^^.^^H. ^ :~^ ,ii>™ -,s. . cr K?: ajornell Imnerattg ffiibrarg gillite Igiatoctcal ICthcarg THE GIFT OF PRESIDENT WHITE MAINTAINED BY THE UNIVERSITY IN ACCORD- ANCE WITH THE PROVISIONS OF THE GIFT ENGINEERING LIBRARY The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004023382 He P O RTS ON THE PHTSICiL, DESCEIPTIYE, AND ECONOMIC GEOLOGY OF BRITISH GUIANA. BY CHARLES B. BROWN, F.G.S., AND J. G. SAWKINS, F.G.S. PUBLISHED BT ORDER OF THE LORDS COMMISSIONEES OF HER MAJESTY'S IREASURT. LONDON: PEINTBD FOR HER MAJESTY'S STATIONERY OPEICE, AND SOLD BY LONGMANS, GREEN, & Co. AND EDWARD STANFORD, 6, Charing Cross, S.W. 1875. Price Fourteen Shillings and Sixpence. CONTENTS. Page Pbeface - - - - . . - 3 to 4 Geneeaii Eepoet on the Phtsical, Desceiptive, and Economic Geology of British Guiana. Part I.— General Physical Features of the colony of British Guiana - - - 5 „ 10 Part II. — General Descriptive Geology - - 10 „ 17 Part III. — Economic Geology - - - 17 „ 30 Geological Eepoet op the Noeth-westeen Poetion OF Beitish Guiana - - - - 31 „ 37 Geological Eepoet on the Cutuni and Sdpinaam EiVEES - - . . - - 38 „ 44 Geological Examinations of the Pueuni and Maza- EUNI ElVERS - - . - - -45„51 Geological Suevet of the Eivee Demeeaea - - 52 „ 55 Geological Eepoet on a Portion op the Essequebo Eivee, and of the Papaeaima Mountains. Part I. — Description of the Physical Features - 56 „ 66 Part II. — Descriptive Geology - - - 66 „ 74 Obseevations made on an Excursion extending from Geoegetown to the Mapuei Eapids, on the Eupu- NUNi; thence to the Mappi near the noetheen BASE OF the GaMUKU MOUNTAINS, AND THENCE UP THE Essequebo to King William the Fourth Cataeact 75 „ - 96 Geological Eepoet on the Eewa and Quitaro elvbrs, and the country between the latter and the Eupununi. Part I. — Description of Eoute Part IT. — ^Physical Features Part III. — Descriptive Geology Part IV. — Economic Geology Geological Eepoet on the Central British Guiana. Part I. — Physical Geology Part II. — Descriptive Geology Part III. — ^Economic Geology Geological Eepoet on the Disteict boeder[ng on THE Cueiebeong, Treng, Takutu, Eupununi, and Upper Essequebo Eivees. Part I.— Physical Geology - - - 130 „ 172 Part II. — Descriptive Geology . - - 172 „ 201 34328. A ) ' /, ■ lit 1 1 1 1 96 „ 97 97 „ 101 102 „ 107 107 Poetion of - 108 „ 122 122 „ 129 129 IV Page Geological Repokt on the Coeentyne Eivee. Part I.— Physical Features , -, - 202 to 216 Part II. — Descriptive Geology - - - 216 „ 232 Geological Report on the Beebice and Demeeaea KlVEES. Part I.— Physical Features - - - 233 „ 245 Part II. — Descriptive Geology - - - 245 „ 255 Geological Repoet on the Mazaeuni Rivee. Part I.— Physical Features - - - 256 „ 266 Part II. — Descriptive Geology - - - 266 „ 277 Repoet on the Raieteue Wateepall - - - 278 „ 297 GEOLOGY OF BEITI8H GUIANA. When these Reports passed through the press I was abroad, and had no opportunity of correcting the prooft". Many errors, chiefly in the spelling of names of places, have thus unavoidably occurred. These,- and some errors in punctuation, I have corrected in the subjoined table of errata, omitting, however, to notice words which, coming under the heading of misprints, will be at once apparent to the reader. C. B. Bkown. June 18th, 1875, 34328a. Wt. 4209. ERRATA. Table of Contents, line 16, for Pararaima, read Pacaraima. „ „ 22, and at page 150, for Camuku, read Canucu. J, „ 37, for Treng, read Ireng. „ - iv. „ 11, for Kaieteur, readKaieteur. Page 8, line 43, for Cuyueimi, read Cuyuwini. „ 16, „ 1, „ granite, „ granitic. „ 20, 26, 29, 30, 121, and 131, the word Curiebrong is incorrectly spelt. »? 21, line 8, for Weynamon, read Weynamou. 5J 24, » 3, „ Pelpee, ), Peepee. tt J) » 7, „ Wamsou, s> Waemou. n »J J) 46, „ Caliohadekeur ,, Calishadekeur. ■'jj )9 ,, 47, „ Maturu-vo-w, ), Maturuwow. )> JJ w 49, „ WatericoTT, yt Watertieow. 3J » f9 58,,,, Warw, » Warn. if 25, J, 54, „ Taispong, >> Taiepong. it 26, », 3, „ Arriosaro, ,» Arrissaro. 99 J> S, 15, „ information. ), observation. ii S) « 54, „ Macudoord, J, Ufacudood. » 28, J, 22, „ Motrayparu, s, Mokayparu, )] 34, » 18, „ Himuzaoaharra, » Himuracabarra. jj >J », „ „ Wazamurie, », Waramurie. » S» 5» 32, „ Itabooto, ,j Itaboo to. ' J» 37, 'w 9, „ the rocks. ), the metamorphic rocks. Pages 57 and 58, the word Makarapan is incorrectly spelt. Page 58,: line 33, for Kaiinaucho, read Karinambo. j> 61, » 29, „ Saeabuta, ,, Sacaouta. 5» » » 32, „ Maratrang, » Marakang. 3» 62, » 10, „ Mavritia, 7» Mauritia. )7 67, » 12, „ many contains. ?, many places contains. if ff u 31, „ W. 55''-W. >i N. 55° W. 68, J, 3, „ This rock. » This latter rock. ff >J » 16, „ Cuyariwaha, » Cuyariwaka. it 71, » 21, „ quartz, gravel J, quartz-gravel. ft J> ,, 37, „ quartz ore, >t quartzose. J» 72, « 28, „ or quartz. » of quartz. SJ 97, ft 11, „ Tahuta, J, Takutu. f> )> » 12, „ Tahutuwow, Jt Takutuwow. )> 98, J» 3, „ tortuous with. 1) tortuous river with. J> » 9, 5, „ Qultaro, !> Quitaro. SJ 3» J> 11, „ earthly, 3> earthy. JJ )J » 32, „ Porto, J» Poto. J> 99, „ 24, „ altitude but >9 altitude ; but. J» 101, ), 6, „ Otonani, » Otonam. 102, description of Diag. on this page refers to Dig. No. 10, page 104, which should occupy this position. „ line 14, for arenoargilaceous, read areno-argillaceous. 104, description of Diag. on this page refers to Dig. No. 6, page 102 which should occupy this position. 106, line 16, for, and being over, read and over. „ „ 50, „ calcopar, „ calcspar. 116, „ 60, ,, Owentick, „ Owenteik. 117, „ 5, „ white red, ,, white, red. , 111, „ II, „ Ayangeanna, „ Ayangcanna. Pages 120 and 131, the word Kaieteur is incorrectly spelt. Pag e 123, line 5, for fertile, in, read fertile ; in. »I 33 }} 6, „ trees j there. », .trees there. „ it a 7. „ oil, » soil. »» 130, „ 10, „ one. 9i me. » 133, „ 1. „ plain as, »> pla^n stretching as. if 138, „ 44, „ them, and. ,1 them; and. -» 147, „ 6, „ night on, i) night, on. » » fi .. „ by and. J9 by, an^ ,. ii n 23, „ Wapiriana, 91 Wapisiana. »9 >i a 39, „ shallow owing, „ shallow, owing. )} 33 17 »3 „ width that. ,J width, that. it 33 » 51, „ north at. ,1 north, at. j» 149, „ 34, „ yards and. „ yards, and. w J» 33 44, „ country and. ,1 country j and. » 159, „ 21, „ well I, » well, I. j> „ » 29, „ them paid, it them, paid. j> 160, „ 24, „ me as, 99 me, as. tj >> » 28, „ rock by. ,» rock, by. » 161, „ 17, „ Alreo, 97 Abreo. j» 163, „ 1, „ foot mountains, ,» foot of the mountains. i> 164, „ 26, „ seen and. 99 seen, and. )j >, 11 27, „ left, formed, ,1 left, formed. »> „ ,1 33 „ line shown. 99 Une, shown. 'J 165, „ 19, „ mountains reaching, „ mountains, reaching. » , » 20, „ Pinniyettinow where „ Pinniyettinow, where j» » ,, 33, „ preceeding, 9) proceeding. )i >» » 42, „ between out. !> between, out. J) „ ,» 43, ,, colours from. J, colours, from. )) 166. „ 15, „ followed and. » followed, and. )» »» »» 21, „ Quitaro, savanna. », Quitaro savanna. )j 167, „ 33 „ river coming, )> river, coming. j> »J 33 22, „ rock and. f> rock, and. » 7J >■> 25, „ village which. 99 village, which. 9» 33 33 41, „ land the, »» land, the. »» J7 if 47j „ deeper and. », deeper, and. >3 33 »» 50, „ beeches. „ beaches, » 168, „ 22, „ river which. „ river, which. >» 3> 33 30, „ parts and, ,» parts, and. ?» 169, „ 14, „ in to. J» in, to. 51 33 33 22, „ weather only, J, weather, only. J> 172, „ 14, „ having. » have. ?» 175, „ 9. „ tin. J» thin. >» 176, „ 5, „ clay with. >, clay, with. 1» 177, „ 2, „ southward as. » southward, as. 31 33 33 5, „ colour which, J, coloui', which. » 3» 33 24, „ taste and J, taste, and. S> 178, „ 20, „ quartz, gravels 9> quartz gravels. »> 179, foot note „ No. 16, » No. 18. » 180, line 81, „ orgin. „ origin. 9> 181, „ 20, „ fort. » foot. 9) 182, „ 15, „ horizontally along. „ horizontally, along. 93 ,> »» ft „ top as. 1, top, as. 91 183, footnote,,, No. 19, 51 No. 21. 33 186, line 4, „ came, » became. 3> 9t 99 16, „ characters its, 5, characters, its. ■»3 » >l 20, „ at. „ on. Page 186, line 39, ,, Cass-kityn, read Cassikitu. „ 188, „ 26, „ Manarswah, „ Manarowah. „ 189, „ 7, „ hitherto „ hitherto, „ 191, „ 24, „ layer some, „ layer, some. n „ „ „ „ amygdaloid „ amygdaloid, „ 192, explanation of Dig. No. 26, for rests and banks, read nests and bands. „ 193, line 43, for crystals and, read crystals, and. „ 203, lines 39 and 42, for Apum, „ Apuni. „ 99 line 46, for day and. >» day, and. }> 205, J? 31, „ fall the. ,j faU, the. 79 207, j» 14, „ and the, JJ from the. J» » JJ 49, „ an. ,j and. ., ?j SJ 50, „ slight, » straight. ?» 209, 99 37, „ large branch. ?» large, branch. J> 210, >J 32, „ shut the. s. shut out the. » 215, .;> 47, „ forest called. „ forest, called. >f 217, „ 27, „ particularly. »> partially. »S 223, JJ 7, „ at, „ as. ?» 236, JJ 24, „ construction. 5» constriction. J» 241, SJ 26, „ Ackaiuron, " Ackaiurou. „ 99 32, „ north-west-north. 3J west-north-west. J» 245, 9^ 6, „ Ackraima, » Ackaima. 3» 99 99 10, „ Arridaro, „ Arrissaro. JJ 246, JJ 12, „ alluvia. JJ alluvial. 3> 249, jy 5, „ Arriosano, JJ Arrisaro. SJ 251, JJ 41, „ Wahmana, » Wahmara. JJ 255, )J 17, „ granite. J> granitic. Pages 258, 267 ,275 , the word Weynamon is incorrectly spelt. j> 262 and 264, „ Culcuie JJ JJ Page 271, line 24, J for Tomehri, ] read^Temehri. 99 273, JJ 45, „ Mazarani, J, Maz urine. 99 275, JJ 1, „ junction of the," JJ junction the. 99 280, j> 17, „ first the, «j the first. 99 99 J) J? „ river called. „ river, called. J» 99 )) JJ „ Arissaro on. „ Arissaro, on. 99 281, JJ 16, „ vras the. JJ was then the. » j» )j 19, „ bateau it. » bateau, it. »» JS JJ 20, „ cataract and. „ cataract; and. 99 283, JJ 6, ,, journey, a, „ journey— a. 99 » >j 7, „ great fall. JJ Great Fall. 99 s» JJ 27, „ passing Partamona, ' I, passing the Partamona. 99 28S, JJ 40, „ Tukine, j> Tukuie. 99 '» JJ 42, „ Oriedouk, Osiedouk. 99 290, JJ 29, „ 88 feet, JJ 81 feet. 297, all the last paragraph is a quotation. PREFACE. The Geological Survey. of this Colony was commenced in November 1867 by Mr. Sawkins and myself, and so conducted till the month of June 1870, at which time Mr. Savrkins retired, and I continued the work single handed. It can be readily understood that to explore such a vast extent of thinly-inhabited country, equal in size to England and Scotland together, covered with boundless forests, and situated within the Tropics, was at best a difficult and laborious undertaking. The cultivated portion made accessible by roads is but an atom of the whole territory, and lies along the sea coast, so that to explore the interior we had to ascend the rivers in boats, and make walking journeys across country along Indian paths. To pene- trate to the utmost limits of the colony it became necessary to make long excursions, sometimes of eight months' duration, upon which, owing to the dangerous rapids and cataracts on the rivers, strong boats with crews of river-men had to be employed, and most of the provisions for our maintenance carried with us. At times, on long walking journeys, we had to depend for sustenance on coarse food procured at the Indian villages passed through on the route. Thus it frequently happened that in places where I wished to stop and examine interesting geological areas, I was obliged to hurry forwards for the purpose of obtaining provisions ; whUst in other parts, comparatively valueless, I was sometimes detained whilst food was being prepared for us. Oftentimes the task of making out the geology of the country was rendered a hopeless one by the dense forests, through which we travelled for days together, hiding completely the contour of the country, as well as the outcrop of the rocks. During four months of the year the rain falls heavily, the rivers are flooded, hiding all the rocks, and the surrounding country bordering them to some extent submerged; even in the high lands the mountain streams and torrents are rendered impassable. Our time during these months was occupied in preparing maps and reports, which were sent in to the Government from time to time. ■ A 2 In the face of all these difficulties I succeeded in tracing all the rivers o:^ any size almost to their sources, and made besides many land journeys on foot, thereby gaining a pretty fair knowledge ot the geological structure of the colony. To make an accurate survey would, however, require an immense outlay, and occupy three times the number of years already spent on the present explorations. A short general account of the physical features and geology of the colony is given in this volume, followed by reports on each district, as examined and described during the continuance of the survey. The attached map, containing the geological work of the survey, is from tracings of Sir R. Schomburgh's large map (reduced one half), furnished by the Colonial Office. As parts of it were found to be incorrect in details, much time has been expended in trying to rectify them. Chas. B. Bkown. Georgetown, Demerara, April 1873. REPORTS ON THE GEOLOGY OF BMTISH GUIANA. General Report on the Physical, Descriptive, and Economic Geology of British Guiana, By CiiAKLES B. Brown, Esq. APRIL 1873, CONTENTS. I. General Physical Featdres of the Colony op Bkitish Gclana. II. General descriptive Geology. 1. Alluvia. a. Alluvium. 6. Muvio-marine alluvium or coast deposit. c. Eiver loam. d. Valley gravels and sand and clay deposit. 2. Sandstone formation. ^ 3. Greenstone. 4. Schists. 5. Gneiss. 6. Quartz-porphyry and felstone. 7. Granite and syenite. III. Economic Geolooy. 1. Soils. 2. Sand. 3. Clay. 4. Building stone. 5. Koad mateiial. 6. Jasper. 7. Porphyries. 8. Granites. 9. Graphite. 10. Iron. 11. Manganese. 12. Gold. 13. Salt. PART I. General Physical Features of the Colony of British Guiana. The Colony of British Guiana is situated in the north-eastern portion o£ South America, between the 1st and 9th parallels of north latitude and 57th and 61st degrees of west longitude, and lies between Dutch Guiana, Venezuela, and Brazil. Its boun- GEOLOGY OF BRITISH GUIANA. daries, as defined by Sir Eobert Schomburgh, and claimed by England, embrace an area of 88,000 square miles, of which about 6,500 IS undulating open savanna, and 3,000 grass-covered moun- tains, the remainder being clothed with dense forests. Its S^^^^^^^ length from north to south is 550 miles, with a maximum breadtn of 286 miles. , The surface of the eastern portion of the colony, from the sources of the Corentyne and Essequebo rivers to the sea coast, may be regarded as a rough inclined plain, commencmg at a height of about 800 feet above the sea, and sloping down gradually to the sea level near the coast. Of this the most elevated portion is mountainous, but no part of it is elevated to a greater height than 2,000 feet above the sea, or 1,200 feet above the river s level in the vicinity of the Essequebo, and 300 feet above the level of the source of the Corentyne. This plain extends westward to the head of the Takutu river, and from that northward to the base of the Canucu, Cumucumu, and Coratamung mountains. Beyond these it spreads across from the Essequebo to the Cotinga^^ P^er, coming up to the base of the Pacaraima mountains, wheire its general level is 300 feet above the sea. The western portion of these two last-menBoned plains is devoid of large forest trees, and is covered with grass, being portions of the great savanna stretch- ing eastward from Brazil. The views from the savannas have a beauty and sirigularity of their own, and it stirs one with a sense of boundless freedom to stand upon a knoll midst one, and view the grassy plain fading away to the horizon in the distance, and melting gradually, as it were, into the atmosphere. The filrst-mentioned portion of the great sloping plain is crossed at Wenkobat by a range of hills leading to the falls of Wonotobo on the Corentyne, and there its general level is only 250 feet above the sea. The next range of mountains rising from it, and lying in a north-east and east-north-east direction, is that froiii Makarapan to Maccari mountains, which end at the Christmas cataracts on the Berbice river. To the northward of this, on the eastern side of the Essequebo, opposite the end of the Pacaraima mountains, comes a cluster of mountains stretching from Akaiwanna to Parish peak, and south- ward about the sources of the Demerara river, the highest being not more than 1,000 feet. Further north, at Ororu-mallali, there are isolated ranges of hills from 500 to 700 feet in height. Northward of the savanna or plain extending from the Esse- quebo to the Cotinga river, before mentioned, lies the great Pacaraima mountains, a wide extent of rough mountainous country traversed by wide valleys, lying chiefly in a north-west and south- east direction, extending from about the 4 th parallel of north latitude to 5° 30' north, gradually rising from a height of 300 feet to above 3,000 feet between the Potaro and Siparuni rivers, and to a height of 7,500 feet at Koraima mountain, at the extreme western limits of the colony. The southern portion is composed of rugged hills and valleys strewn with rocks, and quite devoid of GEOLOGY OF BRITISH GUIANA. 7 large forest-covered areas, whilst to the north, where the moun- tains of sandstone assume table-shaped forms, the whole is covered with dense forests, except about the sources of the Mazaruni river. To the eastward this great mass of mountains narrows rapidly, reaching the Essequebo river in a blunt point at Cumuti and Twasinki. The scenery amongst these mountains — where the view is wholly unobstructed by the dense forest which clothes all the other mountains, and the greater portion of the sandstone table- lands — is grand, varied, and beautiful in the extreme. Peaks and ridges of every variety of form are grouped together, packed one behind the other, fading away in the distance, their sides being clothed with grass and clusters of little dark green groves, with here and there large frownjng masses of rock far up their heights. Nestling between them comes level-bottomed grass- covered valleys, containing small streams near which lie belts of wood. Their northern face forms a bold escarpment, some parts of which are 2,300 feet in height, and from its foot northward to the sea coast extends a vast undulating tree-covered plain, from which rises here and there a few low isolated ridges of from 300 to 700 feet in height. The level of this plain on the Mazaruni river, near Merumd, is 150 to 200 feet above the sea; on the Ouyuni, at Otomong river — the boundary line between British and Vene- zuelan Guiana — 295 feet ; and at Manarie village, between the Barima and Bararaa rivers, 113 feet. From that the ground falls rapidly to the vast interminable swampy land bordering that portion of the sea coast. Between the Cuyuni and Barama rivers comes the Imataca range, which terminates near the sources of the Waini river, and is of no considerable extent or height in this part. Thus we see two great parallel mountain systems crossing thfe colony from west to east, the greater being that of the Pacaraima and Merum6 mountains, which is a continuation of the Parima mountains ; and the lesser the Canucu, Oamucumu, and Cora- tamung mountains, extending from the Takuta river to the Essequebo, but not eastward of it ; which in their widest part occupy a distance of 30 miles. The Sierra Acarai range, which forms the watershed between the Essequebo and the tributaries of the Amazon, does not rise to a greater height than some 2,500 feet, and its northern base is 800 feet above the sea. It decreases rapidly in height to the eastward.. The level of the coast land varies in certain localities, and at different distances from the sea, being below the level of high spring tides at 10 miles inland on part of the east coast, and at its level on parts of the Arabisci coast. Upon this depressed land where the soil is rich are situated all the sugar estates of the colony. The sea is kept from these lands by a line of dams along the coast, and side dams between each estate, the drainage being effected by sluices or *' kokers " when P GEOLOGY OF BRITISH GUIANA. the tide is low. The drainage of the swampy lands behind the estates has to pass through the trenches of the estates, and in wet weather the supply of water being very great, it accumulates rapidly when the tide is high, so that dams have been erected m rear of each estate. With the exception of the cultivated portions, nearly all this land is covered with high forest trees and dense jungle, chiefly of courida {Avicennis nitida), mangrove {Rhizophom mangle), and corkwood near the coast, and mora {Mora excelsa) upon the slightly raised portions. Small areas also are covered with coarse grass and rush in the immediate vicinity of the estates, and are termed "floating savannas." \' From the coast line seaward the ocean deepens very gradually, and at low tide extensive mud flats and sand banks are left bare. Tracing this fluvio-marine deposit inland, it is found to rise gradually until it becomes some 10 or 12 feet above the level of high-water mark, at different distances in various localities from the coast line, and ends at the sloping front of an older deposit of sand and clay beds, which forms a vast extent of undulating country rising to not more than 150 feet above the sea, and stretching back to where the solid rock strata underlying it comes out at the surface. The colony is traversed by numerous large rivers and streams some of which flow northward and empty themselves into the Atlantic Ocean, and others flow southward into the Kio Branco, a tributary of the Rio Negro. The watershed between the two systems, though 250 miles inland, is only 350 feet above the sea. Of these there are five large principal ones, viz., the Esse- quebo, Corentyne, Mazaruni, Cuyuni, and Berbioe. The Esse- quebo, Mazaruni, and Berbice are rivers belonging entirely to the colony, while the Corentyne is a boundary river between it and Dutch Guiana ; and the Cuyuni, coming from Venezuela, runs a course of only 120 miles in it, from west to east. The rivers next in size to these are the New River, Demerara, Ireng, Ootinga, Rupununi, Takutu, Rewa, Quitaro, Puruni, Waini, Barima, Potaro, Siparuni, Burro-burro, Mahaica, Maiconi, and Canjd Of these again the Cotinga and Takutu are boundary rivers between the colony and Brazil, and they, together with the Ireng, are tributaries of the Rio Branco. The Essequebo river rises in 0° 40' north latitude in the Acarai mountiiins, at a height of 850 feet above the sea, and flows at first in a north-east direction to its junction with the Cuyucirni river, then pursues a comparatively straight general course in a northerly direction, emptying itself into the Atlantic Ocean in the 7 th parallel of north latitude, after running a dis- tance (including windings) of 600 miles. About 43 miles from its mouth it is joined by the Mazaruni river, which is itself joined by the Cuyuni at 8 miles from its mouth. Tlie estuary of the Essequebo is about 14 miles in width at its mouth, and contains a number of large islands. The Corentyne rises in the second parallel of north latitude. flEOLOGY OF BRITISH GUIANA. 9 at a height of 700 feet above the sea, about 100 miles to the eastward of the Essequebo, and running in a north-north-west direction approaches within some 30 miles of the latter river in about half its course, then flowing north-north-east, discharges its waters by a broad estuary into the ocean, in the sixth parallel of north latitude. Of all the rivers the Mazaruni has the most singular course, for rising in the table land of the Merumd mountains, part of the Pacaraima group, at a height of 2,400 feet above the sea, near the 60th degree of west longitude, it runs^,6a:grward for some miles, curving round to the sotrth in 68° 8' 30" west longitude, and 5° 34' 23" north latitude, and descendsTo a level of 2^000 feet. From this it flows a tortuous course in a^spest-north-west direction to the Cako river mouth in 60° 44' 0" west, and 5° 47' 11" north, being joined on the way by numerous large tributaries, and descending by a set of high falls at Ohi-chi to a level of 1,400 feet above the sea. Flowing smoothly along at this altitude, in a north-north-west direction to Sericoeng, it is precipitated down a succession of lofty falls, occupying a distance of 8 miles, to a level of 500 feet. Passing along at this level with a north-north- east course, it plunges over two more sets of falls to a height of 150 feet, and emerging from the sandstone mountains in 6° 26' 14" north latitude, turns suddenly to the east-south-east for a distance of 105 miles to Teboco cataract, in 59° 44' 40" west longitude, and 5° 45' 29" north latitude, passing on the way near the foot of the Merum6 mountains, 20 miles to the northward of its source. From Teboco it traverses a winding course having a general east-north-east direction, through a level country to the Essequebo river. The Kupununi river rises in the same great plain as the Takutu river, some 20 miles to the eastward of it, at a height of 745 feet above the sea, and flowing north passes through a deep and narrow valley in the Canucu and Cumucumu mountains, while the Takutu flows to the westward on the plain, close past their western termi- nation. The average height of these mountains is 2,000 feet. Hence if the Rupununi does not follow a fissure in them (which is more than probable), it must at one time have had its upper course at a gi-eater elevation than their present summits, and it, together with its branch streams, must have been the chief agents in effecting the entire removal of an immense mass of rocky country. Owing to the peculiarly heavy specific gravity of by far the greater number of forest trees, floating wood is seldom met with, and the large trees which fall into the fiver from its banks sink and decay upon the spot. The colour of the water of the rivers varies greatly, ranging from milk white to dark blackish-brown. Those which>have their sources in mountainous tracts amongst forests are principally of dark colours, whilst those whose courses run for considerable distances in savannas, where the banks are of white clay, contain whitish and milky waters. The dark colour of these rivers is 10 GEOLOGY OF BEITISHT. GUIANA. owing to an infusion of vegetable colouring matter, principa y derived from wallaba tree leaves and bark, which in small streams imparts a faint acid astringent flavour to it. Some small streams rise as springs, and contain clear colourless water. The water in the estuaries of the large rivers, for some distance up from their mouths, and the sea water along the coast stretching oceanwards for over 12 miles, is of a vellowish gray muddy colour, from the enormous amount of fine earthy sediment in suspension. The water of the rivers themselves, even when in flood, is never so highly charged with solid matter, so that thia sediment must_be stirred up by the currents and waves passing over the muddy- shallows off the coast, and carried by the tide into the rivers mouths, as well as seaward; The surfaces of the rocks in the beds and on the banks of the rivers, of both coloured waters, are covered with a thin black or brown polished and metallic looking coating,* and in some instances by a dark black stain. The brown coating resembles in appearance a thin layer of tar, while the black looks as if black- lead polish had been applied to the rock. Sometimes these stains occur over every portion of a group of rocks, at others only in patches upon them ; as often upon the underneath inclined portions, as on the upper horizontal surfaces. I have frequently observed that on coarse friable rocks the coating is of a brown colour, and on hard fine-grained rocks it is chiefly black. In some places it is a true coating, in others it looks like a decom- posed portion of the rock, and may be due to some sort of electro- chemical action produced by the water, containing salts of iron and manganese in solution, flowing swiftly over the surface of the rock. All the rivers, above the points on them to which the tide reaches, are crossed by numerous bars of rocks forming cataracts and rapids of various sizes, from a few inches to 50 feet in height, and upon some of them amongst the sandstone mountains are large and beuatiful falls, ranging in height from 20 to 800 feet. It is these impediments to the navigation of the rivers that have so long prevented the opening up of a fine and extensive territory, i PAET II. General Desceiptive Geology. 1. Alluvia, a. Alluvium. — Alluvium of recent deposition is found bordering small branch streams, and in swampy depressions all over the country, as well as at the bends of some of the large rivers. It is a dark variety of loam, and appears to be very productive. b. Fluvio-marine Alluvium or Coast Deposit. — This great deposit extends along the whole sea coast of the colony, stretching inland , to various distances in different places, as * This coating is composed of the oxides of iron and manganese. .GEOLOGY OP BKITISH GUIANA. 11 g 8 o ■« u O-s. id i^ will be seen by glancing at the map, being seldom more than 35 miles in its widest portion, and not less than 5 miles. Its level on the coast is a few feet below the level of high water of spring tides, and rising gradually inland it attains a height of some 10 or 12 feet above that level, resting upon the sand and clay deposit. {See Fig. No. 1 .) The thickness of this deposit, as shown by borings, is about 100 feet, and it is com- posed of layers of sand and bluish clayj .| containing portions of decayed wood and g vegetable matter. The soil upon it on the estates is a dark loam, and on the imculti- vated portions, in rear of them, of a black bog earth, chiefly of decayed vegetable remains, similar to that deposited in sUted-up lakes. The following sections were obtained by borings at various periods for artesian wells, and give in a rough way the sequence of the diflPerent materials of this deposit. 1. On Plantation Woodlands near Mahaica Creek. 5 feet of surface soil, fine sand, blue clay. soft mud mixed with sand, rotten wood and decayed vegetable, matter, stiff bluish clay, red and gray clay, reddish clay. 12 ft. 10 in. stiff yellowish-gray clay, ^vith a little sand and ochre. 3 ft. 10 in. streaked bluish-gray clay. 5 ft. 4 in. bluish-gray clay streaked with yellow. 1 1 3 pq 30 14 2 2 13 92 ft. in. o O 2. Near Georgetown Waterworks^ 27 feet of stiff clay. 43 „ hard buff-coloUred clay. i 70 In portions of this deposit between the Demerara and Berbice rivers, numerous low narrow strips of yellow sands, called sand reefs, slightly raised above the sea level, run parallel to the coast and contain numbers of sea shells of the genera, Mactra, Venus, ♦ These borings were made by Mr. Lloyd for the town council of the city of Georgetown. 12 GEOLOGY OF BRITISH GUIANA. PUcatula, Marginella, Fasciolaria, Nassa, &c.j of the same species as those now inhabiting the ocean off the coast. These reefs no doubt mark the different lines of coast of former times, as the currents forming land beyond them caused a recession of the sea. A large portion of detrial matter, forming this great deposit, has been brought by currents from the mouth of the Amazon river.* c. River Loam. — On the river's edges the fluvio-marine deposit passes into a fluvatile loam, which borders them to tlieir sources. The outlines of this deposit are not shown on the map, because from the points on each river where the first rocks appear they have been mapped to its exclusion. Besides it would be impos- sible to trace out their boundaries in the forest covered portions of the country. On the large savannas, where the boundaries of this deposit and the valley gravels are more clearly defined, it has been mapped. It is formed of an upper portion of yellowish and gray homo- geneous loam, resting upon a lower portion of coarse and fine gravel beds. In these are patches and layers of hydro-oxide of iron. The soil upon this is of a dark vegetable nature. d. Valley Gravel and Sand and Clay Deposit. — These two post- pliocene deposits are most probably equivalents of each other, the former being seen on the great savanna, and on the large rivers in the Pacaraima mountains, and the latter between the highlands and fluvio-marine deposit of the coast, where it forms low undulating land. The valley gravel is composed of gray and reddish loam, con- taining blocks and beds of quartz gravel, and layers of hydrated- oxide of iron. Behind the coast region the sand and clay beds form a tract of country averaging from 60 to 150 feet in height, its southern edge being in the eastern part of the colony, some 35 miles from the sea, and in the western part approaching to within a few miles of the shore. Outlying patches of these sandbeds are often seen, having been preserved from denudation, as that of Waramurie on the Marooca river, and elsewhere. The soil upon it is poor and sandy, but in the valleys cut by small streams a good yellowish loam is often seen. This deposit consists of white and mottled false-bedded sands, resting upon white and drab-coloured (jlays. These beds form a low escarpment at the southern limit of the fluvio-marine deposit, facing north, which has long been taken for a ridge running parallel to the coast. Artesian borings show that these beds underlie the above-mentioned deposit near the sea shore, at a depth of about 100 feet. Although no sea shells have been found in them, still from their great extent they must have been deposited in the ocean, probably at a time when the sea washed the base of the sandstone escarp- ments. * This fact has been recorded by Sir Chas. Lyall in his Principles of Geology. GEOLOGY OF BEITISH GUIANA. 13 In Mr. Lloyd's borings for artesian wells in Georgetown, the following beds of this deposit were passed through : — 1. Boring at Newburgh,half a mile south of the Waterworks. At a depth of 118 feet sand was met with, the overlying beds not being recorded. Then came 44 feet of white clay with sand. 9 15 3 18 9 9 9 18 9 9 3> brown clay. sand. clay. white sand. white clay. lumps of white clay in sand. stiff brown clay. coarse sand, sand. •3 a 152 2. Boring near the Waterworks. '70 feet of fluvio-marine beds. 38 n sand. *3 1^ 32 13 clay, sand. ■a 27 J6 » coarse sand, containing pieces of decayed wood, sand with white clay. 216 2. Sandstone Formation, This formation constitutes the greater portion of the northern part of the Pacaraima mountains, spreading westward into Vene- zuela. Tracing it eastwardly, it crosses the Essequebo river, in a low narrow belt, at Oumuti and Twasinki mountains, and the Berbice river near Marlissa rapid. It forms a high mountain range at Itabru near the Berbice river, and is seen crossing the Corentyne in two places, oile at Cabalebo river, and the other higher up near Akalikatabo island. The upper portion of the Maccari mountain is also formed of the same sandstone. It is composed of interstratified beds of coarse conglomerate, red and white sandstone, and red shale. Interbedded with the sandstone are three great layers of greenstone, partly contemporaneous and partly intrusive. This greenstone is of a coarse variety of diorite, composed of horn- blende and felspar ; the crystals of the latter in some instances showing the strias of Plagioclastic felspar. To make out the actual relations of the sandstone and green- stone would be a most difficult task, requiring an immensity of time, and could only be performed by following the outcrop of each layer of greenstone. 14 GEOLOGY OP BRITISH GUIANA. During my explorations I have been able to examine their rela- tive positions in crossing the sandstone area in two places, and by exploring the sandstone escarpment in eight. In all of these 1 found a different arrangement as regards the position and elevation at which the greenstone layers occur, and a different constitution of the underlying rocks. In some places the sandstone above and below these layers has been altered, chiefly by the development 6f large and small felspar crystals in that rock, and by its assuming a greenish slaty appearance for some distance above and below the planes of con- tact. In others it is hardly altered at all, which would lead one to suspect a contemporaneous origin, while in the former cases it is no doubt intrusive. It is very evident that the igneous action at the time was deep seated and very active, and may in some measure account for the total absence of organic remains in the sandstone. The occurrence of great layers of conglomerate in the neigh- bourhood of the greenstone, and the presence of sun cracks and ripple marks in the shales, on the other hand, lead us to suppose that it was deposited in a shallow sea ; whilst the fact of the igneous rock being a greenstone contradicts this assumption, and they can only be assimilated by the supposition that immense and sudden upheaval and depression took place, which tbe undisturbed state of the sandstone forbids. The absence of fossils in the sandstone is very singular, and prevents one from arriving at the age of the geological epoch during which it was deposited. It appears to me, however, to be an equivalent of the new red sandstone. In some layers there are numerous thin beds of fine red jasper. The total thickness of this sandstone forhaation, including the layers of greenstone, is about 7,000 feet; the three layers varying in thickness in different localities from 400 to 1,000 feet each. The sandstone, as a whole, lies nearly in a horizontal position, dipping northwardly with but few local disturbances, and as far as could be seen singularly free from faults and dislocations. It forms two extensive and one minor plateau, the first having a high escarpment to the north, its base being from 85 to 250 feet above the sea. To the south its escarpment is not so regular, and its base is at an elevation of from 1,000 to 1,400 feet. The sandstone at Maccari and Itabru rests immediately upon the quartz-porphyry and felstone, and has no greenstone layers. In other places it rests upon quartz-porphyry, schist, and greenstone. It is evident that the sea at one time covered the whole face of the country up to the sandstone escarpment, and surrounded the mass of the Paccaraima mountains entirely. The perpendi- cular faces of the great table mountains of sandstone were evidently produced by the action of the sea, and no one can view the singular and lofty mountain of Roraima without being and -spread out in a great layer over 700 feet in thickness, forming evidently at one time a con- tinuous area, since partially removed by denudation. It also spread over the granite to the north of the sandstone escajrpment, on the plain of the Mazaruni river. Over the whole surface of the colony the' rocks are traversed by extensive dykes of greenstone. This rock, like that forming the layers in the sandstone, is composed of hornblende and fel- spar. Its texture, which is usually crystalline-granular, varies greatly even in parts of the same mass, becoming sometimes almost compact, at others porphyritic^ It is a true plutonic rock, which varies slightly in mineral, character in various places, being chiefly diorite and diabase. Its colour also varies from dark-green to, greenish gray, gray, and dark Amygaloidal greenstone or vesicular diabase is seen in only two places, (on the Kupununi at Urua, and on the Kewa river), and some of its cavities are filled with crystals of calcspar, a white stellate zeolite (natrolite), and a dark green minera.lj probably glauconite. The dykes of greenstone- pierce through granite, gneiss, quartz- porphyry, and sandstone, and are connected with the layers and masses of the same rock, having been the feeders which sup- plied the material of those masses during the deposition of the sandstone. 4. Schists. Mica schist, hoorblende schist, quartz schist, talc schist, and chlorite schist are found associated with gneiss in many localities, and appear to be in layers in that rock, their fussile structure being parallel to its foliation. These rocks are principally of highly crystalline varieties, and contain nests and veins of quartz. ' 5. Gneiss, f . The surface of a very large portion of the colony is composed- of gneiss, which is seen iii large' rounded bosses in the rivers' beds. 16 GEOLOGY OF BRITISH GUIANA. It is often of a granite variety, but more frequently is true gneiss with extremely contorted foliation. Its bedding is exceed- ingly obscure ; the only place where it can be clearly made out is on the Quitaro river, where it is seen apparently in beds of great thickness, dipping east at an angle of five degrees. These show the foliation to be at right angles to the bedding. There seems to be no regularity with regard to the strike of the foliation,* for on the Upper Corentyne river, where I examined this structure very carefully, I found the strike of the foliae to vary from east and west to north and south in a short distance, and have recorded the following directions of strike in my notes, viz., east and west, east-north-east and west-south-west, south-east and north-west, east-south-east and west-north-west, and north and south. The angle of the dip of the foliation also varies from 80 to 15 degrees from the horizontal plane, on either side of the line of strike. The directions of the rolls of gneiss generally agree with the strike of the foliation, but there are exceptions also to this. At one place on the Cotinga river, near "Wanakara hill, a long roll of gneiss lying in a north-east and south-west direction is foliated from north-west to south-east In many areas the gneiss contains large and small nests of quartz, and in places immense numbers of garnet crystals. It rests chiefly upon granite, but is also seen overlying quartz- porphyry. 6. Quartz-porphyry and Felstone. These rocks are associated in layers of considerable thickness, occupying extensive areas over the surface of the granite, and underlying the gneiss. In some layers the quartz crystals are well developed in the form of double hexagonal pyramids, in the felspathic matrix, along with chlorite crystals, which are in little clusters. The quartz crystals are usually small, and often of rounded forms, the angles of the crystals not having beeh fully developed. In other layers the quartz crystals die out, and the rock still containing felspar crystals becomes a porphyritic felstone, and from that passes into a true felstone by the loss of the felspar crystals. In Report No. 8 I have described a third rock associated with the quartz-porphyry and felstone, which I called a hornblende porphyrite, but have since termed it a porphyritic felstone. The porphyry often assumes a fissile structure, and the felstone passes into a sort of petrosilex. The colours of these two rocks vary from liver-coloured to various shades of gray, green, and black. In many places the quartz-porphyry can be traced passing into granite, through an intermediate rock containing mica. As an accessory mineral this rook often contains iron pyrites. * Humholdt records that in Venezuela the strike of the foliation of gneiss -was uniformly N.E. and S.W. GEOLOGY OF BRITISH GUIANA. 17 7. Granite and Syenite. A very large proportion of the rocks appearing at the surface of the interior of the colony is composed of granite, whilst syenite associated with it occupies a very subordinate position. There are many varieties of the former rock as regards texture, colour, and composition. It sometimes assumes a porphyritic texture, containing large crystals of orthoclase, which themselves contain small crystals of quartz and mica. The quartz in the granite ranges from transparent, colourless, and white varieties, to a curious bluish chalcedonic or opalaceous variety, and sometimes in the same specimen silver-white potash mica is seen along with dark green magnesian mica. Large black crystals of schorl as an accessory, as well as garnet crystals, are seen in a few places in it. The granite lies at the base of all the rocks of the colony, and is of great antiquity, but coarse veins of it have pierced through the gneiss, and even the sandstone formation in one place. A small veiu of gray granite is seen in the greenstone at Christmas cataract, and also another in the same rock near the Chi-chi falls on the Upper Mazaruni river, while similar veins are seen piercing the main mass of granite itself. It usually is seen in rolls lying across the rivers, or in great ridges running across the country, which trend in various directions from north-east, east-north-east, to east-south-east. The specific gravity of a specimen of granite from the penal settlement I found to be 2 "6 506, and that of the decomposing portion of the same rock was 2'554. PART III. Economic Geology. 1, Soils. The soil on the coast region is usually of a dark coloured loamy nature, and is very fertile. That upon the estates that have been long under cultivation requires to be highly manured to give large returns of sugar. Upon the river deposit the soil is chiefly of a stiff yellowish loam, which appears to be fertile. The soil upon the greenstone is generally of a dark red colour, and is held in high estimation by the Indians of the interior, who always choose it for their provision grounds. The following table is made from a list of the analysis of soils made in London for the Colonial Company by Mr. John New- lands, F.C.S., that was kindly furnished me by Mr. E. T. Hadow. I have only copied one analysis of the surface soil of each estate, in the subjoined table, as it is sufficient for the purpose of giving the reader a correct idea of the composition of the soils of the coast lands. 34328. B 18 GEOLOGY OF BEITISH GUIANA. — Hampton Court. Haarlem, West Coast. Windsor Forest, West Coast. Peter's Hall, Demerara river. Farm, Demerara river. ♦Organic matter and com- 26-317 9-515 9^295 8-346 11-165 bined water. Insoluble silicious matter - 59-600 73 • 553 77-396 77-372 73-820 Potassa -345 •055 -325 •150 -054 Soda •161 -016 -169 •298 ■087 Lime ■171 -250 -184 •264 ■189 Magnesia - ■452 -474 1-437 1^059 -377 Peroxide of iron -; '- 1^778 4-169 5-819 5^439 2-618 Alnmina. 10-733 11-475 5-135 6-998 11^263 Sulphuric acid -079 ■032 , -109 Mere trace. -081 Chlorine -039 -013 ■042 -030 -003 Phosphoric acid -119 -099 -046 -044 •097 Carbonic acid -206 -349 -043 Mere trace. •246 100-000 100-000 100-000 100-000 100^000 * Containing nitrogen -846 -156 -169 -127 ■198 Moisture in soil as received 12 •584 8-086 10-714 12-225 10^623 ^continued.') Success, East Coast. Mara, Berbice river. Ma Eetraite, - Berbice river. Triends, Berbice river Albion, Corentyne Coast. ♦Organic matter and com- 8-073 11-518 15-834 16-211 9-342 bined water. Silicious matter 75-053 73-796 67-292 70-734 70-769 Potassa ;- •235 -019 •040 -290 -313 Soda •009 1 -015 -013 •498 -144 Lime •122 •176 -154 •259 -384 Magnesia - •108 -151 •144 •227 -501 Peroxide of iron 11-072 2-764 2-932 4^266 5-134 Alumina 5-140 11-226 13-117 7-318 13-197 Sulphuric acid Trace -069 •103 -085 -075 Chlorine -026 •023 •014 •074 -013 Phosphoric acid -044 •139 •185 -020 •106 Carbonic acid •118 •104 •172 •018 •022 100-000 100^000 100^000 100^000 100^000 * Containing nitrogen •201 •271 •301 •325 •166 Moisture in soil as received 6-063 8-224 17-272 11-610 9-440 2. Sand. The white sand at the sand hills on the Demerara, and in many other places (of which there is an inexhaustible supply), is very pure and well adapted for glass making. " Experiments " were made with it in Boston, United States, which proved " highly satisfactory, and produced a better glassware than is " generally manufactured from the sands in the United States."* * A Description of British Guiana, by Sir B. Schomburgh, page 92. GEOLOGY OF BRITISH GUIANA. 19 3. Clay. The white clay at Oreala appears to be well adapted for the manufacture of porcelain and earthenware. Portions of it are very pure, whilst others contain some traces of oxide of iron and silicious grains, which deduct from its value m that respect. A similar clay can be obtained in many places on the Berbice and Demerara rivers. As the upper portion of the clay bed lies on a level with high- water mark, and is covered by some 50 feet of sand beds, the cost of obtaining a large quantity would no doubt be considerable, and incommensurate with the value of the article. In places too numerous to mention, all over the interior of the colony, beds of white and red clay, mixed with mica scales, resulting from the decomposition of gneiss and granite, occur, from which the Indians manufacture rude earthenware articles for culinary purposes. A red earthy clay with mica spangles, found near the mouth of the Essequebo river, is used as a substitute for puzzalana in making a hydraulic cement for the Georgetown sea wall. There are also many beds of clay in the coast region which are suitable for brickmaking. The bluish clay immedia,tely beneath the soil is extensively used for mending the roads, after having been burnt in heaps like open kilns. 4. Building Stone. There is every variety of building stone in the interior of the colony, with the exception of limestone, but the cost of transport being very great it is not used to any extent. Tn the tidal portion of the Essequebo river, and in the mouth of the Mazaruni at the penal settlement. Palmers point, &c., granite of a good quality has been quarried for many years, almost entirely for the construction of the sea wall at * George- town, and for macadamising the streets of that city. From the beds of sandstone good stone for building, paving, and other purposes could be obtained, but as the distance and difficulty of transport would be very great, the cost would be enormous, in fact far beyond the value of the material. The chief difficulty in transport would be in passing the dangerous cataracts of the rivers, which must be done before the sandstone area is reached. On the Corentyne river, however, some of this rock could be obtained below the cataracts, at Akalikatabo island, which still is at too great a distance from the coast to be profitable. 