130 The Giwloci!/ of the Gold Fields of British Guiana. 



hornblende-<fi-;initite usually sho\vin;j; a more or less well-marked 

 gneissose structure. Arramarri or " Evil Spirits' " Cataract at the 

 head of the series where the portage path crosses, is over a belt of 

 granitite traversing granitite-gneiss. 



The river above Devil's Hole portage and Arramarri Fall, as is 

 usually the case where large falls obstruct the river course, expands to 

 a great width, containing innumerable islands divided" by wider or 

 narrower and more or less shallow channels, the rocks exposed in which 

 are mostly great rounded masses of giieissose-granitite. 



About four miles above the Devil's Hole portage a vein of coarse 

 aplite having a pegmatitic structure occurs. About a quarter of a mile 

 beyond this some gneissose rocks, containing porphyritic feldspars 

 conspicuously developed, are seen. 



Immediatel}^ below Dukwarri Cataract gneissose-granitite exhibiting 

 a marked schistose structure occm's, and Dukwarri Cataract is caused 

 by a belt of hornblende-gneiss, about two hundred yards of which are 

 exposed. 



Above Paku Rapid schistose rocks again occur, and about two 

 miles south-east of Dukwarri, at Pakutout Cataract a dyke of 

 amphibolite is crossed for a distance of about two hundred yards. 



For about two miles to the west from Pakutout the rocks in the 

 channels between the islands are more or less schistose-felsites. 



Above a small rapid (called St. John's) the river flows smoothly 

 and slowly in deep channels between islands, and but few exposures of 

 rocks occur for about three miles further up, where just below the foot 

 of Kuyari Cataract is an exposure of diabase. 



Kuyari Cataract, at the foot of the series known as Amamuri, 

 is formed by a belt of compact gneissose porphyritic augite-granophyre. 



The Amamuri series of rapids and cataracts descend over rocks 

 of gneissose-granitite having an intrusive mass of granitite in the 

 middle of the series, while near Powis Island, a belt of hornblende- 

 schist extends across tlie river at the last rapid at the top of the 

 series. 



Above Amamuri is a curving stretch of fairh' still water, extending 

 about seven and a half miles along the river, in which only a few rocks, 

 consisting of felsite-schist, are exposed. 



At Otomung Rapid felsite-schist gives rise to a small rapid 

 extending across the I'iver in a west-north-western direction. 



The rocks exposed in the river from Otomung Rapid to the 

 Kanaima Itabu, at the many small rapids occurring through the course 

 of this itabu, and also in the main channel of the river for about four 

 miles above the upper end of the Kanaima Itabu, are generally felsite- 

 schist. About two miles up the itabu from its mouth a belt of gneissose 

 granitite occurs and gives rise to a rapid. 



Rounded masses of gneiss and of gneissose-granitite again appear in 

 the river for about four miles below, and also in the vicinity of the 

 Akarabisi Creek. 



About two miles above Akarabisi the rocks exposed consist of 

 granophyre. 



