slate anticline shows' that, except in containing more calcareous materials, the basement beds of the Meadfoot Group are hardly distinguishable from the fossiliferous beds and merge into them, that the latter are not persistent and contain a variable associa- tion of grit, and, as far as surface-evidence goes, that there is no marked boundary between the fossiliferous beds and the over- lying slates, interlaminated. beds, &c. In all horizons where the planes prove sufficiently coherent there are quarries opened for local building purposes; In the • Trant. Boy. Qeol. Soc. Corn., vol. ■vii., (1848), p. 61. 22 DEVONIAN. basement beds west of Manely there are rocks indistinguishable from types met with at Tywardreath and Par. East of the Coombe Hawne and Castle Dore Fault. — From Coombe Hawne to near Gribbin Head Beacon the cliffs are com- posed of grey and dark-grey slates with bands or patches oi igneous rock here and there, suggestive of constant repetition by folding. The slates locally contain harder sitty seams of pale- grey tint, sheared out and distorted obliquely along the cleavage, as is the case about half-way between Coombe Hawne and>Polrid- mouth and at a quarter of a mile south of Polridmouth. In places dark, probably phosphatic, nodules occur in the slates. In the characters of the rocks and. their association with igneous materials the coast section is a replica of the Torcross section. Where the harder bands or lenticles are sufficiently developed the bedding is often shown to cross the cleavage. The cleavage dips are generally nearly due south. At the headland the slates are more or less siliceous, and seen from above, cracks suggestive of bedding traverse the cleavage of the beach stacks at lower angles, in one case suggesting an inverted anticline with vein- quartz at the axis (Fig. 4). Fig. 4. Beach Stacks at G-ribbin Head. From Gribbin Head to Polkerris the coast is not so accessible. It consists of grey slates with igneous rocks here and there, evidently in part at least contemporaneous, as to the west of Hambland. Brown patches suggestive of decomposition of cal- careous films were noticed at about half a mile south of Polkerris. West of Polkerris the grey slates and igneous materials overlie calcareo-siliceous interlaminated shales which weather irregu- larly to a rusty brown and seem to contain films of crinoidal limestone. A fault parallel to the coast cuts off the projecting headland at, about 300 yards from Polkerris Inn. Near this there is an igneous band, perhaps a tuff. .In the cliffs, on the east side of Goodyear Beach, the calcareo- siliceous beds, with some beds of grit, seem to crop out along a feature which runs northward to the Polmear and Lampetho fault. In the railway south-west of Lampetho grey and buff grit- shales and beds of lilac shaly quartzite (like Taunus quartzite), with small fossil cavities dip JST.E. North-east of Kilmarth there are also signs of fossiliferous beds. Between Kilmarth and Trenant 5 feet of rough, shaly greenish- grey grit, dipping S.S.E. at 60°, is exposed in a quarry, and east and south of Trenant it is possible that anticlines of the calcareo- siliceous beds may occur. The cliffs from Goodyear Beach to Polmear consist of grey, greenish, and yellow-buff argillaceous sjates with pulverulent MEADFOOT GfiOUP. 23 weathering, with a soapy feel, and small patches of much decom- posed igneous rock. A crushed zaphrentid was found. These rocks seem to strike more or less along the coast. It is probable that the calcareo-siliceous beds and slates with grit bands between Lampetho and Polkerris underlie them, and are there- fore anticlines. The relations of the rocks on the north of the Polmear and Lampetho fault have been discussed in Chapter II. Whether the Dartmouth Slate patch is bounded on the west by a fault or not is uncertain, but there can be no doubt as to the correspondence of the rocks on either side of St. Austell Bay. The argillaceous slates south of Polmear are also evidenced between Par Green and Tywardreath, from the Quay on the south of Par Harbour westward in the cliffs between Crinnis and Fishing Point. Igneous rocks are present here and there, and silty inter- laminations occur frequently, generally at the base of the cliffs. Sometimes the argillaceous slates are stained reddish, buff, and brown; the cliffs are broken by small thrusts and intersected by lodes. Fossils are present in the siliceo-calcareous beds, but cnnoids are almost the. only recognizable organisms. These are sometimes found in unbroken stems, some inches in length, near the foot of the cliffs east of Charlestown. Appletree Point, east of Charlestown, is composed of interlaminated beds with corru- gated quartz bed-veins in places, very occasional crinoidal lime- stone films and zaphrentids. The beds are vertically contorted, and the same phenomenon is suggested in the slate cliffs to the east by different angles of schistosity and the displacement of decomposed igneous bands by faults and thrusts. The inter- laminated beds, are more or less continuous in the lower part of the cliff eastward to Crinnis Beach: south of Charlestown, they are locally present. On either side of Phoebe's Point the silty laminse are broken and. distorted along low-dipping cleavage planes and dark lenticles cross the cleavage at various angles, as observed on the coast east and south of Polridmouth. A similar phenomenon is observable at Gwendra Point, As at Torcross the slates and interlaminated beds between Ghvendra Point and Rope- horn are highly charged with pyrites, which is seen to' replace crinoidal remains, and they are accompanied by igneous rocks of Torcross types. Near Ropehorn obscure traces of crinoids and zaphrentids occur in grey slates, which rest on siliceo-calcareous interlaminated beds at Ropehorn. Toward Gerrans Point dark lenticles or impersistent (probably phosptatic) bands occur in dark slates. Grey slates with igneous rock in places occur from here. to the. Black Head diabase. These slates were quarried for roofing purposes 60 or 70 years ago. In the cove between the diabases of Black Head and Drennick these grey slates with brown-stained bands and nodules overlie the diabases on either side, the latter exhibiting a rather wide chilled margin. The Black Head diabase is in Sheet 353, the north part of the Drennick mass is in this map. On Hallane beach dark slates are associated with siliceous limestone, partly decomposed to a hard brown rock with organic traces, probably bryozoon. Pyrites renders the fossils in the hard 24 DBVGJflAlif. dark bands too obscure for identification, Tbese rocks, perhaps from contact alteration, are occasionally whitish, they. contain masses of igneous rock, probably ' processes from the Drenmck diabase. . On the west side of the Hallane Valley the diabase makes an irregular junction with the slates which are partly inte'rlaininated with siliceous bands and lenticles, and often brown-stained. These, bands and lenticles are irregularly replaced by quartz. Unbroken crinoid stems occur on the slate surfaces as on Oharlestown beach. Some fossils were obtained in the Van, the cliff below the igneous rock on the west side of Hallane beach'. The following were collected on the coast between the Coombe Hawne' Fault and Pentewan : — A doubtful coral, west end of Crinnis beach. Petraia sp., on the north side of Eopehorn. Crinoidal remains and columns, from beach below Polkerris Inn, near Fishing Point, Polgaver beach Cliff, 1^ miles east of Oharlestown Church and half a mile east of Oharlestown Harbour, Porthpean, Hallane beach. Bryozbon, from Hallane beach, and perhaps from li miles east of Oharles- town Church. A possible suggestion strikes us that the bryozoan remq,ins at Hallane may have been referred to Protovirgula dichotoma, M'Coy, by Peachj who reported the discovery of that form at the Van and Black Head.* ■ Rensselseria ? Polgaver Beach. . Spirifer? Polgaver Beach. Orthoceras sp. Polridmouth, north side of Ropehorn. Cyrtoceras sp., from Polridmouth ; was figured by G. 0. Crick in 1899. Orthoceras, from Polruan. In 1841, Peacht noted the discovery of corals erinoida and spirifers in calcareous slates at the Van, and crinoids, &c., near the Black Head, Ropehorn, Porthpean, Oharlestown, Par, Polkerris, coast from Oribbin to Polridmouth,t and on the Fowey and Polruan coasts. In 1895, J. H. Collins! figured various crinoid remains from Punch's Cross, the Van, Crinnis,' and St. Veep. In his ' Working List ' he records the following : — From Polridmouth, Cyathophyllwa pluriradialis, Atrypa desjuamato, A. aapera, Phacops latifrons. From Crinnis, Petraia celtica, Cyathocrinus planus, Periechocrinus moniliformis. .From the Gribbin, Conularia quadrisulcata, Petraia celtica, and Actinoceras From Coombe Haven (Coombe Hawne), Actinoceras devonicans. For the other fossiliferous localities in this map the reader is referred to the ' Working List. 'II In 1898 Mr. Upfield Greenlf described a new species he named Nereitopsis.eomubicus and obtained in Point Quarry, Polruan. * Trans. Boy. Qeol. Soo. Corn., vol. x.,188I, p. 90. t Ibid. 'Vol. vi., p. 12. j Polridmouth is spelt Pridmouth by Peach, Collins, &c. §'Trans. Soy. 0(oC Soo, Com.,\ol. xiii, 1896,.p. 73. llbid., vol. xi., 1893, p. 421. ■ "f lUd., vol. xii., 1899, p. 22Y. GKAMPOUND GRIT. 25 In the same year Mr. Collins* identified specimens in the Penzance Museum as follows : — ■ Rhynohonella pengellyana. K. strioklandi. Orthis circularis. Streptorhynchus gigas. From Fowey ■{ Spirif er hystericus. is. paiadoxus. Athyris undata. Pterinaea costata. L Ctenocrinus rhenanus ? r Orthis striatula. From Polridmouth ... < Spirifer primsavus. ( PterLnea lamellosa. Davidson was unable to corroborate the occurrence of Spirlfera speciosa ScUoth., at Fowey, St. Veep, and Polruan mentioned by M'Coy.t He describes internal casts of the ventral' valve of Streptorhynchus gigas M'Coy, from Polruan, and Streptorhyn- chus ? persarmentosus M'Coy, as common at Polruan and Fowey. He mentions the occurrence according to M'Coy of Atrypa aspera Schloth., at (Polridmouth) Pridmouth, Menabilly, and' Fowey.J Grampound Grit. The Grampound Grit is a name given to the arenaceous and conglomeratic rocks, which extend westward from Pentewan throTigh Grampound, by me in 1890, from the descriptions of the type in De la Beche's Eeport, p.p. 83 and 92, near Pentewan and near Grampound. From Pentewan a generalized boundary which enters this map near Nansladron has been drawn, as the surface evidence was not good enough to separate the grits from the slates which are probably folded in a synclinal tongue ex- tending westward to Lanhadron from the upper sluices of the reservoir near the mouth' of the Pentewan Valley. West of Nansladron these beds are very imperfectly exposed, and where visible between Levalsa and Resoorla seem to consist of Weathered sandstone, mostly earthy, associated with slate and occasional beds of harder grit, so that their northern boundary is here vague and unsatisfactory. Mr. Reid contributes the following notes : — "Coarse grit appears in the angle of the high-road half a mile north-east of Trencreek. Around Trencreek sandy slate and sandstone are everywhere ploughed up, and in the valley, just south of our limits, a thick bed of massive sandstone with a west-south-west strike is exposed in'a quarry. Similar deposits extend westward to the St. Austell high-road ; but in a quarry nearly a quarter of a mile north-northwest of the ninth milestone these sandstones give place to a sandy conglomerate, containing pebbles of vein quartz and quartzite up to 1 ^ inches in diameter. "Coarse grits^ occur at several spots in the neighbourhood of Grampound ; but they seem to alternate with slates. The quarry close to Grampound Mill shows purplish-grey hard flaggy slate and black slate with carbonaceous matter ; the quarry on the west side of the stream, and nearly opposite is in massive grey grit, which is extensively quarried for road metal. ' Trans. Boy. Geol. Soo. Corn., vol. xii., 1899, p. 233. t ' British. Devonian Brachiopoda,' Pal. See., vol. xvi., 1862, p. 30. X Ibid., vol. xvii., 1863, p. 58. 26 DEVONIAN. "The grit of Grampound is a hard compact greyish grit, of moderately coarse grain, but containing larger pebbles of slate (or perhaps contemporaneous clay- galls). It is composed mainly of rounded quartz- grains ; but yields also a considerable number of grains of quartzite. Unfortunately no fossils could be found, the only one yet discovered in the Grampound grit being an Urtlus, probably a new species, obtained in a quarry just beyond the borders of this map, in the Newquay sheet. " The strike of the rocks in the neighbourhood of. Grampound is everywiere west south-west ; the dip, or at any rate the dip of the limbs of the folds is north-north west." The northern boundary of the grits would appear to run from Levalsa to Paramoor Wood and from Paramoor by Pengelly, on the north of Tre winnow Vean and Nantellan, westward, as on the south of this line the grits are exposed at and near Trewinnow Vean, and in a quarry half a mile south of Gram- pound Eoad weathered to a pale-brown. South and south-west of Nantellan tough massive grits broken by irregular joints and associated with grey and greenish hard partly arenaceous mudstones are exposed. In the quarry south of Nantellan there are signs of an anti- clinal structure. To the north of this apparent boundary, how- ever, sandy beds are associated with the slates, and these associa- tions are seen at, and in the railway-cuttings near, Grampound Road, and are also evidenced in places from Resugga Castle westward. So although slates largely prevail near Garlenick, and this may indicate a syncline trending through Trevan Wood for a short distance westward, a boundary has been taken fiouth of Sticker by Hewas Water to Trenoweth Mill, near Resugga Castle. Near Hewas Water a peroxidated rock apparently made up of slate fragments was detected, and similar bands seem to occur in the slate south of Sticker. In the shafts of Commerce mine, judging from the dumps or tips, similar soft rocks which suggest decomposed felspathic tuffs or clastic mixtures of slate and felspathic material, as well as more gritty bands, occur. Peroxidated silty beds also occur in the slates in a pit in a depression about half a mile north of Grampound Road. In a quarry at Halezy, near this, about 5 feet of grit, dipping S., at 45°, was exposed in slates in a quarry. Grit dipping south was also seen in a quarry west of Lone Downs. North-east of Lone Downs there are no exposures, and those at Carwinnick are in quartz-veined slates. North-west of Lone Downs the grits are evidenced by surface stones. Quartz-eyed Slates. — In default of any better indications we must take the slates Characterized by quartz-eyes, which on the coast south of Hallane seem to largely replace the siliceo- calcareous interlaminated beds, as the representatives of that series traced inland. The surface evidence which is meagre near the coast does not enable one to trace the type continuously. North of Polglaze a north and south strike was observed in some outcropping slates, the igneous mass on the east showing a .nearly, parallel deflection. At Levalsa Moor the cleavage strike is east and west, but at Clark's shaft, near Newmill, it is again north and south. Slaves witb. quartz-eyes and films are seen west of Mulvra, by the high road from St. Austell to Sticker at GEAMPOTJND GEIT. 27 the turning to Nanphysick at Trelower, &c., and there are also evidences of the .occurrence of interlaminated beds in the slate in places. Between Hewas Water and TrethuUan Castle the quartz-eyed slate type is very much in evidence, and also through St. Stephen's Coombe to Gwendra, near St, Stephen's, Eesugga Lane end, Terras Mine, and Penhale westward. At half a mile east of Resugga Lane-end there is a quarry in hard dark rocks with nearly horizontal planes, and stones approaching the calc-flinta type were also seen at Bodinnick iron mine, a disused open pit between here and Resugga Lane-end. Similar slate types to those north of Tywardreath occur east and south-east of Tregorrick. Within the aureole of contact alteration the slates and interlaminated beds are often peroxi- dated, the interlaminated beds also display schorlaceous altera- tion. Every variety of interlamination from a softish silty rock with argillaceous films at intervals to argillaceous rock with thin im- persistent silty films is to be seen, and these types are to be found all round the granite as far as I have seen, and include types which occur on the borders of the Dartmouth Slates as well as among the higher fossiliferous horizons of the Meadfoot Group. Mr. Barrow describes them on the north of the granite. It seems as if tihe type represented by the calc-flintas had become gradually modified southward, perhaps less calcareous. South of Lostwithiel and Fraddon the comparative absence of this type where beds representing its stratigraphical horizon must be present, as proved by the small patch at Treesmill, bears out this view, Mr. Barrow furnishes the following notes on the beds of the Meadfoot Group, north of the iSt. Austell Granite : — . " A little south of the Kirland, near Bodmin, a slight, though in good sections, a well-defined change occurs in the dominant constituent of the Lower Devonian Rocks. Though still finely-banded silts, as in the overlying Staddon group; there is a far more marked difference in the composition of the laminae, which now consist of fine-grained pale-yellowish siliceous material, alternating with films of originally dark-grey mud. In spite of their fineness, the siliceous films follow the law of breaking down of a grit ; they break up into minute lenUoles (in this case only visible under the microscope), which in the aggregate are parallel to the margins of the siliceous bands. The mud films, however, are cleaved diagonally, the cleavage planes cutting the margins of the harder material at an acute angle. The term ' cleaved ' is here used as the term popularly applied to this structure ; in reality the mud films are also cut up into, lenticles, but these are so thin and the length of the lenticles is so much greater than the thickness as to produce a microscopic appearance of parallelism. This difference of structure afEecls equally the rock produced by the metamorphism of the granite, where the crystallization follows the strain planes bounding the lenticles, just as in areas of regional metamorphism This persistence of difference in cleavage of the two constituents of the banded silts enables the type to be recognised close up to the margin of the granite, and to the south of Bodmin it is specially abundant. Excellent hand specimens can be obtained about the roadside between Trebyan and Tredinnick, all more or less meta- morphosed, but showing perfectly the original difference in .direction of cleavage in the two components of the rock. These banded silts and associated rocks continue for a considerable distance to the west without much apparent original differences. The banded type again shows its persistence when metamorphosed, though the cleavage is destroyed, in the ground to the south-west of Lanivet. In this area the fields are often 28 DEVONIAN. strewed with fragments in which the bedding is perfectly clear though the mud films . are converted into schorl, the siliceous films being represented by reconstructed silica or quartz. But at some distance to the north-west of Lanivet a distinctly new type seems to set on. In the Mulberry Mine the banded silts still form the dominant rock, but to the north of the mine numerous openings reveal the presence of much thicker, though still very fine, siliceous rocks associated with thicker bands of softer material, some of which must clearly have been a reddish marl originally. The difference of type of cleavage or breaking down, however, still persists between the soft and hard material. But the greatest variation occurs about the roadsides near the Mill, about a mile north-east of Withiel, where a mass of much darker and harder killas occurs separated by subordinate films of pale sandy or felspathio material. Close to the mill the Killas is almost black, and there is at least one band of hard, dark calcareous mudstone. This altered hard, dark mud, or killas, forms almost the whole of the hill to the north of the mill ; curiously enough, no sandy films are seen on the fields here, which are strewed all over with the killas fragments ; the sandy material easily decomposes, and for this reason it has been taken to be largely composed of felspar, bands of this having proved singularly liable to total decomposition. Bocks of this type may be present in the eastern area, but no trace of them has been met with ; outcrops, however, in the ground south of Bodmin are not good, so that it is not possible to say definitely that these dark killas beds are not present." Staddon Geits. Near Bury Down Camp there is a quarry in grey, greenish, and pinkish, more or less arenaceous mudstones, which has been included in the upper part of the Staddon Grits, and an indica- tion of the presence of the Bodmin silty types, described more particularly by Mr. Barrow further on. The exposures in the tract south and south-east of this are few. BufE and greenish sandstones associated' with slates are evidenced south of Trewen. Grey-brown grits broken by irregular joints and occasionally containing small flakes of shale are exposed in a small quarry near Trevawden. From this to the boundary of the Meadfoot Group, east of Woodsaws, sandstone and hard grit stones ar& often met with on the surface. Between the faulted patch of Dartmouth Slates and Toreland, near Lankelly, grits are evidenced on the west side of the Port- nadler fault; they are probably the lower beds of the Staddon Grits. The shifted continuation of the Staddon Grits from the valley bounding Buckabarrow Downs toward Bodmin Road affords few exposures, the evidence being chiefly obtained from surface stones, which from the rare occurrence of fields under cultivation are often very unsatisfactory. The southerly extension of the grits, however, between Higher Clowne and Menaburle is certain. In the north of the wood east of ORoselyon there is a quarry in more or less arenaceous mudstones yielding large blocks. By the valley near Bagstone tough, dense grit and finely- laminated arenaceous beds were seen in an old quarry. On the north of the plantation between Bagstone and Trewindle there is a quarry in greyish mudstones with nearly horizontal major planes yielding large blocks. Near Dawna fi quarry displayed 'hard shaly grit, slate, and laminated arenaceoius materials. At- aboui a quarter of a mile north of Boconnoc Church drab laminated arenaceous mudstones dipping south were seen in a^ quarry. They are included in the Meiadfoot 'Groiipf, but may be STADDON Fig. 6. Bedding in Penhellick Quarry. At Connonbridge there are signs of vertically zigzagged bed- ding, and between here and West Trevillis harder bands denoting bedding show anticlinal structure in the smaller of two adjacent quarries. The three patches of contemporaneous igneous rock shown on the map are, no doubt, greatly exaggerated; they seem to be rather thin schalstein bands intercalated in the slates, such as we find, for instance, at Hope's Nose, Torquay. The banded types of Middle Devonian, which have been described at Bodmin by Mr. Barrow, are often fossiliferous, but it 12979 c 34 DEVONIAN. is very seldom that anything but crinoid markings can be distin- guished. East of Pelyne, at the cross roads south of HoUowpark, dense mudstones, with rather irregular silty bands, were exposed. Hard-banded slates and traces of fossils were visible south-east of Westpark. On the east side of the valley west of HoUowpark a small quarry displayed blue-grey shale with siliceous gnarled bands in places, and numerous traces of crushed fossils. The rock resembled a type of fossiliferous Looe Beds, near Kil- minorth in Sheet 348, but these resemblances between Devonian slaty and shaly rocks of widely different horizons are common. North of Braddock there are several exposures of fossiliferous interbanded shales, some of them apparently containing decom- posed calcareoiis films. Banded and interlaminated rocks also occur west of Penkestle and south and west of HoUycoombe, where they render the Staddon Orit boundary extremely uncer- tain. This is also the case near Castle Canyke, north of Turfdown and north of Fletchersbridge, where interlaminated rocks with traces of crinoids, which may belong to the Middle, have been included in the Lower Devonian. ■North-east of Crlynn the banding crosses cleavage planes, and there are traces of crinoids. Traces of fossils were noticed at West Taphouse, in a quarry by the lane east of Tithe Hall, the slates recalling the fossiliferous beds at Trevelmond in Sheet 348, which Giles compares with fossiliferous slates at Bodmin. A cast of a Zaphrentid coral was seen in the slates near Trago Powder Mills, about half a mile to the east of Largin Wood. The dark slates between Doublebois and St. Neots are probably the uppermost Middle Devonian Strata in this map, and prob- ably occupy the same place in the series as the rocks of Ivy- bridge. 35 CHAPTER VI. THE OLDEE IGNEOUS ROCKS. The igneous rocks of this sheet belong to two distinct periods, separated by the period during which the great post- carboniferous earth-movements took place. The greenstones and the volcanic rocks associated with Middle Devonian sedi- nients belong to the first of these periods ; the granites and fel- sites, with the exception of a felsite occurring to the north of Hendra, about one mile soiith-west of Withiel, to the second. The present chapter deals only with the rocks formed during the first period. Many of the exposures to which reference is made are too small to be represented on the one inch map. Igneous Rocks in the Daetmottth Slates. Some decomposed sheared green igneous rock is associated with the Dartmouth Slates on the coast on the west side of the cove west of Parsons Cove ; the rocks are here much broken by small' thrusts. On the east side of the valley, about 300 yards north of East Coombe (west of Lizzen) blocks of green diabase and of green amygdaloidal rock, possibly contemporaneous, were noticed on the surface, and seem to have been " ripped " up nearly in situ. Surface-stones suggest the presence of sheared felspathic tuff at about 200 yards further north on the west side of the valley. On the north side of the road, on the east side of Trigamelling, a brown decomposed felspathic igneous rock was exposed. At about a quarter of a mile west of Lansallos surface stones suggest the presence of brown amygdaloidal igneous rock in the slates. On the east bank of the Fowey at a quarter of a mile above the bend near Mixtow Pill, 4 feet of sheared diabase occurs in the slates, above a mass of slate interlaced by quartz veins. On the opposite side of the river there is a mass of diabase in the dark slates and grits taken as a synCline of basement beds of the Mead- foot Group. On the same side of the river at 280 yards to the north sheared green igneous rocks occurs in the purple and green slates. From here to Golant no traces of igneous rock were noticed, but on the opposite side of the river, 130 yards south of PenpoU Creek, 2 to 3 feet of green sh-eared diabase is visible in the variegated slates. Green sheared diabase is exposed at the mouth of Penpoll Creek. On the north bank 2 feet of similar rock is visible at about 560 yards from the mouth of the Creek, and some decomposed igneous rock occurs about 200 yards further east. On the south bank, seven-eighths of a mile from the mouth of the Creek, shared dark-green igneous rock was seen, and igneous rock is evidenced a little over half-a-mile west of this. Greenish porphyritic diabase occurs at the south end of Great Wood at the mouth of Lerryn Creek. By the lane to Newham Farm, at about 60 yards from the farm-gate, soft dark-green decomposed igneous rock, which does 12979 C 2 36 IGNEOUS BOCKS. not appear to exceed 5 feet in thickness, occurs in the Dartmouth Slates, which seem to be traversed hy a fault at about 20 yards from the farm-gate. On the east side of the river due west of Newham sheared igneous rock was seen under smooth slates. A dark-blue-green igneous rock was also visible under slates at the bend in the river about 720 yards above the last observation, . whether in Dartmouth Slates or overlying beds was not clear. In the Great Western Railway cutting a mile south of Lostwithiel Station, on the east side, a foot or two of green fine felspathic rock, probably a tufE, was noticed with a nearly north and south outcrop in greeiiish slates. Judging by a few dark- green igneous stones on the surface, there may be igneous rock in the Dartmouth Slates at about a quarter-of-a-mile north of Trebethavy. A foot of green sheared igneous rock was seen in the Dart- mouth Slates at half-a-mile east of Trezare. Whether any of the above traces are of contemporaneous origin the evidence did not show, but as contemporaneous igneous rocks have been found in the Dartmouth Slates near Kingswear and elsewhere it is not improbable. Igneous Rocks in the Meadfoot Group. Owing to the large area occupied by the rocks of the Meadfoot Group, we shall first note such traces of igneous rock as have been observed in them on the east of the Coombe Hawne and Castle Dore Fault ; next those met with in the area west of this line of disturbance, in each case commencing with the coast section. At Pencarrow Head (south shore) a band of sheared decomposed igneous rock, probably contemporaneous, is intercalated in the calcareous Slates at about 50 feet above mean tide. A band of sheared igneous rock was also observed at three- eighths of a mile S.S.W. of Lanteglos Church. Green sheared igneous rock is associated with the slates on either side of Coombe Hawne Beach on the east of the fault. A mass of green sheared diabase occurs in the dark slates and grits which have been taken as an outlier of the Meadfoot Group north of Fowey. The following are in the area north of the Dartmouth Slate anticline. There are traces of yellow decomposed rock probably of igneous origin at 130 yards north-west, and at a quarter of a mile south- east, of Cartole; in a quarry at a quarter of a mile south of Tregarrick and by the road about 200 yards south-west of this quarry; also a trace 560 yards west of Tregarrick. South of Woodsaws, east of Lanreath, a few igneous fragments were seen on the surface in places. Some sheared diabase was exposed in a quarry on the south-east side of Lower Treire. Small patches of brown decomposed igneous rock were observed on tlie soutli of the first, third, and last letter in the word Penpoll on the map, near St. Veep. Sheared slaty igneous rock was visible at the turning to Tencreek, north-east of St. Veep. Further east diabase occurs in the fossiliferous quarry between Highgate and IGNEOUS BOCKS. 37 Tregenua.* Green sheared porphyritic diabase is met with in the shites south-west of Ethy, on the north side of the bend in Lerryn Creek. At the south end of Great Wood igneous rock occurs in the vicinity of the Dartmouth Slate boundary. In the Railway-cutting at Trap Wood, east of Restormel, a sheared igneous rock, probably originally an andesitic basalt (E. 3,692), is exposed. It may be a contemporaneous mass. A boss of rock almost wholly composed of epidote crystals (E. 3687) has been mapped as diabase near Brownqueen. Avoiding reference to the occurrence of igneous rocks within the zone of contact metamorphism, we will now mention such exposures as have been noted proceeding round the coast from the Coombe Hawne fault westward. Near the fault grey-green sheared brown-weathered igneous rocks occur in the dark slates of Little Coombe Hawne. At about 150 yards south there is igneous rock of Torcross type, and in several places between here and Polridmouth, but the bands are so disturbed by small f aults- that their relations to the slates are uncertain. The types with leucoxene patches so common at Torcross are present. In one place a green decomposed porphyritic rock, much split up by joints, occurred in a manner suggestive of synclinal structure. On the east side of Polrid- mouth Beach 2J feet of green sheared igneous rock was seen. Several bands were observed on the shores of the promontory, which terminates in Gribbin Head. One of these, at half-a-mile south of Polkerris Quay is traversed by cleavage along which its boundaries are distorted. At Polkerris in the reefs on the north side of the beach one or more bands of sheared pale grey igneous rock occur in dark slates displaced by contortions and thrusts. A band near the headland ,is probably a tuff. On rounding the headland we reach Goodyear Beach, at the north end of which buff and brown decomposed igneous rock is seen in the slates; broken and dis- placed by contortions and thrusts. Between Goodyear Beach and Polmear there are traces of igneous rocks, so decomposed as to be hardly recognisable, in the weathered argillaceous, grey slates with their greenish and straw- coloured mottling. For a considerable distance from Polmear the prevalent schistosity dip in these slates is eastward. Green sheared igneous bands were recognised at about a quarter of a mile and 130 yards from the commencement of the low cliff near Polmear. By the road to Par, at 660 yards from Polmear, yellow-brown igneous rock is exposed in argillaceous slates. The rock reefs at Par Pier consist of similar argillaceous slates with soft igneous rock. Dull grey and green decomposed igneous rock was noticed in similar slates (in part with hard lenticles) about halfway between here and Fishing Point. At Fishing Point igneous rocks, similar to those of Par Pier reefs, * This is probably the rook " on Tanoreek farm almost at the foot of the hill, near Tallow Water " referred to by C. W. Peach in 1846, in a paper entitled "Notice of the discovery of Serpentine, and of its associated Rooks in the Pariah of St. Veep, near Fowey." Trans. Roy> OeH. Soc. Corn., vol. vi., p. 351. 38 IGNEOtrS ROCKS. are associated with slaites and interlaminated beds faulted on the west against slates with occasional beds of grey quartz- veined grit, which form the cliffs of Polgaver, Shorthorn, and Crinnis Beaches, and contain decomposed argillaceous igneous rock. Sheared green igneous rock occurs in slates and inter- laminated beds in the cliff under the old engine house of Crinnis and Carlyon Mine, at Morish Beach, and in the cliff opposite Gull Island. Near Charlestown decomposed igneous rocks, reddish or orange- brown, are seen in the cliffs in two or three places ; it is possible that the same band may be repeated by plications and thrusts. Here we leave the coast to note the few indications of igneous rock outside the contact zone between Par and Charlestown. At the limekiln near Par harbour sheared grey igneous rock is visible in the slates by the road and in the adjacent Railway- cutting above. Sheared dark-green igneous rock also occurs at about 330 yards to the south (near Porth). Green sheared igneous rock is exposed in the railway-cutting at about 230 yards east of Merthan. Fragments of similar rock were found in the tip from the Appletree Mine. To return to the coast. The cliffs of Duporth Beach exhibit a mass of dark-green igneous rock with a tendency to spheroidal structure accentuated by hematite veins. Its upward prolongation seems to be cut up and displaced by thrusts probably crossing vertically-curved or zig- zag bedding. This rock is the Duporth Serpentine, described by Dr. Boase,* IIenwood,t De la Beche,t J. H. Collins, § and J. A. Phillips. II It cannot be traced many yards inland beyond the cliff-face. To the south of this mass .8 feet of decomposed green igneous rock is to be seen in the cliff In the cliff near Porthpean, at a quarter of a mile south of Carrickowel Point a large mass of decomposed greenish igneous rook, probably shifted and displaced by thrusts, forms a con- spicuous feature in the cliff, but cannot be traced inland. The same mass repeated, or a second, is encountered at about 80 yards to the south, 15 feet thick in some places, in others nipped out by thrusts. At Phoebe's Point, on the north side of the elvan, greenish igneous rock occurs, perhaps 15 feet in thickness. At Gwendra Point sheaired igneous rock is visible. On Gwendra Beach, at about SO yards south of the Point, a baud of greenish sheared and decomposed igneous rock, about 30 inches thick, occurs along the planes of the slates, which show no appreciable signs of contact alteration. This band seems to strike west for a quarter of a mile, as it was exposed in the road to Trenarren House. Igneous rock is shown at 40 and 160 yards north of Gerrans Point, and in two or three places between Gerrans Point and the Black Head diabase. Some of the above exposures are amygdaloidal. The Black Head quartz diabase is almost entirely included in the adjacent map, she et 353. A rock suggestive of its chilled * Trans. Roy. Qeol. Soo. Com., vol. iv., 1832, p. 280. + lUd. vol. v., 1843, p. 12fi. t ' Report on the geology of Cornwall ,' etc. (Mem.. Geol. Sui-v.'). 1839 § Miw. Mag., vol. i., p. 222. II QuaH. Journ. Geol. Soo., vol. xxxiv., 1878, p. 473. IGNEOUS EOCKS. 39 margin occurs in this map in tlie cove on the east of the Drennicfc diabase. The Hallane diabase (described by Phillips*) can be traced for a mile m a north-westerly direction. It forms a tough brown rock exposed in the lane south of Trevissick; beyond this its extension has been proved by surface-stones. The large mass of diabase at Menagwins and south of Roseweek is mostly decom- posed, the freshest exposures being near its south-western termi- nation. The evidence in the centre of the mass is so unsatisfac- tory that there may not be as much diabase as is shown on the map. On the north of Molingey Mill a trace of sheared igneous rock is visible in the slates. In Polyear Mine, on the south side of Commerce Common, a sheared grey, apparently basic, igneous rock, was encountered in the shaft at 30 to 40 fathoms. .There are also slight and doubtful traces of igneous rocks on the east of the stream less than a quarter of a mile south of Sticker, and at over a quarter of a mile south of Commerce Common. A tough grey igneous rock occurs at 200 yards south of Nanphysick, which at first sight suggested a resemblance to the Duporth Serpentine. This rock may continue eastward to a small exposure by the lane, near the high road. Somewhat similar rocks occur at Metheroes and Bosithow, on either side of Hembal (west of St. Austell). Mr. J. A. Phillipst described the rock in the mass on the north of St. Mewan, and gave an analysis. He speaks of an old quarry in a similar band on Blowing House (site of an old blast furnace) Hill, which is a small patch of altered ophitic diabase in St. Austell about a quarter of a mile W. 20° N. of the Church. This rock (E. 4,022) was seen in the altered slate south of the Yiaduct over the Bodmin Road near the Smithy, St. Austell. There is another small patch, apparently not noticed by Phillips, by the high road east of St. Mewan's Church, and also a large mass north of Trewhiddle and east of Tregongeeves. The lastrnamed is well exposed in a large quarry opened for road metal at its western extremity. Here red-stained and apparently unaltered killas, probably contorted, rests on hard blue diabase. The mass of igneous rock, which extends for 550 yards south- east from Terras is exposed in an old quarry near its western margin. West of the alluvium similar rock continues for three- quarters of a mile. It is exposed in quarries at 220 and 530 yards from Hallivick. In a pit near Fraddon sheared greenstone is associated with Some calc-flinta. Many of these diabase occurrences are just in or on the border of the zone of contact alteration. The following are well within it. In a quarry on the west of Lostwithiel a band of hornfelsed greenstone occurs in cleaved * QiMi,rt, Jonrn. Geul. Sue, vol. xxxiv., 1878, p. 475. t Ibid, p. 471. 40 IGNEOtJS EOCKST micaceous slates. Further north, north of Leadenhall Wood, banded greenstone occurs. Igneous rock is associated with the calc-flintas in Ford Plantation, south of Lanhydrock. By the stream at Maudlin there is a quarry in altered diabase. w. A. E. TJ. Greenstones have been met with in the rocks of the Meadfoot Group to the south of Bodmin. The comparatively large area covered by these rocks is not due to the presence of a number of thick bands, but rather to the repetition by folding of one band of no great original thickness. They occur in association with the altered calcareous rocks to which the term calc-flinta has been applied. They appear to have been originally rather fine grained, but they have been so affected by mechanical deformation that often no trace of the original structure is left, except a few fragments of broken felspar crystals, suggesting that the original rock was somewhat porphyritic. They contained a considerable amount of iron ore, still largely preserved, but ground to powder or dust; the powder is arranged in approximately parallel planes along which the rock splits, with the result that the splitting faces are blackened with it. It thus comes about that well away from the granite margin the very fine and almost fissile greenstone has the appearance of a slightly altered black chloritic slaty sediment. As the greenstones are followed toward the granite margin they become coarser in texture, and assume the character of a very fine grained actinolite-schists. In actual outcrops the rock cannot be traced nearly to the granite, but a shaft was sunk through it, not far from the granite margin, on the south side of the road near St. Ingunger, three and a half miles south of Bodmin. The rock is sufficiently coarse to allow the hornblende to be easily recognised. A microscopic section i(5,491) shows that it closely resembles the clear brown hornblende which, in the Cornish greenstones, occurs always where the rock is in imme- diate proximity to the granite. The greenstones that so closely resemble altered dark shales in hand specimens are often seen under the microscope to have the lenticular structure due to mechanical deformation. The dominant component of each lenticle is either felspar or actinolite, though a small quantity of felspar occurs in the actinolite lenticles, and vice versa. Crushed iron ores and their alteration products are associated with both, but are commonest in fels- pathic portions. The latter are built up of minute grains and remnants of small laths, which show the milling to which the rock has been subjected. The actinolite lenticles consist of a number of minute wisps and feathery aggregates. As is usual in such rocks, the iron ores were originally a mix- ture of magnetite and ilmenite; the former breaks down less than the latter, and is more stable ; the ilmenite is largely altered to leucoxene and minutely granular sphene. A greenstone, somewhat resembling a hardened slate, was pierced in several of the shafts sunk to the more southerly copper vein of the Tretoil Mines, and abundant fragments are seen on the IGNEOUS KOCKS. 