Page:The Zoologist, 1st series, vol 4 (1846).djvu/308

1474 scribed. Its outer margin is formed by a moderately steep beach, of course calcareous sand mixed with larger fragments of coral and shells, extending back for twenty yards or more, with a few scattered tufts of grass and other herbage. The higher or vegetated portion of the island is surrounded by a more or less continuous, low, wall-like bor- der of coral rock, its faces much decomposed by the weather, and hollowed out in a singular manner into innumerable intricate wind- ing openings, some of which are large enough to admit a man's body. This rock, which varies from a conglomerate to a coarse sandstone, is in general soft and crumbles readily in the hand, but at one end of the island, blocks of sufficient size and hardness to be used for building purposes were obtained in abundance. This bed of sandstone is not more than a few feet in thickness, and exhibits proof of its recent for- mation, by containing shells and fragments of coral, specifically iden- tical with living inhabitants of the reef, and occasionally eggs of tur- tle,* apparently as if, while in situ in the loose sand of what was then a mere sand-bank, some chemical agency had converted the whole in- to a bed of stone. The centre of the island is considerably lower than the margin, the highest part of which is about twenty-four feet above high-water mark. Various attempts were made to procure fresh water by digging, but without success. One pit, dug to a depth of sixteen feet near the centre of the island, presented the following succession of strata : — 1stly, a layer, three inches thick, of rather fine coral sandstone;2ndly, a deposit, nine inches in thickness, of moist pulverulent black earth, resembling peat, but without any traces of woody fibres;3rdly, and extending to the depth of thirteen feet from the surface, are successive deposits, varying from coarse coral conglo- merate and sandstone to unconcreted calcareous sand mixed with a few small scattered fragments of coral and shells;4thly, a layer of masses and large fragments of coral (of species now alive on the reef), bleached and water- worn, loosely imbedded in coarse sand ; and here the boring was discontinued in consequence of the ingress of salt water, which ebbed and flowed with the tides. The greater portion of the centre of the island affords a superstratum of rich black mould, well manured with the dung of sea-fowl ; and in a small garden established there, many culinary vegetables were found to thrive well.

Owing to the slight range of tide at Raine's Islet, the reef is com- pletely uncovered only at low- water spring- tides, the rise and fall

A specimen of this description from Ascension is exhibited in the Museum of the Geological Society.