The answer to such a question is not far to seek. The corals and crinoids are exclusively marine families, and so any stratum in which their remains occur must have had a submarine origin. It matters not in this case though the specimens be fragmentary, showing a broken and drifted appearance. For even supposing that they did not live at the spot where their petrified relics are now exhumed by the operations of the quarryman, granting that they were drifted from a distance, still they could only have been drifted from one part of the sea-bottom to another. The state of keeping of the specimen often tells vastly on the value of its evidence when it belongs to a land or fresh-water tribe. Thus, in one of the limestones of West-Lothian I have found a black carbonized stem of sigillaria. Now, the sigillaria was a land-plant as much as any of our hazels or willows, and where the evidence from the associated organisms coincides, furnishes its own testimony as to the origin of the rock which imbeds its remains. But the stem in question was a mere fragment, and showed moreover a worn macerated surface. Such a fossil had evidently no value as a test of the origin of the limestone, which might have been elaborated either in an inland lake or in open sea. That it had really a marine origin, and that the sigillaria actually was, as it seemed to have been, a drifted plant, I ascertained beyond a doubt by detecting on the same slab hundreds of encrinal stems along with the shells, and thin, delicate, silvery spines of productus. Thus, then, the organisms of the land may be carried into the sea, and in dealing with their fossilized remains in the deposits of former ages we must be very careful in the use of evidence derived from fragmentary and drifted specimens. But no such caution is needed in regard to the productions of the sea. If they be fragmentary and drifted, we may believe they were rolled about by tides and currents previous to their final entombment; but still they remain as good a test as ever of the marine character of the rock in which they occur.[61] [Footnote 61: The exceptional instance, of the accumulation on the land of blown sand imbedding the broken remains of marine shells, needs only to be noticed here.]