41 tip heaps. A curious example of this type of gTeenstone was obtained from a field on the left of the road, about a mile and a quarter east-north-east of Lanivet, on the northern outcrop of this rock A patch of f elspathic material on the margin of this specimen has a structure resembling adinole, suggesting, that it contains the original junction of the greenstone and slate, which latter has been altered to adinole by the greenstone intrusion, and not by the granite further south. Close to the farm of Tredinnick, about three miles south of Bodmin, a fairly large quarry has been opened in a rather com- pact fine dark greenstone, which lies well within the aureole of metamorphism of the granite. The bulk of the rock is homogeneous, and clearly a very fine actinolite schist ; but small local variations are observed; in some parts the white specks, marking original felspars that have been more or less broken up, are more abundant than in others, and more rarely small patches of the rock are distinctly brown coloured, due to the formation of contact brown mica. The rock at Tredinnick • can be traced across the fields in a south-easterly direction, becoming gradually more coarsely crystil- line. It may be noted that it shows the typical reddish brown decomposition that generally characterises the greenstones, and , not the white alteration described later. The rock nearest the granite from the shaft at St. Ingunger, already referred to, has under the microscope a well-marked parallel structure shown by the arrangement of the crystals of pale brown hornblende. The associated felspar lenticles are built up of almost quadrangular grains, only a few of which show plagioclase banding. In the felspar a number of minute crystals of biotite are locally embedded. The iron ores, though broken up, are little altered. The structure is essentially that of a granulite. Ii! a considerable number of cases the finer types of greenstone, described above, are altered to a soft, nearly vi hite material super- ficially resembling china-clay. It is difficult to decide whether pneumatolytic action plays any part in this alteration ; it can hardly be clafmed as normal, for in most cases the greenstones decompose to a reddish brown earth. Further, it does not seem to occur, or at least is very rare, in areas quite outside the granite aureoles, and where no clear marks of pneumatolysis have been met with. (Sections made from a series of specimens showing the alteration irom the very dark green to the white rock suggest decomposition alone as the cause of the change. The felspar in extreme cases becomes practically isotropic, but the actinolite can still be tiaced, preserving its outline, though altered to chlorite. Every trace of the iron ores has disappeared, except the original replacement mineral, minute grains of sphene. The ultimate product is so soft that no section can be made of it. The greater part of the greenstone, at the Tregullan Quarry nearly two miles south of Bodmin, has been more or less altered in this way, and a great quantity of it has been thrown out from the quarry on the service-road. The best series of specimens showing the progressive change can be obtained from the quarry 42 IGNEOUS ROCKS. where three roads meet, about a mile and a quarter slightly north or east of Lanivet. The same alteration has been noted in the tip heaps at the Tretoil Mines. As may be imagined, this alteration renders the greenstones useless for ro^d metal, and its incoming has led to the closing of several quarries that started in sound rock. In addition to the undoubted greenstone already described, some igneous material has been met with in a rather large quarry close to the road, opposite the Monastery, to the south of Lanivet, the original character of which is doubtful. The rocks in the quarry have all a more or less persistent brownish grey tint, due to the presence of a great number of small crystals of brown mica, which have been produced by the thermal action that accompanied the intrusion of the adjacent St. Austell Granite. Some greenish patches also occur here and there containing actinolite, but they form but a small portion of the whole. There is no difficulty in seeing that there are at least two different rocks, one of which is obviously an altered gritty shale, but ihe other part is difficult to make out. The whole mass has been so strongly afEected by dynamic action that the junctions cannot be followed for more than a few feet, so that macroscopic evidence of the nature of the doubtful material is unsatisfactory. Many white specks are seen in it, some of which are certainly felspar crystals, and micro- scopic sections show that practically all have been crystals of felspar, though some have entirely recrystallised after being greatly deformed. In these brown rocks a number of small cracks occur, mostly filled with minute veins of quartz, or quartz and felspar ; there are also numerous cracks in the green material filled with actinolite needles, as in the case of the greenstone already described. A series of slides (5,493 — 5,499) have been cut, and these show well the variation in the effects of dynamic action; the porphyritic felspars {white spots) being at times little affected, while at others they have been dragged out, all trace of original ' structure being obliterated and a new mosaic set up in its place. The matrix also shows equally well the varying extent of the crushing, some small lenticles having escaped, the little felspar laths being left ; these are numerous and rather short, having the composition apparently of an acid oligoclase. Distributed through the latter are small patches of felspar associated with some altered basic mineral, which has now entirely disappeared, and been replaced by the brown mica. The distribution of the latter is often irregular, being much more abundant in some parts than others ; this is clearly due also to crushing, for in the few patches which have almost escaped, the brown mica is fairly evenly distributed. The evidence is sufficiently clear that the rock was not a lava, but there is a possibility that it may have been an ash. If so, the material was probably more acid than the greenstones already described. The rock in this quarry south of Lanivet cannot be traced many yards to the east ; but to the west a few fragments have been found here and there, suggesting the repeated outcrop of its folded IGNEOUS EOCKS. 43 edge. There is not sufficient to show on the map; indeed, the fragments are mostly on a steep slope, and their reaj point of origin cannot be traced. It seems fairly clear that ' the rock, which is close to the calc-flintas, has been brought up on the crest of a sharp " pitch-anticline." Small outcrops of altered greenstone, associated with or close to the calc-flintas, are not uncommon in the area to the south of Withiel and St. Wenn, but the rock in most cases has been met with only as loose fragments scattered unevenly over the ploughed fields, where it clearly forms but a subordinate element in the rocks of which the ground is formed. They are probably small infolds rather than minute intrusions, but the real size of the intrusion they belong to cannot be ascertained. One patch large enough to show on the map occurs close to the small farni on the west edge of Eehre Common (Kirriers, on the six-inch map), and lying about half a mile north of the Truro road. A small opening, recently made, enabled a fairly fresh specimen to be obtained, which is greenish in tint, and largely composed of actinolite. It is sufficiently near the edge of the granite to be fairly well crystallised, and the actinolite is in sufficiently large crystals to be identified with a hand lens. A little further north, in the angle of the 'Marsh, the area shown as calc-flinta on the map, is plentifully strewed with frag- ments of finer greenstone, and illustrates well the mode of occur- rence of this material in patches, the outcrop of which cannot be traced. The Quaktz-Porphyrt, near Hendra, of Pre-folding Age. In the fields to the north of Hendra, about a mile south-west of Withiel, numerous loose fragments were met with, formed of a greatly crushed acid igneous rock, and in one place a small open- ing has been made of the rock in situ. • It is clearly of pre-folding age, and has been involved in all the movements by which the killas has been affected. A few small specimens of the least crushed rock have been found which is a very compact pale grey semi-translucent rock, somewhat resembling the older rhyolites. Sections show no trace of original cavities or any other structure suggesting that it may have been a lava; it is thus probably a very fine grained intrusive sill of felstone or quartz-porphyry. In section the ground mass is micro-felsitic, and does not appear to be a devitrified glass. There does not appear to have been any original white mica, but even in this least crushed specimen some sericitic mica has been developed along small crush planes. The phenocrysts are quartz and potash-felspar; no plagioclase can be detected now even if it ever existed. Brown mica is seen from another section to have been present in small quantity, none can be detected in this. No schorl is present in any of the sections, and the rock is clearly not allied to the normal Cornish elvans. A more crushed specimen shows far more sericitic mica developed along the curving crush planes that break the rock up into lenticles. In this specimen the mica often flows round the original crystals without actually touching them; but where it 44 IGNEOUS KOCKS. does touch the phenocrysfe are much broken and altered. (Plate TI., fig. 4.) A greatly crushed specimen is completely cut up into lenticles, the margins of which are thickly coated with the flaser-sericite ; the phenocrysts even of the quartz are now so broken up that the rock begins to resemble a greatly crushed grit with small quartz pebbles. Acid rocks of this age are very rare in this part of Corn- wall ; otherwise the rock itself is intersting only as a fine illustration of the effects of dynamic action on a felsite or fine quartz-porphyry. G. B. Volcanic Rocks in the Middle Devonian. North of Bury Down, between West Trevillis, Bara, and "West Park, the Middle Devonian Slates are associated with schalsteins. They consist of decomposed rather tough rocks, whose distri- bution can only be ascertained by surface-stones and large masses used in building up the hedge-banks. The only approach to an in situ exposure is near the end of a deep-cut lane north-west of Woodlay, between Bara and Trevillis; here the schalsteins out- crop, but do not afford as good specimens as those used for the hedge-banks. The distribution of the stones suggests two patches between Bara and West Park, as shown on the map ; the most southerly of these may extend west to Botelet, the farm near Hollow Park, as a specimen was procured near that place, also near Bara. These occurrences justify the belief that, although there is no evidence of superficial continuity, the apparently impergistent volcanic horizons south of Liskeard are present in this map. The surface evidence being very imperfect, and the probability of faults being admitted, one cannot deny the continuity of the tuffs and lavas between these different localities beneath the surface. W. A. E. IT. Peteogeaphy of the Greenstones. Under this group are included the. dark green basic igneous rocks which occur in the Devonian and pre-Devonian strata of the south-west of Cornwall. Many of them are intrusive, while others may be interbedded or contemporaneous lavas and ashes. Locally they are known as ' blue elvans,' and are much quarried for road metal. Since they are. older than the Armorican folding, which is presumably of late Carboniferous date, they are often much crushed and schistose. Chlorite and hornblende have re- placed their original augite, and to the abundance of these minerals they owe their dark green colour. Their principal ingredients, in addition to those mentioned, are plagioclase felspar and iron oxides. Olivine has not been found in them in this part of Cornwall, and both augite and quartz are rare. Those which have been most affected by shearing have been con- verted into hornblende-chlorite-schists ; in others the original igneous structures are still decipherable. The greenstones whicsh IGNEOUS BOOKS. 45 lie in the vicinity of the granite usually show some thermal alteration with , production of new minerals ; in other cases the vapours emitted by the granite as it cooled have formed pneu- matolytic deposits, especially along cracks and fissures. The least altered, greenstones of this area show clearly that the original types were ophitic diabases, proterobases and picrites, together with diabase-porphyrites and rocks belonging to the " pillow lava " or spilite class. Examples of all these in much better preservation are common in the- Middle and Upper Devonian of the Plymouth* and Padstow districts. From a petrographical standpoint they may be classified into the following groups, the ophitic (along with the picrites), the porphyritic, and the schistose. The first type is intrusive ; the second may occur as tliin sills or as lavas, while the rocks of the third type develop by excessive crushing from either the first or the second. ?'/i,e Ophitic Greenstones. — These rocks may better be described as uralitic diabases and proterobases, seeing that their structures are sufiiciently well preserved to leave no doubt as to their petro- graphical character. Many examples occur in the neighbour- hood of St. Austell and to the west of this along the southern margin of the granite. The component crystals are sometimes a quarter of an inch in diameter, so that the rocks are rather coarse grained. The larger felspars often show bright cleavages in the hand specimens. As a rule, however, they are not so coarsely crystalline. Remains of augite were noted by J. Arthur Phillipst in the St. Mewan diabase, and may be found also in one or two others. It is of the purplish brown colour usual in the rocks of this group, and is fringed with pale green uralite, compact or fibrous. In nearly every case, however, this mineral has been replaced by hornblende, which may be massive with broad twin planes or may consist entirely of fine acicular crystals matted together to form irregular aggregates. The massive hornblende has often a fibrous border. Yellow green and dark green are the colours of this fibrous amphibole. Brown horn- blende is visible in some of the slides, always compact, and probably for the most part primary; it must have been fairly common in some of these rocks, a fact which indicates some con- nection with the hornblende-diabases or proterobases so common in the Middle Devonian of the district west of Plymouth. The felspar, so far as can be determined, is plagioclase, though some orthoclase may be present, as was indicated by Phillips. + In the least altered rocks it forms mostly good prismatic crystals, yielding rectangular sections with the usual types of multiple twinning. The low refractive index and small extinction angles indicate a considerable abundance of oligoclase, and this is con- firmed by the chemical analyses. Often these eumorphic crystals are broken and torn apart by movement. The felspar is very *'The Geology of the Country around Plymouth and Liskeard' (_Mem. Oeol Surv.'), 1907. t J. Arthur Phillips ' On the so-called ' Greenstones ' of Central and Eastern Cornwall.' Quart Jimrn. 6eol, Soc, vol, sxsiy., 1878, p. 472. % loo. eit. 46 IGNEOtrS BOCKS. tiommonly invaded by swarms of minute pointed needles of green horntleiide, and where the crushing has been severe it may be reduced to a fine granulitic mosaic Apatite is rather common in these rocks, and is conspicuous in the sections, as it occurs in well formed hexagonal prisms. These are frequently bent, broken, and displaced by crushing. Some contain many dark enclosures or cavities filled with chlorite. The iron ores occur in irregular grains or reticulate masses, and must be titaniferous seeiil'g that they are usually more or less completely converted into sphene (leucoxene). Biotite of pale brown colour is often seen in the sections forming dense scaly aggregates mixed with chlorite and actinolite. It may be partly of secondary origin, as in similar rocks in Argyllshire,* but is certainly also developed by contact alteration. Patches of chlorite, biotite, and pale actinolite occur which may be "pilite" after olivine, but this cannot be proved beyond doubt. In the St. Mewan diabase and that of the Black Head, the latter of which lies slightly beyond the southern border of the sheet, quartz occurs in such a way that it must be regarded as primary. la. 16. Ila. 116. III. IV. SiO, .. 50-42 50-41 46-89 46-96 47-68 50-24 TiOj tr. tr. AlsOs ,. 19-10 18-91 20-46 20-53 17-13 19-19 PeO ,. 1103 11-11 11-15 11-18 10-71 1 15-30 FejO, 2-50 2-44 219 2-09 11-73 MnO 0-40 0-42 tr. tr. 42 tr. CaO 5-81 5-90 8-37 8-42 6-28 5-02 MgO 1-80 1-72 5-83 5-91 tr. 0-93 KsO V67 1-60 tr. tr. 2-94 ) NajO 5-13 5-22 3-87 3-80 2-53 I 7-21 LijO 013 Oil J P»05 0-74 0-83 0-31 0-32 tr. 0-20 H,0 (hygro.) .. 0-27 0-30 0-20 0-22 0-33 I 0-80 HjO (comb.) 0.71 0-67 0-77 0-67 67 FeSs 0-43 0-42 tr. tr. — 100-14 100-06 100-04 100-10 100-42 98-89 la. and 16. Duplicate analyses of Greenstone from Sanctuaries near St. Austell, by J.Arthur Phillips (_Qiiart. Jour. Geol. Soc, vol. xxxiv., 1878, p. 472). lid. and 116. Duplicate analyses of Greenstone from Terras, St. Stephens, by J. Arthur Phillips {Quart. Jour. Geol. Sac, vol. xxxii. 1876, p. 176). III. Analysis of Greenstone from Blowing House Hill, St. Austell, by J. Arthur Phillips (Phil. Mag., vol. xli., 1871, p. 99). IV. Analysis of Greenstone from Gewans, St. Austell, by J. H. Collins {Mineralogical Magazine, vol. i., 1876, p. 224). Analyses of three of the diabases of this sheet were prepared by Phillips, and are of great value as showing the chemical peculiarities of these rocks. They are quoted here from his original papers, along with another analysis by J. H. Collins. The first of these represents the composition of the diabase which is quarried at the "Sanctuaries," a little west of St. Austell.t This analysis presents some features unusual in the diabases being exceptionally poor in lime and rich in potash and soda. The alkalies form 6'8 per cent, of the rock; as a consequence * Geology of The Seaboard of Mid Argyll (ilfem. Geol. Surv. ScoUand\ 1909 p. 52. " ' t loc, oit. IGNEOUS KOCKS. 47 of this we find that the microscopic sections are exceedingly rich m oligoclase. This feature is still more marked in the analysis of the Gewans greenstone by Collins, in which the alkalies are T-21 per cent., and is very characteristic of some of the West Cornish greenstones. It is even more pronounced in the diabase of Newlyn (Gwavas Quarry) near Penzance, in which the alkalies are 9-28 per cent, according to an analysis by Dr. Pollard.* It appears also, though less marked, in the proterobases of East Cornwall, which sometimes contain 7 per cent, of alkalies ; some of these rocks, in fact, have chemical affinities with the essexites.t The second analysis is of the greenstone near Terras,J at the western edge of the map, while the third shows the composition of the diabase of Blowing House Hill, St. Austell.§ In these also- the alkali percentage is rather high for the diabases, and these rocks also contain much acid plagioclase of the oligoclase group. The small amount of magnesia and very abundant oxides of iron in the third analysis would indicate either that the material selected for chemical investigation was greatly altered in some way or that the analysis is not quite satisfactory. So far as can be inferred from chemical investiga- tion, the greenstones of the St. Austell area include rocks which are fairly normal diabases with others which contain an unusual amount of alkali felspar. Both in the Land's End and in the Plymouth Sheets the same peculiarities are presented by the intrusive igneous rocks. We append a few notes on the microscopic characters of some of the more important ophitic diabases of this quarter. The St. Mewan. rock, from the old quarries on the hill top, varies a good deal in general character, being in some cases light coloured and felspathic, while more frequently it is dark green (the latter variety is that which Phillips analysed). It is often consider- ably decomposed, and the joint planes are lined with secondary products and stained with limonite. Most of the specimens show ophitic structure, the short rectangular sections of plagioclase felspar being embedded in masses of uralitic hornblende which have no definite form. A slide of this rock in the J. Arthur Phillips collection, which is preserved in the museum of the Geological Society of London, contains a little purplish brown augite, but in nearly every instance this mineral has been con- verted into hornblende which sometimes has a uniform extinction over a considerable area, but more frequently . consists of felted prisms of pale green or dark green colour. Mixed with the hornblende there is often much greenish biotite in very fine scales. The fresh appearance of the amphibole and abundance of brown mica show that the rock has been affected by contact alteration by the granite. There is much apatite in well shaped hexagonal prisms, and these, like the felspar, are often broken * ' Geology of the Land's End District ' QMem. Oeol. Surv.), 1907, p. 35. t ' Geology of the country around Plymouth and Liskeard ' (ifcm. 0eol. Surv.'), 1 907, p. 100. J; J. Arthur Phillips 'On the so-called 'Greenstones ' of Western Cornwall,' Quart. Journ. 6eol. Son., vol. xxxii., 1876, p. 175. § J. Arthur Phillips ' On the Chemical Composition and Microscopic Constitution of certain Cornish Bocks.' PhiloiopMcal Magazine, vol. xli., 1871, p. 99. 48 IGNEOUS ROCKS. and displaced, though there is no pronounced tendency to a schistose structure. Blue tourmaline {as reported by Phillips) appears occasionally in the slides. As might be inferred from the chemical analysis, the felspar is largely oligoclase and some albite is present; this is clearly proved by the low extinction angles and refractive indices of the mineral when in a fresh' condition. One of the slides of this diabase contains a little original quartz. On the opposite side of the highway, not far scnith of this quarry, the diabase is now being extensively worked for road metal. This rock (north-east of Tregongeeves) is very like that described, and has abundance of oligoclase and well preserved ophitic structure. Its hornblende occurs principally in tufted bundles of sub-radiate needles. The rock contains a good deal of granular epidote and leucoxene or sphene after titaniferous iron oxides. It shows on the whole less contact alteration than the Sanctuaries diabase, but a few thin veins of purplish axinite may be observed in the quarry. Both axinite and felspar are often penetrated by acicular hornblende. In addition to secondary green amphibole (fibrous or compact) there is a brown variety of this mineral which is probably primary. The diabase represented on the map by a small outcrop, west of Trevarrick, St. Austell, has also well marked ophitic structure. In some slides there is fresh purple augite, bordered by uralite. In others brown hornblende, which seems to be primary, occurs in addition 'to uralite, fibrous or compact. Biotite, of green and brown colour, is very plentiful in this rock, and has appar- ently been produced by contact alteration of chlorite. Its abun- dance accords with the closer proximity of this mass to the border of the granite. The biotite occurs in well defined plates, and as fine scaly aggregates penetrated by needles of actinolite. These two minerals also are scattered through the felspar in crowds of minute crystals. Apparently this rock is a contact altered proterobase or hornblendic diabase. The greenstone mass at Terras, west of St. Stephens, the composition of which is represented by the second of Phillips's analysis (p. 46) is more variable in character than those nearer St. Austell. Parts of it are clearly ophitic, while other portions have a schistose structure. This rock sometimes contains a little residual augite, but for the most part this mineral is uralitised. The hornblende forms large paramorphs after augite, with occa- sional cores of pyroxene, and is often compact at the centre but surrounded by a frayed border of fine divergent green prisms. Felspar is not so abundant in this rock as in that of St. Mewan, and is not of so acid composition ; it has mostly a refractive index rather above that of Canada balsam and must belong to andesine. The crushing to which the rock has been subjected has reduced the felspar to small irregular grains so that their extinctions cannot be determined. The characteristics of the analysis are thus reflected in the mineral composition of the rock. In the schistose varieties the ophitic structure is lost, and the felspar becomes granulitic. Distinct indications of contact alteration are afforded by the well crystallised and very fresh prisms of green IGNEOUS ROCKS. 49 amphibole which swarm in the felspar, but biotite is much less common here than in the St. Mewan and • Trevarrick diabases. This is to be accounted for by the greater amount of lime and less . alkalies which enter into its composition. The locality described by Phillips as Blowing House Hill (see p. 46) is about a quarter of a mile westward of St. Austell Church. No slides of this rock are in the Phillips' collection at the Geological Society or the British Museum. The rock represented in the fourth analysis (by J. . H. Collins) comes from Gewans, near St. Austell, and probably cor- responds to a small old quarry north-east of Tregorriek. It shows ophitic structure, but is rather fine grained ; the augite is entirely uralitised, but there is some compact brown hornblende which is probably original. The other greenstones of the St. Austell neighbourhood, so far as they have been microscopically examined,- are also of the ophitic type. Quartz Diabases. — Although quartz may be found in some slides of the ' Sanctuaries ' greenstone which is quarried a quarter of a mile north-east of St. Mewan's Church, it is not common in this rock, and is absent from most specimens of it. But in the diabase. of the Black Head,* which lies immediately to the south of this map, and enters it for a short space on the west side of St. Austell Bay, quartz is a normal constituent which may be found in any slide of the rock. This diabase is rather coarse grained with eumorphic porphyritic felspars, some- times a quarter of an inch in length. Most specimens of it are much decomposed ; sometimes they contain granules of fresh augite of pale brown colour, but for the most part this is re- placed by carbonates and chlorite. There is little epidote, and uralite also is exceedingly scarce. The iron oxides are platy or reticulate, and very often covered with leucoxene; pyrites abounds in some of the sections. The felspars are plagioclase, usually too much decomposed for identification, but the freshest have often a lower refractive index than quartz. There are two geiierations of felspar, one porphyritic, the other in the ground- mass. The quartz forms moderately large, irregular masses, often moulded on the felspars; it contains fluid cavities with bubbles, and there seems no reason to doubts its primary nature. Picrite (Serpentine). — The only representative of the ultrabasic rocks known to occur within this area is found at Duporth, on the shore of St. Austell Bay, where it is well ex- posed in the cliffs. This interesting rock has been described by Mr. J. H. CoUinst and by J. Arthur Phillips,^ both of whom have given analyses of it. There is more than one variety, the commonest being mottled with rounded pale green spots (about one-sixteenth of an inch in diameter) in a darker green matrix, sometimes blotched with red. The pale spots are * J. ArtKur Fhillips 'On the so-called 'Greenstones' of Central and Eastern Cornwall.' Quart. Journ. Qeol. Soc, vol. xxxiv^ 1878, p. 475. t J. H. CoUins 'Note on the Serpentine of Duporth, St. Austell Bay.' Mi item- logical Magazine, vol. i., 1876, p. 222 ; also Rep. Brit. Ass. (Plymouth, 1877), p. 68. X J. Arthur Phillips ' On the so-called ' Greenstones ' of Central and Eastern Cornwall,' Quart. Journ, Qeol: Soc, vol. xxxiv., 1878, p. 474. 12979 D 50 IGNEOUS ROCKS. SO soft as to be scratched with the finger nail, and the rock has a soapy feel. In the microscopic slides it proves to be in a state of advanced decomposition. In ordinary light the sections look almost structureless and transparent except, for irregular plates of brown biotite, marked with granules of iron oxide along their cleavages.* In polarised light, however, the apparently, homo- geneous matrix shows well the poecilitic structure (lustre- mottling) of the peridotites; it consists of pseudomorphs after olivine enveloped by the remains of another jnineral which has probably been pyroxene. The olivine is replaced by scaly talc and serpentine, the pyroxene by brown carbonates and nearly isotropic chlorite. The biotite occurs with the pyroxene m the inter'^paces between the grains of olivine and is probably primary. The other ingredients are brown carbonates, iron oxides, and limonite; except the biotite none of the original minerals is left. Evidently this has been a picrite or peridotite containing biotite. The presence of an asbestiform mineral is recorded by Collinst and Phillips; the former has analysed it and . described it as ' duporthite.' The second variety of the Duporth rock is darker coloured, harder, and shows black crystals of augite with fresh cleavage surfaces. The micro-sections contain brownish augite enclosing rounded serpentinous pseudomorphs after olivine. The augite is also penetrated by straight, narrow, lath-shaped pseudomorphs, the' sb,ape of which instantly suggests that they _ represent plagioclase felspar. They prove, however, to consist nearly always of colourless tremolite, and most of the augite plates are surrounded on all sides by an outgrowth of similar white am- phibole with brilliant polarisation colours. Yet the outlines of the rectangular pseudomorphs are quite distinct from those of the olivine grains. It appears certain that in decomposition the felspar has been removed and its place taken by tremolite (sub- stitution pseudomorph). The rest of the rock consists of a nearly isotropic chlorite or serpentine full of innumerable needles of tremolite. Apatite also is fairly common in this specimen, and there are turbid patches which may be saussurite after plagio- clase. It may be noted also that the white tremolite which envelopes and enters the irregular ophitic augites have the same extinction over the whole extent of a single augite plate. This rock has been an ophitic olivine diabase; it shows singularly little foliation or crushing, but on the other hand is very com- pletely decomposed. The abundance and fresh condition of the pyroxene leads to the assumption that the tremolite is a secondary product after olivine. The two analyses which have been made of this rock are given below. From the descriptions given by Collins and Phillips it seems that the specimens analysed were both of the blotched picrite or serpentine ; if that be so the differences between the two analyses are rather striking: They are principally in the relative amounts of magnesia and alumina; the sum of these two com- ponentsis nearly the same in each case. It is now well known that « J. J. H. Teall, ' British Petrography,' 1888, p. 129. t J. H. Collins, ' On Duporthite,' Mineralogical Magazine, vOl. i., 1876, p. 226. IGNEOUS EOCKS. 51 in rocks of this type part of the magnesia may be precipitated with the alumina, and weighed as such, unless special precautions are taken. Probably neither of these analyses is above criticism in this respect. (H) 37-09 trace 19-90 2-02 15-54 (I) SiO, 35-74 TiO, Al»03 12-23 FeO 13-84 FesOs 4-68 MnO .0-98 CaO trace MgO 22-13 NaaO 0-25 KjO trace HjO (hyg) •0.) ... 0-72 H2O (com b.) ... 9 29 P2O6 0-lS trace 15-90 trace 8-65 0-21 10004 99-31 (I) Analysis of the Serpentine of Duporth, J. Arthur Phillips (^Quart. Jour. Geol. Soc, vol. xxxiv., 1878, p. 474). (II) Analysis of the same rock as above. J. H. Collins (Min. Mag. vol. i., 1876, p. 224). The Porphyritic Greenstones . — The rocks of this group never have their structure so well preserved as the ophitic greenstones, no matter where they occur. Their fine grained matrix seems to have yielded readily to crushing stresses and flowed around the phenocrysts, many of which are bent and shattered, forming elliptical and lenticular phacoids with only obscure traces of crystalline form. Probably for this reason also no augite is found in them, and there are no signs of olivine. The felspar phenocrysts may be one-eighth of an inch in diameter. They are often so much decomposed and filled with secondary mica that their composition cannot be ascertained. Of the fresh felspar, however, a very large proportion is oligoclase and albite, having refractive indices lower than that of Canada balsam, small and moderate extinction angles and usually positive optical sign. In some of these rocks albite is exceedingly common, both as pheno- crysts and in the groundmass. This is a feature of the spilites which occur in the Middle and Upper Devonian near Plymouth and in other parts of Britain, and is of so unusual occurrence that it marks these porphyritic greenstones of the St. Austell sheet as having close affinities to the Plymouth schalsteins. A good example of a porphyritic greenstone with much albite is found near Nanphysick, west of St. Austell. At Lanivet and Woodlay similar rocks occur. Chlorite, mixed with dusty leucoxene, is very abundant in most of the sections, and horn- blende may be present as patches of green needles and fibres; neither of these forms good pseudomorphs after any ferro- magnesian mineral. The iron oxides are very commonly changed to leucoxene; pyrites and apatite are both common in these rocks. The porphyritic structure makes it likely the greenstones of this type are lavas or thin sills as distinguished from the ophitic rocks which are thick intrusive masses. Some of them contain rounded areas of quartz and chlorite which are in all probability 12979 !> 52 IGNEOUS EOCKfB. amygdules (Lanivet and Higher Bara). The Lanivet greenstone has suffered contact alteration, and is full of minute scales of brown -bibtite.^ The Schistose Greenstones. — Nearly all the finer greenstones of this area, especially the northern portion of it, have been con- verted into greenstone schists or fine hornblende and chlorite schists in which the igneous structures have been obliterated. The only traces of their porphyritic minerals are lenticular patches of hornblende and of felspar, around which a schistose matrix flows; but this occurs so seldom that it is probable that most of these rocks were not porphyritic. They contain much green fibrons hornblende without crystalline form ; chlorite occurs also especially in the weathered types. The felspar is granulitic and crushed to a very fine grained condition. Quartz is rare or absent, but iroh oxides, more or less changed to leucoxene, and small grains of apatite and pyrites are common in the slides. These rocks are crushed rather than recrystallised, and amphi- bolites with well formed grains of felspar, such as occur in the Scottish Highlands, have not been met with in this area. Many of them have a very well marked schistosity and a platy char- acter; folia of nearly pure hornblende may often be noted. Probably they were originally fine grained, but locally the coarse ophitic diabases have been crushed to schists (as for example at Terras). Examples of this type occur at Lanivet, Tretoil Mine, Kirriers, and Tremore in the northern half of the sheet, and at Leadenhall Wood. • Contact Alteration of the Greenstones. — Where the basic igneous rocks are suificiently near the granite they all show thermal alteration. The commonest new mineral is brown biotite, which seems to replace original chlorite. This is very abundant in the Lanivet greenstone ; it occurs also in great quantity in a diabase from a quarry near the smithy on the Bodmin Road a little west of St. Austell. This mica forms very minute scales which have often hexagonal outlines, and are scattered in immense numbers through the felspars and other components of the altered greenstones. Its presence in most of the ophitic diabases around St. Austell has already been noted. Clear brown recrystallised hornblende is found only in the inner contact' zones, but is well shown by a greenstone^ which Mr. Barrow obtained from a shaft south of St. Ingunger. In this rock the alteration has not sufficed to obliterate the schistosity, which is still very obvious. None of the greenstones of this area has beeru f olind to contain fresh pyroxene of contact origin such as occurs at Tater Du* and other localities in the Land's End sheet; where pyroxene is found in the Bodmin and St. Austell rocks it is either primary or connected with pneumatolytic pro- cesses. The felspar of the greenstones recrystallises under contact alteration, especially when it had previously been re- duced to 'fine granulitic aggregates by shearing, but in none of the rocks sliced from this area has this process gone so far as to T ' Cteology of the Land's End District ' (^Mem. Geol. Surv.'), 1907, p. 37. IGNEOUS KOCKS. 53 produce felspar crystals of any considerable size. A mosaic of small irregular grains filled with biotite is the usual consequence. It seems very probable that the fine acicular green hornblende, so common especially in the schistose greenstones, is in no small measure a contact product. The principal reason for believing this is that in exactly similar rocks from the Newquay Sheet to the west, and the Liskeard and Plymouth Sheet to the east, where granite masses are absent, the place of the hornblende in these greenstone schists is taken by chlorite and calcite. In the Bodmin and St. Austell area hornblende prevails everywhere, except in the Black Head quartz diabase which lies at the extreme southern limit of the area and is furthest from the granite. The green acicular hornblende may be , partly of secondary origin (uralite), but its abundance in the rocks around the granite indicates that a slight rise of temperature favours its development ; but where the thermal changes are more advanced, as in the inner contact zones, the green hornblende tends to disappear and brown hornblende becomes prominent. Ejfects of Pneumatolytic Action on the Greenstones. — Within the contact aureoles the greenstones often contain minerals which indicate the effect of the boric and fluoric vapours which were given off by the granite.* The most characteristic of these is axinite, from which fact we may infer that, in presence of lime, borates or borosilicates of tliat base are more readily formed than of the others usually present in rocks. Tourmaline occurs also, but is less coinmon, and fluorspar is still more rare. Not many of the greenstones of this sheet are known to contain these minerals, and the importance of the axinite formation in the greenstones is quite small as compared with the great develop- ment of axinite veins in the calcareous beds of the Meadfoot series which lie to the north of the granite. The veins in the greenstones usually contain, in addition to axinite, one or more of the following minerals, pyroxene, epidote, hornblende, garnet, quartz, and felspar, while zoisite, zincblende, sphene, and fluorspar are sometimes present. In the quarry of greenstone near Tregongeeves, St. Mewan, thin veins of purplish axinite are common. It is accompanied by feathery green amphibole which penetrates it in innumer- able needles. Quartz occurs also in these veins, surrounding the axinite. The greenstone of Lanivet contains a few colourless spots which are probably axinite, but it is not known to form veins in this rock. Tourmaline of dark blue colour and strong pleochroism occurs in the Sanctuaries and the Terras greenstone as recorded by J. Arthur Phillips,t but only in occasional crystals. J. s. F. * J. J. H. Teall, ' British Petrography,' 1888, p. 169. + ' Geology of the Land's End District ' (Jbfem, Genl. Sun.'), 1907, p. 38. t Quart. Jmrn. Geul. Soc, vol. xxxiv. (1878), p. 473, and vol. xxxii. (1876), p. 76. 