Page:A Treatise on Geology, volume 1.djvu/253

 CHAP. VI. is also similar, as may be seen by consulting the classification of Cuvier and Brongniart.—About Aix-la-Chapelle, the same formations and groups appear; and the general features, at least, are retained through Westphalia (Essen, Paderborn) and along the plains of northern Germany. On the Elbe, about Dresden and Pirna, the lower green sand is called quadersandstein, the representative of the chalk planerkalk. In the Carpathians is no chalk, the green sand being greatly developed. In the Alps is no chalk, and beds of green sand are intercalated among the upper Jurassic oolites (Salève). But the most remarkable case is the addition of another limestone rock, above the upper chalk, very coarse and sandy in texture, but containing layers of flints, in St. Peter's Mountain, near Maestricht. This rock seems, by its composition and organic contents, to offer an imperfect transition from chalk to the calcaire grossier, one of the next incumbent tertiary strata (Fitton). Murchison and Sedgwick suppose the shelly marls of Gosau to present a somewhat different case of transition from the cretaceous system of the Styrian Alps to the tertiary rocks. The whole cretaceous system of America may be taken together into two great masses,—a chalky, or at least calcareous, mass above, and a green sand mass below. Thus very general analogies appear at very distant points, and the most constant of the formations is the sedimentary or green sand group. (Rogers, in Rep. to Brit. Assoc.)

Organic Remains.—The fossils of the cretaceous system are eminently marine: nearly all the plants which it contains (they are few) are of marine types; and the sponges, stellerida, mollusca, Crustacea, fishes, and reptiles, all appear to have been inhabitants of the ocean. Mammalia are not known in the cretaceous rocks. It appears that (excluding the Maestricht and Gosau beds) nearly the same large proportion of extinct genera, and the same differences of proportionate development of molluscous groups, is traced in the cretaceous as in the oolitic system; so that both the oolitic and cretaceous fossils are reliques of a condition of land