5. Road Material. Eock for this purpose is obtained from the granite quarries at the mouth of the Mazaruni river, and occurs in abundance in the interior. But the same difficulties present themselves in pro- curing it in the latter instance as just mentioned with regard to building stone. B 2 20 GEOLOGY OF BKITISH GUIANA, Within the tidal portion of the Essequebo, Cuyuni, Mazaruni, and Demerara rivers, there is an abundance of granite and gneiss suitable for this purpose. , The greenstone is on the whole the best material for roaa making, and it can to some extent be procured on the Essequebo, near the foot of the first cataracts, and on the Demerara above Lacodia. 6. Jasper. This rock occurs in layers in the sandstone of the Pacaraima mountains, where it is met with in abundance, alternating with sandstone, for upwards of 100 feet in thickness. It also forms irregular patches, plates, and strings in the same beds. Its usual colour is a fine red, varying to purplish and light red._ Where layers are exposed at the surface, the ground for miles is strewn with blocks and small pieces of this rock, and in the gravels of some rivers running from these mountains it is seen as round, smooth, waterworn pebbles. The Indians use it for striking fire with steel in lieu of flint, and call it cako. This, like many other varieties of jasper, might be used for inlaid work. 7. Porphyry. Many of the quartz and felstone porphyries could be made useful as ornamental stones. One variety of the former rock near Maringdouk cataract, on the Siparuni river, is very beautiful, being composed of reddish felspar crystals in a black matrix, together with crystals of quartz. Being exceedingly hard it would take a fine polish. Some green varieties of felstone on the Upper Berbice river when polished resemble nephrite. 8. Granites. There are many kinds of granites which when polished would also make fine ornamental stones, especially those containing opalaceous quartz at Wonotobo and Achramucra cataracts, and on the Upper Berbice ; also the porphyritic granite on the Curielrong river. 9. Graphite (Plumbago). Thin layers of this mineral occur in decomposed mica-schist in two localities, viz., on the Barima river at Maruciiru creek and at the mouth of the Oarabung ; but they are not of sufficient purity to be of any economic value. 10. Iron Ore. Iippure ores of iron are most extensively diffused throughout the interior in beds in alluvial deposits, and on the surfaces of the greenstone masses. They are chiefly composed of brown LiBmatite in parts, and clay impregnated with hydro-oxide of iron in others, often containing in their purest portions angular grain of silica. .GEOLOGY OF BRITISH GUIANA. 21 The largest mass of this ore occurs at Mount Wahmarra on the Upper Demerara river. Near Darunow village, pn the Upper Eupununi savanna, there is a large patch, probably a vein, of fine specular iron ore in greenstone. 11. Manganese. Very small quantities of manganese ore, or bog manganese, are met with associated with the iron ores. In fissures in some altered shale beds on the Mazaruni river, beyond Weynamon river, this mineral is seen as reniform coatings. 12. Gold. In his introduction to the Life of Sir W. Kalegh, p. Ixii., Sir R. H. Schomburgh says that "In 1721 the Council of Ten " in Holland granted a privilege, whereby it was enacted that all " persons disposed to work mines in Guiana might do so upon " certain conditions, and Mr. Hildebrand, a miner, was sent from " Holland for that purpose. A shaft was sunk at a short distance " from the first cataracts in the Cuyuni, but the small quantity " of ore found did not repay the expenses of working it, and the " attempt was abandraed." The spot here mentioned may possibly be the one at which the Britisb Guiana Gold Mining Company had their workings about seven years ago, some 40 miles up the Cuyuni river, above the first set of cataracts. The quartz containing gold at this mine is in a thoroughly decomposed gneiss and schistose rock, and appa- rently not as a true vein, but rather interfoliated with the gneiss, similar to the development of quartz schist in gneiss in other parts of the colony. At the surface it is some 10 feet in width, but separates into narrow bands as it passes downward. Owing to the neglected state of the workings, and the tangled growth of shrubs and trees over the place, which hid everything at the time of our short visit there in 1868, I could form no opinion of its value; but beyond a doubt the quartz contains gold, specimens of which I procured. The gold mining company, however, worked the quartz for some years, as well as placer diggings to the south-west of it, but did not procure gold in sufficient quantity to repay their outlay. This may have been owing as much to the expense of labour and cost of getting -stores, machinery, &c., above the cataracts to the place, as -the absence of gold in paying quantity. Some 50 miles further up the Cuyuni river we obtained small particles of gold by washing in the sand near a quartz vein, and in the alluvium a,t the foot of a hill. / Schomburgh also states that he saw a piece of gold at Fort San Joachim attached to quartz which came from the Takutu river, and that he " observed minute particles of gold in the dry bed of that river." I examined the sands of the Takutu river by washing carefully in many places for gold, but without success. Amongst the panicles of magnetic iron, the remnant of washed o 22 • GEOLOGY OF BRITISH GUIANA, sands, were minute crystals of garnet, and small particles of a yellow mineral. There are many promising looking veins of quartz in schists, gneiss, quartz-porphyry, and granite, which contain a black mineral and iron pyrites, but in none of them could I detect any gold, nor did I ever obtain that metal by washing in any river except upon the Cuyuni. / At a place bearing the name of Gold Mines, near Groote creek, I have been informed by a resident there that the remainsof an adit, arched with bricks, can be seen in a hill side, which is said to have been a gold working of the Dutch. / There is a cataract above Ouropocari bearing the Indian name of Caricurie, which means gold. It did not receive this name on \ account of gold being found at the spot, but owing to an Indian tradition that many years ago a Spanish boat bringing down gold from the interior was upset and lost there. During my travels over all parts of the interior I never met any Indians wearing gold ornaments, nor ever had any gold shown to me by them ; but whenever I questioned them as to whether it existed in their neighbourhoods, they always answered in the negative. 13. Salt {Chloride of Sodium). Common salt occurs in small quantities in patches upon the surface of the river Loam, on the savannas in a few localities near the Chemow, Ireng, Watama, and Takutu rivers. It is found in hollows in minute crystalline particles, mixed with fine sand, after the evaporation of the water left in those places by the heavy rains, and is collected by the Indians of those districts. Baeometkical Observations showing the Height above the Sea Level of various Places in British Guiana, taken during the Expeditions of the Geological Survey. Name of Station. Height in Feet. l;;«*Santa Rosa mission, Marooca Barama river, near Aranka - Manarie village Tiirkparu village, Barima river CanyabaUi village Waramurie shell mound, Marooca I/' Matope cataract, Cuyuni river t-^Camaria „ U^ "Woka mountain j/^ Aruka-matuba cataract „ //Warrerie gold mine hUl „ t^ Tomona rapid ^^ "Wakuapang cataract ^' Appa river mouth 23 100 113 45 25 33 30 59 377 133 207 140 , 216 190 192- , GEOLOGY OF BRITISH GUIANA. 23 Name of Station. Height in Feet. t- l/Maripa cataract, Ciiyuni riter . . . . . t'Tamamure „ „ . . . . . p^Otomong river mouth „ . . - J- „ hill „ , - - - ■ ^ Between Cuyuni and Cartoonie rivers - . - . Cartoonie village - - . . . Camp on Cartoonie river ...... „ Purunie „ - - . . . Junction of Puruni and Mazaruni rivers . - . . Cowenamou village ,, „ - - P- Foot of Water-barru mountaiti on Carabung river - „ Macrebah fall „ „ - - • Top of „ „ „ ■-"..■ „ first table land on path leading to the Upper Mazaruni river ■ Camp of 5th November 1868 on path . . . . „ 6th „ » - - - ■ Top of mountain above Stenaparu river . . . . „ next mountain on the path - - - - ■ A little beyond last observation . . . - . Top of next mountain ...... Highest part of table land -.---' Camp of 7th November at precipice foot . - . . Table land beyond ..----■ Large river -------- Ashieparu river ..--.- Mountain beyond ------ Mazajuni river at upper end of path . - - Buhuri-bunactt island, Essequebo river - . . ^ Rupununi river mouth - - - - - Curassawaka „ Rupununi river - . . Annai mountain, near „ - - . Monushuballi hill, near „ - - - Carenacru village, on savanna - . - . Savanna west of Ireng river - - Enamouta village, near'Unamara river - - - Mountain pass north of Enamouta - - - - Highest part of do. do. - ' - ConewyuteUi river in second valley . - - - Pass between ConewyuteUi and Curiewakie river valley Curiewakie river ' - Camp of January 28th, 1869 . - . - Top of pass to next valley on Cowieparu river Highest point of same pass - - - - - Cumparuyamo valley ----- „ village ----- Top of ridge north of do. - Valley beyond last observation - - . - Cumararing mountain top - - - - - Camp on Marakang river . - - - - Ridge beyond to the north - - - - - Heads of large river in valley beyond Next ridge to the north-west - - - - Valley beyond ------ Karakanang village ------ Ridge top north-west of Karakanang „ not far beyond - - - - - Valley beyond to the north-west - - - . - Ridge bounding last valley on north-west - Weyanock river ------ 195 . 275 295-, - 425 318 300 295 265 180 ■, 223 170. 175' 367 963- 1,480 1,425 1,925 2,215 2,385, 2,565 2,590 i 1,945 1,657 1,525 1,537 1,915 1,299 63 200 240 7f5 370 475 295 500 750 928 720 964 900 1.007 1,388 1,705 1,586 1,805 2,117 1,450 2,630- 1,336-, 2,370 2,035- 2,630 2,025 2,026 - 2,425 . 2,805- 2,143 2,740 2,674 24 GEOLOGY OF BRITISH GUIANA. Name of Station. Height in Feet. Mountain ridge two miles on Next ridge ------ _ Ridge beyond Pelpee river - Ourindouk fall fording Cotinga river Ridge beyond - - . - River in valley beyond last observation Mountain between Wamsou and Waetipu villages - Waetipu village -.'.-- Table land at south end of Waetipu mountain „ between Waetipu and Roraima - Ridge near Roraima - - - - - „ at foot of „ - Foot of Roraima mountain - - , - Sloping side of Roraima to highest point ascended Ipelemouta village near Roraima - - - Peepee river village - - - - Marooca or Pirara landing . - . - Karinambo village, Rupununi river Pirara - - - - - Quatata village - - . . . Between Mopay and Pipicho villages Mora river lanoing, Rupununi river Cawulibar village - . . - River beyond last observations - - , Ridge north of Cawulibar valley - - . Camp in valley to the north - . - . Itabay village - - . - Pass north-west of Itabay - - . . Uorora river - - - - - Valley of Ireng river near last observation - Pass across mountains to the north Sheepaouta river - - - - . Quonga village - - . - Kicuche river valley - - - . - Mora river ------ Mora villSge - - . - Essequebo river, foot of Cumuti mountain - Top of Cumuti mountain - - „ rock - - . . Mouth of Rewa river on Rupununi river End of path on Quitaro river leading to Atai-aipu rock Hill top on same path - - . Ataraipuruwow river Foot of Ataraipu rock - - - Side of Coomacaba rock - - _ Caliohadekeur „ Maturuvow village, Quitaro savanna Curawashinang village „ - . Watericow or Watuticaba village, Quitaro savannv End of Tomboro mountain „ Between Tomboro and Carawaimentovv mountains • Cotoewow village - - - Coomoctabawow river - - Carawaimintow mountain - - - Saberewow river - ■ . - Between Heherap and Matuatowow villages Matuatowow village - - - - - Warw village - . - . Head of Takutuwow river - - - . 3,125 2,880' 2,690 2,400- 3,025-. 2,380- 3,390 3,570 ■• 3,804, 3,705 4,260 . 4,507- 4,925. 5,14a.. 3,725" 2,450 251 261 330 323 370 249 330 590 1,405 845 974 1,180 412 355 1,005 340 1,978 425 340 495 177 1,400 1,310 205 357 573 415 857 910 1,150 590 740 670 777 767 895 803 1,210 835 945 925 1,007 900 GEOLOGY OF BRITISH GUIANA. 25 Name of StatioQ. Height in Feet. Savanna near last observation - - - Head of Rupununi river ------ Waripuow village - - . . - - Irribisinow village - _ - - - - - . - Savanna near Aruauwow river - . - - - Parearabatonwow village - - . - Granite rook near Cobanawow river - - - - - Warraweow river - - - Otonam hill, near Warraweow river - - - - - Shea rock - - - - -,- „ village -------- River north of Shea - - - - - - Landing on Quitaro river at end of path leading to Maturuow village -------- Furthest point reached on Rewa river - - - - Pacutout cataract, Siparuni river . - - - - Cataracts and rapids „ - - - - - Maringdouk cataract „ - - Surama landing. Burro-burro river - - - - - On path to Archiculloch village, near Burro-burro river Archiculloch village - - - - - - Paloureouta „ ------ Annai „ - - . - - - Cuyariye river - . - - - - Between Annai and Surama - . - - - Surama village ------- Taramu „ - - " " „ river head ------- Camp beyond Taramu river head - - - - - Itabay village ------ Curapowta river ------- Carona fall, Ireng river HUl west of Carona fall - . - - - Mataparu river -' - - - - - Awarapearu river, west of Caraoara - - - - - Caracara village - ■ Hill north of Caracara ------ Awarapearu river, north of Caracara - - Coniapeur village - - - Quarquia „ - " " Tarawa „-'''''' Mowaiieteur mountain foot ------ Owenteik village - - - - - Mowarieteur ,.--"'""" Otomanda -----■"" Encaco village ------- Jackiquocki village - Elichiliqua „ - ' „, ^ , Mountain top one mile north of last observation Saranieparu river -„,.:,,,■," Mountain path on top of highest table land Emoy river - - ■ " ' " _ Arnick river ----"" ] Taispong village ---""_' Caruputa „ - '." Potaro river, near last observation - - - - - Top of Kaieteur fall - - - - " Landing place three miles below the fall - - - - 960 745 690 630 745 645 690 655 777 1,195 705 675 415 385 205 305 335 228 620 970 340 393 385 650 305 395 775 1,225 860 795 500 1,035 800 945 1,000 2,180 1,726 2,060 1,335 998 1,005 2,207 2,090 1,495 1,965 2,088 2,735 2,798 2,670 3,135 1,750 1,485 1,890 1,437 1,385 1,130 308 196 2G GEOLOGY OF BRITISH GUIANA, Name of Station. Height in Teet. Tumatamari cataract foot ----.. Foot of Amutu „ ...... „ Arriosaro mountain ... . . Top „ „------ Landing on Curielrong river below Amailah fall . . . Top of Amailah fall - . . . . „ Twasinki mountain ...... Foot of King WUliam IV.'s cataract . . . . „ Manarowah „ ' - Top „ , „----- Foot of next great cataract - - - - . ■ . i, great cataract at camp of November 5thj 1870 End of path on Canerua river landing to Woyawais country, Essequebo head ....... Camp on Essequebo, not far above last information Cassikityu river mouth -..-.. Hill between Murray's and King William IV.'s cataracts - Essequebo river opposite last observation Yarewah village, Takutu river ..... Cotinga river mouth -..-.. Warara-sararu cataract -...._ Waiquah river fording ... . . TerchUewan village ---.... Junction of Cumparu and Cotinga rivers .... Camp, 22nd January 1871 ---... Cumararing village - ..... „ mountain pass -.-... Mountain north of Cumararing village .... Tacar-erimone village --.-.. Arawaitah „ ...... Escarpment foot north of Wailongteur river ... Top of same escarpment ---... Foot „ „ on north side .... Karnang river -....._ First Orindouie faU top ---... Uwahparaduie village ---... Camowta rapids, Ireng river - . . . . Top of Orindouie great fall, Ireng river .... „ Wantuana „ „ .... Landing below Orindouie fall - . . . Waramepai village ---... Waipah „ - . - . . General level of ridges between Ireng and Karnang rivers - Highest part of ridge north of Wailongteur river - Ireng river bend north of Cumararing ... Mountain top north of Waiquah valley ... Tamarchelle village, Cotinga river - - Aringwong village --.... Warabara-chilen village, Macumucu river - Suwara-oura river mouth on Takutu river - - . Dahdaad village --.... Cursato mountain top .... Cocobeanarruwow village ^ - - . Macudoord river, near Pinniyette mountain Mepitewow ,,-... . . Coarawow „ - . - . . , . Gravel ridge on savanna near Rupununi river Rupununi river near Mount Pattighetiku Berbice river east of Primes inlet - - 66 84 60 725 83 1,280 825 210 231 329 468 762 825 828 741 746 205 160 90 108 195 303 590 1,065 1,377 1,672 1,580 1,350 1,488 1,488 1,900 1,616 1,598 1,590 1,652 1,560 1,929 1,942 1,769 1,780 1,698 1,560 2,174 1,332 1,037 383 270 268 180 200 1,300 240 375 254 338 400 283 200 .GEOLOGY OF BRITISH GUIANA. 27 Name of Station. Height in Feet. Primes inlet, Essequebo river - - - . , . Foot of sandstone clifF, Maocari mountain - . . - Top of quartz-porphyry „ .... „ Maccari mountain ...... Essequebo river opposite Maccari mountain . . - Foot of Wonotobo cataracts portagCj Corentyne river Highest point of „ „ „ . - Head of Wonotobo „ >, .... Corentyne river above Wonotobo cateracts . . . - Camp of Sunday, 24th September 1871 .... Foot of King Fredrick WiUiam IV.'s cataract, Corentyne river Top „ „ „ „ Camp of October 8th, 1871, New river .... Landing on New river of track cut by Survey to the Essequebo river First breakfast place on track ..... First ridge crossed „ ..... Second „ „ ..... First camp on track ....... Second «------- Third „ Top of mountain north of third camp .... „ spxu" of Amuccu mountain ..... Fourth camp on track ...... Fifth „ Sixth „ ...... Seventh „ ...... Essequebo river track end ...... Pani river mouth on Curuni or Corentyne river ... Camp of December 2nd ...... Near site of old Indian village, Cutari river .... Aramatau river ....... Hill near do. ....... Great cataract on Aramatau river ..... Camp on path cut by the Survey from the Corentyne river above Wonotobo cataracts to the Berbice river .... Hill crossed on track ...... Second camp „ ...... Third camp „ ...... Hill beyond last observation ..... Fourth camp on track ...... Berbice river at end of track ..... Landing of track on Corentyne river .... First village on path from Etuni river to Demerara river Second > „ „ „ - - Hill on path near Demerara river ..... Harewah river ....... Camp of February 5th, 1872, on Berbice river ... Foot of Christmas cataracts „ ... Camp of 18th, furthest point reached in boat ... Berbice river opposite Itebru mountain .... Top of Itabru mountain at precipice .... „ „ near Itabru cataract ... High ground in forest between Berbice and Demerara Camp on small savanna near " Burnt ground " . „ Itaburro river, branch of Demerara ... Paintecobra village landing .---.. Top of Wahmarra mountain - - _ - Head of Demerara great cataracts of Ororu mallali . . - Foot of „ „ jj - - - 200 890 678 1^270 190 Ijl5 218 205 210 250 370 420 501 670 675 765 733 747 776 693 1,240 1,030 719 710 719 716 698 585 675 680 670 773 746 329 329 374 329 296 283 192 240 160 180 200 30 150 169 200 88 720 728 177 170 180 150 762 88 25 28 GEOLOGY OF BRITISH GUIANA. J^ame of Station. Height in Feet. Hill on portage of Demerara great cataracts of Ororu mallali Enowdah village - - - - Mabouroo river ....-- Top of Mabouroo mountain - - - - *- „ sand beds near Giles' . . . - Foot of Frazer's hill - - Top of „ „ Siberie hiU ...--. Sororieng landing, Mazaruni river - - - Hill near do. „ . . . - . Portage landing, Peaimah fall ... Hill on portage at „ . . . . . Canip of 4th September at foot of Aruwai falls HiU top above landing of Aruwai fall portage Highest point on portage >» » - - Landing at head of Aruwai faUs . . - . . Foot of Sericoeng falls ... . . Top of table land on portage . . . . . Large stream „ . - . . . Camp „ - . . . . Top of Sericoeng falls at portage landing . . - . Village Motrayparu above Siparimer fall . - . . Caywaeck village - - . ■ . River landing, Carabung path end - - - . . Camp one mile on -from last observation . . . . Mouth of Cukuie river - - ... „ Aapow „ - - . . . Camp past Ackai .... . . Ouruway cave - - ... Top of mountain near Cowaeng village . . . . Camooda mountain top ... . . Foot of Chi-chi falls portage . . . . . Tops of first cliff „ - Highest part of „ - Landing on Mazaruni river above Chi-chi falls . . . Camp on Haiacker river branch . . . . . „ Mazaruni river at furthest point reached at end of , path to Karanang river . . . . . HiU on Haiacker savanna . ' - Waioclaypaloota village ...... r/^Warumatta , „ - / t-i Top of watershed between Mazaruni and Ireng rivers crossed by path / *rs' I in the same direction as the first. I observed that the range of mountains from Makarapan does not come within more than 8 or 10 miles of the river, and curves more towards the northward than indicated on the map. This range terminates in an exceedingly high massive mountain at the south-eastern base of which are numerous small conical hills. We left the top of the mountain at 2.45 p.m., and descending rapidly through a heavy shower reached the Essequebo at our camp at 5 p.m. On the 20th we continued our homeward journey, and next day at mid-day landed at the foot of Cumuti mountain. Ascending it to the Comuti rock I took bearings to the mountains which lie in ridges nearly north and south between this spot and the Demerara river, and which have not been placed upon any map. A heavy •rain prevented my exploring the top of the ridge, so I was com- pelled to return on the following day for that purpose. On my way up in the early morning I visited the look-out at Cumuti rock, and witnessed a singularly beautiful sight. In look- ing down upon this in fine weather you gaze upon the tops of forest trees far below, spreading like a gTcen carpeting away to the horizon eastward, relieved here and there by bands of sparkling water in the numerous channels of the great river. Now all was charged, and a dense sheet of white mist covered the face of the whole country, obscuring the sun, then a little way above the horizon, whose rays lit up the fleecy mist till it resembled a sea of molten silver. We proceeded along the ridge for a long distance, but the forest was so dense that I could not obtain a satisfactory view to enable me to see whether this group of mountains is continuous with part of the sandstone table land. Descending the mountain to the camp we went a little way down river, and camped on an island where we spent Sunday the 23rd. The rainy season appeared to have thoroughly set it, and heavy showers were frequent both night and day, with the river rising steadily. Owing to the great height of the waterwe were able to evade some of the most dan- gerous cataracts through channels amongst islands where the boat was lowered dovra by its tow rope. These channels are called Itaboos, and by them we passed YucaribI, Etanimd, Owspart, Habacuhaha, Twasinki, and Haiawah cataracts, only running down Pacutout and the great Waraputa cataract. When we reached Cumparu river, nearly opposite to Curi-curi point, on Tuesday 25th, we entered it, went up a few hundred yards, and camping got things prepared for a walk to the Demerara river. The rain delayed our start till 7 o'clock next morning, and on 172 GEOLOGY OF BEITISH GUIANA. the way we stopped for two hours at a small stream, so that it was 3 in the afternoon before we came out upon the Demerara river at an old deserted wood-cutting place. The land over which the path led was low and swampy, adjoining the Essequebo for a short distance, and then it became more undulating, with some ridges from 100 to 200 feet above the level of the river. On the way we crossed three good-sized streams, and at almost three-fourths of the way across we emerged from the high standing forest upon an open tract, where numbers of dead trees, fallen and erect, are to be seen blackened and charred by fire. This is called the " Burnt Ground," and it continues to within a mile or two of the Demerara along the path. Amongst the dead trees clumps of small trees and shrubs, some of them 20 feet in height, of quite a different growth to the original forest having sprung up, leaving large areas almost destitute of vegetation, save a common coarse fern and a few bunches of grass on the arid white sandy soil This devastation of primeval forest has been caused by a fire, which must have spread during some remarkably dry season, many years ago, as is attested by the height of the after-^owth., Next morning we left the Demerara river at the Cumparu stream, and walked back, during a heavy rain, to the Essequebo at the other Cumparu river (without stopping on the way) in 4^ hours. The path is exceedingly tortuous, and must be a quarter longer than a straight course from river to river would be. We left the Cumparu in the afternoon, and running down aU the lowest set of cataracts in the river, reached the settlement on the evening of the 29th, and waiting four days there for the contract steamer, returned in it to Georgetown on the 4th of May. PART II. I. Alluvial Deposits. From more protracted investigations of the alluvial deposits of the savannas than I had hitherto been able to make, I have been led to arrange them under the following heads : — Ca. Loam, sand and gravel beaches of rivers. Recent period. < b. Kiver loam. \b'. River gravels. Post-pliocene : c. Valley gravels and clays. No. 13. General section of alluvial deposits, Becent alluvium. b. River loam. b'. River gravels. D. Iron oxide. c. Valley gravels. GEOLOGY OF BRITISH GUIANA. 17 a, — Loam, sand, and gravel beaches of rivers. Under this heading is placed the black clayey loam deposited by small branch rivers on the savannas, the small patches of recent alluvium at the bends of some of the large rivers, and the extensive sand and gravel banks exposed in the large rivers that traverse the savannas. The quantity of alluvial matter deposited every year by the rivers, when in flood, is very considerable, and I had oppor- timities of obtaining the thickness of this, deposited in three places very remote from each other during the last rainy season. These were on Potaro river, below Tumatamari cataract, on the Upper Essequebo and Takutu rivers. At Tumatamari this'coating of baked mud on the rocks and sandbanks was in places 6-lOths of an inch in thickness. On the Essequebo river, below Primes inlet, it was 3-8th3 of an inch thick, and composed of a dark clay, with minute particles of mica and sand throughout it, thoroughly baked by the sun. On sandbanks in the Takutu it was in some hoUows 2 inches thick, and had small bird tracks, raindrops, and impressions of leaves upon it. On the savanna, between the western end of the Canucu moun- tains and the village of Berkutone, there is a superficial coating of light sand, which is blown into small ridges by the wind. It is the result of the washing away of the clay with which it was mixed by the rains. The undulating country between the .Demerara river and the Essequebo traversed by the Cumparu path is covered with a light white sand. Great sand beaches and gravel banks occur in the Takutu river, both above and below its junction with the Ireng, and also on the Ireng and Cotinga on a smaller scale. On the former river some of these sandbanks are one or two miles long, and some 200 to 300 yards wide, occupying the grea,ter portion of the bed of the river. Amongst the white quartz pebbles of these gravels, some of which are from 2 to 3 inches in diameter, are pebbles of flint, hornstone, and reddish and yellowish quartz. In the sand amongst the gravels are small garnet crystals and magnetic oxide of iron grains, which proves that they are derived from the disintegration of the gneiss of the Canucu moimtains. In the lower course of the Takutu the gravel beaches are made up of every variety of common quartz, great quantities of red jasper, small agates, and black botryoidal quartz. In the Cotinga and Ireng als0 jasper pebbles are very common, and have been washed down from the sandstone formation of the Pacaraima mountains. . At the heads of the Camoa and Nappi rivers, not far from the •Canucu mountains, there are fine broad level tracts of recent mud-like alluvium, and similar deposits are situated in all the depressions in the savannas. Upon the surface of the river loam on the level savannas there is sometimes seen a soil of dark loam from 18 inches to 1 foot thick, which has gradually been deposited by yearly floods. 174 GEOLOGY OF BRITISH GUIANA. b. River loam, and b'. River gravels. The river loam forms the upper portion of the great tracts of alluvium deposited by the large rivers of the colony, whilst the river gravels {b') lie beneath it, and form the lower portion of the same great deposit. The area occupied by this in the lowlands of the country is exceedingly extensive. On the Essequebo the banks of the river are formed of this loam, but its lower portion is not seen. On the Cotinga and Takutu rivers, however, where sections of these beds are exposed in their banks of 30 feet in height, the homogeneous loam is seen resting upon the gravel beneath ; and where the base of the latter is visible the upper portion exceeds the under in thickness. I will now give a detailed description of these deposits as they occur in different districts. A dark-coloured alluvium of an arenaceous nature occurs near Colomeh river on the Curiebrong, but is of the usual yellovdsh loam in other portions of the river. A short distance above the great portage on the Curiebrong river there is a set of gravel beds similar to those seen on the Mazaruni' at Oamacousa. These form a thickness of 20 feet above water, but their base is hidden, and they are composed of loosely cemented gravel beds of different textures inters tratified with layers of loose sand, all stained of a dark brown colour, and showing false bed- ding. The pebbles in them are very slightly waterwom, and some are quite angular. The banks of the Essequebo river, from the mouth of the Rupununi up to Murray's cataract, are composed of grey and yellowish arenaceous clay of homogeneous structure, and beyond this, as far as I went, where the banks were not formed of rock or of recent alluvial clay, this same loam extended. In some places it becomes almost pure white, and then contains a large proportion of Kaolin, being derived from the decomposition of granite and felsitic rocks. In one place, some miles below the Ouruow river, this clay assumed a bright pinkish or reddish-pink tinge, and contained a large proportion of finely titurated silver- white mica. No. 14. Section of alluvial deposits at Yarewah V., Takutu river, u. Recent aHuvium. b. Kiver loam. b'. River gravels. /. Red shale. GEOLOGY OF BRITISH GUIANA. 175 Not far below the mouth of the Macumuca river, on the Takutu, upon the evenly planed surface of the red shale, just above the level of the river water at the time of my visits, rests the river gravels and loam deposits, exposing a vertical section of 30 feet in height, composed of two equal portions, the lower of coarse sand, and the upper of gray loam of homogeneous structure. Amongst the coarse sand in one place there occurs a layer of fine white sand, and above it a layer of more argillaceous materials, ex- ceedingly firm, and stained with tin coatings of iron-oxide. Ir- regular patches of hydrated oxide of iron occur frequently. The banks of the Ireng river opposite our camp of January 1st gave a perpendicular section of 30 feet composed of arenaceous loam, the lower parts of which are partially consolidated. The lower portion is of a red and yellow colour, and is impregnated with oxide of iron, whilst the upper is of a yellowish colour and finer texture. Irregular masses of clay impregnated with hydrated oxide of iron are frequently seen in many places, and especially where water laden with salts of iron in solution is seen trickling through the loam and sands, and depositing the oxide as it becomes exposed to the air. There are no divisions into layers or beds except between the lower and upper portions, and this is irregular and not clearly defined. Not a trace of bones, shells, or vegetable remains can be discerned anywhere in them. In the mouth of the Pirara river, about one mUe up, there is a spot where the river has cut away some of the grey loam and left a cm-ious development of hydrated oxide of iron standing in rough and jagged pinnacles, some of which are hollow and funnel shaped. These are composed of angular grains of quartz sand cemented by iron, and are exceedingly hard and have a stalactitic appearance. They have been formed by the percolation of water saturated with salts of iron through the loam and sand. Some curious beds of leaves are shown in a section of the gravels and sands on the lower Takutu river not far from its junction with the Ireng ; they are in false bedded layers of from 2 to 4 inches each having a total thickness of about 2 feet, and are seemingly but little changed in composition since they were deposited. Pieces of wood thoroughly decayed and blackened occur amongst the leaves and are very friable, whilst in the gray clay above them there are scattered leaves and casts of the cylindrical stems of some plant. The scattered leaves when dry peel off the clay leaving clear impressions. The bank there has fallen down, and in some degree dieguised their true position so that it is difficult to say whether they belong to this or a more recent deposit. Not far up the Cotinga, from a bed of gravel cemented by hydrated oxide of iron, I obtaiued an impression of a leaf the leaf itself having been destroyed. 176 GEOLOGY OF BRITISH GUIANA. No. 15. Section of Alluvial Deposits near the month of the Cotinga River. Scale 10 feet to J an inch. b. Eiver loam. b'. Partially consolidated river gravel and sand. g. Decomposing gneiss. Near the Murawai river, a branch of the Cotinga, the river gravels rest upon gneiss rock, as consolidated sand beds, with the gray loam on top. Higher up the Cotinga sections of the same deposits forming the banks of the river shovr the gravels cemented firmly together by Vfhite clay with the loam in two portions of grayish and yellowish colours. The gravels are always false bedded and often contain large angular or slightly worn blocks of quartz. The materials composing this deposit on this river have been derived from the disintegration of the granite and quartz-, porphyry of the Pacaraima mountaias. Beds of hydrated oxide of iron are seldom seen on the Cotinga river beyond Warara- sararu, but the whole deposit is often of mottled red colours from the percolation of iron-saturated water through it. Above Tuanu- sararu no gravel beds occur, and the alluvium ends at the base of the mountains, the river comuig out of a narrow gorge bounded by rocks. No. 16. <^ ^# Section of Alluvial Deposits at Warara Sararu Cataracts, Cotinga River, b. Eiver loam. v. Eiver gravels. e. Granite. On the Wailongteur river the alluvial deposit seen is of reddish and mottled clay 20 feet thick belonging to the river loam. The banks of the Suwara-oura river are composed of a reddish yellow arenaceous loam, 15 feet in thickness, resting upon gneiss rocks and of a homogeneous structure, not a single pebble being seen in it, though quantities of gravel are now being carried along its bed by the stream. Between Dahdaad and Cocobean-arruwow villages there is a great level plain many miles in extent of river GEOLOGY OF BRITISH GUIANA. 177 loam, and this deposit forms the greater portion of the savanna along the Takutu river from Suwara-owra river southward as well as along the Eupmiuni river in its course south of the Canucu mountains. The Kupimuni in its course through these mountains is bordered also by the same deposit of a gray colour which also forms its banks in the savanna to the north. , The tract of country between the Berbice and Essequebo rivers, and from the Essequebo to the foot of the Maccari mountain is composed of the river loam of a yellowish colour. AH the great level tracts of country bordering the Ireng are composed of the same alluvium which has been deposited by that river. Everywhere in the large rivers where the bank on either hand is being washed away this loam and consolidated gravel form almost perpendicular faces. Saline Efflorescences. On the surface of the river loam within 200 yards of the Chewow river, a branch of the Pirara, and at a distance of five miles from the Ireng river, there is one of those places where salt is obtained from the surface of the ground by the Indians. At this spot there are numbers of small bare patches of ground of a grayish colour amongst the surrounding grass-covered alluvium which are incrusted with salt. No. 17. v.-.- :-'-:■. ^ Salt Efflorescence on Alluvium, Ireng savanna, a. Salt patch. b. River loam and sands. On examiniag these I found a layer of grayish-brown dusty soil an inch thick caked on top into a slight crust having a strong saline taste and composed of an earthy substance containing fine crystalline particles of chloride of sodium. Below this comes a coarse white sand to a depth of 30 inches (as far down as we could dig) which does not contain a particle of salt to the taste. This sand at a depth of 1 foot is moist and mixed with sufficient gray clay to cause it to adhere together when pressed in the hand. These salt patches occupied only a space of 100 yards by 50, and beyond this area not a particle of salt was to be found. On the sur- rounding surface there is a thin sort of dried-up vegetable coating which shows that the land there is inundated during the rainy season. The Chewow river was very low at the time of my visit, and contained water (without the slightest brackish flavour) in, small dirty pools in its bed full of lilies and rushes. Near the head of this river there is another salt patch, also one near the Ireng not far off, and a third on the Pirara river to the north-east. The guide informed me that after every rainy season, when the country becomes dry and parched, the salt comes out on the sur- 34328. ' M 178 GEOLOGY or BRITISH GUIANA. face and is then very pure and white, and in greater quantitj^ than at any other time. When removed by the Indians it continues to form, and the portion taken away is soon replaced. The Indians gather it, mix it with water, strain and boil down the solution obtained and get an impure salt which they harden by heat. C. — Valley Gravels and Clays. This ancient alluvial deposit occupies very large areas of the savannas, and amongst the savanna mountains of the Pacaraima chain. In the former localities it forms an undulating country rising from 70 to 100 feet above the level of the river loam deposit, whilst in the latter it occupies different levels along the valleys of the rivers of those districts. It is of a much greater age than the preceding deposit-, its base resting usually at a higher level. The great stretch of savanna between the Canucu mountains and Karinambo village on the Rupununi where this deposit occurs forming the watershed between the branches of the Essequebo and the head waters of the Rio Branco, is composed of red and gray clays, with beds of hydrated oxide of iron forming the crests of all its ridges. But south of the Cursato mountains, and near the Rupununi to the east of them, these iron beds are never seen, and instead of red and yellow clays we find quartz, gravels, and blocks with grayish clay. On its surface between Aringwong and Carenacru villages there are some water-worn blocks of sandstone, and between the former place and Curewakiteh village where iron beds were exposed they contained a few quartz-pebbles and pieces of water- worn sandstone. On the high ground near Pirara landing in the iron beds there are pebbles of quartz and sandstone, and going westward towards Quatata village, at about two miles from it, there are water-worn pebbles of sandstone. Beyond this to the Ireng river there is noly one spot where small pebbles of sandstone are to be seen, and these are accompanied by quartz pebbles. These quartz pebbles and blocks have I think come from the sand- stone formation, and point either to the former existence' of sandstone along the course of the Rupununi, or to a great change in the river system of this district, when rivers from the Pacaraima mountains, probably the Ireng, traversed this portion of the country now occupied by the Rupununi. From Pirara landing, on the Rupununi river, to the Oanucu mountains, the surface of this deposit is composed of a stiff reddish clay, containing iron pellets. Between the Macummucu river and the base of the Canucu mountains at Mount Ilamikipang, a layer of iron oxide is exposed containing quartz- pebbles. A short dis- tance south of Ohipedarinow village, an isolated ridge of iron ce- mented clays and pebbles occur, not far from the Takutu river. Near the old village of Pirara the surface of the valley deposit is of a bright red loam, which, when baked by the sun, is extremely hard. Beyond the last granite ridge on the Ooarawow river there is a great stretch of undulating savanna of red loam and quartz gravel with quartz blocks, and scattered on the surface of the latter are GEOLOGY OF BEITISH GUIANA. 179 very curious brown pellets of iron, one-fourth, of an Incli in diameter. From Cau-urua old village up to Patighetiku moun- tain, the path leads along the edge of the valley gravels, and there they are 30 feet higher than the river loam, and composed of quartz gravel and watenvom blocks, derived from the quartz- schist. Here it is very observable, that the branch streams of the Rupununi river have produced the present contour of the sur- face of the savanna, after it had been modelled by the main river. In the Waiquah, Cumparu, and various other river valleys in the Pacaraima mountains there is a thick deposit of partially rounded quartz blocks and pebbles, most of which have been brought down by the rivers and deposited at different levels. Before leaving the subject of recent deposits it may not be out of place to mention that I have examined these in many places for gold, by aid of the washing pan, but without success. As it has long been reported that gold was found in the Takutu river, I washed its sands and gravels, as well as the base of the alluvium of its banks, in many places for that metal, both below Yarewah village towards the, Ireng, between the western end of the Canucu mountains and Suwara-oura river, and on a branch stream called Coarawow, some 3 miles from the Takutu river and 12 miles from Tauarutu mountain, but without finding a single grain. By these washings a large proportion of magnetic iron , sand and garnet crystals was obtained, but nothing of any value. 2. Sandstone Formation, Dufing this journey I had opportunities of examining the sand- stone formation on its northern escarpment at Amailah fall, on the Curiebrong, as well as its southern edge at Cumararing mountain, and of a large portion of its surface, exposed between the upper portion of the Ireng river and the latter place. I will proceed to describe the Ireng area first, and then the Amailah sandstone afterwards ; as in the former district the sec- tions are much clearer, owing to the open nature of the country, and there the association of trap rocks with the sandstone is more clearly revealed. Journeying northwards from the sandstone escarpment at Mount Cumararing, the outcrops of the different sandstone beds are crossed, presenting good sections, and a fine opportunity of studying their sequence.* As before stated (Report No. 5) the crest of Moimt Cumararing is composed of beds of sandstone dipping north, and these have been eroded by a small branch stream running into the Ireng, producing a large valley, on the northern side of which we again find the bage of this formation. The basement beds are composed of a series of quartzose sand- stones, jointed and compressed, lying upon a greenish felsitic rock of exceeding hardness, which is apparently bedded irregularly and rests in its turn upon quartz-porphyry. This felsite contains a sort Diagram No. 16. M 2 180 PEOLOGY OF BRITISH GUIANA. of concretionary structiire, like dark coloured patches of the same substance, in horizontal positions in it. Upon the quartzose sand- stone lie coarse massive beds of sandstone-conglomerate, dipping north at an angle of 8°, and having a greenish-white argiUaceous bed on top. The relative thickness of these beds cannot be ascer- tained/: but the whole exposed in the face of the hiU together does not amount to more than 200 feet. Greenstone Layer in Sandstone North of Cumararing Mountain. 1. Sandstone. 2. Greenstone. From the top of the second ridge, 1^ miles north of this sec- tion, there occurs a great layer of diorite interstratified with the sandstone, of about 300 feet in thickness, and is identical in com- position with that of Cumuti and Roraima mountains. This rock is a coarse crystalline-granular compound of white felspar and greenish-brown hornblende. Although the true contemporaneous or intrusive natiu-e of this greenstone is most plainly shown, as before stated, still the actual junction is so disguised by subaerial denudation and decomposition, that it is quite impossible to say positively whether it is of the former or latter nature. I had pre- viously seen the actual contact of these rocks at Cumuti mountain (Report No. 5), where the greenstone rests upon the sandstone, but not any section in which the sandstone rested upon green- stone, showing the contact. North of Karakanang village I ob- served a dark, slaty, green rock resting upon the greenstone (Re- port No. 5), and possibly it is a shale altered by contact with the greenstone. This then would give the greenstone an intrusive character. North of Cumararing, however, I traced the sandstone overlying the greenstone to within a yard or two of their junction, and found that the former was not altered in the least degree at that distance from the point of contact. Not far north of this there is a true eruptive dyke of a, different kind of greenstone, which must intersect the last described layer of igneous rock, and is evidently of a later orgin. It is about 50 yards in width, lying in a E.N.E. and W.S.W. direction, and can be traced for a long distance by its line of dark coloured blocks of rock, and the patches of bright red earth, which result from its de- composition. It evidently has an inclination to the north, for it has suffered from a fault which has lowered one side and given it the appearance of a side throw, for a distance equal to its own width. The sandstone on either side of this dyke is not altered apparently, and its bedding is not in the least disturbed, but dips north as GEOLOGY OF BKITISH GUIANA. 181 before, at an angle of 8°. Against it comes a soft, friable, whitish sandstone on the north, and a hard jointed conglomerate on the south. ' ' / ss 4 , j^ % - fe Greenstone lying upon Sandstone N.N.E. of Tacara-erimone V. 1. Sandstone. 2. Greenstone. The sandstone continues for 1^ miles beyond tliis dyke, and forms a low escarpment, some 300 feet in height, upon which the base of a second great layer of greenstone rests. The beds here dip gently north at an angle of 5°. At this place again the actual contact is disguised by detritus that has fallen from the hillside, This bed is exposed at the surface for a distance of 2| mUes, which with a dip of 5° to the horizon, gives a thickness of 1,000 feet. On the side of the great slope, from the top of the last-mentioned escarpment down to the WaUongteur river, there are great blocks of this greenstone in the form of rounded, weathered, and split masses, covering its upper eroded surface. It is a similar green- stone to that of Cumuti rock also, but not so coarsely crystalline. This greenstone can be traced to the bed of the WaUongteur river, in which it forms large masses, and on for about one quarter of a mile to the edge of the forest, which hnes the river, where it is overlain by beds of yellowish thin-bedded shale, dipping north, and forming an undulating tract of country to the fort of the next escarpment. The face of this is composed of outcropping beds of gray and pinkish, soft sandstone, with here and there, every 20 feet or so vertically, a hard bed of sandstone, of a reddish colour, and with interstratified bands of white, grayish and banded beds, of a flinty looking siliceous rock. On its very summit some layers of red jaspar are seen, which may correspond with those seen on Karakanang mountain top. If so, this greenstone is continuous with that of the above district, and probably also with that of Tawailing mountain to the east. The sandstone containing the jaspar is of a soft \yhite or pinkish colour, with layers of minute rounded quartz grains in some parts of it. 182 GEOLOGY OF BRITISH GUIANA. No. 20. Greenstone Layers in Sandstone at Cumararing Mountain. 1. Quartz-porphyry. 2. Greenstone. 3. Sandstone. Taking the sections just described from Cumararing mountain, fhe base of the sandstone, we. have a total thickness of 4,800 feet of sandstones and shales, containing two great interstratitied layers of greenstone, one of 300 and the other of 1,000 feet in thickness. All the way down from the top of the escarpment, north of Wailongteur river to the Kamang, the soft reddish friable sand- stone beds form the surface of the ground and have in the valley below an almost horizontal position. Farther on iii Toobaborome mountain, the dip is in a south-westerly direction, at a very> slight angle showing an entire change in the lie of the beds. The horizontal beds, with jaspers strewn aU. over their surface, cover the whole plain to the lower falls of Orindouie on the Ireng, where there are beds of exceedingly hard fine-grained sihcious sandstone containing layers of red jasper. The sandstone continues, lying almost horizontally along the Ireng with jasper beds on top as far as a point due west of Toobakeng mountain. Journeying up the Ireng from this in a corial but few rocks are to be seen, and these are aU sandstones as f^r as Camouta rapids, where a third layer of greenstone occurs, occupying a distance of one quarter of a mile of the river. Some two or three miles to the south-west of this, on the Chemapeur river, I saw some beds of bluish-black thinly laminated crystalline rock which I take to be a trap. It is laminated parallel to its bedding and resembles an altered shale. One slab of this rock in the bed of the river was adhering to a block of conglomerate of a friable nature, composed of pebbles of various rocks in an earthy cement. The upper fall on the Ireng river called Orindouie is produced by beds of red sandstone containing pebbles of quartz, which dip a little to the south of west, at an angle of 5° to the horizon. These beds are jointed vertically in two directions, and at the foot of the sloping side of the precipice, on the eastern side, they form rows of jagged pinnacles. The top beds of Wantudna are com- posed of thin bedded jasperous sandstone, containing beds of red jasper and are almost horizontal. In the face of, the great table land at Amailah, on the Curlebrong liver, we have again associated sandstone and greenstone ; but here, as in most other cases of the kind, in a country densely clothed with vegetation, and subjected to the disintegrating powers of a tropical climate, all minor geological details have been obscured -or completely hidden by debris and forest. On approaching the foot of this great escarpment, at a distance of about one mile from the Oolomeh river, a small tributary on the west, the granite rocks GEOLOGY OF BRITISH GUIANA. 