54 CHAPTER VII. GRANITE AND ELY AN. Tlie main mass of the St. Austell granite occupies an area of between 30 and 31 square miles, or together witli the outlying patches of St. Dennis, Belowda Beacon, and Penvivian, it com- prises 32 square miles, and is the smallest of the five large granite masses of the West of England. The most elevated portions of the district are within its boun- daries, the highest point being Hensbarrow Beacon, which rises to 1,000 feet above sea level, or nearly double the height of the more elevated portions of all but the immediate killas tracts. In its general physical features, with the exception of Helman Tor (600 feet), it presents no rugged outlines, but consists of a series of low, flat, dome-like elevations separated by broad drainage hollows called moors, as Criggan Moor and Eedmoor, and by steep-sided valleys as in the case of the River Fal, the St. Austell River, and the numerous streams in the eastern part of the granite mass. The subterranean dip of the margin of the granite below the slates is not known with accuracy, but at Carbis, near the Roche Rock, the dip is about 45°, as estimated from the depth at which granite was cut in the shaft at Cornubia Mine.. Judging from the width of the metamorphic aureole on the northern side of the mass it is probable that the dip is considerably less than this in some places, and the general circumstances suggest that in this neighbourhood it flattens out in depth. The outlying patch of the granite forming the picturesque hill upon which St. Dennis stands appears to be an independent in- trusion, while that of Belowda Beacon has the characters of the main mass. In addition to the insular patches already mentioned the granite has sent out offshoots, apophyses or tongues into the contact rocks. Chief among these is the well-known Roche Rock, which is greatly tourmalinised (see pp. 64-66). A tongue of tourmaline granite or aplite is seen exposed in a quarry between St. Dennis and Trelavour Downs. Tongues of granite are said to occur in the Roche Mine. The indented western margin of the St. Dennis outlier is also worth noting. The final phase of eruptive activity is marked by the presence of dykes of elvan, aplite, and pegmatite which occur in both the granite and the killas. At the most elevated points solid granite is exposed at the surface, where it is sciilptured by weathering into the character- istic tors Which form such a feature in the scenery of the granite areas in the West of England. The greater portion of the granite is, however, covered by a mantle of decomposed and fragmentary material derived from its breakdown, and this material varies in nature from a fine sandy material, known as ' growan,' to coarse subangular fragments and blocks of large size which occur to a considerable depth on the slopes and tops of the hills. In the erosion hollows much of the material has been transported from the higher ground, and may GRANITE AND EL VAN. 55 be regarded as true alluvium. The enormous remarkably well- rounded, half-buried boulders, ranging in size up to 36 feet in length and in weight from a few tons up to hundreds of tons, which lie scattered over the moors and pasture lands in such count- less numbers in the parishes of Luxulian and Lanlivery, appear to have been derived from the abrasion and rounding oi che cuboidal blocks into which the granite weathers. These boulders work gradually down towards the hollows, with other detrital material covering the hill slopes. The general form of tors and the loose blocks derived from the granite is determined by the jointing of the region, being the effect of weathering along the fissures, joints, and pseudo-bedding planes of the granite. The jointing is roughly threefold. The principal series of joints or fissures has a bearing about N.E., and corresponds in direction with the lodes of the region. A second series is roughly at right angles to the first, and corresponds with a second series of lodes. The pseudo-bedding is roughly horizontal, or slightly inclined, and the planes vary from a few feet to many feet apart. Another series of joints appears to be present and to correspond with the direction of the principal iron lodes, being about N. 30° W. in the Luxulian district. Small parallel valleys have been formed along the line of the last series in the region of Lanlivery and Tjuxulian. The granite, as a whole, may be described as a grey porphyritic granite in which the large felspars vary from an inch up to four inches in length. The quartz occurs in rather coarse grains; biotite, a little muscovite, and, in some cases, schorl are also present, while the felspar of the ground mass consists of orthoclase and oligoclase. Certain parts of the granite show varieties of texture, while distinct departures from the normal type occur as special phases. In particular should be mentioned the non-porphyritic pale biotite granite on the south side of Hensbarrow Beacon. The extensively kaolinised nature of the granite in the central and western portions of the mass will be referred to in describing the nature of the china-stone and china-clay rock. The other secondary modifications of the granite in these areas are the greisen and schorl rock, also described under pneumato- lytic alterations. In the east the granite is fresh when compared with the china- clay areas of the central and western parts. With the exception of slightly rotted zones and of the development of luxullianite, described under the section dealing with pneumatolysis, the rock may be described as a coarse-grained porphyritic granite, the felspar phenocrysts of which vary from an inch or so up to five inches in length and three inches wide. At Helman Tor and Lockengate the coarse-grained granite contains phenocrysts up to foiir inches in length, giving to the rock a remarkably fine appearance. The weathered surface of the granite near Tregarden Quarry and other places shows that the felspar phenocrysts resist decom- position more strongly than the ground mass and project boldly from the rock. The felspars, as usual in Cornish granite, are arranged parallel to one another, and are more or less horizontal. The phenocrysts frequently show zonary structures, indicating 56 GRANITK AND EL VAN. successive stages in the growth of the crystal. In some cases brown mica occurs along the planes of zoning. While never losing its porphyritic character, except locally, the grain and the porphyritic crystals of the granite become, as a whole, less coarse westwards, and in approaching the china-clay areas the biotite is lighter in colour and often converted to pals hydrated varieties. This bleaching of the biotite is due to the actions to which the china-clay owes its origin. D. A. MCA. Many specimens have been examined microscopically by Dr. ■Flett, who reports upon its general characters as follows : — They often contain large phenocrysts of orthoclase felspar, which maie conspicuous white spots on polished or dressed sur- faces of the stone, These are usually Carlsbad twins, with fairly perfect crystalline faces. Large porphyritic crystals of quartz are not rare '{e.g., at ■Gready), but they are less perfectly shaped than the felspars. The matrix consists of biotite, muscovite, albite, orthoclase, and quartz, with a varying amount of tourmaline. Any of these minerals may occur enclosed within the porphyritic felspars, ■sometimes with a zonal arrangement. Apatite, zircon, and •magnetite are constant accessory minerals, while cordierite, topaz, andalusite, and fluorspar are frequently present. In the fresh and well-preserved granite of the quarries at Gready and Golden Point, near Luxulian, and in Dyer's Quarry the felspars are white or grey, and are of two kinds — albite and microperthite. As in the granites of Land's End and Scilly, a form of plagioclase, very rich in soda, is abundant; it contains a little lime (as the bulk analyses of the granites show), but its refractive indices are never above those of quartz, and- conse- quently it belongs to the felspar series from oligoclase-albite to albite. The bulk of the felspar and all the large phenocrysts are orthoclase, veined with albite (microperthite). The soda felspar often shows good polysynthetic twinning in these veins; the orthoclase is simply twinned on the Carlsbad plan. Much of the albite also occurs as small, well-shaped crystals, with the usual complex twinning. ' These crystals are of earlier formation than the microperthite, which, except when it occurs as phenocrysts, is always of irregular shape. Professor Busz* has recorded the crystallisation of albite on the surface of orthoclase in the pegmatitic veins of the Gready Granite, and very perfect crystals, though small, may be found in such situa- tions. t Microcline is very rarely seen in the Cornish granites, but traces of cross hatching may be found occasionally in the larger perthite crystals. The biotite, which is black or bronze coloureid in the hand specimen, is reddish brown or jrellow in thin section. It contains Uthia, and may be assigned to the lithionite group; very strongly (Jeochroic halos occur in it around enclosed zircons. The mus- covite is always colourless and transparent. Parallel growths * K. Busz, ' On the Granite from Gready, near Luxulian.' Rep. Brit. Au., 1904, p. 663. t S. Haughton, ' Notes on a Compariaon of the Granites of Cornwall and Devon , with those of Leinster and Mourne.' Jour. Boy. 6eol. Soo., Dublin (1867), vol. ii., p. 106. GBANITE AND EL VAN. 57 between the two micas are very frequent; sometimes they are joined along a plane of basal cleavage ; at other times the centre of the growth is a red-brown biotite, while the whole exterior is muscovite, and there is no sharp demarcation. The muscovite is not unfrequently simply twinned, and pleochroic halos occur ' in it of a weak greenish colour. The abundant quartz, which is transparent and vitreous in appearance, is filled with minute cavities, usually of irregular shape, each containing a liquid bubble and often also a small cubical crystal. It sometimes occurs as rounded spots enclosed in the felspar, and adjacent spots may have the same position of extinction, but true micropegmatite is very rare in these rocks. , Of the accessory minerals zircon is interesting because the high radioactivity of the Cornish granites depends principally on the presence of this mineral. When enclosed in biotite, muscovite and tourmaline, it, is surrounded by pleochroic halos. Apatite is fairly abundant, and occurs in irregular grains rarely with good crystalline form. Magnetite is invariably present in- small amount, and pyrites especially in the altered rocks. Much interest attaches to cordierite, andalusite, and topaz,, all of which are common in the granites of Cornwall, though rare in those of other parts of Britain. Of these, cordierite is the only one which can readily be detected in the hand specimens; its crystals are pseudo-hexagonal prisms with plane end faces, and are usually changed to soft dark green aggregates of muscovite and chlorite (pinite). The occurrence of these minerals seems to indicate that the granite has dissolved considerable amounts of the slaty killas which surrounds it. Many fragments of baked slate are found within the granite, some being a foot or more in diameter, but most of them are much smaller than this. They usually contain andalusite and cordierite, and often the granite in their vicinity is especially rich in these minerals. Their rounded shape indicates that they have undergone absorp- tion in the magma. 'The andalusite and cordierite, however, are not grains detached from these hornfelses, but well-shaped crystals which have crystallised from solution.* . In the St. Austell area several granites contain cordierite in a fresh condition. It was first reported from the granite of Gready by Professor Busz.t It crystals are six-sided, and consist of three interpenetrating twins. The mineral is colourless and transparent in section, resembling quartz in appearance, but easily distinguished by its characteristic weathering and the yellow pleochroic halos surrounding enclosed zircons. It is never altogether fresh, and sometimes occurs only as minute cores in the centre of pinite aggregates. Quartz and biotite are the commonest enclosures. Other granites which contain fresh cordierite are those of Golden Point Quarry and of PentrufE, on Carclase Downs. Andalusite occurs in the granite of Gready and a few other places in this sheet, but is much less common than in the Land's End area. The crystals are rhombic prisms or sometimes * ProfesBor Lacroix ascribes the same origin to the cordierite of the Pyrenean granites. ' Le Granite des Pyr€n6es et ses Fh€noilietteB de Contact.' Bull. Carte Geol. France, No. 71 (1900), p. 17. + loo. eit. 58 GKANITE AND ELVAN. irregular grains, and they very usually have a rosy colour and strong pleochroism, especially at their centres. The outer por- tions of the crystals and some of the smaller grains may be colourless. The andalusite rarely contains inclusions. It weathers to white mica. In the granite of Golden Point Quarry long prisms of andalusite may be found penetrating the large twinned crystals of cordierite. Topaz in grains and small clusters of grains is very frequent in the granites of this map ; in fact, it seems to replace to some extent the andalusite which is more common elsewhere in Corn- wall. The two minerals have much in common, the former being a silicate of alumina (AU SiOj) while the latter has some fluorine instead of oxygen (Al2Si04F2). This indicates that in the magma from which the St. Austell granite crystallised iluorine was more abundant than usual, a fact which may be connected with the large development of kaolinisation in this area. . Of the localities where topaz occurs in the granite the following may be men- tioned : Dyer's Quarry, Menacuddle, Melangoose, and Castle an Dinas. The mineral is always clear, colourless, and fresh, except that thin tfilms of white mica are sometimes forming along its cleavages and borders. It is easily recognised by its high refractive index and perfect cleavage ; small grains of colourless andalusite may best be distinguished by their negative optical sign in convergent light. The topaz rarely contains enclosures except small prisms of zircon and fluid cavities, which are often of large size and irregular shape. The larger grains have fre- quently fairly perfect form, and yield sections which are square or rectangular, with their corners truncated. Like the andalu- site and the cordierite, these crystals are undoubtedly primary, and belong to an early period of crystallisation before the black mica of the rock had completely separated ; but they are later than zircon and, perhaps, apatite. Topaz also occurs, however, mixed with white mica and fluorspar in aggregates which are of very late formation, and belong to the pneumatolytic period which followed the consolidation of the rock. Although not invariably present, tourmaline is so widely dis- tributed that it may be regarded as a normal constituent of the granites of this area. Its colour varies greatly, brown, yellow, blue, and lilac being the commonest shades, while it is sometimes green or colourless. Very often these colours alternate in well- marked concentric zones, the deep brown kind nearly always forming the centre of the crystal. Strong pleochroic halos are frequent in it, as in the biotite; the tourmaline is never decom- posed. Microscopic sections show that the sequence of crystallisation in these granites presents some interesting features. The earliest minerals are zircon, apatite, and magnetite, which occur as inclu- sions in all the others ; biotite follows, and is succeeded by muscovite; after which come oligoclase-albite and perthite, and ultimately quartz. This is the normal order of consolidation. Andalusite, cordierite, and topaz are early minerals preceding white mica, but probably contemporaneous with part of the biotite. The tourmaline, white mica, and topaz have a long period of formation ; this is best exemplified by the two first-' mentioned. The tourmaline began to crystallise with the biotite. GKANITE AND EL VAN. 59 and may be found enclosed in felspar ; it went on crystallising till the orthoclase and even the quartz had separated out. It is not uncommon to find shapeless masses of tourmaline enclosing idiomorphic crystals of quartz, orthoclase, and albite even in rocks whic'h may be regarded as quite normal types of Cornish granite, and not specially altered in any way (Fig. 1, PI. I.). .Sometimes an early crystal of tourmaline has been partly surrounded by felspar and protected in this way from subsequent deposit; such crystals are idiomorphic. This long period of growth is the cause of the ill- defined shape of the totirmaline crystals of the Cornish granites. The zonal bands of the inner portions of the tourmaline crystals often indicate that they started as idiomorphic crystals at a time when a considerable part of the rock was still liquid. The outer zones become progressively more and more irregular. These phenomena are still more clearly shown by some of the elvans which contain tourmaline. It is evident that the schorl is a primary mineral to a large extent, and though it may represent biotite, it does not replace it in every case. In the schorl rocks it is certain that much of the tourmaline was formed in place of previously existing biotite, but in the granites part of the tourma- line is a primary mineral. Precisely the same phenomena are shown by the white mica. It begins to crystallise after the biotite, but before the felspar, and goes on forming till the felspar and the quartz have ceased. It is not uncommon to see poecilitic plates of muscovite filled with quartz grains and small crystals of felspar. The muscovite also makes networks or spongy masses with uniform extinction spreading through the alkali felspar as if the two minerals were of simultaneous formation as a regular intergrowth. This kind of muscovite is quite different in habit from the minute scales which are so frequent in the felspar of Cornish and other granites, and may be of secondary origin. In this continued crystallization of tourmaline and muscovite it is not difficult to trace the- operation of the gases which were contained in solution in the magma. Both these minerals contain hydrogen and fluorine ; the tourmaline is also rich in boron, and there is abundant evidence that vapours containing these elements were given off in large quantities as the granites cooled. They produced very extensive post-consolidation changes in the granitic rocks, but even during the crystallisation they were operative and largely determined the mineralogical composition of the rock and the sequence of its constituents. To the post-consolidation or pneumatolytic stage in the history of the granite, the fluor spar which is so abundant in many speci- mens from the neighbourhood of St. Austell is to be ascribed. Though frequently colourless it may be violet or dark blue, and is then conspicuous in the hand specimens; the crystals are never large, and have regular shapes only when they have formed in cavities. The darker coloured crystals may show zonal (Fig. 5, PI. I.) and hour-glass struetuies, and a weak anomalous double refraction is very frequent. The fluor spar is very common as grains scattered through the felspar, especially the plagioclase; it may also be 60 GEANITE AND EL VAN. found in thin laminae interposed in the cleavage planes of the muscovite. Its principal method of occurrence, however, is as an interstitial deposit in cavities which may have been of miaro- litic origin or formed by the removal of other minerals euch as felspar. Professor Bonney, in his microscopic study of 'Trowles- worthite, the best known fluor-bearing granite of the west of England, was led to the conclusion that the fluor spar replaces original quartz, and this may partly be true of the rocks near St. Austell. The fluor spar occurs in nests or clusters which have no very well defined outlines ; it is always accompanied by muscovite, topaz, tourmaline and more or less quartz. These minerals indicate that gases containing fluorine chiefly were at work, but for the formation of the tourmaline some boron must have been present also. Enclosures of fine grained Granite. — Besides the black lumps of micaceous hornfels which are so common in all the Cornish granites, there are also small rounded pieces of a dark fine granite which must have consolidated before the main mass, and has been disrupted and partly dissolved by the invading magma. They are very rich in brown biotite, and have consequently a dark grey colour. Small phenocrysts of biotite and of plagio- clase felspar occur in them ; the latter are sometimes andesine, and are more basic than the felspars of the normal coarse granite. Muscovite is common in these rocks, but neither topaz, cor- dierite, nor andalusite occurs in them, and the absence of tour- maline is even more remarkable. This distinguishes these older granites from the fine grained granites which are intrusive into the normal coarse granite of the Land's End and of Scilly, but similar granites were found by Mr. Barrow* to occur as inclu- sions in the granite of the Scilly Isles. In J. Arthur Phillips' papert on concretionary patches and fragments of other rocks contained in graiiite he has given analyses of the granite of Oready and of a dark ovoid inclusion in it. These analyses are quoted here. He has noted thai the I. II. SiOz 69-64 65-01 A1,0, 17-35 17-37 Fe^Oa 1-04 4-95 FeO 1-97 1-86 MnO trace trace CaO 1-40 2-11 MgO 0-21 \M K2O 4-08 1-82 NaaO .B-51 4-14 \ trace trace HjO (hygr 0.) ".'. 0-13 0-18 H2O (coml 3.) ... 0-59 1-25 99-92 100-03 Sp. grav 2-72 2-73 I. G-ranite, Gready, Cornwall (Anal., J. Arthur Phillips). n. Dark inclusion in Gready Granite (Anal., J. Arthur Phillips"). dark inclusion is a fine granite of rather more basic character * ' The Geology of the Scilly Isles ' (^Mem. Geol. Surn).'), p. 8 (1906). •)■ Quart. Jour. Geol. Soc, vol. xxxvi. (1880), p, 7. GBANITE AND ELVAN. 61 than the main mass, that it contains more plagioclase felspar, and that tourmaline seems to be absent. J. s. F. Varieties oe Granite. The granite, with the exception of these secondary modifica- tions, is remarkably uniform in character, but distinct phases or possibly separate intrusions, the boundaries of which are diificult to map, are met with. The most definite example is that of Hensbarrow Beacon, where on the Downs immediately to the south of the Beacon, a medium grained non-porphyritic granite with pale biotite occurs over an area of about 50 acres, enclosed in the broken line shown on the map. The blocks of this granite which lie scattered over the Downs are broken, trimmed, and used for building. A variety occurring at Chilbrook,. near Tremodrett Mill, a mile and a half from Roche, is a non-porphyritic greisenized tourmaline granite. A small microgranitic or aplitic intrusion occurs within the broken line at the top of the hill above Corgee, one and a half miles south-west of Helman Tor. The rock is a fine grained aggregate of quartz and felspar with scattered needles of tour- maline, which take the place of mica. It has been quarried in a small way for building material. In some of the china-clay pits thin veins of aplite are occasionally seen. The independent intrusion of granite on which iSt. Dennis Church stands has characters difEerentiating it from those of the main mass. It has a somewhat variable texture, but may be de- scribed generally as a fine grained porphyritic granite of a dark brownish hue. It is very tough, but does not yield well shaped stones for building owing to its poorly developed jointing. The felspars (orthoclase) varying up to an inch or so in length are tinted or colourless, and are set in a fine grained groundmass of quartz, felspar, and biotite. A characteristic of the granite is the abnormally large size of some of the grains of quartz which occur as porphyritic crystals in the mass, and suggest a rock allied to granite-porphyrites . , While the granite outlier of Belowda Beacon is similar to that of the main granite mass it is somewhat finer in grain, and the small outlier of Castle an Dinas is a fine-grained porphyritic granite with sedimentary inclusions and tourmaline. Exceptional pegmatitic modifications of the granite occurring as veins, are found on Trelavour Downs and on Tresayes Downs. At Tresayes Downs there is a wide extremely coarse pegmatite vein in the killas a few yards from the margin of the granite. It consists mainly of enormous orthoclase crystals, roughly parallel and arranged vertically, some of which are graphically intergrown with quartz. Some quartz occurs interstitially fre- quently associated with tourmaline and a little fluorspar. There is also a little pale mica. The vein has a north and south direc- tion nearly parallel with the margin of the granite at this place, and is nearly 50 yards in width. The vein was formerly worked for felspar for use in glass making, but the work was abandoned about 1880. 62 GRANITE AND ELVAN. The following is an analysis of the felspar by Phillips : •?- SiOj 65 AljOa FejOs CaO MgO K2O Na«0 H,0 19 0-5 1-57 trace 10-37 2-4 0-83 According to Mr. J. H. Collins, another pegmatite vein occurs on Kernick 'Hill, in the Treviscoe Valley.* On a small scale pegmatite veins occur in other places, but have not been of any commercial importance. Instances are to be found in Kestles China-stone Quarry, near St. Dennis, and in the Bunny Mine, on Hensbarrow Downs. Veins of pegmatite can be seen in the great quarries of Gready and Colcerrow, near Luxulian, where they often contain cavities in which well-termi- nated crystals of the component minerals are found. Dr. Flett states that these are principally a white or creamy perthite, on the surfaces of which small prisms of albite are placed in parallel growth; quartz in hexagonal prisms; apatite in beautifully perfect crystals often showing very numerous faces ;t gilbertite in radiating rosettes ; tourmaline, fluorspar, and muscovite. Professor Busz| notes that the apatite is of a pale sky-blue colour, and in the pegmatite veins occurs intergrown with tourmaline; the fine crystals come mostly from miarolitic cavities in the rock. In the granite of Trelavour Downs, near St. Dennis, there is a very coarse vein of dark brown mica, which is here and there associated with quartz and felspar. This vein is mentioned by De la Beche,§ and is stated to have been worked for lithia. Fig. 7. -% — r %r IPOOT Diagram illustrating the cross-sectional arrangement of mica vein on Trelavour Downs. According to Mr. Collins, the vein has an east and west direction. The structure of the vein is remarkable, and exhibits a segre- gation banding. Thus, near the country rock the vein consists of medium-grained dark-brown mica and pink felspar, the rock being massive or finely banded. Upon this are imposed layers of fine and then coarsely crystalline mica, while the central portion of the vein consists of coarse felspar, mica, and quartz. * ' The Hensbarrow granite district,' 1878, p. 9. t U. H. Solly. Apatite from a new locality in Eastern Cornwall, Mn Man vol. vii. (1887), p. 141. " •'■' K. Walter. ' TTeber Apatit vom Epprechtstein in Bayern und von LuxuUian in Cornwall.' Neues Jahrbuoh, B.B. xxiii., 1907, p. 581. t loo. cit. § ' Report on the Geology of Cornwall,' etc. (>7e/«, 6eol, Siirv.') GRANITE AND EL VAN. 63 An analysis of the mica in this rock made by Dr. W. Pollard in the laboratory at Jermyn Street in 1906 shows it to contain I'Sl per cent, of lithia (LijO). D. A. moa. The north-eastern part of the St. Austell granite retains its normal composition and texture until quite close to the margin, where the rock seems a little less coarse. Only one actual junc- tion is exposed, and here the rock seems much finer, but it is too much altered for its original characters to be determined. To the south of the great alluvial-flat of Eed Moor the granite seems on the whole fairly sound and comparatively free from greisen- lines and tourmalinisation, as may be seen on the ground about Kilmar Tor ; but, on the north side of the Moor, the granite is traversed by numerous quartz-schorl veins. Large blocks of the latter are common on the Moor, having been either turned up during the stream-tinning or gathered from the fields and dumped on the edge of the great flat. Q,uartz-schorl rock is specially abundant on the ground to the north of Bokiddick, where it is seen built into the field walls ; in many cases it forms thin films in the granite, the latter showing little trace of true greisen action. This mode of occurrence of the schorl is specially well seen in the granite quarry that is situated some 300 yards south of Reperry Cross, where the six roads meet. Specially fine examples of radial masses of schorl needles may be obtained a little east of the old chimney of Trebell, or Mary-Louise, Tin Mine; they are indeed good enough for museuni specimens. Close to the high road at the north-west corner of Conce Moor, due south of Lanivet, the marginal portion of the granite is more or less koalinised ; but much of it is so red-stained that it does not seem suitable for china-clay. It is at this point that the actual junction with the killas is seen, both rocks, however, being completely decomposed. In the ground about Conce Moor a fair number of loose blocks of a rock allied to luxulianite have been met with; the finest occur on the more southerly of the two small isolated granite patches that rise like small islands from the surrounding alluvial deposits. The blocks are lighter in colour, and contain less schorl than the type rock, though it is composed apparently of the same minerals. A small patch of similar material occurs at an old adit, close to the chimney of Trebell Mine, but it is greatly deconiposed. The mode of occurrence and underground extension of the northern portion of the granite is interesting on account of the wide extension of the altered rocks along a portion of its margin in this area. Along much of its margin the granite must plunge down rapidly beneath the killas, and probably ends off altogether, for the breadth of the aureole of alteration is singularly constant. But from Red Moor westwards its true limit is more difficult to trace. The roof of the mass clearly dips down at a low angle below the marsh, much of which rests on a killas floor, while the latter forms the actual surface for some distance north of the Moor. But the killas-roof cannot be of any great thickness here, for a shaft near Lesquite pierced the killas and reached the 64 GRANITE AND ELVAN. underlying granite. Ifo plans of the trials appear to have been kept, and the exaot depth could not be ascertained. To the west of this isolated hill of granite the northern margin of the intrusion must again plunge steeply down, for no marked extension of the aureole of alteration is seen here ; but as Lanivet is approached the aureole widens rapidly. This is shown by the widespread alteration of the calcareous bands. As the latter are peculiarly liable to alteration by heating, this extension might be ta'ken as due simply to the nature of the rocks ; but fortunately at one point a very fine flinty biotite-hornfels has been developed, clearly proving the underground extension of the granite, though at a great depth. The fine hornfels occurs in a little scar on the right-hand side of the road below the great quarries near Tremore, that have already been described. Indeed, at Withiel Mill, still further north, there are several thin films of a dark calcareous mudstone that have been altered to some extent by heating; the adjacent dark killas, too, is greatly hardened, although no brown mica seems to have been developed. From this point the granite appears to recede southwards, for further West the normal killas shows little sign of hardening ; the intru- sion, however, still appears to extend undergi'ound a considerable distance north of the observed outcrop at the surface, for the alteration of the calc-flintas still continues over a wide belt of ground. The description by Mr. TJssher of the southern part of the St. Austell granite in which important china-clay works occur will be found in Chapter IX. G. B. Pneumatolytic Alteration of the Geanite. One of the most remarkable alteration-types of the granite is the tourmaline-quartz rock, or schorl-rock, which occurs in such exceptional abundance in the St. Austell region. In most of the tourmaline-bearing rocks that mineral is of secondary origin, and occurs as a metasomatic replacement of mica and felspar in the vicinity of veins. In some cases it appears to be an original con- stituent of the rock. The varieties of the schorl-rock are often very handsome and suitable for use as ornamental stone. The most beautiful variety is that known as luxulianite, from the fact of its occurring largely in the parish of Luxulian. It is from a large block of this rock that the sarcophagus of the Duke of Wellington was cut. A modification of this rock, containing fluorspar, is known as trowlesworthite. The ordinary schorl-rock, of which the rugged mass of the Roche 'Rock is composed, consists of tourmaline (both blue and brown) and quartz. As a whole, it is of remarkably uniform texture, and is traversed by thin cracks or lines of rifting running in an east and west direction. In some cases these cracks are filled with schorl, on each side of which the rock is very sehorlaceous but shades off into a more siliceous aggregate of schorl and quartz at a distance from the fissure. The presence of kaolin in some of the schorl rock dug up near the Roche Rock appears to corroborate the evidence that the GRANITE .VND ELVAN. 65 whole schorl rock mass is derived from the tourmaliiiisation of a granite apophysis which are intruded along one side of the calcareous band represented by the calc-flinta shown on the map. The sedimentary rocks in the vicinity show tourmalinisation. At the western end of the rock there occurs tourmalinised killas- breccia cemented by quartz. Tourmalinized granite is widely spread in the central and western parts of the mass. In many of the china-clay pits it occurs as veins and masses {e.g., Singlerose and Lantern Clay Works) traversing the decomposed granite, while the Carlo- iquitor Eock, north of Eetew, at the western end of the granite mass, and the schorl rock of Burngullow Common (St. Mewan Beacon) are similar in character to the Roche Rock, all of which are referred to by early writers. The alteration of granite to china-stone and to china-clay is described in the section dealing with those commercially useful materials. D. A. mca. Dr. Plett has examined microscopically a number of specimens of altered granite from the region, and contributes the following notes: — The changes which have been produced in the granite by vapours passing through it after its consolidation are of three sorts. The first is tourmalinisation, which is characterised by the formation of abundant tourmaline and quartz, replacing felspar and mica. The second type is greisening, in which white mica with quartz are formed at the expense of felspar ; the third is kaolinisation, in which the felspar passes into kaolin, white mica, and quartz. Topaz appears as a new product in many of these rocks, but never in such quantity as to give rise to topazfels, an aggregate of quartz and topaz found in some of the mining districts of Saxony. Between each of these altered types and the unaltered granite there are transitional forms in which the original minerals and structures of the rock are more or less completely preserved. Moreover, these pneumatolytic modifica- tions of the granite are not sharply distinct from one another ; schorl rocks, for example, often contain white mica, greisens'usually are rich in tourmaline, and much tourmaline and quartz occur in connection with the kaolinised granites which are worked for china-clay. Tourmalinisation. — Excellent examples of this process are furnished by many parts of the St. Austell granite mass. The schorl rock of Roche consists essentially of quartz and tourmaline. No remains of the original granite structure can be traced in it, and if the rock was formerly porphyritic like the majority of the granites of this district it has lost this character completely. Its felspar also has disappeared, and the rock consists now principally of quartz and tourmaline with a little apatite and iron oxides ; white mica was not found in any of the specimens sliced. The quartz forms a mosaic of grains entirely irregular in shape, and filled with small cavities containing a liquid, a bubble and sometimes a mmute crystal. The tourmaline shows more idiomorphism, and some of the smaller crystals have fairly perfect forms, but the larger have never well defined faces. They are always intensely zonal, the colours being principally blue and brown with occasionally greenish shades produced by the mixture of these ; fringes of nearly colourless tourmaline sometimes surround the larger crystals. Usually the centres are brown and the outer zones blue, but this is not invariable as sometimes these colours alternate, and crystals may be found which have a blue core surrounded by a zone or zones of brown, while the exterior again is blue. In the quartz there may be minute needles of pale blue, lilac or colourless tourmaline. Brown tourmaline contains magnesia in fair amount and it is reasonable to infer, as had been done by Professor Bonney* and * T. G-. Bonney. ' On the Microscopic Structure of Luzullianite,' Min. Mag., vol. i. (1877), p. 216. 12979 E 66 GRANITE AND EL VAN. Mr. Scrivenor,* that it has been formed at the expense of biotite, the only mineral of the granite which could yield this substance; the blue tourmalme contains more alumina and alkalies, and must have derived part of its com- ponents from the felspar. The tourmaline contains far fewer liquid enclosures than the quartz, and its inner zones are often idiomorphic, whUe the outer ones have little regularity of form. Both in the brown and the blue tourmaline there are many intensely pleochroic halos around small enclosed crystals of zircon. The Eoche Rock is a very typical example of the granular schorl rock which is so common in Cornwall ; this type is found in veins or lining fissures and also in irregular masses like that which occurs at Roche. Another type of schorl rock, differing in microscopic structure from that above described, is found at Carngrey and in a few other parts of this sheet. In this the quartz forms a mosaic of small irregular grains ; the tourmaline occurs as long thin tapering needles which have good hexagonal cross sections. The colours and pleochroism range from lilac to deep indigo blue, and the needles are arranged in spreading tufts and radiating clusters which penetrate the quartz in all directions. Here and there small grains of yellow or brown tourmaline can be seen, always very irregular in shape ; they are presumably original and have -apparently suffered corrosion. Fringes of blue tourmaline usually surround them. This kind of schorl rock presents many analogies to luxuUianite, from which it differs essentially in containing no felspar. The quartz tourmiline rock of the finer veins which traverse the granite and killas presents a great variety of microscopic structures. It is sometimes a fine granular aggregate ; more frequently the schorl occurs as minute needles matted together in a matrix of quartz. Many of the veinstones known as " peach " to the miners are of this nature, and this type is often brecciated by repeated movements of the walls of the fissures in which they were laid down. Sometimes the veins have a comby structure with large prisms of tourmaline standing perpendicular to the edges of the vein and embedded in a matrix of quartz or quartz with fine tourmaline. Large blocks or nests of xadiate tourmaline prisms occur in some of the china clay pits ; their interstices may have been filled with quartz which has been dissolved away at a later period. Dr. Butler describes similar masses of acicular tourmaline with kaolin entangled in their meshes. The beautiful tourmaline granite which was named luxuUianite by Pisani,t has been described in a special paper by Professor Bonney,J and is referred to in most works on descriptive petrology. The original locality for it is Treven- naok Farm,§ about a mile and a half south of the village, where it occurs as loose blocks strewn about the fields. Rocks of very similar type have been described from the Land's End district,! ^^^ occur in other parts of Cornwall, though they are by no means common ; they seem to have been formed along veins or fissures up which gases were rising. The large felspars are orthoclase with microperthitio structure and occur principally as pink phenocrysts, Carlsbad twinned. Their outlines are fairly perfect though most of them are losing their crystalline form by pneumatolytic solution. The groundmass consists of quartz and tourmaline with little residual felspar, and the process of tourmalinisation has evidently been arrested at the stage when the finer part of the rock had been nearly completely reconstructed whUe the porphyritic minerals were still in large measure intact. No biotite is found in the rock and it is by no means certain that this mineral was originally present ; topaz, muscovite and fluorite are also absent from all specimens I have seen. The tourmaline is of two kinds ; it occurs as irregular grains of dark brown colour and as fine blue needles forming stellate groups embedded m quartz. (Fig. 2, Plate I.) The brown tourmaline is seemingly primary, and, as Dr. Butler has pointed out, is suffering • J B. Sorivenor, ' On the Granite and Greisen of Oligga Hesd,' Quart. Journ Geol. Soo.,_ vol. lix. (1903), p. 151. t Piaani, Comptes Sencku, vol. lix. (1864), p. 913. J loo. oit. § J. H. Collins. ' The Hensbarrow Granite District ' (1878), p. i. II 0. Le Neve Foster. ' On a Rook resembling Luxqllianite from St. Just,' Trans, Boy. Cfeot, Soo, Corn., vol. X. (1879), p. 8.' - - . GBANITE AND ELVAN. 67 resorption and eroaion, as is indicated by ■ its very irregular shapes and concay© outlines * The stellate blue tourmaline of the matrix often forms dense star-like growths which give a black cross in polarised light like " a spherulite. Its colour varies, being blue, bluish green, or lilac for -th6_ extraordinary ray, and sometimes yellowish. Many of the needles are stained brown by deposits of secondary iron oxides but there is always a marked difference in shade between the early and the latter schorl. The tourmaline stars very frequently are implanted on the surface of felspars and of the older brown tourmaline ; both of these minerals have deep rounded indentations filled with stellate schorl and quartz. Evidently the new tourmaline is being formed partly from the felspar and partly from the older tourmaline. The quartz is a coarse mosaic of polygonal grains which often show zones of growth indicated by dusty bands of fluid cavities and small tourmaline needles as pointed out by Dr. Butler. Iron oxides, weathered cubes of pyrite and small grains of apatite with a few small zircons are also present in the rook. In some of the slides we have found small dark brown tetragonal prisms which can be referred with some certainty to tinstone ; they are perfectly idiomorphic and lie -in the secondary matrix. In luxullianite the process of metasomatic replacement has stopped at a half- way stage. There are other rocks in this district which show the further alterations in the conversion of porphyritic granite schorl rook. At Single Rose Clay Works, near St. Austell,t schorl rooks occur in which large white quartz pseudomorphs with- very little tourmaline, lie in a matrix of granular ; quartz and tourmaline of much darker colour. The shapes of the felspar phenocrysts are only vaguely defined, and in them there are some patches of kaolin penetrated by radiate idiomorphic prisms of quartz. Here the felspars have been destroyed, but the porphyritic structure of the granite has not yet vanished. Very similar schorl rooks have been described from Trevalgan. J There can be little doubt that by continued action of mineralising vapours the large white quartz pseudomorphs ultimately also disappear, and a granular schorl rock is the final product. Greisening, or the conversion of granite into an aggregate of quartz and mica, is a common phenomenon in all the mining districts of Cornwall, and is very well exemplified in several localities in this sheet. Le Neve Foster§ has stated that ' Criggan, about 2 miles E.N.E. of Boche, on the northern edge of the great Hensbarrow mass of granite, affords the finest display of greisen in the county of Cornwall.' At the Bunny mine, about 2J miles south of Roche, Qiere is also much greisen. Slides of the rooks collected at the latter locality show various stages of the process of alteration. The least altered granite contains quartz, orthoclase (microperthite), albite or oligoclase-albite, white mica, and a little brown tourmaline and magnetite. There is also much topaz in this rock, partly in large grains with well-defined shapes, though not exactly eumqrphic, and partly in spongy masses which spread through the felspar in such a way as to make it certain that the topaz is a secondary product. The compact, large grains are primary, and where they abut against quartz in the sections, they retain their shape, but when they are in contact with felspar they send outgrowths into it ; these outgrowths are usually in optical continuity with the original topaz, and they are filled with small irregular enclosures of quartz. In the greisened rocks the same minerals occur, but the felspar becomes very scanty, and is replaced by aggregates of quartz and white mica, which at first preserve the shapes of the felspar, but in further development become more coarsely crystalline and have no definite forms. Secondary topaz continues to increase in amount, but the quantity of the tourmaline remains very much the same as before. At the same time, much fluorspar makes its appearance in the rock ; it has a well-marked purple colour, and often forms rather large patches in which small rectangular sections of musoovite are embedded in * Francis II. Butler. ' Kaolinisation and other Changes in West of England Rooks,' mn. Mag., vol. xv. (1908), p. 128. + J. J. H. Teall. ' British Petrography ' (1888), p. 315. t Clement Eeid and J. S. Flett. ' The Geology of the Land's End District,' Mem. Cfeol. Survey (1907), p. 55. § 0.,Le Neve Poster,.' On some Tin Stookworks in Cornwall.' Quart. Journ. Ge'ol, Soc, vol. xxxiv. (1878), p. 657. 