Page:A Treatise on Geology, volume 1.djvu/308

 292 Bruckner mentions a trainée of blocks north of Mecklenburg Strelitz, which runs from N.N.W. to S.S.E. They are said to be in general more abundant on the elevations than in lower ground, the largest masses being nearest the summits, as if the lighter gravel and sand had been removed from them.

De Luc observed, in Lower Saxony, circular ridges of hills with a single outlet from these natural amphitheatres; and on the inner faces of the hills abundance of granite, porphyry, &c. There can be no doubt that the great masses of granite, porphyry, transition limestone, &c. scattered over the north of Germany, have been derived from the Scandinavian mountains, because the limestones contain organic fossils peculiar to the transition rocks of Sweden; the porphyries and granites are equally identified by their mineral characters; and the distribution of the groups of blocks on the south of the Baltic, as well as the traces of their passage across Scania, completely agree with this conclusion. The era when these blocks were drifted across the Baltic, though modern when compared even with tertiary strata, is yet very remote, for they lie under the ancient peat mosses of East Friesland; and there appears reason to think that more than one such migration of erratic blocks has accompanied the upward movements of the Scandinavian primary regions. "Almost the whole surface of North America, as far as examined, may be said to be covered with an investment of earth, pebbles, and boulders, obviously of diluvial origin. The thickness of this deposit varies, though its average depth may be said to be from ten to twenty feet. All that low and level tract described as the Atlantic plain, and also the lower sections of the great valley of the Mississippi, appear to be the districts where it conceals the underlying strata to the greatest depth."—"The boulders may almost invariably be traced to formations which lie at some miles' distance, to the north-west and north. This distribution of the diluvium from the north and north-west is not confined to the rivers whose