183 terminate, tLen comes a tract of one quarter of a mile in width in which no rocks are to be seen, but which I believe to have been the sandstone outcrop, now obscured by alluvium, and after this we have a coarse crystalhne greenstone, precisely similar to that at Cumuti mountain, with its horizontal bedded structure very prominent.* Upon this, at a height of about 400 feet on the mountain side, comes the sandstone formation, which consists of red and white coarse sandstone with coarse conglomerate on top, occupying a vertical distance of about 800 feet. The junction between the trap and sandstone is completely hidden by the great blocks of conglomerate which have fallen from above, together with the loamy detrital matters derived from the sandstone beds and the dense foliage. This layer of greenstone, 400 feet in thick- ness, is very coarsely crystalline, having large semi-transparent crystals of hornblende of a brownish colour, in a crystalline base of white felspar, most probably anorthite. No. 2]. 1 Greenstone Lat/er at Amailah on the Curiebrong River. 1. Granite. 2. Greenstone. 3. Sandstone. The precipice over which the Curiebrong river precipitates itself exposes a section of the sandstone formation at the top of the great table land of 171 feet in height. This is composed of thick beds of hard, coarse, pebble-conglomerate for 101 feet, overlying 70 feet of thin-bedded sandstone and shale, arranged in alternate layers of thin red shale and gray sandstone, of Various thicknesses, from one-eighth of an inch to two and three inches. Against the foot of this section are enormous blocks of conglomerate, which have fallen from the beds above and obscure all below. The thin sandstoiVe beds contain surfaces exhibiting most perfect ripple marks, from small narrow wave-like ones, to those wide undulations produced by strong currents ; also well-developed sun cracks and casts of rain drops. Here then is evidence of a shallow water deposit, where there was a flow and ebb of tide which was succeeded by a great deposit of coarse conglomerate, containing pebbles of quartz, jasper, and trap. I examined the thin-bedded sandstones very closely, as far as I was able, for bird or reptile tracks, but without success, only observing upon one slab a cast bearing an indistinct resemblance to a track, but which could not be depended upon. Just beyond the mouth of the Colomeh river at the foot of the AmaUah gorge, the first blocks of Conglomerate are met with, and * Diagram No. 19. 184 GEOLO&Y OF BRITISH GUIANA. the river's bed Is there ahnost filled with them. Both on this river and on the Potaro, before reaching the mouth of their valleys, no detached blocks of this conglomerate or sandstone are to be seen, proving undoubtedly that they have all been destroyed in the river's bed before reaching the open plain. There are two detached mountains to the north of the sandstone escarpment near by which are sandstone outliers. No. 22. Crreenstone Layer upon Sandstone, Twasinki Mountain. 1. Greenstone. 2. Sandstone. At the base of the Twasinki mountain there are' 50 feet of white sandstone beds, dipping in a N.W. direction at an angle of 30°, upon which lies Y70 feet of the same coarse greenstone as is seen close by at Oumuti. This greenstone is in three great layers, presenting steps facing towards the east on each of which is a talus of red clayey earth, and the crest of the ridge is capped with a thick layer of impure hydrated oxide of iron. From finding similar layers on aU the "greenstone hiUs, I imagine that they are derived in part, if not entirely, from the decomposition of the surface of that rock. No. 23. LINES ""^ BEDDINE. S-^fiflT ^o^ivr_ Sandstone Escarpment, Maccari Mountain. 1. Conglomeiate. 2. Sandstone. The long narrow range of Maccari mountains has its upper half composed of sandstone, of this formation, having a total thickness of 620 feet. It is first met with at a height of 520 feet on the mountain end, and rests upon the quartz-porphyry, but a huge mass of reddish clay and blocks of sandstone hide their junction. GEOLPGY OF BRITISH GUIANA. 185 It is divided into two equal portions, the lower of fine grained red sandstone, in beds varying in thickness from two to six feet, and the upper of coarse whitish pebble-conglomerate. The sandstone portion is jointed vertically and displays false bedding in a marked degree. One great joint is seen near its base at an angle of 12° to the horizon, cutting across the bedding in a most curious manner. The lowest beds have layers of white quartz of spindle shapes embedded in them, and also circular spots of a lighter colour than the mass of the rock itseH", with plates of white mica in their laminae. The pebbles in the conglomerate are of white quartz, either scattered irregularly throughout the sandstone, or in some cases forming the whole mass of the rock. The cementing material of the quartz grains and pebbles is a white clay, in very minute quantities, and is sometimes wholly wanting. The perpendicular faces of sandstone are covered with a white lichen, and the sloping portions with moss and shrubs. At Yarewah village, and again near the mouth of the Macu- mucu river, in the bed of the Takutu, there are beds of a purplish or dark-brown shale, containing layers of silver-coloured mica scales and black irregular stains of oxide of iron, with a sort of conchoidal fracture. These beds dip in a due south direction, at an angle of 5° to the horizon. They resemble some of the beds of the red sandstone, but like similar beds on the Rupununi river, their true position cannot be easily determined. Though I searched carefully for fossils in the shales and sand- stones I was unable to find anything whereupon any dependence could be placed. On a large block of sandstone in a brook close to the Ireng river, above the lower Orindouie fall I obtained a specimen of coarse fluted rock singularly like the cast of a Sigillaria, which had been washed down from the mountains to the east. . I went to see a " shining substance " in some rocks northward of Cumararing mountain, guided by an Indian of the village, who had informed my interpreter of its existence. He took me to a mass of gray sandstone rocks on the side of the hill that had fallen from a precipice near its crest, and then began to search for the block in which he had seen it but without success. We all spent a considerable time in searching amongst these rocks but could see nothing. This sandstone was in blocks and slabs of a gray colour and coarse texture vrith thin layers of scattered specks of oxide of iron and white mica. There was nothing like a vein or any indications of gold or other metals of value. I have not yet sufficiently examined the various sections which I have got recorded in my notes of the beds or layers of green- stone associated with the sandstone formation to enable me to arrange and correllate each one at present, and as it will neces- sarily occupy some time, it wiU be left for a future report. The determination of their true character, as to whether they are intrusive on the one hand or contemporaneous on the other, cannot be accomplished imtil the whole has been thoroughly examined. All that can be said at present is, either that these eruptive rocks 186 GEOLOGY OP BRITISH GUIANA. have burst up from beneath, and been forced out in great layers between the sandstone beds at different times, or that they have been ejected during the time that the sandstone was forming in the bed of the ocean and thus came inter bedded with it. One can form some idea of the activity of the igneous action exerted during the epoch of this sandstone formation when he considers that the out-crop of these traps can be traced around an area of 150 miles in length and 50 miles in breadth. The immense denudation that has taken place since they became sur- face rocks may be inferred when we view the many distant isolated tracks of greenstone aU of which have evidently formed at one time a continuous layer. Though there is no data whereby the Geological age of the sandstone can be determined in the absence of Palaeontological evidence, still it is evident that its association with greenstone layers betokens an extreme age. From its lithological characters its containing these inter-bedded greenstones, and having rippled- marked surfaces on some layers, it closely resembles the new red sandstone of Connecticut, U.S. MICA-SCHIST. At the portage of the first cataracts at the Ouriebrong river there is some partially decomposed schist with thin quartz veins and strings. Between Yiemah and and Apanachi rivers there are some perpendicular beds of a gray argillaceous rock, full of square cavities, from which some mineral, most probably iron pyrites, has been dissolved. Near a portion of the Essequebo river where it takes a great bend to the south not far from Rock Danigo, and south of the month of the Cuyuwini river there is a small hill of mica-schist, descending to the river s edge. It has its foliation vertical, is jointed irregularly with the slope of the hill (an angle of 50 degrees), and again more regularly jointed at right angles to its foliation, so that it breaks up into elongated rhombs. Thin lines and swellings of quartz occur here and there in it. Besides these there is a large quartz-vein 2 feet 6 inches wide lying across the river of a pale amber colour, which does not appear to contain any minerals or metals. I examined it thoroughly and washed in the sands accumulated below it and obtained a good quantity of magnetic iron sand but no gold. There is a small development of chlorite-schist on the Cass-kityu river on granite. 4. Hornblende-schist and Hornblende-rock. A patch of hornblende-schist occurs at the granite ridge edge, on the southern side of the shallow valley of the Mepitewow river. At the Casowedie river there is a long low hiU, partly covered with trees, and ranging N.N.E. and S.SW. which is composed of a highly crystallized dark green hornblende rock. It is a quarter of a mile in width, and appears to be an eruptive mass in the GEOLOGY OF BRITISH GUIANA. 181 g-anite of this region. This seems to extend across, country to the Kupunum river at Mount Patighetiku, which rises about 300 feet above the savanna and is entu-ely composed of the same rock. On its surface there is a thick covermg of red clay, producing a marked contrast in colour, with the yellowish clay upon the granite. It IS very coarsely crystalline, and decomposes to some depth on each block or exposed mass, producing red oxide of iron. Just above Paumbo islahd on the Essequebo river, there is a development of rudely bedded rocks, composed of finely crystalline green hornblende and white felspar, which has a shght though irregular parallel arrangement of its mineral constituents. 5. Gneiss. At a small river some 10 miles above Paumbo island, in the Essequebo river, there is a beautiful mass of gneiss of a dark colom: and close wavy texture, full of large elongated and com- pressed crystals of pinkish felspar. About two miles beyond this crystals of garnet make their first appearance in this rock but as the gneiss is much weathered on the surface, the garnets are partially decomposed. The gneiss at Murray's cataract and onwards to King William IV.'s fall is of a coarse gray variety, containing quartz nests and garnet crystals. Its planes of mineralization are in most cases vertical, and the rock appears to be cleaved, breaking easily parallel to them. Some masses resemble granite iu their mode of weather- ing, and have flat or rounded forms, but still the planes of fohation are nearly vertical, they break up into irregular squares on the top surfaces of which the fohation is seen very highly developed in all forms of contortion. No. 24. Section across the Western Channel of King William the FourtKs Cataract, a. Gneiss. b. Biver. 188 GEOLOGY OF BRITISH GUIAITA. The gneiss of King William IV.'s fall is massive and has the wavey foliation inclined at an angle of 65° to the west, the cleavage or joint planes at about the same angle to the east, v?hile a rude sort of bedding is nearly horizontal, or inclines also the west. The rock has broken on its bedding and jointage or cleavage planes, and thus produced smooth sloping surfaces of rock on the western side of each channel and jagged steps on the eastern. ' This rock is of a gray colour and coarse texture, and contains immense quantities of garnet crystals in clusters arranged in Enes. It is impossible to obtain any good specimens of these crystals owing to those that can be broken out by .the hammer being in a state of partial decomposition. Some small veins of felspar and quartz traverse the gneiss of the western fall and contain small quantities of black mineral resembling pitch-stone. I observed that in the bends of the river the planes of mineral- ization are almost vertical, and lie in the same direction as the course of the river in many places, but are chiefly east and west. Between Mararowah and Pamu cataracts there are numbers of rocky islets and detached masses of gneiss rock rising in some instances from 15 to 20 feet above water. Ordinary gneiss forms all the rock masses in the river and on its banks up to the third great fall, at which I spent Sunday October 3rd, but there it changes to a syeintio gneiss, its mica being replaced by hornblende, and all its garnet crystals having disappeared. The strike of the foliation at this fall is nearly east and west, whilst lower down at Manarswah fall, it is about south- east and north-west. Some two miles south of the third parallel of north latitude, the gneiss becomes granitic for a short distance, and at a large cataract beyond it assumes a porphyritic texture, having a green mica, and enclosing larger crystals of white felspar. From this place to the mouth of the large river coming in from the west, all the country is composed of the ordinary gray gneiss, without garnets, which occurs every here and there as detached masses in the river's bed, in curious forms, exhibiting most extensive degrees of contorted foliation. (See sketch on next page.) In some places it is extremely conipact or schistose, and of a dark colour, in layers between common gneiss. Some of the detached masses above aUuded to are 25 feet in height and 20 feet in diameter. I observed that on those rocks that are very high, their upper portion is of purplish colour, from a lichen growing upon them, the bottom edge of which forms an even but not horizontal line, showing that it cannot be the edge of the level of the water in the rainy season. Below this comes a zone of gray lichen, the bottom of which is evidently the high-water line of floods. Their upper portions, down to the end of the purple band, are grooved and channelled similar to those blocks now partially disclosed by the washing away of the alluvial banks. From this I infer that the river is there re-occupying its ancient course, and that these great blocks have been at one time surrounded by alluvium up to GEOLOGY OF BRITISH GUIANA. 189 the edge of the purple band, and like those on the river's'edge and in the adjoining forest, have had their grooves and channels JVo. 25. Patch of Gneiss 2 feet square. Upper Essequebo River. Coarse white quartz and felspar. ' 2. Purplish felspar with a little mica and quartz. 3. Pine-grained felspar and mica. 4. Granite vein. cut by the rain water falling from the trees that then grew around them. About half a mile east of the large river before mentioned the last exposm-e of gneiss is seen, before coming to the granite development, and it is there of exactly the same texture as hitherto indicating no change whatever. Gneiss occurs again before reach- ing the Cuyiiwini river beyond the masses of granite, and there in one ppot contains a mass of quartz-schist. Beyond the granite, near the Ouyuwini river mouth, there is a wide tract of country composed of gneiss, which ceases at the mica-schist, some distance below rock Danigo, and does not occur again till a little distance past the Taruma village at Onoororo river, where there is another wide band. Near rock Danigo there is a coarsely foliated rock close to a mass of granite composed of a greenish quartzose rock, intimately blended with mica, and having lines of white mica crystals in parts as weU as bands and. felspathic layers. These decompose readily, leaving the bands of quartz sticking out, in plates an inch thick, beyond the edge of the rock. In the great bend of the river, below the exposure of mica-schist, there is a junction of granite and gneiss, in which is seen a boss of iSne-grained whitish granite, 190 GEOLOGY OF BKITISH GUIANA. with a shell of coarse gneiss on top, amongst which, and chiefly in contact with the granite, are fine foliations of mica. A coarse vein of granite ran across the former rock. The isolated hills to the east, between Murray's and King William IV.'s cataracts are of similar gneiss to that in the river adjoining. Gneiss occurs from a short distance up the Cotinga to the mouth of the Mauitzie river, generally in a very decomposed condition. In one place near Mount Wanakara it is seen in rolls, lying N.E. and S.W., and having a vertical foliation, trending N.W. and S.E. It contains garnet . crystals. A little beyond the mouth of the Zuruma river gray gneiss is seen, resting upon granite rolls, and having a vertical foliation and cleavage, but none is found to the north of this. Great flat masses of gneiss, with large felspar crystals, are exposed in the Suwarraowra river bed, as well as in the Takutu to the eastward. I examined the rocks of the Canucu mountains on their north-western side at mounts Quariwaka, Ilamikipang, and Ouratawuiburi, and found at the first place clear developments of common gneiss, at the second a somewhat similar rock, but more nearly resembling gneissose granite, and at the third the same rock as the latter. In the last two positions the rocks con- tained small garnet crystals, large glassy crystals of felspar, and had a decided parallelism in the arrangements of their mica crystals. I therefore placed them under the head of gneiss. At a place not far north of Dahdaad village, where a chain of deep ponds of water most clearly marks out an ancient course of the Takutu river, rocks of gneiss of a porphyritic character occur in isolated patches, and resembles those seen in thp Takutu, near Suwara-owru river. They extend to the Takutu to the westward, and their foliation has a strike of nearly due east and west. A low ridge south of Cursato mountains is composed of gray gneiss with a small vein of quartz in it. A short distance beyond the greenstone rock, between Catuanariba and Damwow villages, there is a ridge of a most curious rock, which has a greenish coloiu- and is much decomposed on its surface. It contains a great quantity of grayish silica, a little felspar, and fine crystals' of mica. Besides this it is studded with partially decomposed crystals or clusters of crystals of small garnets, which gives the whole a rusty appearance. This rock appears to be intermediate in composition between quartz-schist and gneiss. One nule east of Daruwow river, vertically foliated massive rocks are exposed, of common gneiss, and this is the first deve- lopment of that rock met with coming north. From this on, with the exception of two low ridges of quartz-schist off the end of Tarucupani mountain, the only rock to be seen down to Perapoko river, is gneiss. One of the spurs of the mountain jutting out westwardly from the main mountains, not far south of Oabarooda village, is a bare mass of this rock shaped like a great dome, with two flat-topped wings branching north and south from it, and their bases clothed with vegetation. It is some 300 feet ia height, and GEOLOGY OV BRITISH GUIANA. 191 has a graet crack in the masses north of the dome, which is almost vertical, and about a foot wide at the top. The gneiss exposed in the Eupimuni river near Cabarboda is extremely foliated and contains a large percentage of quartz in layers and nests, and veins of quartz-schist. The whole mass of the Canucu mountains is formed of gneiss and granitoid-gneiss, through which extremely hard rock the Rupununi has cut a deep and wide valley to the plain beyond, and at the commencement of this plain near the northern slope of the range at Mapare river, the last gneiss rock is seen. There is a black quartzose rock with reddish and white crystals of quartz, like that seen near Ranidekeur mountain on the Quitaro river occurring in the gneiss not far below Perapoko. Igneous Dykes and Masses in the Gneiss. Near the mouth of Mauitzie river on the Cotinga, there is a dyke of greenstone 30 feet wide, crossing the river in a N.E. and S.W. direction ; and there is a small trap dyke in the bed of the Kupununi, some 4 or 5 miles above Aripai river. A short distance below "Watawarie inlet, on 'the Rupununi river north of the Canucu mountains, there is a patch or roU of a hard, green, finely crystalline, trap rock, with here and there small circular cavities, containing kernels of foreign minerals. Des- cending further to the rapids above Urua village I again saw this same rock very extensively developed, and having at the latter place a horizontal layer some 3 feet thick, of amygdaloid the vesicular cavities of which were filled with three minerals besides having a little iron pyrites scattered in specks throughout. The cavities are circular and lined with dark green crystals, inside of which is an opaque white mineral, and frequently when this is absent, crystals of calcspar. Besides these kernels there are large cavities lined with botryoidal forms of the same white mineral. The surface of this rock is smooth and covered with a black polish from the action of the water upon it, is irregularly jointed, and weathers in onion-shaped balls here and there, as well as in irreo-ular polygonal pieces. The amygdaloidal portion is massive, and without jointing, and forms a curved bed without any actual division between it and the compact portions above and below ; the only difference being that the cavities are more numerous alono- an almost horizontal zone, and die out gradually above and below. The full thickness seen of this layer is 15 feet. The same rock, with cavities in it, is seen a few hundred yards down the river forming a small rapid ; and just below the site of the old mission of Urua it occurs without cavities, and its horizontal surface is marked by splits, dividing it into irregular vertical columns. This rock is evidently a diabase containing an amygda- loidal layer, which has been forced up through the gneiss, and spread out either amongst it or upon its surface. 192 GEOLOGY OP BRITISH GUIANA. 6. Quartz-schist. The first massive rock met with in ascen^ng the Cotinga river is quartz-schistJ* It occurs in gneiss, but as only about 20 yards of its width are visible, its mode of occurrence is not clear, and it appears to be interbedded Avith the gneiss. It is of a dark grayish black colour principally, but changes horizontally to white and brownish-white colours, in bands. It is a coarsely foliated rock the direction of which is in an almost vertical plane, lying in an east and west direction. Coinciding with this is a set of well marked jointing or cleavage planes, whilst another set of joints is almost horizontal, and a third inferior set runs vertically at an acute angle to the first, so that the rock breaks up into irregular rhombs of great size. This rock is chiefly composed of quartz No. 26. Hi I |i lii 11' ill -IS.INOHES.- 'li'ii' iiiiii Ml !'l|l| I llljl I" HI ' I'lill !'ii|| lll'll III li i iii I 'I ' I 'll|ii ii 1 n i|ll lllll il ii III! Ml II' II II I'ai 111 11' 1. Blackish quartz with chlorite and mica scales. 2. Lines of decomposed felspar, chlorite, and iron py 3. White quartz rests and banks. rites. associated with small plates of specular iron mica and chlorite, arranged in laminae, and more or less intimately blended through- out the mass. When thoroughly mixed with the quartz it gives it a dark grayish-black colour, and when scattered in thin plates throughout it gives a greenish-brown tint to the whole. The quartz has a granular structure and a vitreous lustre, and is extremely hard. Where its foliations are free from the colouring minerals the quartz is then of an opaque white variety, banded vfith clear colourless sorts of the same mineral. It also contains some decomposed felspar crystals and a few specks of iron pyrites. About one mile above this development in the river's bank there are sections of this same rock much decomposed, and they may be continuous with each other ; but owing to the great denudation produced by the river, the connexion cannot be traced. Some seven nules north of the Cuyuwini river on the Essequebo, - is a mass of quartz-schist, protruding in a wedge-shaped there GEOLOGY OF BRITISH GUIANA. 193 form into the river from the gneiss for a distance of some 50 feet, and terminating in a point. It is jointed in all directions, much iron-stained, and portions ef it are of a granular texture. Some parts contain plates of chlorite, mica, and specular iron more or less intimately blended. In parts the quartz is of a vitreous lustre, and there the greenish colouring being thoroughly diffused, the rock assumes a very curious appearance. Where the specular iron forms lines in folise it decomposes leaving the hydro-oxide in its stead, and this it is that gives the surface su3h a rusty appearance. Near Dahdaad village, in the gneiss, there is another small development of this rock containing small cavities (from which I imagine the specular iron has been dissolved) filled with a white clayey material. White quartz-schist occurs- zw situ rising above the alluvium of the undulating savannas in many places to the west and south- west of Cursato mountain. One mass occurs not far north of Pinniyette mountain, and is surrounded by angular blocks of the same rock, resulting from its decomposition. The whole surface of the undulating savanna of the region is composed of these blocka in heaps, covered with but little soil, and they have been derived from the layers of quartz-schist occurring in the gneissose rocks, which exists at the heads of these rivers, Takutu and Rupununi, as well as from nests and veins in the surrounding gneissose granite. Every block of quartz exhibits a schistose structure in one part or the other by parallel lines from which crystals have been dissolved, but contains no mica or specular iron crystals. Similar masses are to be found south beyond Pinniyette mountain in three or four places, and blocks and boulders cover the undulating savanna around. Far up the Coarawow river on the savanna a large boss of quartz-schist swells up and angular broken fragments of portions of it lie scattered around ; this greatly resembles the quartz nests in the quartz-porphyry of the Pacaraima mountains. It is probable that these quartz-schists occupy a position at the base of the gneiss and hence we have them lying in patches upon the gneissose granite of this region. 7. Quartz-porphyry and Felstqne. This rock makes its appearance in several places between Itawah and Apanachi rivers — branches of the Curiebrong river — and is of the usual kind, seen in other portions of the country before described. Between the first set of cataracts on the Curiebrong succeeding a decomposed schistose rock of a bluish and sometimes greenish- oray colour, quartz porphyry appears, but contains a few crystals and continues down to the Essequebo river below Tumatamari cataract. It contains many trap dykes. Just beyond the mouth of the Cassikitu river the granite gives way and is succeeded by quartz-porphyry. It is of a gray colour, is composed of crystals of felspar in a felspathic base, 34328. N 194 GEOLOGY OF BRITISH GUIANA. along with green chlorite crystals in aggregations, and contains but few quartz crystals. This rock is alone seen in the river to a short distance beyond Cauaiyu rapids where it assumes the appearance of a hornblende phorphyrite. It does not occur agSiin till a little way beyond the mouth of the Camoawow river where it is of a gi'ay colour and has but few quartz crystals. A hill near Oanaiyu rapid, 430 feet high, is composed of grayish-blue porphyrite consisting almost entirely of felspar crystals closely packed in a felspar base. In the Cassikityu river there is a tract of this rock which is succeeded by granite. The quartz-porphyry at Mikang-pati in the Cotinga river is of the usual greenish -gray colour, but contains few crystals of quartz. Just beyond the Waiquah river the quartz-porphyry sets in evidently resting upon the granite to the south of it, and is of a felsitic nature containing small dykes of greenstone. On the low ridge, near Terchilewan village, in it is a pure greenish felstone, resembling a greenish slate, but having a conchoidal fracture. In the valley of the Cotinga river this rock contains small and large veins and nests of white quartz. From this valley to the sand- stone escarpment at Mount Cumararing the moimtains, ridge after ridge, are composed of this rock, of a very uniform com- position, being of a dark greenish-gray colour with distinct crystals of felspar, and but few quartz crystals. At Cumararing mountain the sandstone rests apparently on quartz-porphyry of an exceedingly decomposed nature, the junction is disguised and there is every appearance of a disturbance of the strata. It is white like kaolin, and crumbles in the hand setting free the quartz crystals. Between the quartz-porphyry and sandstone, north of Cumararing, there is a bed of greenish felstone. No. 27. I i ! ifTl i ill. Section near Mora Village, Rupununi River. 1. Foliated rock resembling petrosilox. 2. Quartz-porphyry. 3. Felsite with lines and veins of quartz. 4. Foliated quartz and felspar. 5. Compact felsite. The whole of the ridges around Mora at the great bend of the Eupununi river, are composed of irregular layers of three forms pEOLOGY OF BRITISH GUIANA. 195 of rock, viz., quartz-porphyry, banded quartz-porphyry, and fel- stone. Commencing at the base of the liill behind the village we have a rock composed of thin layers of fijlspar and quartz extremely foliated in a vertical direction, then a band of qu;irtz- porphyry containing quartz crystals, then felstone vcitii quartz veins and lines, then banded porphyry, and finally a compact liver-colotued felstone. All these weather deeply on their surface to a pale cream colour. They seemed to be arrangpd in irregular layers occupying a vertical thickness of 700 feet, and have a sort of perpendicular foHage and cleavage, in some layers, while others are soiid and massive. In the banded porphyry there are some curious concretionary forms, as well as beaiitiful foliated layers of different coloured felspar and quartz. No. 28. 1 1 1 .1 1 I 1 -^ I-.MILES. ^ I.MILE. \^ A Ary 1 ta /*■ ^ ill ^•^ y -3- X X X X >< X X X X X X X X X X X X XX Xl^ X. XX xXx X X ^X '^ x^ x'^x^xx X X X X X X Section from the Essequebo River to Maccari 31ouritain. 1. Quartz-porphyry. 2. Sandstone. 3. Conglomerate. 4. Allaviam. In six places between the foot of Maccari mountain and the Essequebo river narrow bands of quartz-porphyry protrude above the alluvium, forming ridges trending north and south, but only a few feet in height. At the foot of the mountain the same por- phyry appears, and is seen in situ, and in large angular fallen blocks up to a height of 650 feet. In this distance it forms three irregularly shaped terraces, the first being much higher than the second and third, and the whole having an appearance of three great layers. A short distance down the third there are large" blocks of red sandstone and sandstone conglomerate which have fallen from above, and these, together with a yellowish clay massed at the foot of the sandstone, hide the junction of the two forma- tions. These terraces slope at angles of from 50° to 60°, and their tops have an inclination of 30°. This quartz-porphyry is of a greenish colour, with whitish or greenish^white crystals of felspar in it, besides crystals or aggregates of greenish crystals of chlorite, but having no quartz in crystals. It is the same rock as occurs at Ouropocari with quartz crystals, and there is no doubt whatever about its lithological classification. Its surface _ is weathered in some blocks to a depth of three-quarters of an inch, and is of a white or rusty white colour, with pits from which crystals of felspar have been dissolved. N 2 196 GEOLOGY OF BRITISH GUIANA. A small mass of quartz-porphyry exactly similar to that just described appears in one place only, on the path to the Demerara river, from Cumparu river on the Essequebo, and at a distance of not more than one mile from the latter stream. The greenish rock before mentioned (Report No. 5) as occurring below Waraputa great cataract is probably a quartz-porphyry, impregnated with chlorite, crystals of quartz, and small veins of quartz. The felspar crystals in it are green, and can just be dis- tinguished from the mass of the rock, while it contains some specks of iron pyrites. Quartz Veins and Nests in the Porphyry. At the junction of the Curiebrong and Potaro rivers there is a large vein or mass of quartz in which I could not observe any metals ; it is jointed and ironstained, and appears to run at right angles to the latter river. I examined a quartz vein above the first set of cataracts on the Curiebrong river, and though most promising looking, still I was unable to detect any gold in it. It occurs in three places where the river has cut across it, the first of which contains great quan- tities of iron pyrites in good-sized crystals, and the second and third besides this contain a black mineral in great quantities. Between Terchilewan village and the spot where the old village of Torong used to stand there is a hill on the top. of which two veins of white quartz protrude above the surface of the ground, but which cannot be traced far in the direction of their line, which is east and west. They are in a much decomposed schistose- porphyry. I spent an afternoon in the examination of these veins, but could see nothing in them but thin scattered plates of specular iron with here and there small cavities from which the same metal has been dissolved. A somewhat similar vein occurs on the top of Cumararing mountain pass. In the Cumparu valley, protruding above the alluvium from the quartz-porphyry beneath, there are two almost circular masses of white quartz about 50 feet in diameter, and many similar patches are to be seen everywhere in the porphyry mountains, surrounded by angular and waterworn blocks of the same substance. From these are derived those low hUls of rounded blocks and pebbles seen in the mountain valleys, and on the hill sides near the water courses of those regions. Some have the appearance of being in beds but most are in nests and veins. They seem to be entirely destitute of any valuable metals whatever. Igneous Dykes in Quartz-porphyry. Numerous trap dykes intersect the quartz-porphyry on the Curiebrong river in numbers of places between Mona cataract and Apanachi river. To the south of the sandstone escarpment in the Saca-outa river valley there is a great dyke or layer of greenstone in this rock, and another well-marked dyke is seen some five miles south-west GEOLOGY OP BRITISH GUIANA. 197 of it, which is 50 yards wide, and can be traced by the eye for miles eastward and westward. 8. Granite and Syenite. A great mass of syenite three miles wide, lying in an east and west direction, appears ia the Curiebrong river not far from its mouth, and forms the first set of cataracts. The surface of this rock bordering the river and its bed is void of the usual iron polish, and above water in its stead has a gray and reddish lichen adhering to it. One mile and a half above Mona cataract, on the same river, granite sets in, and is of a very coarse texture, having large crystals of felspar scattered throughout. These crystals are some- times 2 inches long, of a pinkish colour, and have mica crystals in them. The rock itself is composed of transparent quartz, white and pinkish felspar, and dark green mica. It forms a surface rock to within one mUe of the Colomeh river, not far from the foot of the sandstone table land, and in this distance keeps -its coarse texture, and has small veins of quartz. Tumune rock in the Essequebo river, beyond the mouth of the Rupununi, is composed of granite. In this upper portion of the Essequebo, at the mouth of a large river on its western side, granite suddenly appears in great masses of solid rock, of a coarse porphyritic variety, forming high rocky banks to the river for some distance, as well as protruding above water in different portions of the stream. For a distance of a few hundred yards between the granite and gneiss there is a strip of alluvium hiding their jimction. This granite is of a darkish colour, and is composed of twin crystals- of a dirty -yellowish felspar of about an inch ia length (occupying the greatest portion of the rock), bFack mica, and but little quartz of a vitreous yellowish gray or colourless variety. As accessories it contains many crystals of garnet and a little iron pyrites. Where it first occurs it is traversed by veins of very coarse granite, containing crystals of white felspar of 2 or 3 inches in length, silver gray mica in plates an inch across, and white quartz. This granite is seen up to a short distance above the last great cataract in the river, some 12 miles south of its first exposure, but is not so coarsely crystalline, and contains quantities of garnet crystals. It assumes rounded forms by weathering, and is seen everywhere in the river's course, and on its bank, in great masses ; sometimes for a bend or two the river may be clear of of them, and then beyond they are again met with, protruding in such numbers as to place a sort; of barrier to the flow of water, thereby forming strong rapids. Amongst the rocks I observed (as in many places elsewhere in this country) great splits which have evidently, been produced by the action of the water and atmosphere, causing decomposition along lines of weakness, aided by an unequal resting upon rocks beneath. 198 GEOLOGY OF BRITISH GUIANA. Near the mouth of the Cuyuwini and just beyond it there is a second development of this rook, which is succeeded by gneiss ; then comes granite again, as far as the mouth of the Cassikityu river. From a mile or two above the Oaniyu rapid granite is seen again, as far as 2 miles beyond the Carocunhi river, where it is succeeded by gneiss, to a point a few miles beyond the Wapuau river, and there again it forms the only rock to be seen extending to the highest point upon the river that I reached. At the first Taruma field beyond the Yucanopito cataract, there is a very dark coloured rock exposed in a long roll, composed of dark quartz and felspar vdth black mica. Beyond the Cuyuwini there are blocks of granite in the river of enormous sizes. In the first development of granite beyond the Oassikityu river, the granite is at first of a white finely crystalline variety, but soon passes into one of a coarser texture and darker colour. One mass of granite near the junction of the Ouruow and Essequebo rivers contains iron pyrites. About 8 miles up the Cassikityu river the granite begins, be- yond the quartz-porphyry, and continues as far as I went. It is at first of a dark variety, but soon passes into ordinary granite,' and in one place contains green mica, a reddish felspar, and opala- ceous quartz. In the first development beyond the Cuyuwini river the granite is coarse, and contains two kinds of mica of silver-white and greenish colours ; also large crystals of felspar and elongated pieces of quartz. On the Cotinga river at Aretiari cataract, - it is of a coarse variety with greenish mica, and has coarse granite veins through- out. Beyond the Mauitzie river granite is again seen as a surface rock, and so continues to Pirawai cataract. The granite ' of Mikang-yepatori is exactly the same as that forming Shea rock and other ridges on the Quitaro savaima, and like them is quite bare of herbage, and outwardly of a purplish coloiu- from a lichen growing upon it. It forms a great roU lying N.N.E. and S.S.W. On a large patch of a shghtly curved siu^face of this rock, in the river bed beside Mikang-yepatori, where the water rushes over with great force when the river is high, I observed the most curious and regularly formed ripple marks as are usually seen on patches of sand. This must have resulted from a wavey texture of the rock, giving it different degrees of hardness, so that the water wore it as described. I have repeatedly seen smooth polished surfaces, of a foot or so in diameter, on rough granite and porphyry blocks before, but not the polished ripple marking. South of mount Pirawai the great granite rocks in the east bend of the river are much split, and have fissures running across them in various directions. Mount Pirawai itself is not a smooth mas- sive structure like m^ny of the mountains about it, but is appa- rently a pile of enormous angular blocks of granite, one particularly large block being situated near its top. Its broken condition "is owing to decomposition and disintegration, and not to any violent disturbance producing ruptures. GEOLOGY OF BRITISH GUIANA. 199 Tuanu-sararu cataract is formed of gray fine-grained granite, ■with a slight disposition to a foliated structure. This rock, which occurs all the way to Pantsikameru cataract, is more or less schis- tose in parts, breakiag up at times into spindle and tabular pieces, but not externally exhibiting foliation, and occasionally appearing in massive rolls. It appears to me to be a rock, intermediate in composition between quartz-porphyry and granite. Beyond the last-mentioned cataract common granite appears, and is soon after succeeded by the intermediate variety. The rocks thereabout have the black coating so frequently seen upon them, but which is- not found of the same sort on any rocks further down the Cotinga river. This polish does not appear to me to be a deposit from the water, but the result of a chemical action of the latter upon the decomposing sm-face of the rock. A copper coloured rusty-looking polish is seen on some of the rocks in the lower parts of the same river. The rocks forming the great ridge between the savanna and the valley of the Waiquah river, are composed of a whitish granite containing but little mica, which has quartz veins in it. This huge roll of granite is continuous with that at the Unamara river, and skirts the edge of the quartz-porphyry. Near the pass on the ridge there are two curious rocks, one called Piatzang, which is very large and tabular, and the other of a rounded form, and having a height of about 20 feet, is spht vertically and horizontally into four divisions, aU of which are weathering into spherical masses. On the northern side of the Waiquah valley a boss of the same granite appears through the porphyry. Cursato mountain on the Takutu savanna is composed of granite of a slightly gneissose character, and has large glassy felspar crys- tals throughout it, similar to that of the western end of the Canucu mountains. Its sides are covered with blocks and masses of this rock, resulting from decomposition and subaerial denudation. The whole group of mountains between mount Cursato and mount Pinniyette are of a gneissose granite, containing quartz nests here and there. East of Pinniyette are low ridges of granite, lying almost due east and west, which are situated one behind the other at intervals, so that in going south to the Coarawow river they are crossed at right angles, and are found to change gradually, until they quite lose all trace of a parallel arrangement of their mica. This granite is of different textiu-es, sometimes coarse and at others fine, and its mica is usually green, changing sometimes to black. Some granite with opalaceous quartz of a bluish colour is seen near the Coarawow river. In the beds of this and the Cumatawow river, the roUs of granite there exposed are of a coarse variety with black mica and glassy felspar crystals forming the greater portion of the rock. This granite occurs in ridges and isolated rock patches, protruding through the alluvial deposits of the savannas from the latter river eastward across to the Kupununi river south of Cau-urua, and 200 GEOLOGY OF BRITISH GUIANA. northward as far as a place midway between Catunariba and Daruwow villages. In the Tawaiwow river its component minerals are much crowded and compressed, the felspar crystals being sUghtly rounded. In the course of the Rupununi through the Canucu mountains there are two bosses of granite in the gneiss, one not far beyond Perapoko river, and the other near Aripari. Close to the edge of the Berbice river, due east of Primos inlet on the Essequebo, there is a smaU tract of syenite-porphyry, which contains a dyke of greenstone. Quartz Veins and Masses in Granite. At the great cataract passed before arriving at the mouth of the Cuyuwini river, there is a cm'ious low dome-shaped mass of quartz surrounded by granite, but as there are water channels completely enclosiag it, its contact with the granite is not seen. It is of a semi-transparent variety, stained with iron, and much jointed and crushed, but contains no metals. It has a slight indication of circular jointing round a centre and is 30 feet in diameter. Igneous Dykes and overlying Masses. Arrissaro Mountain is composed of horizontal masses of coarse greenstone of a greenish gray colour. It has evidently been forced up in a molten state through the granite as attested by the great dykes inunediately opposite its western end in granite rocks in the river, and then spread out over its surface to a thickness of over 650 feet, that being the height of the mountain above the level of the river. In the Curiebrong river in, the first set of cataracts, in syenite, where the river runs E.N.E. there is a great dyke of greenstone, part of a coarse and part of a fine texture. In a detached block of this rock there is a triangular block at its end, joined to it by a thin neck, produced by denudation, which has a most curious appearance. Mona cataract is composed of great coarse rocks of greenstone similar to that of Cumuti rock, and to the bedded rock at the Colomeh river tmder the sandstone. It lies in rude beds from 10 to 20 feet in thickness, and is most curiously fluted and grooved by water. It may have been at one time continuous with the Colomeh and Cumuti greenstone, and now owes its isolated position to extreme denudation. Near the Urana river on the upper portion of the Essequebo river, there is a small dyke of greenstone, 2 feet in width in the granite, and it is the only igneous rock to be seen on the river from near Murray's cataracts upwards. On the crest of the Cursato mountain there is a small dyke of greenstone, crossing a large mass or dyke of a coai'ser variety of the same rock ; both are of greenish tints and extremely hard. Not far from a small river, about midway between Catunariba and Daruwow villages, there is a ridge of partially decomposed GEOLOGY OP BRITISH GUIANA. 201 greenatone, and a similar one occurs in the direction of Saeraeri mountain. Some three miles north of this there is a low ridge of greenish rock, similar to the last-mentioned one, covered with a heavy red clay soil. On the side of this there is a large patch of dark-looking smooth rocks, covering about half an acre of ground, composed of fine specular iron ore. I could not make out whether it is a vein, or large deposit in the greenstone. During these investigations I was unable to discover any minerals or metals of value. Other products coming under the head of Economic Geology such as building stone and road material, though in great plenty, are useless owing to their distance from the coast, and the diflSculty of transporting them thither. This concludes my observations on the Descriptive Geology of the portion of the colony recently examined. 202 GEOLOGY OF BRITISH GTJIANA. EEPORT No. 10. Geological Report on the Corentjme River. Bt Chas. B. Brown. August 1872. CONTENTS. Pakt I. — Physical Features and Description of JotritNET. Part II. — Descriptive Geology. 1. Alluvium and fluvatile loam. 2. Sand and clay deposit. 3. Sandstone. 4. Quartz-porphyry. 5. Schists and Gneiss. 6. Granite syenite. 