12979 E 2 68 GRANITE AND EL VAN, perfect ophitic fashion. (Fig. 6, Plate I.) At other times it spreads along the cleavage planes of the white mica. Very finegrained, almost crypto- crystalline, aggregates of a pale yellow mineral are also visible in this rock (7401) ; they resemble kaolin, but have too high a double refrac- tion for that mineral. In the hand specimens these patches have a faint greenish-yellow colour, and are very soft ; it is probable that they are gilbertite. It ij a curious fact that in this stage, though the potash felspar (orthoclase) has almost entirely vanished, there is still much beautifully clear soda felspar (albite) in the slides ; evidently the latter mineral has much greater powers of resisting the pneumatolytic changes than the microperthite. The perfect greisens from the Bunny mine (7400) contain no felspar nor any recognisable pseudomorphs after it. They are essentially granular aggregates of quartz and white mica. The quartz is filled with liquid enclosures which contain small cubical crystals and a mobile bubble. The mica is partly quite colourless, partly bronze-yellow in the hand specimens, or very faintly yellow in the slides ; the latter variety has marked pleochroio halos around small enclosed crystals of zircon. Both micas fuse very readily in the flame of a Bunsen burner and colour the flame bright red ; hence they are rich in lithia. They are sometimes practically uniaxial ; at other times the axial angle is fairly large, and these peculiarities show that they belong to the lithionite group. These greisens, are full of topaz, containing more of this mineral than any other Cornish rooks with which I am acquainted ; they may, in fact, be regarded as intermediate between topaz-fels and true greisen. The topaz occurs in grains which have no characteristic shapes ; often a central part can be recognised nearly free from enclosures and a spongy external portion filled with irregular grains of quartz ; the compact centre is primary, while the spongy perphery is a secondary outgrowth. A little tourmaline is present, mostly brown, sometimes with blue edges ; and magnetite, zircon and a few grains of cassiterite can also be identified. The rock has small miarolitic cavities which may be occupied by secondary minerals, that have apparently infiltrated from the mineral veins. The process of kaolinisation in the granite is described in the chapter on China Clay and China Stone. (See p. 105.) J. S. F. Elvans. Between Pentuan (Sheet 353) and the St. Austell granite there are numerous examples of elvans. None of these can be traced continuously on the surface for much more than half-a-mile, except the Pentewan elvan (Pentewan Stone) and the Polgooth and St. Stephen's Coombe dykes. The Pentewan elvan is nearly a mile in length, only a small part near Kings "Wood being included in this map. From the evidence furnished by surface-stones this elvan has been represented as reappearing to the north of Nansladron and continuing for nearly half-a-mile. Elvan is visible in a quarry at about 200 yards north of Trevis- sick. It seems to run nearly east and west at or near the surface. It may be connected underground with the Towan elvan, which can be traced for half-a-mile from east to west, and is exposed in a quarry north of Towan and in the wood near its western termination. At Phoebe's Point there is a nearly vertical white and greenish elvan about 30 feet thick. It cannot be traced to Castlegotha, but may have a subterranean connection with the Towan elvan and with an elvan exposed in Penrice Deer Park at about 260 yards north of Lobb's Shop. North of Penrice and east of Kose- week an elvan was seen in a quarry beyond which it could not be traced. A hard mass of elvan is exposed by the high road to St. Austell, near Levalsa Moor; its prolongation eastward is probable from GKANITE AND EL VAN, 69 the occurrence of occasional blocks in Shepherdshill Wood. Westward it is evidently continuous at, or near, the surface for three-quarters of a mile, as we then encounter exposures which show branching. The branch cannot be traced at the surface, but is evidently continuous with another exposure half-a-mile ofE at the north-west end of Commerce Common. Although beyond this there are no indications of surface outcrop, the dyke may continue for two miles in the same line of direction to an exposure on the top of a small quarry north-west of Arvose, and el van stones were seen in mine tips at Hewas Mine. In South Polgooth Mine, just north of Commerce Common, an elvan is said to occur, but the only evidence obtained was a few surface stones. The Polgooth elvan is visible at intervals for nearly a mile and three-quarters, running irregularly westward from a point south of Molingey Hill. In the centre of its course it is well exposed in a rather decomposed condition in a long quarry on the south of Polgooth. From this to Newmill it follows a lode, and is not always at the surface. It is exposed in a quarry south of Molingey Mill, and in a quarry north-east of Sticker at its western terniination. This elvan seems to come to the surface again at three-eighths of a mile and continuous for nearly half-a- mile north of west, being well exposed in three quarries (near a place called Pothole on the 6-inch map). South of the Polgooth elvan quarry, at a distance of about 220 yards, there is a thin elvan dyke, 18 inches in, one place, which cannot be traced for more than a quarter of a mile. Between this and the Polgooth elvan surface-stones render the occurrence of another elvan dyke probable. On the north of the line of the Polgooth elvan between Pol- gooth and Newmill, elvan stones occur in the debris from William's Shaft and Stitch Shaft. These may, however, be due to the northerly dip or underlie of the elvan and not to' another outcrop. The manager of Polgooth Mine said that a strong elvan had been encountered at 60 feet from the surface near Trewhiddle. This probably refers to a shaft west of Mulvra, and may denote the subterranean course of an elvan (with large porphyritic felspars) which is exposed at the turning to Bosinver by the Truro and St. Austell road, and of which there was some slight indication at about 200 yards south of Tregongeeves. At Wheelers Shaft, over a quarter of a mile south of Tregon- geeves, Mr. MacAlister notes an elvan 18 feet wide with a northerly underlie. The Gover elvan is exposed in the i-ailway at somewhat less than a mile west of St. Austell station, where it may be 40 feet or more in thickness. A specimen (4,185) from an outcrop in the stream below proved to be granite porphyry with zonal tourmaline. Further south in the old pits or stock works which are much overgrown the elvan is occasionally exposed, but its thickness and hade cannot be properly estimated, the neighbour- ing killas is often intensely peroxidated and sometimes quite white or buff-white. 70 GEANITE AND ELVAN. Further west there are numerous exposures of elvan which for purposes of description may be divided into two groups, viz., those which occur west of the exposure of elvan west of Bosinver (in the high road from St. Austell to Truro), with which they may have some subterranean connection, and those which may be connected with the Polgooth elvan. As the latter are the most southerly, and their outcrops do not extend so far west, we will commence with them. At Ninnis, north of Sticker, there are some signs of elvan at the surface. At about a quarter of a mile west-south-west of Ninnis, a thin elvan dyke is evidenced running in the direction oi-iSi Austell Consols Mine; it should cross the adjacent roads where ponds are marked oh the 6-ihch map, but the surface evidence of its presence does not extend much beyoiid 100 yards. At half-a-mile west of this, and about a quarter of a mile W.N.W., of the presumed continuation of the Polgooth elvan, near Pothole (on the 6-inch map), an elvan is shown in quarries and by surface stones running west-by-south for over a quarter of a mile. Its thickness may be between 30 and 40' feet. At half-a-mile west-by-north from this there is an overgrown quarry, by the road to St. Stephen's Coombe, from which elvan may have been extracted, as it is in line with a quarry 350 yards to the west, showing 25 feet of vertical elvan yielding large blocks. The elvan is red-stained in the railway-cutting further we^t, where, probably from branching westward, the rock is ex- posed in two bands. At about 550 yards from this in a west- north-west direction elvan was again seen in situ, near a disused- mineral tram-track. The next evidence is afforded by a quarry about 200 yards east- north-eaat from Carnwinnick where 12 feet of elvan (quartz- porphyry with traces of tourmaline) was exposed ; beyond this no further indication was found. The next group commences at TrethuUan Castle or Camp, 'at a mile and a quarter west of the exposure by the high road near Bosinver. In a quarry on the north side of TrethuUan Castle and in the railway at about 50 yards from the road-bridge, this elvan is to be seen. It is about 40 yards wide, a rather coarse quartz-porphyry, partly red-stained, and with aplitic margins for a foot or more. The west-north-west direction of this dyke, which cannot be traced beyond the railway, prolonged for two miles meets a section of elvan in a little wood on the east of the alluvium, south of Terras. At about half a mile east of this exposure there are surface-stones which might possibly denote the outcrop of a decomposed elvan. As we proceed toward St. Stephen's Coombe along the railway, at 130 yards from the TrethuUan Castle elvan, we encounter another dyke, about 26 yards wide, at 30 ;^ards further another elvan, in rotten condition and about 21 feet' wide, is separated by about 20 feet of slate containing a '6 feet wide band of aplite from a Ted-stained elvan varying from 36 to 57 feet in width. The last three elvans occur at a farm, called Trewithian on the 6-inch map. These and an elvan exposed on the south of the railway just north of ©owgas, may have an underground connection on the east with the TrethuUan Castle elvan. The Trewithian GKANITK AND EL VAN. 71 elvans may be oft'-shoots from the Brannel elvan^ exposed in a quarry on the nortli side of tlie stream south of Brannel about 30 feet wide. This rock is broken, by nearly vertical east and west joints meeting irregular joints, into blocks sometimes over a cubic foot in size. It has been ploughed up in the fields on the hill above the quarry. At 80 yards east of the road-bridge by the railway south of Brannel, there is an elvan dyke 30 feet wide, and about 25 yards from it a limonite lode bounds another elvan about 39 feet in width. These dykes cannot be traced beyond the railway, where their direction seems to be north and south. In the railway sections the slates penetrated by these elvans exhibit fine inter- lamination, and Mr. J. B. Hill noticed their resemblance to typical Mylor bels. The Brannel elvan may have subterranean connection with those of South Terras Mine, south-west of Resugga. If so the prolongation of its direction would meet an elvan encountered in a, now inaccessible, quarry 250 yards south Tolgarrick. This should meet, probably underground, an elvan 280 yards west, which crosses the alluvial valley and the uranium lode in a direction about E. 10° K. It is exposed in pits south-east of Tolgarrick, in one of which it forms a hard massive rock about 15 feet in thickness. On the west of the alluvium, south of Wheal Blanco, it may be 40 feet thick, but unless shifted north by a fault there is no proof of its westerly extension. About 70 yards south of Tolgarrick there are very doubtful signs of an elvan at the surface. At 220 yards west of Tolgarrick elvan is exposed in a quarry ; its direction appears to be north-west, so that it may possibly be connected with an elvan which follows the north-west and south- east tin lode of Terras Mine for about 200 yards from the alluvial margin at 550 yards .^jQuth of Hallivick. This elvan contains patches of tourmaline. West of Wheal Blanco, and three- quarters of a mile west of Tolgarrick, surface stones suggest an elvan outcrop, which was confirmed by the exposure of a soft brittle elvan in a pit south of Creaking Gate. On the west margin of the St. Austell granite no elvans have been detected in the killas. On the east of the granite there is a remarkable absence of elvan in the killas. Only one thin band was detected, in a quarry south of Lostwithiel, in the wood about 200 yards west of Castle. The rock is white from partial kaolinisation, it cannot be followed east or west, the directions in which it appears to run. The cuttings of the Newquay Branch-railway at the east end of North Hill Wood showed two thin elvans in the coarse granite. Pine granite was seen in an old quarry on the west side of the stream west of Carpella, near the killas junction. The exposure was not sufiicient to prove whether it is an elvan or not. At Dyer's quary, about half-a-mile west of Meledor, the aHered killas is intersected near contact with granite by an elvan pass- ing into porphyritic schorlaceous greisen. Immediately -east of Burgotha on the map, a quartz-porphyry dyke apparently 73 GEANITE AND. EL VAN. Fig. 8. running N.N.W. and S.S.E., is bounded by porphyritic granite on one side, and by fine scborlaceous granite on the other. An old quarry north of Chytane clay-pits and east of Uurtny Row shows about 20 feet of quartz-porphyry with chilled or aplitic margins, bounded by schorl-rock from 9 inches to a foot in width. The schorl-rock is bounded by porphy- ritic granite on both sides. In the highest face of the quarry the granite has an appear-' ance of synclinal struc- ture probably due to accentuated joints, dip- Elvan Dyke in Quarry north of Chytane Clay-works. ping N. at 65°, meeting floors, or pseudo-bedding cracks, dipping southward at about 45° (Fig. 8). The Wheal Remfrey Brick and Tile Works are on the west side of the valley, half-a-mile north of Retew. The material is obtained from a pit west of the kiln opened along a pale-greenish- yellow decomposed sandy elvan about 40 feet thick (like that in the quarry north of Chytane), bounded by decomposed shorlaceous granite with schorl-rock veinstones. The elvan seems to run W. 10, N., but has not been traced in the killas on the east. W. A. E. tr. North of the area just described good examples of elvans may be observed at Restowrick Downs, Trelavour Downs, Yonder Town, and Hensbarrow Downs in the granite, and also in the neighbourhood of Tregoss Moor, Little Brynn, and Royalton in the Meadfoot series. The dominant type is a fine grained light-coloured rock having frequently a yellowish or greenish hue and a fluxion structure. The phenocrysts are not usually abundant, but the elvan on Tregoss Moor and that in the open workings of Castle an Dinas Mine are crowded with crystals of felspar and quartz. The latter appears to be continued eastwards to Brynn Mine, but it cannot be traced for the whole distance. An elvan with pale mica has been traced in a north-westerly direction across Hensburrow Downs, the felspar crystals of which have been largely replaced by needles of schorl, giving the rock a remarkable appearance. The elvan which crosses Trelavour Downs is seen in the entrance of Kestle's china stone quarry at the margin of the granite near St. Dennis. According to Mr. Collins it has a width of about 20 feet. This elvan is again exposed in a quarry on Trelavour Downs, where it has a well marked fluxion structure, the con- torted flow lines being well exhibited in weathered specimens. In Kestle's quarry the elvan is of a buff hue and contains phenocrysts of limonite after pyrites set in a fine grained ground mass. A similar elvan is seen in the abandoned railway cutting on the south of Kestle's quarry GRANITE AND ELVAN. 73, A fine grained non-porphyritic elvan with a pronounced flow structure extends from Hendra Downs to Curyan. In a line with it further eastwards a quartz-porphyry dyke extends from Cocksburrow to Yonder Town. A similar elvan 12 feet wide occurs in the Bluebarrow china- clay pit on the south of Stenalees, but it has a different direction. An analysis of the elvan on Trelavour Downs by Mr. Collins shows it to have the following chemical composition : — SiOa ... 72-43 A1303 ... 18-08 FeO FesOs '.'.'. 2-20 MnO trace CaO MgO ... „ K2O 1 NasO r 4-12 LijO trace F ... „ Water i Hygroscopic "^**®'^ J Combined ... •29 3-69 100-81 Bp gr. 2-45 S. A. MCA. Elvans have not been met with in the ground immediately to the south of Bodmin, but a few occur to the west of Laniyet and in the Withiel district, and are shown on the map. Though there is a certain amount of variation in these elvans, and indeed in different portions of the same elvan, all have certain features in common. The margins are always fine grained, the texture of the ground mass becoming distinctly coarser towards the centre of the intrusion, though even here its composition can only be ascertained in microscopic sections. It is always com- posed of small — and, in the marginal rock, very small — grains of quartz and felspar with which minute flake-crystals of white mica are associated in very variable quantity. Sometimes these are as abundant as the quartz grains, while in other specimens the mica is almost entirely absent. The origin of this mica is obscure ; its greater abundance in one part of the same elvan than in another suggests that it must be secondary, but the examination of numerous sections does not show any connection between 'the increase or decrease of this mica and the greater or less decom- posed state of the rocks. Idiomorphic crystals of brown schorl, often visible in the hand specimen, are rarely absent, though they vary greatly in number in different specimens. Similar crystals of blue schorl are far less common, this mineral tending to occur in aggregates of minute crystals arranged in radial groups ; in a fair number of cases these aggregates of minute blue crystals envelope the much larger brown ones. Larger and clearly original crystals of both white and brown mica may be recognised in the thin sections of some of the specimens, but neither are at all common. The most easily recog- nised phenocrysts consist of quartz and felspar, which vary much in size. Close to the edge of the elvan these phenocrysts are 74 GRANITE AND. EL VAN. smaller and fewer in number; near tte centre they are usually larger and most abundant. The largest felspars are always orthoclase or potash, felspar, but in many cases these envelop patches of acid plagioclase. Most of the dykes in this area contain a small amount of bliae fiuor spar, and this often replaces the lime-bearing felspar, so that the larger crystals of felspar have blue patches within them marking the position of the formerly enclosed plagioclase (Fig. 5, PI. II.). , . , . The most easterly of th« group is exposed in a small quarry in Bodwannick Wood to the north of Lanivetj where it is quarried to some extent for road metal. The rOck is pale coloured, and has a fine matrix in which phenocrysts of quartz and f elsjiar are embedded. In sections it has the micaceous base referred to above, and crystals of brown schorl in considerable number ; blue crystals are rare. The larger crystals of orthoclase have within them a belt of microgranite suggesting a temporary cessation of growth, afterwards renewed when the material attained its pre- sent position. This feature is not uncommon in the other specimens. Blocks of this rock occur in such numbers in the walls in the immediate neighbourhood as to suggest that it was once more extensively quarried, or else that it formed a large number of loose blocks before the ground was enclosed ; the latter seems more probable, as the rock is locally well-known for its extreme hard- ness and durability when dried, and thus was likely to form many blocks at the surface. In the great quarries about Tremore, though there are at least three exposures of elvan, only the largest can be followed to the top even of the steep banks that flank the valley here. It is thus clear that small outcrops of this material may be present in open ground without giving any sign of their presence at the surface. The smallest of these outcrops occurs by the side of the road lead- ing into the east quarry ; it is only some 2 feet broad, and may be described as consisting wholly of fine marginal material. The second occurs at the north end of the east quarry; this is about 10 feet broad, and has a slightly coarser central portion contain- ing small crystals of quartz and felspar ; in all essentials it is identical with the specimen from Bodwannick referred to above. The third and largest elvan at this locality occurs in the west, quarry, and is specially referred to by De la Beche as having been formerly cut and polished and forming a handsome stone. The' peculiarity of this {see De la Beche, ' Report on Cornwall and Devon,' pp. 180 and 501) elvan is its apparently composite nature, for either it has an exceptionally broad selvage edge on its southern side, or else there are two dykes or separate intrusions here. The latter seems the more likely explanation, for the broad selvage is not uniformly fine, but is slightly coarser in its central portion. The main intrusion varies considerably from point to point, for though all the central portion contains fair- sized phenocrysts of quartz and felspar, some parts contain numerous blotches or patches of the small "blue schorl crystals already described, while these are absent from an adjacent part of the rock. GRANITE AJSfD EL VAN. 75 ' A series of slides lias been made of the different phases of this elvan commencing with the fine southern edge and ending close to the northern. The first taken from the actual junction with the killas shows the latter to be penetrated in an irregular manner bjr the elvan material, which has had singularly small effect on the killas at the contact. The actual edge of the intrusion is some- what cracked, and minute films of violet or bluish fluor occur in these cracks. Within the body of the rock fluor also occurs in minute patches; the marginal rock contains a great number of small very thin crystals of a clear mineral determined by Dr. Flett to be white mica. These are quite unlike the small micas that so often occur in the ground mass of the rocks, and have probably resulted from a form of greisen action. The central portion of the selvage edge has almost a bluish tinge owing to the great number of small aggregates of minute blue schorl crystals already described. Good illustrations of this material enveloping the larger crystals of brown schorl occur in this slide (Fig. 2, PI. II.). A few grains of apatite occur here and there, and the plagioclase is locally replaced by blue fluor spar. The inner portion of the selvage rock contains rather more of this fluor spar, but the little blue schorl crystals are rare or absent. A remarkable feature of the southern part of the main intrusion IS the great, number of small flecks or patches of blue fluor it contains; these are easily seen in the hand specimen and give a distinctive aspect to this portion of the rock. The bulk of these are seen in a thin section to occur as replacement products after plagioclase, and this slide shows perfectly the complete alteration of a plagioclase (Fig. 5, PI. II.) crystal embedded in a larger crystal of orthoclase, the latter being entirely unaffected, obviously because it contained practically no lime. The phenocrysts in this- part of the rock are • mostly small.., The more markedly porphyritic portion, specially referred to by De la Beche, is a handsome pinkish-red rock with fairly numerous larger crystals of quartz and felspar and a much larger number of smaller ones. The ground mass is here sufficiently coarse to allow the individual grains of quartz and felspar to be easily identified under the microscope; they are associated with much less white mica than some of the other specimens. The radial patches of blue schorl needles are fairly abundant, and as before at times envelop the much larger brown crystals. Replacement of the plagioclase by bhie fluor is comparatively rare. A specimen taken about 6 feet from the other or northern edge of the elvan is a pale flesh-coloured rock with large crystals of orthoclase and specially large patches of the blue schorl aggre- gates, but in this case apparently without any core of brown schorl. White mica is present in exceptionally small quantity in the groundmass, and this is noticeable as the rock is more decomposed than most of the other specimens. The decomposition is well shown by the orthoclase, which is pale coloured in the hand specimen ; it contains more inclusions than usual, which consist of quartz, plagioclase, biotite, and at times apatite. The latter mineral is present in all the slides made from specimens of this elvan; but it is never present in sufficient quantity to form a feature of the rocks. The development of fluOr spar in the elvan 76 GRANITE AND ELVAN. is specially worth noting in view of the great development of axinite in the adjacent calc-flintas, described on page 89. The specimens collected from the other outcrops of elvan show no characters differentiating them from those already described; for the most part they are considerably decomposed. An unusual type was found by accident on the small tip-heap of a shallow shaft in a field on the north side of the Tremore Road and in line with the open work mine of Mulberry Down. It seemed at first an ordinary veinstone, but is really an elvan greatly altered. Most of the quartz crystals and portions of the larger orthoclase have survived, but the rest of the original rock hasheen almost entirely replaced by fine granular quartz. The original brown crystals have been cracked, andbroken, and a large quantity of a highly double-refracting type of chlorite developed on their margin. No new white mica appears to have been developed, and there is little of this mineral present in the rock, which is unusual with this type of alteration. g. b. Petrogeaphy of the Elvan s. The elvan dykes, though they must be later than the granite, seeing that they intersect it, belong to the same magma and present the same mineralogical peculiarities as the granite does. They consist of granite-porphyry (quartz-porphyry) and show comparatively few variations in composition and in structure. In colour they are white, grey, greenish, or pink ; the porphyritic crystals include quartz in double pyramids, often slightly cor- roded, and idiomorphic felspar, which for the most part is micro- perthite (Carlsbad twinned) with smaller crystals of oligoclase and albite. Both biotite and muscovite are often visible in the hand specimens, while dark needles and radiate stars of tourmaline, and blue or purple grains of fluorspar occur frequently. In the microscopic sections the quartz is transparent but contains many enclosures of the groundmass,- as well as fluid cavities which are often negative crystals. The felspar is rarely fresh, being usually more or less altered to muscovite and kaolin. The micas form eumorphic six-sided plates; the biotite is commonly bleached or weathered to chlorite. Porphyritic muscovite, rare in granite porphyries, is exceedingly frequent in the el vans of the St. Austell sheet, though not common in those of the Land's End area;* it occurs as flat six-sided plates, perfectly fresh, and often shows twinning in polarised light. Pleochroic halos are very obvious in the biotite and are found also in the muscovite, where they are of pale greenish colour. The tourmaline, when primary is usually brown and when secondary is blue, though exceptions to this rule may easily be found. Primary topaz and tinstone have not been seen in any of the slides, but they occur in similar rocks in the Land's End sheet. We may also mention apatite and zircon, which in small crystals are never absent from these rocks. Pinite after cordierite is not very common but occurs in the Pol- gooth elvant and a few others. • C. Reid and J. S. Plett, 'The Geology of the Land's End District' (Mem. Geo', Surv.), 1907,'p. 66. I- Sir Henry de la Beche, ' Geological Report on Cornwall,' etc, (Mem. ffeol. Surv.') (1839), p. 183, GEANITE AND ELY AN. 77 The gfoundmass is fine grained, especially near the margins of the dykes where it has often a banded fluxion structure; it is essentially a mixture of orthoclase and quartz in minute anhedral crystals, the structure being that known as " microgranitic." Micropoecilitio types, in which the quartz forms rounded spongy masses enclosing small felspars, also occur, but are scarce. Typical granophyres with micropegmatitic groundmass do not occur in this sheet, but frequently we may observe narrow halos of micropegmatite surrounding the phenocrysts of quartz and felspar, while the rest of the matrix is microgranitic. The larger felspars may contain small isolated quartz grains in their external parts, which extinguish simultaneously and are evidently in graphic intergrowth with the felspar (Fig. 3, PI. II.). Occa- sionally one sees a phenocryst of micropegmatite with idio- morphic outlines (as in an elvan from a quarry north of Chytane Clay Works, 4188, and in the Brannel elvan, 6947). These facts show that in the Cornish elvans micropegmatite was not the last product of consolidation, as it is usually in acid igneous rocks, but that there was a period intermediate between the crystallisation of the phenocrysts and that of the matrix when graphic structures were for a time produced. This is exceptional in granite porphyries. Pneumatolytic alteration of the Elvans. — All the processes of pneumatolytic change which have been described in connection with the granite are exemplified also by the elvans, but in modi- fied forms, as might be expected from the different structure and history of these rocks. The. new products are, as in the granites, quartz, tourmaline, muscovite, topaz, kaolin, and fluorspar. They arise by the action of the acid vapours on the felspar and partly also on the biotite originally present. Most of these minerals occur also as primary ingredients of the rocks, but it is usually not difficult to distinguish between the original and the secondary constituents. Tourmalinisation is not very frequent, but may be seen in some of the Tremore elvans and elsewhere. The original tourmaline is in brown zoned prisms of good size (sometimes one-eighth of an inch long), compact and idiomorphic. It is often enclosed, partly or completely, in porphyritic quartz and felspar. There is also a tourmaline of the second generation belonging to the period when the matrix crystallised; it forms mossy growths on the older tourmaline prisms, sometimes in optical continuity with them (Fig. 2, PL II.). Where the early tourmaline is protected by being surrounded by porphyritic quartz, the later tourmaline has not grown upon its surfaces. The later tourmaline is blue or yellowish, the early tourmaline nearly always brown, though perfectly idiomorphic blue crystals maybe found enclosed in felspar phenocrysts in rocks which have not been tourmalinised (as in the elvan at Gover, 4185). The secondary tourmaline which formed in the rock after it had consolidated occurs in fine blue needles with quartz, exactly as in luxuUianite ; the prisms are often arranged in star-shaped groups. Ingrowths of this nature spread gradually through the rock replacing the original groundmass of quartz and felspar (as in the Tremore elvan, 5513). 78 GRANITE AND EL VAN. ■Grreisening is much more frequent in the elvans than tour- malinisation, in fact more than half of the granite porphyries microscopically examined from this sheet, have the felspar of their groundmass replaced by quartz and mica to a greater or less degree. This -is so eharaeteristic of Cornish .elvans tha-t. one- is tempted to believe that it is not secondary and that in presence of the abundant vapours which the magma contained quartz and muscovite crystallised out in place of felspar. To a small extent, indeed, this muscovite may be original, an integral part of the second generation of crystals in the rocks, but there are several features which show clearly that it is mostly a product of pneu- matolytic action. It is not in optical continuity with the por- phyritic muscovite, but its minute scales are sprinkled everywhere ■through the matrix and are generally embedded in quartz in such a way as to produce a secondary micropoecilitic structure. Adjacent flakes of mica are not in optical continuity. It is a very significant fact that the groundmass is sometimes greisened along fissures, while the rest of the groundmass still contains the original felspar ; this indicates clearly that the change may result from secondary processes (Gover elvan, 4185). In many cases the matrix is greisened while the felspar phenocrysts are intact ; a parallel case is furnished by the tourmalinised granites in which the porphyritic felspars have resisted secondary change, as has been described in luxullianite, while the matrix has been com- pletely altered. That the greisening is not due to weathering, by which also secondary mica may be developed at the expense of original felspar, is sufficiently clear from the fact that in some cases it can be shown to be anterior to the kaolinisation,: where the same elvan has suffered both of these alterations. Secondary topaz sometimes develops along with the white mica, though its scarcity in the elvans is in striking contrast with its abundance in the granites and the 'china stones.' Veins of secondary topaz occur in the elvan which occurs in Dyer's Quarry (4183). (Fig. 1, PI. II.). The elvan found in a quarry north of Chytane Clay Works contains a mineral which seems to be topaz and may be primary; it is enclosed in porphyritic felspar. Fluorspar also is by no means common in these elvans, but in the Treiriore elvan, as reniarked by Mr. Barrow, it is often visible as bright blue specks, and the microscope shows that it forms generally in the oligoclase felspar (Fig. 5, PI. II.) which, with the exception of apatite, is the only lime-bearing mineral in the rock. Kaolinisation is very wide-spread, especially in the elvans of the country which lies to the south of the St. Austell Granite. The rocks affected are white or pale yellow, and are soft, though usually not very friable. The amount of kaolin they yield is small, and for this reason, and because they are not easily dis- integrated, the kaolinised elvans are not made use of as sources of china clay. From a theoretical point of view, however, they possess a high interest, as they throw a good deal of light on the nature and sequence of the processes involved. In none of the elvans from this sheet which have been examined with the micro- scope does kaolin occur in any quantity as an ingfedient of the GBANITB AND ELVAN. 79 groundmass. On the other hand, the matrix is never fresh, it is always greisened or converted into an aggregate of fine quartz and scaly mica. • The felspar phenocrysts of the kaolinised el vans are replaced by soft white or yellow kaolin, which, under the ■microscope, has low polarisation colours and exceedingly fine- grained structure .(Fig. .6, PI. II.). We have seen that in the greisened elvans the porphyritic felspars are often left unattacked after the matrix has been completely altered. Instances of the micasation of the porphyritic felspar while that of the groundmass is still partly pre- served are very scarce (Brannel el van, 6947). Hence it seems most probable that in the rocks under discussion the matrix was first greisened and thereafter the remaining felspar in the pheno- crysts was converted into kaolin. Among the best examples of elvans with kaolinised porphyritic felspar are those of Pentuah, St. Stephen's Combe, and Polgooth. The kaolinisation seems tp be a different process from the greisening, for it is rare to find white mica and kaolin together in a pseudomorph. There are also elvans in the St. Austell district which have a groundmass composed entirely of quartz and white mica (greisened), while the porphyritic felspars are completely replaced by kaolin and radiate bunches of blue tourmaline. This supports Mr. Mac- Alister's opinion that tourmalinisation and kaolinisation are closely connected, for no tourmaline occurs in the groundmass of some of these rocks. The best examples of this group come fronii the elvan on Hensbarrow Downs (7432) and that which occurs in the Gover Mine (6951). J. s. F. 80 CHAPTER VIII. THE METAMORPHIC AUEEOLE, The main mass of St. Austell Granite and the smaller outlying patches are surrounded by well-marked aureoles of contact metamorphism. The general distribution of the altered rocks is represented on the map by two symbols (m and c), which are so distributed as to give, by their nearness to each other, an indication of the intensity of the metamorphism. The symbol m refers to altered forms of non-calcareous sediments; the symbol c to certain peculiar banded hornstones, which usually contain calc-silicates, and must therefore represent various forms of more or less calcareous sedi- ment. 'These hornstones were first recognised as a distinct group of rocks by Mr. Ussher,* and subsequently termed calc-flintas by Mr. Barrow, who surveyed an area near the northern margin of the map, where they ofccur in a belt of country running east and west, and have no visible connection with granite. On the west of the St. Austell granite there are few exposures of altered killas, which generally presents the usual spotted type in surface fragments ; but schorlaceous interbanded rocks are evidenced in places, and on the north of Fraddon the spotted slates are associated with some calc-flinta bands and a hornfelsed diabase. About Indian Que'en the spotted killas is much decomposed, and contains, to judge from the mine-tips, bands of calc-flinta type in places. On the south of the granite the breadth of the contact zone, as indicated by spotting in the killas, varies considerably. South of Burthybruen it exceeds half-a-mile. At St. Stephens it is seven-eighths of a mile, and at Brannel and Hendra it exceeds a mile. Through decomposition it is impossible to ascertain the limits of contact alteration at St._ Austell ; the zone may be about half- a-mile in breadth. From St. Austell to St. Blazey it is generally rather less than three-quarters of a mile. At Dyer's Quarry, half-a-mile west-north-west of Meledor, the contact is well seen between the schorlaceous granite and killas altered to tourmaline-biotite-hornfels and biotite-topazfels. At Little Grugwallons, near Burngallow Station, the railway- cuttings, including a siding, display soft grey, red, and brown- stained killas, in which less fissile materials of a dull-greenish colour suggest the presence of contemporaneous basic rocks. Both rocks are argillaceous, and so decomposed that one cannot say whether they are altered or not. The bedding in one place seems to be vertically zigzagged. Of interlaminated beds exhibiting peroxidated and schorlaceous types of alteration, with veins of schorl, there are many examples. For instance,^ north of Tregonissey (north of St. Austell). Some- times these siliceous bands are an eighth to a quarter of an inch ' Summary of Progress ' for 1903 iMem. Oeol. Sm-v.), p. 21. Mi5T AMORPHIC AUEEOLE. 81 thick, as noticed in a mine-tip of Barker's Flatrod Shaft just out- side the contact zone north of West Wheal Eliza. The same types of altered (spotted) slates or shales and inter- laminated beds can be recognised in the contact zone all round the granite. The uralitic diabases of Terras and Metheroes, near Hembal, the altered ophitic diabase west of Trevarrick Terrace, near St. Austell, and a band of diabase hornfels near the Smithy, south of the railway over the Bodmin Road, St. Austell, are all in, or on, the borders of the contact zone. The altered interlaminated beds, especially the schorlaceous types, show small contortions, or gnarling, well. The close parallel joint (tin-bearing) planes in Wheal Menear (east of Pharnyssick) are so strongly suggestive of bedding that the real nearly horizontal bedding, shown by fine interlamination, might be overlooked. On the east of the granite the contact zone varies in breadth from three-quarters to seven-eighths of a mile. In a cutting by the Newquay Branch-line (south of Font's Mill, on the six-inch map), west of Porcupine, some altered killas with chiastolite crystals was detected. From Par northward grey slates, reddish and decomposed in places, and with local thin harder interlaminations and seams, prevail. In these rocks, both inside and outside the contact zone, there appear to be occasional bands approaching calc-flintas in character, to judge from the strata by the road north of Porcu- pine, by surf ace^stones on the slope north-east of Par Station, and by occasional stones in mine-tips at Lanescot and Polharmon Mine, north of Pelean. These would be too insignificant to merit notice were it not for the occurrence of 30 feet or more of calc-flintas, apparently outside the limit of spotted alteration west of Trees- mill. Here there is a quarry in the corner of a field (shown in the accompanying sketch, Fig. 9, on the horizontal scale of eight yards to one inch). Fig. 9. Quarry in calc-flintas west of Treesmill. Proceeding eastward we encounter pale-grey broken slates or shales for 10 yards ; an appearance of fault then brings on calc- flintas, rotted irregularly from the surface downward, to soft whitish, buff, and orange-brown material for about three yards, where they are overlain by sound, even-bedded calc-flintas, which continue for nine yards. These are often more or less shaly; they weather brown or whitish, and when broken exhibit darker or paler impersistent banding. These beds 12979 ^ 82 METAMOEPHIC AUREOLE. dip at about 45° eastward, and are succeeded by soft pale-grey slates or shales exhibiting terminal curvature and an appearance of disturbance, also manifested by the calc-flintas. -near the junction, and probably due to roots or other superficial agencies, the beds being here overlain by about five feet of loam, stony at base. With exception of the signs north of Porcupine and Pelean and of some very doubtful traces in the woods west of Castle, calc- flintas were not recognised between Treesmill and Lostwithiel From Strickstenton northward interlaminated beds and grit- shales, often very finely-laminated, are met with. A large block of altered igneous rock, with much epidote, was noticed by the road north-west of Polharmon, at about half-a- mile south-west of Strickstenton. It is suggestive of a dyke or boss of basic rock in the vicinity. South-west of Lostwithiel schorl-rock occurs at the granite junction by the high road west of Pelyn. The finely laminated and interlaminated rocks prevail between Castle and Lostwithiel, where they are generally puckered, and denote vertical or highly-inclined bedding crossed by cleavage or shear-planes at intervals. At Rosehill Quarry, in the south of Lostwithiel, the pale-buff and grey, finely interlaminated rocks show this zigzag puckering, crossed by planes of schistosity, dipping eastward at about 30°. In a quarry by the lower road, near Lostwithiel School, finely puckered, nearly vertical bedding is seen, crossed in part by cleavage or shear-planes. These planes are in places close together, and are rich in mica. A band of hornfelsed green- stone is visible in the quarry. In a quarry in the wood near Poldew dark-grey, pale-weathered, spotted slates, with coherent planes, dip north-east at about 35°. Bedding is not apparent, but cracks and quartz veins suggest vertically zigzagged folds, snapped and displaced by cleavage planes. Between this quarry and Demesnes a quarry in finely-inter- laminated beds and slates or shales gives a schistosity dip of 30° to the north. Calc-flintas come on in Lostwithiel at the Wesleyan Chapel, east of Lostwithiel School, and from here northward totheLanhy- drock Woods they are well represented. At about 300 yards north of the chapel the rocks are nearly altogether decomposed to orange-brown soft material. The calc-flintas are well shown in a quarry north of Lostwithiel, where they contain veins of axinite. Between Demesnes and Chark, opposite the turning to the latter, there is a roadside quarry opened for roadstones in evenly- bedded, vertically-contorted calc-flintas, which, although only about 360 yards from the granite, seem to be less altered than those in the quarry north of Lostwithiel. Between Eestormel Castle and Ford the alluvium is flanked by a river terrace on the west. Stones of banded calc-flintas and of diabase hornfels, occur on the surface, where the terrace may be masked by Head, and at about a quarter of a mile east of Woodland these rocks are in situ. The evidence was insufficient METAMORPHIC AUREOLE. 