The Konatvaruk River. 171 



the river about half a mile south-west of Long Falls. The series 

 of cataracts and rapids, known as Long Falls, extend for about 

 a quarter of a mile, and along them coarse gneiss or gneissose- 

 granitite is constantly exposed, a vein about twelve to fifteen inches 

 across of black, fine-grained quartz-porphyry cutting through the 

 gneiss at the head of the falls. The river follows a very winding 

 course through coarse gneiss and gneissose-granitite, the bands of the 

 latter here and there giving rise to rapids. Tacuba Falls, another long 

 series of small cataracts and rapids, which extend for about four 

 hundred yards, are over coarse gneissose-granitite at the head, and over 

 grey gneiss of medium texture at the foot and lower parts. 



Below Tacuba Falls the course of the river is, compared to the upper 

 reaches, free from sand -banks and fallen trees, and, in consecjuence, rocks 

 are more frequently exposed. The rocks immediately below the cataracts 

 consist of coarse granitite, traversed about two hundred yards from the 

 foot by a dyke of diabase about five feet across, a little below which is an 

 exposure of fine-grained quartz-porphyry intrusive through the granitite. 

 About a quarter of a mile below, the granitite is intersected by a dyke 

 of diabase varying in breadth from eight to ten feet. About a mile 

 north-east of Tacuba Falls the granitite is traversed by a belt of diorite 

 and of quartz-mica-diorite or tonalite. This belt is about sixty yai'ds 

 across, and at its western side consists of a fine-grained dioi'ite which 

 gradually changes to a coarse-grained quartz-mica-diorite. The eastern 

 side is much altered by weathering, and is intersected by a dyke of fine- 

 grained diabase, about thirty feet in breadth, which gives rise to small 

 rapids. About three-quarters of a mile from the diorite the granitite, 

 which, varying in texture from coarse to fine, is exposed at intervals along 

 the course of the river, is traversed by an elvanof quartz-porphyry, twenty 

 feet in width, giving rise to small rapids, and at a distance of about one 

 hundred yards from the rapids by a dyke of diabase about twenty feet 

 across, the intrusive rock being of medium texture. For the next 

 quarter of a mile of its course the river passes between great masses of 

 coarse-grained, grey granitite, which in one place are traversed by a 

 narrow dyke of diabase of very fine texture. Below these exposures of 

 granitite fine-grained quartz-porphyry is visible about two hundred yards. 

 About a quarter of a mile from the lower part of the exposure of 

 quartz-porphyry the coarse granitite, the prevailing rock to below 

 Temple Bar Cataracts, is traversed by two narrow bands of hornblende- 

 schist which are about five feet and about eighteen feet, respectively, 

 in width. 



At Temple Bar, at a distance of about two miles from the junction 

 of the Konawaruk with the Essequibo, the river falls over a mass of 

 coarse grey granitite, and its course is interrupted by some small 

 islands, so that it passes down three channels. When the river is very 

 low the rock is exposed over a large area, and the difierence of level 

 between the head and the foot of the cataracts is about forty feet. The 

 broad rounded mass of granitite exposed at the northern fall is fairly 

 iniiform in structure, ha^'ing, like all the granitites of the district, a moi e 

 or less distinct gneissose appearance, and showing in places dark-coloured 