7. Greenstone. PART I. Physical Features. Having made all the necessary preparations for a long journey over the eastern portion of the colony^i^^sent my men two boats and stores by the schooner " Sophia " on the 29th of August 1871, with instructions to await my arrival at Skeldon in the mouth of the Corentyne river. Starting next morning by the overland route I reached .New Amsterdam in the evening and next day went with Mr. E. King in his conveyance to the Benab and from that in the police boat to Skeldon estate. On the morning of the 1st September my men and boats arrived in the schooner "Daylight," from New Amsterdam. The " Sophia " having had her foresail blown away was obliged to run into Berbice river and the men took passage in the " Daylight," which was on the point of leaving for Skeldon at the time. The sea breeze blew so strongly off Skeldon and in the long reaches of river southward of that place that it produced a short chopping sea in which my boats, if deeply laden, could not have lived. Consequently, I was obliged to hire a small sloop to take the stores to Oreala whilst I followed with the boats and their crews. The sloop got under weigh in the afternoon of the same day as the tide turned to run in, and we started in the boats about an GEOLOGY OF BRITISH GUIANA. 203 hour after. The Eevd. T. W. Veness accompanied me, partly for the purpose of visiting the mission under his charge at Oreala. With a strong fair breeze and tide we made good progress, and at 10 p.m. reached a small wood-cutting settlement on the west bank of the river where we remained for the night. At this place the river's bank is raised only a few feet above the ordinary high tides, and both sides of it are clothed with high forest trees, presenting the same appearance as the level tracts along the Essequebo, in its tidal portion. It also contains a number of low muddy tree-clothed islands. About three hours' paddling next morning with the flood tide, brought us to Oreala mission and village where we remained for two days. Near Apoacka river mouth, the low level coast alluvial land ceases and the Oorentyne river winds past a slightly elevated tract of undulating country that rises to a level of 60 feet above the sea, and forms perpendicular or sloping cliffs for a short distance beyond Oreala. In two places below Oreala mission the cliffs are almost perpendicular from their bases having been washed away and are therefore void of vegetation disclosing fine sections. Where the cliff is sloping at Oreala it is clothed with taU trees, which only reach as far as its crest. Behind this comes a large tract of open country similar to the Kupununi savanna and having the same vegetation. Opposite the site of the Mission the river comes from the eastward, and between it and the high land lying N. and S. there is a tract of low level alluvium some 8 feet higher than the ordinary higher than the ordinary high tide level. This borders it as far as Siparuta where the river again passes along the edge of the high land. The trees growing upon this high tract are very different in size and appearance to the mora trees on the low land bordering the river and the couridas of the swampy lands below Oreala. They are chiefly of small stunted growths of Bartabally, Haiawah, Baracara, &c. On Monday the 4th we left Oreala with the rising tide at 7.30 a.m. and at 10.30 a.m. reached the Siparuta cHffs. These are about 80 feet in height and similar to those of Oreala. The river there makes a great bend to the eastward,* then north for a short distance turning gradually to the eastward again, and then south-eastward as far as Apurn, where it changes its direction to the south-west, north-west, and finally due west to a point not far to the sotith of Siparuta at Parura river. We remained for the night at a small Arowaak village called Apurn, where the banks of the river were about 12 feet above the high tide march. > The tide being against us nearly all the forenoon of the follow- ing day and then only flowing for some three hours in the afternoon, prevented our accomplishing as great a distance as we had done on the previous days. We therefore did not get far beyond Kayaiwa cliffs before night set in. These cliffs are * These and subsequent courses refer to the du-eotion of the river in ascending it. 204 GEOLOGY OF BRITISH GUIANA. similar in height and composition to those of Siparuta, and are parts of the same high land. On Wednesday 6th we had the current running strongly against us all day, the tide not reaching so far up as this (owing to the height of the river at the time), but only damming back the water, thereby causing it to rise a foot or two without checking its north- ward now. We met with the first rocks protruding above the surface of the water in the vicinity of the Matapi river, a amall branch on the east side, and in the afternoon the first hill or low ridge lying in an east and west direction, nearly opposite to Tomatai. Passing the mouth of the Cabalebo, a large tributary coming in on the east, the river bent suddenly round to the westward for a consider- able distance. The next morning Mr. Veness who had accompanied me thus far turned back in a corial which three Indians from the mission had brought up in our company for him. A short distance beyond Tomatai there were numbers of rounded rocks forming small rapids, while on the northern side of the river there was a low ridge, some 150 feet in height, lying east and west. Turning a slight beiid, where the river alters its course from west to west- south-west, we came to some large rolls of granite, lying N. and S., forming two or three small islands. The river onwards for four or five miles was straight, and lying beyond it was a range of lulls some 200 or 300 feet in height. At the end of this long reach there is an island some three miles in length, beyond which are numbers of very large rounded granite rocks forming the rapid of Baccacai. The banks of the river in this part are some 10 feet above the level of the water, showing a gradual rise in the level of the country from the coast upwards. Later in the afternoon we came to the place where the river ran, through the low hiUs we had seen in the morning, and there its width was narrowed to about 300 yards, but widened again on passing through them. Our course next day up to 11 a.m. was in a south-west direction, along a fine expanse of river with granite rocks of rounded forms scattered here and there in its bed. In a south-west bend ws passed a large island called TuwabaUi, and early in the afternoon the islands of Oaremalambo and Languana. Beyond the latter there is a small island with huge granite rocks at its northern end. This part of the river is broad and placid, with only a slight current, and is bounded by level forest-covered country, without a single hill or mountain to seen. That night we camped on a small island in mid-river, with long sand spits at each end, one running north-east and the other south-west, and both of considerable length. We passed a few isolated granite rocks next morning, soon after starting, and then over a long distance of wide river to a south-west bend, where it again narrowed considerably, and rocks and one or two small islands were to be seen. From Akali- katabo island to Temehri rock, near which we spent the foUoAving day (Simday 10th), the river was so studded with rocks and GEOLOGY ©F BEITISH GUIANA. 205 wooded islands that In no place could a view of its full width be obtained. These islands are chiefly composed of a clayey allu- vium on rocky bases, with large loose rocks at either end, and amongst them the water flows smoothly and swiftly in- various channels. Temehri rock is a large elongated, dome-shaped mass of rock, remarkable for a gigantic Indian figure engraved upon it. We continued our journey on Monday the 1 1th, and soon came to a small cataract about a mile on, amongst rocks and islands, succeeded by two others interspersed with numerous small rapids in a part of the river lying in an east north-east direction. In three hours from the time of starting we cleared the cataracts and rapids, and gained still water above them, where the course was due south, and the river still studded with rocks. At noon we came to another rapid with smooth water above it, and with a few islands occupying a part of its channel. Beyond this the river's course was south-west for a considerable distance, and only one row of islands lined its western shore, while few rooks occurred in its bed. Next day we traversed some wide southerly reaches of the river, and in the afternoon came within sight of the western part of the Wonotobo falls. At 3 p.m. we landed at the foot to explore them, and seek if possible some passage for our boats. This is an extensive and beatiful set of falls, produced by the river passing over a granite step, lying in a north-east and south- west direction. The river is precipitated in three great and four minor channels, at various distances apai-t, all uniting in a large basin below of 4,954 feet in width, and about 400 yards in length. From the north-western corner of this basin the river narrows to 337 yards in width, and with a depth of 71 feet in its centre passes onwards in its course to the sea. Of the three principal places where the water rushes over the fall the western contains the greatest body of water, and running north-west at first curves round, terminating with a north-east course. It is a long sloping cataract, down which the water rushes in a foaming mass, leaping in waves over the rocks in its channel. Where it turns north- west it is joined, by a small but steep cataract which crosses from the head of the middle fall. The middle fall has cut its way back for a distance of some 400 yards, whilst both the eastern and western fall terminate at the ends of the rocky islands which sepa- rate them. It is by far the most picturesque of the three, and is very nearly perpendicular. The eastern fall curves round from due north to west at its foot, being turned by a pile of rocks, beyond which lies a sand island. A small channel, about 50 yards in width, leads from the north-east end of the basin, curving from east to south-east for a distance of some 300 yards to the continuation of the falls to the eastward, which is composed of three great steps in two channels. Viewed from the basin the last 30 feet only of the falls is seen, amongst tree-clothed rocky masses, but by taking the level between the foot and the river, where we again embarked in our boats at their head, I ascertained the total height to be just 90 feet. The last rounded granite rolls, 206 GEOLOGY OF BRITISH GUIANA. producing the face of the fall, is flanked by great boulders and angular masses of the same rock, beneath which a large portion of the water finds its way down to the basin. We were engaged on the five succeeding days in cutting a path and making a portage for the boats round to the head^ of the falls on the eastern bank, a distance of 62 chains and 80 links (three- quarters of a mile), over very rough ^ound. In the forenoon on the 19th we continued our journey from the head of the portage in small channels, broken by numerous small cataracts, amongst rocks and islands. At noon we came to a large cataract where it was necessary to unload the boats. After pass- ing this the tree-covered islands were not so numerous, though the granite rolls and isolated rock masses were more so, producing a characteristic view of the usual falls scenery so common on all the large rivers of the colony. The granite rocks were of all sorts of No. 29. .^f Weathering of Granite above Wotiotobo Falls. fantastic shapes, irregularly spheroidal being the most common. Many were much larger at their apex than at their base, and some were perched upon others in such positions that it appeared as if a slight push would easily displace ihem. The whole surface of the river was one scene of confusion of broken water and white lines of foam. The total width of the river is about three miles in this part, and its sides are Hned by low hiUs of from 150 to 200 feet in height. During the afternoon we had to unload the boat twice at large cataracts, and camped at the foot of a third large one. After combating with cataracts all the following morning, we succeeded in gaining the still water above them by 10 a.m., where the river ran placidly along amongst numbers of large islands. Early in the afternoon we passed the northern end of an island, where two large channels on the west joined the main stream, which was there some 300 yards wide. We skirted this island in comparatively smooth water, broken only by a rapid here and there, during the remainder of the afternoon till evening closed in, and we camped upon it. The following day we passed the upper end of the island, which must be at least 8 miles in length, where the river bent round to the west for a short distance, and was obstructed by large rocks, forming a large cataract. Beyond this I observed three large channels running north, to the westward of the large island, and concluded that they were the ones which join the main channel, above the head of the falls. The river gradually resumed its GEOLOGY OP BEITISH GUIANA. 207 original southerly course beyond some large Islands, being turned by a range of hills some 300 feet in height, and again spread out to a great width, amongst bare patches of rock. During the afternoon we were hauling up rapids and cataracts, and there was scarcely 1 00 yards of smooth water between each. Fortunately these cataracts, with but one exception, were long and sloping, and the boats were hauled up without being discharged. Next morning we cleared this set of cataracts, and turning a short south-easterly bend of the river, traversed a long southerly reabh, where the current ran with but little force, and large islands were numerous. The width in one place, where clear of these, I judged to be 600 yards. In the afternoon we passed up another set of high sloping cataracts, the rocks of which were of a dark brownish black colour, and the coating of iron oxide. On the following morning the course traversed was due east for a couple of miles, and the stream was studded with islands; it then became south-east for a few miles, in a wide channel with numerous rapids, and but one cataract. Beyond this the river was smooth and ran with a very slight current, spreading out to some 500 yards in width, but still having, a row of islands along its western side. I had no means of measuring it, so densely clothed were both banks with foliage to the water's edge, render- ing the measurement of a base line an impossibility. As it con- tained huge rolls and masses of gneiss rock here and there, inter- mixed with small islets, it presented one of the characteristic views of tropical river scenery. On Monday, 25th, we passed along a great southerly reach of some 6 miles in length, at the end of which there were some hills, with a peak of greater height than any we had hitherto seen. As we approached these hills, which were on the west bank, the river's course became clear of islands ; and spreading out to a width of over a mile, its bed became studded with large rounded granite rocks. Here the river bent round to the south-east for some distance. Next day our course was south-east, generally in channels amongst large islands, where small cataracts and rapids were numerous, the water lying in apparently still pools above each. On the rocks of these, where the water was most deep, were im- mense numbers of the large species of lacis with beautiful pink flowers. In small channels atnongst these masses of plants (spread out for acres in extent) the water found its way, and upon them the footing for the men was exceedingly insecure, and the labour of hauling up rendered more tedious than usual. On the following forenoon some low hills were seen, and soon after, on rounding a bend of the river, we came to the foot of the great cataract, which Sir E. Schomburgk has named King Fre- derick William the Fourth fall. The remainder of the day was spent in exploring the spot, and in searching for a good place, along which to make a portage. Selecting an even an compara- tively slight line through the forest, on the east bank, where there was a gentle gradient, we marked out a path from the foot to the 208 GEOLOGY OF BRITISH GUIANA. top of the cataracts, and were occupied till the 3rd of October in preparing the portage, and getting one boat and stores over. The distance across was 61 chains (three-fourths of a mile), with a oradual ascent to a height of 80 feet in about half that distance, and a descent of 30 feet from that to the river above the head of the cataracts. This singular set of catai-acts very closely resembles that on the ' Essequebo river, immediately above King William the Fourth's fall. The main set is on a channel along the eastern bank of the river, where the greatest body of water rushes over in two leaps, in a northerly direction, into a channel lying north-east. There it joins the water that passes over the westerly falls, and is pre- cipitate down a steep slope, with steps here and there, for a dis- tance of three-quarters of a mile to the river below. The total height of the set is 50 feet, and the two upper steps are 15 and 10 feet respectively. The 15-feet fall is 50 yards wide and of great depth, the water running in a solid mass through a gap without breaking or showing any particles of foam for the first few feet, excepting on either side, where it comes in contact with the rocks. From its foot onwards the water is converted into a mass of foam, which surges and eddies in all directions with a deafening roar down the long rock-bound channel to its foot, where it heaps up a succession of angry waves. On getting my boat to the head of these cataracts I sent back the luggage boat to Orealla for supplies, which I had arranged beforehand were to be sent there from New Amsterdam, by the 1st of October ; and with the remaining stores continued the ascent of the river on the 4th. Before leaving I gave instructions to the captain of the luggage boat to come up as for as the place where we parted, and remain there till I came down river, it being my intention to follow the Corentyne to its main source, return to meet the luggage boat with the fresh supplies, and then explore a large branch, marked on the map as the Pani river. I should have preferred having the luggage boat to come higher up river to meet us, but was afraid if it did so, that we might pass each other amongst the numerous islands. After leaving our camp at the head of King Frederick William cataract, we followed a good-sized channel on the western side of the river, and passed up a number of large cataracts and rapids, the course changing from south-west to south-east. Above these we had smooth water amongst large islands for some distance, and I found to my surprise that our course was still southerly, though from the distance we had come, if the map was correct, we ought to be travelling due east. I at first imagined that there must be some mistake in the map, but on finding next day that we were stiU going south and south-south-east, I concluded that we were on a branch of the Corentyne, that had been hitherto unknown. The river was crossed by numerous barriers of rock, forming cataracts between large islands, for a considerable distance, and then for an equal distance became studded with small islands, amongst which the water ran with rapids here and there. Some GEOLOGY OP BEITISH GUIANA. 2()9 20 miles above King Frederick William fall the islands became less numerous, and both banks of the river could be seen at one time. In this distance we passed two large streams coming in on the west side, one being 100 and the other 50 yards wide. The first, joining amongst islands, we did not observe was a creek, till the temperature of the water proclaimed the fact, it being 5° lower than that of the main river. Below the second stream there was a number of formidable cataracts, near which we spent Sunday, the 8th. Low hills lined the river above this, and its width was about 300 yards. The portion of river passed over on the 10th was more winding than hitherto, and as there were few islands in it, both banks could be seen. It also contained very few groups of rocks, and presented a fine broad uninterrupted surface, varying from 300 to 400 yards in width. Next day our course was south-south-west against a strong cur- rent amongst large wooded islands to the foot of a set ' of rapids, produced by rolls of gneiss rock lying north-west and south-east, where the river spread out to a width of three- fourths of a mile: Above this we passed the mouth of a large stream on the east, of 111 yards in vridth, and from 6 to 1-5 feet in depth, joining the main river where its width was 277 yards, and depth from 8 to 14 feet. There its course became south-west for over 2 miles, and then west for a considerable distance, with low banks not more than 4 to 5 feet above the level of the water. The river from this on became more winding, but preserved a general south-west direction for some 30 miles, then it made a bend round to the north-east for a distance of 8 or 10 miles, and finally took a general southerly com-se for some 40 miles more, crossing the second parallel of north latitude. There above a cataract a large branch comes in from the south- east, of greater width than the main river, but being shallower does not contain such a large body of water. The measurements of the two give a width of 126 feet and a depth of 15 feet for the main i-iver; and 134 feet and 9 feet for the branch. From the mouth of the large river on the east side mentioned above, there are numerous small, and one large branch creeks to this river, and on the western side there are three large streams. In this distance also, there are only two cataracts and a few small rapids ; and low hills approach the edge of the river every here and there. We followed the main river for three days after passing the branch, and in an almost due west direction, having to cut through a few " tacoobas " that had fallen across from bank to bank ; and finally came to a row of massive rounded granite rocks, lying in a south- west and north-east direction across the river, which completely obstructed the navigation. The river had attained such small dimensions, and its water was falling gradually day by day, that I did not deem it prudent to follow it further, especially as we were quite at the limits of the colony in this direction. This I ascertained by meridian altitudes of fixed stars. There we en- camped on the west bank of the river, at a distance of 410 miles 34328. , o 210 GEOLOGY OF BRITISH GUIANA. (roughly estimated) from the mouth of the Corentyne, for the purpose of making a land journey across to the Essequebo, to ascertain some estimate of the distance to that river, as well as the geology of the intervening country. Having no chronometers I could not determine my longitude, and by this trip across, hoped to be able to determine it roughly. The level of the river here was 670 feet above the sea. On Thursday 26th we started, 6 men and myself, with provisions for a few days in packs, and each armed with a cutlass, for clearing the vines and cutting off the tops of small trees, so as to mark the route for our return. We came to the foot of a ridge shortly after starting, and traversed its side for some distance, at a height of 100 feet above the level of the swampy tract at its foot ; and then descending to a small creek and manicole swamp, crossed over a ridge beyond, 300 feet high. We went entirely by compass, the men carrying their loads and cutting their way through the under- growth of small trees, tangled vines, and bush ropes, as I directed them. Crossing after this a number of low ridges, and intervening manicole swamps, of soft iron-stained bog mud, we camped at a small rivulet, after 6 hours walking, at an exceedingly slow and tiresome pace. During the two succeeding days we traversed a low swampy country, intersected with streams, some of considerable size, running in a northerly direction ; and now and then obtained glimpses of a high mountain before us, the foot of which we reached late in the evening on the second day. The land passed over was low and undulating, the soil being a dark vegetable loam lying on a stiff yellow and gray clay. Fearing that our stock of provisions would not last if we went much further, I ascended the moimtain next day (Simday 29th), to get observations. Through gaps in the tree tops .T got views of the surrounding country from east through south to west. To the north-west a mountain, one of the cluster we v/ere on, shut the view, but a level forest-covered plain, seen far off to the south- west, was the one in which the Essequebo ran. A high mountain separated from ours by a deep guUey, hid the view to the north- north-west and north-east. These are the Amuccu mountains, and the one we were upon was 1,240 feet above the sea. Its sides are precipitious and covered with great masses of rock, one of which near the top was partially detached and fully 50 feet in height. The whole country from east to south-east and south to south-west, is a hilly tract of forest-clothed country, of vast ridges and domes one after another for miles and miles ; all probably of about the same height, viz. 1,200 feet. The mountain close to us to the north is evidently very much higher. Descending the mountain to our track we commenced our return walk, in order to obtain a larger supply of provisions. In 1 hour and 40 minutes walking from the foot of the mountain, we performed the distance that it took us the whole previous day to accomplish when cutting our way. This will give some idea of the almost impenetrable nature of the forest there. The following afternoon we reached the boat, obtained 7 days' GEOLOGY OF BRITISH GUIANA. 211 provisions and got back to the Amuccu mountains at 9.30 a.m on the ] st of November. On the way back I climbed a ridge and had a glimpse of the country to the north, showing some low hills to the west-north-west, north-west, and north, not far off rising from an undulating forest-clothed plain. Our route due west took us along the foot of the mountains, parallel to their trend, and over a high spur that joined their southern flank with the mountains to the south. Beyond the spur the country was again of a swampy nature and intersected with rivulets. We got a number of views of the main range of the Amuccu mountains, which appeared to me to be at least 2,000 feet in heio;ht. On the morning of the 2d we passed a tract of level country, for a distance of fully a mile where the surface of the ground was dotted with small hollows or pits, of various sizes and shapes in a most curious manner. These holes were usually circular, but often of elongated forms, and of from 4 to 6 feet deep each. The bottoms of some, were hard, of others soft, and had no fissures. These pits covered a surface many acres in extent, that to all appearence is never wholly under water, in wet weather. The surface of the ground is a hard brownish grey arenaceous clay. 'Beyond these, for a considerable distance, the country is low and swampy and full of little hiUocks and ridges of clay, as the above- mentioned part was full of pits. Passing this swamp'we had good level country, in which ran a large stream in a southerly direction with high clay banks of reddish and yellow colours. On Friday the 3rd our course led us over an undulating country at first which became ridgy, the intervals between each ridge being occupied by soft manicole swamps, containing small winding streams. The soil in these consisted of a black bog mud, upon a gray arenaceous clay and sometimes sand. The following day our journey was over a similar country where the ridges were higher and in greater numbers ; and in the afternoon we crosSisd a large creek 23 yards wide running swiftly in a north-west direction. Beyond this we had more undulating land, and this as we proceeded became more and more level. On Sunday the 5th we passed over a level tract which had evidently been recently some 5 feet under water, as inferred from the mud stain on the tree leaves, and» conjectured that we were not far from the Essequebo; so pressing on with renewed hope, we had the satisfaction of reaching that river at 11 a.m., after a tedious and harassing jom-ney. We came upon a part of it a few bends from the mouth of the Cassikityu river, where its banks were high and the water flowing sluggishly. We only remained for two hours on the bank of the river to rest, and then commenced our return journey with aU possible haste. Having a well defined, though exceedingly rough, track to follow, we went alone at a good pace, and reached our boat on the after- noon of the 7th. The distance . traversed from river to river I estimated at 30 miles. I measured the width of the river at our camp immediately below the granite rocks, and found it to be 74 feet wide, and 6 feet . o 2 212 GEOLOGY OF BRITISH GUIANA. in its deepest part, its current having a velocity of 1 ■ 73 mile per hour. The explorations of this part having been completed, we started on our voyage down river to King Fredrick William's fall stopping at the first open sand beach for the purpose of procuring altitudes of stars for latitude. There I remained two nights for that pm'pose, and succeeded in getting good observations of meridian altitudes of a) Eridani, aj Cassiopeia, and 3) Pisces Australia, from the mean of which I obtained the latitude as 1° 49' 55" north. I failed in getting satisfactory altitudes of four other stars, owing chiefly to thin misty clouds, tha^ from time to time passed across the sky. During the remainder of the journey down to King Fredrick William's fall I obtained the latitudes of our various camps. On Saturday the 18th we reached the head of a large catatact which we passed up on the 5th of October ; and next day in going down it we took a channel which led us more than two miles to the eastward, bringing us out at mid-day on a large river, apparently joining this in an easterly direction. This I at once concluded was the Corentyne river of Schomburgk's map, which we had missed by following the western side of the river after passing King Fredrick William falls. Running down it in a west- south-west direction for a distance of seven miles, we passed numbers of large channels of the river we had been up coming into it on our left hand, and at the western end came to the main channel by which we had ascended. During the afternoon we ran down a number of dangerous and difficult cataracts, and arrived at our old camp at the head of King Frederick William's cataracts, where we found the crew of the luggage boat awaiting - our arrival. Giving my men one day's rest we ascended the river with both boats to the branch river on the west spoken of above, and com- menced our ascent of it. Our course was at first east-north-east for some distance, up numerous small rapids, then curved to the northward and eastward in a wide channel. Here two large islands abreast at a cataract — marked Goodall's on the map — ■ divided the river into three channels. I purposely traced the south bank of the river to see if there was any communication between it and the other river, but found none. It is very evident from the map that when Schomburgk saw the large channels of the new river he imagined them to belong to this river, which he had descended, thinking that they branched off at Goodall's cataract. We passed up another cataract beyond on the 23rd, where the water was very shallow owing to the river spreading out so much, and came to smooth water above, where the river lying in one channel, bent from east to north and- then to east-south-east. Then came a few islands, and a wide shallow cataract with a long slope of good height. At this place the river turned east for some distance, and then altered its course suddenly, coming from the south. This point is named Point Right About on the map, and the river has a comparatively GEOLOGY OF BRITISH GUIANA. 213 straight course from it for some 12 miles In a southerly- direction. Early in the afternoon of the 25th we came to a small branch on the west, occupying the place assigned to the mouth of the Pani on the map, but instead of being of equal width to the Corentyne at their junction as there niarked down, I found it to be 23 yards wide and 7 feet 6 inches in its deepest part.* From these dimensions this river cannst have a greater length of course than about 20 miles, whilst on the map it is made to rise in the i Amuccu mountains, and has a course of 125 miles given it, making it actually cross the position of the new river. From this on to its junction with the Cutari the Corentyne has a winding course, sweeping round in great curves and keeping a general south-south-east direction for the entire distance. Here and there at long intervals it is crossed by rocks forming small rapids, and in two places large cataracts, one just below the Sipariwinni river mouth, and the other not far below the mouth of the Cutari river, called Sir W. Raleigh's cataract. In many places low wooded hills can be seen approaching its banks. On December 1st we arrived at the foot of Sir. W. Raleigh's cataract, which is in two steps, one of 10 and the other of 6 feet, composed of coarse granite rock. In hauling up this next day we found a woodskin with three paddles in it, tied to the trees at the side of a small island, showing that a small party of Indians had been ascending the cataract when we arrived at its foot, and had been so alarmed at the appearance of two large boats that they had abandoned their things and fled. During the afternoon we encountered many rapids and came to a fork of the river, the branch on the left hand being the Curuni or Corentyne, and the one to the right being the Cutari. Of these the former appears the larger, but as the latter is marked on the map as the boundary of the colony I ascended it and came to a large cataract in the afternoon. Continuing our journey on the 3rd we came to another fork, and took the branch to the right, it being the Cutari, and the other the Aramatau. The former at their junction is 146 feet wide and 19 feet in its deepest part ; whilst the latter is 137 feet wide and 10 feet deep. We ascended the Cutari for five days, passing on the 4th day at noon the site of an old provision ground and village now overgrown with lofty cecropias, palm trees, and shrubs. This evidently is the place at which Sir R. Schomburgk embarked on his memorable descent of the Corentyne river. From his reports to the Geographical Society it will be seen that in the year he attempted an ascent of that river, but was unable to get his boats past Wonotobo falls. Some years after he crossed * On my return down river after the winter rains had added to their heights, I fonnd the Pani riyer to be 30 yards wide and 10 feet deep ; while the Corentyne close by was 186 yards wide having a uniform depth across of 15 feet, except in one place where it was 17 feet. 214 GEOLOGY OF BRITISH GUIANA. over from the Qiiitaro savanna, to the Essequebo near its source, and from that by the Capu and Wanamu rivers to the head of the Ontari, descending it and the Corentyne in woodskins, reaching the coast in safety after undergoing many privations. From the 8th of November the long dry season began to break up, and we had frequent light showers from that time up to the end' of the month, when the heavy rains set in, and the river began to rise steadily. On the night of the 7th of December the river rose 25 inches, so that it was in flood, its water being turbid and laden with sediment. All the rocks in the river were hidden, and its bank only a foot or two above water. Had it not been for this rise of water, we could never have gone so far up the Outari as we did, and though we cut through a great number of " tacoobas " (fallen trees), yet we passed over a much greater number. We had also to cut through the branches of trees, that overhung the water in many places, meeting together in the centre of the stream. One of the last fallen trees or " tacoobas " cut through was 2 feet 9 inches in diameter. The river became very narrow being in one place where I measured it on the way up, along a log, only 64 feet wide and 9 feet 6 inches in its deepest part. The banks were low and the adjoining land y-ivampy, being intersected with small branch streams. I could not ascertain the latitude of the furthest point reached, nor in fact any point on the river, owing to the rainy and cloudy state of the weather. I considered however from my sketch survey that we were only about 8 miles from the southern boundary of the colony, and the barometer showed a height of 700 feet above the sea. During the night of the 8th the river feU. 14 inches, and was rapidly falling, so I considered it better to descend whilst there was water enough, in case the rains ceased and the river subsided to its ordinary level, leaving us without sufficient water to float our boats, and thousands of tacoobas to cut our way through. We accordingly descended the Cutari, and arrived at the mouth of the Aramatau river on the morning of the 1 1th. We measured these two rivers at their junction, and found the Outari to be 146 feet wide with a maximum depth of 1 9 feet, while the Aramatau was 137 feet wide and 10 feet deep. Ascending the Aramatau for a day and a half, we came to a high set of cataracts where the river spread out in little channels over the face of a roll of rock. This river lies in a valley between low hills rising from 150 to 300 feet above it, its course is southerly. It was also falling so I did not deem it prudent to go any further, but remained a day at the cataract, in order to get an observation for latitude. The sun shone for a short time in the afternoon, and the sky became cloudy, but by 7 p.m. it cleared again and remaraed so tin 10 p.m. during which time I procured a good meridian altitude of a) Eridani which gave the latitude as 2° 6' 26" N. , On the 13th we turned the bows of the boats down stream, having completed all the requisite investigations in this quarter, and were glad at entermg on this stage of our journey, not so much with the prospect of retm-ning to the coast, as to get out of GEOLOGY OF BRITISH GUIANA. 215 these narrow, damp, and gloomy streams Into the wide main river again, where we hoped to meet with finer weather. Arriving at the junction of the Cutari and Curxmi rivers I measured the width and sounded the depth of both, finding the former to be 72 yards wide with a maximum depth of 17 feet, and the latter to be 75 yardsj and maximum depth 14 feet. The rapids below this are exceedingly dangerous, the river widening out and becoming so shallow that it was difficult to steer safely amongst the numerous pointed rocks. Below the Sipariwini river we found an Indian path, and followed it for a short distance, arriving at a small village, where there were no people, but as there were many articles of household use, some bows and cutlasses of Dutch manufacture, "we concluded that the inhabitants had only gone away for a time. We also saw numerous old encampments, and some large locust trees that had been cut down and stripped of their bark. On the 20th we arrived at the junction of the main channel of this, and the small channels of the new river, and measured its width and depth, finding it to be 138 yards wide with depths across varying from 8 to 28 feet. On reaching the main channel of the new river we found it to be 272 yards wide, having a depth from west to east varying from 6 to 30 feet. From these measurements it wiU be seen, that the new river is fully twice the size of what has hitherto been regarded as the Corentyne river, but which really is only a branch. We crossed King Frederick William's portage on the 21st, and ran down the numerous cataracts between it and Enapogo, a spot some 12 miles above Wonotobo falls, spending Christmay Day encamped on an island near the 4th parallel of latitude. From the foot of Enapago we made a land journey across to the Berbice river, cutting our way through the forest in a due west direction. We started on the 26th at 3.30 p.m an J passing over a slight rising rocky ground at first, came to a swamp containing pools of water, covered with a rusty scum, and strongly impregnated with iron oxide at which we camped for the night. There was originally an old path from this to the Berbice but all trace of it has lonof since been effaced by the growth of trees upon it. The next and two succeding days we continued cutting our way through the dense undergrowth of the forest over a slightly undulating tract of country, and across numbers of small streams, some containing clear and others dark brown water. The subsoil was usually composed of white sand, and the soil in the vicinity of the dark water creeks was a bog earth, filled with matted roots, some- what resembling a sort of peat. On the 28th we passed at mid-day through a white sandy track, where the growth of forest trees was low, and of a difierent sort to the rest of the forest called by the Indians " Murie bush." On the 30th at'an early hour in the morning we came to the edge of the Berbice river, at a part where is was some 60 yards wide, and running with a very slight current. After resting a short time we turned about and made our way back to our boats on the 216 GEOLOGY OF BRITISH GUIANA. Corentyne, arriving there at mid-day on the following day, having taken just 8^ hours quick walking to accomplish the distance which 1 estimate at 16 miles. In walking over such a rough track as rapidly as possible, the delay caused by stepping and climbing over large logs and tree roots, is so great that it requires a great amount of exertion to keep up a speed of two miles an hour. Late in the afternoon of the Ist of January 1872, we reached the head of Wonotobo falls, having run the great set of cataracts above them in safety, but at a very great risk,; and next day carried our boats and few remaining stores over our portage to their foot. We experienced a good deal of rain all the way down the river and on our jom-ney across to the Berblce, so that I was glad to have the tent of my boat, which had been left there in September last, once more erected as a protection from rain and sun, having been just 3 months and 20 days traveUing in an open boat, with scarcely any protection from the elements. We left Wonotobo on the 4 th and arrived at Apura village at 11 p.m. on the 6th taking up our quarters in an Indian house for then ight, and next''day (Sunday). I spent one day at OreaUa to re-explore the cliffs and savanna, and at 8 p m on the 9th left on my way to Skeldon, starting with the falling tide, and taking advantage of the cool of the night. We had a strong head wind with a drizzling rain about midnight and paddled on till the tide turned to run in, when we made fast to the bush in a sheltered spot, at 2.20 a.m. Fortunately the rain ceased as the tide washed and we aU got a little sleep. At 7. a.m we continued our journey and reached Skeldon wharf at 11 a.m. There was only one schooner at Skeldon bound for Berbice, but it was too small to carry my boats, so I remained for three days at Skeldon House the guest of Dr. Leary, awaiting the arrival of a larger schooner, which was expected. At Skeldon Mr. N. Winter and myself made a slight exami- nation of a singular mound of sand, in which we found bones of animals and Indian pottery, clearly proving that it was the site of an ancient Indian village. He was fortunate enough to find a curious little image carved in a sort of Jade, which once was used as an amulet. Stone hatchets having been found there clearly proves that the original occupation of the place dates back to the stone period of this country. On the morning of January 14th, I left Skeldon in the schooner "Daylight," with my men and boats, and arrived at New Amsterdam in the afternoon. PART II. 1. — Alluvium and Fluvatile Loam. The land bordering the mouth of the Corentyne river is com- posed of alluvium similar to that along the coast of the colony. This continues uninterruptedly along both margins of the river in GEOLOGY OF BRITISH GUIANA. 217 a southerly direction as far as Apoacka river, where it rests against the sand beds of the Orealla deposit. It spreads away east and ■west for many miles, forming an enormous tract of low-lying swampy country. Near the mouth of the river the surface of this deposit is below the level of ordinary high tides ; while opposite Powis island, some distance up, it is a few feet above that level. At the head of the tide, at the time of my visit, its upper surface was at a height of 10 feet above the level of the water. In the immediate vicinity of the coast it is composed of layers of dark clayey loam and sand, but higher up the river it consists of heavy gray and yellowish arenaceous loam. Beyond the sand beds to the river's sources, wherever it winds through level tracts, it has deposited the same gray clayey alluvium. This deposit varies slightly in its characters in different localities ; for instance, along the river, from the upper end of Siparuta cliffs to Paruru it is of a yellowish arenaceous variety, the lower portion of which is a bluish clay very thinly laminated. Opposite Mawarli island its lower portion consists of white and gray clay interlaminated with thin layers of vegetable matter. At the bend of th« river to the south of the fourth parallel of latitude there is a horizontal layer of recent brecciate conglomerate and semi-consolidated sand, occupying a considerable area upon the surface of the granite. It is stained outwardly of a blackish colour, and has a slag-like appearance. This deposit is about 3 feet thick, and is hard only on its surface. On breaking it, the conglomeritic portion is seen to consist of small-sized water-worn blocks and pebbles of granite, particularly decomposed, and ce- mented by oxide of iron. The sand portion is made up of angular and worn quartz grains and worn crystals of felspar, cemented by oxide of iron. On the new river, after passing the third parallel of latitude, the river's banks were not more than 5 feet above the level of the river, and are composed of a gray and yellowish gray argillaceous clay. In about the parallel of 2° 50' north latitude there is a cliff section shown of from 20 to 30 feet in height, composed of red and yellow mottled clay below with yellowish loam above. The lower portion for some 10 feet in height is decomposed granite, and has some thin vertical veins of quartz and iron oxide. Upon this is a layer of angular pieces of white quartz, with 4 feet of gravel and iron oxide pebbles partially cemented together. Above this comes gray and yellowish sandy clay, which appears to be the river alluvium elevated to this position. To the southward this passes almost imperceptibly into yellowish loam, and from that into a fine white clay. This latter rests on an extremely fine pure white sand, containing spangles of white mica. Beyond this the bank dwindles down to the level of the water in a short distance. Between the head waters of the new river and the Essequebo, in the numerous swamps bordering the small streams, the alluvium is of a dark colour, containing much vegetable matter. The tops and sides of the intervening ridges are covered with a heavy yellow clayey loam. 218 GEOLOGY OF BRITISH GUIANA. The alluvium formiEg the banks of the Cutari river is of a yellowish and sometimes grayish loam, and that on the Aramatau is precisely similar. 2. — Sand and Clay Deposit. On ascending the Corentyne river as far as the mouth of the Apoacka river, one comes to the edge of an undulating tract of land raised some 60 feet above the level of the sea, forming a cliff along the river's margin, which continues up as far as Orealla. The edge of this high land is called the OreaUa cliff, and the slightly undulating grassy plain extending westward for a con- siderable distance is called the Orealla downs or savanna. We again meet this same deposit forming the Siparuta and Kaiylwa cliffs on the west bank, higher up the river. It forms in fact a great tract of country between this and the Berbice river, stretching from the termination of the alluvium of the coast region southward to the high land, where the underlying rocks are raised to a higher level than the surface of this deposit in the vicinity of Wonatobo faUs. The structure of these beds is well shown in the three localities above mentioned. In the first or Orealla cliffs we find false- bedded layers of coarse white sand, of from 60 to 75 feet in thickness, lying in places upon irregular layers of an exceedingly fine white clay. This clay is slightly stained in lines and specks with red iron oxide. Amongst the loose and semi-consolidated sand beds are small lenticular pieces, of the same kind of hard white clay as at their base. About midway between the Mission landing No. 30. 70 FEET.< Section of Cliff at Oreala, »aSS 1. 1 foot dark soil. 2. 15 feet of red sandy loam. 3. 33 feet of white sand beds with thin seams of white clay. 4. 1 foot of white clay. 5. 20 feet of false-bedded coarse white sand. and the main cliff, or perpendicular portion between high and low water mark, there occurs a bed of fine white clay, or Kaolin, having a slightly curved surface inclining towards the river. Its thickness cannot be ascertained, on account of its position under water, only 18 inches of it being exposed during low water of GEOLOGY OF BRITISH GUIANA. 