83 to permit of tlie separation of the calc-flintas from the igneous materials, and the same is the case further on, where these rocks are well exposed in the plantation east of Ford, south of Lanhy- drock. In the valley there are three or four quarries in the plantation, in one of which calc-flintas and spotted slate seem to be in vertically-plicated association with igneous rock. A quarry at the northern edge of the plantation exhibits hard, dark, even, in part platy, rocks, dipping N.N.E., at 32°. The dips in the other quarries in the plantation and south-east of it are in a similar direction. The prolongation of these rocks to Lanhydrock is very doubtful. There is some evidence of the occurrence of calc-flintas on the south side of Lanhydrock House, striking through Great Wood parallel to the band near Ford. In the dark slates in the wood, west-north-west of Brownqueen, as previously mentioned, there are bands approaching to the calc-flinta type. , Near Maudlin, and from thence toward Lostwithiel, the altered rocks are finely-laminated argillaceous and siliceous beds, and display puckering and contortions in places. Altered igneous rock is quarried near Maudlin Mine. The quarry has been excavated in a stream-channel. On the north face the rock is liard, and quarries in very large irregular blocks. The sides are chiefly composed of orange-brown decomposed mat'irials, in which there are hard pieces of dark rock (? calc- flintas). This suggests rotted calc-flintas, but it may have resulted from the decomposition of the igneous rock, as in the quarry near Hallivick, west of Terras, and in the quarry near Tregongeeves. W.A.E.U. In the portion of the metamorphic aureole encircling the St. Austell granite, that lies to the south and south-west of Bodmin, good natural exposures of the altered killas are by no means common. In the ploughed fields, however, a number of frag- ments can be obtained sufiiciently fresh to give a fairly accurate notion of the the true composition of the rooks. In a few cases the altered killas has been penetrated by shafts, from one of which exceptionally good material has been obtained; but quarries in anything but the calc-flintas and greenstones are rare. The material upon which the heat derived from the granite has acted is mostly of a fine texture, and consists largely of banded silts, or alternating laminae of very fine mud and fine silty sand. The rapid variation in texture of the banded silt is accompanied by an equally rapid variation in composition ; one mud film may be markedly chloritic, while another (close to the latter) may be largely composed of pale micaceous material; there is consequently a great variation in the structure and com- position of the films of these beds when thermometamorphosed. The original variation in texture has a profound influence on the structure assumed by the altered rocks ; for different structures were set up in the silts before they were heated. Anterior to the intrusion of the granite the sediments were subjected to powerful 12979 F 2 84 MET AMORPHIC AUEEOLE. dynamic action, resulting in their being folded, buckled, and cleaved. The more muddy films easily allowed an interstitial movement to be set up within them; while the more siliceous films not only ofEered more resistance, but were actually protected by the easily-yielding nature of the softer muds. A totally different structure was thus left in these rooks ; a well-marked cleavage is usually set up in the mud films, which meets the junction-plane with the sand films at a high angle. In the latter a curious lenticular structure is set up (roughly parallel to the bedding), and the extent to which this structure is produced depends on the natural resistance of the material, aided by the protection afforded by the adjacent softer material. The sandy films may at times be entirely free from movement planes, though more commonly they are present to some, and at times to a con- siderable extent. Now tl»ese structures are not obliterated by the heat alteration due to the granite ; they are intensified, in the sense that they are far more easily visible to the unaided eye. It is only when almost in contact with the granite that the crystalli- sation is coarse enough to partly obliterate this original dynamic structure. In the mud films that originally contained much chloritic material small crystals of biotite have been developed, the basal planes of which are often almost at right angles to the plane of foliation ; but in the groundmass the micaceous material is rigidly parallel to the original cleavage plane produced by dynamic action. The larger biotite crystals clearly play the role of ' spots,' and often include extraneous' material. A similar structure is set up in the muds that contained much pale mica- ceous material, but the ' spot ' is now formed of white mica ; it is really a very fine phase of the spangle-schists so common in the large areas of regional-thermometamorphism ; the ' biotite spot ' phase being extremely abundant in similar areas, but the structure in these Cornish rocks is simply much finer. Similarly in the sandy films the micas of the groundmass tend to form parallel to the interstitial movement planes and not to the true bedding; the metamorphism is strictly thermo-dynamic, and not simply thermal. In the special cases where this dynamic action has had little effect on the sand film, this parallel arrangement is largely lost, and the micas, especially the brown mica, tend to a criss-cross arrangement, or to a purely thermo-static metamorphism. Singularly fine illustrations of the structures set up in some phases of these silts are shown in the sections of the specimens obtained from the tip heap of a shaft close to the south side of the road, near St. Ingunger (to the south of Bodmin); the pit is roughly in line with the vein worked at Trebell Mine, the old chimney of which is such a con- spicuous landmark.* One of these specimens (6,504) shows well the varying structure and composition of these films ; the tendency to criss-cross arrangement of the biotite being well marked. * TMb locality is easily found and the material is ideal f lom the point of view of making sections of these altered rocks ; it must he clearly understood that such specimens are distinctly rare. MET AMORPHIC AUREOLE. 85 The best illustrations of the development of the micas as spots, with the basal plane at right angles to the foliation, can be found loose in the fields on the north side of Red Moor, where the killas forms a thin skin over, or roof to, the granite. In the rocks further removed from the granite the biotite ' spots ' can be traced for a considerable distance, as is shown in the sides of the St. Austell Road, about two and a half miles south of Bodmin. The shallow section commences close to the steep bank above Trebyan, and the gradual diminution of the biotite crystals can be traced as the hill is descended, and we get steadily further from the margin of the granite. The material is too decomposed to make good microscopic sections, but the mica crystals are easily seen with a hand lens. Andalusite is common in these rocks, as a rule its presence Imparts a spotted aspect to the rock, though this is not always the case. Owing to the paucity of good material, it is not possible to say how far this mineral extends from the margin of the granite; where the aureOle maintains its normal breadth it is still fairly fresh in a specimen collected from the fields (5,'531) at a distance of 400 yards from the granite ; it is still identifiable at 500 yards, though the specimen is much decomposed. As usual, ' spotting ' is very common in the more altered rocl:). 120 PLIOCENE, PLEISTOCENE AND BECENT. with, and in these again the fall is small, though all once drained into the main hollow. Two of them however no longer do so, but drain away from it, one occurring at the extreme north-east end of the Moors, the other at the west. In the first case the water now flows into the small stream near Lanhydrock and so into the Fowey; in the second into the stream at Lanivet and finally into the Camel ; in both cases the change of direction o± drainage is now assisted by deep artificial trenches. Thus the Moor or marsh has been changed from a hollow with one stream flowing through it and draining in a southerly direc- tion, to a watershed from which the water drains away in three different directions. If at these new points of emergence the valleys be examined, they show signs of rapid deepening and cTitting back; indeed m the two instances here dealt with, the upper portions are quite new and have been entirely formed since the great uplift. G. B. Pleistocene. ' Besides the deposits based by stream-tin gravels filling basins, for which a Pliocene date of excavation has been suggested in the above notes, there are the deposits based by stream-tin gravels filling the submerged rock-valleys which were excavated during the elevation that succeeded the formation of the raised beaches. The sequence of events formulated by the writer in 1879,* which established the relative ages of the raised beaches. Head and fluviatile stream-tin gravels, and submerged forests, has only been disputed as regards the stream-tin gravels. Mr. Codrington in 1898,t regards the stream-tin gravels found in the rock- valleys as older than the raised beaches, and of glacial age. The researches of Mr. Tiddeman in South Wales and of Messrs. Muff and Wright in South Ireland have since shown that, as far as the coasts they describe are concerned, the raised beaches are pre-glacial. In a general sense it does not follow that the raised beaches are pre-glacia,l, and the occurrence of erratics such as the Saunton boulder, and the evidences of glacial drift stranded, in the Scilly Islands during partial submergence tend to militate against this view. In treatment it is necessary to take the Head and raised beaches together, and the stream-tin gravels and submerged forests to- gether, from association in the same sections. The Head proper, or Coast Head, is confined to those parts of the old beach cliffs which have not been obliterated by the sub- sequent advance of the sea. It is therefore found in patches at various heights alnd of very variable thickness. Some of these arfe on the uppermost and more gentle slopes nearer to the source of derivation of the ancient talus, as in the case of most of the small patches between Polperro and Polruan ; some of them are the infiUings of the heads of truncated valleys, where the talus * 'The Post Tertiary Geology of Cornwall.' Printed for private circulation, Stephen Austin & Sons, Hertford, 1879, p. 50. "+ Quart. Journ. Oeol. Soc, vol. liv,, 1898, p. 274. PLEISTOCENE jLND EECENT. 121 was shed in lines of drainage along which it gravitated or was washed seaward, as south of Lizzen in the East Coombe Valley, the West Coombe Valley, Coombe Hawne, Little Coombe Hawne, and north-east of Castle Gotha. Here and there patches of Head form the cliff and rest on the old beach platform as near East Coombe, near the Watch Houfie, Lantivet Bay, between Polrid- month and Gribbin Head, South of Polkerris, and west of Spit Point. Insulated stacks and peninsular combs of Head have been noticed in the following places : — 'A small pinnacle on the old-beach plane on the west side of West Coombe; two pinnacles on isolated pedestals of old beach plane just below the Watch House. Narrow combs project from the mass south of Polkerris, and a narrow ridge is visible not far from Southground Point on the east. The following signs of raised beaoh have been observed. Between Polridmouth and 'Gribbin Head, between 300 yards and 600 yeards from the latter, the clifEs are composed of pale- buff clayey Head with local stones. Upon the well-marked beach platform at its base, in one or two places, at from 3 to 4 feet above high-water-mark there is a trace of raised beach consisting of red-brown sand, occasionally blackish, cementing pebbles and subangular stones of quartz and local Devonian rocks. Else- where it is apparently concealed by a wash from the overlying Head. At from three-quarters to a mile north of Little Gribbin the cliffs are composed of pale-buff Head, the stones in which exhibit a more or less linear distribution. At its base, which is from 8 to 16 feet above high-water-mark, quartz pebbles are occasion- ally present. At the point near Polkerris, east of Callyvardor Rock, ' Raised Beach ' is engraved on the old geological map. The point is capped by 8 feet of Head which seems to contain quartz pebbles occasionally. They may however have been cast up by storm waves to the height of 30 feet above high-water, at which they occur.* The neck of higher ground which separates the north shores of St. Austell Bay from the broad valley which opens eastward at Par Harbour terminates in a plane sloping eastward to Par Harbour Pier, from the 50-foot contoiir to about 8 to 10 feet above high-water. From Par Harbour Pier, for a quarter of a mile westward, the surface of this plane consists of raised beach, or contemporaneous estuarine materials. For 130 yards further west the ground rises above the 50-foot contour, and a capping of Head, attaining 15 feet in thickness, overlies the beach. The platform on which the beach rests is very little above high-water- mark at its eastern extremity. In the garden of a house (perhaps the Candle Factory) by the inner shore of the harbour the deposit consists of small quartz and granite pebbles with rounded and subangular boulders and beds of green-grey sandy material, 6 feet thick, and at base 8 feet above high-water. On the north side of Spit Point 4 feet of pebble-gravel, chiefly quartz, rests on 3 feet of 'finer gravel with boulders and this again on 1 foot of Geol. Mag., 1879, p. 166. 122 PLIOCEHE, PLEISTOXiENi; AND. DECENT. grey loam with quartz pebbles ; the. base is 8 feet above the pre- sent beach.* . , . •On the south side of Spit Point is a deposit of fine grayel with, pebbles, mostly quartz, one of flint, 8 feet thick; its base is 5 feet, above high-water. . Near this, 10 feet of fine gravel alternating with greyish sand rests upon large pebbles and unworn blocks of the subjacent rock, at 10 feet above high-water ; the layers appear to have a seaward dip. There is a cleft in the low clifE about 350 yards from Par Harbour Pier. Here the deposit is 10 to 12 feet thick and composed of comminuted slate with quartz pebbles and occasional worn fragments of whitish elvan and angular and sub- angular pieces of slate. In ihe upper part, from 5 to 8 feet, there are bands, or courses, of finer material apparently dipping seaward. Below this, the materials are coarser and large frag- ments are found. The base is from 12 to 13 feet above high- water. The elvan fragments suggest a drift of shingle from the, west. The modern, beach here is of quartz ot granite sand. _ ' Behind Par Post Office and Par Inn there is a cliff 25 feet in height capped by from 10 to 12 feet of Head (brown and yellow- brown loamy clay with stones) on 4 to 5 feet of subangular gravel and occasional boulders of grit, quartz, slate, and granite in coarse sand. The larger stones are in orange-brown sand in the lower part of the deposit under a black-stained band. The base of the gravel is about 8 to 10 feet, above the alluvium which is here about 12 feet above O.D. Rather more than a mile from this, up the Luxulian Valley, just above St. Blazey, there is a fine terrace on the borders of Prideaux .Wood consisting of about 20 feet of brown gravelly loam with occasional pebbles. Opposite this the alluvium is flanked by Head in Tywardreath Highway. The upper part of the Wheal Rashleigh clay pit sections, at half'a-mile west of St. Blazey, for from 6 to 12 feet, consists of Head, generally brown, sometimes whitish, consisting of granite debris, dark veinstone fragments, and altered killas, generally small. Finer materials and paler colors denote bedding. The larger stones occur through the accumulation and locally at its base, which rests irregularly on the decomposed granite. The tract round the pits is so disturbed by excavation that one cannot reconstruct the lines of original drainage. . :To return to the coast. Fishing Point is capped by drab com- minuted-slate sand with quartz pebbles and subangular pieces of slate running in bands, at base from 15 to 20 feet above high- water, but rising landward. Though its reef platform is present and Head occurs at Porthpean, no further signs of raised beach have been detected on the coast in this map. The river terraces and masking slopes of Head which are encountered inland are to some extent the representatives of the raised beaches and coast Head with which in places they may be actually contemporaneous. On the north and south of Bridgend, Lostwithiel, the alluvium of the Fowey, which is little above high- water level, is flanked by ground which rises gently eastward ' The Post-Tertiary Geology of Cornwall," 1879, p. 16. PLEISTOCENE AND HECENT. 123 to and above the 100-foot contour; a similar terrace feature is noticeable on the opposite side of the river between Restormel and Lanhydrock, by the Lerryn River above Lerryn, and by its tributary south of St. Nectan Chapel. Narrow terraces are shown opposite Bodmin Road Station, south of Glynn, near Holtroad Downs, and near Drawbridge. Besides these there are well-marked terraces on either side of th^ Fowey, north of Doublebois House, and on the south bank between Drawbridge and Bellasize. There are no really good exposures of the deposits. North of Terras, especially near Kernick, there is a well-marked terrace of the Fal, in which 10 to 12 feet of loam, with granite debris and fragments of altered killas partly worn, was exposed. This terrace rises to over 50 feet above the alluvium. There may be a river terrace at Tolgarrick, south of Terras. The broad alluvial flats, to which attention has been directed in the central part of the area, have their representatives on a smaller scale at lesser elevations as : — Between Paramoor and Penstrassoe, ' south of Sticker, where the height of the ground averages 200 feet above O.D. South of St. Nectan Chapel, between 250 and 320 feet above O.D. South of Bocaddon, near Lanreath, at between 200 and 300 feet above O.D. At Halgavor Moor and Tregullan, at and near Retire Common, and between Retallick and Trewollack, near St. Wenn, there are flattish tracts near sources .of drainage at heights ranging between 200 and over 400 feet above O.D. In the Geology of Plymouth and Liskeard, p. 127, the deep grooving of the submerged rock-valleys is referred to the period of elevation which succeeded the formation of the raised beaches. Mr. R. H. Worth* adduced as an argument against the merely fluviatile erosion of these valleys, the infinitesimal fall of the rock bed of the Tamar for over two miles above Saltash. If we assume a pause to have taken place in the elevation of the beaches of sufficient duration to have permitted the sea to . convert the mouths of the then existing valleys into creeks, planing their rock bottoms in the process, the phenomenon may be explained without recourse to the ice action suggested by Mr. Worth. This explanation might tally with the information received by De la Bechet respecting the latest tin-streaming in the lower reaches of the valley between Tregoss Moor and St. Columb Porth. This information, if correct, would prove the extension of the sea up this valley before the deposition of the stream-tin gravels to a bar of hard rock over which the tin gravels were subsequently swept in a cascade so as to bury, without detaching, mussels adhering to the rocky wall. Mr. Reid quotes the passage in the geology of Newquay, pp. 70, 71, and gives the surface of the alluvium near Treloy, in the direction of which place the section is said to occur, as 40 feet above mean tide. If as high up as Treloy the phenomenon could only be explained by estuarine, conditions- contemporaneous -with the raised beaches. * Trmt. Devon. Assoc, vol. xxx., 1898, p. 386. + ' Report on tie Geology of Cornwall,' etc. (jS/cot. 6eol. Surv."), 1835, p. 405. 124 PLIOCENE, PLEISTOCENE AND RECENT. The elevatory movement continued and any deposits that existed in the elevated estuaries were subsequently swept away, for as Mr. J. B. Hill observes in ' The Geology of Falmouth and Cam- borne,'' p. 96, " the conditions which permitted of the formation of the stream-tin involved the destruction of normal alluvial deposits, both older and contemporaneous." In dealing with the stream-tin gravels it must be borne in mind, as pointed out in the ' Falmouth Memoir' {op. cit), th.a,t the intermittent torrential action to which their transport is ascribed would lead to the removal of lighter materials and even of stream-tin detritus, so that we have in these gravels a very inadequate representation of the processes of erosion and deposi- tion during the period to which they belong and, except in the higher basins perhaps, they may be merely regarded as residua which the dwindling water power was unable to sweep away. In this connection W. J. Henwood remarks* : — " If the tin ore found in stream-works were torn from veins in the neighbour- hood by diluvial action, an immensely larger mass of the con- tiguous strata must have been simultaneously removed; but of such substances, the quantities occurring in stream-works bear but a small proportion to the masses of the tin beds." The stream-tin gravels belong to the same general epoch as the Head with which they were originally classed in 1879, but exact contemporaneity is not implied by this correlation. It is not improbable that the shedding of talus on the raised-beach plane commenced at a much earlier stage than the formation of the etream-tin gravels. In the valley between Roche and Luxulian, Henwoodt gives accounts of the following sections of stream works : — Merry Meet- ing, Mullinis Moor, Grove, Levrean, Watergate, and Pendelow (centre of vale), in order. Merry Meeting being nearest to the head of the valley, and all " undoubtedly, on the continuation of the same bed of tin ore," also of Broadwater "Works, up a small tributary vale opening from the north. In another place| he gives a more detailed section of Levrean Works, another Pendelow section, and sections of Pit Moor, Upper Creany, Lower Creany, works IN .W. of the railway bridge ov.er the high road between Lanivet and the Indian Queens, Gun- Deep in St. Dennis, and Golden Stream about half a mile S.E. of Castle-an-dinas. The following are condensed accounts of Merry Meeting and Levrean Works: — Merry Meeting Works in the Fore-Monr, Roche. ,_ , „ . ft. in. ft. in. Mud 2 to 3 feet, on granitic gravel 2 feet, on silt 4 to 5 feet 8 to 30 fcrramte gravel and sand mixed with silt, nuts often found 4 * Tram. Roy. Geel, Soe. Corn., vol. iv., 1832, p. 66; t Ibid, p. 60. J Jowrn.Boy. Inst. Corn., vol. iv., 18T4, p. 214, &o. PLEISTOCENE AND RECENT. 125 ft. in. ft. in. Vegetable matter, apparently marsh peat, or /en, with charred appearance, 1 foot, on silt with vegetable remains, 1 foot, on vegetable remains with charred appearance, 1 to 3 feet, on similar vegetable matter giving place to silt, 8 to 10 inches 3 8 to 5 10 Tin ground, ore as sand and pebbles, little rounded, mixed with quartz, granite and schorl-rock stones, and with many masses of quartz, some as large as 15 feet square 4 to 30 The ore is of best quality and in largest quantity where the shelf of friable granite is softest. The shelf is sometimes impreg- nated with tin ore to a depth of 20 feet or more. The tin ground is sometimes horizontally divided by friable granite, which was seen to be a lateral projection from the granite banks nowhere exceeding 10 feet outward. ' False Shelf ' was also detected in the Grove Works, where it consisted of a horizontal mass of friable granite, 9 feet thick, and about 30 feet broad, and apparently disconnected with the granite walls or banks. Here the tin-ground beneatS the false shelf was about 20 feet thick, and in one place " much mixed with granite clay." Levrean in St. Austell Parish. ft. in. ft. in. Granitic sand and gravel — 10 Peat (/««) often mixed with, and sometimes divided by, very thin layers of granitic sand — 10 Upper tin-ground ; granitic material, particles and granules of tin and, rarely, minute specks of gold ... 3 to 6 False shelf, angular and sub-angular masses of granite in granitic sand without any tin ore 1 to 14 Tin-ground ; angular and sub-angular granitic and veinstone materials mixed with granitic gravel and sand, grains and particles of tin oxide, and less frequently flakes- of schistose matter with specks of gold 10 to 15 A few ancient shovels of wood, bound on the edges with iron, have been found in this bed. The shelf is of granite of unequal hardness. In Watergate, Pendelow, and Broadwater sections vegetable matter (fen), from 4 to 6 feet thick, rests on the tin-ground. In the Pendelow section (not in the centre_of the vale) peat, I foot thick, with remains of ferns, nuts, leaves, branches of furze, alder, hazel, trunks of oak, and occasionally a few flints, rests on the tin-ground, which is from 2 to 4 feet thick and rests on an uneven granite shelf. In Gun-Deep, St. t)enis, there is a foot of peat on the tin-ground. In the sections of Upper and Lower Creany Works on Red Moor the top soil is peat, 6 inches at Upper, and 2 to 3 feet at Lower Creany, on granitic clay with fragments of slate from 1 to 3 feet thick. Beneath this, penetrated to a depth of 2 to 3 feet by the roots of marsh-plants, is the tin-ground, from 4 to 5 feet thick. It consists of angular and subangular fragments of quartz, granite, and veinstone materials. Either the shelf in these sections is slate soil or kaolinised granite, or it is a false shelf or bed separating aii lipper from a lower tin-grotmd. 126 PLIOCENE, PLEISTOCENE AND KECENT. Whether of pliocene age or of later date, these upland basins would appear to have been areas of deposition, fed by materials from the surrounding higher land, until drained by the cutting back of the general arteries of drainage ; so that it is not im- probable that there may be in them stream-tin gravels of earlier date than those in the estuaries. In cutting the Par Canal at Pons (? Fonts) Mill, near St. Blazey, De la Beohe* tells us that granite blocks, arranged as if intended for a bridge, were found beneath 20 feet of gravel. The thickness of gravel may be due to stream- washing. De la Beche (J,oe. c«Y.i) also records a section seen in a shaft sunk in the low ground near Par Estuary, presumably either at or east of East Crinnis Mine ; the details are as follows : — ft. in. 1. River deposits _ ... •:• 1 6 2. Confused mass of mud, sand, clay and stones, which has been much disturbed by the steam-tinners 7 t) 3. Mud clay and vegetable matter, apparently ^ old surface ... 8 4. Fine sand, containing sea shells like cockles, and, on the top, rolled pebbles 4 5. Mud, clay, sand, wood, nuts and other vegetable productions mixed together 3 6. Tin-ground resting upon an uneven surface of slate ... 6 inches to 6 Rashleigh's section at Sandrycock,t compiled in 1792, cannot be very far from the above, and was probably taken in a part" less disturbed by the" old men's, workings. In this section beds 1, 2, and 3 in the above are apparently represented by the following : — ft. in. a. Vegetable mould 3. inches on alternating beds of gravel, sand and loam ... 8 6 6. Light-coloured clay, traces of decaying roots 5 3 c. Black peat 4 1 d. Light-coloured clay 16 inches on stiff light-brown clay with bluish spots, containing decayed vegetable matter ... ... 5 2 The black peat and underlying clays may represent bed 3. The underlying sea-sand is represented in the following three beds in Eashleigh's section, e, f, g: — e. Sea sand and clay, mixed /. Very fine micaceous sea sand, comminuted shells and bits of slate I J. Coarser sand without shells , Below this Nos. 5 and 6 are represented by h, and i : — h,. Solid black fen with few vegetable remains 2 10 i Tin-ground on killas 1 foot to 6 At Poth (Porth in E. Smith's reference to the works in 1814), very near the sea, " about a quarter of a mile from high water mark," horns of deer and of wild oxen were found " nearly at the bottom of the sea-sand and upon the sea-mud." " An extra- ordinary high tide destroyed this work entirely in the winter of ft. 3 in. 4 6 * 'Report on the Geology of CornwaU,' etc. {Mem. Oeol. SurvX 1839, p. 103. t Trans. Roy. Geol. Soc, Corn., vol. ii., 1822, p. 281. Pleistocene and recent. 127 1801." Rashleigh's account of Poth. Stream Work is given in the last page of his " Specimens of British Minerals," London, 17'97 and 1802, from which the last quotation is taken, and it is practically identical with his description of Sandrycock, In an accompanying illustration he shows the tin-ground on a very uneven shelf of clay and slate. The total depth from the surface in the Poth and Sandrycock sections amounts to 44 feet 7 inches. Whilst Henwood described Sandrycock as a mile above Par, and identified Poth with Porth, from Eashleigh''s sections one would suppose that these works were very near. Henwood gives sections of the Carnon Bestronguet, Happy Union, and Porth Works to scale in regard to high and low-water. By these we gather that the surface at Porth was about 2 f-eet, and at the Happy Union Works 6 feet, above high-water. * More precise information is necessary to show whether the original surface during the last hundred years has been buried under a few feet of "drift from china clay workings and mining debris, or remains the same. Colenso tells ust that Happy Union Works (in sheet 353) were begun in 1780, and that, a short time after, work was carried on seaward and up the valley, in which direction the works were called Wheal Virgin, the seaward works being Happy Union. These works, when he wrote in 1829, were about a mile apart. In Wheal Virgin, probably within the south border of our map (347), the tin-ground is not so thick as in Happy Union, and only 32 .feet from the surface. On the surface of the tin- ground were " several oak stakes, sharpened and driven into the ground, and supported by large stones." There were ashes and other signs of old men's workings, but whether the tin-ground was then at the surface or worked from above Colenso was unable to determine. Over the tin-ground no sea-sand, but silt and river gravel was encountered, " with a considerable quantity of. wood, chiefly oak and willow with the roots of the same and other trees in all places where there is any soil." E. Smith, writing in 1814,t describes the Upper Pentowan (Pentewan) work as about one mile north of the beginning of the sea-beach arid three-quarters of a mile from the Lower Works. The section observed by him is as follows :., — 1. Soil with trees growing thereon 2. Deposit of mud mixed with small gravel, waving thus : ffffff 20 3. Small-grained spar and killas ... ... 3 4. Grpwan (or decomposed gyanite), spar, killas, &o., similar to .tliose which are now found on Hensbarrow and other neigh- bouring Hills •• S 5. Gravel, at the bottom of which are oak trees and branches of great size ^ > ^ 6. Tia-ground .■■■ 5 * Journ. Boy. Inst. Corn., vol. iv., 1874, p. 191, table 3. t Tram. Roy. 0enl. Soe. Corn., vol. iv., 1832, p. 38. t Trann. _ Ti„„„^ • Fatwobk and Virtue Mine— The mine has been described by Dr. Boase.* The country rook near the lode is contorted finely banded tourmalmized sediment. The main lode has an east and west bearing with an underlie northwards or a vertical position. Its stanniferous rock at the sides of the lode is 15 fathoms in width consisting of numerous short interbedded veins, or ' floors, arranged one above the other. The rock is also traversed by small strmgs in all directions. The tinstone is accompanied by quartz and schorl. The lode itself is a hard brecciated mass intersected by numerous veins striking in a north-westerly direction, and seldom more than 5 fathoms apart. (Compare with description of Park of Mines, which appears to have similar peculiarities.) FowEY Consols.— The lodes have been described by Henwood,t whose obser- vations afEord practically all the information there is ooncernmg them. De la Beche has also referred somewhat fully to the mine, and m particular to the Financial Transactions in 1837 as a comparison with those of the Consolidated Mines (Gwennap), which he has also given in detail for the year 1836, with a table showing the costs, lords' dues, value and tonnage of the ores, and wages from 1823 to 1836.± In addition to this a surface plan, of the lodes and a cross section of the mine are given in plates 10 and 11 of the same work. The bearings of the different lodes are shown on the geological map 347. They are all vertical or have a northerly underlie. The copper ore sold from Fowey Consols and Lanescot up to the time the mine was abandoned realized 2^ million pounds sterling. § . . Bone's Lode.— From the 90 to the 120-fathom level the lode varies from 6 inches to 3 feet, and consists of quartz, slate, copper and iron pyrites, and carbonate of iron and chlorite. Jeffrey's Lode.— From the 90 to the 120 the lode varies from I to 2^ feet in width, and consists of the same materials as those mentioned. Cross Spar Lode. — From the 35 to the 200-fathom level the width varies from 6 inches to 12 feet, and consists of qu.irtz, earthy limonite, chlorite, iron and copper pyrites, and native copper and carbonate of iron. Vugs in the lode are lined with minute quartz crystals sometimes containing bismuthine. Cooh's Lode.— Fvom the 35 to the 57 fathom level the lode varies from ^ to 2 feet in width, consisting of quartz, slate, and copper and iron pyrites. Ann's Lode.— A.t the 57 fathom level the lode is 1 to IJ feet in width, consisting of the same materials as those in Cook's Lode. William's Lode. — From the 35 to the 90 fathom level the lode is 6 inches to 3 feet in width consisting of quartz, earthy limonite, vitreous and black copper, iron and copper pyrites, carbonate of iron, and, in vugs, sulphide of bismuth. Trethan's Lode — From the 35 to 70 fathom level the lode varies from ^ to 5^ feet consisting of earthy limonite, copper and iron pyrites, and quartz. Blaok Lode. — 4 feet wide at the 36 fathom level, and contains quartz and copper and iron pyrites. Kupfernickel, millerite, and other nickel ores occur in a cross course. The following minerals are recorded : silver, cadmiferons blende, silicate of zinc, antimonite, cuprite, magnetite, marcasite, melanterite, sulphide of tin, and apatite (Francolite). De la Beche states that the shoots of copper ore dip away from the granite, which lies on the west, and that their pitch appears to coincide with certain beds in the killas which is also dipping eastwards, and across which the lodes cut.|| The same writer has noted that much of the lode material consisted of angular * Dr. H. S. Boase, ' Contributions toward a knowledge of the Geology of Cornwall,' Trails. Boy. Geol. Sue. Corn., vol. iv., 1832, p. 250. t Trans. Roy. Geol. Sue. Corn., vol. v., 184S, table Ixxxix., p. 130. % ' Report on the Geology of Cornwall,' etc. (_Mem. Geol. Surv."), 1839, p. 600. § J. H.lCoUins, 'Cornish Mines and Cornish Miners,' 1897. {| ' Report on the Geology of Cornwall,' etc. (^Mem, Geol. Sm-v.'), 1839, p. 335, MITflWG. 145 fragments of slate cemented by yellow copper ore and quartz. Specimens of veinstone obtained from the burrows reveal interesting peculiarities in the history of the lode, as illustrating one of the numerous operations determiiiing the structures of the lodes. The figure (Fig. 19) is a diagram of a piece of veinstone consisting of alternate veins of quartz and films and layers of killas, the latter often chloritized or silicified. In this case the original fissure, parallel with the cleavage of the slates contained fragments of killas cemented by quartz. The lode was again opened, but this time not along the old plane of Assuring, but between a thin film of killas attached to the wall of the vein, and the country rock. Infiltration of quartz and minerals again took place, and the vein once more cemented itself firmly to the killas. The re-opening of the lode again and again appears in this case to have taken place always between the thin film of killas cemented to the quartz vein and the country rook from which it was detached. Thelodes extend through the sett for nearly two miles. Killas TTiiioo Veins of quartz intervening breccia ir;ii„- "■"'**■ laminae of Mllas. cemented ^"'^'• by quartz. Fig. 19. — ^Fragment of veinstone from Fowey Oonsols Mine (natural size). GooNBAEROW. — Zippeite has been recorded from here. GovER. — Worked for both tin and iron ore. The iron ore was obtained from a lode traversing an elvan.* The tin ore was obtained from the elvan. Great Beam. — Worked for both tin and china clay, but the mine has been abandoned for over 30 years. In addition to the large open workings from which china clay and tin ore were obtained there are several shafts, the deepest of which extends to 92 fathoms below adit. The cross section (Fig. 20) shows N.50W, S.50E. Fig. 20. — Cross section through Great Beam Mine * A. K. Barnet, ' Observations on the Elvan Courses, Grreenstone, and Sandstone of Cornwall, with Remarks on their Associated Minerals,' iUt Eep. Royal Cornwall Polytech. Soc, 1872, p. 143. 12979 K 146 ECONOMICS. the underlie of the lodes, and their relation to one another. Their bearing is N. 30° E. In general character the lodes are similar to those of the Bunny with the exception that the lodes are wider. They do hot appear to be faults. A group of these veins traverse the pits from end to end, and are of a type characteristic of the district. Tin ore with melaconite, olivenite, pharmaco- siderite, wolfram, talc, and wavellite was also found. Henwood makes the following observations : — North Lode.— WiAth from 4 to 6 feet, consisting of decomposed schorlaceous granite, clay, tinstone, and wolfram. Middle Lode.—Yxom 2 to 2| feet wide, oonsistiiig of a small vein of tinstone and schorl in decomposed granite. South Lode.— 6 to 6 feet in width, consisting of veins of tinstone with wolfram, some earthy limonite and black copper ore, quartz, and schorl. A cross vein from 2 to 3 feet in width consists of quartzose granite with tinstone.* It is said to have been stopped owing to bad management in 1872.t Great Dowqas. — The mine is now being worked. There are several loden with a bearing of from 15° to 20° south of east. The sett is traversed by an elvan on each side of which a lode is situated between it and the killas.J The deepest workings are 33 fathoms below adit on the Groffin lode, which is situated several fathoms north of the elvan. It was the quantity of mundic contained by this lode which led to the restarting of the mine, but attention is now being paid to the tin ore. This lode is a zone of crushing traversed by many fissures, and frequently stained by oxide of iron resulting from the decomposition of the pyrites. In some places it reaches the enormous width of 50 feet, and there are no definite walls. The killas in the lode is rotten and soft. The pyrites occurs encrusting the walls of small vugs or as a massive infilling. In some places the lode is drusy and stained brown, the cavities having contained originally pyrites which became decomposed leaving a mere skeleton of quartz. Quartz in small crystals occurs abundantly, frequently with cassiterite, and as the material is pulverulent it would be readily dressed. Other minerals recorded from the mine are native copper and bismuth, bismuthine, fluor spar, and cobalt ore. Several other lodes occur both to the north and the south of the Goffin lode. They all underlie north. The material from one of these lodes is a hard greenish siliceous and chloritic brecciated killas with tourmaline. According to Henwood all the lodes contain tin ore and generally pyrites, and with the exception of the Great Stope Lode (Goffin), vary from 6 inches to 1^ feet, the south lode being an exception, as it is from 6 to 9 feet in width.§ Great Hewas Mine. — The main lode has been traced for nearly two miles. West of Hewas Mine it has been tried in Little Ventonwyn (or Wheal Elizabeth), and is now being worked in Yentonwyn Mine. Eastwards it traverses South Polgooth Mine. The bearing of this lode is E. 10° S., and it has a northerly underlie. The amount of elvan debris found on the old burrows shows that an elvan must have been encountered in the workings. Some of the lode stuff is brecciated. De la Beche states that the lode is dislocated by another having a direction similar to those of the Gwennap district in Camborne. || Tin ore occurred with mispickel and arsenical copper compounds, &c. Galena was also found. Great Royalton. — The mine has been tried by several companies and has again recently been opened up. An elvan of 15 or 16 fathoms in ,width traverses the sett and is the same as that which was worked in the Brynn Mine on the east and Castle an Dinas on the west. Wherever it is exposed in this mine it is soft and kaolinized. The tin ore occurs in the elvan in the form of linings of joints and small fissures varying from a mere line of rifting to a few inches in width. The rook on each side of these strings is altered to hard greisen, beyond which * Tmns. Roy. Owl. Sob. Corn., vol. v., 1843, Table xc, p. 130. t J. H. Collins, ' Hensbarrow Granite District,' 1878, p. 38. I ' Report on the geology of Cornwall, etc' (Mem. Cfeol. Surv."), 1839, p. 332. § Traiu. Boy. (Jeol. Soc, Corn., vol. v., 1843, Table Ixxxiv., p. 130. II ' Eeport on the geology of Cornwall,' etc. {Mem. Geol. Sure), 1839, p. 366, MIITING. 147 the elvan is soft and kaolinized. Originally the elvan was a fine grained porphyry The tm occurs with schorl rock of varying texture, usually fine, but needles of schorl are frequently visible to the naked eye. Generally it is ' peach.' A shaft 10 fathoms in depth has been sunk on this elvan, at a point at which It 18 intersected by a line of 'old men's workings' running north and south. At the 10-fathom level a drivage has been made westwards, while two cross-cuts have been driven north and south respectively to the sides of the elvan The tm stone occurs in a series of north and south cracks cutting across the elvan. They vary from a few inches to a foot or more apart through a distance of many fathoms. Although the general bearing of these cracks is more or less uniform, they coalesce here and there forming tin bunches a foot or more in width. Here and there the elvan is fractured irregularly constituting a breccia. These cracks can be traced into the killas which is soft and bleached. The company designs to work the whole elvan as an open-cast as was done in the Brynn and Oastle-an-Oinas pits. In addition to these stanniferous veins there are lodes in the killas with an east and west direction. The material from these is a breccia, that is to say while there are leaders or veins in the lode the intervening country rock is ramified through with cracks filled with peach and tin stone. Hallow Mine.— Worked formerly for tin and iron. The lodes are the same as those worked in the Great Beam Mine and have a similar bearing. According to Mr. Collins the workings extend to a depth of 20 fathoms, and in one place the lode yielded about 80 lbs. of black tin to the ton. An iron lode 20 feet in width, was seen at 20 fathoms from surface, containing a large amount of siliceous oxide of manganese.'* Indian Queens.— See Toldish and Ruthvoes. Wheal Jacob.— Mr. Ussher states that the mine was first worked for tin but it is now opened up as a clay pit. Wheal James.— Situated on an iron lode which has been traced southwards over six miles, and northwards for some distance through Tregawne The lode has a bearing of N. 10° W. Lanescot.— Part of the Fowey Consols Mine in the southern part of the sett. The cross section, Fig. 21, shows the positions of the lodes. Native copper with sulphide of bismuth, silver ore, and cassiterite occur with zinc blende and calamine. Lanivet Consols. — Mr. Barrow learns in, that the lode (copper) hades to the north * and was worked to some depth below sea ; level. A considerable amount of ore was raised, but the mine had ceased to pay for some time before it was closed. Near the surface, where the rock is soft and decom- posed, the vein was followed for a far greater distance than in the deeper mine, of which plans have been kept ; in the latter the work was concentrated on the richer part of the lode. The lode occurs at the foot of a hill, so that the old shallow workings caught almost the whole of the drainage from the slope and conducted it into the later, deeper workings, from which it had to be pumped. Wheal Mary. — Situated between Wheal Frederick and St. Dennis Consols China Clay Works. The mine was worked to 10 fathoms below adit, but with little success.f Adjacent to the St. Dennis Crown Mine. Fig. 2] . — Cross section through Lanescot Mine. ' The Hensbarrow Granite District,' 1878, p. 39. Op. cU., p. 39, 12979 K 2 148 ECONOMICS. MaudliS Mine.