Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

July, 1836. ASCENSION. _ 587 sional green castor-oil plant, and a few grasshoppers (true friends of the desert), may be met with. Some grass is scattered over the surface of the central elevated region, and the whole much resembles the worse parts of the Welsh mountains. But scanty as the pasture appears, about six hundred sheep, many goats, a few cows and horses, all thrive well on it. Of native animals, rats and land-crabs swarm in numbers : of native birds, there are none ; but the guinea- fowl, imported from the Cape de Verd Islands, is abundant, and the common fowl has likeM'ise run wild. Some cats, which were originally turned out to destroy the rats and mice, have increased so as to become a great plague. The island is entirely destitute of trees, in which, and in every other respect, it is very far inferior to St. Helena. Mr. Dring tells me, that the witty people of the latter place say, " we know we live on a rock, but the poor people of Ascen- sion live on a cinder :" the distinction in truth is very just. On the succeeding days, I took long walks and examined some rather curious points in the mineralogical composition of some of the volcanic rocks, to which I was guided by the kindness of Lieut. Evans. On the basaltic masses, which are daily washed by the tide, most curious calcareous incrusta- tions have been deposited. They resemble in form certain cryptogamic plants, especially the Marchantiee ; their surface is perfectly smooth and glossy, and their colour black, which seems owing to animal matter. I have shown these incrust- ations to several geologists, and not one guessed their true origin. Any one would suppose that they had been the product of fire, rather than of a deposition of calcareous matter, now constantly undergoing a round of decay and renovation from the action of the breakers. Near the settlement where these incrustations occur, there is a large beach of calcareous sand, entirely composed of comminuted and rounded fragments of shells and corals. The lower part of this, from the percolation of water containing calcareous matter in solution, soon becomes consolidated, and is used