Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/579

 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 hills 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 diameter appears, with detached blocks of hornblendic rocks superposed. At Acuramalli Rapids trap rocks rise a few feet above the river, also at those of Curamucu, where greenstone and hornblendic 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 diameter, also petrosilex, 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