1^71.] SAWKINS — BEITISH GUIANA, 429 



Arriving at Uriburoo Hill there is a bold escarpment of trap 

 and schist, with iron pyrites. A stream runs down the cliff, as a 

 cascade, on the west side of the river. On each side of the river, as 

 high as the Ubaroo creek, trap dykes occur traversing the river ; 

 and between these is a ferruginous gravel, sand, or clay. The land 

 beyond this is low and swampy, and traversable only during the dry 

 seasons. 



Observations made on the Essequebo River, its tributaries, and 

 southern mountain-ranges. 



At the junction of the Mazuruni and Cayuni rivers with the 

 Essequebo is the penal settlement, and on the opposite shore the 

 village of Bartica, the only settlements of civilization on these rivers ; 

 and as the geology between this point and the sea has been already 

 given, I commence the following observations from Bartica, which 

 is built on a low sandy deposit resting on granite and porphyry. 

 This low land continues to the cataract of Aretaka ; but before 

 arriving at Camaka Serima, dikes of greyish trap with iron pyrites 

 and felspathic hornblende occur. At Camaka Serima grey granite, 

 somewhat gneissic, rises, dividing the river by several islands and 

 forming the Aretaka cataract, where the granite appears in large bold 

 masses, sometimes showing lines of scaling or peeling in concentric 

 layers like an onion, at others of decided gneissic structure. The 

 entire area occupied by these falls or cataracts is composed either of 

 granite proper or of members of the granitic family ; at the head of 

 them is Gluck Island, and a great extent of still water expanding 

 to lacustrine dimensions, where no rock is seen in situ, but large 

 sand-banks render the water very shallow. 



A few miles up the river the Arissara hiUs appear ; and near their 

 base granite occurs ; and a little up the river a trap dyke crosses 

 it. 



From this, for several miles, nothing but sand and clay is seen. 

 At the Cumuka rapids, granite with quartz-veins 2 inches in dia- 

 meter appears, with detached blocks of hornblendie rocks superposed. 

 At Acuramalli Rapids trap rocks rise a few feet above the river, 

 also at those of Curamucu, where greenstone and hornblendie rocks 

 form obstructions in the river. 



A short distance above this are the hills and islands of Buhuri 

 and Banaca, and the Waraputa falls, where the granite extends across 

 the river, some of it being very dark from the quantity of black 

 mica it contains. There are veins of quartz a few inches in dia- 

 meter, also petrosUex, gneiss, and syenite, diffused much in the same 

 manner as at the Malalli falls on the Demerara river, with which 

 this is in all probability connected. A depression in the land to the 

 south-east also corresponds with that on the Demerara river. 



After passing the nest rapid there is a collection of granite rocks, 

 all having a scattered and confused position detached from each 

 other, some larger ones on smaller. To one of these the name of 

 Paiwori Cayra is given by the natives, from its resemblance to the 



