Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/582

 base of extreme hardness ; it usually contains crystals of hornblende, and occurs in regular layers of great thickness, some of which are massive and break with a conchoidal fracture, while the others are slaty and split vertically. It often occurs in isolated patches in the valley and Unamara river. Although this rock has been called and laid down on the map as quartz-porphyry, I should rather regard it as an altered sandstone or quartzite, as by further investigation I found the lines of stratification sufficiently distinct to justify such an inference.

Large dykes of greenstone occur, similar to those in granite, traversing this formation, which extends to the Marakang river, where it passes under an escarpment from the top of which sandstone like that observed in the Mazuruni and Carubung has roiled down. At the base of the hill a greenish bedded rock, dipping north, with greenstone dykes and quartz veins, lies upon the conglomerate and white quartzose sandstone, occupying in vertical height some hundreds of feet ; and upon these are beds of considerable thickness of red and yellowish sandstone ; the latter are slightly contorted.

Continuing up the valley of Murapang the stratigraphical arrangement is as follows :

Grey sandstone in thin beds.

Yellow sandstone.

Pinkish sandstone.

White hard sandstone.

Conglomerate, dipping from 5° to 10° N.

Strike of the hill N.W. and S.E.

Not far from the Karakanang river there are low rounded hills of white and pink argillaceous sandstone, on the surface of which quartz crystals occur in such quantity that they are called Crystal Mountains.

The mountain to the north-west of the village presents the following section : —

150 feet of dark green slaty rock resting on granite.

175 „ red shaly sandstone.

175 „ hard white quartzose sandstone.

100 ,, coarse pebbly conglomerate.

200 „ pink and grey interbedded argillaceous sandstone.

100 „ red ferruginous sandstone and beds of red jasper.

The hills beyond the Karakanang river are formed of the white argillaceous sandstone with small water-worn pebbles of quartz &c, on which lie beds of hard red jaspideous sandstone.

Beyond the Peepee river to the Cotinga a red thin-bedded sandstone occurs, containing red jasper; and at the falls of Orinedouke, on the Cotinga also ; and from that to the pyramidical mountain of Waetipu and Roraima, the sandstone forms the surface-rock.

Waetipu mountain is composed of horizontal beds of sandstone and conglomerate of a light yellowish or grey colour. Height estimated at 5000 feet.

Roraima is a flat-topped mural mountain, rising to the height of 7500 feet above the sea, with perpendicular walls of 1500 to 2000