2iy spring tides. Measured along the shore, from south to north, this bed has a length of some 40 yards, of which only 25 yards is composed of true kaolin, the remainder being mixed with fine white quartz grains, which become coarser and more numerous northward, till in the distance of a few yards it changes to a white sand bed containing but a slight admixture of white clay about half way up it in the false-bedded sands. The false bedding inclines to the northward, whilst the beds themselves seem to incline to the south. At the bare-topped part of the cliff there is a superficial covering of reddish loam, 1 5 feet in thickness, with a dark soil on top. Some portions of the mixed sand and clay beds are partially consolidated, and almost resemble a friable sandstone. The Orealla savanna is precisely similar in soil and foliage to that of the Eupununi river. It is about 4 miles long, and from 2 to 3 miles wide, and is bounded by forests. Its surface is gently un- dulating, the highest part being 90 feet above high-water mark. Its soil is usually composed of a dark arenaceous loam, with brownish sand on top, blown into little patches by the wind ; but above the mission it is devoid of any superficial covering. No. 31. Sectiou of Cliff at Siparuta. The Siparuta cliffs are composed of friable beds of partially consolidated coarse white and varied coloured sands, the cementing material being a white clay. There appears to be but little regularity connected with their deposition, the whole being thoroughly false-bedded, and sometimes exhibiting a slight dip to the south ; but this latter feature may be owing to the disturbance of the face of the cliff. The direction of the false bedding, in- clining as it does invariably to the northward, shows that the 220 GEOLOGY OF EKITISH GUIANA. current at the time of its deposition ran from south northward. Interstratified -with these sand beds are layers of a fine white and sometimes brown clay in beds a few feet thick, and in others re- duced to mere thin laminae. These occur in one part of the cliff at the level of the water, and in another place close to the top. They likewise form small nodular patches, scattered irregularly through the beds. The sand beds are composed of a coarse sand, chiefly quartz, having a slightly bluish, opalaceous cast, being more or less waterworn, and sometimes exceedingly fine-grained, but never containing any pebbles larger than a pea. Where water trickles down the face of Siparuta clifi", or percolates' through the sands which are partially cemented by white clay, it seems to wash out the clay and deposit a brownish vegetable matter in its stead, giving the sands a dark brown or black tinge. The interlaminated beds of clay are also discoloured in some degree by the vegetable infiltration, which has acted more strongly on portions of the cliff over which water is now trickling. At Kayaiwa the cliffs are similar to those at Siparuta, except that the beds of white clay are wanting, and are represented by nodules and strings of the same substance. Near its southern termination, on the river's edge, there are beds of sand mixed with a sort of decayed vegetable matter of a brownish to deep black colour. This substance, intimately coating the small quartz grains, gives the rock a highly bituminous appearance. The grains are slightly opalaceous, and have a bluish cast when imbedded, which is lost on removing their brown coating. This quartz with an opalaceous appearance is probably derived from the decomposition of the granite at and above W^onotobo great cataract. These three chffs do not present clear continuous sections, being clothed in their sloping portions with shrubs and trees. Above Tomatai, on the northern side of the river, about half a mUe inland, this same deposit, rising to a height of 60 feet above the river, is met with ; its surface is covered with a dark soil mixed with iron gravel, while blocks of iron-cemented clay are embedded in it. Between its edge and the river is a level patch of alluvium of yellowish arenaceous clay, raised about 8 feet above the river's level. In crossing from the Corentyne river above Wonotobo cataracts, I passed over a band of this deposit where the white sand formed the surface of the ground, and supported a low growth of trees and shrubs quite different to those of the surrounding forest. 3. Sandstone. About a mile north of the mouth of the Cabalebo river, there is an exposure of whitish sandstone forming an island in the river. This rock is jointed and very friable, and is composed of angular compressed particles of white quartz, with very little cementing material. It contains scattered plates of silver-white mica through it, which have in some instances become of a brownish colour from decomposition. It is very diflicult to make out the position of the bedding of this rock, but it appears to have a strike nearly north and south, and to dip west at an angle of 80°. GEOLOGY OF BRITISH GUIANA. 221 Near the mouth of Tomatai river there is a small rocky island of sandstone of an extremely hard jointed variety which does not show any signs of original bedding. It is of a grayish-white colour, and is undoubtedly the same sandstone as that at Cumuti and in the Pacaraima mountains. Its component quartz grains are much compressed and but slightly rounded, while the small cementing material it contains is a slightly reddish clay, Jfear Akalikatabo island where two hills approach the river on either hand, there is a large development of sandstone, occupying portions of the river for a distance of almost one mile. It is of an extremely hard whitish and reddish variety, so completely cut up by jointage planes that it is almost impossible to trace its bedding. At the first place where it is met with it forms two rocky bluflfs, which narrow the river considerably, and is composed of a coarse hard quartzose sandstone, so confusedly jointed that its bedding can be clearly made out in only one spot, where it appears to dip at an angle of from 50° to 90° in the direction of south 1 8° west. In some parts of it there are waterworn pebbles of quartz. The alteration produced in this rock seems to consist in the conversion of its white clay cement into a felspathic material together with the development in it of some small black crystals. From this on for a short distance the river hides the subjacent rock, and then comes a continuation of the same sandstone of a finer texture, forming sm^H rapids and isolated patches. Amongst this comes a boss of granite, and beyond it a small area of sand- stone abutting against huge granite masses. No. 32. Plan representing the Association of the Granite and the Sandstone. 222 GKOLOGY OF BKITISH GUIANA. This last area has three large patches of sandstone appearing above the water, besides many smaller ones. Of these three the one seen nearest to the western shore is exceedingly altered, having been converted into a hard siliceous rock of a grayish colour, but still showing its laminated structure by weathering on its edges in lines, where its layers are of alternate hard and soft material. These lines also show the original false-bedded nature of the rock. This mass lies within 50 yards of a large granite boss, towards which it dips at an angle of 60° in a south-south-west direction. It is traversed by three small veins of granite from 1 to 6 inches wide, similar to that forming the granite mass of the south, but of shghtly finer texture. This granite contains greenish mica, much opalaceous quartz, and but little felspar, and is similar of that of the Wonotobo falls. Some crystals of opalaceous quartz are seen in the sandstone, near its contact with Ihe granite veins. The two other patches are very friable from the action of the water, but are also extremely jointed in every direction. They dip at gentler angles in south-east and southerly directions, and break easily along the lines of original bedding. They have a reddish iron crust upon them and filtered in their joints, between which the rock itself is soft and crumbles away, leaving little box like forms remaining. The most westerly patch has a few thin quartz veins in it. Almost midway between the three sandstone patches just described, there is a mass of granite running in a south-south-east direction, with a patch of sandstone firmly adhering to it. It would appear from this, and the fact of veins of gramte (similar to the mass to the southward) traversing the sandstone, that the granite of this district has been forced up subsequent to the deposition of the sandstone. The sandstone is evidently a continuation of the Maccari mountain sandstone. 4. Qtjartz-Poephyry. Nearly opposite the mouth of the Mawarli river there are some large rocks of a kind of quartz-porphyry or a variety intermediate between that rock and syenite. It is composed of grains of opalaceous quartz and green hornblende in a grayish felspathic Not more than half a mile on there is another development of the same rock, though of a slightly different nature, containing crystals of green mica instead of hornblende, and resembling a mica-porphyry. Beyond this to the first small rapid there are numbers of rocks of this kind protruding above water of a schistose nature, but with few mica crystals in them. In the easterly bend of the river above Temehri rock quartz- porphyry is again met with, and gives place to granite. It is a similar rock to that seen near Tomatai. A short distance above the head of the great cataracts beyond Wonotobo falls, a change is perceptible in the form of the rocks, and the great rounded roUs and domes give place to oblong spindle-shaped and tabular masses rising vertically above water. GEOLOGS- OF BRITISH GUIANA. 223 These are composed of a variety of felsitic porphyrj', and are of a gray colour containing a little mica. Their texture is crystalline granijarj and they appear to be of an intermediate variety between quartz-porphry and granite, or a very felsitic granite. Some 10 miles beyond the last development quartz and felspar porphyry occur. It first appears in a dykehke form close to the coarse granite of the district, but beyond it spreads out at a surface rock, rising in irregular domes and obehsks above the river. One of these latter forms is a vertical rhombic prism having a rude pyramidal termination singularly hke an enormous crystal, while another runs upwards for a height of some 10 feet, with irregular curved faces terminating in a point. This porphyry is composed of greenish-wh;te crystals of felspar with slightly rounded edges as if compressed, together with irregular patches of a finely crystalline green mineral, arranged with a sort of parallelism in a vertical direction, and a gray felspathic base or matrix with crystals of opalaceous quartz, scattered sparingly throughout. The green mineral may be hornblende, but as the rock is slightly decomposed near its surface, it is soft and resembles mica. Owing to the area exposed being in the middle of the river amongst a labyrinth of islands and channels, its mode of occiu-rence with relation to the granite cannot be ascertained, but it probably hes upon the granite, and may be in some way connected with the greenstone dykes at the cataracts a little lower down river. In the easterly bend of the river near the fourth parallel of latitude, quartz-porphyry of the intermediate variety occurs toge- ther with gray felsitic porphyry. The quartz-porphyry besides containing crystals of quartz has also a few mica crystals On the New river close to the southern boundary of the colony two small developments of quartz-porphyry are met with, which must be extensions of the mass of that rock lying to the southward. In crossing over from the head of the New river to the Essequebo, on approaching Amuccu mountains the quartz-porphyry sets in, and is the only rock to be met with from that onward. At the foot of Amuccu mountain it is of a variety of reddish felstone-porphyry, containing greenish crystals most probably of chlorite. On the side of the mountain it is very similar to the porphyry of Mora mountains on the Kupummi river, but contains more felspar and chlorite crystals. Clear quartz crystals occur but sparingly in it, and its quartz, as a general rule, seems to be distributed in a net- work of thin veins, ranging from white opaque to transparent varieties. Some enormous semi-detached blocks of this rock stood out from the side of the mountain, and in many places the bare mass of soUd rock that formed the mountain was exposed. All along the base of the Amuccu mountain, which we skirted, the quartz-porphyry and felstone occurred, of various colours from gray to bluish, reddish and hver colour. In some pieces were small crystals of iron pyrites. 224 geology of british guiana. 5. Schists and Gneiss. In ascending the Corentyne river no gneiss is met with until the fourth parallel of latitude is passed ; but from this on to the head of the Cutari river in the second parallel, and on the head water of the New river to about 2° 25' north latitude, it forms the surface rock with only a few exceptions. Where first met with there seems to be a gradual passage from the granite to true gneiss, the intermediate rock being of gneissose granite. It is foliated, but the foliation is not shown by weather- ing on the surface," and it is jointed in a plane lying east and west inclining south at an angle of 45°. This jointing or rude cleavage resembles bedding in some degree. It weathers into curved forms resembling granite, and lies in massive rolls across the river in a direction coincident with its foliation. The direction or strike of these rolls varies in short distances from east and west to north-east and south-west. The texture of this rock is coarse, and the felspar crystals have flattened forms. It there occupies a distance of about 1 5 miles in length of the river's bed, and passes into granite. Beyond this granite the gneiss again appears and is much mixed up with granite veins, containing also a ddrk quartzose layer like that seen on the Rewa river at Eanidakeur, and in the Canucu mountains. Between this and King Frederick William IV. 's cataract the gneiss is massive, and seldom shows its lines of foliation on the surface. It contains rounded masses of green mica in small plates compressed together, sometimes sticking out from the rock at others leaving rounded cavities from which they have been dissolved. In one place this rock contained a few small crystals of garnet, and was pierced by a finely crystalline greenstone dyke. The gneiss forming King Fredrick William IV.'s cataract is of the ordinary variety, and is foliated in an east and west direction having the planes of lamination dipping north at an angle of 60°. The foliation shown by weathering is very fine and but slightly contorted, in some cases being quite regular and parallel. It is traversed by veins of coarse quartz and felspar crystals, with sometimes large crystals of mica. Some seven miles up the New river there is some hornblende schist, similar in outward appearance and foliation to the gneiss. Five or six miles further on the gneiss inclines towards mica-schist for a short distance becoming true gneiss again of a very beautiful variety, having its black mica in twisted layers round the felspar crystals, and containing large sized garnets. In many places this gneiss contains nests and strings of quartz. It is foliated in a vertical plane in a north-west and south-east direction, and its rolls usually lie in the same direction with one exception at a rapid just before approaching the hills on the west bank where they are north and south. The set of falls just below the mouth of the second large branch stream on the west is composed of a very coarse gneiss with GEOLOGY OF BEITISH GUIANA. 225 garnets, and contains a large dyke of greenstone. This green- stone is of that beautiful variety wherein the hornblende crystals have a stellate form and the felspar a greenish tinge, and is the same rock as the Tacarierimore dyke in the Ireng district. It contains whitish iron pyrites in small patches. In the other branch of the Corentyne this same dyke is met with. The gneiss there lies in rolls trending with the greatest regularity in a north-west and south east direction, being also foliated in planes with the same strike. Above this garnet gneiss and common gneiss alternate for a considerable distance, and form large high rocks rising sometimes 20 feet above the river's surface. Five miles north of the mouth of the first large river joining this on the east, there is a vein or layer of quartz-scbist in the gneiss of the ordinary schistose-granular variety. Near it the gneiss is coarse, containing very little mica of a light green colour and a large proportion of flesb-red felspar with enclosed crystals of the same mineral of a Avhite glassy variety. Just below the mouth of the above-mentioned river, where a ridge of gneiss extending across in a north-west and soutb-east direction forms some rapids, there is a high dome of this rock most beautifully foliated in every degree of contortion. A large nest of quartz, 8 feet wide and 20 feet long, is seen rising like a wall above the river in this gneiss. It is chiefly of a white coloiu", but parts are stained of an amber colour by iron. From this place on to the termination of the gneiss at the granite exposure, very little of it is to be seen in the bed of the river. In one place I observed a layer of coarse white rock, 2 feet in thickness, composed of felspar containing a little quartz and mica, resting on domes of gneiss. Beyond this the gneiss became slightly granitic containing light green mica, not far from a small roll of granite. Above the granite came a small development of true mica-schist foliated in vertical planes and followed by massive gneiss rocks for a distance of five miles to the edge of tbe granite. The last patch of gneiss is seen some distance on, and is about 4 miles in width flanked by granite. It is of a common foliated variety striking in a north- west and south-east direction ; and in one place contains a large vein of quarz and felspar with large nodular patches of quartz along its centre, which is 6 feet wide in tbe middle tailing off to points at either end in a distance of 20 feet. From tbe junction of the Oorentyne and New river up to one of the sources of the former as far as I went the whole country is composed of gneiss and schists. At the point at wbich tbis river enters tbe other the foliation of the gneiss is vertical striking east- nbrtb-east and west- south-west, and is slightly contorted. It contains nests of quartz and is exteriorly of a uniform black colour with a sUght metalic polish. This river at first follows the direc- tion of the foliation of tbe gneiss thereby leaving wall-like and tabular forms. of that rock rising up from its bed. Some distance on, after passing a dyke of greenstone, this rock merges into a sort of dark mica-schist of coarse texture, composed of dark layers of mica and white felspar, whose foliation inclines 34328. P 226 GEOLOGY OP BRITISH GUIANA, at an angle of 50° to the northward. Interfoliated with the schist is a band of exceedingly coarse granite composed of white felspar, semitransparent quartz and whitish mica. This granite is again seen some distance on in the same rock, in true layers and veins of from 1 to 2 feet in thickness. Some distance on beyond a de- velopment of dark coarse mica-chist there is a patch of gneiss, lying upon a boss of gray granite, having a thin layer, 1 foot thick, of a bluish-gray felspathic loolcing rock between them. Near the great bend called Point Rightabout there is a patch of coarse white granite, containing much felspar and but little mica, resting upon gneiss. It contains small veins and separate crystals of schorl. Directly opposite the same point a blackish mica-schist, containing small crystals of felspar, occurs. The gneiss round the bend in the long southerly reach has con- torted foliation striking east and west, and contains in one place a large granite vein, 2 feet wide, of coarse felspar with a Kttle quartz and mica and patches of crystals of schorl, some of which are an inch across. A short distance on the same granite veins containing schorl are seen intersecting the gneiss at obtuse angles to its foliation which is much contorted. Then the foliation is seen changing its strike from west to north and north-west. Where the gneiss on this river contains nests of quartz its foliation immediately becomes contorted, resembling the woody fibre round a tree knot. Some distance beyond the Pani river there is a dyke of green- stone of some 5 yards in width, running north and south, above which the gneiss is foliated at a high angle dipping east and striking north and south, and contains green hornblende crystals arranged in folias together with nests of quartz. Further on it resumes its original east and west strike and becomes granitic, re- sembling in hand specimens true granite^^ but viewed in mass its true gneissic character becomes immediately apparent. The dyke appears in square and angular blocks, with slightly rounded edges, crossing the river, and on the western side alters its course to the south-south-west. Some of its blocks on the river's bank are exceedingly decomposed, weathering in concentric layers of alight brown rusty colour. Where not affected by decomposition it is exceedingly hard, ringing like metal when struck with the hammer. Its crystals are intimately mingled and its felspar crystals of a greenish colour are hardly distinguishable from the hornblende with which they are associated. From this on to the rapids, some 12 miles below the Siparlwini river, the gneiss alternates with mica and hornblende-schist in the vicinity and to the south of a great mass of exceedingly coarse hornblendic rock most beautifully crystallized. This rock weathers in great blocks some of which are 20 feet in diameter, showing its coarse structure exteriorly. It is composed of large crystals of dark green pyroxene closely segregated in a fine crystalline base of felspar and pyroxene, and is a porphyritic greenstone. There appears to be also a light green semi- GEOLOGY OF BRITISH GUIANA. 227 transparent mineral in the base, probably a green felspar. This rock resembles the hornblende rock of the Casowebie and Eupununi rivers on the Takutu savanna described in Eeport No. 10, but differs from it in having a felspar base. There appears to be some connexion betvreen this rock and the occurrence close by of hornblende-schist in the gneiss. Im- mediately north of this mass or dyke true gneiss is again seen and continues as a surface rock up to the rapids about 12 miles above the Sipariwini river. At one place in that distance it contains two veins or large nests of quartz. The mica-schist above mentioned is of a dark variety foliated in a north-west and south-east direction, dipping to the north-east at a high angle, while some gneiss adjoining it is foliated in a similar direction, with a dip of 45 degrees. No. 33. river's bank. OUNCTION Plan of Junction of Gneiss and Hornblende-schist. No. 34. Foliated Columnar Hornblende-schist. The hornblende-schist also agrees in foliation with the surround- ing gneiss, and in one place its laminse are highly contorted. There this rock weathers in irregularly rounded, leaning columns somewhat resembling petrified wood, where the contortion is extreme but where it is not so intense it assumes a vertical position. This development abuts against a coarse gneiss foliated in an east and west direction like the schist, and at their junction the wavey texture of the latter conforms to the irregular wavey p 2 228 GKOLOGY OF BRITISH GUIANA. edge of the gneiss. Near the same place there is a large surface of rock exposed where the schist is seen doubled backwards and forwards and intermingled with the gneiss in a most extraordinary- manner. The association of the two is at once understood, if we suppose the existence of a wavey layer of schist in the gneiss, exposed by the horizontal slicing off of the rock by denudation. By this means the anticlinal waves are cut oif and the synclinal ones are hidden so that all we see is the edges of the layer along the surface of the gneiss at different angles forming most curiously woven and intermingled lines. This hornblende-schist is com- posed of black hornblende intimately blended with lenticular grains of quartz, with here and there bands of pure t[uartz of different widths, from 1 line to 4 inches, continuing of even width for a long distance at times and tailing off or forming swellings at others. Near the rapids 12 miles above the Siparuwini river there is a wide band of quartz-schist interfoliated with hornblendic gneiss in a north and south direction. The latter rock is exceedingly hard and quartzose and of a dark green colour, while the quartz- schist is grayish with small green crystals scattered thinly through- out. Its quartz-folise have a vitreous appearance and it contains iron pyrites. It is very similar to the development of the same rock on the Ootinga river described in Report No. 10. No. 35. Section and Plan of Granite Vein in Gneiss. 1. Gneiss. 2. Quartz-schist. 3. Granite. From this on to the sources of the Cutari the gneiss is inter- sected with numbers of large and small coarse granite veins and dykes. One of these dykes, 54 feet in width, is seen at Sir. W. Ealeigh's cataract where the planes of contact between it and the gneiss are easily seen. Along its southern edge the contact is very uneven and it envelopes completely a large lozenge-shaped piece of gneiss, clearly proving its injected origin. The gneiss there has its foliation in an east and west direction dipping north at an angle of 60 degrees. GEOLOGY OF BRITISH GUIANA. 229 On the Aramataw river the principal rock seen is gneiss, which is intersected by a dyke of greenstone lying along the river in a north and south direction for 8 miles. This greenstone contains large crystals of felspar and a few of hornblende, besides a glassy green mineral probably a felspar scattered sparingly through- out it. The. gneiss is of a common red variety at first with regular east and west vertical foliation. Higher up at the great cataract its foliation is contorted in a most marked manner and has a layer of interfoliated hornblende-schist, so that where the gneiss has been eroded in horizontal planes of a few feet square it has all the appearance of containing rectangular blocks of schist. In one place it contains a layer of a pale bluish-gray rock resembling a granite vnth bronze-coloured crystals of mica. It also has a band of quartz-schist containing iron pyrites. The low hills on both banks of the river are composed of decomposed gneiss from which has resulted a deep red loam. 6. Granite and Syenite, In ascending the Corentyne river to King Frederick William IV.'s fall four great granite areas are met with, and on the New river masses of the same rock come to the surface in three places. The first commences at the bend of the river beyond the first rapids above Tomatai, where this rock is seen lying in huge rolls, in a north and south direction. It is composed of coarse crystals of opalaceous quartz, green mica, and two kinds of felspar, one of a pinkish and the other of a greenish colour. The great rounded masses and blocks of rock at Bacacai rapids are formed of a coarse variety of granite similar to that above mentioned. With the exception of the small area of sandstone upon it, this granite continues all the way to the rapids and cataracts above Tamehri rock. Beyond the quartz-porphyry granite of the same variety becomes a surface rock, and continues so as far as the next band of quartz-porphyry, some 10 miles beyond Wonotobo cataract. That great range of cataracts is produced by rolls of a coarse granite lying in a nerth-east and south-west direction, composed of greenish mica, colourless and bluish opalaceous quartz, and white felspar. Above Wonotobo for three miles the same granite lies in rolls trending west-south-west and east-north-east. At the end of an island in a south-west bend of the river, not far from Wonotobo great cataract there is a patch of jointed granular quartz, somewhat resembling quartz-schist. Portions of it are white, opaque, and granular, whilst others in layers are colourless or opalaceous and semitransparent. At the foot of Wonotobo middle fall there is a large nest of a similar rock of an opalaceous variety. In the granite near the edge of the quartz-prophyry development, beyond the fourth parallel of latitude, there is another patch of jointed quartz, having a platystructure, and of 230 GEOLOGY OF BEITISH GUIANA. a semi-transparent milky variety, stained in parts with oxide of iron. Above the small development of quartz-porphyry a very coarse variety of granite appears, which contains large crystals of felspar, and continues to the large cataract situated in the western bend of the river. Further on comes the same variety of rock as at Wonotobo cataracts, thickly studded with felspar crystals ; and there a wide dyke of greenstone traverses it for a distance of 5 miles in a southerly direction. This greenstone is of a coarsely crystalline variety and greenish colour and is 30 feet in width. The next development is between this and King Fredrick William's falls where there appears to be a gradual passage from the gneiss, to a whitish granite, and then a further change into a dark granite. Just opposite the first hills of any size the granite is a coarse variety of the ordinary kind. In the granite opposite the hill with a peak there is a huge nest or short vein of quartz having a sort of schistoze structure of a white and pale amber colour. It is lying in a south-south-west and north-north-east direc- tion, is some 50 yards in length, and forks at one end. Its greatest width is some 10 feet, and it is jointed at right angles to its strike. Proceeding up the new river four developments of granite are passed over, the first being a narrow belt rising up from beneath the gneiss. The next development not far on, at the great bend of the river to the west, is composed of a dark granitic rock exactly like that I examined last year at the Taruma's field on the upper Essequebo. It occurs in one place apparently as a layer 8 feet thick, and in another in a large boss like ordinary granite. It is composed of bluish-gray quartz and felspar and black shining mica, rather coarsely crystalline. Next to this conies a kind of syenite, passing into hornblonde-schist and diorite, and then the same dark granite again. At a bend of the river there is a cliff 70 feet high, the upper 60 feet of which is composed of red loam, passing gra- dually into an extremely decomposed mass of granite, which in its turn passes into solid granite. The decomposed por- tion, 10 feet in thickness, is as soft and friable as loam, but retains its crystalline structure, as seen by the different colours of the mineral constituents ; the deep red portions representing the mica, the soft greenish patches hornblende, and the white clay rhombs the crystals of felspar, while the quartz remains un^ changed. When we see a hard rock like this thoroughly decom- posed and rendered as friable as loam to such a depth from its surface, we may. well wonder at the power of the chemical forces that have wrought such a change. It would appear that this granite runs in a narrow band in a north-east and south-west direction, and that it lies in the whitish granite of this district. At the mouth of the large creek coming in on the east granite rocks are again seen, but only appear in the bed of the river in three places onwards to the edge of the gneiss. In the second j)lace where it appears it has all the character of a vein, and is weathering in large nodular pieces with concentric layers. GEOLOGY OF BRITISH GUIANA. No. 36. 231 Granite IVeathering in Concentric Layers. \. River loam. 2. Granite. Trom beyond the narrow belt of gneiss to the furthest point of the river to which I ascended, the whole surface of the country is formed of granite, shown by small developments here and there in tbe bed of the river along the entire distance. In two places small dykes of greenstone occur, and in one spot a large dqme of gneiss 10 feet high and 30 feet in diameter, of a porphyritic variety, is seen resting upon the granite. The granite over this area is usually of a common variety, but in one place contains greenish to black mica, and in another crystals of opalaceous quartz, and twin crystals of felspar. It is usually of a gray, coarse-grained description, passing sometimes into porphyritic varieties. The last granite seen on the river, forming a barrier of great water-worn blocks across it, is of a coarse ordinary descrip- tion, and that seen for a short distance going westward to the Essequebo on the hiU sides is precisely the same. In many places the granite is seen weathering in spheroidal blocks decomposing in concentric coats ; in others large dome-shaped masses are also seen weathering in layers from a quarter of an inch to one inch in thickness. No. 37. Granite Mass Weathering in Layers. At the small rapids beyond point Kight About a coarse variety of granite forms veins or layers in the gneiss. Between the junctions of the Sipariwini and the OutaH with the Curuni or Oorentyne, numbers of large and small veins of coarse granite intersect the gneiss in various directions. The first of these occurs at the small rapid above the Sipariwini river, where it is seen as a ridge rising above the river, of a uniform width, and composed of a very coarse granite containing a large per- centage of fekpar. About two miles on three large veins of the same porphyritic granite cross the river. In these the crystals of felspar are of great size, some measuring 8 inches by 4 inches, and containing themselves small crystals of quartz and white mica. The felspar crystals of the mass of granite measure from ^ to 1 inch in diameter. In places where these dykes were seen 232 GEOLOGY OF BRITISH GUIANA. abutting against the gneiss, there is no perceptible change in the texture or arrangement of the constituents of that rock, and in one instance the dyke ran parallel to the planes of foliation. In another instance one of these dykes, 50 yards wide, ran at right angles to the foliation of quartz and hornblende-schist. Sir Walter Ealeigh's cataract is produced by a dyke of the same porphyritic, coarse granite lying between an east-south-east and south-east direction — of 18 yards in width — which sends off lateral branch dykes and veins- into the surrounding gneiss, varying in width from two inches to many feet. The chief dyke is a curious and beautiful rock, very solid, and worn into a rounded mass at the western end of the fall. On its smooth surface the edge of the large silvery mica crystals are clearly shown, forming short black stripes in every direction, amongst the quartz and felspar crystals. The quartz crystals enclose part of the mica and are colourless, the felspar liaving a reddish tinge. To the north of the great dyke there is a smaller one at the head of an island which contains minute crystals of garnet, and crystals of a greenish-blue glassy mineral in a semi-decomposed condition. At the junction of the Cutari with the Curuni there is a great jointed mass of very fine-grained granite of a reddish colour, con- taining'a large proportion of felspar, and is probably a dyke in the gneiss, lying east-south-east and west-north-west. On the Outari and Aramatau rivers granite of different kinds occurs in many places as dykes in the gneiss. In one place it contained hornblende crystals, and in another a bluish felspar resembling labradorite. In crossing from the Corentyne river above Wonotobo to the Berbice granite rocks are met with only for a short distance from the river. They are of large rounded forms rising above the heavy clay soil, and in one place are traversed by a small dyke of greenstone. 7. — Greenstone. The Matappi rocks — the first met with in ascending the Corentyne river — are composed of a grayish, crystalline-granular greenstone of extreme hardness. This exposure is evidently part of a great layer, and most probably underlies the sandstone ■which is seen not far to the westward dipping west. One mile beyond Cabalebo river a few blocks of this rock, of a greenish colour, and somewhat similar to the dyke at Cumararing in the Ireng river district, are seen. Beyond this, above the first rapids, greenstone hills approach the river on both sides, and that rock is seen in the river at their base, occupying a space 300 yards wide. It is coarsely crystalline in texture, and apparently rudely bedded. Near the northern edge of the sandstone "at Akahkatabo island, there is a small patch of fine crystalline greenstone of a dark green colour. GEOLOGY OF BltlTISH GUIANA. 233 EEPORT No. IL Geological Report on the Berbice and Demerara Rivers. By Chas. B. Brown. Januaet 1873. CONTENTS. Part I. — Physical Featuees and Desciption of Route. Part II. — Descriptive Geology. 1. Alluvium and river loam. 2. Sandbeds, Post pliocene. 3. Ironstone beds. 4. Sandstone. 5. Greenstone. 6. Gneiss and Hornblende-schist. 7. Quartz-porphyry and Pelstone. 8. Granite and Syenite. PART L Physical Features. On my arrival at New Amsterdam from the Corentyiie I made preparations for a journey up the Berbice river, and after a delay of two days finally started on the morning of the 17th January 1872 with the flood tide. We reached Mara estate that evening, and next afternoon came to the first rising ground at Bartika, where the land is raised some 8 or 12 feet above the high- water mark. The banks of the river are low all the way to Mara, being at that place very slightly raised above ordinary high water, and are clothed with low trees, bordered on the muddy slopes by moco- moco and a small leafed prickly shrub called " Boodoorie bush." Just beyond Mara the river begins to narrow considerably, the estuary seeming to end there. The Bartika savanna is situated on the east side of the river, and continues almost up to the site of the old Dutch fort and town of Nassau, the former capital, of Berbice. There the land is raised some 15 feet above the river, and on it in low forest growth are the remains of numbers of roof- less brick buildings. 234 GEOLOGY OF BRITISH GUIANA. At Diluca river there is high ground raised some 50 feet on the western side of the river, which is the northern edge of the great deposit of sand beds which forms the face of country back to the highlands of the interior. On the morning of the 20th we passed. the mouth of the Wieroni river, a fine large stream on the west, and along the foot of high savanna land extending from Peereboom to the Etunie river, taking up our quarters at a small settlement opposite the Wickie river. At Peereboom the savanna is 69 feet above the level of the river, and is portion of a great elevated tract of slightly undulating land, which spreads out both north and south, as weU as across almost to the Demerara river. The Berbice just below the AVieroni mouth is not more than 150 yards wide, and the fohage along its banks up to this is low with a tail mora tree here and there. Next day I went back on the savanna to an Arowaak villao-e to obtain a guide to take me across to the Demerara river, and then returned to the boats. On the 22nd we reached the mouth of the Etunie, and ascended it as far as the Indian village spoken of, where we obtained a guide. That night we got to the Alteka river mouth and camped. The Etunie near its mouth is not more than 25 yards in width, and like the Berbice contains very dark coloured water. It is exceedingly tortuous, and its banks are lined with low swamp bush, with the exception of that portion where it runs close to the open savanna, and expands in large rush-covered ponds in which the Itah palm grows. After passing the Alteka the Etunie is reduced to half its original width, and flows swiftly amongst swampy land, where the trees grow out of small clay hummocks. The influence of the tide is not felt above this at this season, and the water rushes down with considerable force. At 10 a.m. we reached the Arowma river mouth, and there stopped to make preparations for our land journey, upon which we started at 1.30 p.m. We took a patli leading in a westerly direction, rising gradually from the river till it became about 100 feet above its level, then over a level sandy tract of country studded with " Murie bush " and blackened stmnps of trees and logs, the latter showing that at one time it was covered with forest, which has been destroyed by fire. We came to an Indian house at 3 p.m., situated on the edge of the forest. We passed over a less sandy soil through this forest, and across several small streams (one of which was the Etuni head), coming at 5.20 p.m. to a second Indian village, at which we remained for the night. At 7 a.m. next morning we continued our journey over a path leading in a westerly du-ection, across numerous small streams, each of which ran in small deep valleys they had cut out for them- selves. Emerging from the forest to open sandy country we crossed it in two hours, and once more our way lay through bush, and over a number of streams, aU of which ran towards the Demerara river. We crossed a large creek in the afternoon called GEOLOGY OF BRITISH GUIANA. 235 Harewah three times, and at the third crossing struck an old timber path, which we followed for some distance to a cross path. Taking the cross path we came upon another timber path, then through an Indian provision field, and descending gradually came at 4.45 p.m. out on the Demerara river, at a small settlement close to the mouth of the Quitaro river, and above the .Demerara rapids. We had frequent showers of rain on the way through. We put up at the settlement for the night, and next day started in the rain for our boats in the Etunie, which we reached at 10.45 a.m. on the 26th. That afternoon we ran down the Etunie to the Arowaak village on the savanna, where we stopped for the night, and by 8.30 next morning were ag^in on the Berbice river. The banks of the river onwards are of their usual low nature, but the forest trees are more thickly interspersed with Moras. In a few places the river runs close to points of the edge of the elevated country, and in one place discloses a white cHfF of 50 feet in height. I found the courses of the bends of the river very defective on the map. After leaving the Etuni we did not see a single Creole habitation or settlement on the river's banks, and only a few Indian inhabitants are to be met with higher up. At 5 p.m. we reached the mouth of the Eberoabo river and spent the following day (Sunday) there. On Monday the 29th we came to Camacaboora village, situated on high ground, with a white sandy sterile soil, and the surround- ing foliage is stunted and sparse. The river up to Manacca presented the same appearance as lower down, being of a wadth of from 90 to 100 yards, but beyond that it contained small islands and bays at its bends, at which it widened out to 150 and 200 yards. AVe passed a cliff on the west bank some four or five miles beyond Manacca where the banks approached within 40 yards of each other, narrowing the river exceedingly, but soon receding again to their usual distance. Two rniles below the Yuwacurie river, on the west bank, there is a high sloping cHflf of white and reddish false-bedded sands, like that of Kaiyiwa on the Corentyne, which I ascended and found to be 90 feet in height. It is wooded along its edge for about 50 yards, and behind this comes a level table land of fine open grass country. Some few miles back the ground rises gently, culminating in a tree-clothed ridge, which hid my further view of the country. From the edge of the cliflf a considerable tract of forest-covered country can be seen to the north-east, east, and south-east, which is low and level for a considerable distance, and then rises in ridges of about the same level as the cliff upon which we stood. Owing to the height of the river the tide did not flow past Cama- caboora, though it had the effect of raising the water some 2 or 3 feet vertically. Next day we passed Mappa lake in the forenoon, and came late in the day to a small Indian village on the west bank, the last human habitation on the river. I landed and made inqunies from a man there regarding the position of the path to the Demerara river, and learnt that there were two higher up, one coming out at 236 , GEOLOGY OF BRITISH GUIANA. a village on that river, and the other at a creek head where there were no people nor means of descent. Obtaining a promise from him to come and guide us over on our return dovm river, we went on and camped. The river was very tortuous and bordered in many places by inlets. The general course of the river passed over on the 31st was in a more southerly direction: than hitherto, it having been almost south-west previously. Its banks '^yere also higher, its width much reduced, and bordered by a vigorous growth of tall mora trees. Upon this day we met with the first rocks, which appeared at the landing of a path leading to the Demerara river ; and camped at a spot just above the head of the tide when the river is low. On the 1st of February we passed a small stream with a cascade at its mouth, called Idure-wadde, and in the forenoon came to the foot of Marlissa rapids, the first on the river. This rapid is very narrow and shallow, and it is diflScult to see how the whole body of water passes down it, unless a good portion runs between the interstices of the rocks below. The granite rocks forming the rapids are externally of a black coloiu", from the ' oxide of iron coating upon them. The current above the rapids ran swiftly for a considerable distance. In the afternoon we reached apart of the river where it had a basin-like appearance above which both sides closed in with rocky points, leaving a passage for the riv^r between of only 20 yards in width. Above this construction the river widened out again into a large basin, and bent round to the east. At the far end of this reach the river poured down a long narrow cataract into the basin forming a pretty sight. This cataract is called Itabru, and is some 50 yards long, 20 yards wide, and from 10 to 15 feet high. At the foot almost in the middle of the rusli of water, is a large rock rising high above water. A conical hill 100 feet in height stands close to the west bank facing the fall. The northern side of the basin is a mass of rock, broken pieces of which line both sides of the fall, and form the two necks on either hand. On the south side of the fall there is a bay with a' gently sloping sand beach, from which a narrow track devoid of rocks was found leading over the neck of land and down to a little sandy bay above, evidently the old portage. We arrived at the foot of the cataract at 4 p.m and had the portage path cut through by 5 p.m camping then on the sand beach. Next day we carried the stores to the head of the fall, and took the boats on skids on the rocks up the north side. By 2 p.m we had the boats reloaded and continued our journey, coming almost immediately upon a small cataract ; and after that passed up two rapids and a cataract, camping at 4.30 p.m at the foot of a third. From the top of Itabru cataract a high massive mountain to the west can be seen, which lies in a north and south direction and must be some 1,000 feet in height On the following day we hauled up two cataracts, at one of which we had to make a portage ; and in the afternoon passed up some rapids, where the river widened out and consequently became GEOLOaT OF BRITISH GUIANA. 237 SO shallow that there was hardly enough depth of water for the boats. At 9 a.m on the 6th we came to the foot of Christmas cataracts after passing numerous shallow rapids amidst rocks and islands, and succeeded in getting the boats up the first with much labour, having to portage the stores. This cataract is 8 feet in height and is immediately succeeded by another having a total height of 15 feet down which the water falls frteejply in the centre, having cut back a deep recess, but with a long incline of 100 yards on each side. On the right hand the land rises abruptly forming a low ridge of about 100 feet. The river runs almost west from the falls foot, but above it has a sharp bend coming round from the south, across which are two more large falls. From Itabu cataract almost the whole way to Christmas cataracts, the river runs at no great distance to the eastward of a high range of mountains, portions of which have mural precipices. Here I determined to take on only one boat with a strong crew so as to economise time and ensure a successful journey to the point I was striving to gain, namely, the old camp at which Mr. Pollard and myself spent the night of April 14th last year, when we crossed over from the Essequebo. Leaving one boat in charge of three men, and taking the other with a crew of 12 men and supplies for one month's consumption, over a portage which we made, we went on. It took us just two days to clear the whole set of cataracts, and gain Stillwater above. The river, now reduced to little more than 50 yards in width, bent round to the west at the back of the hill spoken of, and then turned south for a considerable distance, where portions of its course were obstructed by small rapids, small islands, and rocks. At two cataracts we passed the river narrowed to a width of only 15 yards but widened out above them. On the afternoon of the 9th the portion of river passed up became very narrow, and we met the first " tacooba " lying across it, which had to be cut through before a passage was eflFected. This was followed by three more, and the river divided into two channels, the main one being greatly reduced in size and very shallow. The mora trees became fewer in number, and the prickly soweri palm trees grew along the water's edge. Very few rocks were to be seen ; and in the small ponds or basins at the bends the Victoria regia grew luxuriantly. Next day the part of the river traversed was very narrow, and ran swiftly past ponds and itaboos. Its banks also were low being only a foot or two above the river, and were composed of a gray soft clay extending inland, forming swamps clothed with soweri palms and low twining bush. The total width was here not more than 10 yards. Floating patches of grass spread out on the surface of the water, where it lay comparatively still, and long trailing vines and creepers hung down from the trees, whose branches stretched across, foraging beautiful wall like patches of foliage. Clusters of fallen trees or single logs lay across here and there, most of which had to be cut through to get the boat past. Many of these tacoobas of considerable size lay half submerged, and being 238 GEOLOGY OF BRITISH GUIANA. extremely hard caused serious delay in cutting them through with the axe, each requiring to be completely severed to allow one portion to sink down, and make a passage for the boat. On the 11th we passed a large branch stream of black water coming in on the south-west, and above the junction the water of main river became much lighter in colour. On the following day after passing along a similar narrow portion of the river, we came to a place where it suddenly expanded to a width of .50 yards and ran with a very slight current. Here the banks on either side became high, and the channel was not obstructed by fallen trees.. Traversing this open river we came at 4 p.m. to the end of the track we had cut when we crossed over from the Corentyne in December last, and camped not far beyond, so as to obtain the latitude of the spot by meridian altitudes of stars. This I fotmd to be 4° 15' 16" north. The level of the water in the river was some 4 feet lower than on the occasion of our first visit. The river for a distance of 3 miles beyond this lay still and smooth, with large patches of granite rock studding its bed, leavino- narrow channels between them, with only sufficient water to enable us to pass. It then became winding, narrow, and shallow again, flowing swiftly in one or more channels, and having a depth of only 2 feet 6 inches and a width of 30 feet. The branches of trees met across over head and were so thickly clothed with drooping vines that they had to be cut off with cutlasses to allow the boat to pass. Eight of the men waded ahead of the boat with cutlasses and axes, cutting off tree limbs and fallen trees, whilst the other fom- brought up the boat. No prickly soweri palms (Astrocaryum jauari) grew in this swampy portion as they did lower down. Owing to the number of " tacoobas " to be cut and branches to be cleared away, we did not go more than 1 mile by 10 a.m. next day, and during the afternoon for similar reasons our progress w extremely slow. Late in the afternoon the banks of the river became higher and the river widened and deepened a little. On the 15th we traversed a portion with very little current, where it was some 40 yards wide and with few obstructions so that we made better progress than on the preceding day. We passed numbers of ponds or inlets on both sides marking the remains of old courses of the river, and the banks were high and lined with a tall growth of Mora trees. Later in the afternoon we again entered upon a narrow swift running portion. Where the river is shallow and runs swiftly it is also very narrow, and this diminished width is owing to its passing through a low tract of country, which, when the river is flooded in the rainy season, allows the water to spread out over the neighbouring land, and so lose its widening and deepening power. On the 1 6th, in the afternoon, we came to one spot where a bar of rock crossed the river, leaving a channel only 15 yards in width, and with not sufficient depth gf water to float the boat when all hands were out. On the 17th the river improved a little in width but " tacoobas " were so numerous that we only went a distance of 4 mUes. Late GEOLOGY OP BRITISH GUIANA. 