Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/454

344 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9, At the distance of fifteen miles or so from the river, the land rises into scarped, low, more or less wooded heights, constituting the serranos, interspersed with grassy slopes and plains. These serranos by easy gradations lead us on to the range of the Itacama Mountains, which trend east and west and attain an elevation of about 3000 feet. The range occupies a breadth of about sixty miles; and its southern slope is bounded by an undulating grassy plain presenting an aspect similar to that of the Llanos, excepting that woodlands occupy the margins of the streams, and that a species of palm grows on the moister portions of the soil. This plain, the mean elevation of which is about 800 feet above the sea-level, stretches southward as far as the river Yuruari, which marks off the savannah from the forest-region of the Caratal, the subsoil of which is a ferruginous clay affording firm attachment for timber trees of large growth. The Caratal district, so far as it is known, is broken up into ridges and peaks of about 1500-2000 feet elevation, with narrow and deep dividing valleys.

It is to be observed that the Itacama Mountains divide the eastern part of Venezuelan Guyana into two hydrographical basins, to the north that of the Orinoco, and to the south that of the Essequibo, which by its tributary, the Cuyuni, and its numerous affluents drains the country to the south of the Itacama range, and to the east of the basin of the Caroni.

II. Geology of North-east Venezuela.—Mr. Wall*, in his "Geology of a Part ofVenezuela," has described the geological features of a portion of Venezuela to the north of the Orinoco; and, so far as I can judge by reading his account, the arrangement and nature of the rocks in the district to the south of the river seem to concur in a great measure with those to the north.

That author has established the existence:—First, of a series of micaceous and siliceous schists, with interbedded crystalline limestones; and in a few restricted localities the schistose beds alternate with gneiss. This group of metamorphic rocks, to which he has assigned the term Caribbean, exhibits great disturbance and contortion; the strike is ordinarily east and west; the metalliferous minerals are gold disseminated in gneiss west of Valencia, a sulphuret and carbonate of copper in the schists at Las Teques, near Caracas, and argentiferous galena near Carupano. Secondly, of neocomian strata overlying the schistose rocks to the south; and, thirdly, of an arenaceous series belonging to the upper miocene, and termed newer Parian by the author, which overlies and abuts against the neocomian rocks. In Venezuelan Guyana, the metamorphic series and the upper miocene strata are developed, but neocomian beds have not been observed.

III. Metamorphic Series of Venezuelan Guyana.—The section attached (fig. 1) will suffice to show the regularity of the bedding, and the somewhat undisturbed conditions, of this series. The trend is usually east and west, and coincides with that of the Caribbean system of Northern Venezuela; the dip is from 70°-75°, to the north ordinarily;


 * Quart. Journ. Geol. Soc. vol. xvi. p. 460 et seq.