The Fotaro and Kurihrong Rivers. 163 



quartzite. Mr. Dunn found more marked signs of the presence of gold 

 in the sands of this creek just Ijelow the diabase than in any other place 

 in the sandstone-formation which he examined during the Kaieteur 

 Conglomerate Expedition. A dyke of diabase very similar to the rock 

 of the Orimetuk sill traverses the conglomerate at the Waremure Creek 

 on the Kaieteur Plateau, about one and a half miles from the fall, where 

 the clastic rocks near it are much indurated. 



The path from the Oi'imetuk Creek to the plateau passes over 

 sandstone to near the top, and then over coarse conglomerate and 

 pudding-stone. 



The excellent account of the Kaieteur Fall and Plateau given b}^ 

 Brown in his " Report on the Kaieteur Waterfall " (p. 278, et seq., 

 of the " Geological Reports ") requires no addition. His description 

 is very complete and accurate. 



Many of the mountains in the district explored by IVEessrs. Anderson 

 and Dunn above the Kaieteur Conglomerate Plateau consist of coarse- 

 textured diabase or gabbro, as, for instance, the Akobenang Mountain 

 which rises to a height of 3,250 feet above the sea level. Thin sections 

 of these rocks which I have examined show that some of the masses 

 consist of unaltered intrusive diabase, whilst others are of more or less 

 metamorphosed gabbro. The former are probably laccoliths in the 

 sedimentary rocks, the latter mountain-masses on the flanks of which 

 the sandstones and conglomerates were laid down. 



The Kurihrong River. — The east bank of this river at its junction 

 with the Potaro and for a distance of about seventy yards up consists 

 of quartz, while near the west bank schistose quartz-porphyry^ more or 

 less altered, is visible. The quartz, which is quite free from gold, 

 is a mass in the quartz-porphyry. About a quarter of a mile from the 

 mouth quartz-porphyry and felsite occur which are much weathered. 

 For the next half a mile or so the bed of the river, which is here broad 

 and very shallow, is covered with quartz-sand ; whilst very numerous 

 large angular boulders of milk^^-white quartz and broad sand-banks 

 interrupt its course. North of the belt of quartz-boulders the river 

 crosses a dyke of epidiorite trending in a northerly direction. From here 

 the channel of the river is fairly clear for about a quarter of a mile, 

 and then is again interrupted \>\ a second belt of sand-banks and 

 quartz-boulders. One hundred yards above this sericite or quartz- 

 porphyiy schists are visible at intervals for about two hundred yards ; 

 whilst at about a mile and a half from the mouth of the Kurihrong 

 River a dyke of diabase runs south-west and north-east, the rock being 

 of medium texture. This is succeeded for about five hundred yards 

 by broad exposures of sericite-schist crossed by a wide dyke, about 

 eighty yards across, of diabase trending north-west and south-east. 

 The outer parts of this dyke is a normal ophitic diabase of a fairly fine 

 texture, weathering into angular blocks, but towards its middle the 

 rock becomes coarser, approaching in structure to gabbro, and in the 

 middle of the dyke, where the rock is granitic in its mode of weathering 

 into great rounded masses, it passes into a very coarse-grained light- 