239 in the afternoon we reached a spot where the water ran in two channels in the hollows of large rocks, one being 3 feet wide and 2 feet deep, and the other 5 feet wide and 6 inches deep, the water in these two gutters flowing at the rate of 4 miles an hour, and representing the full amount of water contained in this part of the river. There we built a sort of dam of rocks and earth across the small channel, and unloading the boat hauled it up the larger one. In other rocky places the quantity of water in the river was represented by a width of 15 feet with a depth of 1 foot. At 5 p.m. we came to a place where the river ran between rocks, and was 11 feet 6 inches in width and 4 feet deep. It being late we camped for the night and obtained the latitude of the place (4° 4' 41" north), showing that we had made a southing of only 14 nules in live days. The river being exceedingly "low, (and owing to the lateness of the season there was no chance of its rising,) I was induced to abandon my boat and try and perform the remainder of the journey on foot. The following day was spent in making preparations for the journey, and on the morning of Monday 19th we started, 11 in number, leaving two men to take care of the boat in our absence. We had as usual to cut a track through vines and undergrowth with cutlasses, and kept as near the river as possible, striking across the bends when feasible. Soon after starting we crossed some low ridges, and then passed along a level tract of country to a ridge 100 feet above it. Crossing this we struck the river where it was narrow and very shallow, and camped. The^followlng day at noon we passed close along a portion of the river where it was lying in a large pool, its water apparently not running. The width of this lake-like expansion was from 50 to 60 yards for a distance of about one mile, when its banks became low and it narrowed once more. Along the western shore there was level tract some SO feet above the river. On the 21st we passed through a low country with no rocks to be seen, and on the 22nd at noon came to our old path leading from the Essequebo river, and soon gained our camp of April 14th 1871, on the edge of the Berbice. I found the river very much lower than on the occasion of my former visit, and lying in a pond-like expansion from 30 to 40 yards in \^idth. Leaving camp at an early hour next morning I commenced my return journey vrith feelings of great satisfaction, having accom- plished the object with which I set out, and by walking with all possible speed reached the boat on the forenoon of the 24th. "We commenced our descent of the river at 1.30 p.m., and after con- tending with many difficulties in shallows and tacoobas left dry by the subsiding of the river reached Christmas cataract on the evening of March 1st. In the narrow portion of the river it was so shallow that all the men had to get out and drag the boat along by main force through the sand bars, and in some places dig channels with their paddles. The water in the wide portions showed no indications of running, and its surface was covered with a thin silvery scum in some 240 GEOLOGY OF BBITISH GUIANA. places, and a slightly riisty one in others, from the salts of iron In solution being oxidised by the action of the atmosphere and de- composed vegetable matter. A small green aquatic plant also formed a dusty green covering in many parts. Next day we got the boat down Christmas cataracts, rejoining the other boat, and continued our descent of the river. Arriving on the 4th of March at a point opposite the high mountains where there was a steep rocky precipice we landed and struck off through the forest to them. After passing over a level wooded country for about one-eighth of a mile we came to the foot of the mountain, and ascended two small terraces with short levels on top of each. Then the ascent became steep up to the top to a level of 720 feet above the sea. On arriving there we made a slight detour to the left, coming to the top of the precipice, a short distance down the side of the mountain, from which a most extensive view presented itself, embracing a vast undulating tract of forest-covered country, from south-south-east through east to north-north-east. Away to the east- south-east a high dome-shaped mountain could just be discerned in the haze on the horizon, which I think must bet situated on the Cabalebo river, in Surinam. The hiUs on the Corentyne at the great easterly bend, and some low ridges to the north-north-east, were the only hiUs of any consequence in that portion of the view to reheve the dead level of the country. Stretching out from the south of the hiU we were on vras a low range which dwindled away as it reached a point south-east of us at no great distance oflF, being evidently the one marked on the map as crossing from Maccari mountain to Christmas cataracts. After spending a short time on the edge of the precipice we followed the ridge northward, and came to a deep gully lying east and west. We descended in the guUy close to the precipice, to its foot, passing some enormous blocks of sandstone on the way, and gained our boats again. Near Itabru cataract I descended the mountain on the west, which is a northern continuation of the above and of equal height. Its top is so thickly studded with trees that only gUmpses of the surrounding country can be obtained. We passed Itabru cataract on the morning of the 6th, and MarHssa rapid the same afternoon, arriving next day at the landing of the path to the Demerara river. I remained there and sent on one boat to the village, not far below, to bring up the Indian guide, who had promised to show me the way to the Demerara, on my way up. The men returned next day and reported that they found no people at the ^Tllage, that it appeared to be permanently aban- doned, and that there was a new made grave in the middle of one house. I therefore made up my mind to cross over by this path to the Demerara without a guidje, taking my chance of its coming out at a vUlage. During the remainder of the afternoon I had the necessary stores packed up in waiaries, and made arrange- ments with the men about their going down to Berbice and on to Georgetown with the boats as soon as they returned from accompanying me to the Demerara. GEOLOGY OF BEITISH GUIANA. 241 At 7.40 a.m. on the 9th I started with 11 men along the path, in a westerly direction over a slightly rising tract of country, and through some old clearings where we had great difficulty in finding our way. From that the country was level, and clothed with a low forest growth principally of " murie bush." The soil at the old clearings was a white sand, and on the level high portions of the path it was a yellowish sandy loam. We crossed a few creeks running in deep hollows or little valleys. At 2 p.m. we emerged from the forest on an open sandy tract clothed with coarse grass and small shrubs, amongst which were the blackened stems of large dead trees. This is evidently a " burnt ground " like that met with between the Etunie creek and Demerara river, extending north and south as far as I could see, bul; being not more than five miles in width. From it, looking south and south-west, were two ranges of tree-clothed hills some distance ofi", and a small ridge three or four miles to the north. On the opposite side of the " burnt ground " we came to an old Indian field, partially grown over with low trees, where the path became so obscure that it was with the greatest diflioulty we traced our way through it and got upon the well-marked path beyond. Were it not that some Indians, had recently gone through and marked the track by breaking twigs and small trees here and there we never could have found our way so faint was the trail. Late in the afternoon we came upon a long and narrow natural savanna, with a light-brownish sandy soil clothed with fine grass and sprinkled over with numerous Cucurit and Ackaiuron palms. From this, looking south-west, there was a high wooded range some three miles ofi". At the far end of the savanna we entered this forest again, and descending slightly to swampy ground with a small creek running south, camped for the night. The next day (Sunday, 10th) we left camp at 7 a.m. and going in a north-west-north direction came at 9.30 to a large stream of dark water running north. During the early part of the afternoon we crossed another large creek twice, and numerous small ones, and at 2 p.m. passed through an old Indian clearing. Descending slightly from this we came, at 2.45 p.m., to a large dark-water creek, some 10 yards wide and 3 feet deep, at which the path terminated. There, after a protracted sdarch, we found some old woodskins hid in the swamp bordering the creek, one of which was good, a second was split nearly in two but could be repaired, whilst aU the rest were mere remnants. The first woodskin was soon repaired, but the split one took us tiU dusk that night and an hour or so next morning before it was rendered serviceable. Next day I had the stores, instruments, &c., placed in the two woodskins, which just held them and one man each to propel them, and sent nine of the men on their way back to the bateaux on the Berbice, keeping four with me. At 9 a.m. we started on our journey, two of the men and myself walking along the edge of the creek in a muddy swamp, the other two bringing down the wood- skins. Eain fell heavily after we started and added to our discomfort. Our journey then wore a very dismal aspect on 34328. Q 242 GEOLOGY OF BRITISH GUIANA. account of all retreat to our boats in case of accident being cut off; besides this we did not .know at what place we would meet the Demerara river, or whether there were any villages on that part. Every now and then we shouted to the men in the woodskins so as to find each other's whereabouts, not being able to see through the thick jungle. After proceeding in this manner for some time the men on the creek discovered a woodskin, and hailing us we got together and repaired it in about two hours. We arranged the loads in this and the good woodskin, with myself and one man in the first and one man in the latter ; the two other men going in the decayed woodskin, which leaked badly. In many places we passed under fallen trees, having to lie on our backs in the canoes to get under them ; in others we had to evade or pass over some with barely sufficient water to enable our small crafts to pass, but fortunately most of the tacoobas had been cut by Indians or we never could have got along. The stream was very winding, running through a swampy tract, where it spread out in many places in two channels or itaboos, the sm-rounding land being submerged, and the trees, chiefly cork wood, growing on small islands a few feet above water. If we had not found the third woodskin our situation would have been most perilous, for we would then have had to wade from tree-root to tree-root for miles. A short time • before we stopped for the night we found an old water-logged corial, which was soon baled out, its leaks stopped, and the two men in the split woodskin trans- ferred to it. For this piece of luck we felt very thankful, it being a most unusual thing to find abandoned corials or wood- skins in even the most thickly inhabited portions of the colony. A little after 5 p.m. we camped on the edge of the creek on a spot where the high roots of a clump of corkwood trees had gathered a little loam and leaves, forming a sort of spongy island. We tied our hammocks to the trees, not being able to find any palm leaves to bmld a shelter. Early next morning (at 4 a.m.) heavy rain fell, giving us aU a good wetting. A short time after leaving camp we came out of the creek upon the Demerara river, where it was about 20 yards wide and flowing swiftly in a north-west direction. Running down stream we came to a village landing, and walked up to a small Indian settlement, situated on a slight rising ground; called Paintecobra. There we remained to rest and dry our sodden clothes and stores. That night I obtained altitudes of stars for latitude, giving me for the position of the viUage 5° 6' 53" north. These were obtained with difficulty owing to the thin vapour floating over the river, and the heavy dew which condensed on the horizon glass and sextant. The following day was spent in exploring Wahmarra mountains and the district. This mountain lies on the northern side of the river, and its top, which is level, is 762 feet above the sea, running northwards as a sort of table land for many miles. Part of the ascent was along a hunting path, but the greater portion was up GEOLOGY OP BRITISH GUIANA. 243 the sides of a small stream which was precipitated down the rocky- face of the momitain in a series of high cascades. Early next day we left the village in our two old woodskins and corial, not being able to purchase any craft there, and commenced our descent of the Demerara river. It runs in a westerly direction at first for three miles through a low swampy tract, its banks here and there being raised two or three feet above the water and then turns west-north-west for a considerable distance. Its bends are short and very tortuous, with itaboos and inlets here and there along which the water ran swiftly, having been increased by recent rains. In the afternoon the portion traversed had high banks which were clothed with Mora trees, whilst on the low swampy portions higher up the forest growth is chiefly corkwood. We passed two or three gravel beaches at the mouths of small streams where the river runs a northerly course, and in one place passed over a rapid where a bar of iron-cemented rock stretches across under water. From many bends glimpses of hills of from 300 to 500 feet in height, were obtained on both sides of the river. That evening we reached an Indian village called Anaimapeur, at which we remained for the night. As we wished to purchase strong woodskins to carry over the great cataract of Ororu-malalli we stopped at a village called Booboo, where we bought two new ones; and at Pongabi, a partially deserted place lower dovra, we procured a third. The river increased in size and had high clay banks during the forenoon, but about four mUes below Pongabi it passed through a swampy tract, and ran swiftly, having numerous itaboos. At the end of the swampy portion there is a range of hills, some 500 feet in height, lying east and west, where the river is deflected to the eastward for over a mile, resuming its full width and height of banks with Mora foliage. After passing a large inlet on the east, of half a mile in diameter, we came to the village of Orura-cobra not far above the great cataract, whose roar we could distinctly hear, and put up for the night. This place I found to be in 5° 18' 2" north latitude. We left the village next morning, and paddling down three bends of the river came to the head of the great cataract, over the portage of which we carried our woodskins, &c. Low hills approach the river on both sides, and in the gorge between them masses of greenstone rock forming barriers across the river produce this fine cataract. The river passes from the plain above in one channel at first down numerous steps of rock with great velocity, and then spreading out amongst the rocks around a group of small islands near its foot, empties itself by three mouths into a large pool below. The difference of level between the top and foot fs 63 feet in a distance of about 500 yards. In the pool there is a large island with a sand beach, and a few rocks rise above the surface of the water. From this on to Enowdah village the river widens considerably, and its banks are high. From Enowdah, on the 18th, I made an excursion to Mabouroo Q 2 244 GEOLOGY OF BRITISH GUIANA. mountain and rock, taking a guide from the village. The path led in a south-west direction along the level country bordering the valley of the Mabouroo river, at a height of about 80 feet above it, crossing the deep valleys of numerous small tributaries of that river. At noon we crossed the Mabouroo river and ascended a low ridge, some 200 feet in height, which we followed for a con- siderable distance, then turning north-west we ascended the mountain quickly to its summit, which we reached 1.10 p.m. From the top of the precipice, at a height of 844 feet above the sea, we had a fine panoramic view ranging from north-north-west through east to south-south-east. The range of hiUs at the great cataract bore south-east and ran north-east and south-west stretching away to the eastward, for a long distance south of which the country appeared to be perfectly level. The hiUy tract to the eastward seemed to continue northward for a long distance ; but as the day was squally and dense masses of mist were con- stantly passing over it, the outlines of the country northward were rendered obscure. It was difficult to trace the valley of the Demerara river, and only one patch of its water could be seen far away to the north. After spending an hour on the rock we descended rapidly and arrived at Enowdah village at 5.45 p.m., having walked back in the rain. Next day we were detained by heavy rain till noon and then continued our journey. Some distance down the river near the place where we stopped for the night, from a sand cliflf 60 feet high, I obtained a good view of Mabouroo rock bearing south 40° west. A similar mountain of the same range lying north-west and south-east, called Sarabaru, bore south 72° west. At this place I met Mr. Couchman, who kindly promised to lend me his bateau to go to town in if I waited till he returned down river in a day or two. As I was informed that we could not go beyond Dalgin "in woodskins, owing to the roughness of the river, I very gladly accepted his offer. Continuing our journey on the 20th we passed through a narrow portion of the river having numerous itaboos and low adjoining land. At Cumparu the river is deflected from its southerly course to the south-south-east for a distance of. some 10 miles, and at a short distance from that place the greenstone rocks form three small rapids having gravel shallows below each. We ran these rapids in our woodskins with perfect safety having to keep just along the edge of the broken water. On reaching the village of Waburie-cobra in the afternoon rain began to fall, and we had to put up there for the night. Next day we reached Mr. Couchman's wood-cutting grant at Camudi-cobra, and on his return down river we went, on the following morning, to his residence lower down. Hiring two men to bring back the small bateau he lent me, we continued our journey on the 23rd, passing the Quitaro river, and running down the rapids to their foot arrived late in the afternoon at Mr. Forsyth's, where we hung our hammocks for the night. These rapids impede the navigation of the river for punts in GEOLOGY OF BRITISH GUIANA. 245 the dry season, and are at the head of its tidal portion. Though the tide does not actually flow up to the rapids' foot still its influence is felt, the water there being dammed back, and rising and falling about 12 inches. On Sunday the 24th we got to Seba at 9.30 a.m., and to Ackraima in the evening, where obtaining leave from the owner, we hung our hammocks in the waterside " logic " for the night. From the extensive hill clearing at Seba there is a fine view of the country to the west disclosing a high range of hills to the south-south-west, -belonging probably to the range of the Arridaro mountain on the west, and the Tiger hills on the east. On the way down from Seba numerous small habitations are seen dotted here and there along the river's edge, giving an air of life and civilization to the otherwise gloomy river. The river at Seba is not more than 60 yards in width, but from that on it begins to widen gradually^ and at Ackaima must be at least 100 yards. At the latter place the tide rose and fell about 2 feet 6 inches, but did not flow with a swift current. In coming along next day I landed at Siberi hill and found its height to be only 153 feet, while on the map under the name of "Rashwaima hill it is marked as 250 feet. "We reached Christian- burgh at noon, and went on to Dalgin. The level of the land above high-water mark at the latter place is about 4 feet, extend- ing back from the river for 300 roods to the foot of the high sandy deposit. ' At New- Saw mills the river passes close to a cliff of the white sand deposit. Opposite the Loo the water contains sediments in suspension, and in the long reach at Kuliserabo creek the high water almost floods the land, this being the head of the estuary of the river, from which onwards it begins to widen rapidly. In the reach above this, and from that downwards, when the tide recedes it leaves narrow mud flats along the river's edge. The high sandy deposit approaches the river above Berlin, and continues as far down as Woodlands, where it recedes, coming out again at the Sandhills. Leaving Dalgin we came down rapidly with the tide to the Sandhills, where I spent a short time, and then crossing over to Phillips's obtained shelter for the night. Next day the 27th we concluded our journey by arriving safely in Georgetown after an absence of seven months. PART II. Descriptive Geology. 1. Alluvium and River Loam. The clayey alluvium of the coast extends along the Berbice river up to Baracarabana river, and is very slightly raised above the level of high-water mark. Beyond that place and at Bartika 246 GEOLOGY or BRITISH GUIANA. the banks o£ the river are composed of a yellowish and grayish arenaceous clay, raised some 12 feet above it, belonging to the river loam deposit. It is easy to distinguish between the coast alluvium and the river loam, the former being composed of various thin layers of sand and gray and bluish clay, while the latter is hx one layer of homogeneous structure. There being no actual contact seen it is very evident that they pass one into the other. The. river loam as on other rivers in the colony forms the banks of the Berbice to its source, and is seen where the river is wide and flows slowly. Where it runs swiftly through itabo portions, on the other hand, it passes through low swampy lands of gray and dark coloured recent alluvia clays. Some six miles beyond Mappa lake on the west bank there is a thick bed of impure iron oxide, similar to that seen in so many places in this colony. It very nearly resembles the iron rocks of Karanambo on the Eupimuni river, but contains no sand grains or pebbles, being as it were a mass of clay riddled with holes and ca\'ities in every direction, which are lined with hydrated oxide of iron, giving it in hard specimens somewhat the appearance of a coarse cinder or clinker. It is easy to see that water hi^ly charged with iron salts, percolating through the clay has deposited the oxide upon the walls of the cavities, but what has produced the cavities is less easy of comprehension. 2. Sandbeds and Clay Deposits. At Hitia hill this deposit is first seen upon the west side of the river, forming land raised to a height of 50 feet. The nortliern face of this elevated tract runs in a north-west direction across to the Madewini river on the Demerara. The Berbice river runs in a wide but shallow valley through these sandbeds, from this to the fifth parallel of north latitude, which narrows gradually up to that point. These sandbeds are the western extension of the great Oreala deposit, which vary very shghtly in their lithological characters in different parts. About half a mile below the Wickie river on the west bank, where the lower part of this deposit is seen at the level of low- water mark, I found it composed of pure white clay without any admixture of silicious grains. Its upper portion is much dis- coloured by red oxide of iron, and passes upwards into a gray or • white clay containing grains of sand. From this it passes into white sandbeds, and in places to a reddish loam. Owing to the fohage on the hill side hiding the structiu-e of the sandbeds, I could not ascertain whether they were false-bedded or otherwise. Upon the savanna above the soil alternates in patches, sometimes of white sand, but more fre(juently of hard reddish loam with a fine brownish sand on top. At the edge of the savanna on the Etunie river the white arenaceous clay is again seen. One would be led to believe by the map that the " Sand hiUs," as they are called, were long narrow ridges lying in an easterly direction across the low alluvial tract of cpuntry spreading from the coast inland, but this is not the case. They are in reality the GEOLOGY OF BRITISH GUIANA. 247 points of a slightly elevated tract of country seen only at intervals from the river when in its winding course it approaches their base. Near Alteka creek on the Etunie river there are. some large blocks of rock, and on the opposite side of the river a low cliff of red earth. These rocks are isolated blocks of large size, composed of grains of sand cemented firmly in layers by a blackish material composed of oxide of iron and decomposed vegetable matter, and resemble the black rocks of a similar ng,ture in Siparuta cliff on the Corentyne river. They differ somewhat in having a reddish tinge and bright red patches of a fine grained mineral substance scattered through them. These at one time formed part of the sandbeds. From the Etunie river to the Demerara this deposit forms an undulating country of from 90 to 180 feet above the sea, covered chiefly with a poor white sandy soil, but near the Demerara river with a darker soil in the valleys along the watercourses. Not far from the Demerara river the land rises and the subsoil is of a whitish clay, with numerous blocks 'of iron-cemented sands on top, and lumps of a reddish white friable pisolitic rock. The high cliff below the Eberoabo river on the east bank is composed of white clay and sand, the clay at the base being almost pure white ; the band about half way up the cHff contains a large per-centage of sand. The next section shows a thickness of about 50 feet, of which the first foot above water is white clay, then comes white sand with a thick layer of red sand, and with small quartz pebbles on top forming a thickness of 15 feet. Upon this rests 11 feet of white arenaceous clay inter stratified with layers of pure clay ; the remainder of the cliff above is a pure white sand containing small nodules of white clay. Beyond the Manacca river, and between it and the Yuwacuri, are two more cliff sections. The first consists of a white clay base vnth a curved surface, upon which rests reddish and white sandbeds. The second is composed entirely of false-bedded sands, chiefly of a pure white colour from top to bottom. About one quarter of the way up there is a band of a partially consoHdated sandbed, of a brownish colour, held together by a, large proportion of brownish clayey matter, and containing pebbles of white quartz. This section is 90 feet in height. The last section of sandbeds appears in low cliffs above the second development of greenstone rock. On the Demerara river not far below Enowdab village, there is a section of the sand and clay beds in the river's bank, showing 10 feet of false-bedded sands in thin layers resting on white clay.^ The upper part of the clay is of a light drab colour, passing into mottled purple and white or pink and white. Not far from Sarubaru river on the east bank there is a cliff 140 feet in height of white sandbeds resting on clay, which only appears at the water's edge. In some layers the clay contains coarse white sand and quartz pebbles, and has in one or two places beds of partially consolidated sand, highly charged^ with brown vegetable matter. 248 GEOLOGY OP BBITISH GUIANA, At Curicuyah pond the thin-bedded drab-coloured clay is seen, the beds having slight dips east and west, which may have been produced by a sort of slip. In these beds there is a carbonized tree stem of 6 inches in diameter, lying in a horizontal position. Frazer's cliff, Kashwima, Kuliseerabo, and many other hills, are formed of these sandbeds. The last spot where this deposit occurs in descending the river is below Sans-Souci, at a place known as the Sand hills. These hills, some 60 feet in height, are composed in their lower portion of clay, and in their upper of white sand. Besides these there are minor divisions of both, varying in com- position laterally like these at Orealla. The clayey portion at the south end of the section passes upwards into a bluish drab- coloured fine-bedded clay and from that into a coarse, black, sandy bed, impregnated with bituminous matter, like that of Siparuta. This layer at the north end of the section, where it is 2 feet thick, is very hard and composed of finer sand materials. The drab-coloured clay beneath it is of a similar thickness, and in layers of about 2 inches each. This passes downwards into a white clay having a small amount of silicious particles, and into drab-coloured clay again. The white sand portion which occupies half the height of the cliff is very fine grained, but contains a few angular pieces of quartz, and is extremely false bedded. Kesting upon its top is a dark sandy loam of 2^ feet in thickness in one part, thinning out to the northward, which contains pieces of bones of small animals in so friable a condition that they cannot be separated from the sand without crumbling to pieces. This evidently shows that the spot was the site of an ancient Indian village. The top of the clay portion at the northern end is at a lower level than the other, so that there the sand portion occupies two-thirds of the height of the cliff. At the base of the sand beds are two small springs of water, produced by the drainage of the sandbeds accumulating on the top of the impervious clay, and forcing its way out at the face of the cliff. 3. Ironstone Beds. From the level land bordering the Demerara river near the fifth parallel of north latitude, rises the mountain of Wahmara 750 feet in height, composed entirely of beds of impure brown ironstone (hydrated sesquioxide of iron), similar to that so frequently noticed and mentioned in reports on other portions of the colony. The sloping ravine, down which runs a small stream, ^ives an almost continuous section, but at the same time the water running down obscures portions of its bedding. At a cave under a cascade the bedding is clearly shown by a layer 10 feet thick, resting horizontally, or nearly so, upon a similar bed of unknown thickness. At the base of the mountain these beds are undoubtedly of sedimentary origin, containing angular grains of quartz. About half way up the mountain the beds for gome thickness are pisoHtic, whilst some are made up of aggluti- GEOLOGY OF BRITISH GUIANA. 249 nated masses of waterworn blocks and pebbles, of the same iron- stone cemented in a less hard though similar material. Some beds are very compact in parts, and are of brownsh>nd brownish-red colours. This rock occurs generally near or upon greenstone hills and mountains, as at Cumuti, Arriosano, and elsewhere. Further down the Demerara the ironstone beds are seen on the river's edge in many places, and in one o£ these contain partially water-worn pebbles of quartz, forming a sort of conglomerate. On the way to Mabouroo mountain these rocks are met with forming portions of the high ground in that region, and on the top of the mountain they are met with enclosing grains of quartz. This latter feature proves that they are of sedomentary origin and could not, in this instance at least, have been formed of decom- posed greenstone. 4. Sandstone. On the western side of the Berbice river above Itabru cataract there is a mountain range not far from the river, the upper portion of which is composed of horizontal sandstone beds, resting on quartz-porphyry. They bear a close resemblance to those at Maccari mountain, and are evidently the eastern extension of the same beds. Ascending the mountain side beyond the terraces to a height of 262 feet,. I came to the first blocks of sandstone con- glomerate, at first in small numbers, but higher up becoming ex- ceedingly numerous, and lying in confused heaps. At a height of 481 feet the true base of the sandstone formation is reached, and this rock continues to the top. No. 38. X X X X X ^ Jc >«- X ^ , ^ X ^ xJlX X X X ^ X x5c iTx x^x X XX X X X XXX X X >c X Section through Itabru Mountain, Berbice River. I. Sandstone. 2. Grey felsitic rock. 3. Felstone. 4. Alluvium.. On the surface of the sandstone on the top of the mountain there is some red and brown iron oxide, and amongst it I observed a decomposed iron-stained rock, exceedingly like a decomposed greenstone. On the eastern face of the mountain a ^eat section of sandstone is exposed, of thick beds of sandstone and pebble conglomerate, having a very slight dip to the west with & north and south strike. Between some of these beds were thin wavy layers, of fine red shale, containing plates of silvery-white mica. 250 GEOLOGY OF BRITISH GUIANA. No. 39, Section of Sandstone at Itahru Mountain, Berbice River. 1. Sandstone. 2. Red shale. 3. Conglomerate. On the face of the mountain in a gully there are a few flat slabs of coarse greenstone, which must either have been washed down from the top, or are part of a small layer at the base of the sand- stone. Some 8 nules below Marlissa rapid there is a small patch of coarse white sandstone on the eastern side of the river in a northerly bend, which is jointed and friable, and its dip and strike cannoi; be made out. Its surface rises, when the river is very low, only a few inches above water, and on either side is covered with a heavy grey loam. It is precisely similar to the sandstone crossing the river just below Cumuti mountain on the Essequebo, and the same kind of rock as crosses the Corentyne at Cabalebo. 5. Greenstone. The first rocks met with on ascending the Berbice river appear near the fifth parallel of north latitude, and are composed of green- stone of a coarse variety and dark grey colour, similar to that of Cumuti mountain, but not of so coarse a texture. They protude in small masses and water-worn blocks just above the level of the alluvium, and in the section of the river's bank. The next occurrence of this rock a few miles on is of a different variety, containing a greenish-tinted felspar and some iron pyrites. Beyond this are some beds of sandstone. No more rocks appear until a place is reached where the river makes a bend to the west and north-west, at the spot marked on the map as the head of the tide, where greenstone is again seen. Then comes an interval of alluvium, and beyond a small development of curious rock, which appears to be partly of igneous and partly metamorphic origin. It is apparently bedded dipping south-south-west at an angle of 20°, ' and its eastern portion is evidently an ancient amygdaloid (in greenstone), of a pale purplish colour, contamlng cells lined with a white mineral incrustation. The middle portion showing a dip GEOLOGY or BRITISH GUIANA. 251- is more elevated, and of a pale whitish and purplish tint, having an ashy appearance, but with a laminated arrangement of its con- stituents, which have rounded irregular shapes. In one part it contains a round water-worn flint pebble. This middle portion appears to be a metamorphosed conglomerate, and if so, it indi- cates the intrusive character of the greenstone. Close to the edge of the alluvium of the river's west bank there is a third variety of this rock of exceeding beauty, of a deep purple colour, spotted with light-red patches of angular fragments and crystals of felspar. Portions of it are also amygdaloidal with filled cells, and have small veins of a soft white wavy mineral, to- gether with small circular pieces of transparent silica. The length • of the whole development seen is not more than 20 yards, and 5 yards in width, raised to a height of 4 feet above the level of the river. A few hundred yards to the eastward are rude beds of a fine- grained purplish and light-red rock, also resembling an altered sandstone or red shale, retaining its jointed shale-like structure, and breaking easily along its planes of stratification. It contains a yellowish opaque silica blended with it in irregular little veins, and also some of the white wavy mineral before mentiojied. Close beyond this, greenstone of a greenish gray colour is seen, which forms the west bank of the river up to the edge of the quartz- porphyry and granite at Marlissa rapids. At Idure-wadde cas- cade in this portion the greenstone is composed of rude layers, forming high land on that side of the river, in the lower part of which there is a band of crystalline purplish igneous rock, similar to that described above, and differing only in being of a more crystalline texture. The rocks forming the second step of Christmas cataracts are composed of greenstone, forming a dyke of some 200 yards in thickness, rising through quartz-porphyry, and probably spreading out on its surface. In it there is a small vein of grey granite having minute branches. The surface of the greenstone on the hill to the south is exceedingly decomposed into a soft rusty rock, preserving its crystalline texture; and some blocks 2 feet in diameter have been thus decomposed throughout. In crossing over from the Berbice to- the Demerara river, in the bed of a tributary of the latter river, I observed some coarse greenstone rocks. Near the top of Wahmana mountain, on the Demerara river, I found one small water-worn block of coarse greenstone, and oil the east bank of the river in the long westerly bend below it, there were some blocks of the same rock, which must underlie the iron rock of that mountain. Layers of a coarse variety of greenstone appear further down the river, where a high hiU approaches the river on the west. This rock evidently spreads out over a con- siderable tract of country. Below this greenstone there is a patch of fin^-grained, green, hornblendic rock, weathering unequally in parallel and wavy lines on its surface, from the unequal hardness of its component parts. 252 GEOLOGY OF BEITISH GUIANA. This rock again appears at Anaimapeiir village landing, and there contains a vein of whitish granite, one foot in width, lying north and south. From the hills above Oraru village down to the foot of the great cataract, greenstone rocks are the only ones seen, and they constitute the clusters of mountain ranges in the vicinity. At the end of the portage at the foot of Ororu Mallali great cataract, a small patch of the rock underlying the greenstone is seen, having been bared by denudation. It is a sort of porphyritic syenite, being coarsely crystalline and composed of felspar crystals, placed close together with rounded edges, in a hornblendic base. The greenstone at the plane of contact is of a compact variety, becom- ing coarsely crystalline as it is traced upward from the syenite. , Along the eastern side of the basin the syenite rests partly against and beneath the greenstone, and in one place is seen in, a small round boss enveloped in the latter rock. In one part of the syenite rock there is a small vein of greenstone, showing evidently that the latter rock has been forced up through the syenite, and spread out upon its surface. Between Enowdah village and Mabouroo mountain the same greenstone is seen, resting upon the syenite and syenitic-granite, at a height of 324 feet above the sea, and from that to the top of the mountain this rock forms great massive layers, having a total thickness of 520 feet. Just below Cumparu on the north side of the river the green- stone comes to the river's edge, forming low hills, and continues for some distance crossing it in three places. At Hamacuyah landing there is a mass of this rock, and from that on to Yaramacuyah it is seen in many places. It also forms the rapids below the Quitaro river mouth, and continues from that to the Tiger hills. 6. Gneiss and Hornblende schist On the Berbice not far from the highest point reached there is a small patch of gneiss on the granite of a reddish colour containing veins of reddish felspathic granite. There is a very small development of hornblende-schist about half way down the Itaburro creek near the Demerara river. 7. Quartz-porph2/ri/ and Felstone. Before reaching the gi-anite near Marlissa rapid, oh the east bank, there is some greenish quartz-porphyry, which appears to be continuous with the greenstone. Beyond the granite again above Marlissa there are numerous rocks of felstone and quartz-porphyry, forming small islands and rapids. The first development of it is a liver coloured rock of fine grain, exceedingly jointed and hard, containing smaU thin veins of white quartz and little clear grains of quartz crystals, with greenish patches throughout the matrix. At another spot above this the true greenish quartz-porphyry appears containing rounded and perfect crystals of transparent quartz facets, of felspar, and a green GEOLOar OF BRITISH GUIANA. 253 mineral in a felspathic base. These rocks weather of reddish and white colours, are much jointed, and probably bedded, or in layers. Just before turning the bend to the eastward, which forms the basin at the foot of Itabru cataract, large rocks run out in two points on both sides of the river, continuous with the mass of rock along the north side of the basin, up to the fall itself This rock belongs to the felstone and quartz-porphyry series, and is of a very curious variety, which I have not met with elsewhere. It appears to have a rude bedded structure dipping due south at a high angle, and is jointed and irregularly broken. It is of a pale greenish white colour and coarse globular structure, being apparently a compressed mass of felspathic nodules. On examination I found it to be composed of circular pieces of pale yellowish or greenish white quartz-porphyry, embedded in a matrix of pure white felspar, of not so firm a texture as the balls themselves. The balls contain a great quantity of transparent rounded quartz crystals, besides small crystals of white felspar,' and form the greater portion of the rock ; the cementing material being of about half a line in width, filling the spaces between the balls, some of which are over an inch in diameter. In some instances "two balls have run together as it were, and become united. I have little doubt but this is a layer in the quartz-porphyry and not a dyke. The surface of this rock at the cataract has large circular pot holes worn in it by the stream, and these contain sand and quartz-pebbles of diiFerent varieties. The rocks on the south side of the cataract are of a gray and reddish felsite composed of a felspar base with embedded crystals of white opaque felspar, jointed in every degree and breaking into squares and cuniform pieces. Quartz poi-phyry and felstone continue up to the edge of the granite and are of many varieties. Beyond Itabru some distance the weathering of the quartz-porphyry gives its surface a schistose or foliated appearance. Between Itabru and Christmas cataracts to the west of the river, the surface of the quartz-porphyry exposed in the forest is decomposed for some depth, losing its colour and assuming a soft earthy texture. It is much jointed, having an earthy fracture, and passing upwards into a light greenish rock of a similar nature containing discoloured patches. In its upper part at a height of from 200 to 262 feet above the sea, at the base of the sandstone, it resembles an indurated grayish-white clay, enclosing pebbles of quartz, and its surface is covered with blocks of slaggy looking iron oxide. At the cataracts further on it is of a beautiful purplish colour with foliated texture, containing quartz crystals of the usual double hexagonal pyramid, and crystals of white opaque felspar. At an island one mile on from this the quartz-porphyry is of a greenish cblour, and exactly the same as that of Ouropocari on the Essequebo river, containing white crystals of felspar and glassy quartz. There is a dyke of greenstone near this. Immediately below Christmas cataracts the rocks are of a light green compact felstone, entirely devoid of quartz crystals or grams. The compact reddish gray felstone forming the first step of the 254 GEOLOGY OF BRITISH GUIANA. Christmas cataract is massive, and minutely jointed in vertical planes. Westward of this beyond the greenst'one dyke the rock of the third and fourth cataract is a quartz-porphyry of a reddish gray colour, containing well-formed crystals of white felspar, besides quartz, and is extremely fissile. Its main jointed planes agree with those of the greenstone dyke. Some miles on this rock passes into a porphyrite of a greenish colour, being composed of a green felsitic base containing crystals of white opaque felspar. It continues for some distance to a small rapid, where there is another dj'ke of greenstone beyond'which .it changes gradually into a coarse quartz-porphyry, containing green crystals of hornblende. This development of quartz-porphyry assumes many varieties of texture and colour, and in one place its felspar crystals are of a red colour. Some distance beyond this comes a third dyke of green* stone, in a coarse variety of quartz-porphyry containing iron pyrites. 8. Granite and Syenite. About one mile below Marlissa rapids on the Berbice river granite is met with forming a high roll, lying north-east and south- west, and from that to one mile above the rapids it appears in many places. It is finely crystalline and composed of two kinds of felspar, transparent quartz and dark green mica ; the whole rock having a reddish tinge. Beyond the quartz-porphyry some 20 miles above Christmas cataracts granite again becomes a surface rook, and continues as far up the river as I went. Where it first occurs it is of a coarse variety containing two kinds of felspar of reddish and greenish white colourSjdark green mica, and opalaceous quartz. Its quartz further on changes to a Semi-transparent colourless variety. In many places it consists of a common gray variety, and in one place is porphyritic. Near the junction of the large branch with this river, amongst many domes of this rock, is a long roll trending south-south-west and north-north-east. In two places there are large nests or veins of quartz in the granite. Some distance beyond this the coarse granite contains a large proportion of felspar, the crystals of that mineral being set closely together, almost to the exclusion of the quartz. Not far from the highest point reached the granite assumes a slightly gneissose texture and contains veins of felspathic granite, which are also seen piercing the granite where I had the last opportunity of examining it. In one place there is a small patch of finely crystalline green- stone, weathering in spherical balls with concentric coatings, close to a boss of granite. On the Demerara river a short distance below Anaimapeur village granite rocks are seen occurring here and there, and from the base of the country upon which the alluvium and greenstone rests, down to the gneissic developments at Seba. Near Anai- mapeur this rock is of a white colour containing very little mica, a few large scattered crystals of felspar, and some hornblende, being GEOLOGY OF BRITISH GUIANA. 