stamp as undoubtedly of carboniferous age the rock which contains them, whether it be sandstone or conglomerate, limestone or shale, and whether we meet with it among the newly-raised blocks of the quarry, or among the pebbles of the sea-shore. Each geological formation, I repeat, beginning at the oldest known to us, and ending with those that are still forming in our lakes and seas, has its own set of organic remains whereby we can detect it wherever it may chance to occur, from the equator to the poles. Each has its _style_, so to speak, just as we can at once tell whether a drawing represents a Hindoo, Egyptian, Assyrian, Greek, or Gothic temple, simply from the general _style_ of the architecture. Could we but voyage back in time as we can sail forward in space, we should find each of the geological formations not less clearly defined than are the different nations and countries of the present day.[58] Were the reader suddenly set down in an out-of-the-way street of Paris, he would probably not be long in discovering that he stood on French ground. Or if spirited away in his sleep he should awake on the banks of the Nile, he would soon ascertain himself to be in the land of the Ptolemies. And so if you transported a geologist blindfold into a quarry where ammonites and belemnites abounded, mingled here and there with bones of ichthyosaurs and plesiosaurs, he would tell you at once that the quarry lay among liassic strata. Or if he were placed in a ravine where the rocks on either hand displayed fern-stems, lepidodendra, stigmariæ, and sigillariæ, he would tell you that the surrounding district was one of carboniferous rocks, and that probably at no great distance there might be found smoking engines and dozens of coal-pits. Or could you set him down in some dark night upon a wild coast-line, and show him, perchance by the flare of torch-light, bones and scales of osteolepis, pterichthys, and dipterus, lying on the rocks around, he would tell you that the grim crags which shot up into the gloom were as ancient as the era of the Old Red Sandstone. In any case the character of the rock would signify nothing, nor would he care about the general features of the landscape, though these too become important characteristics in certain cases. Show him but a few recognisable fossils, and you give him, as it were, an "Open Sesame" to which the rocks unfold their gates and reveal a store of wonders yet more varied than those in the cave of Ali Baba. [Footnote 58: See _ante_, pp. 31, 32, and the Table of Rocks at the end of the volume.]