— in addition to ores of copper and tin there occurred chalcedonic quartz, jasper, chlorite, fluor spar, and garnet with wolfram pseudomorphs and scheelite, chalybite, melanterite, covellme, cronstedtite, mispickel, and pyrrhotite. Mbnabilly. — Molybdenite recorded from here. Wheal Meneae (' Minear Downs ').— The tin bearing killas has been worked -in the form of a large open pit over 200 yards in length and from 50 to 90 yards in width. The numerous strings and branches which traverse it strike E. 25° S. towards Boscoppa Mine. Mr. Ussher found on «zamining the mine that the killas here is altered and in part finely laminated in a more or less horizontal manner, but that even parallel joint-planes a few inches apart give the appearance of a sharp !dip of 70° towards the N. by E. These planes, if not evidently metalliferous, are found to be more or less so in depth, and have been followed down in a shaft sunk at the western end of the pit. The mine has been described by (Sir) Clement Le Neve Foster. The mass constitutes a stockwork. The killas dips SSE. at 20 to 25°, While the numberless veins which vary from J inch down to a mere knife edge, underlie at about 20° N. They are parallel and run quite independently of one another at distances varying from 2 to 12 inches apart. There is a considerable amount of tourmaline. Foster states that at the S.W. side of the pit there is a so-called lode which is a mass of tournialine schist 6 or 8 inches wide, situated between two tin-bearing bands.* According to Mr. Collins the pit is 150 feet deep. Sixty head of stamps were used in crushing the material which produced on an average 4 lbs. of black tin per ton.f Mulberry Mine. — A large open-work mine in the killas, recently re-started about a mile and a half north-west of Lanivet.J Mr. Barrow finds that the excavation is about 300 yards long by 30 to 50 yards broad. Minute cracks occur in a belt of ground trending north and south and no trace of a master vein could be seen. The tin-bearing cracks seem practically parallel and trend north-north-east ; so that neither the belt nor the cracks correspond in direction with normal tin lodes. The killas is of the banded silt (Meadfoot) type, but it is distinctly more siliceous at the north end of the mine, and in trials and openings still iurther north thicker bands of rather siliceous rock occur. Much less ore has been met with in these siliceous beds. The banded killas has been completely tonrmalinised at the face of the cracks, and all sedimentary material, other than quartz, has been absorbed in the formation of small crystals of schorl, which are arranged criss-cross fashion. A specimen taken nearly 2 inches from the crack still shows the banding and puckering of the original killas. In the more muddy films about one half is replaced by schorl : but in the more siliceous laminse there is much less of this mineral and the outline of the origin clastic quartz-grains is often preserved. A black film of tin-ore occurs in the crack ; the rock on being powdered and vanned yields small crystals or grains which show the usual strange variation in tint, transparency, and depolarisation so characteristic of these minute grains of tin ore. A fair amount of copper and wolfram are associated with the tin. Nanjeath. — A vein of limonite worked at Nanjeath, St. Stephen's, near St. Austell, yielded ore having the following analysis :- Ferric oxide Manganous oxide Silica Alumina Lime Magnesia Phosphoric acid ... Sulphur Water 77-83 0-17 12-43 2-19 014 Trace 0-63 Trace 7-05 100-44 54-48 Bletallio iron * ' On some Tin Stockworks in Cornwall,' Quart. Jonrn. Geol. Soc, vol xxxiv., 1878, p. 656. ■^ 'Origin and Development of Ore Deposits in the West of England,' Journ Rov Inst, of Cornwall, vol. xi., 1892, p. 122. J See also Foster, ' On some Tm Stockworks in Cornwall,' Quart. Journ. Geol Soo vol. XXXIV. (1878), p. 635. . "., MINING, 149 NoKTU Bonny Mine. — Situated in the China clay district near Hensbarrow Beacon. The neighbourhood has been extensively explored by old generations of miners. Mr. Collins states that in this mine five lodes have been worked down to water level. In 1873 the workings extended to a depth of 20 and 30 fathoms respectively on two of the lodes, which consist of quartz, tin stone, schorl, and a little wolfram, the average width of the veins being IJ to 2 feet. The country rock is kaolinized, but in the immediate neighbourhood of the lode it is greisen* The lodes have a bearing of N. 35° E. Pak Consols. — The ores contained copper and zinc sulphide, tin ore and chlorite. Mr. Ussher states that the lodes are partly in and partly outside the metamorphio zone surrounding the granite.f Park op Mines. — This mine has been described by (Sir) Clement Le Neve Foster.J The country rook is a light thinly bedded killas dipping from 30° to 90° K. There are numerous small veins varying in width from a mere knife edge to ^ inch. These consist of quartz and they have a north and south direction, and an easterly underlie. On each side of these veins the killas is tourmalinized. Occasionally the veins are as much as an inch or two in width and contain cassiterite. The tin ore was principally derived from lateral ofiE-shoots of these north and south veins, " for in the proximity of these little insignificant strings leniicnlar masses of tinstone occur interposed between the planes of bedding of killas (floors). The dip of these is generally 60° to 70° (underlie, 20° to 30°), and they are consequently east and west tin lodes." These east and west tin layers, however, do not continue far from the north and south veins, so that they cannot be appropriately termed lodes. These tin layers are occasionally as much as an inch in thickness, but die out as they leave the north and south veins. In one place there is a stanniferous zone 7 fathoms long from north to south, and extending for 10 fathoms along the dip. The layers in this zone are from 1 to 2 inches thick. Another zone, east of this one, is 10 fathoms long from north to south and extends 40 fathoms along the dip. This chute extended from surface to below the 20-fathom level (35 fathoms from surface). In an east and west direction it measured from 6 to 10 feet. These chutes were connected by a very rich lenticular mass of nearly pure tinstone measuring from 12 to 15 feet along the dip, 1 to 6 feet in a north and south direction, and extending east and west for 8 fathoms. At the boundary of the stanniferous deposits the killas was stained by oxide of iron. The average produce of these deposits was 5 per cent., or about 1 cwt. of black tin to the ton. In the southern part of the mine the produce of black tin from poorer shoots was from i to 1 per cent. The mine is 45 fathoms deep. Le Neve Foster con- sidered that the north and south veins were produced originally by shocks, and that the beds were cracked along the cleavage, thus affording a repository for tin ore and schorl carried there by vapours. Pembroke Mine. — From the 28 to the 120 fathom level the lode varies in width from 1 to 8 feet, and consists of quartz, clay, slate and chlorite with copper and iron pyrites, vitreous and native copper, melaoonite, redruthite, zinc blende, and carbonate of iron. The fluccan which traverses the lode is stated to heave it 60 fathoms to the right.§ The bearing of this fluccan is W. 25° N. The distribution of the various ores of copper in this mine has been described by Richard Taylor. || Yellow copper ore occurred principally in the eastern part of the mine near the cliffs. In the central part of the mine (Figs. 22-26) the yellow ore was mixed with grey and black copper ore, while in the western part the yellow ore occurred only at a depth, the ores above being all grey and black. * ,' The Hensbarrow Granite District,' 1878, p. 41. + Summary of Progress for 1903. (^Mem. Geol. SwriB.'), p. 22. J ' On a Deposit of Tin at Park of Mines,' Bep. of Miners' Assoc, of Cornwall and Devon, for 1875, p. 22. § W. J. Henwood, Tram. Boy. Oeol. Soc. Corn., vol. v., 1843, Table Ixxxvii., p. 130. II ' On the Relative Positions of the Yellow and Vitreous Sulphurets of Copper, in the Lode of Pembroke Mine,' Trans. Boy. Geol. Soc. Corn., vol. vi., 1846, p. 99. 150 ECONOMICS. SecLUyeLO.Lk tOOfms Pig. 23.— Pembroke Mine. Loiigitudinal section. Pig. 22. — PemlDroke Mine. Cross section on western side of the cross course. In Boscundle Mine, situ- ated further westwards on the same lodes, but on the western side of the Great Cross Course which passes in a direction N. 22° W. through St. Blazsy Highway, both grey and black copper ore occurred with rich yellow ore thickly coated with the grey and black ores. Tin ore was also present. Further westwards the lodes con- tained only tin ore. The same changes were noticeable in the character of the ore in the lodes of East Crinnis and their westerly exten- sions. (See Oharlestown United Mines and Kast Crinnis.) , Pengelly Mine.— Situated in the Parish of St. Ewe, but the exact locality is not known. The mine is probably not far from tjie St. Austell Consols. The lode has an east and west strike, and is about 7 inches wide. Kupfernickel was raised at about 28 fathoms from surface.* Sulphide of antimony with kupfernickel, niccolite, millerite, and annabergite with copper pyrites and chalybite also occur. Penrose Wheal.— Situated in the Goss Moor on the north of St. Dennis. It is stated to have yielded very rich grey copper ore.f PoLaoOTH. — Reference to the map (Pig. 27) will show that the lodes of this mine have widely different bearings, but form a junction in star-like arrangement on the north of Polgooth Village. In addition to Pig. 24.— Pembroke Mine. Cross section. * W. G-regor, Trans. Roy. Gsol. Soc. Corn., vol. i., 1818, p. 224. + J. H. Collins, 'The Hensbarrow G-xauite District,' 1878, p, 46. MINING. 151 .Sen level 0?JT. Fig. 26. — Pembroke Mine. Eastern side of the cross course. Fig, 25.— Pembroke Mine. Longitudinal section. tin ore the lodes are charac- terised by the presence of ery- thrine, smaltine, iron pyrites, amethystine quartz, chlorite, calcite, and dolomite. St. Martin's Lode. — Bearing E. 33° S. to E. 23° S. The lode has a northerly underlie and is 1 to 4 fathoms in width at the 32 fathom level ; at the 90 it is 5 to 7 fathoms in width. The lode consists of quartz, slate, and tin ore, but in depth there is also iron and copper pyrites. An elvan was met with in the workings . The lode has been traced to the east of the valley at New Mill, being accompanied by an elvan most of the way. Screeds iorfe.^Bearing E. 50° 8., and underlying S. 26° to 30°, it meets Martin's lode at the junction above mentioned. At the 32 fathom level the lode is from 2 to 2J feet in width and consists of slate, quartz, and tin stone. Polgooth Lode. — Bearing E. 5° N. and with a northerly underlie. It varies in width from 6 to 12 inches, but near the junction above alluded to it is 10 to 14 feet in width. The leader consists of quartz with chlorite (peach),- some iron pyrites and tin stone. The killas in the vicinity also frequently contains tin ore. ' This- lode is said to heave Screeds Lode and Martin's Lode 15 feet to the right. Vanvean Lode. — On the south of Polgooth Village. Bearing E. 5° N. It varies from 6 inches to li feet and consists of quartz, killas, and tin stone. It intersects Screeds and Martin's Lodes. New Glands Lode. — Situated about 100 yards south of the junction alluded to. It has an east and west bearing. Screeds and Martin's Lodes are intersected by it. In the Mulvra or eastern part of the mine, the Little Mulvra Lode with an east and west direction varies from IJ to 2 feet in width, consisting of granite, clay, tinstone and iron pyrites. The Snailcreep lode has also an east and west direction, and from the 38 to the 48 fathom level it is 6 inches to 1 foot in width, consisting of quartz, schorl, cassiterite, and much clay.* The cross section shows the relative positions of the lodes in the eastern part of the mine. * The notes have been arranged largely from the following works in the Train. Roy. Oeol. See. of Cormcall : — W. J. Henwocd, vol. v., 1843, table Ixxxv., p. 130 ; John Hawkins, ' On some Bemarkable Phenomena attendijig the Lodes of Polgooth Tin Mine,' voL i., 1818, p. 143. 152 TKEXJOnVMR SOOIfOMtCS. t »MiUi ELVAN? X&S0^^^ 'otgooth. LodLe XodjR ^f SaiAiOO'SH. Fig. 27.— Sketch plan of the lodes of Polgooth Mine. I'iG. 28. — Saotion through eastern part Of Polgooth Mine. There are several other lodes in the mine :— Ragg's North Lode on the north of the Polgooth Lode in the Mulvra part. The Mnlvra Lode on the south of MINING. 153 the Snailcreep Lode. On the west of the junction of the lodes is Philleys Lode situated between Martin's and Polgooth Lode. There is a fluccan about a q^uarter of a mile east of the junction along Martin's Lode and Screed's Lode'with a bearing E. 40° N. It is stated to have a throw of 30 fathoms. Gold has been found in the neighbourhood of Polgooth.* According to Henwood there are three elvans in the sett. The Little Elvan Course at the 85 fathom level is heaved, with Martin's Lode, 30 fathoms by the fluccan. It is a fine grained dyke 2 fathoms in width with a northerly underlie. The North Elvan, which is also fine grained, varies in width from 1 foot to 2 fathoms. It is somewhat decomposed and contains schorl and tinstone. It sends ofE many veins into the killas. The ReskUling elvan at the 85-f athom level is 3 to 8 fathoms in width. It is a coarse-grained quartz porphyry. It is in this mine that the phenomenon of an elvan heaving a lode has been seen, it being recorded that the Reskilling elvan intersected and heaved both Martin's and Screed's lodes. The plans recently consulted in the work of mapping the lodes are those in the keeping of the Home Office, and an old plan dated 1823 in the possession of Messrs. Shilson and Coade, St. Austell. As regards the evidence of elvans heaving lodes the plans are contradictory. The mine has been worked again and again under slightly different names, and the grants of setts have varied as the mine was worked from time to time. PoLMEAR Mink. — The mine which was recently being tried includes the old Polmear and the South Polmear mine setts. The sections show the extent of the recent workings (Fig. 29). The deepest workings are about 63 fathoms 4 itiHiffiffi Quarry Lode. Plough Share Lode. Pig. 29. — Polmear Mine. Longitudinal sections. below adit. The country rock is a fine dark mud slate, with horizontal cleavage and extensive jointings All the lodes are vertical or have a slight northerly underlie, and all present the same general characteristics. The material of the lodes is a Mlas breccia, brought about by dislocation of the walls, producing in the first place contortion, and then brecciation of the mass. The fragments of the kiUas show irregular contortions, and a cleavage on a small scale not noticeable in the country rock. The lodes vary from a few inches to many feet in width. Among the fragments of killas there occurs quartz, copper pyrites and bornite. In the main part of the lode there are generally one or two leaders traversing the mass and containing ores of copper. Vugs also occur. Iron pyrites is exceedingly common. It occurs as a finely crystalline mineral with zoned quartz crystals. Chlorite also is seen sometimes surrounding large quartz crystals embedded in it. Arsenical and iron pyrites, zinc blende, and copper ores found. There are occasionally emissions of carbonic acid gas in the workings. Prideaux Wood Mine.— A mine worked for tin and copper. Bismuth sulphide has been recorded from here. Prosper and Mitchel. — The working has been described by (Sir) Clement Le Neve Poster.f * R. N. Worth, 'Rooks and Minerals of Comwall,' 5iih Ann. Sep. Hoy. Corn. Polytech. 8oe., 1886, p. 70, + ' On some Tin Stookwdrks in Cornwall,' Quwrt. Journ, Geol. Soa., vol. xxaav., 1878, p. 654. 154 ECONOMICS. The pit varies from 60 to about 130 feet in width, and for adistanoe of 800 yards the workings are traversed by numerous small tin veins bearing B. ' JN. There are also in some parts veins with a north and south direction. The rook is a light killas stained brown by oxide of iron, and near the veins is occasionally tourmalinized. The veins are seldom over i of an inch .in width, and consist ot quartz, cassiterite, and a little gilbertite. As it came from the pit the ore produced 3 lbs. of black tin to the ton.* Foster also gives an interesting note stating the reasons why such low-grade ore could be made to pay at a time when black tin was only £42 a ton. The rock is soft and the tinstone occurs in large grains, so that the material is easily stamped through coarse screens, and as there is no metallic sulphide the stufE is readily dressed. In addition to this water power near by was used. Prosper WHEAL.f — Mr. Barrow notes that tin ore occurs in a number of minute cracks which traverse a narrow belt of killas. The whole is quarried, and the bulk of it is stamped. The material is far softer than an ordinary lode. From Lanivet westward the belt has been worked for about 1,200 yards, its maximum breadth being about 100 yards, though it is often less. In some parts it seems only to have paid so long as the killas was close to the surface and thoroughly decomposed. The Ore occurs as small crystals of cassiterite which coat the surface of minute cracks ; but it is not clear if any finely divided ore occurs in the body of the adjacent killas. Schorl undoubtedly occurs in the adjacent killas, but the rock is too soft to make sections that would enable the amount of tourmalinization to be ascertained. The proportion of wolfram and copper is small, and gives little trouble in dressing the ore. The mine is at present worked by an adit driven through the sloping face of the east end of the belt of killas, which is too poor to pay for quarrying. The adit leads into one of the deep open works, and the west end of thii is quarried away by men working on the face. The total returns from this mine amount only to 297 tons ; but this refers only to the period from 1882 to 1906. The huge excavations must have taken many years to complete, and records go back to 1836. Reperry Mine. — Sulphides of antimony, lead, and iron, with ochre and cassiterite were found in this mine, the exact position of which is unknown. Restormel Iron Mine. — The principal workings on these lodes are situated about half a mile north of Lostwithiel, and consist largely of a series of open pits extending for a distance of about half a mile. The lode has been seen at various points northwards for some miles, and extends into the adjacent map (sheet 336) on the north. Mr. Ussher finds that the presence of the lode is indicated in the Great Wood at Lanhydrock, where the lode with a bearing of N. 10° W. was seen to crop out for a distance of 60 yards, and to consist of quartz and iron ore. The bearing varies from due north to N. 26° W. In the principal pits there are two parallel lodes a few fathoms apart, with an easterly underlie of 5° to 20°. The ore, which consists mainly of brown and red haematite, has been worked out by a series of levels, cross cuts and winzes (Fig. 30). Some of the ore consists in the deeper levels of alternate layers of gothite and red haema- tite. In the section (Fig. 30) the levels are not shown, as they are driven in the country rock. Henwood states that where the two lodes come together the width is 2 to 4 fathoms. There is a considerable amount of quartz present, frequently also occurring in vugs.J Patches of pyrolnsite and psilomelane were occasionally seen.§ Psilomelane occurs as a coating on the iron ores. Other minerals recorded from the mine are native bismuth with bismuth and uranium ochre and barytes. Retire Mine. — Yielded haematite and limonite. Rocks and Goonbarrow. — Situated in the heart of the china clay district east of Hensbarrow beacon. The old Rocks Mine and Rook Hill Mine form part of the sett. The lodes have a bearing N. 50° E. Those indicated on the 1-inch * ' Origin and Development of Ore Deposits in the West of England,' Journ. Roy. Inst, of Cornwall, vol. xi., 1892, p. 122. t See also Poster, ' On some Tin Stookworka In Cornwall,' Quart. Journ. Geol. Soc, vol. xxxiv. (1878), p. 654. X Trans. Boy. Geol. Soc. Corn., vol. v., 1843, p. 128. § J. H. Collins, ' Hensbarrow Granite District,' 1878, p. 46. MINING. 155 map are known as ' Webb's,' ' South,' ' Books,' and ' Groonbarrow ' lodes respec- ' tively, taken in order from south to north. The G-oonbarrow lode underlies to the south- east ; the others underlie to the north-west. According to Mr. Collins there are no less than ten lodes in the sett, which are inter- sected by ferruginous cross courses and by the Ruby iron lode. The lodes have been worked on to depths of from 40 to 60 fathoms from surface. According to Mr. Collins the Rocks Lode consists >of an irregular band of schorl rock of varying texture and composition, and containing tinstone here and there. It varies from a few feet to over 10 fathoms, and has no definite walls. One rich bunch of ore occurred under the road leading from Trever- byn to Bugle. In Rock Hill situated on the sharp rise below Old Cleaves China Clay Pits the lodes have been worked opencast, as there are such a number of them that they con- stitute a stockwork. In Rock Hill the material yielded 6 to 10 lbs. of black tin to the ton, but the produce was not uniform. Pseudomorphs of schorl and oxide of tin after porphyritic felspar occur.* Ruby Iron Mine. — The lode with a bearing N. 20° W. can be traced from the south-west of Trethurgy, through Wheal Ruby, Knightor, Treverbyn and, according to Mr. Collins, extends northwards through Rescorla, Rosevear, Bilberry, Colbiggan and Withiel.f (See Hallow and Bocks and Goon-, barrow Mines.) The back of the lode has been pitted about ^ of a mile West of Harros. In the Ruby Mine the workings extend to a depth of 40 fathoms. The lode is vertical and varies frpm 6 to 12 feet in width. The material is red haematite. The average produce is BO"/^ of iron, and an analysis by Mr. W. Baker of Sheffield, ^^j^ published in Mr. Collin's paper, states the "^ composition to be : — Peroxide of iron, 96-2°/„ ; silica, 2-l°/„ ; alumina, l-3°/<, ; magnesia, 0-4°/o ; phosphoric acid and sulphur, nil. St. Austell Consols.— It was in this mine that nickel, cobalt, and uranium ores were found in a series of north and south veins intersecting the tin lode. The sections indicate the ground actually removed in the cross viens, and the positions of these veins where they intersect the main lode. (Pigs. 31-33.) The only account of the mine available is one by Mr. R. H. Williams.J * ' Notes on the Eocks and Goonbarrow Mines,' Bep. Mmeri Assoc. Cornwall and Devon, for 1872-3, p. 66 ; 'Hensbarrow Granite District,' 1878, p. 39. i" 'The Hensbarrow Granite District,' 1878, p. 44. J 'Note on the occurrence of Nickel and Cobalt at St. Austle- Consols Mine,' 39t/i Annual Report, Roy. Inst., CorniuaU, Appendix vii., 1858, p. 32. r^ ^ffSiOOl t^mu (0 156 ECDNOMies . ^^ W. FiCr. 31. — St. Austell Consols. Longitudinal section showing niokelliferous branches. The main lode, known also as the ' Grreat Stopes Lode,' has a bearing of E. 25° S., and a width varying from 1 inch to 1 foot, consisting mainly of tin and copper with cobalt and arsenical ores here and there, but no nickel or uranium ores. This lode appears to have been rich in tin ore for 200 fathoms east of the principal nickel cross course. The nickel, cobalt, and uranium ores occur mainly in the cross lodes which intersect the main lode at right angles. The most important of these is in the western part of the mine, where it intersects the main lode and a Gaunter lode situated north of the main lode, at which points the lodes are 30 fathoms apart. Fig. 32.— St. Austell Consols. Cross sec- tion of main lode showing niokelliferous branches. This nickel cross lode was very rich in nickel and cobalt (Smaltine and Knpfer- nickel) for from 6 feet to 15 fathoms in length, con- sisting mainly of ferruginous quartz. Mr. Williams states that where copper ore was found in the cross vein nickel was always absent. The uranium occurs mainly at the sides, but was also found in the body of the lode. Barytes has been found in the mine. Up to 1857 over 126 tons of nickel ore, containing from 25 to 30°/^ of nickel were sold for £7,045. A little arsenic has also been raised. 1^ \ \ OJ Fig, \AtiU.Levaf. , 33.— 'St. Austell Consols. Cross section showing ' Great ' and ' Nickel ' branches. Silver Vein Mine.— Silver ore occurs in the gossan of a cross course in the Beacon Mine, which is probably another name for the Silver Vein Mine. MINING. 15" South PoLGOOTH.-*-The lodes are the same as those which were worked in the Great Hewas Mine. The cross section (Fig. 34) shows the positions of the lodes, all of whichhave a sharp hade to the north. Fig. 34, — South Polgooth Mine. Cross section. South Teeeas Mine. — Now known as the Uranium Mine. Situated in the Valley of the Fal. The country rock is killas with intrusive greenstone which has been quarried for road metal. The sett is traversed by three elvans. The mine attracted some attention lately on account of the general scarcity of uranium for scientific purposes. The uranium lode has a bearing nearly north and south and an underlie to the west of about 10°. It is said to vary in width from 3 to 5 feet, but the uranium ore is confined to a leader a few inches in width, consisting partly of pitchblende and calc- and copper-uranites with copper pyrites, mispickel and galena, and small quantities of nickel, cobalt, and chromium ore in a veinstone of quartz and green garnet rock, Assays by Messrs. Johnson, Matthey & Co., show that the so-called " green ore " contained 6-2°/o of uranium oxide, while the " dark ore " contained 36°/ of the same." The lode has been explored to the 50-fathom level. The Great Lode is another lode which has been worked at surface for magnetic iron ore and umber, but which in depth, about the 50-fathom level, contains zinc blende, mispickel, copper pyrites, tinstone, and some silver. Schorl also occurs. This lode has a bearing of about E. 20° S. and occurs in a greenstone in which Mr. Collins has found scorodite, pharmaoosiderite, and olivenite. An analysis of the magnetic iron ore by Mr. E. Riley, F.G.S., gave the following percentage composition : — Peroxide of iron, 62'81 ; protoxide of iron, 31'28 ; silica, 1"84 ; alumina, '69 ; oxide of manganese, '46 ; lime, '37 ; magnesia, trace ; phosphoric acid, '05 ; carbonic acid, 2'3 ; sulphur, '04 ; combined water, '53 ; moisture, trace. (Total, 100'37.) Analysis of similar ore from the same lode is given in Kendall's book " The Iron Ores of Great Britain," 1893 (p. 125). The proportions here given are as follows : — No. 1. No. 2. Magnetic oxide of iron 84'24 — Peroxide of iron Protoxide of iron Protoxide of manganese Silica Alumina Lime Phosphoric acid .. Sulphuric acid ,. Water 3-84 69-36 18-36 1-06 0-18 7'51 7-44 1-35 0-86 trace 2-10 trace 0-14 trace 0-03 trace trace 2-00 1-53 100-00 100-00 63-67 62-83 Metallic iron Between the years 1890 and 1903 over 440 tons of uranium ore were raised, realising about £18,000. In 1901, 79 tons, realising £2,923 were raised. Stennagwyn. — Tin oxide and sulphide with wolfram, uranite, autunite, tavistockite and torbernite occurred in association with apatite, fluor spar, gilbertite, talc, wavellite and opal. * Prospectus of the Badlum and Uranium Syndicate, Ltd. 158 ECONOMICS. ToLDiSH. — The main lode, known as the Graverigan lode, has been worked upon in the form of opencast pits in Toldish and Indian Queen's Mine, near Ruthvoes. The bearing is N. 33° W. It can be traced north-westwards through the farm of Treliver by the red colour of the soil, and by old trials here and there. In its north-westerly extension it has a bearing N. 50° W. The material is mainly red haematite, but brown haematite also occurs, and the mine was worked largely for ochre and umber. An old report (unpublished) states that the lode consisted of the oxide of iron and quartz. A cross cut at one part revealed three feet of iron ore, eight feet of quartz, and again ore. In the abandoned railway tunnel, which is now used as a reservoir, the lode was seen to contain 16 to 18 feet of clean iron ore. Manganese also occurs. {See Treliver Mine.) About 350 yards west of Toldish lode there is another which has been worked upon in Parka Consols. It has a bearing of N. 17° W., and contained tin ore. The lodes of Toldish were worked for manganese as far back as 1754.* Dr. Boase has also referred to this mine.f Tower Consols, known also as ' Wheal Click ' and as ' Magnetic Iron Mme. Mr. Hooper, of the Rock Hotel, states that there is an east and west lode of magnetic iron ore a few yards south of St. Gomonda's Church and the school. First worked about 1843. In i;he field in front of the school the shaft is 30 or 40 feet in depth, but is filled in. The lode has a bearing of one or two degrees north of east. Limonite and red haematite also occur mixed with a little quartz. According to Mr. Collins there was also present a little copper pyrites.J Treliver. — There are several old openworks and shafts on the south of Mr. Truscott's [house at Treliver. Formerly worked for iron ore. According to De la Beohe' there is an east and west lode, which on the west of the mine meets with the Indian Queen's, Toldish, and Gaverigan lode. There appears to be two north and south lodes running under Treliver. Trerank Iron Mine. — Known also as " Pits Mingle " and as " Dyehouse " Mine. The lode has a north and south bearing, and has been worked in opencast pits now grown over. The material consists of hard siliceous limonite. Trbtoil Mine. — Mr. Barrow learns that the lodes hade to the south, and were worked to some depth below sea-level. A considerable amount of copper ore was raised. Near the surface, where the rock was decomposed, the vein was worked for a greater distance than in the deeper mine. The lodes crop out at the foot of a long sloping hill, so that the old surface excavations intercept the drainage and conduct most of it to the deeper workings, thus adding greatly to the cost of working. The amount of water still caught by these old excavations and carried into the mine is shown by the adit to the east of TreguUan, where there is sufficient water to work a good sized water-wheel even in summer. Ven ion wyn Mine. — A mine which has been working profitably on a small scale for some years. The tin ore does not require -to be roasted, as it is remarkably free from sulphides. The principal lode is the continuation of the main lode in Hewas Mine on the east. In Ventonwyn it has a northerly underlie of a few degrees, and crosses the bedding of the killas, which varies from horizontal to a dip northwards of a few degrees. In approaching the lode, however, the hade of the bedding increases, while near the lode it has a dragged-out structure, with the hard portions of the killas forming eyes or lenticles in the mass. The lode itself is a plane of shearing, and consists of a fissured, broken, and mineralized killas, varying in width from a few feet to two or three fathoms. In 1903 when the mine was examined the lode at the 30-fathom level was 20 feet wide, and was yielding excellent tin ore. Here and there in the lode, or in the country near it, well polished slickensides occur, some of them much curved. The tin veinstone is a dark green chloritic rock traversed by small quartz veins. A cross course of about 12 inches in width consists of quartz. Parallel with it there are a few smaller strings. WoODLEY Iron Mine. — An anonymous report states that a lode nine feet in width contains both red and brown haematite as well as manganese, the ore being remarkably free from sulphur and phosphorus. A shaft of a few fathoms was sunk, and a level driven to cut the lode. This level intersects an elvan containing tin ore. Other lodes in the sett have been found by means of prospecting pits. * Borlase, ' Natural History of Cornwall,' 1758, p. 130. f ' Contributions toward a Knowledge of the Q-eology of Cornwall,' Trans. Boy. Geol. Soc. Corn., vol. iv., 1832, p. 166. J ' Hensbarrow Granite District,' 1878, p. 46, MINING, 159 OUTPUT OP OOPPEK ObE and COPPEE PROM 1815 TO 1907, AND OP BlACK Tin feom 1852 to 1907. The figures enclosed in brackets indicate the largest amount raised by the mine in one year. Name of Mine. Black Tin. Cppper Ore. Coppfer. Remarks. Tons. Tons. Tons. Ambrose Lake 14 150 8 1872 to 1875. Beam (Great Beam, Old 380 In 1837; 1852 to 1856; Beam). 1868 and 1869 ; 1870 and 1871. "Belovely, Wheal 4 l' In 1894; 1899 and 1902. Belowda (B. Hill or 24 1872 to 1875 ; and in Belowda Beacon). 1880. Blencowe 29 In 1873. Bluebarrow ,. 3 In 1905 and 1906. Open- work (China clay .pit). Bodmin United 680 43 In 1854 and 1855. Boscoppa 27 1872 to 1876. Boacundle 1,115 (217) 205 26 Tin ore- between 1852 and 1863 ; copper from 1851 to 1854. Boskillian 7i In 1903 to 1906. Brynn Mine 18 In 1870. Bunny Mine 257 In 1873, 1874 ; 1902 to 1907. Burngullow 3J 1897, 1898. Openwork. Burney House (Mine 8 In 1874. near). Carolaze 50 From 1869 to 1880. Carthew Consols 113 7 in 1851. Car vath United 112 1858 to 1860. Castle an Dinas Mine ... 24 In 1852, 1872 and 1873. Charlestown and Charles- 6,660 2,915 432 Copper from 1819 to town United Mines. (807) 1850; tin in 1837, 1838 and 1839, ; and between 1852 and 1875. Chytane (St. Enoder) ... 5 In 1873. Commerce 76 116 10 Copper from 1817 to 1820 ; tin 1901 to 1907. Criggan (or Criggan Crinnis 64 1882 to 1885. Openwork. 38,330 1,996 From 1815 to 1833. Crinnis Consols 80 7 In 1869. Crinnis and Carlyon (and 408 37 Prom 1878 to 1881. Great Crinnis Consols) Cuddra 530 5,895 375 Copper from 1815 to 1841 ; 1861 to 1869. Tin ore in 1837 ; and from 1861 to 1872. Duke of Cornwall 3,922 164 From 1855 to 1858. East Beam 5 In 1837 ; from 1863 to 1865. East Crinnis and South 12 70,919 7,344 ■ Prom 1820 to 1841; Par. 1860 to 1862. Tin from 1882 to 1887. Copper mainly from East Crinnis. East Cuddra 26 n 1864 to 1865. East Mulberry 5 In 1873 and 1874. East Polmear .,. 57 5 In 1862 and 1864. 160 ECONOMICS. Name of Mine. Black Tin. Copper Ore. Copper. Bemarks. Tons. Tons. Tons. Wheal Eliza (and Eliza! 9,281 , 135 13 : From 1864 to 1892. Consols). (763) i Fatwork and Virtue . ...' 9 In 1853. Fortescue, Wheal 2 cwt. In 1864. Fortescue Consols 15 i From 1871 to 1874 ; and in 1880. Fowey Consols ... 28 319,790 25,020 From 1822 to 1867. Tin in 1882. G-arker and PentrufE ... 4 In 1899. Openwork. Gaverigan 13 In 1837, 1838, and 1866' Goonbarrow 30 In 1868 and 1869. Goonbarrow and Mollinis 26 In 1863. Gover 75 From 1869 to 1881. Great Crinnis 3,758 225 .From .185 4 to 1869 ; and in 1877. Great Dowgas 129 In 1838; and from 185G to 1859, and in 1907. Great He was United ... -867 From .1854 to 1860. and the Criggan Moors are at an elevation of aboiit 400 feet and a little over, while their tributaries with minor flats can be traced to 500 and even 600 feet, with here and there valley detritus up to between 800 and 900 feet, as in the fine open-cut in the angular ddbris of :the depression on the west of'Hensbarrow. The Conce Moor, Bokiddick Downs, and Breney Common, on the west, of Helman. Tor, and the Red Moor on the east are at an altitude of about 450 feet, while the minor flats and tributaries run up to 500 feet.. The other flats on the south have comparatively rapid slopes to the principal streams draining- them. The principal streams and rivers carrying the drainage of these flats to the sea traverse valleys, the sides of which are fairly steep; while there is generally a quite recent alluvium where the fall of 172 ECONOMICS. the river bed is not rapid. As they get nearer the sea the valleys widen out considerably, and contain great thicknesses of alluT vium, below which stream-tin has been worked. On the other hand, the tributaries leading to the moors from the high land contain thin coarse detritrus, and frequently in the flatter hollows a layer of peat. These deposits approximate closely in their nature to ordinary ' head ' or ' shoad ' material. Owing to the irregular washes here and there filling the low- lying ground near the heads of some of the moorland basins, they here and there appear to be connected by the detritus bridging over the low divides separating the moors, e.g., the detrital material situated in the low ground separating the moor on the east from that on the west of Trescoll. The streams now flowing in them are too small to have assisted in the slightest degree in the formation of any of these moorland hollows, or to have trans- ported the detritus to its present position. In both the moorland basins and the valleys leading from them similar deposits are met with ; but in the valleys there is, in addi- tion, ordinary river alluvium, which is entirely wanting in the waterlogged peaty upland basins. These alluvial deposits have been studied by W. J. Henwood and others.* These sections have been of great use in enabling a generalised account to be made as to the nature of the material and the con- ditions under which it was deposited. In the upland basins the tin-bearing gravel resting' directly on the solid ground, or ' shelf,' varies from a few inches to 30 feet. Upon this rests poor or non-stanniferous material consist- ing of alternate layers of peat, gravels, sands, and clays for a thickness of 20 feet. A section at Pendelow (near Levrean) showed a thickness of from 18 to 24 feet, the stanniferous gravels at the base being from 2 to 4 feet. Over this lay alternations of peat (3 layers), and sands and gravels varying from 6 inches to 8 feet in thickness. * Rashleigh, S., ' Section of the Stream Works at Poth, in St. Blazey,' British Minerals, Part II., 1802, pi. xxi. Bonnard, A. H., ' Sar le gisement, I'exploitation et le traitement de I'etain, dans le Duche de Oornouailles,' Journ. des Mines, tome xiv. (An. xi.), 1803, p. 443. (Section of the deposits of the river 3 miles south of St. Austell.) Smith B., ' On the Stream Works at Pentowan,' Trans. Geol. Soc, vol. iv. (first series), 1817, p. 404. Hawkins, John, ' Observations on the Alluvial Strata at Poth, Sandryoock, and Pentuan,' Trcmx. Roy. Oeol. Soc. Corn., vol. ii., 1822, p. 285. Oolenso, J. W., 'A description of Happy Union Tin-stream Work, at Pentuan,' Trams. Roy. Geol. Soc. Corn., vol. iv., 1832, p. 29. Henwood, W. J., ' On some Deposits of Stream Tin-ore in Cornwall, with remarks on the theory of that formation,' op. Bit., p. 57. (Sections rjf the Fore Moor (Roche); Watergate, St. Austell ; Pendelow ; and Broadwater, Luxulian. Also the Oamon Stream Works, Boase, H. S., ' Contributions to a Knowledge of the Geology of Cornwall,' op. eit., p. 246. (Deposits near Roche.) De la Beohe, Sir H. T., ' Report on the Geology of Cornwall,' etc. (,Mem. Oeol. Sure.'), 1839, p. 395. (Sections near Par and other places.) Henwood, W. J., 'On the Detrital Tin-ore of Cornwall,' Jburn. Roy. Init. of Cornwall, \o\. iv.,-1874, p. 191. (Sections at Pendelow, Levrean, Pitmoor, Red- moor, Upper Creany (Gready), Tregoss Moors, Treloy.) Symons, R., ' Alluvium in Par Valley,' Journ. Roy. Inst.. Cornwall,' vol. v., 1877. p. 882. Ussher, W. A. E., ' Post-Tertiary Geology of Cornwall,' 1879. STREAM TIN. ^ 173 At Levrean another section shows similar conditions, but the tin-gravels vary from 10 to 15 feet in thickness, and were said to contain specks of gold. The complete section ranges up to 24 feet, the upper parts containing a second gravelly layer of from 3 to 6 feet, with tin ore and specks of gold. Teat, sands, and gravel make up the rest of the section. At Pitmoor, near Levrean, the tin ground is from 3 to 10 feet thick, being overlain by sands, gravels, and peat having a thickness of 6 or 7 feet. In the Redmoor east of Helman Tor, at Lower Creany, the tin-ground varies from 4 to 5 feet, the rest of the deposit consisting of from 3 to 6 feet of peat, <;lay, and granite sand. Specks of gold have been found in the tin-ground. At Upper Creany, near the last locality, the tin-gravels, also containing gold, is 4 or 5 feet thick, being overlain by a few feet of clay and fragments of slate, covered by peat varying from half a foot to 3 feet in thickness. The Goss Moor, one of the largest of the upland basins, has been extensively worked, and near Boyalton, in a part known as the Golden Stream working, shows the following section. The basal tin-gravels, in which there is an abundance of fragments of el van, is from 2 to 3 feet thick, and is overlain by clay and fragmentary material, principally elvan, from the elvan course not far away, of 5 to 6 feet thick. In the northern branch of the Goss Moor, at a place immediately north of the railway bridge over the high road, about a mile west of Koche railway station, the tin-gravel layer is from 1 to 2 feet thick. Above this the material consists of fragments of rock, the layers being from 3 to 4 feet thick. In the Fore Moor between Bilberry and Bugle, on the east of Boche, the tin- ground varies from 4 to 30 feet in thickness. Above this there are two layers of peat of from 1 to 3 feet in thickness between layers of fragmentary mateiial, gravels, and silts, the thickness of the deposit over the tin-ground being from 16 to 20 feet. At Broadwater, near Luxulian, the total thickness of the deposits is from 21 to 24 feet, the tin-ground being 7 feet deep. Above this are layers of granite sand and mud, with vegetable remains. At a place called Watergate, near Pendelow, the tin-gravels vary from 2 to 20 feet in thickness, being overlain by peaty layers between coarse and fine detrital material of a thickness of about 12 feet. In the streams which drain the upland basins, just described, there is the second class of stream-tin deposit. In them the deposits are of considerable thickness, and near their estuaries there is abundant evidence of the silting up of the ancient valleys. Evidence obtained from shafts sunk in the alluvium of the tidal river between St. Blazey and Par shows that the deposit is from 64 to 66 feet thick. At the base of all the valleys the tin gravels may occur. Above them are alternate layers of peat of three or more feet in thickness, and gravelly deposits with sands and clays. In the river south of St. Austell over 25 feet of mud and gravel was sunk through before the first peat layer was met with. At Forth, near Par Harbour, over 13 feet of light sands and clays overlie the first layer of peat, four feet thick. Below this comes clay with plant remains, and then about 10 feet of sea-sand and estuarine deposits at a depth of 26 to 36 feet from surface. Below this is another layer of peat, and then the tin gravels, the layer of which varies from one to six feet in thickness. At Sandrycock Stream "Works, situated in the middle of the valley, west of Par Harbour, the tin ground is of same thickness as at Porth, and is overlain by nearly three feet of peat, above which is 13 feet of sea-sand, with shells and clay. Above, this is covered by four feet of clay, four feet of peat, and about 14 feet of micaceous clays and gravels. 174 ECONOMICS. Speaking of tlie stream-tin deposits in the valleys extending from St. Austell to Pentewan, Borlase makes the following obser^ vations : — ' The most considerable stream in Cornwall is that of St. Austell Moor, which, is u. narrow valley, about a furlong wide (in some places wider) running pear three miles from the town of St. Austell southward to the sea. The ground of this moor is all adventitious for about three fathoms deep. The uppermost coat consists of thin layers of earth, clay, and pebbly gravel, about five feet ; the next stratum is about six feet, more stony, the stones pebbly-formed, with a .'ravellv sand intermixed; these two coverings being removed, they find great numbers of tin stones from the bigness of a goose-egg, and sometunes larger, down to the size of finest sand. _ „ j. - j- . ' It occurs in a layer of loose rounded stones, varying from a foot in diameter to the size of a small pebble.