255 a syenitic granite. A small dyke of greenstone pierces it in this portion. At Pongabi tKere are some large syenite rocks containing large crystals of pinkish felspar. The rock on which the Mabouroo greenstone rests is a syenite- granite, usually of fine texture, but when it becomes coarse it passes into true granite. Below the foot of Ororu Malalli, id the basin 200 yards in front of the fall, syenite rises above the surface of the riTer, and is there very similar to that at Pongabi, containing the same large pink felspar crystals, and having a sort of linear arrangement of its felspar crystals.- Just below Yaramacuyah a coarse white porphyritio granite is seen for about one nule, and in one spot is apparently resting upon greenstone. At the foot of Tiger hills the same white granite appears and continues as far as Arowakie creek. Near Arisaribo river mouth on the east bank it is again seen at a point. At Seba there is a great mass of granite gneiss rising 100 feet above the general level, the imperfect fohation of which lies north 73° west and south 73° east. It has a few jointage planes coin- ciding with the foliation, and some highly porphyritic bands running parallel to the same planes. Traversing it in every direction are veins of coarse and fine grained granite, of widths from a few inches to two or three feet. Some of these veins are fine-grained along their sides, and coarsely crystalline at their centres. 256 GEOLOGY OF BRITISH GTjIANA. EEPORT No. 12. Geological Report on the Mazaruni River. By Chas. B. Beown. January 1873. CONTENTS. Part I. — Phisical Featckes and Desceiption or Route. Part II. — Descbiptive Geology. 1. Alluvium. 2. Sandbeds. 3. Sandstone. 4. Greenstone. 5. Mica^schist. 6. Gneiss. 7. Quartz-porphyry and Felstone. 8. Granite and Syenite. PART I. Physical Features. The object I had in view in undertaking this journey was to determine the actual geographical position of the Mazaruni river, which I found had been placed upon the map furni.shed to the (jreological Survey far south of its true course. Also if possible to determine the position of the heads of the Ireng and Potaro rivers, which were said to have their sources in_a^ mountain called Ayangcanna. The Mazarimi was originally laid down by Mr. HiUhouse, pro- bably from a sort of sketch survey, and Sir Robert Schomburgk had adopted Mr. Hillhouse's work ^s regards the lower com-se of this river, but had I believe moved the position of its upper course considerably to the north, after having found it occupying the position of the Koraima mountain. Having procured two pocket chronometers from the Imperial Government, which, with the instruments already in the possession of the Survey, completed all that was required wherewith to obtain astronomical observations, I started on the 9th of September last from the penal settlement with my two boats and the usual number of men, and was accompanied by Mr. John Bagot, whose services I had engaged as assistant. GEOfceCfY OF BRITISH GUIAKA. 257 As we ascended the river I procured the latitude and longitude of Its various points, by altitudes of the sun and stars, filling in the intermediate portions by a sketch survey. From the head of the tide at Curutuba rapid up to Turisie, which we reached on the afternoon of the 17th, the river's course was impeded by cataracts and rapids, with still water between each ; and so studded mth tree-clothed islands that in no part of it could both banks be seen at the same time. The boatmen followed the main channel, and this led sometimes along the main land on one side, sometimes on the other, but chiefly amongst the labyrinth of islands and rocks which occupy the river's bed. These cataracts are not of a formidable nature, with but one exception in Yaninzaec, where there is a short portage for luggage, of which we availed ourselves. The others we towed the boats up in the usual manner. Before teaching the Puruni river I found that my surmises were correct, and that both latitude and Ibngitude of the different cata- racts were exceedingly incorrect. As we proceeded the error of course assumed gigantic proportions, tiU at Teboco, the most southerly point of the Mazaruni, between the 59th and 60th degrees of longitude, the river is actually some 40 miles to the north of the position marked upon the map. I need only remark that from that on to the source of the river the error never decreased in magnitude. This cannot be wondered at when we remember that from the Carabung river mouth (on the lower Mazaruni) onwards the whole of this magnificent stream has been placed down in maps by guess work, gathered from accounts given of it by Indians. When we reached Turisie cataract we saw for the first time the full width of the river, but only for a short distance above and below the place where it swept rapidly down the cataract. Above islands and rocks became as numerous as below, the water running slowly amongst them ; and so continued till we came to the Issano river mouth on the evening of the 18th, Here near the close of the day we obtained a glimpse of some of the' jutting ends of the great table land which extends southward to the'Ireng river, eastward to the Potaro, and westward into Venezuela. These seemed such an infinite distance off that one would think they could not be reached for a week, creeping slowly up stream as we were. Our course up to this had been in a south-west direction, but here it became west for a considerable distance ; and though passing a small island at long intervals, the river was remarkably free from obstructions, with both banks in view. Heavy forests lined these, the undergrowth encroaching on the water. On the north side of the river were low hills, which a little further on stretched southwards for 10 miles or so, causing the course of the river to be deflected from due north to west. Passing this north and south portion, we rounded the quick bend to the westward, cleared Teboco cataract on the morning of the 19th, and turned northwards for a distance equal to that we had traversed south. The long tongue of hiUs here is called Karanang, and averages 34328. B 258 aEOLOGT or beitish guiana. about 500 feet in height. Two large streams, the Semang and Karanang, join the Mazaruni, one above and the other below Teboco, both coming off the mountains to the south. Amongst these southern mountains is a high peak backing a flat-topped mountain, which Mr. Hillhouse has called Sir W. Raleigh's peak. These mountains are also part of the face of the sandstone mountains continuous with those seen on ascending the Potaro river. Om- com?se on leaving the Karanang mountain bend was almost due west for some 15 miles over a broad expanse of river of about half a mile'in width running parallel to the mountains on our left, at distances varying from 6 to 1 2 miles, from their base. The river then had a bend northwards past Sororieng, where a low cluster of hills on its northern side is crowned by a curious high dome of rock to which the name is attached, " Sorori " meaning swallow, and " eng " nest. We camped on Saturday the 20th on the opposite side of the river to Sororieng village landing, and next day Mr. Bagot and I went to the village some 3 miles in the forest to try and get to Sororieng rock ; but though we had a man who had promised to guide us, yet on reaching the village he said there was no path to it, that we could not go and return in one day, besides various other excuses. None of the other men at the village would go, so we bad to give up the trip and return to our camp. I hired an Indian here, who professed to know all about the river as far up as Peaimah fall, to come with me to that place to show where any villages were, in case I found it necessary to gfet woodskins for the rest of the journey, but he left us two days after. Just beyond the Sororieng the Merumd joins the Mazaruni river, coming, like the Semang and Karanang, from the high mountains to the south, and like them is a fine large stream of almost 100 yards in width at its mouth. The Mazaruni river then winds about the plain keeping a general north-west direction gradually approacffihg the base of the sandstone escarpment till at a distance of about 60 miles from Sororieng it is fairly in amongst them/ and high frowning cliffs approach it on either side. Its course here suddenly alters and it no longer flows in a south-east direction, but comes due north down the valley, or wide flat- bottomed ravine. In this distance it is joined by three more large rivers, named respectively Aping, Oarabung, and Weynamow. After passing all these large branches the Mazaruni is greatly reduced in size though still a large river. In traversing the river from Sororieng onwards day after day, we never tired gazing at the mountains on oiu- left when the clouds and mists that often veiled them passed away, and saw new beauty in them at every turn. There is some uniformity in the. general level of their tops, which shows clear indications of a table-land edge, but small rivers and streams have during countless ages marked them with indentations and ravines, and left wedge- shaped points jutting out from the face of the mass in all directions. The upper portion in general is precipitous, while the GEOLOGY OF BRITISH GUIANA. ^59 lower part comes down in a slope to the great wooded plain below. Where trees and shrubs can get a footing on their sides there they flourish, looking in the distance like moss upon a wall, but in many places where the rock is quite perpendicular, or it may be overhangingj the pinkish white 'sandstone beds show themselves as great precipices sometimes of 1,000 feet in height. Eain fell frequently as we passed along, and when the sun burst out after a shower it lit up rills of water tumbling down the walls of the rOck, which added to the beauty of the view. The castellated tops of some were very singular and almost artificial looking. Turning the bend to the south before mentioned we came to the foot of Peaimah great fall near the 61st degree of west longi- tude, and in 6° 21' 57" of north latitude, on the 1st October. I had been up as far as this before with Mr. Sawkins in November 1868, and knew the position of the portage path, so we fell to work to open it out wide enough for a bateau to be dragged through, to place rollers, and prepare it generally. We were four days in getting our boat with stores, &c. over the portage a distance of three-quarters of a mile, passing over a steep hill 100 feet above the river, and descending 50 feet again to the river above. I knew too well that there must be other and higher falls above, but not knowing where to look for Indians to get informa- tion or woodskins from, forced me to adopt one course whereby the most time would be saved, and that was to take one boat with 12 men and go on to see for purselves. We went on at mid- day on the 5th between high bare sandstone cHiFs bounding the valley on either hand, and low flat-topped hills flanking them. As evening closed in we came to a place where the flanking hills hemmed in the river on both sides, rising steeply from it. We arrived soon after at a large cataract bounded on both sides by steep rocky hills, then returned to a path end on the north bank a short way back and camped. This proved to be the portage path of Indian travellers. Sunday the 6th was spent in following it through to the head of the fall, in tracing the river's edge bacjswards half way to camp over a rough rocky country, in striking across from that point till the portage path was met, and camp afterwards reached late in the afternoon. From this day's explorations we learned that the portage path was of great length, and that as it led round a long set of very large falls it could not be shortened ; that it led from our camp up a hilll65 feet high at an angle of 56° amongst large rocks, and that from the hill top it passed over uneven rocky ground rising gradually to a height of 289 feet above its foot, descending to the head of the falls at a level of 275 feet above its starting point. This set of falls we afterwards found is called Aruwai, and occupies a distance of two miles of river. It is composed of two large perpendicular falls each of 40 feet, and a number of slightly smaller ones having a total height of 270 feet. K 2 260 GEOLOGY OF BRITISH GUIANA. There was nothing left for us to do but to begin work at once by widening the path and lashing skids up the hill side, and placing rollers all the way to the upper end. On Monday the 7th we commenced our task, and by midday on the 15th finished it. We measured the portage and found it to be one mile and seven-eighths in length. Mr. Bagot and I had constructed a rude sort of sledge by which all the stores were hauled up the hill side by blocks and tackle. We then hauled the bateau up the hill, also by block and tackle, in two hours ; and next day by 1 p.m. had the satisfaction of launching it on the river above. We had all our stores carried over and continued our journey at midday on the 17tb. W^hilst we were employed as above stated two Indians passed through the portage going up river. From them we learnt that beyond this we would meet with another set of great falls called Sericoeng, where the portage was too steep and high to allow us to take our boat over. I got them to promise to return to the head of this fall, show us the way on, and provide woodskins above Sericoeng for our further journey. They had a woodskin above the fall, hidden somewhere, and left the one they came up in. We found a fine open river above for many miles, bounded as before by high precipice walls a mile or two from either side, but with no flanking hiUs. We were now above them. Away to the south was a most singularly-shaped mountain, like a great box standing on the top of the level of the high table land whose edges approached the river. Next day, at 9 a.m., we came to the foot of Sericoeng falls, and found the portage path, Thinking it was not long I followed it vdth two men for a long distance up to 1.50 p.m., imagining every moment we would come out on the river ; but we had to turn back vpithout doing so, getting to camp at 5 p.m. On the 19th I organized a walldng party, taking instruments and as much pro- visions as possible, and started to waUc along it. As we did not get under weigh till late we had to camp before getting through. The following day, at 10 a.m., we came on the river at the foot of a large fall, at a fine extensive sand beach, and sat down to rest. We had hardly been there five minutes before we saw three Indians coming over the rocks alongside the fall above us. One proved to be the man who had promised to come and meet us. He at once told the interpreter that he had only one woodskin at his place, and could get no more. He promised to go up to another village for woodskins, which would take him five days. Mr. Bagot, myself, and the interpreter remained meanwhile encamped at Sericoeng, and the men were employed in making two journeys to the boat and back with loads of stores, it being my intention to take on as many men with me as I could get crafts for. The foot of Sericoeng falls, from which we started, was 520 feet above the sea, and the place where we again came upon the river was 1,246 feet, leaving 726 feet for the height of the Sericoeng set of falls. Of the falls occupying this height I saw only the &EOLOGT OF BRITISH GUIANA. 261 upper and lower ones, which, would acoount for 250 feet of height. This was owing to the path heing upon mountains at some distance away from the river's edge, but still not too far to admit of our hearing at times the muflfled roar of the various great falls. "Whilst there we followed the river's edge downwards for a few miles, and came to a large and singular fall where the river descended to a lower level by three great steps, the bottom one being over 100 feet in height, and perpendicular. There was a large and almost circular basin below, bounded by high cHiFs. From the north side of this basin we cut down some low bush to get a good view of the fall, and thereby disclosed the box-shaped mountain before spoken of. It was not far off, and bore due east Its shape here was very singular, and resembled an enormous cathedral in ruins^ without a spire, and with ivy clinging to its walls. Singularly enough its position was on a forest-covered glacis, seen above the hiUs to the south, immediately above the fall, so that it added greatly to the beauty of the view. On the 24th the Indians returned, saying that they had brought two woodskins and had a third at their village above. I im- mediately altered my plans, and determined to go on with three of my men and some of the Indians, and send back the bateau to Peaimah to join the other. Then for both to go down to the Merum^ river, and ascend it to the path landing, at which place I would join them by crossing over from the upper Mazaruni by the Merum^ path, when my work on this river was finished. I gave aU the necessary instructions to Mr. Bagot, who took charge of the return party. On Sunday the 27th, at noon, I bid adieu to Mr. Bagot, and walking to the end of the next fall, went on in one of the two woodskins with three of my men and two Indians, and took with me provisions for one month. Our course was southerly up the river, which lay smooth and broad in a wide tree-covered valley, flowing at a height of over 1,200 feet above the sea, with high sandstone escarpments still not far off from both sides. I got another Indian with his woodskin to join our party, and carry some portion of the stores. We came to two villages, and at the second met a part^_ of Indians who had come down, they alleged, to place their services at my disposal. One of them who spoke a little English was of the greatest service, not only on the portion of the river with which he was acquainted, but also during the remainder of the journey. The first set of Indians went with us as far as they knew the river ; then this man and another went on with us to the head of the next great set of falls, called Chichi, the foot of which we reached on Sunday the 3d November. On the second day of our voyage after leaving Sericoeng falls we passed a large river running into the Mazaruni on the west, called Camarang, and on the same day in the afternoon passed the end of the path which leads across the mountains to the head of the Carabung river, and which Mr. Sawkins and myself tr.•*'-'.«»■': Junction of Schist and Sandstone at Peaimah Fall. 1. Sandstone and conglomerate. 2. Schist. masses of conglomerate hide the schist completely. Although one layer in the schist has undoubted water-worn quartz pebbles, and greaily resembles an extremely altered sandstone, yet owing to 268 GEOLOGY OF BRITISH GUIANA. the great unconformability of the two formations it cannot be an altered portion of the sandstone series. Above Peaimah the great escarpment along the northern foot of which the river runs is composed of great horizontal sandstone beds, and the low hills further on are of the same rock, with coarse conglomerate beds at their base. At the first cataract above Peaimah, the sandstone appears to have been thrown up in one spot at a high angle. The Aruwai cataracts are produced by beds of coarse whitish false-bedded sandstone conglomerate. No. 42. I > 40.FBBT. Section of Sandstone at Aruwai Falls, showing false Bedding of that Sock. No. 43. Sandstone Beds below Aruwai Fall. At the upper landing of Aruwai portage these beds dip south 62° west at an angle of 2°, and are of a silicious sandstone con- taining a few pebbles of quartz. They are vertically jointed, the joints of some beds not passing into those above. The sandstone beds between this and the foot of Sericoeng falls are usually horizontal, but some show a decided dip to the north-west at an angle of 3°, and the sandstone forming the escarpments bordering the river have also horizontal bedding. At the foot of Sericoeng falls the sandstone on the river's edge appears to have been tilted up, whilst the beds on either side some 10 to 20 feet above it are undisturbed. The lower portion appears altered as well as disturbed, and is composed of angular water-worn quartz, as well GEOLOaY OF BRITISH &UIANA. 269 as grains and pebbles of an indurated red fine-grained sandstone or shale. The sandstone appearing on the slope of the mountain along the path, about half way up, is of a light yellowish friable variety, whilst that near the top is a white, soft, coarse sandstone. On the level top of the mountain there is a coating of slaggy looking ironstone, and small iron pellets in the soil. The soil is a gray clayey loam with quartz gravel. Siparimer falls are produced by horizontal beds of coarse conglomerate of about 30 feet in thickness resting on sandstone, and containing pebbles of red sandstone and jasper as well as those of quartz. In the sandstone beds above them there is a thin bed of pebble conglomerate which shows a slight contortion, and proves that the sandstone usually so horizontally bedded has been affected by local disturbances. From Siparimer fall to the great No. 44. Section of undulating Sandstone Beds, Siparimer Fall, fall below, the sandstone beds have a general dip to the north-east at an angle of 6°, showing also some local curved strata. One bed 10 feet in thickness is made up of large rounded blocks of sand- stone containing small quartz pebbles. A bed of fine-grained quartzose sandstone having a vitreous appearance lies under this. The fall above Siparimer is produced by beds of coarse conglomerate, which I think correspond with those at Amailah fall on the Curiebrong. From this on to the village of Mokaparu beds of sandstone showing extreme forms of false bedding, dipping north at an angle of 5°, form low cliffs along the river. Just beyond the village the sandstone disappearsand is replaced by a layer of greenstone. From opposite Marudima mountain to the westerly bend near the Camarang river, sandstone beds are again met with which probably underlie the greenstone. The last exposure at the above-mentioned bend is composed of white semi- transparent quartz grains, with very little cementing material, the quartz particles having taken a semi-crystalline structure as it forced together, and the whole rock is extremely hard. Not far from the river on both sides along this portion are high escarp- ments of sandstone, apparently bedded horizontally, and the base of these rests upon the greenstone layer. At the Woosowter cataract beyond the Cukuie river, beds of white sandstone again make their appearance for a distance of 200 yards, rising to a 270 GEOLOGY OF BRITISH GUIANA. height of 4 feet above the river and dipping south-west at an angle of 5°. Lying conformably upon it is the greenstone layer. No. 45. Section showing Junction of Greenstone and Sandstone, 1. Sandstone. 2. Greenstone. 3. Alluvium. the sandstone retaining its usual outward appearance at the plane of contact, but on examination it is found to contain numerous small crystals of white felspar. A short distance on it rises to a height of 10 feet above the river on the north bank, where trees and alluvium conceal its further development. Beyond the greenstone, which again occurs at a distance of a quarter of a mile, sandstone cliffs of about 20 feet in height line both sides of the river, and so continue all through the savanna portion. The beds in these are of the usual white and pinkish varieties with few quartz-pebbles, and are extremely false bedded ; the general direction of which shows that the currents at the time of its deposition flowed southwards. The beds have slight dips in various directions, but more commonly to the south. On the sandstone on the savanna at the Partang river there is a layer of conglomerate, and the sandstone dips south-west at an angle of 3°. Beyond Ackar village there are some compact white argillaceous sandstone beds, dipping south at an angle of 15°; while not far beyond the sandstone beds dip south-west at an angle of 10°. From the landing along the path to Cowaeng village the first mile is sandstone, and from that onwards is greenstone, which rests upon the sandstone. Turning south from Cowaeng to Camooda, about half-way sandstone is again met with evidently resting on the greenstone. The sandstone forms high precipices on both sides of the river from the savanna portion up to Chi-chi falls. It is of a white colour, but the outside has a reddish and yellowish cast, from lichens of those colours growing upon .it. This sandstone is horizontally bedded, and has not been disturbed by the small exposure of greenstone in the beds of the river in that portion. The section of sandstone disclosed at the face of the fall shows coarse sandstone and conglomerate beds on top, 20 feet of hard purple shale between, and thin-bedded brownish and white sand- stones at the base. In these latter beds are fine even surfaces of ripple marks so clearly formed that they show the direction of the current that produced them flowed from east to west. Examples of sun cracks in the thin laminae of purple shale between the GEOLOGY OF BEITISH GUIANA. 271 rippled beds also occur, but no trace of the remains of any form of life whatever. No. 46. > IS.FEET, Section of false-bedded Sandstone, near Chi-chi Fall. Near the top of the precipice on the portage at Chi-chi fall, the sandstone in one place dips south at an angle of 10°, but soon resumes its horizontal position again. The surface of the country from the top of the precipice onwards to the valley of Wailah- paruj is composed of hard coarse conglomerate having an incHna- tion to the west and containing pebbles of jasper. Beyond the Wailah-paru to the head of the Chi-chi falls where rocks occur they are of white sandstone. From a short distance above the latter spot to half-way up Haiacker creek no rocks are to be seen, being hidden by alluvium, then comes greenstone which continues to a branch river at the village landing. In this branch white sandstone beds are again seen, dipping west at an angle of 2°. The savanna ridges and all the surrounding hills beyond are of sandstone and con- glomerate. From the mouth of the Haiacker creek to the fall on the Mazaruni at which I turned back, the sandstone beds are seen in the river's banks in many places, chiefly in a horizontal position, but in one place they dip south-west at an angle of 5°. The fall just mentioned is formed of horizontal beds of coarse quartzose sandstone in an extremely altered condition, even more so than on the Corentyne below Tomehri. Here it contains large and small crystals of felspar, and semi-crystalline patches of a grey mineral. No layer of greenstone can be seen, but some small water-worn blocks of that rock lie at its foot, which have been washed down by the river, clearly proving that a layer of this rock exists not far above it. Between the Haiacker river and the village of Waioclay-paleuta the path leads over an undulating country of pebble sandstone, containing beds of white argillaceous sandstone dipping slightly to the west. Not far from the village there is a low hill composed of the slaggy-looking ironstone resting on sandstone. The junction can only be traced by the difference in colour of the soil, which is a dark-brown olay on the ironstone and a light sandy loam on the sandstone ; and also by iron-stained water trickling out of the ironstone. The village is also situated on low ironstone hills which flank a low range of greenstone, j 272 GEOLOGY OF BBITISH GUIANA. From "Waioclay-paleouta village in a southerly direction along the valley of the Haiacker, the sandstone continues to the base of the mountains or narrow table-land forming the watershed between the Mazaruni and Ireng rivers, where there is a great layer of greenstone capped with sandstone. The top of the sand- stone beneath the greenstone is again met with in the valley of the Ireng river further on, and continues all the way to Ourindouik fall on the Ireng. In one place along this latter portion there is a bed of red jasper. The savanna across from the Mazaruni to the Ow-weang river is composed of white sandstone, and the fall on the latter river is produced by coarse false-bedded conglomerate. From the landing on the Ow-weang the path led upon sandstone at first, and then ascending steeply came to an escarpment of greenstone and along it for some distance, then down almost to the level of the starting point to. the sandstone again. The remainder of the way to Merum€ mountain was all sandstone. Descending the steep face of the Merume, the first 500 feet is composed of white sandstone, beneath which is 300 feet of reddish sandstone resting upon 100 feet of coarse conglomerate, the upper part of which is composed of large boulders and the lower of finer materials. Then comes a layer of brecciate conglomerate of five feet in thickness resting upon a hard red shale. The next 400 feet is composed of reddish and brown sandstone upon a boulder conglomerate, below which is a layer of rock resembling quartz- porphyry, and a greenish compact rock upon white sandstone and conglomerate. At the base of the section is 50 feet of coarse greenstone. Between this and the landing on the Merume river comes white sandstone, and at the landing a compact light green rock. On the way down the Merume river sandstone is seen in three places, the first two of which are small developments of hard red sandstone dipping north-east at an angle of 10°. The third forms the small fall, and is composed of a very hard red thin- bedded sandstone dipping north-east at an angle of 30° having a strike in a north-west direction. Just beyond it in the river are blocks of conglomerate, and a hill composed of sandstone and conglomerate. Further down river are small exposures of red shaly rock slightly contorted. 4, Oreenstone. At the Turisie cataract a dyke of greenstone 1.00 yards in width crosses the river from east to west. On weathering it breaks up into most curious shapes, and is pitted with large and small circular basin-shaped depressions. It is fine grained, of a greyish green colour, and much jointed. Beyond it the river is studded with rocks, some patches of which have a schistose structure, but are essentially hornblendic, and in one spot resembles hornblende schist. About one mile above Turisie cataract the rocks assume rounder forms, are coarser looking, and darker coloured, and are composed of coarsely crystalline felspar with hornblende, evidently a true diorite. This rock with little change of form continues GEOLOGY OF BRITISH GUIANA. 273 quite up to Issano river, from which onwards all rocks are hidden by alluvium and water for a considerable distance. In one place the diorite contains scattered crystalline grains of quartz of an opalaceous variety ; but as it occurs only in one portion of the rock it must be looked upon as merely a local difference in composition not altering the true nature of the rock. Iron pyrites crystals are very numerous all through this rock. At an island near Issano a fine-grained decomposed greenish jointed rock, thoroughly impregnated with iron pyrites, contains a large quartz vein, and is I think a greenstone. This quartz vein contains an abundance of a black mineral running in lines through it parallel to the walls of the lode, in some places one-eighth of an inch thick, bi;t in others a mere line. There are numbers of drusy cavities of various sizes in it from which iron pyrites crystals have been dissolved leaving a little earthy rust. This vein is similar to that near the mouth of the Ouriebrong river, and at Warrerie gold mines on the Cuyuni river. Although a most promising looking vein I could see no gold in it. This reef runs in a north 20° west direction, and has a side branch about 2 feet in width lying north-west. The main vein is from 6 to 10 feet in width, and is surrounded by great blocks which once formed part of the vein above. There is a vein of white quartz in the greenstone opposite the Ockuwa river of a milky variety and rusty looking in pa;rts, but does not contain any black mineral. Between Issano river and the bend of the Mazarunl to the southward the only rooks seen are fine-grained greenstone, and in one place a dyke of granular rusty quartz resembling quartz-schist. Close to the same bend there is a dyke, 30 yards wide, of green- stone like that of Turisie. From that onwards for some distance down the southerly bend the rocks are all of coarse diabase, which in one place contains large crystals of augite disseminated in a base of diabase with thin veins of quartz. The Karaman^ mountains are composed of coarse greenstone exactly like that of Arlssaro mountain on the Essequebo river. In the great westerly coinrse of the river there are some patches of coarse greenstone rising above the river, and the ridges near Sororieng village are composed of a finely crystalline greenstone which decomposes on its surface to a reddish rusty rock. Above Ouranapai there is some greenstone, and a few miles below the Carabung river a dyke of the same rock crosses the river from south to north, having a branch running north-west. This is a coarse green porphyritie variety, with large light-green crystals of felspar scattered here and there through it. Near Arasoucou and Mazaruni mountains greenstone of a coarse crystalline texture occurs here and there for a space of some miles. In one place this rock has some crystals of mica and a few grains of quartz, and is pierced by quartz veins. The green- stone occurring south of the great bend of the river beyond is described under the heading of schist. 34328. S 274 GEOLOGY OF BRITISH GUIANA. About one mile above Peaimah fall there are a few large blocks of greenstone of a coarse variety on the vyest side of the river, •which must be part of a layer in the sandstone. The layer to which these belong extends across the point of land coming out just above our upper landing at Peaimah fall. Near the latter spot it seems to dip to the north-west, whilst the sandstone con- glomerate 200 yards from it is lying in a horizontal position. To the east of the greenstone at the same place, and within 300 yards of it, in the middle of the river, the compact greenstone is seen weathering exteriorly in schistose forms, like that seen further down the river. Here and there along the banks of the river from Mokayparu village up to half a mile beyond Woosouter cataract, greenstone rocks are seen. Near the former place the banks of the river in some places are composed of red, yeUow, purple, and white clays, resulting from decomposed greenstone. Near Apiopai village there is a large curiously-shaped rock, of the greenstone layer, left on one side of the river, having resisted the eroding action of the water. It is some 60 feet in diameter and 20 feet high, the lower part being formed of coarse greenstone passing abruptly upwards into a finely crystalline rock of the same composition. Along that portion of the river from the Cako to a little beyond the Cukuie river, slaggy-looking ironstone rocks occur in many places, associated with the greenstone. One or two developments* are composed of reddish earthy ore, presenting smooth botryoidal or mammilated surfaces on a, large scale. One portion is vertical and one foot wide, resembling a vein. The greenstone there seems to rise considerably and forms low hills on the south, but has been entirely denuded from the sandstone to the north, over the extensive vaUey. On descending the eastern end of Comooda mountain the green* stone outcrop is hidden, but in the valley of the Iruwa river I saw two smaU blocks of that rock. Near the Terpong creek below Chi-chi falls there is a large boss of greenstone, which appears to have suffered considerable dis- turbance subsequent to its consolidation by the injection of true white granite, which encloses broken blocks of the greenstone, and is twisted up with it in a most curious manner. This greenstone is finely and distinctly crystalline composed of white felspar and green hornblende. The great layer from the watershed of the Mazaruni and Ireng rivers to the bed of the Ireng beyond, mentioned under the sand- stone heading, is similar in composition to that so frequently described before, being of a greenish-gray colour, and of coarse and fine textures. 5. Mica-schist, Tupacu cataract is formed of a belt of mica-schist of a dark grayish-green colour, which is foliated in an east-south-east and west-north-west direction, inclining at an angle of 60° to the north- ward. In the midst of it are two rolls of white, granite containing GEOLOGY OF BRITISH GUIANA. 275 silvery-white mica. At the junction of the schist is exceedingly quartzose, containing nests of quartz, minute specks of garnet, and thin lines of iron pyrites, parallel to its foliation. A greenish-gray schistose rock occurs below Sororieng landing, forming a small island, and is again seen near the landing, where it contains a large vein of quartz, and strings and nests of that mineral. It is very difficult to say whether this is a true quartzose schist or a schistose variety of quartz-porphyry. About one and a half miles beyond the Weynamon river mouth, just beyond a large development of greenstone, there is a mass of bluish-gray rock, which appears to be a sort of coarse mica-schist. Near the termination of the north-western course of the river schists of greenish-gray colours occur, containing lines .^nd nests of quartz, and some mica, being a rock intermediate between mica and hornblende schist. It is in most places foliated at an angle of 45° to the horizon, dipping north ; but round the great bend at the foot of a cataract its foliation is almost horizontal. This rock is a finely crystalline hornblende schist, greatly resembling a fine greenstone, save that it contains nests of quartz, and shows its foliation upon weathered surfaces. It is in clos^ proximity to a mass of greenstone on the north bank of the river, evidently overlying it, while another mass of greenstone forms a cataract to the south. Upon this latter rock rest large blocks of a hard, compact, greenish rock, likg that last described, and showing a foliated structure or weathering, which is not a schist but resembles the rock at the contact of the greenstone and sandstone at Cumuti mountains. From this on to the next cataract, which is produced by a mass of greenstone, this apparently foliated rock is seen in many places, and at the cataract appears to pass into the greenstone. A somewhat similar but more schistose rock forms a vertical dyke one foot wide in the greenstone at the same place. Between the latter-mentioned cataract and Peaimah fall the rocks in the bed of the river are of a slate-coloured schist, in contorted layers, which is an argillaceous mica-schist. It contains a great quantity of quartz in nests and veins, and in parts con- tains rounded knots of a brown mineral. Its colour is bluish arid slaty-gray with a silky lustre. It is minutely contorted in places, and flat and slate-like in others. The strike of its foliation is in a north 35° west direction to east and west, varying in dip from horizontal to 40° and 50°, lying in fact in short anticlinal and ynclinal curves. Its foliation appears to coincide with the original bedding of the rock. In one of its layers of coarse schistose texture I observed true water-worn pebbles of quartz. 6. Gneiss. The small cataract immediately above Ousayway rock is com- posed of gneissose syenite, but the rocks do not pass into true gneiss till Carawaramu cataract is reached. At Epikereek cata- act the gneiss is fine-grained and foliated in an east and west S2 276 GEOLOGY OF BRITISH GXJIANA. direction. It is crossed by a dyke of columnar greenstone lying in a north and south direction, and at the contact of the two rocks the gneiss is exceedingly coarse; this rock continues to Itakie cataract, where it gradually changes into syenite. About one mile above Itakie the syenite and granite pass again into true gneiss, and beyond at Curabirie cataracts it becomes granitic, but resumes its true structure further on. At Pacoa- pacca it is foliated at an angle of 5° to the horizon inclining to- wards the north, and is of a white variety. It is there apparently bedded, with its foliation parallel to the planes of bedding. Near Cabowara cataract there are two dykes of greenstone in the gneiss, and at a distance of half a mile on there is a third. Cartowerie cataract is produced by gneissose syenite, which becomes true syenite, and a little below Turisie cataract changes again to syenitic gneiss, having its foliation in a north-west and south-east direction. 7. QuartZ'porphyry and Felstone. The rocks at and in the vicinity of Teboco cataract are of quartz- porphyry of a greenish colour, weathering white and red- dish white. The first development is light green, and of fine texture, with numerous small quartz crystals scattered through- out. Teboco cataract is formed by a light grey-coloured coarsely crystalline quartz-porphyry, containing scattered crystals of light- greenish white felspar, besides small clear pyramidal quartz crystals. A broad dyke or mass of greenstone crosses the quartz-porphyry above Teboco, just at the bend of the river. From about one mile on the porphyry is repifesented by a purplish felspathic rock containing small lenticular patches of a light-green mineral. Nearly opposite the Carubung river mouth there is a develop- ment of bluish felstone, without any embedded crystals, which passes beyond into a quartz-porphyry of a slightly reddish colour, containing quartz crystals, and continues for some distance in the river's bed. Some way beyond the Weynamou river there is a green-banded compact felstone. 8. Granite and Syenite. From the mouth of the Mazaruni river up to Osayway cataracts the only rocks, with one exception, appearing at the surface, are of granite. The rapids of Guru tuba, Marshall's cataract, and the Kesterbrake are produced' by rolls of a fine-textured grey granite, which at the second-named locality are traversed by coarse and fine-grained granite veins. The granite of Warimambo cataract is of a coarse variety, containing scattered crystals of hornblende and opalaceous quartz. A.i Crab cataract the granite is of a coarse variety containing a large proportion of light-green mica, and is traversed by fine- grained granite veins. At Waipopekai it contains nests and veins GEOLOGY OF BRITISH GUIANA. 2T7 / of quartz, some of which are slightly opalaceous. The granite of the small cataract above Mari is slightly gneissic, breaking into irregular squares, while that of Parowacassie contains thin lines of quartz, traversing it in all directions. The granite varies greatly over small areas, being often syenitic, and at Maccarie contains an excess of quartz. A little beyond this it has a small vein of greenstone. Approaching Ousayway rock the granite becomes gneissose-syenite, of a coarse texture, containing patches of black mica in the crystals of green horn- blende. About one mile above Cabowaro cataract syenite occurs, con- taining a large proportion of dark-green hornblende, being in fact almost made up of that mineral, with a little pink felspar and white quartz. In some places it is porphyritic. Grey granite occurs at Sororieng village, and a little below Camacusa village there is a patch of granite. Below Ouranapai there is a mass of syenite which contains a few crystals of black mica, while at Ouranapai itself the rocks are all of granite. 278 GEOLOGY or BRITISH GUIANA. EEFOKT ON THE Kaieteur Waterfall in British Guiana. By CiiAS. B. Beown. August 1870. During the last expedition of the Geological Survey, whilst de- scending the Potaro river, in April, I came quite unexpectedly upon a large fall which the Indian guides called Kaieteur. At the time our provisions were extremely low, from our having made a land journey of 19 days, during which time all our stores were carried in packs by the men, and were necessarily very limited in quantity at starting. As we were only able to obtain supplies of cassava bread at each village through which we passed, we then had only that article of food to subsist upon. We had come from the Burro-burro river, vi^ the valley of the Ireng, round the head of the Siparuni river and on to this, and were striving to regain our boats, which we expected to meet us at Tumatamari cataract ; thus we were obliged to hurry forward after only two hours' stay at the head of the fall, during which time I made a sketch of it, and took its elevation above the sea level with an aneroid barometer. I was much struck with the beauty and grandeur of this fall, and regretted extremely that I could not remam longer to make ■ proper observations of its height, width, &c. I had therefore to content myself with mere estimations, which at best are exceed- ingly doubtful and unsatisfactory. When we reached the river again at a distance of 3 miles below the foot of the fall, I of course took the height of it above the level of the sea, and by subtracting the number of feet from that of my last observation, and making some allowances for intermediate cataracts, arrived at the con- clusion that the height of the fall was about 900 feet. In the geological report which I furnished to the Government on my return to Georgetown, I gave a short account of the fall, and my estimate of its height, to which I added the following remark : — " These measurements I give as the result of my short and hurried " investigations, and as such they must be regarded until future " explorations determine them with accuracy." His Excellency Governor Scott, deeming it advisable to have the exact measurement of this fall made known, directed m,e, on the 24th of June last, to make preparations for a journey to it, for the purpose of making a thorough examination of it with re- gard to its height and width ; stating at the same time that Sir GEOLOGY OF BEITI8H GUIANA. 279 George Yoimg, Mr. Mitchell, and Mr. E. King would accompany me. I therefore at once procured the necessary supplies for one month's consumption for our party, and the number of men which I thought it necessary to take. Our party left Georgetown in the contract steamer on the 28th of June and arrived at the penal settlement the same afternoon. Captain Kerr, the superintendent there, very kindly placed the despatch-boat Lady Woodhouse at our disposal, which with the small survey bateau Victoria, and two small corials hired on the following day, formed our means of transport. I engaged 1 5 river men who had been with me on former journeys, amongst whom were my captains Peterson and Deeges. These, together with our cook and my Ackawais interpreter, composed the crews of our four boats, eight going in the Woodhouse, five in the Victoria, and two men in each of the corials. On Friday the 1st of July we started on our journey, and directing our course across the mouth of the Mazaruni river, entered upon the broad waters of the Essequebo^- up which we paddled till 5 p.m., reaching a deserted place called Ouyah, where we spent the night. We found the stream running against us all the afternoon from the time we passed Bartika point at the confluence of the two rivers, there being no ebb or flow of tide owing to the great height of the river. In the dry season the tide flows as far up as the foot of the first rapid above Camakaserima, some 18 miles above the Grove. On the following day we reached the above-uamed place at 10 a.m., and during the afternoon hauled the boats by tow ropes up three cataracts, through other channels amongst the islands than those I had previously passed ; their names were Woodalli- quihaha, Moorie, and Itaball. The first-mentioned one lies in a line with Aretaka rapid, but to the east of it. Late in the afterr- noon we made an unsuccessful attempt to get up a channel in Tabinetta cataract, but failed owing to the force of the current, and were obliged to camp on an island at its foot. Our progress being so very s1o\y', having to fight our way against the angry stream, we determined not to lose the whole of the next day (Sunday), and so worked up to 11 a.m., thereby getting up Tabinetta cataract. On Monday we hauled up Marihi, the largest of the whole set of cataracts in this part of the river, and the same afternoon up Itaballia cataract, keeping close to an island, and directly over the spot where I once camped in December 1868. Only one or two of the many high massive rocks of the neighbom-hood were left with their points above water. That evening we camped at the foot of Ahara rapid, now swollen to the dimensions of a cataract. Early next morning we hauled up this rapid and along. a channel where we usually paddle with ease in ascending, but along which we now had to drag the boats by the low branches of the trees overhanging the water. Getting soon after into water unbroken by rapids, but running with great velocity, we made slow progress against the stream. The clay banks of ,the, river were entirely covered with water, which we found reached as far 280 GEOLOGY OF BRITISH GTJIANA. inland as could be seen, and as we proceeded further on we found that it was only here and there in the neighbourhood of low hills that there were spots of dry land. Along both sides of the river where the banks are low there are usually low narrow ridges lying parallel to the river, a few yards from its edge, raised some two or three feet above the top of the bank, which have been deposited in time of flood like the present by the deposition of sediment from the still water covering the land. Next to this, inlahd, comes level land slightly lower than the banks, which reaches for a long distance back. When the water overflows the ridge it floods the surrounding country to a depth of 3 or 4 feet. It was only in a few places that we could find land, and in order to cook -our meals were often obliged to camp at earlier hours than we should have done under ordinary circumstances. On the evening of the 5th we found a resting place for the night only a few yards long and two inches above water. We sighted first the mountain on the river called Arissaro on the 6th, and at 3.35 p.m. on the same day came to Yucurit island opposite Yucurisi creek, and landing at the house of a half-bred Brazilian determined to pass the night there. The owner and his family had deserted the place, owing, I suppose, to the height cf the river, which covered one half of the earthen floor, and completely surrounded the house. Fortunately one-half of the house had a staging of Ita palm planks raised 3 feet above the ground, which furniehed us with a dry floor, and made our waterbound condition more bearable than it would otherwise have been. Insects abounded here, being driven in by the rising waters, foremost amongst which were termites and small centipedes. We passed Dahalibani river at noon next day, and in the after- noon experienced a heavy rain and thunderstorm. At 5.30 p.m. we came to the mouth of the Curl-curu river, where we expected to find land, but to our great disappointment aU was covered with water. We took the small corials and penetrated a short distance inland as far as we could get through tangled vines and " bush ropes " amongst the stems of the trees, but found that the water became deeper the further we went, so we retm-ned to the boats, and had to sleep in them. On the 8th, at noon, we had a heavy fall of rain, and the same afternoon reached the first rapid in this part of the river called Curatoka, which was hardly discernible, owing to the height of the river. At 2 p.m. on the 9th we entered the mouth of the Potaro river, and found it extremely high, but with very little current, being dammed back by the great body of water flowing down the Essequebo past its mouth. The change in the colour of the water was very apparent, the boats gliding from a turbid stream laden with sediment in suspension, at once upon water of a translucent brownish-black, which had a clean pleasant appearance. Viewed in a body the water resembled an infusion of tea in colour, this tint arising fi-om the tannin in it derived from vegetable matters. At 5 p.m. we reached Tumatamari cataract some 5 miles up the Potaro, and found though a great body of water rushes over it. GEOLOaT OF BEITISH GUIANA. 