a foot in thickness, full of bones, was sometimes produced. At length a new change supervened, the area was again inundated and drifted over with sand, and the hollow trunk was filled to the top and buried under many feet of sediment, never to be re-opened till, after the whole had been hardened into sandstone and elevated to form a part of the modern coast, when the old tree and its forest companions which had shared the same fate with it, are made to yield up their treasures to the geologist. This history is no fancy picture. It represents the results of long and careful study of the beds holding these erect trees, and of the laborious extraction of great numbers of them, and the breaking-up of their contents into thin flakes, to be carefully examined with the lens under a bright light in search of the relics they contained. Fig. 11 in Chap. I. represents the extraction of one of these trees, which happened to be partially exposed by the wasting of the cliff; but many others had to be laboriously mined out of the rock by blasting with gunpowder. [Illustration: FIG. 140_a_.—Section of base of erect _Sigillaria_, containing remains of land animals. _a_, Mineral charcoal. _b_, Dark-coloured sandstone, with plants, bones, &c. _c_, Gray sandstone, with Calamites and Cordaites.] It is evident that the combination of circumstances referred to above could not often occur; and it is therefore not wonderful that only in one place and one bed has evidence of it been found, and that even in this some of the trees have been filled up at once by sand and clay, or so crushed by falling in or lateral pressure, that they could receive no animal remains. In one respect this is a striking evidence of the imperfection of the geological record, since, but for what may be called a fortunate accident, many of the most interesting inhabitants of the coal forests might have been altogether unknown to us. On the other hand, it shows how strange and unexpected are the ways in which the relics of the old world have been preserved for our inspection, and that there is probably scarcely any animal or plant that has ever lived of which some fragment does not exist, did we know where to look for it. It may be well to remark, in closing this chapter, how many new forms of life, air-breathing and otherwise, make their first appearance in the Carboniferous, and have continued to prevail until now. Here we find the first specimens of Amphibians, Spiders, Myriapods, Orthopterous and Coleopterous Insects, and of the Crabs among ten-footed Crustaceans. In the latter group Woodward has recently described the oldest known crab, from the Coal-formation of Belgium. [Illustration: INHABITANTS OF THE ENGLISH SEAS IN THE AGE OF REPTILES. _Pliosaurus_, _Ichthyosaurus_, _Plesiosaurus_, _Mososaurus_, and _Teleosaurus_.] CHAPTER VII. THE EMPIRE OF THE GREAT REPTILES.