INCRUSTATION OF SHELLY SAND.) The rocks of St.Paul appear from a distance of a brilliantly white colour.

This is partly owing to the dung of a vast multitude of seafowl, and partly to a coating of a hard glossy substance with a pearly lustre, which is intimately united to the surface of the rocks.

This, when examined with a lens, is found to consist of numerous exceedingly thin layers, its total thickness being about the tenth of an inch.

It contains much animal matter, and its origin, no doubt, is due to the action of the rain or spray on the birds' dung.

Below some small masses of guano at Ascension, and on the Abrolhos Islets, I found certain stalactitic branching bodies, formed apparently in the same manner as the thin white coating on these rocks.