* A section of a stream-work in the valley of the Fowey by S. R. Pattisont shows that the deposit consists of alternate layers of peat, sand, and gravel. In the peat was found remains of deer horns, hazel nuts, and ferns. Gold in SiANNiFERotrs Ghavels. Although gold has been found in the stream tin working in other parts of Cornwall, this district has received more notice than the others on account of the exceptionally common occur- rence of that metal. The gold does not occur in such quantity as to make it profitable to work those streams for it alone, as the amount which would be obtained would be very small. Ita Occur- rence has been recorded by Carew, 'Borlase, and others Carew has described how exceptional quantities of gold in some dressed tin ore from a tin stream in St. Stephens was mistaken for mundic by the tin buyers, but -the tin-streamers generally recognised its presence, and separated it from the tin before selling. De la Beche, judging from the abnormal amounts of gold in the stream tin of Ladock Parish, suggested the possibility of the presence of a lode containing exceptional amounts of gold. It was found particularly in a stream-work near Ladock Parish Church. In Creed, on the south of St. Austell, a nugget of over 15 dwts. was found. As already stated, grains of gold have been found in the stream works of Creany and Levrean, but the precious metal has also been recorded from the parishes of St. Ewe, St. Austell, Luxulian, Lostwithiel, St. Mewan, and Cardinham. Building Stone. Granite. — Although a large part of the St. Austell granite has been kaolinized, a considerable area has entirely escaped secondary modification, and is consequently capable of yielding excellent blocks of granite suitable for large engineering works and public buildings. The most important quarries are those of Tpegarden, Carbean, and Colcerrow, situated near Luxulian, and of Carn Grays, near Carclaze Downs. * W. Borlase, ' Natural History of Oornwall,' 1758, p. 162. t ' On some Post-Tertiary Deposits of Cornwall,' Trans, Boy. Geol. Soo. Corn., vol. vii. (1847), p. Zi. BUILDING STONE. ara . Tlie crusbing stresses of cubes of granite from Colcerrow Quarry were ascertained bj David Eircaldy for Messrs. Freeman and Sons, witli the following results : — Colcerrow Quarry. Expe/riments carried out in May, 1904. Dimensions of cubes. Inches. Base. Sq. ins. Stress. Lbs. Lbs. per sq. in. Sides. Base. Tons per sq. ft. 3-98 3-98 3-96 4-00 X 3-98 = 3-98 X 3-98 = 3-97 X 3-96 =• Mean 15-92 15-84 15-72 359,900 32.1,500 306,400 22,607 20,234 19,491 1,453-8 1,3012 1,253-4 15-82 , 328,933 20,777 1,336-1 The granite of St. Austell has been used in public buildings in Oxford, London, and Eome. London Bridge, the British Museum; and Crystal Palace were constructed partly of granite raised from the quarries of the eastern part of the St. Austell Granite mass. The stone is used extensively locally, and has also been employed in the Plymouth Breakwater and Light- house ; the Docks at Keyham, Devonport, Portsmouth, Cliat- hain, Pembroke, Cardiff, Dover, Alderney, and even as far away as Northumberland. Exeter Market Place was constructed from stone raised at Colcerrow, which has also yielded the largest proportion of the stone of the district used in the above-mentioned structures.* The material produced at Golden Point Quarry (Tregarden), north of Luxulian, is a coarse porphyritic biotite granite, con- taining felspars of from 2 to 4 inches in length, but occasionally as mjich as 5 inches, and showing a zonary structure. These felspars occasionally occur as cruciform twins. Schorl appears to be an original constituent of the granite, and occurs as small nests or needles, or in stumpy crystals. Basic spheroidal con- cretionary masses and inclusions of sedimentary material are found in the rock, as well as lumps of fine grained dark granite. There is a three-fold jointing in the quarry — the cleaving way has a general direction of N. 20° E., and the toughway E. 20° S. The pseudo-bedding is well exhibited, and constitutes the third jointing plane, of which the quarry men take advantage in hewing the blocks of granite. Of the less important quarries may be mentioned two, situ- ated a quarter of a mile south and west of Treverbyn respectively. The quarry on the south is on the east side of the road between Treverbyn and Carthew, and consists of sound porphyritic tour- maline granite, which is used for building. The other quarry is ♦ ' Mineral Statistics,' 1858, Pt. II., p. 134. 176 ECONOMICS. on the east side of the road leading to Tresayes Downs and Eoohe, and consists of a coarse grained granite with a little pale mica. Sound granite occasionally porphyritic, but not having the handsome appearance of that from the quarries described, occurs at Hallow Farm between Bugle and Bilberry. Here and there small quarries have been opened out in partially kaolinized granite, which is easily dressed and used locally in small buildings. A quarry of this nature is situated near Woon, on the south side of the road between Bugle and Carbis. The material is a soft tourmalinized granite,, used locally for buildings. There are some small porphyritic tour- maline granite quarries in the valley of the St. Austell river south of Carthew. A considerable amount of building material for local use is obtained from loose blocks of granite lying about the Downs in the higher land of the district. The pale mica graniteof Hens- barrow Downs is used in this way, the stone being derived from loose blocks. Large numbers of boulders of schorl rocks which have been shed by the Eoche Rock occur half-buried in its vicinity, and have been used extensively in Roche Village and the neigh- bouring farms, outhouses, and walls. D. A. M^A. The following notes are by Mr. TJssher, unless otherwise stated : — Luxullicmite. — ^The luxuUianite of which the Duke of Welling- ton's sarcophagus was made, formed part of a mass in a field about 150 yards south of Tregonning (south of Lostwithiel), the remains of which are still to be seen by the hedges. It was not found in situ. Amongst the granites exhibited at the Museum of Practical Geology the following are from our district. Polished columns of luxuUianite and of a similar granite from Lanlivery, with yellow-buff, not red felspar, polished cubes of grey-brown schorlaceous granite from St. Austell, and of red schorlaceous and grey porphyritic granite from St. Blazey. There is also a polished cube of the Dowgas Elvan. Greenstone. — Duporth Stone is not worked now, but its suit- ability as a decorative stone* may be seen in the shafting in the triforium in Truro Cathedral. Killas. — Both the Middle and Lower Devonian slates and shales are quarried and used as local wall-stone and building- stone where their planes are sufB.cient]y coherent to permit of quarrying out in fair-sized pieces and being dressed.' Moat of the quarries opened in the beds of the Meadfoot Group east of Lostwithiel, around Boconnoc and Lerryn, and south of Lanreath, also south of Lostwithiel, near Tywardreath, and between St. Austell and Porthpean, have furnished a large pro- portion of the local building materials and wall-stones. The Middle Devonian rocks display sinlilar characters to those in the area south of Liskeard. They are intersected by cleavage planes dipping at low angles. with occasional signs of " W. D. Thomas, ' Excursiou to Cornwall,' Proc. Oeol. Assoc, vol. x., 1888 p. 202, BtriLDING STONE. 177 vertically-gnarled bedding and irregular joints. Thes« joints in a quarry in Margate "Wood, east of Bodmin, permit the rock to be quarried in large blocks. On tbe west of Pinsla Park a quarry yields quadrangular blocks. Near Kingswood, at tbe letter k on the map, tough blue- grey mudstone is quarried in irregular blocks used for building. There are quarries west of Lower Hill, between Trevorder and Holtroad Downs, near the Inn south of Trenay, in Quarry Wood near Polmenna, west of Doublebois Station, between East Tap- house and Middle Taphouse, near C!onnonbridge, and at a mile west of Connonbridge. The last-mentioned quarry yields large blocks which harden on exposure, and have been used in building the Wesleyan Chapel in the vicinity. A quarry in the band coloured as Staddon Grit, at half-a-mile north of Crickapit Mill, furnishes local building and wall-stones. The rock is of the usual Middle Devonian type, argillaceous slate, with nearly horizontal cleavage planes parting readily at inter- vals between which they are coherent. It is probably a Middle Devonian infold ; there are signs of curved bedding with a high northerly dip. Near the second milestone from Bodmin, by and near the road to Bodmin Road. Station, there are two quarries in soft grey-bufE argillaceous silty-banded slates which have been included in the Staddon Grits. Similar materials have been quarried by the road east of Castle Canyke. Somewhat similar rocks have been quarried south-east of Braddock in the Staddon Grits, near Boselyon, where the planes undulate, but yield large blocks, and near Bury Down Camp, where they are more or less arenaceous and of grey, greenish, and pinkish tints. It would be waste of time to particularize the numerous quarries opened in the Meadfoot Group for local building pur- poses. A few examples will suffice. On the west side of the stream south of the school at Boconnoc Park a large quarry has been opened in lead -coloured, siliceous, slaty or shaly rock, which is quarried -ill large flat slabs from 2 to 6 inches in thickness. In texture the rock is silty. The planes are nearly horizontal. No proof was obtained as to the true bedding. Dark grey slates yielding tabular masses are quarried near Boconnoc House. South of Coombe, south-west of Trevego, finely-laminated arenaceous and argillaceous beds have been quarried in flat pieces, splinters, and masses 3 feet long by 1 foot wide. In the quarries south-east of Lostwithiel it is often im- possible to distinguish cleavage from bedding, even where fossiliferous material is present. At the west end of Lostwithiel, just north of the last letter of that word on the map, there is a quarry which affords, through- out a section about ^O yards long and from 15 to 30 feet in height, an. excellent example of the puckered and vertically- curved bedding so characteristic of the district south of Lost- withiel, and resembling the Middle Devonian slates of the Bod- min and Doublebois area. The rocks are somewhat silty slates, with bands and seams of dense silty material. 12979 M 178 ECONOMICS. The major planes of schistosity , when distiiiguishable are nearly horizontal, and the principal joints run north and south. The utility of the material depends on the cohesion o± the laminseand the facilities afforded by the planes of schistosity and joints. -■ i * j.i. The altered interlaminated and finely-laminated rocks o± the Meadfoot Group near Lostwithiel are exposed in many quarries opened for local building purposes. The Dartmouth slates are locally used as wall-stone and for building. A quarry was opened in them near Penquite, north of St. Sampsons. The rock is purple slate marbled with green, with coherent planes, and yields fair-sized flattish blocks. The Grampound grits have been quarried as a local buildmg- stone here and there along their outcrop. There are quarries on the south and s'outh-west of Nantellan, in which, these grits are tough, massive-bedded, broken by irregular joints, and closely associated with hard, more or less arenaceous, dense mudstone, capable of yielding large blocks. These approach in character the rock in the Ladock Quarries, but are not so coarsely brec- ciated. These beds are mostly weathered, and where evenly- bedded and the joints permit, as in a quarry three-eighths of a mile south of Grampound E/oad Station, can be used as a building or wall-stone. Dr. Boase* says that at Trevillick, about one mile north of Grampound, the slate is raised in thick slabs, affording a good building stone. He also describes the Grampound greywacke. RooriNG Slates. There is no slate or shale in the area capable of comparison with the Delabole slate. The dark beds between Doublebois and St. Neots yield a rough roofing slate and flat slabs, but these are not largely worked. Dr. Boaset mentions the use of the slate of Sticker for roofing purposes. PeachJ records the trial of slates in a quarry opposite^ the rock near Lerryn for roofing purposes, for which they proved unsatisfactory. EOADSTONE. Mention has already been made of the use of the Brannel Elvan as a roadstone. The best roadstones in the district are, however, furnished by the harder diabases and the calc-flintas, which have been quarried for that purpose near St. Mewan, west of Ti-evarrick Terrace on the outskirts of St. Austell, near Tre- gongeeves, where there are stone-crushers, and near Tregorrick. Wherever the calc-flintas occur they are quarried for roadstone, and this accounts for the frequent sections met with where this type prevails. In the narrow band at Treesmill, for instance, north of Lostwithiel, east of Chark, and near Eord, south of Lanhydrock, ^the calc-flintas are quarried for roadstone. ;''C!,.' - ' ■ W. A. E.U. * Trails. Itoy. Gefil. Sue. Cam., vol. it., 1832, p. 263. t Ibid, p. 275. X -raiif, vol. vl. (1816), p. 237. BRICKS SKD TILES. 179 The niost important quarry for roadstone is -one situated on the : eastern bank oi the Fal, near Gaverigan. The material quarried is handed calc-hornfels. The material, although tough, is broken by hand to the size required for road metalling. As this band of tough rock extends eastwards to the Roche Rock, ■ other quarries might be opened up on it, particularly between Trerank and Tresayes. Roadstone was formerly and is still occasionally produced from a' quarry at Higher Trelavour, near St. Dennis. It is situated in the killas about '40 yards from the granite margin, and consists of hard spotted slate, which is here and there tourmalinized and traversed by tongues of granite which are also broken for the same purpose. On the west of Tresayes a quarry was formerly worked for roadstone, 150 yards from the granite. As a whole the rock is soft, but in certain places it has been tourmalinized into a hard black rock suitable for roadstone. The fine-grained elvan on Trelavour Downs has been exten- sively worked for roadstone. It is not very hard, but is excellent for wear. The heaps of material rejected from the wdrkings on the peg- matite vein on Tresayes Downs, and also some of the hard sub- angular debris obtained from the moors, is used for the same- purpose. D. A. MCA. Quartzose grit or quartzite was quarried for roadstone in the valley between Polscoe and Collibeacon, north-east of Lost- withiel. Staddon grit, quartz stones, and any such comparatively hard materials gathered off the fieldg are also used for roadstones. Bricks and Tiles. . Wheal Remfrey Brick and Tile Works are situated by the Fal Valley, about half a mile north of Retew. Here a pit. has been opened along a decomposed sandy pale-greenish-yellow elvan, about 40 feet thick, in decomposed schorlaceous granite with schorl-rock veinstones. The materials manufactured consist of firestone bricks and two ■ kinds of building bricks. The firestone bricks are obtained from the completely decom- posed parts of the schorlaceous granite The ordinary brick clay is obtained from the upper part of the china clay pits under the overburden, and is mixed with sand from the elvan, ground up. The remarks about the greater suitability of the upper part of the clay in Trerice clay pit for standing fire applies generally, and it was from the upper part of the stopes beneath the over- burden that the bricks, tilestones, or slabs formerly used in floor- ing the " Dries " were made, but now it is found more profitable to purchase such materials from places outside the district where their manufacture forms the staple industry. 12979 M 2 180 ECOKTOMICS. On the west of the high road at half a mile north of Qrani- pound Road Station there is a disused brick pit in an old alluvial, or Head, valley-deposit, consisting of from 5 to 15 feet of loam containing fragments of killas on grey, red-stained, argillaceous slates with peroxidated silty beds containing shale fragments. "Watee Supply. The St. Austell water supply is obtained from Carnestents disused china clay pit, about a quarter of a mile south of Penisker and three-quarters of a mile north-west of the railway viaduct at Oover. A feeder to the Gover stream rises in this pit. The supply is obtained at about 500 feet above O.D. Thence it is piped to a reservoir, near Trenance, on the 400 foot contour at 1,220 yards W. 35° N., from St. Austell church. The reservoir has two open tanks, the rest covered. The water is conducted down the hill and across the Bodmin Road, as the highest part of the town supplied by the syphon pipes is below 300 feet. The population supplied is over 11,000.* Mount Charles supply is derived from a spring just outside the gate of Trenance Farm (200 yards from the iSt. Austell reservoir), at about 430 feet above O.D., and is piped from thence. At Hornick, near the granite, east of St. Stephens, a well was sunk through red and buff altered interlaminated beds in which water was obtained at between 90 and 96 feet. The water supply of the Port of Par is derived from the main of the St. Austell Rural District Council, to whom an annual rent is paid (from information kindly supplied by the Secretary of the Par Water Company, Mr. J. Eolkinghorne). The Lostwithiel water supply is piped direct to the reservoir from a spring which rises in a field at Maudlin, near Lanhydrock (from information kindly given by Mr. "W". Pease, Town Clerk of Lostwithiel). W. A, E. V. A good supply of water is generally available for the farm houses in the granite area to the south of Bodmin, and the wells rarely go dry even in summer, provided that they are appreciably deeper than the base of the alluvial deposits of Red and Conce Moors. Rather deep drains have been recently cut in these, and have had the effect of slightly lowering the water level in the adjacent granite; but this seems to be easily remedied by slightly deepening the shallower wells. In killas areas, farm houses, well down in the valleys usually have no difficulty in obtaining good water from one of the very numerous springs that flow along master- joints in the killas; but higher up the hillsides the springs tend to go dry in summer. Bodmin derives its water supply from springs issuing from the granite in the area to the north (about St. Breward). The supply is unusually good, while the water itself is not only good, but of exceptional softness as the Cornish granites contain very little lime felspar, and the water issuing in springs from them con- tains singularly little lime. * 11,377 according to ' Waterworks Directory and Statistics," 1903, London, p. 290. AGEICULTUEE. 181 The asylum has a separate supply derived from a powerful spring in the killas, that rises about a mile north of the town. A still more powerful spring issues from a master joint in the killas on the north side of the town, and is brought down in pipes to the south side of the church. This has neyer failed even in the driest summer, and for many years was the chief source of supply of drinking water for the part of the town nearest to the church. It is both pure and soft. G. B. As with the exception of the tunnel reservoir between Ruthvoes and Toldish reserved for I^ewquay, there is no storage for water in the region comprising St. Columb Major, Indian Queen, St. Dennis, Roche, and the north of Luxulian water for domestic pur- poses is obtained from wells and springs. Many springs are situated about the edge of the Moorland hollows, but much of the water is obtained from wells varying from 15 to 60 feet in depth. Mr. Mewton, of Roche, states that a proposal has recently been made to supply water to Roche by means of raising it from tiie workings of the old Tower Consols Mine situated near' the church. There has been another proposal to bring the water to Roche in pipes from a spring at Treverbyn. D. A. MOA. Agriculture. * This area forms a fairly typical sample of the representative agricultural aspect of Cornwall. The barren permanent grass, heather, and marsh land of the granite heights, the rich meadow lands in the broader stream valleys, the shallow soil of the Dartmouth Slates, and the more variable soils made by the rocks of the Meadfoot Group and Staddon Grits, the clayey soils of the Middle Devonian Slates. Although the Ordovioian rocks are not present in the map, the varieties of Devonian sediment furnish very similar soils. Of course, as is usually the case, the masses of basic rock form the richest soil, and as these are liable to decomposition as at Tregongeeves and near Terras, they some- times rot to a considerable depth. The igneous materials asso- ciated here and there in the Meadfoot Group, too small to be' indicated on the 1-inch map,, are often so decomposed as to be scarcely recognizable. No doubt many such have escaped detec- tion, and these and the slightly calcareous rocks are not without a favourable influence on the productive capacity of the soils. w.A. E. u. 182 APPENDIX. BIBLIOGRAPHY. 1797. Eashleigh, P.— Specimens of British Minerals selected from the Cabinet of Philip Eashleigh. 410^ London. (Poth section given in last two 1817. Smith, E.— On the Stream Works of Pentowan (read June 3rd, 1814). Trans. Geol. Soc, vol. iv., pp. 404-409. 1818. HAWKINS, J.— On some remarkable Phsenomena attending the Lodes of Polgooth Tin Mine. Trans. Boy. Geol. Soc. Corn., vol. i, p. 143. Majendie Ashhurst. — Contributions towards a knowledge of the Geo- logical History of Wood Tin. Jbid., p. 237. Account of Copper raised in Cornwall in the years 1815, 1816, 1817. Ibid., p. 252. 1819. Eashleigh,^ the late P.— An account of the. Alluvial Depositions at Sandrycock. (Drawn up in 1792, and communicated by John Hawkins, Sept. 1819.) -Jbid., vol. ii., p. 281. Hawkins, J.— Observations on the Alluvial Strata of Poth, Sandrycock^ and Pentuan. Ibid., p. 286. Account of Copper raised in Cornwall in the years 1818-1822 inclusive. Ibid., p. 428. 1820. Sedowick, Eev. Prof. A.— On the Physical Structure of those Formations which are immediately associated with the P.imitive Eidge of Devonshire and Cornwall. Trans. Camb. Phil. Soc, vol. i., p. 89. 1828. Account -of Copper raised in Cornwall during the- years 1823-1827 inclusive. Trans. Roy. Geol. Soc. Com., vol. iii., p. 342. 1829. COLENSO, J. W.— A description of Happy-Union Tin Stream-work at Pentuan. Ibid., vol. iv., p 29. Hen WOOD, ^. J. — On some of the Deposits of Stream Tin-Ore in . Cornwall, with Eemarks on the Theory of that Formation (read in . 1828 and 1829). Ibid., p. 57. See also Henwood, W. J., in /omj-h. Roy. Inst. Corn., vol. iv., pp. 214-255. 1830. Carne, J. — An account of the Discovery of some varieties 6f Tin-Ore in a Vein, which have been considered pecdiiar to Streams ; with remarks on Diluvial Tin in general. Trans. Roy. Geol. Soc. Com.j vol iv., p. 95. Hawkins, J. — Some account of the soft Growan at the Beam Mine, in the Parish of Eoche, and at Uarclaze Mine, in the Parish Of St. Austle (read October 1830). Ibid., p. 475. 1831. BoASE, H. S., M.D. — Contributions towards a knowledge of the G«ology of Cornwall (read October 1830 and 1831). Ibid., pp. 199-207, 234- 289. 1832. Account of Copper raised in Cornwall in the years 1828-30th June 1832 inclusive. Ibid., p. 492. 1837 and 1839.— Sedgwick, Eev. Prof. A., and [Sir] E. I. Mdrchison.— On'the Physical Structure of Devonshire and on the Subdivisions and Geological Eelations of its older Stratified Deposits. Trans. Geol. Soc, ser. ii., vol. v., parts i and ii-., pp. 633-687 and 688-703. See alsq Trans. Brit. Assoc, 1836, p. 95. . . . ' 1839. DelaBeghb [Sir]. H. T.— Eeport .on the Geology of Cornwall, Devon,' and 'W'est Somerset. {Geol. Survpy.) 8vo., London. - Winn-, Dr. J. M.— Notice of Fossil Bones found in Pentewan Valley. Ann. Rep. Roy. Inst. Corn., No. 21, p. 45. 1340. Lonsdale, W. — Notes on the Age of the Limestones of South Devonshire. Trans. Geol. Sue, ser. ii., vol v., p. 721. Winn, Dr. J. M.— Notice of Antlers found at Pentewan. Ann. Rep. Roy. Inst. Corn., No. 22, p. 38. 1841. Peach, C. W.— An-Axic o uu li ul L fag-fossil-ei^anic Eemains found on the South-east Coast of Cornwall, and in other parts of that County. Trans. Roy. Geol. Soc. Corn., vol. vi., p. 12. Phillips, Prof. John.— Figures and Descriptions of the Palaeozoic Fossils of Cornwall, Devon, and West Somerset. Geol. Survey. 8vo., London. Bibliography. 183 1843. Hen WOOD, W. J.— On the Metalliferous Deposits of Cornwall and Devoq. The substance Of papers read, 1830, 1831, 1833, 1834, 1835, 1836. Trans. Roy. Giol. Hoc. Corn., vol. v.,-, p. 115. Peach, C. W — On the Fossil Fishes of Cornwall. lUd., vol. vi., p. 79. Whitney, N, — Bemarks on the minor Fractures of Rocks, &c. Ibid., p. 104. Williams, Bev. D.— On the Killas Group of Cornwall and South Devon. Ibid., p. 122. 1844. Cough, ,B. Q.^On the Silurian remains in the. strata of the south-east Coast of Cornwall. Ihid., p. 147. 1845. Peach, C. W.— On the Fossil, Geology of Cornwall. Ihid., p. 237. 1846. MUECHISON, Sir R. I. (letter from).— A brief review of the classification of the Sedimentary Rocks of Cornwall. Ibid., vol. vi., p. 317. Peach, C. W. — Notice of the discovery of Serpentine and of its associated Rocks in the Parish of St. Veep, near Towey. Jbid., p. 351 . - Williams,. Rev, D. — ^On an important Slate term-in the Killas: series, of Cornwall and South Devon, &c. 76id., p. 334. 1847. M0KCHISQN [Sir], R. I.— A .brief Review of the Sedimentary Rocks of Cornwall. Edin. Neio. Phil. Journ , vol. xliii., p. 33. Peach, C. W.^On the Fossil Geology of Lantivet and Lantick Bays, ■ "near Fowey. Trans. Hoy. Geol. Soc. Corn., -vol. vii., p. 17. .' 1848, On the Fossiliferous Strata of part of the South-east Coast of Cornwall. Ibid., p. 57. 1849. Giles, J. — On the Fossiliferous Rocks of the Liskeard District. Ibid., pp. 97-98. - Peach, C. W.— Additions to Cornish Geology. Ibid., p. 100. ■ 1850. Pengelly, W.— On the Ichthyolites of Bast Cornwall. Ibid., p. 119. , .Peach., C. W., — On the Fossils of the Blackhead Slate Quarry, near St. Austell, and on the Fossil Fishes of Cornwall. Ibid:, p. 121. — — Notes on Cornish Fossil Geology. Ibid, p. 125. 1851. Notice of the Geology of St. Pinnock. Hid., p. 175. Couch, B. Q.-^Notice of the occurrence of the Horns' and Bones', of several species of Deer in the Tin Works of Cornwall. Jbid.j 186. Goodwin-Austen, R. A. C. — On 4he Superficial Accumulations of the Coasts of the English Channel and the changes they indicate. Quart. Jmirii. Genl. Soc, vol. vii., p. 118. McCoy, Prof. F^ — On some new Devonian Fossils. Ann. andMag. Nat. Bint., ser. 2, vol. viii., p. 481. 1852. Pattison, S. R.— On the Geology of the South Coast pf Cornwall. Trans Roy. Geot. Sool CoTn.,vol. vii., p. 208. Peng ELL Y, W. — Remarks on the Geology of the South Coast of Cornwall. . Ibid., p. 211. Sedgwick, Rev. Prof. A. — On the Slate Rocks of Devon and Cornwall. Quart. Journ. Geol.Soo.,-v6l. viii., p. 1-lQ. 1853. Stockek, H. M. — Account of some Remains found- in the Pentewan Stream- Work, and of the circumstances under which they were found. Rep. Penzance Nat. Hist, dnd Antiq, Soc, vol. v., p. 88; An Essay on the China-stone and China- clays 6f Cornwall. 20«A Ann. Rep. Roy. Polytech. Soc, Corn., p. 77 -; Edin,' New Phil. JoUrfi., vol. Iv., p. 91., and Vol. Ivi., p. 50 (1854). 1854. Couch, R. Q. — Notes on the Bones found in the Alluvial Deposits of Cornwall. Trans, Roy; Geol. Soc Corn , vol. vii., p. 233. 1855. — On the Zoology of the Post-tertiary Deposits of Cornwall. , ifejti, vol. vii., p. 263. ..' ' ; Sbduwick, Rev. Prof. A., and Prof. F. MCCOy.— A -Synopsis of the Classification of the British Palaeozoic Rocks. ''4tb., London and Cambridge. ■ t 1858. Williams, Capt. B. H. — Notice of the occurrence of Nickel- and Cobalt at St. Austle Consols Mine, near St. Austle, Cornwall. 3'9<^ Ann, Rep. Roy. Inst.-Com.:p. 32. ■ ,' .: (. \ " 1863. Williams, ■Capt. W. H.— Oa Mineral Deposits [near St. Austell]. : 4bth Ann. Rep. Roy. Inst. Cdrn., Tp', 44. ' .■,'■: [''■,■";■ J < 1864. Davidson, T. — A Monograph of the British Devonian Brachiopoda. PaZ. Soc, vol. xvi., pp. 21. 47 (for 1862). '■■ . .'...-CJf. .18^5. ^..^ yj(U iStrf., vol. xvii., pp. 83, 84 (for 1863). y 184 bibliogea:PhY. 1868. Peach, 0. W.— On the Fossil Pish of Cornwall. Trans. Roy. Geol. Soc. Corn., vol. ix., p. 31., and Geol. Mag., p. 568. Woodward, H., E. Ray Lankestek, and E. Wyatt-Edgell.— iish Remains in the Lower Devonian of South Devon and Cornwall. Oeol. Mag., vol. v., p. 247. See also Quart. Journ. Geol. Soc, vol. xxiv., p. 546. 1869. Peach, C, W.— Remarks on (with a list) some of the Organic Remams of Cornwall, in the Museum of the Royal G-eological Society of Cornwall. Trans. Hoy. Geol. Soa. Com., -vol. ix., p. 49. 1870. PowRiB, J., and E. Ray Lankestbr. — The Fishes of the Old Red Sand- stone of Britain. Pal. Soc, vol. for 1869, p. 59. 1871. Pearcb, R.— ^fote on Pitchblende in Cornwall. Trans. Boy. Geol. Soc. Com., vol. ix., p. 103. 1872. Flower, H. W.— On the Bones of a Whale found at Pentuan. Ibid., vol. ix., p. 114. 1873. Collins, J. H.— On the Mining District of Cornwall and West Devon. [Plate 30. Transverse section of Fowey Consols.] Inst. Mechanical Engineer.!, July 1873, pp. 89-118. ■ — Note on the Rocks and Goonbarrow Mines, near St. Austell. Bep. Miners' Assoc. Cornwall and Devon, 1872-3, p. 66. 1874. Henwood, W. J.— Observations on the Detrital Tin-ore of Cornwall. Journ. Boy. Inst. Corn., No. xv., p. 191. 1875. Phillips, J. A. — The Rocks of the Mining Districts of Cornwall and their Relations to Metalliferous Deposits. Quart. Journ. Geol. Soc, p. 319. 1876. Collins, J. H. — On the occurrence of Soorodite Pharmaoosiderite and dlienite in Greenstone at Terras Mine, St. Stephens. Journ. Min. Soc, vol. i., p. 16. Note on the occurrence of Achroite at Rock Hill, in the Parish of St. Austell, Cornwall, and on the Black Tourmaline of the same locality. Ibid., p. 55. 1877. Note on the Serpentine of Duporth in St. Austell Bay, Cornwall. Ibid., p. 222. BoNNEY, Prof. T. G. — On the Microscopic Structure of Luxullianite; Journ. Min. Soc, vol. i., p. 215. 1878. Collins, J. H. — On the Hensbarrow Granite District. 8vo., Truro. Note on Cornish Mineral Localities. Journ. Min. Soc, vol. i., p. 92. Preliminary Note on the Stratigraphy of West Cornwall. Trans. Boy. Geol. Soc, Com., vol. x., p. 1 . Phillips, J. A. — On the so-called Greenstones of Central and Eastern Cornwall. Quart. Journ. Geol. Soc, vol. xxxiv., p. 471. 1879. On Concretionary Patches and Fragm.ents of other ■ Rooks contained in Granite. Ibid., vol. xxxvi. ' UsSHEK, W. A. E.— The Post-Tertiary Geology of Cornwall. Printed for Private Circulation, Stephen Austen & Sons, Hertford. Supplementary articles on the same subject. Geol. Mag., pp. 27-81, 102-110, 166-172, 203-211, 251-263, and 307-313. 1880. Cock, David.— A Treatise, Technical and Practical, on the Nature, Production, and Uses of China Clay. London,* Simpkin, Mar- shall & Co. ; Wolverhampton, John Steen & Co. Collins, J. H. — Note on the occurrence of Stanniferous Deer Horns in the Tin Gravels of Cornwall. Trans. Boy. Geol. Soc, Corn., vol. x., p. 98. Note on the supposed Serpentine of the Parish of St. Veep. Ibid., p. 101. Peach, 0. W.— On Fossils from the Rocks of Cornwall, some of them new to the list. Ibid., p. 90. 1881. USSHER, W, A. E.— Prehistoric Europe. Geol. Mag., pp. 131-134. Whitley, N.— The Evidence of Glacial Action in Cornwall and Devon. [Spit Point, p. 133.] Traras. Boy, Geol. Soc, Com., vol. x., p. 132. 1885. Solly, R. H.— On Apatite from Levant Mine, Cornwall. [Francolite from Fowey Consols.] Ibid., vol. x., p. 240. 1886. Worth, R. N.-The Rocks and Minerals of Cornwall and Devon. 5ith Am. Bep, Boy. Com.. Polytech. Soc, p. 74. (See also Ibid, p. 26. Remarks by Sir W. Warington-Smyth.) BlBLIOGEAPHy. 185 1887. Solly, R. H. — Apatite from a new locality in Eastern Cornwall. Min. Mag., vol. vii., p. 141. WoKTH, R. N. — The Clays and Fictile Manufactures of Cornwall and Devon, bbth Ann. Rep., Ibid. 1890. Reid, C. — Pliocene Deposits of Britain. Memoirs Geological Survey. Teall, J. J. H., Dr. — Metamorphism in the Hartz and West of England. Trans. Boy. Geol. Sac, Corn., vol. xi., p. 221. UssHEE, W. A. E. — The Devonian Rocks as described by De la Beche, Interpreted in accordance with Recent Researches (with Map). Ibid, p. 273 ; also Trans. Brit. Assoc. (Leeds), pp. 801, 802. 1891. Worth, R. N. — The Succession of the Plymouth Devonians. Irans. Roy. Geol. Soc, Corn., vol. xi., p. 381. 1892. Collins, J. H.— A Working List of the Palasozoic Fossils of Cornwall. Ibid., p. 421. 1898. Illustrations of Cornish Fossils. Ibid., p. 553. 1894. Illustrations of Cornish Fossils. Ibid., p. 645. 1895. Notes on Cornish Fossils. Ibid., vol. xii., p. 73. 1898. CODRINGTON, T. — On some Submerged Rock Valleys in South Wales, Devon, and Cornwall. Quart. Journ. Geol. Soc, vol. liv., p. 251. Collins, J. H. — Notes on Cornish Fossils in the Penzance Museum. Trans. Roy. Geol. Soc, Corn., vol. xii., p. 233. Smith Woodward, A. — On some new Specimens of Pteraspis coiunbica from the Devonian of Lantivet Bay. Ibid., vol. xii., p. 229. Worth, R. H. — Evidences of G-laoiation in Devonshire. Trans. Devon. Assoc, vol. XXX., p. -378. 1899. Crick, G. C. — Note on some Fossil Cephalopoda from Cornwall. Trans. Roy. Geol. Soc, Corn., vol. xii., p. 238. 1901. UssHER, W. A. E. — Excursion to the Start, Prawle, and Bolt Districts. Proc. Geologists Assoc, vol. xvii. (Map), p. 121. Insertion of General Boundary Line for the Dartmouth Slates. In Sumni. of Progress for 1900, p. 60. 1902. Position of the Dartmouth Slates below the Meadfoot Group ; Boundary of Dartmouth Slates between Lanreath and Polperro. In Summ. of Progress for 1901, pp. 28, 29. 1903. Remarks on the Devonian and Carboniferous Rocks in South Devon Snd Cornwall. Ibid, for 1902, pp. 160-162. Waterworks Directory and Statistics. 8vo., London. 1904. Busz, K. — On the (Gfranite from Gready, near Lnxulian. Rep. Brit. Ass., p. 563. Drevermann, F. — Ueber Pteraspis dunensis. F. Roem. sp. Zeitschr. d, D. g. Gesell., vol. Ivi., p. 278. UsSHER, W. A; E. — The Geology of the Country around Kingsbridge and Salcombe. Memoirs Geological Survey. ■ -' Rocks repeated by plication on shores of- St. Austell Bay. Hornstoues [calc-flintas) at Lostwithiel, Fraddon, &c. In Summ. of Progress for 1903, p. 21. 1905. Barrow, G., C. Rbid, and W. A. E. Ussher. — Calc-flintas and Watergate Anticline. Ibid, for 1905, pp. 26, 27. Reid, C. — Suggested correlation of the Grampound and Staddon Grits. Ibid, for 1904, p. 23. 1906. Rbid, C, and J. B. Scrivenor.— The Geology of the Country near Newquay. Mem,oirs Geological Survey. Hill, J. B, and D. A. MacAlister.— Geology of Falmouth and Camborne. Ibid. 1907. B arrow, G., and D. A. MacAlister. — Lower Devonian Rocks between St. Columb Major and Lanivet. In Summ. of Progress for 1906, pp. 34-36. Reid, C, and Dr. J. 8. Flett.— The Geology of the Land's End District. Memoirs Geological Survey. The Geology of the Country around Mevagissey. Ibid. UssHEE, W. A. E. — The Geology of the Country around Plymouth and Liskeard. Ibid. Walter,. K^ — ^Feber Apatit vom Epprechtstein in Bayern und von LuxuUian in Cornwall. Neues Jahrbuch,'BJB. xxiii., p. 581. 186 EXPLANATION OF PLATE I. Photomicrographs of Granites and China Stones. Pig. 1.— Tourmaline Granite (E 3687), Carbear's Quarry^ near Gready Luxuliaii (magnified 15 diameters). In the centre of the view there is a mass of brown -tourmaline enveloping idiomorphic crystals of quartz. Above and below it terminates in spongy growths ramifying through felspar. On the right there is achloritised biotite with dark plebchroic halos ;.it is partly enveloped in tourmaline. The rest of the field consists of turbid felspar and transparent grains of quartz. Pig. 2.— LuxuUianite, Luxulian (E 7397), (magnified 9 diameters). The left half - of the field shows stellate needles of tourmahne embedded in t[uarti. On the right there is a large brown corroded grain of primary tourmaline with blue fibres planted on its surface. Above and below this there are crystals of turbid felspar which are being eaten into by the secondary growth of quartz and schorl. Pig. 3.— China Stone, Purple Quarry, St. Dennis (E 6961), (crossed nicols, magnified 27 diameters). This photograph shows the abundance of well shaped albite crystals in some china stones. There is also orthoclase and quartz. The felspar contains many fiuid cavities and small plates of white mica. ■ Pig. 4.— China Clay rock or Kaolinised Granite (E 6966), Treviscoe, St. Stephens (crossed nicols, magnified 12 diameters). The photograph shows a little quartz, and larger felspar crystals through which dense aggregates of fine kaolin are spreading along cleavage cracks aiid other fissures. The isolated areas of felspar often extinguish simultaneously, which proves that they are parts of large crystals that have been isolated by the advancing kaolinisation. ■ Pig. 5.— China Stone (E 6962), Tregargas, St. Stephens (magnified 15 diam- eters). This is a mild purple china' stone containing a good: deal of blue finer apparently formed in secondary cavities. Though of irregular form the fluor has idiomorphic zones of intense blue colour, having the outlines of cubes. Fig. 6.— Fluor-bearing Granite (E 7401), Bunny Mine, St. Austell (magnified 33 diameters). In the centre of the view there is a large crystal of muscovite, with grains of fluor spar, which photograph in darker shades, lying along its cleavage planes. Above and below this there are patches of bluish-grey Uuor enclosing plates of muscovite. • EXPLANATION OF PLATE IL Photomicrographs of Cornish Elvans, Pig. L— Elvan (E 4183), Dyer's Quarry, Meledor -(magnified 29 diameters). A vein of granular secondary topaz crosses the field obliquely. The cleavage and small fluid inclusions of the mineral are visible in the photograph. The matrix of the rock is mostly quartz aiid biotite; Fig. 2.— Elvan (E 5510), West Quarry, Tremore (magnified 27 diameters). A large crystal of pbrphyritic browii tourmaline, rather corroded, surrounded by a mossy outgrowth of later blue tourmaline ; similar patches of mossy tourmaline in the ground-mass. ' . . ■ Fig. 3.— Elvan (E 5516), Little Quarry in, Bodwannick "Wood, Lanivet (magnified 9 diameters). A large enmorphic orthoclase phenocryst with a zone of enclosed grains of quartz.. There .are smaller phenocrysts of felspar, quartz, and tourmaline, and fine groUnd-mass. J^?-J-T:^^^^^^^ Porphyry (E 5507), West of Hendra Farm. Withiel (mag- nifaea 9i diameters). The view shows broken grains' of porphyritic quartz in a granuhtic matrix, full of sericitic mica. ' Pig. 5.— Elvan (E 5512), West Quarry, Tremore (magpified 14* diameters, mcols crossed). The porphyritic felspar, contains many small patches of fluor spar which are isotropic and photograph as black Spots. Pi<*- ^.-P^^'LXE 914). Pentuan, St. Austell (magnified 31 diameters, crossed nicols) The. fine .ground-mass is greisened and hag been converted into an aggregate of quartz and white mica. The porphyritic, felspars are kaolinised pj *et)laeed by kaolin (with some white mica, and quartz). The. kaolin photographs in dark grey tones. 187 EXPLANATION OF PLATE III. Photomicrographs of Altered Sedimentary Rocks, i&c. Fig. 1.— Spotted Slate (E 4824), fixed north of Ohillbrook Roche (nicols crossed, magnified 10 diameters). In this slate there are many rounded spots which are fine-grained, while the matrix around them (mostly biotite and muscovite) is more coarsely crystalline. Fig. 2.— Spotted Slate (E 4853), Higher Trelavour Quarry, St. Dennis (magnified 29 diameters). The spots are dark and consist essentially of biotite in single crystals or in groups. The matrix is rich in muscovite. Fig. 3.— Schorl Schist or Tourmalinised Slate (E 1759), Belovely Beacon (magnified 9 diameters). In the secondary aggregate of quartz and schorl which has replaced the original slate, the cleavage and slip-cleavage of the slate are perfectly retained. Fig. 4. -Schorl Schist or Tourmalinised Slate (E 4827), Victoria Railway Cutting, Roche (magnified 29 diameters). In this rock the banding of the killas is preserved, but the tourmaline is in zoned hexagonal prisms with good outlines. The quartz forms a mosaic of clear grains. Fig. 5. — Felspathic Band in the altered Meadfoot Series — Felspathic Horn- stone (E 5458), quarry north-west of TreguUan, south of Bodmin (crossed nicols, magnified 37 diameters). The rock consists essentially of quartz and albite, and remains of the clastic structure are still discernible. Fig. 6. — Limurite (E 4927), Rosevanion, St. Columb Major (magnified 22 diameters). Large idiomorphic crystals of axinite, with well marked cleavage, enclose many small grains of epidote and pyroxene. Irregular, inter- stitial masses of quartz, colourless but full of inclusions, lie between the axinites and may be recognised by the absence of cleavage and their paler colour. 188 ITor Explanations of Plates, see pp. 186 and 187. Geology of Bodmin & St.AiistdL. Flale I. Fig. 2, Fig, 3. Fig. 4. Fi^.5. Photomicrographs or Granites. Huth, coll. Geologrj of ±Sodmin, & St. Austell. Plate R Fifi.l Fifi. 2 . rxg.3. Fig. 4. Fig. 6. Photomicrographs of Elvans. Hath., coll. Geology of Bodrrun, & St. Austell. Plate in. Fig.l. Fig. 2. Fig. 3. Fig. 5. Fig,. 4 Fig, 6, Photomicrographs of Sedimentary Rocks. 189 INDEX. Actino'Iite in calc-flinta, 88-90 ; green- stone, tee Hornblende ; schists, 40, 41,62. Adinole, 41, 100-101. Agriculture, 181. Albite in calc-flinta, 98-100 ; china- stone, 117 ; elvan, 76 ; granite, 56, 58, 59 ; greenstone, 48, 51 ; greisen, 67, 68 ; pegmatite, 56, 62. Albite-tourmaline rock, 103. Alluvial tin, 120, 123-128, 130, 170- 174. Alluvium, 120, 122-130. Alma Iron Mine, 1 63. Alviggan, Wheal, 110, 132. Ambrose Lake Mine, 159, 164. Amygdaloid, 35, 38, 52. Analyses, adinole, 101 ; cale-flinta, 100 china-stone, 114 ; elvan, 73 ; felspar, 62 ; granite, 114 ; greenstone, 46 inclusions in granite, 60 ; iron-ores, 148, 157 ; serpentine, 51. Andalusite hornf els, 92-96 ; spots, 85 in granite, 57, 58. Andesine, 60. Andusitic basalt, 37. Annabergite, 139, 150. Anticlines, 6, 8. Antimonite, 144, 154. Apatite in Elvan, 75, 76, 78 ; granite, 57, 58, 111 ; greenstone, 46, 50, 51, 52 ; hornfels, 95 ; pegmatite, 62 ; Powey Consols, 144 ; Stennagwyn, 167. Appletree Mine, greenstone, 38. Appletree Point, interlaminated beds, 23. Argentiferous galena, 135, Armorican movement, 5. Arsenic, 135, 166, 164-165. Arvose, elvan, 69. Augite in calc-flinta, 88, 89, 90, 98 ; greenstone, 44, 45, 48-53 ; killas, 94, 103, 104. Aureole of metamorphism, 80-104. Autunite, Stennagwyn, 157. Axinite in calc-flinta, 82, 88-90, 98, 103, 104 ; greenstone, 48, 53 ; killas, 94, 101, 103, 104 ; St. Colomb Major, 187. Bagstone, grits, 27, 29. Bakek, W., 155. Bara, schalstein, 44. Barbolingey, veinstone, 110. Barnet, a. K., 145. Barrow, (i., 12, 27-33, 40-44, 60, 63, 64, 73-76, 103, 147, 148, 154, 158. Barytes, St. Austell Consols, 156. Basalt, 37. Beaches, modern, 130 ; raised, 120-122, Beacon Hill, f ossiferous Devonian, 11. Beam Mine, china clay, 106 ; tin-ore, 169. Bedwindle, grits, 29. Bellazize, Terraces, 123. Belovely, Wheal, 159. Belowda Beacon, anticline, 92 ; granite, 54, 61 ; Mine, 137 ; tourmaline slate, 187. Belowda Hill Mine, 137. Belowda Mine, 133, 159. Benallack, iron output, 165. B£R»ER, Dr., 106. Bigbees Iron Mine, 167. Bilberry, detrital tin, 171 ; Ruby Iron Lode, 155. Biotite in calc-flinta, 98 ; china clay, 112 ; granite, 56, 57, 59-61 ; green- stone, 41, 42, 46-63 ; quartz- porphyry, 43 ; serpentine, 50 ; -spots, 85, 92, 94 ; killas, 94, 97. Biotite hornfels, 92, 94-97. Bisoovillack, veinstone, 110. Bismuth, 154, 142, 144, 146, 147, 163. Blackhay Iron Mine, 163. Blackhead, diabase, 23, 38, 3d, 46-49, 53 ; slates, 17, 23. Black tin, see Tin-ore. Blanco, Wheal, 1 37 ; elvan at, 71. Blencowe Consols Tin Mine, 131, 137, 159. Bloomdale Works, china stone, 110. Blowing House, diabase, 39, 47, 49. Bluebarrow Pit, china clay, 107 ; elvan, 73 ; tin-ore, 159. BoASE, Dr. H. S., 38, 93, 102, 105, 106, 144, 158, 177, 178. Bocaddon, 123. Boconnoc, Devonian, 11, 20, 29 ; slate quarries, 176, 177. Bodwinnick Iron Mine, 27, 134, 137, 163. Bodmin, calc-flinta, 27 ; elvans, 73 ; faults near, 12 ; greenstone, 40, 41, 53 ; metamorphic aureole, 83, 91 ; Pliocene plane, 119 ; slates, 32 ; slate-quarry, 177 ; water-supply, 180, 181. Bodmin Asylum, grits, 30 ; fossils, 32 ; water-supply, 181. Bodmin Consols, 164. Bodmin Bead Station, terraces, 123. Bodmin United Mine, 159. Bodwannick Wood, elvan, 74. Bodwen Mine, 137. Bofarnel, gold, 142 ; grits, 29. Bokiddick quartz-schorl, 63. Bokiddick Downs, detrital tin, 171 ; elevation, 171- BONNARD, A. H., 172. 