Two-thirds of every iceberg float beneath the water. What a carrier power, at once for erosion and transport, in every one of these frozen floating mountains! The Polar ocean still maintains its great southward current to the equatorial seas, modified by the headlands and inequalities of bottom which occur in its progress; and then, as now, the icebergs driven along this highway of waters would drop, at intervals, portions of their stony load, to take up at other stations whatever was prepared to adhere to them. Hence the difficulty vanishes as to the large detached blocks so often found on the elevated sides of mountains. Hence, too, the explanation of those collected groups which are entirely free from any admixture of clay. And hence, upon the retreat of the waters and the elevation of the land, it is reasonable to infer that many districts would be swept bare again of their mud, while the bowlders would remain, and that in other quarters ridges and the deeper accumulations would be formed. “Both theories,” however, as stated by Mr. Page in his excellent treatise, “Rudiments of Geology,” “are beset with difficulties; and though the latter accounts more satisfactorily for most of the phenomena of the erratic block group, still there are many points respecting the distribution and extent of the deposit to be investigated before either can be finally adopted. All that can be affirmed in the present state of the science is the composition and nature of the clay, gravel, and bowlders—the course of the currents concerned in their deposition—the fact of the land having a configuration of hill and valley, not differing much from what now exists—and the peculiar scantiness, if not total absence, of organic remains.”