One of the things that first struck me, as I got on deck this morning, was the extreme whiteness of the sand. I could see it gleaming bright through the transparent green of the sea, three fathoms below our keel, and, in a little flat bay directly opposite, it presented almost the appearance of pulverized chalk. A stronger contrast to the dingy trap-rocks around which it lies could scarce be produced, had contrast for effect's sake been the object. On landing on the exposed shelf to which we had fastened our halser, I found the origin of the sand interestingly exhibited. The hollows of the rock, a rough trachyte, with a surface like that of a steel rasp, were filled with handfuls of broken shells thrown up by the surf from the sea-banks beyond: fragments of echini, bits of the valves of razor-fish, the island cyprina, mactridae, buccinidae, and fractured periwinkles, lay heaped together in vast abundance. In hollow after hollow, as I passed shorewards, I found the fragments more and more comminuted, just as, in passing along the successive vats of a paper-mill, one finds the linen rags more and more disintegrated by the cylinders; and immediately beyond the inner edge of the shelf, which is of considerable extent, lies the flat bay, the ultimate recipient of the whole, filled to the depth of several feet, and to the extent of several hundred yards, with a pure shell-sand, the greater part of which had been thus washed ashore in handfuls, and ground down by the blended agency of the trachyte and the surf. Once formed, however, in this way it began to receive accessions from the exuviae of animals that love such localities,--the deep arenaceous bed and soft sand-beach; and these now form no inconsiderable proportion of the entire mass. I found the deposit thickly inhabited by spatangi, razor-fish, gapers, and large, well-conditioned cockles, which seemed to have no idea whatever that they were living amid the debris of a charnel house. Such has been the origin here of a bed of shell-sand, consisting of many thousand tons, and of which at least eighty per cent. was once associated with animal life. And such, I doubt not, is the history of many a calcareous rock in the later secondary formations. There are strata, not a few, of the Cretaceous and Oolitic groups, that would be found--could we but trace their beginnings with a certainty and clearness equal to that with which we can unravel the story of this deposit--to be, like it, elaborations from dead matter, made through the agency of animal secretion.