281 yet from the water at its foot being so high it is itself greatly reduced in height, being only 6 or 8 feet at its southern side and a few feet at its northern. The water of the river washed the foot of the hill at the end of the portage, so we had to run the boats some distance amongst the trees to get a landing place, and then camped on the hill top on the side of the path. It will be seen by a perusal of the foregoing that it took us eight days and a half to reach the Potaro river instead of five, the usual length of time it has taken to perform this journey on my three previous expeditions up the Essfequebo. Early on the morning of the 10th I went with my captains and examined both sides of the cataract, selecting a channel on the south side up which to haul our boats. We also crossed to the northern shore, below the cataracts, to the spot where we camped on the 28th of April, which was all under water. Sounding at a spot which was the edge of the river I found a depth of 13 feet of water. We were all the forenoon engaged in packing up the provisions for our fm-ther journey, which was to be performed in the two corials and the small bateau it being considered impracticable to haul the large bateau up the cataract, and in the afternoon the boats were taken up and their loads carried over the portage. Leaving Peterson and three men with the lai'ge bateau, and taking 13 men as the crews of the three boats, we started onwards from the head of the cataract at an early hour the following morning ; and not having a swift current to contend with made a good day's journey, passing the Curiebrong river at 3 p.m., hauling up Chowrah rapid at 4.30 p.m., and camping at the foot of Cobanatout cataracts at 5 p.m., at the end of the long portage. Though none of us knew anything about the Cobanatout cataracts, having on our way down river come across this portage, yet we determined next morning, if possible, to haul the boats up them. Soon after starting we came to the first of these cataracts, named Morowaseema, and unloading the boats, carried the stores along a portage the whole length of aii island, a distance of about half a mile ; then dragged the boats up and crossing to the main- land, carried a portion of the things over another portage, .594 yards in length. The boats were then taken up two more cataracts of no tn-eat size, the first being called Cobanatout, which is in two steps, with a total height of three feet, and the second being called Auritout. If the river was lower these two cataracts would not present jnuch of an obstruction in the ascent. The river here separates into small channels, amongst a number of small islands ; and a group of low hills lie on its northern side. Proceeding on we passed the upper end of the long portage ; and a mile or two further we came to Pacutou falls. It being late when we reached this- place, we camped after landing everything, to be in readiness for the morrow's work. This fall presented rather a formidable appearance, but we thought that we might be able to get the boats up the four cataracts of which it is composed. At 6.30 a.m. on the 13th we commenced carrying the loads over all the party working with the men ; and in three hours and 282 GEOLOGY OF BRITISH GUIANA. a half all the stores, &c., were placed at the upper end of the pathj at the head of the falls. We then got the boats up through a narrow channel to the top of the first cataract, about three feet high ; and coming to the second, some eight feet in height, took one of the email corials up with difficulty, and reconnoitred the third. To our disappointment it was found that this cataract was impassable, on account of its steepness, and of the force with which the water rushed down it. The fourth cataract was still more formidable, so we had to return to the end of the portage, above the first cataract, and from thence drag the boats one by one up the steep hill to a height of some 50 feet above the river, then along the even path, a total distance of 1,078 yards, to where the luggage was deposited, and there launch them. In this work the whole strength of the party was called into action ; and everyone working cheerfully and well, rollers or skids were cut and laid, and the boats dragged across on them. It was 4.30 p.m. by the time we had the boats loaded and ready to start again. From the upper end of this portage the flat-topped sandstone mountains are first seen ; they form the northern escarpment of the table land. Continuing onwards we cleared a small rapid, and bivouacked im- niediately above it at my old camp of April 26th. Here I observed that the water was about three feet lower than it was at that time. Starting early next day we continued our journey. At almost every bend of the river fine views of the sandstone mountains were disclosed, uniformly covered with dark green foliage, excepting here and there, where the steep bare pat'ches of whitish rock formed great precipices. In some places the almost uniform flatness of the mountain tops was relieved .by deep .gorges and gaps. We made good progress against the stream, the current not flowing with much rapidity; and by mid-day reached Amutu fall, the approach to which up a long reach of river js very beautifiil* This fall is divided by an island, and on its eastern side, where the greater body of water pours over, is almost perpendicular for some 15 feet. Unlike the other cataracts mentioned, this one is formed by ledges of sandstone, and is close to the foot of the mountains. The standard barometer here stood at 29'968 inches, temperature 84 degrees, giving a height of only 84 feet above the level of the sea. At this portage, which is only 440 yards in length, there is one hill to haul up from the river, which is steep and very rooky, so that much time was here consumed in cutting skids on which to run the boats. As usual all hands set to work, and by half-past 5 o'clock in the afternoon the boats were all above the portage, and reloaded for an early start on the morrow. -This fall can never be ascended by boats on account of its height. At 7 o'clock next morning, the 15th, we entered the end of the valley, with high mountains on either side, partially shrouded in dense clouds of mist. Soon after the rain began to fall heavily and did not cease till after 10 a.m., at which time we reached Warratu. As soon as the rain commenced all the grand views of mountain scenery were hidden by the mist ; and on its clearing off as the rain ceased, some fine cascades pouring down a precipice on our right hand were disclosed. Warratu is not a large cataract. GEOLOGY OF BEIXISH GUIAKA. 283 its portage being about 100 yards long, so that we found it only necessary to carry the stores and luggage over, and consequently were not detained there any length of time. As the rain-clouds broke^ away the sun came out brightly, driving away the mist and fog clinging to the rnountain gorges, and thereby disclosing to our delighted gaze a portion of the object of our journey, a view of the great fall, far off at the head of the valley, pouring its foaming water over the precipice edge into the depths below, as it has done for ages past. One is struck with awe, and impressed by the greatness of nature's work, when he sees the great power that is here revealed ; which through unnumbered ages has been cutting its way unnoticed back from the mountain edge at Amutu to its present position, thereby forming this broad and deep valley. As it receded from its first position, when it probably poured its waters into the ocean, then washing the base of the sandstone cliffs, its branch streams running in at right angles helped in the great work of denudation by cutting side gorges and widening the whole valley. Viewed from where first seen I should say that some 400 feet of it, from the top downwards, can be seen, and about one half of the width of the top, a bluff hiding the rest. Every now and then clouds of thin white mist from the foot rose up and covered it like a veU, and then passed away to the eastward, the breeze being westwardly at the time ; but one cloud I observed always crept along the precipice under its western edge as far as could be seen from here, and is the one that rises from its western foot, which, in early morning, I saw on my first visit. Before passing Partamona village we met some Indians, to two of whom I communicated, through the interpreter, that we wanted guides on the following day to the foot of the fall, and as much fresh provisions as they could supply. Soon after this we reached the " landing " at 2.30 p.m., at the foot of Tukuie cataract, about three miles from the foot of the fall, at which We landed all the stores, knowing that we could proceed no further in our boats. Another Indian came up to us, and from him I learnt that on account of the number of small cataracts beyond Tukuie we would have to pursue our further journey on foot. Sir G. Young and Mr. Mitchell were anxious to return to town as soon as possible after seeing the fall, while it was necessary for Mr. King and myself to remain until all the required measure- ments were taken. Consequently it was arranged that we should all visit the foot of the fall together on the following day, Mr. King and myself remaining there while Sir G. Young and Mr. Mitchell would return to the landing and ascend to the head of the fall on the day after, taking the standard barometer with them. By this arrangement they could see the views there pre- sented, and at the same time take simultaneous barometrical observations with myself, the tim«s of such being arranged by flag signals. We would then all return and meet at the landing on Sunday afternoon, and they would leave the next morning on their return journey. The Indians brought us on the following morning a large quan- tity of sweet potatoes, plantains, &c., which we bought with beads 284 GEOLOGY or BEITISH GUIANA. and knives. By 8 a.m., everything being ready, we started with two Indians as guides, and five of our men as carriers of pro- visions, &c., and were accompanied by 1 1 Indians, who escorted us of their own accord. We traversed the weU-beaten path which leads 'to the head of the fall for a few hundred yards, and then struck off to the river, coming out on its western side at Oriraedouk cataract. Here the path ended, and we followed the river's edge, sometimes amongst blocks of rock and boulders close to the water, at others some few yards in the forest amongst great massive rocks, and having often to cut our way through thickets of tangled vines. At 10.45 a.m. we reached a spot about a quarter , of a mile from the foot of the fall, at a point from which its whole face could be seen. This is perhaps the best view of the actual fall and precipice on either side that can be obtained, and one can here fully realise its immense height. The day was dull and cloudy, and some rain fell soon after we reached the spot, causing a dense mist to hang about the fall. Some of our men lost their way, and taking the wrong path at starting reached the head of the fall, and returned to the landing ; only one joined us at 5 p.m. The man carrying the canister containing my sketch book, &c., also lost his way, and did not arrive till 2 p.m. Meanwhile I chose a good barometrical station, 13 feet above the level of the water, and compared the two barometers so as to get the difference between them. I then commenced a pencil sketch, at which I made slow progress, being repeatedly interrupted by light showers of rain. At 3.30 p.m. Sir G. Young and Mr. Mitchell, who had visited the basin of the fall, left for the landing camp, the latter carrying the standard barometer with him, after settling about our signals and the station for the barometer above on the morrow. All but two of our Indians returned also, so that the party at our bivouac that night consisted of Mr. King, nine men, three of them Indians, and myself. We had poles rigged up and lashed together under a large flat rock in a kind of cave, and there slung our hammocks for the night in this most romantic spot, with a frowning precipice on either side and the fall in front, with its ceaseless roar sounding in our ears. Sitting over the fire that night the interpreter related to us a tradition connected with the fall from which it derives its name. The story commences as usual with " Once upon a time " there lived an old Indian at a village above the fall, an exceedingly feeble old man, whose feet became infested with Chigoe fleas to such an extent, that he gave his friends anil relatives an immense amount of trouble in picking them out for him every morning. So they determined to rid themselves of the nuisance, and accord- ingly placed the old man in a woodskin, just above the edge of the fall, and shoved it out into the stream. The strong current hurried him to the brink, and swept him over into its foaming water, and he was seen no more. But not long after, strange to relate, his woodskin appeared at the end of a small island, in the smooth water just below our camp, in the form of a long slab of rock, while on a slope on the right-hand side of the fall a large square rock represents his canister similarly petrified. After this tragedy GEOLOGY OF BRITISH GUIANA. 285 had been enacted the Indians named the fall Kaieteur, which means old man fall. Lying in my hammock that night I could just discern the fall through the deep darkness which prevailed, looking like a huge ghostly apparition. The night being chilly and damp, and having no rug to wrap up in, I could get but little sleep, and continually dozed off and woke up at short intervals ; every time therefore my eyes opened I saw the fall before me. Just before the moon appeared above the mountain on the left two bright stars rose in the sky beyond the edge of the fall above, seeming to come out of the very water, and then the first light of the moon rested on its crest, shedding a golden light across it, which had a most beautifnl and charming effect. After this till morning broke all the water was ht up by the moon's rays, and could be seen with great distinctness. Early next morning, as the sun shone on the mist, on the right- hand of the fall, a beautiful rainbow was produced, reaching from its foot to almost half-way up the precipice. The day was fine, and I continued my pencil sketch. At 8.45 a.m. Mr. Mitchell and some of the men appeared at the edge of the head of the fall, on the western side, looking extremely small. We exchanged signals to, set up barometers, and soon after signalled each obser- vation, taking five simultaneously, during the interval between 9 a.m. and 10.30 a.m. We next tried to measure the width and take the depth of the river, Mr. King swimming with the line, but the current was too strong and swept the line down stream with such fotce that we could not manage it. In the afternoon I twice observed that a strong breeze issued from the cave behind the falling water, driving the eastern edge of the fall outwards, and giving a quarter turn to the bottom of the column of water. Mr. King, the men, and myself walked . back to the camp at the landing, which we reached at 5 p.m., and met Sir G. Young and Mr. IVfitchell there. Getting the result of the upper observations I made a rough calculation from the mean of both, and found to the satisfaction of all that the height came almost up to our expec- tations. In this I did not allow for the mean difference between the two barometers, which was subsequently taken into the calculation. On the following morning, the 18th, Sir G. Young and Mr. Mitchell started on their return in the two small corials with six men, and were accompanied by two Indians in a woodskin. At Tumatamari they were to leave ,the corials, and descend the Essequebo in the " Lady Woodhouse." Mr. King and myself started for the top of the fall at 10.15 a.m., taking six men and an Indian with us. The path is good and the ascent gradual for some distance, then becomes rather steep for a few hundred feet to a gully filled with immense blocks of sandstone, between the interstices of which a small stream runs. From this the path leads up the mountain at a steep angle for a distance of about 400 feet, then the ascent becomes gradual again to the top of the table land, over 1,000 feet in vertical height above the starting point. It then leads along the table land in a south-westerly direction for a considerable distance, coming out of the forest about 286 GEOLOGY OF BRITISH GUIANA. three quarters of a mile from the head of the fall on a small open tract of country. The walking is then over flat rocks, through low shrubs and bush to the head of the fall. We arpived there about an hour after mid-day and commenced a series of measure- ments. We tried to measure the height of the fall with a line and weight run through a pulley over the edge of the precipice ; but when over 500 feet had been payed out, the mist given off by the side of the fall completely hid the weight and lower portion of the line from view, and we had to abandon the experiment. We found an old woodskin in a small creek near by, in which I crossed, over with a man to the other shore, at a distance of 250 ya«?ds above the edge of the fall, carrying the end of a line with us to measure the width ; but the line became entangled in the rocks at the bottom of the river, and we had to cast it oif and go on without it. I next visited the edge of the precipice on the •eastern side, and found that the width of tlie edge of the fall is 30 feet less than it was when I was here in April, by measuring from it to a rock which I then observed was surrounded by water. On the other side the width is 66 feet narrower than it then was. That evening we encamped in some low bush close to the fall. Late in the afternoon the swallows (which I mentioned in my last report) oame in from all points of the compass in large flights, and here gathering into two or three immense flocks, kept wheeling above us closely packed together, at a height of about 100 yards. I can only convey an idea of the multitude of these birds by saying that they were in myriads. Every now and then as the flocks passed above the fall, thousands would swoop down almost perpendicularly, with extraordinary velocity, and passing close over the edge drop till opposite the great cave, then suddenly change their direction and shoot through the mist on either side into their roosting places. Just before dusk these birds came down in greater numbers, attracting our attention by the strange rushing sound they produced by their downward flight ; sometimes pouring, down in a continuous stream for five minutes at a time. Then single birds and small flocks kept arriving till it was quite dark. When a single bird shot down only a black line marking its course could be seen. I was unable to procm'e a specimen of one of these swallows to ascertain their size, but as far as I could judge they appear to be almost as large as the common gray plover, and are of a black colour with a white patch under the throat.. At 6 o'clock next morning the thermometer stood at 70°, whilst the water at the same time was 73°. The great valley below the fall was filled with mist up to 8 a.m., when the breeze sprang up and dispersed it. I continued my observations at an early hour, assisted by Mr. King. We measured a base line of 2*42 chains, and then with a good compass took the angles to a mark on the other side (the rock before mentioned), from which I calculated the width of the fall as it was in April last to be 370 feet. We then took four observations of the velocity of the current before it passes over the fall to within 50 yards of its edge. Setting two compasses at two points 66 yards apart I directed • GEOLOGY OF BRITISH GUIANA. 287 them both at right angles to the base. line. Light pieces of wood were carried out in a canoe some distance above and allowed to float down. Mr. King observed at one compass while I watched at the other, and timed the floating objects as they passed. I also took five observations with the mountain barometer at the upper station at the same time as before. _We again took out the line in the woodskia to measure the width of the river 200 yards above the fall, and were successful. Making the line fast to a tree on the opposite bank we went back and hauled it in straight, and thus got the true width, viz., 134 yards. The remainder of the day was spent in making a water-colour sketch of the front of the fall, and of the country from which the river comes, from a spot on the western precipice edge, not far from where the path emerges from the forest. The day was extremely fine and the sun shining on the spray caused many beautiful rainbows at different periods, one reaching quite from .the top to the foot of the fall. Next morning (the 20th) we sounded the depth of the water at 200 yards above the fall, and found 15 feet 2 inches to be the greatest depth (see Section 3). On the river's edge there are trees upon which the. high- water mark has been left, the water having recently, and evidently for a length of time, stood at a height of 5 feet above its -present level. Eeturning to the same spot as yesterday I finished^ my sketch, and then we all descended the mountain, and arrived at the camp at the landing at 5 p.m. Just as we left the open table-land above, the rain descended in torrents upon us, and did not cease till after we had got] to the camp. On the 21st I took five men and an Indian with me and pro- ceeded to the foot of the fall to take the height of the cataract, from the river below to the edge of the basin. I could not take a barometer with me beyond my first station on account of the diflSculty of carrying it and the chances of getting it broken, as well as the impossibility of suspending it amongst the rocks. I therefore had to take my aneroid. We reached the barometrical station of the 16th, and continued along the western side of the river, amongst enormous boulders of sandstone and conglomerate, amongst which grew shrubs, low trees, and agaves, all interlaced with tangled vines. Through these we had to search for an accessible track to pass along, and had to clear our way with a cutlass. As we approached the basin this growth gave place to a coarse moss growing on the soft eaTth, which covered the flat portions of the rocks and rendered the walking slippery and difficult. Sometimes we were brought to a standstill by a per- pendicular face of rock, and had to retrace our steps and try a, new track ; at others we had to pass through narrow subways and under great rocks. It took us about an hour and a half to walk the distance, which I estimate at 350 yards in a straight line from the barometer station to the outer edge of the basin. As we approached it we felt the breeze coming outwards, and soon became enveloped in mist. At this point the Indian guide refused to go further, and then turned back. The sun cast its rays upon our 288 GEOLOGY OF BRITISH GUIANA. backs, and produced small rainbows in front of our faces, which were most dazzling, and almost prevented our seeing the way in passing over deep fissures amongst the rocks. At the basin the mist and spray completely surrounded us, quite hiding the sun, like a dark cloud. Here we had to take shelter behind the rocks from the blinding storm of mist and rain which assailed us, driven outwards by the hurricane produced by the falling water, and through gap", witness the .strange scene before us. The water in the basin mo3t truly resembled a huge boiling cauldron, to which I before likened it, being lashed into great irregular waves, whose crests were blown into spray, and as they drove outwards in an irregular semicircle were dashed against the rocks in front and the walls of the cave on either side, beating over one rock that I am sure was 15 feet high. The foot of the descending column of water was rendered indistinct by the mist, but great fleecy masses of white foam spurted upwards many yards high in clouds mixed with spray and mist. Standing there, I imagined that it exactly resembled a sea storm raging on a rock-bound lee coast. When I went in amongst the reeking wet rocks to the storm 1 left the sun shining brightly and the neighbouring forests unstirred by any wind whatever. Returning again, I came out of the mist into the sunlight, and by the time I reached the barometer station and looked back, I could hardly believe that such a disturbance of the water in the basin as I had witnessed still continued. The aneroid gave unsatisfactory readings, from the mean of which the difference of level between the edge of the basin and the barometrical station below is 68 feet. To this 13 feet, the height of the barometer station above the level of the foot of the cataract, must be added, which gives 81 feet as the total height of the cataract. At the lower end of the smooth water below the fall, at a distance of three quarters of a mile, there is a long sloping cataract, for which the Indians with me said they had no name. The roar of this cataract drowns that produced by the great fall, on account of its proximity to the path along which we went, so that the sound of Kaieteur can only be heard at a distance of half a mile from Its foot. I may here remark that at about a mile above it on the river I could just hear it oii my approach in April last. Next to this come three smaller cataracts between it and Tukine cataract, which are respectively called Serikabam, Orimedouk, and Oriedouk. At the first-mentioned one, on the eastern side of the river, there Is a beautiful large cascade, part of which falls perpendicularly for some 200 feet. Near this cascade there is an enormous stone pillar on the edge of a precipice, with two flat slabs on top, resembling a gate-post. There is also a fine cascade opposite the landing place. Having taken all the necessary observations, and completed the work for which this journey had been undertaken, we determined to start upon our return on the following day. I made inquiries about the upper fall on the Potaro from some Indians who had just come down from it, and from their descrip- GEOLOGY OF BRITISH GUIANA. 289 tion it is a, long sloping succession of cataracts which, taken together, give a height almost as great as Kaieteur. From similar inquiries I learnt that the fall on the Curiebrong, the existence of which I pointed out in a former official report, fully realised all my expectations, being, according to the Indian account, quite as high as Kaieteur, and also perpendicular. Its Indian name is Amailah. Feeling satisfied as regards the truth of this account, I think I may without hesitation lay claim to the discovery of the existence of this fall. I also think it not im- probable that the Semang and Merumd rivers, coming from the same sandstone table land, have similar falls upon them. "We left the landing at 8 a.m. on the 22d in the bateau Victoria, accompanied by six Indians in woodskins, whom I hired to help in hauling our boats over the portages. In running down Warratu cataract on its western side we met with an accident which might have had a very serious termination. As the boat shot over and cleared the dip of the fall at full speed, she struck on some hidden rocks -\vith such force that the bowman, who was standing up at the time guiding the bow with his paddle, was thrown overboard, Grasping the gunwale of the boat, he saved himself. There we were, the boat grinding and thumping on the rocks in the midst of waves and foam, and I had little hopes of the boat's holding together. The men all jumped over, and so kept her from broaching, and with extreme difficulty we got out of our perilous situation. By the time we reached the shore the boat was half full of water. Unloading we found that the bottom mid-plank was completely shattered, and water was pouring through in many places. These leaks we stopped with tallow and oakum after hauling the boat up. Continuing on, we hauled over Amutu portage, and camped about half way between it and the next set of cataracts. We reached the Pacutou portage at an early hour next morning, and carried everything over by noon. In running the boat over on skids the shattered plank burst through in two places, and we experienced considerable delay in patching it up by first caulking, then spreading osnaburg over it on the outside, upon which we nailed pieces of wood. We reached Cobanatout cataracts at 2 p.m., and lowered down all but the last one, named Morowaseema, where we unloaded, put skids on the rocks, and ran the boat a distance of 10 yards on them before launching it at the foot. We encamped at the foot of Chowrah rapid, and the following day being Sunday we remained there all day. The river was here very much lower than when we came up, and was falling gradually. Next morning, 25th, we ran down the river till we came to the Curiebrong, up which we tm-ned. We went two days' journey up it, and finding that our stores would not hold out if we went further returned, and reached Tumatamari cataract at 2 p.m. on the 28th, lowered down our boats on skids, and camped below it on the northern side. The river above the cataract was two feet lower and below the fall four feet lower thaw when we went up op the nth. 34328. I 290 GEOLOGY OF BEITISH GUIANA. Starting at 6 a.m. next day we reached the Brazilian house on Yucurit island at 4.30 p.m., and remained there for the night. The water there had fallen a good deal, and land was now every- where to be found. The mosquitoes being very numerous pre- vented all from sleeping, so that at 4 o'clock next morning we were glad to leave the place and continue our journey. We ran all the falls that afternoon except Marihi and part of Tabinetta, which were evaded by running down side channels. Having no tide or wind below the falls to contend with we made a good day's run of 46 miles, arriving at Bartika Grove at 5 p.m. on the 30th. Here we were kindly received by P. Grant, Esq., the stipendiary magistrate, and next day went over to the penal settlement, where we became the guests of Captain Kerr, who extended his generous hospitality to us. We left the settlement on Monday morning, August Ist, in the contract steamer, and arrived at Georgetown in the afternoon, after having been away for 35 days. In giving an account of this fall only a slight idea of its beauty or of that of the scenery which surrounds it on all sides can be conveyed. I will now give its actual dimensions as I made them out, together with an outline of its geological structure. Kaieteur fall, as I have placed it on the map from my sketch survey of the Potaro river, taken from its mouth up, is in 59° 19' west longitude, and 5° 8' north latitude. It is produced by the Potaro river flowing over a sandstone and conglomerate table-land into a deep valley below, with a total fall of 822 feet. For the first 741 feet the water falls as a perpendicular column into a basin below, from which it continues its downward course over a sloping cataract in front 88 feet in height, and through the interstices of great blocks of rock to the river bed below. The head of the fall is 1,130 feet above the level of the sea. No. 47. 200.YDS. 3 ^ STATION. B, gigJAtlON.A. Section through the Fall. Spale, 200 yards to an inch. GEOLOGY OF BRITISH GUIANA. 291 1 SQ The accompanying section will enable the reader to understand the way in which this fall has been produced, and also give some idea of the nature of the table lands. The river rises in Ayangcanna mountain, some 40 miles to the south-west of the fall, and flows from an uneven plateau down a succession of im- mense cataracts above Enapowou village to an extensive table land. At one time it must have run over the edge of the table land near Amutu cataract, but during the lapse of time it has cut its way back to its present position at the upper end of the valley. The river comes due north for a mile or so before reach- ing the head of the fall, with no great force of current, and has a smooth surface; but at a distance of about 200 yards from the fall it seems to hasten forward with greater speed and becomes slightly rippled, breaking into little patches of foam here and there as it nears the edge and then rushes over. As it curves over it is of a dark reddish-brown colour in its deepest portions, through which can be seen patches of foam forming beneath and passing out to the surface of the water, changing it into a heavy column of foam of a white colour with a slight reddish tinge. This may be described as descending in seven great systems of inverted rockets of foam so close to each other, both vertically and laterally, that no actual break takes place between them, so that the river falls in one great continuous whitish column of jagged foam. These seven systems are strikingly observable from the con- trast of colour presented between them and their interspaces ; the foam of the latter join- ing edge to edge across being of a pure white colour and of much thinner substance than the former. Where this column of water beats into the basin below dense masses of foam spurt upwards in all directions, while the actual contact is rendered indistinct by clouds of mist. The water then flows away as a cataracf, over and through the interstices of the great boulders, which form the outer edge of the basin, into the river below, and runs onwards with a strong current of a dark brownish- black colour ; the water in the basin is also of a deep brownish colour, and the rocks sur- rounding it are all stained of a similar tint. t2 292 GEOLOGY OF BRITISH GUIANA. In the shallow portions of the lip of the fall the reddish colour of the water is lost the moment it begins to fall. The western side of the descending column of water forms an even edge, but on the eastern side the water falls thinly from the top, forming thin rockets, which shoot out in thin spray and mist, and widening as they slowly descend, form a beautiful veil of gray mist over the edge of the cave on that side, whose outline can then be hardly traced. This mist rises to the top of the fall, and keeps moving outwards along the side of the precipice, and soon becomes invi- sible vapour. When the sun is shining a most beautiful rainbow is formed, which reaches from the top to the foot of the fall, and moving outward with the mist gradually fades away; and with each accession of mist a new one is formed. The edge or lip of the fall is even on the eastern, but has a second ledge on the wes- tern side, and some rockg protrude above water there, now that the river is low. It is curved or angled inwards, and at the angle the greatest body of water flows over. The width of the river at a distance of 200 yards above the edge of the fall is 134 yards, and at the edge itself is 12.3 yards. No. 49. Section across the River, 200 yards above the Edge of the Fall. The depth of the same place was 15 feet 2 inches when mea- sured, the level of the water then being b feet below its highest level wheu.in flood. The accompanying section gives its depth at various distances across. There are no means of measuring the width and length of the basin, but I have estimated them at 200 and 100 yards respectively. The velocity of the stream just above where the greater body of water passes over is 4'09 miles per hour, and 3 miles per hour between that and the western shore. The lip of the pool or basin is formed by the meeting of two sloping piles of rock banked against the foot of the precipices on either side, the ends of which meet almost together at the middle of it. The cave behind must be of immense size from the glimpses of it on both sides. The fact of the enormous flocks of swallows that find a roosting place and home there also leads to this con- clusion. It is now inaccessible, both of the precipices on each side of the fall being perpendicular at their foot, and washed by the water of the basin. On both sides of the fall the beds of sand- stone form even, perpendicular precipices of gray and I'eddish rock void of trees, but as they curve round away from the fall they become sloping and tree-covered. The vegetation about the immediate neighbourhood is very beautiful. All the surrounding country is covered with dense forests, with the exception of a small savanna close to the western GEOLOGY OF teBITiSH GUIANA; 293 side of the fall. On this savanna are scattered groves of low trees with patches of grass, and bare stretches of level rock. The vegetation of this is very curious, there being numbers of small flowering 'grasses and rushes, while representatives of the orchid family, of singular beauty, mosses, and ferns grow in great luxu- riance over it. Amongst the OrchidacecB are three species which I imagine are quite unknown elsewhere ; they grow on decayed wood lying on the rocks, have large roots, and grow very high ; their flowers are large, delicately scented, and in form resemble those of the Cattleya. A large species of agave grows in great numbers here. Its leaves are more of a yellowish-green colour, and their points are of a rounder form than those of the Agave vivipara. Growing along the track from the landing to the foot are great quantities of ferns and mosses, and on the rocks close to the edge of the basin are small scarlet bell flowers and a fine sack-shaped orchid. AU the rocks near the basin are covered with a coarse moss, and beyond on the rocks washed by the waves this gi-owth gives place to a small water plant. Small clusters of dark green shrubs cling in patches to the lower portion of the precipice on either side, and look like ivy on a castle waU. A long kind of grass gTOws in the water on the western edge of the lip. The scenery of the great valley below when viewed from near the head of the fall is extremely fine. Late in the afternoon when the sun is sinking in the west great shadows are cast across it which have a magnificent effect, and the colouring is then very beautiful, the end of the valley being lit up by the golden reflection of the sky over the plain beyond, and the strips of river winding in the depths below look like bands of silver. Viewed from this spot none of the bare precipices on the valley side are disclosed, but all appear to be covered with a rich dark-green clothing of trees. From the small savanna looking south and south-west the mountains of the first plateau are seen in the distance, as also are Cowatapeur and Salieng (two flat-topped mountains), far off in the west. With regard to the geological structure of Kaieteur fall, I may here mention that the table land over which the Potaro river flows is composed of sandstone and conglomerate beds belonging to the upper portion of the great sandstone formation of Guiana. In my last report I have given a description of the lithological characters of this formation, and have there stated that it is probably the equivalent of the new red sandstone. The lower portion is not here represented, and the sandstone rests upon the quartz-porphyry. The upper beds of this rock are here extremely hard, and are formed of a coarse pebble conglomerate lying in a synclinal curve in which the river runs just as it passes over the precipice. _ This conglomerate is some 20 feet in thickness, and is underlaid by beds of reddish-gray sandstone which are not so durable as the conglomerate. It is owing to these circumstances that the fall is of a perpendicular form, for the great hardness of the conglomerate resisting the action of the water for a longer period than thg underlying sandstone, is left as a protruding ledge; while the 294 GEOLOGY OF BRITISH GUIAlfA. wash of the column of water cuts away the softer sandstone below. The back splash of the faU has cut out the great cave behind, and as the conglomerate ledge above breaks away from time to time, as it must do, and the column of water is thereby moved back, so in the same ratio must the cave be cut back, and the perpendicular form of the column preserved. These conditions wUl probably remain in force for ages to come, so there is no reason to anticipate the destruction of the vertical portion of this beautiful fall. There is a great fault in the strata on the eastern side of the precipice, which has produced a great change in this dip of the beds beyond the line of the fall. The conglomerate is composed of waterworn blocks and pebbles of quartz, cemented together by a white clay with quartz grains, of the same reddish-gray material as constitutes the sandstone, and of such great hardness that the embedded quartz splits e^■enly in two with the fracture of the rock. Besides quartz, these contain pebbles of jasper, quartz-porphyry, and sandstone. The sandstones vary much in durability, texture, and colour, and invariably exhibit lines of false bedding. There is a layer of trap rock not far from the landing on the hill side crossing the path that leads to the top. I feel sure that the elevated tract of country about the head of the fall is extremely healthy, and that a journey to it and a short time spent there would be found a beneficial change to those who reside on the low land along the coast. The Indians say that in the dry season the river becomes very low, and consequently the fall narrows greatly. In the month of October it reaches its lowest point, and then the fall is only about one third of its full width. They say it then falls in a continuous column as at present. After October it rises with the autumnal rains, and for a month or two is at its full width ; it then decreases till March, and again is fiUed up by the spring rains. A small sum of money judiciously expended in improving the portages and in making a pathway to the foot of the fall would reduce the time of the journey there and back considerably. The Indians living near by, if directed and paid, could easily fell trees amongst the large rocks, flatten their upper sides and lasli hand- rails to them, whereby the walk from the landing to the edge of the basin would be greatly facilitated. Small thatched sheds could be erected at the various camping places to protect travellers from rain and dew at night. The nearest and best route is undoubtedly the one by which we travelled, but a more convenient way might be opened up for those who wish to evade the cataracts on the Essequebo river. This could be done by cutting a road 18 miles in length, from Christian- burg due west to the Essequebo river, and parties could then ascend the Demerara river to Christianburg in the steamei", and cross over to boats kept on the Essequebo above Ahara rapid. To this report I ha^e attached a map which is the one used by ] the Survey, and was traced from Schomburgk's large map. I have GEOLOGY OF BRITISH GUIANA. 296 added my sketch survey of the Potaro river to it, so that the position of the fall can be seen at a glance. They are reproduced on a smaller scale in the accompanying sketch map. Calculation of Total Height of tlie Fall by simultaneous Observations of Standard and Mountain Barometers. Standard Barometer (Casella's, No. 566), at top of fall, Station B., 5 feet above level of river. Mountain Barometer (Baker's), near foot of cataract, Station A., 13 feet above level of river. At Sea Level. Foot of Fall. f Standard - 30-056 29-660 Difierence of Barometer, \ Mountain - 30-038 29-626 •018 •024 Mean of difference to be added to Mountain Barometer, -021. Time. Standard Barometer. Attached Barometer. Mountain Barometer. Attached Thermometer. 1st observation, 9 a.m. - 2nd „ 9.10 „ 3rd „ 9.30 „ 4th „ 9.45 „ - 5th „ 10.30 „ 28-868 28-900 28-892 28-888 28-888 74° 74° 75° 76° 76° 29-714 29-708 29'706 29-709 29-7)1 73° 73° 74° 75° 75° 5)144-436 5)375° 5)148-548 5)370° 28-887 7.5° 29-709 74° Mean of Standard Barometer - - - 28 • 887 75° „ Mountain „ 20-709 + '021 = 29-730 74° 29-730 28*887 29-730 28^887 76°= 944 '7 in table. 74° = 942-9 „ 58-617 -843 1887-6 2)58-617 29-308 -843 2)1887-6 943-8 -843 28314 37762 75504 796-6234 30 -308) 23868-7020 (814 ft. 234464 42230 29308 129222 117232 296 GEOLOGY OF BRITISH GUIANA. Total height by observations - - 814 ft. Height of Standard above river - 5 ft. Mountain „ - 13 ft. 8 ft. „ Fall and cataract = 822 ft.^ Calculation ,of Height of Cataract by Aneroid Barometer, Station C, 5 feet above the edge of basin. Yime. At Station A. At Station C. 1st observation, noon - 29-748 — 3rd „ 3.30 p.m. - 29-660 — 2nd „ 2.30 „ - - - 29-620 29 -620 = 337 feet. 2)59-408 29-704 = 264 „ 29-704 73 feet. Height of Station A. above river = 13 feet. « C. „ =5 „ 8 Height of cataract = 73 + 8 = 81 feet. Total height of fall :— Height of fall - - 822 feet. ,, cataract - 81 „ Height of perpendicular portion 741 feet. Calculation of width of edge of fall : — Base line AB = 159-72 feet, y C = 22° 30' y B = 62° 30' Log. Cosec. C = 10-4171603 „ Sin. B = 9-9479289 AB = 2-2033593 Feet 2-5684485 AC =370-21 = 2-5684481 Width of fall at edge = 370-21 feet. Height above the sea level taken vrith the Standard Barometer : — Foot of Tumatamari cataract - 65 feet. „ Amutu ditto - - 84 ,, Landing place ... 195 „ Top of Kaieteur fall - - - 1,130 „ Foot „ - - - - 308 „ I have taken the following quotations from Sir John Herschel's " Physical Geography," for the purpose of allowing the reader to draw his own comparisons between the chief waterfalls of the world and Kaieteur. With regard to Yosemite and Ruikam Fossan it will be seen GEOLOGY OF -BRITISH GUIANA. 297 that their exact width is not given, one being mentioned as being the "width of the Thames at Eichmond/' and the other " a large river." The height also of the former seems to have been taken by guess, and the words " unless exaggerated " cast some doubts upon the truth of the statement. " The loftiest waterfall in the world (unless exaggerated) is to be found in the Yosemite valley, in Mariposa county, California, where a river as large as the Thames at Eichmond makes a single leap of 2,100 feet perpendicular, the total height being 3,100 feet. " The communication along the chain of lakes is broken between lakes Erie and Ontario by the stupendous fall of Niagara, the largest and most magnificent, though far from the highest, in the world, the total breadth of river (which is divided into two great cataracts by Goat island) being 3,225 feet, with a descent of 162 feet in one fall, and 149 in the other." The Victoria falls on the Zambesi river are thus spoken of: — " The falls referred to are perhaps the most striking after " Niagara which exist. The river 1,000 yards in breadth is " suddenly swallowed up in a narrow perpendicular cleft 100 feet " deep " ..." in which the river takes its new course compressed " in a deep channel of 15 or 20 yards." The most notable European waterfalls are those of the Ehine at SchafFhausen, not lofty — ^being only 70 feet in height — but very picturesque ; those of the Velino at Terni, and the Anio at Tivoli, both artificial, but of exquisite beauty ; that of Eiukan Fossan, where the Maanelvan, a large river flowing out of the Miosvatu lake in Tellemarken, in Norway, springs 946 feet at a single leap ; the Glommen falls, and those of the Moxa near Stav, in the same county. The falls of the Clyde in Scotland are not wanting in grandeur or beauty. Those of Gavarnie (1,400 feet) in the Pyrenees, and of the Staubbach (1,004 feet as measured barometrically by the writer of the article), in Switzerland, are mere rills, remarkable only for their height, in which, however, both are surpassed by that of the Oreo, a stream which springs 2,400 feet from Monte Eosa, on the Italian side of the Alps, and of '.vhich some further account would be desirable. 34328. LONDON: Printed by Geokge E. 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