184 Reports and Proceedings — Geological Society of London. 



Professor J. B. Harrison, alluding to a series of views of parts of 

 the interior of British Guiana, which he laid on the table, remarked 

 that the photographs had been taken by his colleague, Mr. H. I. 

 Perkins, F.G.S., Acting Commissioner of Mines in British Guiana, 

 during their recent geological investigations into the structure of 

 the goldfields of that colony. The views well illustrate the general 

 characteristics of the densely wooded country in which the gold- 

 bearing areas occur, and give some idea of the difficulties which 

 affect the work of the mining prospector and of the field-geologist 

 in that colony. 



Several of the photographs illustrate rapids, cataracts, and falls 

 which so frequently occur along the courses of some of the vast 

 rivers of that part of South America, and show the differing forms 

 of weathering of various igneous rocks and of horizontally-bedded 

 sandstones and conglomerates in the tropics. 



Among the photographs are several fine views of the Kaieteur 

 Falls on the Potaro Eiver, a tributary of the Essequibo. These 

 falls, which were discovered by a Fellow of the Geological Society, 

 Mr. C. Barrington Brown, in the course of his geological recon- 

 naissance of the colony about thirty years ago, occur near the 

 escarpment of the great sandstone formation which is so largely 

 developed in the Guianas and in Bi-azil. The falls are over a ledge 

 of very coarse siliceous conglomerate, some 18 or 20 feet thick, 

 which overlies a thickness of about 1000 feet of almost horizontally- 

 bedded sandstones. The river above the falls is about 400 feet 

 broad and from 18 to 20 feet deep, and falls vertically, as a great 

 curtain of water, for 740 feet, into a vast chasm at the extremity 

 of a deep valley which it has eroded for a distance of about 17 miles 

 from the escarpment of the sandstones. During the first 3 or 

 4 miles of its course from the falls through the valley, the river 

 descends for about 400 feet by a series of cataracts and rapids. 

 The valley, which is eroded in places through the sandstones into 

 the underlying igneous rocks, is of surpassing beauty, and offers 

 many features of marked geological interest. One of the views, 

 taken when the water was low after a long-continued drought, 

 shows very clearly the great cave which the spray of the falling 

 water has cut out from the softer sandstone strata. 



Others of the views show the somewhat primitive methods 

 employed in prospecting and in working the placer-claims for gold. 



Professor Edward Hull made a communication, illustrated by 

 lantern-slides, on the submerged valley opposite the mouth of 

 the Eiver Congo. The position of this submerged valley has been 

 ascertained by Mr. Edward Stallybrass and Professor Hull, by 

 contouring the floor of the ocean with the aid of the soundings 

 recorded on the Admiralty Charts. The sides of the valley are 

 steep and precipitous and clearly defined, the width varying from 

 2 to 10 miles, and the length across the Continental platform being 

 about 122 miles. It is continuous with the Valley of the Congo, 

 and its slope is uninterruptedly downward in the direction of the 

 abyssal floor. The steepness of the sides indicates that they are 

 formed of very solid rocks. 



