Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/581

 From this no rocks appear above the surface until arriving at " Musara," an abandoned Carib settlement ; and from this to King William IV. Falls, a distance of five days from this point, there are no rocks to be seen but granite, syenite, gneiss, a series of dense hornblendic rocks, and in one instance columnar basalt.

The Falls of King William IV. consist of a succession of rapids about 100 yards apart, closely interspersed with rocks.

The Ascent of the Rupununi.

The Rupununi river is one of the largest tributaries of the Essequebo, entering it at nearly 4° N. latitude ; there is scarcely any current perceptible at their junction ; and high banks of alluvium occupy both sides of the river, which are sometimes broken by large ponds or inlets, conveying the idea of an extensive depression between the Maccari and Paccarima ranges, and again between the Makrapan and the Annai.

The Makrapan Mountain is composed of granite and syenite. From the base of this mountain] the great savannas spread to the south and west into Brazil and Venezuela like large inland lakes, a resemblance which is increased by the difference of vegetation growing on them. The alluvial deposits of the lower Essequebo are covered by the largest and highest forests in the world, whereas on approaching these savannas trees begin to decrease in altitude until they become like the stunted growth on a promontory of a seacoast. This peculiarity is not confined to the river-courses ; for the savannas or grassy plains are only here and there dotted by a dwarf tree resembling the coast-grape, Coccoloba uvifera.

The geology of these savannas is very clearly defined, as they consist of only three distinct, stratified Tertiary deposits, resulting from the disintegration of the adjacent mountains : — 1st, sand, clays, and vegetable mould ; 2nd, red sand and ferruginous gravel, often concreted or haematitic ; 3rd, white clay, resting on gneiss, granite, &c.

On the Annai mountains the savannas, or tracks of land denuded of trees, rise to the summit in a most capricious manner in strips and lines as regular as if laid down by line and compass ; but the rocks do not differ in character from those on which forests grow.

To the south of the Paccarima or Annai range are the Cunuku mountains, which extend from the Takutu river on the west to the upper Essequebo. This range is chiefly composed of granite and gneiss, with trap dykes of the same character as those before described. The savanna from the Rupununi to the Ireng and the base of the Paccarima mountains consists of three Tertiary stratified deposits. At the mouth of the Unamara river there is a vein of quartz, and adjoining it are hills of quartz similar to those of Annai. Between the savanna and the Unamara river there is a ridge of granite intersected by greenstone dykes.

The next hill to the northward is composed of a different kind of rock, which continues to the edge of the sandstone escarpment on the Sacaonta river. This rock in its commonest form is composed of white crystals of felspar and clear crystals of quartz in a siliceous