Even on the steepest slopes there is everywhere a covering of clays and sands, and generally a good thickness of vegetable soil.

It is this which perhaps contributes to the uniform luxuriance of the forest, and delays the appearance of that sub-alpine vegetation which depends almost as much on the abundance of rocky and exposed surfaces as on difference of climate.

At a much lower elevation on Mount Ophir in Malacca, Dacrydiums and Rhododendrons with abundance of Nepenthes, ferns, and terrestrial orchids suddenly took the place of the lofty forest; but this was plainly due to the occurrence of an extensive slope of bare, granitic rock at an elevation of less than 3,000 feet.
The quantity of vegetable soil, and also of loose sands and clays, resting on steep slopes, hill-tops and the sides of ravines, is a curious and important phenomenon.

It may be due in part to constant, slight earthquake shocks facilitating the disintegration of rock; but, would also seem to indicate that the country has been long exposed to gentle atmospheric action, and that its elevation has been exceedingly slow and continuous.
During my stay at Rurukan, my curiosity was satisfied by experiencing a pretty sharp earthquake-shock.

On the evening of June 29th, at a quarter after eight, as I was sitting reading, the house began shaking with a very gentle, but rapidly increasing motion.