CHAPTER XVI. 



THE ESSEQUIBO EIVER. 



From Bai'tica for a distance of about five miles up the Essequibo 

 River there are few exposures of rocks, the land, at all events near 

 to the banks of the river, mainly consisting of alluvial deposits. A small 

 exposure of gneiss is seen about two miles from the town. At about 

 five miles from Bartica there are several exposures of rocks, all being 

 grey granitite, and at about half a mile south of Monkey Juuip Point 

 a coarse diabase is exposed at intervals for about one hundred and fifty 

 feet, large masses of it being seen on the left bank of the river. At 

 Monke}^ Jump the river cuts through a broad dyke of very coarse 

 diabase, which is exposed lor nearly two hundred yards on Ijoth banks 

 of the river. A little south of Monkey Jump grey granitite is exposed 

 at intervals for about five miles, varying a good deal in its texture from 

 moderately fine to very coarse. A dyke of diabase of medium texture 

 trends north 60° east and south 60° west about one mile and a half 

 north of Kumaka Serima through the granitite. The rocks exposed 

 at Kumaka Serima consist of fine-grained grey granitite, through 

 which a dyke of coarse-grained diabase, about sixty feet across, cuts in 

 a direction parallel to the one north of this place. At Bethany 

 Island the granitite is coarser in texture than it is at Kumaka Serima. 

 Near the foot of the Aretaka Rapids gneiss is seen with great boulders 

 of granitite lying upon its surface. From Aretaka to Abuya Marali 

 the rapids and cataracts are over gneiss which vaties greatly in texture, 

 and is intersected by many veins of coarse-textured j^egmatite and 

 of fine-grained granitite. South of Abuya Marali granitite is the 

 prevalent rock to above Moneri Island at the head of the Aharu 

 Rapids, where it again gives place to gneiss. 



At Abuya Marali the granitite is crossed by a narrow dyke, about 

 eight feet in breadth, of a fine-grained compact diabase running in a 

 north-easterly direction. The vi^eathering of this dyke differs from that 

 usuall}^ characterising diabase, and instead of standing out from the 

 other rocks in great masses it has been largely removed by denudation, 

 and a shallow trough marks the line of the dyke. At Abuya Marali 

 and at Itaballi the granitite has caught up blocks of dark-coloured 

 gneiss with higldy contorted foliation, and is traversed by pegmatite 

 veins containing large crystals of feldspar, and patches of quartz with 

 plates of biotite not unfrequently from one to one and half inches in 

 length. Near the head of Itaballi Rapids the granitite is traversed 

 by a narrow dyke of dark-grey diabase running north-west and south- 

 east. From here to above Aharu Rapids the rocks are granitite of a 



