172 The Geology of the Gold Fields of British Guiana. 



patches consisting of basic segregations from the mass ; whilst to the 

 south of tlie main fall an elvan of dark, fine-grained quartz-porphyry 

 traverses the rock. 



The rocks l)elo\v Temple Bar for some distance down the river con- 

 sist of granitite similar to that of the cataracts, but at about a quarter 

 of a mile north-east of them the liver passes over a belt, about eighty 

 yards wide, of very coarse-textured quartz-diorite. For about a 

 quarter of a mile from the diorite many exposures of fine-grained 

 diabase ai'e seen on the banks of the river and in its channel ; then for 

 about one hundred and fifty yards a dark-grey quartz-porphyry occurs ; 

 and from it to the mouth of the Konawaruk there are frequent 

 exposures of diabase, which are in places fine-grained, whilst the rock 

 of the one near the junction of the Konawaruk with the Essequibo 

 is identical in texture with that of the dykes which give rise to the 

 Konawaruk rapids in the latter river. 



