The fact seems especially worthy of remark. The organisms of some of the newer formations differ entirely, in widely separated localities, from their contemporary organisms, just as, in the existing state of things, the plants and animals of Great Britain differ from the plants and animals of Lapland or of Sierra Leone. A geologist who has acquainted himself with the belemnites, baculites, turrilites, and sea-urchins of the Cretaceous group in England and the north of France, would discover that he had got into an entirely new field among the hippurites, sphærulites, and nummulites of the same formations, in Greece, Italy, and Spain; nor, in passing the tertiary deposits, would he find less striking dissimilarities between the gigantic, mail-clad megatherium and huge mastodon of the Ohio and the La Plate, and the monsters, their contemporaries, the hairy mammoth of Siberia, and the hippopotamus and rhinoceros of England and the Continent. In the more ancient geological periods, ere the seasons began, the case is essentially different; the contemporary formations, when widely separated, are often very unlike in mineralogical character, but in their fossil contents they are almost always identical. In these earlier ages, the atmospheric temperature seems to have depended more on the internal heat of the earth, only partially cooled down from its original state, than on the earth's configuration or the influence of the sun. Hence a widely spread equality of climate--a greenhouse equalization of heat, if I may so speak; and hence, too, it would seem, a widely spread Fauna and Flora. The greenhouses of Scotland and Sweden produce the same plants with the greenhouses of Spain and Italy; and when the world was one vast greenhouse, heated from below, the same families of plants, and the same tribes of animals, seem to have ranged over spaces immensely more extended than those geographical circles in which, in the present time, the same plants are found indigenous, and the same animals native. The fossil remains of the true Coal Measures are the same to the westward of the Alleghany Mountains as in New Holland, India, Southern Africa, the neighborhood of Newcastle, and the vicinity of Edinburgh. And I entertain little doubt that, on a similar principle, the still more ancient organisms of the Old Red Sandstone will be found to bear the same character all over the world. CHAPTER IX.