190 INDEX. BoNNEY, Rev. T. G., 60, 65, 66, 102, BoKLASB, C. W., 105, 135, 158, 174- Bornite, 153. Boscundle Mine, 137, 150, 159. BiJscarne Iron Mine, 163. . Boscoppa Mine, 131, 149, 159, Bosinver, elvan, 69, 70. Bosithow, diabase, 39, Boskell, china clay, 109, Boskillian, tin-ore, 159. Bosmaugen, calc-flinta, 21 ; fossil- iferous beds, 20. Botelet, schalstein, 44. Braddock, 34, 177. Brannel, elvan, 71, 77, 79, 178 ; meta- morphio aureole, 80. Breccias, Lode, 132, 144 ; tourmalinised killas, 65. Breney Common, detrital tin, 171 ; elevation, 171 ; brick-earth, 72, 179, 180. Bridgend, terrace, 122, 123, Brizham, Dartmouth Slate, 6. Broadwater, stream tin, 173 ; Pleis- tocene, 124, 125. BEoesER, Pbof. "W. 0., 101. Brown Queen, calc-flinta, 8, 83 ; Mead- foot Beds, 11. Brynn Mine, 137, 159 ; elvan, 72. Buckabarrow Downs, faults at, 11, 12 ; Devonian, 27, 29. BufE stone, 111-112. Bugle, dressing plant, 136 ; detrital tin, 171. Building-stone, 174-178, . Bunny Mine, 137-139 ; dressing plant, 135, 136, 139 ; fluor granite, 68 ; greisen, 67, 68 ; lode-structure, 32 ; output, 159, 164 ; pegmatite, 62. Burney House, output, 159, 163. BurnguUow, output, 159, 164 ; meta- phorism, 80. . ■ , BurnguUow Common, schorl rock, 65 ; veinstone, 110. Burthy Row, elvan, 72 ; schorl rock, 111. . Burthy bruen,'metamorphic aureole, 80 ; .quarry. 111. Bury. Down, fault at, 11, 12; schal- stein, 44. Bury Down Camp, grits, 27, 177. Bosz, Prop., K., 56, 57. Butler, Dr. P. H., 66, 67, 115, 116. Cadmiferous blende, 144. Calamine, 147. Calcareous Meadfoot Beds, pneumato- lysis in, 103, 104. Calc-flinta, 8, 10, 12, 17, 27, 32, 43, 80- 92, 98 ; analysis, 102 ; minerals in, 89,99-101, 103,104; roadstone, 178, 179. Calc-uranite, 157. Californian Stamps, 135, 139. Oallyvardor Rock,, raised beach, 121. Candle factory, raised beach, 121. Cannonbridge, 177. Carbeans, china clay, 107 ; quarry, 174 ; tourmaline, 186. Carbis,. biptite homfels,.?5; comu, bianite, 102 ; dip of granite, 54. Carclaze Pit,' china clay, 109 ; schorl veins, 110 ; tin ore, 139, 159, 164. Carclaze Downs, granitp, 57, 174. Cardinham, gold, 174. Carew, R., 135, 174. Oarlyon and Crinnis, output, 159 ; sheared greenstone, 38, Carminow Cross, 28. Carne, J., 4. Carnestents, water supply, 180. Carn Greys, granite quarry, 174 ; schorl rock, 66. Carnewas Iron Mine, 163. Carnwinnick, elvan, 70. Carpella, fine granite, 71 ; quartz- schorl, 111. Carrancarrow, china clay, 107. Carrickowel, 38. Carthew, 175, 176. Carthew Consols, 159, 164. Carthew House, china clay, 107, Cartole, greenstone, 36 ; fault, 11 ; fossiliferous beds, 21. Carvath Mine, 139. Carvath United, 159. Carvear, greisen, 110. Carwinnick, 26. Cassiterite, see Tin ore. Castle an Dinas, anticline, 92 ; calc- flinta, 8, 82 ; elvan, 71, 73 ; granite, 58, 61 ; shales, 15. Castle an Dinas Mine, 139, 159. Castle Canyke, Devonian, 29, 34, 177. Castle Dore Fault, 6, 8, 11, 12, 15, 17. Castle Gotha, ' Head,' 121. Castlemawgan, 21. Caudledown china clay pit, 107, 109. Central Treviscoe, china clay, 107. Chalybite, 139, 141, 142, 143, 144, 148, 149, 150. Chance, Wheal, 139, 164. Chark, calc-flinta, 82, 178. Charlestown, fossiliferous beds, 23 ; greenstonoj 38. Charlestown Church, fossils, 24. Charlestown United Mines, 140, 159. Chiastolite in hornfels, 96. Childrenite, 142. Chillbrook, granite, 61 ; spotted slate, 187. China clay, 105-111, 115, 116. China clay rock, 105-117, 186. China stone, 105, 111-114, 116-118; analysis of, 114; petrography, 112, 113, 186. Chromium ore, 157. Chrysocolla, 137. Chytane, china clay rock, 114 ; quarry, 111 ; tin-ore', 159, INDEX. 191 Chytane Clay Worksj 107 ; elvan, 72, 77, 7S ; schorl rook, 72. Clay, see China Clay. Cleavage, 13, 15, 23, 32, 178. Cleaves, . China' Blay Works, 107 ; tin lode, 138. Click, Wheal, 158. CoADE & Shilson, Messrs., 153. Coast erosion, 121. Cobalt, 146, 155, 156, ]57 ; output, 135, 164-165. Cock, David, 4, 106. Cockshurrow, elvan, 73. CODRINGTON, T., 120. Colbiggan, 140, 141 ; Ruby Iron Lode, 155, 163. Colcerrow, jiranite quarry, 174, 175 ; pegmatite, 62. Coldvreath Iron Mine, 134, 141, 16.3. CoLENSO, J. W., 127, 128, 130, 172. Collibeacon, roadstone, 179. Collins, J. H., 3, 4, 14, 24, 25, 38, 46- 51, 62, 72, 73, 109, 113-115, 117, 138, 141, 142, 146-150, 154, 155, 179. CoUon, 21. Colwood, 11, 20. Commerce Common, elvan, 69 ; green- stone, 39. Commerce Mine, 131, 141, 159 ; grits, 26 ;. Grampound Beds, 9, 26. Conce Moor, 119 ; detrital tin, 171 ; . elevation, 171 ; granite, 63 ; water supply, 180. Congorlan, fault, 11. Connonbridge, 33. Contact Metamorphism, 42, 52, 53, 80- 104. COOKWORTHY, W., 115. Coombe, fossils, 14, 17, 19 ; quarry, 177. CoombejHawne Beach, 130 ; Devonian, 19, 21, 24; fault, 6, 11, 16-18; greenstone, 17, 36-40 ; 'Head," 121. Copper, ores, 137-158 ; output from mines, 159-164 ; total yield, 135 ;" and tin mines, 131-169. Copper uranite, 157. Cordierite, 57, 58, 76, 92, 94, 96, 97. Corgay Moor, tin, 171. Corgee, microgranite, 61. Cornish stamps, 136. Cornish stone, see China Stone. Cornubia Mine, 54, 141, 142, 163. Cornubianite, 102. Corundum, 95, 96. Cost all Lost Mine, 141-142. Couch, R. Q., 4. Conchsmill, 7. Court Wood, 20, 21. Covelline, Maudlin Mine, 148. Creaking Gate, elvan, 71. Creany, gold, 174 ; Pleistocene, 124, 125. Creed, gold nugget, 174. Criokapit Mill, 177. Criggan, china clay, 107. Criggan Mine, 67, 142, ,159, - Criggan Moor,' 54 ; elevation of, 171 ; detrital tin, 171. Criunis and Carlyon, copper ore, 159 ; sheared greenstone, 38. Crinnis, Devonian, 23, 24, 38. Crinnis Beach, 130. Crinnia Consols, 159. Crinnis Mine, 131, 142. Cronstedtite, 148. Crop Tin, see Tin-ore. Crosby, W. 0., 133. Cross Courses, minerals in, 134 ; Charlestown Mine, 140 ; Pembroke Mine, 150 ; Polgooth Mine, 153. Crow Hill Mine, gold, 142 ; silver-lead, 164. Crown Filley, china clay, 107. Crugoes, epidote-rook, 104. Crushing strain of granite, 175. Cuddra Mine, 140, 159. Cuprite, 139, 144. Curyan, elvan, 73. Dartmouth Slates, 6-8, 13-16 ; igneous rocks iu, 35, 36 ; quarry, 178 ; soil, 181. Davidson, T., 25. Dawna, 28, 29. Daymark, 13. Demelza, 91. Db la Beche, Sir H. T., 3, 25, 38, 74, 76, 106, 111, 123, 125, 143, 144, 158, 172, 174. Desmesnes, 82. Devonian, 6-12, 13-34 ; metamorphism of, 80-104; 81ates,176-178; soils, 181. Diabase, 2 ; in Dartmouth Slates, 35, 36 ; in Meadfoot Beds, 36-43 ; in metamorphic aureole, 80-83 ;. petrography of, 45-49. Diopside, 98-100. Dolomite, 151. Domeliook, biotite hornfels, 95, 102 ; Cornubianite, 102. Doublebois, Devonian, 33, 34, 177, 178; Terrace, 123. Dowgas, elvan, 70, 176 ; tin-ore, 160. Downend, 20. Drawbridge, slates, 33 ; terrace, 123. Drennick, diabase, 39 ; slates, 23. Dressing of tin-ore, 135-137, 139. Duke of Cornwall Mine, 131, 142, 143, 159, 164. Duporth, serpentine, 38, 49-51 ; build- ing stone, 1 76. Dyehouse Mine, 158, 163. Dyer's Quarry, 111 ; elvan, 71,78, 186; granite, 56, 58 ; hornfels, 95 ; metamorphism, 80. Dynamic metamorphism of greenstone, 42. 192 INDEX. East Beam, china elay, 107 ; tin-ore, 159. East Bonny, 107. East Coombe, amygdaloid, 35 ; slates, 7 ; diabase, 35 ; ' Head,' 121. East Coombe Valley, ' Head,' 121. East Crinnis Mine, 140, 143, 159, 164; Pleistocene, 126. East Cuddra Mine. 159. East G-oonbarrow, 107. East Mulberry, 159. East Polmear, 159. East Taphouse, 177. Economics, 131-181. Edith Iron Mine, 144. Egloshellen Mine, 144. Eliza, Wheal, 131, 140, 160. Eliza Consols, Wheal, 131, 143. Elizabeth, Wheal, 146. Elvans, 68-79 ; for briokmaking, 179 ; photomicrographs, 186 ^ roadstone, 178, 179 ; in mines, 137, 139, 146, 147, 151-153, 157, 158. Epidote, in calc-flinta, 88-90, 98, 100 ; greenstone, 48, 49, 53, 82 ; killas, 93, 94, 103, 104. Erythrine, 151. Essa, 18. Ethy, diabase, 36 ; shales, 21. Fahlerz, 142. Fal River, 54 ; tin, 171 ; terraces, 123. Fatwork and Virtue Mine, 133, 144, . 160. Faults, 12, 13, 16, 23. Felspar, in altered killas, 93-96 ; calc-flinta, 98, 100 ; china-clay rock, 118 ; china stone, 112, 113, 116, 117 ; granite, 55, 56 ; pegmatite, 61, 62 ; replacement of, 75, 79 ; analysis, 62. Felspar hornstone, 100, 101. FlEBELKOKN, DR. M., 115, 116. Fine Tin, see Black Tin. Fir Hill, ochre, 164. Firestone, 179. Fishing Point, Beach, 130 ; raised beach, 122 ; fossils, 24 ; greenstone, 37 ; slates, 23. FiTTON, Dr., 106. Fletchersbridge, 34. Flett, Dr., J. S., 10, 20, 21, 44-53, 56-60, 65-104, 117. 118, 89, 101-104. Floors of tin, 149, 144. Fluccans, see cross courses. Fluor spar, 53, 58-62, 67, 74, 75, 77, 78, 104, 111-114, 117, 142, 148, 157, 186. Folds in Devonian, 13, 23, 32, 82, 86, 87, 178. Foliated greenstone, 52, 53. Ford, calc-flinta, 82, 83 ; greenstone, 40 ; roadstone, 178, Fore Moor, tin, 171 ; elevation, 171 ; Pleistocene, 124, 125. Forest Clay Pit, 110. Formations, Table of, 2. Fortescue, Wheal, 160. Fortescue Consols, 160. Fortune, Wheal, china clay, 107. Fossils, 3, 8, 13, 14, 17-20, 24, 25, Foster, Sir C. le N., 66, 67, 104, 133, 137, 138, 142, 148, 149, 153, 154. Fowey, alluvium, 122, 123 ; Dartmouth Slates, 6 ; tin, 171 ; fossils, 19, 25 ; greenstone, 35, 36. Fowey Consols, 131, 144, 160, 164. Fowey Harbour, submerged forest, 128, 129. Fowey River, terraces, 123 ; tin, 174. Foxhole, veinstone, 110. Fraddon, calc-flinta, 8, 27, 80, 91; greenstone, 39. Francolite, 144. Freeman & Sons, 175. Frue vanners, 135, 139. Galena, 15, 134, 135, 139, 142, 143, 146, 154, 164, 165. Gamas Point, 9. Garkar and PentrufE, 110, 160. Garlenick, slates, 26. Garnet, in oalo-flinta, 88-90, 99 ; . greenstone, 53 ; altered killas, 93, 94, 103, 104 ; in mines, 148, 157. Gaverigan, calc-flinta, 91, 97 ; spotted slate, 97 ; iron lode, 158 ; roadstone, 179 ; tin-ore, 160. Geikie, Sir A., 93, l.'$5. Geikie, Prop. James, 129. Gerrans Point, amygdaloid, 38 ; green- stone, 38 ; phosphatic slates, 23. Gewans, greenstone, 47. Gilbertite, 62, 110, 112, 113, 116, 117, 142. Glynn, Devonian, 29, 34 ; terraces, 123. Glynn, Wheal, 164. Gold in tin-gravels, 174 ; in Mines, 142, 153, 173. Golden Point Quarry, granite, 56-58, 174, 175. Golden Stream Works, 124, 173. Gonnamaris, china stone, 110. Goodyear Beach, , , Devonian, 22 ; decomposed greenstone, 22, 37. Goonabarn, 110. Goonamarth, 110. Goonbarrow, output, 160; china clay, 107 ; veinstone, 107 ; Zippeite, 145 ; and Rocks, 154, 155. Goonvean, china stone, 110. Goss Moor, 119, 171, 173. Gossan, yield, 135, 164, 165. Gover, elvan, 69, 77, 78, 79, 145; tin-ore, .160, 162, 163 ; water supply, 180. Graoca, china clay, 107 ; dressing plant, 136. Grain tin, alluvial, 170, INDEX. 193 Crrampound, grits, 3, 9, 10, 17, 18, 25-28 ; quarry, 178. Grrampound Mill, 25. G-rampound Road, bricks, 180 ; grits, 26 ; iron lodes, 134. Granite, 2, 64-68 ; analysis, 60, 114 ; boulders, 55 ; building stone, 174^ 176 ; crushing strain, 175 ; enclo- sures, 60, 95, 175 ; flrestone, 179 ; greisen, 67, 68 ; intrusion of, 5 ; photomicrographs, 186 ; jointing in, 55, 175 ; pneumatolitic action on, 59, 60, 64-68 ; pseudo-bedding, 55 ; sequence of crystallization, 58 ; sub- terranean dip, 54, 63, 64 ; tongues, 54 ; tourmalinization, 64-67 ; -weather- ing, 55. Graphite, 97. Gravels, stanniferous, 170-174. Gready, concretionary patches, 60 ; granite quarry, 56, 57 ; pegmatite, 62. Great Beam Mine, 145, 146, 159, 163, Great Orinnis, 159, 160, 164. Great Dowgas, 146, 160, 164. Great Wheal Grylls, 160. Great Halwyn, 110. Great Hewas Mine, 146, 160, 164. Great Polgooth, 161. Great Wheal Prosper, china clay, 107 ; tin-ore, 160. Great Royalton Mine, 146, 147, 161. Great Tin Lode at Bunny Mine, 138. Great Trevisooe, china clay, 114. Great Wood, diabase, 35, 36 ; grits, 20 ; iron ore, 154. Green, Uppield, 19, 24. Green ore, 157. Greensplat, china clay, 107 ; veinstone, Greenstone, 35-53 ; analyses of, 46, 47 ; for building, 176 ; contact alter- ation, 52, 53 ; pneumatolytio action on, 53 ; schists, 52 ; soil, 181 ; in metamorphic aureole, 80-83. Geegos, W., 150. Greisen, 67, 68,78, 110, 117, 142. Gribben Head, Beach, 130 ; 'Head' and raised beach, 121 ; slates, 17 ; sheared greenstones, 37. G;ribben Head Beacon, 22. Grits, calcareous, in Meadfoot Beds, 17, 18, 20 ; in Dartmouth Slates, 13, 14 ; Looe type, 21, 34 ; roadstone, 179 ; metamorphosed, 85, 93, 94 ; Staddon, 28-31. Grove, Pleistocene, 124. Growan, 54. Grugwallons, 80. Gull Island, greenstone, 38. Gundeep, Pleistocene, 124, 125. Gunheath, china clay, 107. Gwendra, slates, 27. Gwendra Beach, greenstone, 38. Gwendra Point, Devonian, 23 ; green- stone, 23, 38. 12979 Haden Iron Mine, 163. Haematite, 134, 135, 140, 141, 158, 163 ; see Iron Ore. Halezy, 26. Halgavor Moor, 123. Hallam, diabase, 39. Hallane, slates, 26. Hallane, Beach, slates, 23, 24,. Hallam Valley, diabase, 24. Hallivet, china clay, 107. Halliviok, el van, 71 ; greenstone, 39. Hallow, Mine, 147, 163 ; china clay, 107. Hallow Farm, granite, 176. Halwyn, granite. 111. Hambland, volcanics, 22. Hannah, Wheal, china clay, 107. Hannay, J. B., 114. Happy Union Stream Works, 127-130. Harros, Ruby Iron Lode, 155. Haughton, S., 56. Hawkins, J., 115, 151, 172. 'Head,' 120-122; tin-ore in, 171, 172. Hedenbergite, 89, 90. Helman Tor, height of, 54 ; granite, 55 ; gravel near, 119 ; detrital tin near, 171. Hembal, diabase, 39, 81. Hendra, metamorphic aureole, 80 ; quartz-porphyry, 35, 43, 186. Hendra Downs, elvan, 73. Henry, Wheal, china clay, 107. Hensbarrow, granite, 176 ; lodes of, 132. Hensbarrow Beacon, height of, 54 ; non-porphyritic granite, 55, 61. Hensbarrow Downs, elvan, 72, 79 ; pegmatite, 62. Hen WOOD, W. J., 4, 38, 115, 124, 125, 127-129, 143, 144, 146, 149, 151, 153, 172. Hewas Mine, 131, 160 ; elvan, 69. Hewas Water, 26, 27. HiCKLING, G., 118. Higher Bara, amygdaloid, 52. Higher Clowne, 27, 29. Higher Coldvreath Iron Mine, 141. Higher Trelavour, 179, 187. Highgate, fossils, 21 ; diabase, 36. Hill, J. B., 10, 124. Hit or Miss, granite in china clay. 111, Hollowpark, mudstones, 34 : schalstein, 44. Hollycombe, 29, 34. Holtroad Downs, killas, 177 ; tei- races, 123. Holywell, 133. Hooper, J. 158. Hope, Wheal, china clay, 107. Hornblende in altered killas, 93, 94 ; calc-flinta,' 87, 98-100 ; lUeadfoot Beds, 103, 104; greenstone, 42-49, 51-53. Hornf els in granite," 60, 95. N 194 INDEX. Hornick, china clay, 111 ; schorl rock, 111 ; well at, 180. Hornstone, see Calc-flinta; HosKiNG, Captain, 139. Igneous rocks, Table of, 2. Umenite, in oalc-flinta, 98 ; greenstone, 40, 46, 48 ; killas, 93, 96, 97, 102. Imperial Goonbarrow, 160. Indian Queen Mine, 132, 134, 147, 158, 160, 162-165 ; calc-flinta, 80, 91 ; water supply, 181. Inniscaven, 91. Iron lodes, directions of, 134. Iron ore, Bodinnick Mine, 137 ; Col- biggan Mine, 140, 141 ; Edith Iron Mine, 144 ; Gover, 145 : Hallow, 147 ; Nanjeath, 148 ; output from Mines, 163 ; Restormel, 154 ; Retire, 154 ; Euby Lode, 145 ; South Terras, 157 ; Toldish, 158 ; Tower Consols, 158 ; Trerank, 158 ; Wheal James, 147 ; Woodley Iron Mine, 158. Iron oxide in china-clay, 112. Iron pyrites, 135, 137-158, 164, 165. Jackson, W., 106, 113, 114. Jacob, Wheal, 132, 147. James, Wheal, 140, 147. Johnson, Matthey & Co., 157. Jointing of Granite, 55, 175. Kaolin in china clay, J.18 ; elvan, 76- 79 ; greisen, 68 ; Roche Rock, 64j 65 ; see China clay. Kaolinization,78, 79,105-111,115-118 ; of elvan, 78, 79. K^BNDALt, J. D.,' 157. Kernick, china stone, 110. Kernick Hill, pegmatite, 62. Kerrow Moor, tin, 136, 160, 170 ; china clay, 107. Kestles china stone quarry, elvan, 72 ; pegmatite, 62. Kbysee, E., 101. Kilgogue, 15. Killas, for building, 176-178 ; micro- photograph of, 187. Killivreath Iron Mine, 163. Kilmar Tor, granite, 63. Kilmarth, 22. Kingole, 21. Kingswood, elvan, 68. Kinsman, Me., 109. Kirland, calc-flinta, 27 ; grits, 51. KntOALDY, D., 175. Kupfernickel, 144, 150, 156. Laceoix, Pkof., 57. Ladock, gold, 174. Ladock.Beds, 3, 9, 10, 178. . Ladock Iron Mines, output, 163. Lady Rashleigh Consols, 131. Lamellyn, detrital tin, 171. Lampetho, Castle Dore Eault at, 6 ; Devonian, 15, 22. Lancara, 21. Langeth Iron Mine, 103. Lanescot Mine, 147 ; calc-flinta, 81 ; copper ore, 131, 160. Lanhadron, 25. Lanhydrockj oalc-flinta, 8, 82, 83 ; ■ greenstone, 40 ; grits, 29 ; iron ore, 154 ; moor drainage, 120 ; Pliocene plane, 119; roadstone, 178; water supply, 180. Lanivet, altered killas, 85, 86 ; calc- flinta, 8, 27, 87, 90 ; elvan, 73, 74, 186 ; faults at, 12 ; greenstone, 41, 42, 51 ; Mulberry Mine, 148 ; Wheal Prosper, 154. Lanivet Consols, 147, 160, 163, 164. Lanivet Iron Mines, 163. Lanjew Iron Mines, 163. Lankelly, fossils, 19 ; grits, 27. Lankestee, Sie E. Ray, 14. Lanlivery, granite blocks, 55 ; luxu- lianite, 176. Lanreath, Dartmouth Slates, 8, 16 ; flat near, 123 ; Meadfoot Beds, 19, 21 ; slat© quarries, 176. Lansallos, amygdaloid, 35 ; grits, 13. Lansalson Pit, veinstone, 110. Lanteglos, slates, 14, 18, 19. Lanteglos Church, greenstone, 36. Lantern Works, quartz schist, 65, 107. Lantic Bay, slates, 18, 19. Lantic Beach, 130. Lantivet ' Head,' 121. Lantivet Beach, 130 ; grits, 13. Largin Wood, 34. Lavas in Dartmouth Slates, 35,. 36 ; Meadfoot Beds, 36, 37, 44. Lawhire, 16. Lead, output, 135, 164, 165. Leadenhill Wood, greenstone, 40, 52. Lepidolite, see Mica. Lerryn, fossils, 19, 20 ; slates, 21, 176, 178. Lerryn Creek, diabase, 35, 36. Lerryn River, terrace, 123. Leaquite, granite, 63, 64. Leucoxene, 37, 40, 45, 48, 49, 51, 52, 102 ; see Umenite. Levalsa, grits, 25, 26. Levalsa Moor, elvan, 68 ; slates, 26. Levrean, detrital tin, 171-173 ; gold, 174 ; Pleistocene, 124, 125. Limurite, microphotograph, 187. Literature of the Region, 3, 4, 182^186. Lithia mica, 56, 62, 63 ; in greisen, 68. Lithionite, see Lithia mica. Little Bryan, elvan, 72. Little Combe Hawne, ' Head,' 121 ; greenstone, 37. Little Gribbin, beach, 130 ; raised beach, 121. Little Quarry, elvan, 186. Little Ventonwyn, 146. Lizzen, ' Head,' 12L Lobb's Shop, elvan, 68. Lockengate, tin, 171 ; granite, 55 ; Mine at, 137. Lodo breccia, 132. INDEX. m Lodes, 131-169 ; directions of, 131, 132 ; general distribution, 131, 132, see also Mines ; pegmatite, 132 ; structures in granite, 132 ; struc- tures in killas, 132, 133. JJondon Apprentice, flood, 130. Lone Downs, 26. Lonsdale, W., 3. Lostwithiel, axinite, 82 ; calo-flinta, 8, 27, 82 ; elvan, 71 ; Devonian, 15, 20, 21 ; gold, 174 ; greenstone, 39 ; iron ore, 154 ; killas Quarry, 176, 178 ; terrace, 122, 123 ; tuff, 36 ; road-' stone, 178 ; water supply, 180. Louisa, Wheal, granite, 110. Lower Burgotha, china clay. 111 ; elvan, 71, 72 ; sohorlaceous granite, 111. Lower Creany, Pleistocene, 124, 125. Lower Coldvreath Iron Mine, 141. Lower Devonian, 13-31 ; igneous rocks, 35-54. Lower fl ill. Quarry, 177. Lower Ninestones, china clay, 107. Lower Pentewan, stream works, 128- 130. Lower Treire, arenaceous beds, 21 ; sheared diabase, 36. Luna, calc-flinta, 32. Luxulian, detrital tin, 171, 173 : gold, 174; granite, 55, 56, 174; hornfels, 92; iron output, 163 ; pegmatite, 62 ; water supply, 181. Luxulian Valley, ' Head,' 122 ; terrace, 122. Luxulianite, 66, 67, 176, 186. MacAlistek, D.A., 8, 54-56, 61-65, 72, 73, 91-93, 105-109, 111-117, 135-137, 176, 179, 181. Magnetic iron ore, 135, 165 ; consols, 158. Magnetic Iron Mine, 134, 163. Magnetic Separator, 135, 139. Magnetite, 57, 58, 67, 137, 144. Malachite, Bunny Mine, 137. Manely, 22. Manganese, 134, 135, 140, 147, 158, 185. Margate Wood, Slates, 32, 177. Marine erosion, 121 ; sands, 129, 130. Martin's Clay Works, veinstone, 107. Mary, Wheal, 147, 160. Mary Great Consols, 109. Mary Louise Mine, granite, 63. Maudlin Mine, 131, 148, 169 ; calc- flinta, 83 ; diabase, 40 ; killas, 83 ; water supply, 180. Meadfoot Group, 17-31 ; general structure, 6-8, 11, 12 ; anticline in, 92 ; calo-flinta in, 80-92, 98-101 ; faults in, 18, 19, 22, 23 ; meta- morphism of, 80, 104 ; igneous rocks, 36-44 ; quarries, 176-178 ; soil, 181. Melaconite, 146, 149. Melangoose, granite, 58, 111. Melanterite, 144, 148. Meledor Pit, china clay, 110 ; elvan, 71, 186 ; veinstone, 110 ; metamor- phism, 80 ; iron lodes, 134., Menacuddle, granite, 58. Menadue, Wheal, 164. Menagwyns, greenstone, 39. Menear, Wheal, 81, 148. . Menabilly Mine, 148 ; fossils, 25. Menaburle, 27. Merry Meeting, Pleistocene, 124, 125. Merthen, greenstone, 38. Messar, Wheal, 162, 169. Metamorphiq aureole, 80-104. Metamorphism, calc-flinta, 27, 28 ; of Devonian sediments, 80-104 ; greenstones, 52, 53. Metalliferous deposits, 131-174. Metasomasis in granite, 64-68. Metheroes, diabase, 39, 81. Mewton, Mr., 181. Mica, in calc-flinta, 99, 100 ; china clay, 112, 114, 118 ; china stone, 112, 113, 116, 117 ; elvan, 73, 75-79; greisen, 67, 68 ; killas, 93, 94, 102 ; pegmatite, 61-63 ; veinstone, 132 ; see Biotite, Muscovite, &e. Mica vein, 62, 63. Microcline, 56. Micropegmatite, 77. Microperthite, see Orthoclase. Middle Devonian, 32-34 ; cleavage, 32, 33 ; folding, 32 ; quarries, 176-178 ; quarta-veining, 33 ; soil, 181 ; vol- canics, 33, 44. Middle Taphouse, quarries, 177. Mild Purple china stone. 111, 112. Millerite, 139, 144, 150. Milltown, 15. Mines, 131-169 ; see Lodes. . Minear Downs, 131, 160. Minerals, economic, 131-174 ; statis- •tics, 135, 159-165. Mispickel, 137, 146, 148, 153, 157, 164, 165. Mitchell and Prosper Mine, 153, 154. Mixtow's Pill, diabase, 8, 35 ; Base of Meadfoot Beds, 8. Molingey Mill, elvan, 69 ; greenstone, 39. Molybdenite, 148. Monument Hill, Pliocene plane, 119. Moors, 119 ; elevation of, 171 ; soil, 181 ; stream tin in, 170-174. Morish Beacon, greenstone, 38. Mount Charles, water supply, 180. Muff (Maufe), H. B., 120. Mulberry Down, elvan, 76 ; tourma- line rock, 90. Mulberry Mine, 183, 148, 160 ; banded silts, 27. MuUinis Moor, 134. Mplvra, copper-ore, 160 ; elvan, 69 ; quartz-eyed slates, 26. 196 INDEX. MuRCHisoN, Sir R. I., Silurian rocks, 3,4. Murchisonite, 111. Muscovite in granite, 56-60 ; hornfels, 96, 98. Nanjeath, soTiorl rock. 111. Nanjeath Iron Mine, 148. Nanpean, china stone, 109. Nanphysick, greenstone, 39, 51. Nansladron, elvan, 68 ; grits, 25. Nanstallon Iron Mine, 163. Nantellan, grits, 10, 26, 30, 31, 178. Native copper, Great Dowgas, 146. Nereitopsis cornubicus, 24. New Boscundle, 160. Newbridge Wood, Interlaminated Beds, 29. New Caudledown, china clay, 107. New Cleaves, china clay, 107. New Crinnis, 160. New Crow Hill, 164. New Powey, 160. Newham Farm, greenstone, 35, 36. Newmill, elvan, 69 ; slates, 26. New Mills Iron Mine, 163. New Park of Mines, 160. New Pembroke, 160. New St. Blazey, 160. New Terras, 160. Newquay water supply, 181. Newtown, 16. Nicoolite, Wheal Chance, 139 ; Pengelly Mine, 150. Nickel ore, 134, 135, 139, 149, 151, 155, 156, 164, 165. Ninnis, elvan, 69. Ninnia Downs, 160. North Beam, china clay, 107 ; tin-ore, 160. North Bonney Mine, 149, 161 ; china clay, 107. North Goonbarrow, china clay, 107 ; veinstone, 107. North Sill Wood, elvan, 71. Ochre, 135, 158, 164, 165. Old Beam, china clay, 107 ; tin-ore, 159. Old Bonney Mine, china clay, 107 ; tin-ore, 138, 139. Old Cleaves, china clay, 107. Old Pembroke, 161. Old Polgooth, 161. Oligoclase in greenstone, 42, 47, 48, 51, 56, 58, 67 ; see also Plagioclase. Oligoclase-albite, 56, 58, 67. Olivine, 46, 50. Olivenite, 146, 157. Opal 157. Openworks, output from, 161. Ophitic diabase, 39, 45-49. Ores, output, 135, 137-158. Ore deposits, 131-174 ; see Lodes and Mines. Orthoclase, in elvan, 73-77 ; granite, 56, 59, 61 ; greisen, 67, 68 ; Luxulia- nite, 66 ; pegmatite, 61. Output from Mines, 135, 159-165. Par Beach, 130 ; calc-flinta at, 81 Pleistocene deposits, 121, 122, 126 greenstone, 37, 38 ; slates, 17, 23 tin in tidal river, 173 ; -water supply, 180. Par Canal, gravel, 126. Par, Wheal, 161. Par Consols, 131, 149, 161, 164. Par Green, slates, 23. Par Sands, Base of Meadfoot Beds, 7 ; submerged forest, 129. Par Water Company, 180. Paramoor, elevation of, 123. Paramoor Wood, grits, 26. Park of Mines, 133, 149, 161. Parka Consols, 158, 161, 162. Parsons Cove, stacks, 13 ; Dartmouth Slate, 14, 35 ; greenstone, 35. Pattison, S. B., 174. Pawton Iron Company, 163. Peach, 66, 132, 133 ; in clay pits, 109 ; Criggan Mine, 142. Peach, C. W., 4, 7, 13, 14, 24, 128, 129, 178. Pease, W., 180. Peat, 172-174. Pegmatite, 56, 61-63, 179. Pelean, calc-flinta, 81, 82. Pelyn, calc-flinta, 8 ; schorl rock, 82. Pelyne, mud stones, 34 ; Portnadler fault, 11. Pembroke Mine, 131, 140, 149, 161, 164. Penoarrow, Meadfoot Beds, 7. Pencarrow Head, Beach, 130 ; Devo- nian, 17-19 ; sheared volcanics, 36. Pendean, calc-flinta, 91. Pendelow Pleistocene, 124, 125 ; stream tin, 172, 173. Pengelly, grits, 26. Pengelly Mine, 150, 164, Penhale, Castle Dore Fault, 6, 8 ; Devonian, 16, 27. Penhellick, 33. Penisker, water supply, 180. Penkelly slates, 7, 14, 19. Penkestle, 34. PenpoU, diabase, 36. PenpoU Creek, Dartmouth Slates, 7 ; diabase, 35. Penquite, slate quarry, 178. Penrice, elvan, 68. Penrice Deer Park, elvan, 68. Penrose, Wheal, 150. Penstrassoe, elevation of, 123. Pentewan, elvan at, 68, 69, 79, 186 ; grits, 3, 7, 25 ; slates, 17 ; stream tin, 121, 127, 128, 130, 174. PentrufE, granite, 57. PentrufE Mine, 161. INDEX. 197 Pentuan, arenaceous beds, 3, 7, 25 ; detrital tin; 127, 128, 130, 171, 174 ; elvan, 68, 69, 79, 186 ; slates 17. Penvivian, granite, 54. Peridotite, 49-51. Perthite, 58, 62. Peter's Pits, veinstone, 110. Petrography of calc-flinta, 97-101 china stone, 112, 113 ; elvans, 76-79 granite, 56-60 ; greenstone, 44-53 metamorphic aureole, 93-104. Pharmacosiderite, 146, 157. Pharnyssick, 81. Phillips, J. A., 4, 38, 39, 45-51, 53, 60, 62, 95, 114 Phoebe's Point, 68 ; greenstone, 38 ; Devonian, 23. Photomicrographs, 186, 187. Picrite, 2, 49-51. Pilite in greenstone, 46. Finite, 57, 76, 92, 95. Pinsla Park, Quarry, 177. PiKSSON, L. v., 101. PiSANi, P., 66. Pitmoor, Pleistocene, 124 ; stream tin, 173. Pitchblende, 157. Pitsmingle Mine, 158. Plagioclase, in granite enclosures, 60 ; greenstone, 43, 44, 47-51 ; elvan, 74, 76, 78. Pleistocene, 120-130. Pliocene, 119, 120. Pneumatolytic action on calc-flinta, 89-94, 98, 101-103; elvan, 75, 77-79 ; granite, 59, fiO, 64-68 ; greenstone, 53 ; Meadfoot Beds, 92, 93, 101-104. Pneumatolysis, china clay, 106-111, 115-118. Point Quarry, fossils, 24. Poldew, spotted slates, 82. Polgaver Beach, 130 ; fossils, 24 ; shales and grits, 38, Polglaze, 26. Polgooth Mine, 131, 150-153, 161 ; elvans, 69-70, 79. Polgwyn Beach, Grampound Beds, 9. Polharmon, diabase, 82. Polharmon Mine, calc-flinta, 8, 81. Polkerris, calcareous beds, 9, 17, 22 Grampound Beds, 9 ; ' Head,' 121 raised beach, 121 ; greenstone, 37 submerged forest, 129 ; tufC, 37. Polkerris Harbour, beach, 130. Polkerris Inn, fault, 22 ; fossils, 24. Polkerris Quay, greenstone, 37. polkinghoene, j., 180. Pollard, Dr. W., 47, 63. Polmartin, 29. Polmear, Devonian, 15, 22, 23 ; green. stone, 37 ; fault, 6, 16 . Polmear Mine, 131, 153, 161, 165. Polmenna slates, 33, 177. Polperro, ' Head,' 120. Polridmouth Beach, 130 ; fossils 24 25 ; greenstone, 37 ; Head, 121 slates, 23 ; phosphatic nodules, 22 raised beach, 121. Polruan slates, 17-19, 24, 25 ; ' Head/ 120. Polrudden Cove, 9. Polscoe, calc-flinta, 8 ; fossiliferous beds, 20, 21 ; roadstone, 179. Polyear Consols, 161 ; greenstone, 39. Ponts Mill, altered killas, 81 ; gravel, 126. Ponts Pill Creek, fault at, 7, 8, 18 ; slates, 18-19. Porcupine, 81, 82. Porphyritic granite, see Granite. Porphyritio greenstones, 51, 52. Porphyry, sheared, 186. Forth, Pleistocene, 126-130 ; green- stone, 38 ; tin in tidal river, 173. Porthpean, fossils, 24 ; greenstone, 38 ; ' Head,' 122 ; quarries, 176. Portnadler Bay, Castle Dore Fault, 6, ] 1 ; Dartmouth Slates, 6 ; Meadfoot Slates, 6. Portwrinkle, fish grit, 14. Pothole, elvan, 69, 70. POWKIB, J., 14. Prideaux Wood, terrace, 122. Prideaux Wood Mine, 153, 161, 163. Prosper, Wheal, China clay, 107 ; tin mine, 133, 154, 16] ; calc-flinta in, 90 ; tourmalinised sediments, 93. Prosper and Mitchell Mine, 153, 154, 161. Proterobases, 45-49. Pbyce, W., 105, 135. Pseudo-bedding in granite, 55. Psilomelane, 154. Pteraspis cornubica, 13, 14, 17, 19, Punch's Cross, 18, 19, 24. Purple Quarry, china stone, 186. Pyrites, Iron, 137-158 ; output, 135, 164, 165 ; in altered killas, 93 granite 57 ; greenstone, 49, 51, 52 Meadfoot Beds, 104, Pyrites, copper, 137-158. Pyrolnsite, 154. Pyrrhotite, 148. Quarries in granite, 174-176 ; slates, 176-178. Quarry Wood, killas, 33, 177. Quartz in altered slates, 83, 94, 96, 97 ; calc-flinta, 98, 99 ; china clay, 114 ; china stone, 112, 113 ; elvan, 73, 76-79 ; granite, 57-61 ; greenstones, 44, 49, 52, 53 ; greisen, 67 ; pegma- tite, 61, 62. Quartz-diabase, 49. Quartz-eyed slates, 26-28. Quartz-porphyry, pre-granitic, 2, 43, 44, 186 ; see also Elvan. Quartz-schorl rock, 63-67. Quartzite, roadstone, 179. 198 JNDBX. Badium and Uranium Syndicate, 157. Radley, E. Gr., 101. Raised beaches, 2, 120-122. Raphael, folding, 17. Rashlbigh, p., 4, 126-130, 172. Rashleigh, Wheal, clay pits, 109 ; ' Head,' 122. Ready Money, 128, 129. Ready Money Beach, 130. Redmoor, 119, 171 ; granite of, 63 ; Pleistocene, 125 ; spotted slates of, 85 ; stream tin, 173 ; water supply, 180. Redruthite, 139, 143, 149. Regent, Wheal, 140, 161. Reid, C, 10, 25-26, 91, 119, 123, 129. Remfry, Wheal, china clay, 107 ; brick and tile works, 179 ; elvan, 72. Reperry, Wheal, 161. Reperry Mine, 154. Reperry Cross, granite, 63. Rescorla, detrital tin, 171 ; dressing plant, 136 ; grits, 25 ; Ruby Lode, 155. Restineas, iron output, 164. Restormel, calc-flinia, 8 ; Meadfoot Beds, 11, 15 ; iron lodes, 134. Restormel Castle, calc flinta, 82. Restormel Iron Mine, 154, 163. Resugga, elvan, 71. Ressugga Castle, grits, 26. Resugga Lane End, slates, 27. Resurgy Iron Mine, 163. Retew, schorl rock, 65. Retew Iron Mine, 163. Retire Common, flat at, 123 ; green- stone, 43. Retire Iron Mine, 154, 163. Restowrick Downs, china stone, 109 ; elvan, 72. . Retallick, flat at, 123. Retew, Brickworks, 179 : china clay, 109. Retew Iron Mine, 110, 163. Richardson, A. G., 106, 113, 114. Riley, E., 157. Rivers, stream tin in, 170-174. River erosion, 123, 124. River terraces, 2, 122, 123. Roadstone, 178, 179. Roche, iron lode, 134 ; Pleistocene, 124 ; spotted shale, 187 ; water supply, 181. Roche Ooonbarrow, china clay, 107. Roche Railway Station, killas, 93, 102, 103, 133, 187. Roche Rock, calc-flinta, 91 ; kaolin, 64-66 ; tourmaline, 64, 65. Roche Rock Mine, 141, 142, 161, 163 ; granite dip at, 54. Rock Hill Mine, 155, 161. Rocks, china clay, 107. Rocks Tin Mine, 161. Rocks and G-oonbarrow, 154, 155,461. Rocks and Carnsmerry, 161. Rocks and Treverbyn, 161. Rodwannick Wood, elvan, 186. Roofing slate, 178. Ropehorn, slates, 23, 24. Rose, Wheal, china clay, 107. Rosear Pit, Tin Lode, 138. Rosehill Quarry, 82. Rosevear Pits, china clay, 107; Ruby Iron Lode, 155. RoSLEK, H., china clay, 106 ; kaoliniza- tion, 115. Roselyon, grits, 27, 177. Rosemellyn Pit, china clay, 107. Rosevanion, calc-flinta, 8, 87 ; killas, 104 ; limurite, 187. Rosewarrick Iron Mine, 140, 141. Roseweek, greenstone, 39. Royalton, stream tin, 173. Royalton Mine, elvan, 72 ; tin-ore, 161. Ruby Iron Mine, 134, 155, 161, 163. Ruddle, lodes, 132. Ruddlemoor, veinstone, 110. Ruthvoes, calc-flinta, 8, 91 ; water supply, 181. Ruthvoes Iron Mine, 158, 163, 165. Rutile, 97, 99, 100. St. Austell, china clay, 105-112, 114- 118 ; china stone, 105, 111-114, 117 ; copper ore, 131 ; elvans, 68, 71, 76- 79 ; gold, 174 ; granite, 54-68 ; greenstone, 45, 47, 51-53 ; lodes, 131 ; metamorphic aureole, 80 ; population, 180 ; slate quarry, 176 ; tin ore, 131 ; schorl rock, 64-67 ; brecciated veinstones, 133 ; water supply, 180. St. Austell Bay, serpentine, 49-51. St. Austell Consols, 134, 155, 156, 162, 165 ; elvan at, 70. St. Austell Hills, 162. St. Austell Iron Mines, 163. St. Austell Moor, streams of, 1. St. Austell River, 54 : detrital tin, 171, 173, 174. St. Austell Rural District Council water supply, 180. St. Blazey, clay pits, 109 ; gravel, 126 ; iron lodes, 134 ; metamorphic aureole, 80 ; schorlaceous granite, 176 ; tin in tidal river, 173. St. Breward, water supply, 180. St. Columb Major, calc-flinta, 86, 87, 91 ; limurite, 187 ; water supply, 181. St. Colnmb Iron Mines, 163. St. Columb Porth, tin streams, 123. St. Dennis, china stone, 186; elvan, 72 ; granite, 54, 61 ; lodes of, 132 pegmatite, 62 ; Pleistocene, 124, 125 roadstone, 179 ; spotted slate, 187 water supply, 181 INDEX. 199 St. Dennis Crown Mine, 135, 13&, 147. St. Enoder Consols, 162. St. Ewe, gold, 174. St, Ingunger, biotite hornfels, 84, 95 ; cornubianite, 102 : greenstone, 40, 41, 52. St. Mewan, diabase, 39, 45-49, 53; gold, 174 ; roadstone, 178. St. Mewan Beacon, schorl. 111. St. Nectan Chapel, flat near, 123 ; ter- race, 123. St. Neots, slates, 34, 178. St. Neots Mines, 162. St. Sampson, slate quarry, 178. St. Stephens, china clay, 186; china stone, 110, 186 ; gold, 174 ; meta- , morphia aureole, 80 ; iron lodes, 134 ; well. 180. St. Stephens Coombe, elvan, 68, 70, 79 ; slates, 27. St. Stephens Iron Mines, 163, 165. St. Stephens Mine, 161. St. Veep, diabase, 36 ; fault at, 11; fosailiferous beds, 14, 21, 24, 25. St. Wenn, calc-flinta, 86 ; flat, 123 ; greenstone, 43. Sampson stone, see Calo-flinta. Sanctuaries, greenstone, 46, 48, 49, 53. Sand, blown. 130 ; marine, 130 ; from dressing processes, 135-137. Sandryqook, Pleistocene, 126-130 ; tin stream works, 173. Saussurite,.50. Savath, china clay, 107. Scenery, 2. Schalstein in Middle Devonian, 2, 44. Scheelite, 148. Schistosity in quarries, 178. Schorl, see Tourmaline. Sooroditei 142, 157. • ScRiVENOE, J. B., 65, 66, 91. Sedqwick, Prof. A., 3, 4. Serpentine, 2, 38, 49-51, 176. Shales, building, 176-178 ; metamor- phism of, 80-85, 92-97 ' Shelf,' tiQ streams, 170-172. ' Shell,' 110, 111. Shelton Mine, 138, 139, 162. Shepherdshill Wood, 69. Shilson & CoAD, Messrs., Polgooth Mine, 153. Shoad tin ore, 171, 172. Shorthorn Beach, 130 ; shales and grits, 38. Sillimanite, 96. Silver, output, 135, 147, 164, 165. Silveryein Mine, 156, 162, 165 ; grits and shales, 20. Singlerose Clay Works, 65, 67, 107. Slate, see roofing slate, 178. Siickeiisides, Veiitonwyn, 158. Smaltine, 151, 156. tMiTH, E., 126-129, 172. Soils, 181. Solly, R. H., 62. South Caudledown, china clay, 107 ; veinstone, 107. South Crinnis, 162, 165. South Cuddra, 162. South Fowey Consols, 131, 162. South Par, 159, 164. . South Polgooth Mine, 13, 146, li)7, 162 ; elvan, 69. South Polmear, 162, 165. South Terras Mine, 131, 134, 157, 162, 163, 165 ; elvan, 71. South Trebell, 162. Southground Point, 121. Sphene, 40, 41, 46, 48, 53, 93, 98, 100 ; see Leucoxene. Spinel in hornfels, 95, 96. Spit Point, Beach, 130 ; ' Head,' 121, raised beach, 121, 122. Spotted slates. 84, 85, 92, 91-97, 187. Springs, 180,181. Staddon grits, 10-12, 28-31 ; quarries in, 177; soil, 181. Stannite, Powey Consols, 144. Statistics, Mineral, 135, 159-165. Steigee, Gr., 101. Stenalees, china clay, 107 ; elvan, 73. Stennagwyn Mine, 110, 132, 157. Stent, 106, 107, 109-111, 117 ; tin in, 135. Sticker, flats near, 123 ; elvan, 69, 70 ; greenstone, 39 ; slates, 26. . Stockee, H. M., 105. Stooker's Bnrngullow Pit, 110. Stockworks, 132, 133, 138, 139, 148. Stratigraphical Table, 2. Stream tin, 120, 123-128, 170-174 ; gold in, 174. , Stricksteuton, killas, 15, 82. Submerged forests, 120, 1.28-130. Symons, E., 172. Talc in Great Beam, 146 ; serpentine, 50. Tavistockite, 157. Tawell, 20. Taylor, R., 149. Teall, Dr. J. J. H., 53, 94, 107. Terraces, River, 2, 122, 123. Terras, elvan, 70, 71 ; greenstone, 39, 47, 48, 53, 81 ; greenstone soil, 181 ; slates, 27 ; terrace, 123 ; tourmaline in greenstone, 104. Terras Mine, 162. Thermometamorphism, 94-101. Thomas, H. H., 99, 103. Thompson, Mb., 110. Thomson, Me., 105. Tiddeman, R. H., 120. Tiles and bricks, 179,, 180. Tin Hill, output, 162. Tin ores, alluvial, 170-174 ; dressing of, 135-137, 139 ; output from . Mines, 135, 159-164. Tin and Copper, directions of lode, 131, 132 ; Mines. 131-169. Tin Flbors, 144, 149. 200 INDEX. Tin Valley Mine, 162. Titaniferous iron ore, see Ilmenite. Tithe Hall, 34. Toldish Mine, 134, 158, 165 ; water supply, 181. Tolgarrick, elvan, 71 ; terrace, 123. Torbernite, 157. Tourmaline, in calc-flinta, 90 ; china clay, 112, 114, 116 ; china stone, 117 ; elvan, 72-79 ; granite, 46-67, 57-59, 61, 62, 186 ; greenstone, 48, 53 ; greisen, 67 ; killas, 65, 94, 96, 101, 102, 104, 187 ; veins, 63, 65-67, 109-111, 117, 148. Tourmaline-albite rocks, 103. Tourmalinization, 65-67, 72, 73, 75, 77, 92, 93, 101-104. Topaz, 57, 58, 67, 77, 78, 111, 113, 117. Towan, elvan, 68. ' Tower Consols, 134, 158, 163, 164 ; water supply, 181. Towns, 1. Trago Powder Mills, slates, 34. Trap Wood, basalt, 37 ; calc-flinta, 8,21. Trebell Consols, granite, 63 ; tin-ore, 162. Trebethavy, greenstone, 36. Trebyan, biotite spotting, 85 ; Pliocene plane, 119. Tredinnick, calc-flinta, 27 ; greenstone, 41. Treesmill, calc-flinta, 8, 27, 81, 82, 178. Treffiry Consols, 164. Treffrys regulus, 162. Trefrawl, 21. Tregamere, axinite, 91. Tregarden granite quarry, 55, 174, 175 ; hornfels, 92. Tregargus, china stone, 110, 186. Tregargus Mill, gilbertite, 110. Tregarrick, fault at, 11 ; greenstone, 36, 49. Tregavithick, 14. Tregawne, iron ore, 147, 164. Tregenna, diabase, 36. Tregollan, output, 162, 164. Tregonetha, calc-flinta, 91 ; iron out- put, 164. Tregongeeves, elvan, 69 ; greenstone, 39, 48, 53 ; greenstone soil, 181 ; roadstone, 178. Tregonissey, metamorphism, 80. Tregonning, luxulianite, 176. Tregontrees, tin-ore, 161. Tregorrick, slates, 27 ; roadstone, 178. Tregoss Mine, 162. Tregoss Moor, elvan, 72 ; tin stream, 123. Tregrehan Consols, 162. Tregue, 14. TreguUan, adit, 158; albite, 100; axinite, 103, 104 ; calc-flinta, 86, 90, 101 ; felspathio slates, 187; flat, 123 ; garnet, 99 ; greenstone, 41. Tregunnick, 21. 70 75 . Trelavour Downs, elvan, '^1 '^ ' pegmatite, 61-63 ; roadstone, 179 ; tourmaline granite, 54. Treliver Iron Mine, 134, 158, 164. Trelower, 26. Treloweth Mewan, tin-ore, 162. Treloy, stream tin, 123. Tremaddock, tin-ore, 162. Tremain, fault at, ll. Tremeer, 14. Tremodrett Mill, granite, 61. Tremolite, 50, 98, 100. Tremoor, iron output, 164. Tremore, calc-flinta, 86, 87, 89-91 ; elvan, 74, 76, 77, 78, 186 ; green- stone, 52 ; hornfels, 64, 97. Trenadling, 15. Trenance, reservoir, 180. Trenarren House, greenstone, 38, Trenant, fossils, 19 ; grit, 22. Trenay, slates, 32, 177. Trencreek, grits, 21, 25 ; greenstone, 36. Trenewan, 14. Treningle, calc-flinta, 90. Trenoweth, output, 162, 163. Trenoweth Mill, 26. Trenython, Dartmouth Beds, 15. Trerank, albite-tourmaline rock, 103 ; calc-flinta, 91 ; roadstone, 179. Trerank Iron Mine, 134, 158, 164. Trerice, bricks, 179 ; china clay, 109. Tresayes, roadstone, 179. Tresayes Downs, pegmatite, 61. Trescoll, surface wash, 172. Trescoll Moor, tin, 171. Tresibble, iron output, 164. Trethosa Pit, gilbertite, 110. TrethuUan Otstle, elvan, 70 ; slates, 27. Trethurgy, Ruby Iron Lode, 155. Tretoil Mine, 158 ; greenstone, 40, 42, 52, 162, 164, 165. Trevalfry, Meadfoot Beds, 11, 12. Trevan Wood, syncline, 26. Trevanion, tin-ore, 162. Trevarren, calc-flinta, 91. Trevarren United Mines, tin-ore, 162. Trevarrick, greenstone, 48. Trevarrick House, china clay, 109. Trevarrick Terrace, greenstone, 81, 178. Trevawden, grits, 27. Trevega, tin-ore, 162. Trevego, 177. Trevennack Farm, luxulianite, 66. Treverbyn, detrital tin, 171 ; granite quarry, 175 ; output, 162, 163, 164 ; Ruby Iron Lode, 155 ; water supply, 181. Treverran, Dartmouth Slate, 15, 16. Trevillick, grit quarry, 178. Treviscoe, china clay, 186 ; china stone, 109. INDEX. 201 Trevisooe Valley, pegmatite, 62. Trevissick, elvan, 68 ; greenstone, 39. Trevorder, 177. Treweatha Iron Mine, 163. Treweather, calc-flinta, 21 ; fossili- ferous slates, 20. Treweers, 14. Trewheela, iron output, 164. Trewhiddle, elvan. 69 ; greenstone, 39. Trewindle, Devonian, 12, 28, 29. Trewinnow Vean, grits, 26. Trewithian, elvan, 70, 71. TrewoUack, Flat at, 123. Trigamelling, greenstone, 35 ; slates, 14. Tetjscott, Mr., 158. Tungsten, see Wolfram. TnrMown, 29, 34. Tywardreath, Meadfoot Beds, 7, 23, 176 ; Castle Dore Fault, 6 ; Dart- mouth Slate, 15, 16. Umber, 135, 158, 164, 165. Upper Oreany, Pleistocene, 124, 126 ; stream tin, 173. Upper Pentewan Stream Works, 127, 128, 130. Uralite, see Hornblende. Uralitio Diabases, 45-49. Uranium Mine, 104, 157. Uranium ore, output, 135, 165 ; lodes, 134, 144, 154, 155, 156, 157. Ueshbr, W. a. E., 1-40, 44, 68-72, 80, 83, 109-111, 147-149, 154, 172, 176. Valley gravel, 2, 120, 122-130. Van, fossils, 211. Variegated slates, Dartmouth Beds, 14- 16. Veinstones, 132, 133, 144 ; see also under Mines. Veinstone Breccia, 132-133. Ventonwyn Mine, 131, 135, 146, 158, 162. Virgin, Wheal, stream works, 127, 128. Vitreous copper, 143, 144, 149. Volcanic rooks, in Dartmouth Slates, 35, 36 ; Meadfoot Beds, 36-38 ; Middle Devonian, 44. Walter K 62. Watch House, Meadfoot Beds, 7, 18 ; ' Head,' 121. Watergate, Pleistocene, 124, 125 ; stream tin, 173. Water supply, 180, 181. Wavellite, 139, 146, 157. Weed, W. H., 100, 101. Wells, 180, 181. West Beam, 162. West Ooombe, beach, 130. West Coombe Valley, ' Head,' 121. West Crinnis, 162, 165. West Down Iron Mine, 163. West Wheal Eliza, 140, 162 ; meta- morphism, 80. West Fowey Consols, 162, 165. West Goonbarrow, china clay, 107. West Wheal Mulvra, 160. West Par Consols, 162. West Park, schalstein, 44 ; slates, 34. West Polgooth, 162. West Quarry, elvan, 186. West Taphouse, slates, 34. West Trevillis, schalstein, 44. Westwood Quarry, slates, 33. White Stone, 111, 112. Williams, Eev. D., 34. Williams, R. H., 155, 156. Willwake, arenaceous beds, 21. Withiel, calc-flinta, 86, 87 : elvan, 73, 186 ; greenstone, 43 ; lluby Iron Lode, 134, 155, 163 164 ; shales, 27. Withielgoose, calc-flinta, 91. Withiel Mill, 64. Wolfram, 132 ; output, 135, 164, 165 ; Bunny Mine, 138 ; dressing of, 139 ; Great Beam, 146 ; Maudlin Mine, 149 ; North Bonny Mine, 149 ; Wheal Prosper, 154 ; Stennagwyn, 157. Wood Mine, 162. Woodacross, 21. Woodclose Mine, 162. Woodley, schalstein, 44, 51. Woodley Iron Mine, 158, 164. Woodsaws, grits, 27 ; igneous frag- ments, 39. Woon, kaolinized granite, 176. Worth, R. N., 106, 153. Wrikht, W. B. 120. Yondertown, china clay, 107 ; elvan, 72, 73. Zinc-blende, output, 135, 164, 165 ; in calc-flinta, 90, 103, 104 ; greenstone, 53 ; Carclaze Pit, 139 ; East Crinnis, 143 ; Fowey Consols, 144 ; Lanes- cot, 147 ; Par Consols, 149 ; Pem- broke Mine, 149 ; Polmear Mine, 153 ; South Terras Mine, 157. Zinc silicate, Fowey Consols, 144. Zippeite, 145. Zircon, 56, 58, 68, 95, 100. Zoisite, 53, 88, 98, 99. 12979 Of the before-mentioned One-inch sheets, Nos, 311, 326 with 340, 346, 347, 348, 352, 353 with 354, and 357 with 360, are issued colour-printed, price U. 6d. each. Sheet 351 with 358 is also issued colour-printed, price 2s. 6d. * The following sheets are, at present, issued in hand-coloured form only at the Iffices stated : — Sheet'325, 12«. 9d. ; Sheet 339, 9«, 9d. ; Sheet 349, 14g. 3d. ; Sheet 350, lis, 3d. ; Sheet 355, 5g. 3d. ; Sheet 356, 3s. SIX