Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/574

 to contain auriferous deposits as any other portion of it that I have seen.

The greatest elevation between the Cuyuni and Puruni rivers was 320 feet, on the south of which a tributary of the Puruni takes its rise. Down this narrow stream, we cut our way through the branches and trunks of trees that were lying across it. After passing the Tapara and the Tariparu creeks, from the south, granite and syenite occur in two places, and after passing the Waini creek, from the north, the river is divided into many branches by numerous islands composed of a red clay, and obstructed by fallen trees, to avoid which the Indians have cut a passage through the clay, large enough for corrials (canoes) to pass. These clay banks are generally low, and lie on some hornblende and schistose rocks near Maruparu and again further down the river.

Granite occurs near Tuvastimpi creek and a little below, associated with gneiss of a blue colour.

On approaching Curaspara creek a soft mica-schist occurs, near which there is a hill of 600 feet elevation. The ascent is rather steep being on the average 30° of inclination ; the trend is north-east, and south-west. The surface is covered with hydro-oxide of iron, in the form of pebbles, or in concretionary masses, sometimes conglomerated and haematitic.

Near the falls of Marchughi the hydro-oxide of iron occurs forming a soft rock, with blackened surface. Diorite, trap, and greenstone form the barrier across the river, about 15 feet higher than the lower basin. A deposit of iron and manganese occurs on all the rocks in this as in most of the other rivers in the colony. Sometimes I have seen it of an inch thick.

About a quarter of a mile below the junction of the Mapa-aima with the Puruni, are the falls of Payuca, which are divided into three streams. A dyke of greenstone forms the obstruction. The mica- schist dips to the south-east.

Ombaroa Creek enters the Puruni from the north a little below these falls, and the hills of Ruminga and Murupina soon appear, forming the south bank. At the base of these hills are dykes of a dense greenstone. Between these two hills is a small water- course, near which I observed granite, syenite, trap, hornblende- schist and decomposed schist. Near Gasparupa creek there is a curious conglomerate, and also trap with quartz veins. After passing Gangrooma and Langooma creeks greenstone occurs ; and below Cabilli and Humaribara creeks quartz, greenstone, and conglomerate ; and at Paraani creek red and green schist with quartz veins. These extend down to the vicinity of the Maramara creek, where gneiss and blue clay-slate appear. A short distance lower down the river is a bed of conglomerate.

The river soon after passes through a ridge trending north-east and south-west, and soon after another hill is seen about the same height (600 feet) trending more to the south. Then follows the Uricon, which is the highest in the range.

At the base of these hills a ferruginous conglomerate and red