Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/578

 is very shallow by the accumulation of this ferruginous gravel. At the base of Mecropie hill the same occurs.

Derrire hill is covered with hydro-oxide of iron ; and much of it has been brought down, in the form of gravel, into the creek bearing the same name.

At Camoodecabra a trap rock rises, and extends to the Anobaro Creek, forming a dangerous barrier for boats descending the river. Above the Waburicabra another large ferruginous gravel-bank occurs that extends up almost as far as Coomaparo creek.

From Coomaparo there is an Indian path to the Essequebo river, which occupied eight hours' walking. The land rises in undulating swells up to the "burnt grounds," where it attains 200 feet, and, after continuing on that level for a few miles, gradually descends, like steps, until it reaches the low swampy flat of Moraboo, on the east bank of the Essequebo.

In this distance, computed at 18 miles, the only rock to be seen is a quartzite, which decomposes into white sand.

Returning to the Demerara river, the banks continue low until arriving at Acururi Hill, which connects with a ridge that extends to Lucananycabra, chiefly composed of white sand.

By proceeding up the Marbooroo creek about a mile, and then walking south-west a few miles, the Maburu Hill rises to about 800 feet above the sea : one of its sides towards the Essequebo is nearly perpendicular; and from it a fine view of that river is obtained. It is composed of trap, and appears connected with the same range that forms the dyke at the great falls of Malalli.

The falls of Malalli are 35 feet in perpendicular height, and form the greatest barrier to the navigation of the Demerara river.

At the base of the falls may be seen ejections of trap and porphyry between the granite ; and on the confines of the basin below the falls, several interesting examples of weathering and decomposition of the granite.

The trap or greenstone, that has passed up the fissures or lines of weakness, appears very dense, and so fine-grained that it might be taken for petrosilex. The curious contortions and the splitting of veins that have forced their way through masses of granite are exceedingly interesting and instructive.

The hornblendic rocks continue over a distance of ten miles up the river, occasionally rising to the surface, but more frequently observed covered by clays and sands, resulting from the decomposition of these and granitic rocks.

Where the clays or sands form the banks of the river the land is low and often swampy for miles around, intersected by numerous bayous, showing a considerable depression of the country.

On approaching Navaroo creek, granite occurs of a very beautiful character, with purplish felspar and green mica.

There are several large boulders near Kanimapoo's Landing. This series of granite continues up the river four or five miles. A very good yellow-ochre appears to be the result of its decomposition, and occurs in thick beds in this vicinity.