Page:Popular Science Monthly Volume 6.djvu/694

674 deposits of loam, sand, gravel, and rocks, evidently brought from considerable distances by some vast current that once covered the lowlands, and even lesser hills; for, in the Rhine Valley this surface-layer is found at elevations of 300 to 600 feet above the present river-level. The bowlders are of various rocks that are not native to this region, but are found in the Juras, the mountains of the Black Forest, the Vosges, and especially the Alps, of whose mass these constitute a large proportion. A similar drift is found over the wide, rolling country between the Juras and the Alps, and indeed over nearly all the lowlands and valleys of Europe and the world. From the erroneous, but once universal belief, that it was produced by the Noachian Deluge, or the all-submerging flood of which the Sagas of so many nations are full, this deposit was early named the diluvium, or diluvial deposit. It consists, according to this view, of the detritus from mountain ranges, transported and scattered-broadcast over lower levels by the Deluge.

This latest of geological formations rests upon the upper strata of the Tertiary, when they are present, In the Rhine Valley, however, it covers the Miocene or middle Tertiary; and in other regions, the chalk, the Jurassic, or even older formations. Upon the diluvium itself are built most of our cities, and in it will most of us be buried. The melted snows, the rains, and the waters of our streams, penetrate through its loose layers until the more impervious underlying clays (mostly Tertiary) arrest and hold them in readiness to supply our daily needs. The diluvium seldom yields much that is of mineral or industrial value, except the material of our tiles, brick, and mortar. In California, Brazil, Australia, and the Ural Mountains, however, its gravels are rich in gold, platinum, and jewels of various sorts, and in some localities tin-ores are found in it.

Geologists have been long occupied with the study of the producing causes of those vast floods, the effects of which are so strikingly seen in the pebbly plains and terraces of our river-valleys, and in the layers of sand and loam upon our uplands and hills. That there once were there masses of flowing water-currents, like, yet far vaster than, our present rivers, cannot be intelligently doubted. The absence of marine shells and the universal abundance of the remains of land-animals in the deposits in discussion forbid the belief that the sea covered our own and the adjacent continents during this latest of geological eras.

All the hypotheses advanced in explanation of the phenomena we have mentioned cannot be here adduced; we can only say that the great majority of recent geologists agree and assert that these immense streams were chiefly produced by the melting of snows and glaciers, that must then have extended not merely from the Alps and Pyrenees, as at present, but from the north, southward over a large portion of Europe; even the smaller ranges, such as the Vosges and Black Forest, then having each its glacier system.