Page:Popular Science Monthly Volume 20.djvu/250

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One can not see that this view better suits the facts than to suppose there were two centers of dispersion, one for Greenland and the other for the continent. From Greenland to the southwest edge of the glaciated area the distance is twenty-five hundred miles, two fifths greater than from the Laurentian highlands, and requiring a descent of over seven miles of vertical elevation from the center to the circumference. It seems unnecessary to add to the difficulties of height incurred in the shorter distance. Provided there has been no great elevation of the land, Davis' Strait seems to contain enough ocean-water to carry off all the glacial products poured into it from either side. The facts of ice movement already stated for Labrador and the Arctic Archipelago show motion easterly and northerly in the teeth of this imagined current from Greenland. Hence, as we find phenomena of glaciation in agreement with our view of radial dispersion from Labrador, whose existence was unknown to Torell, it seems as if it were altogether unnecessary to look so far as Greenland for the source of the ice-flow.

Terminal Moraines.—Years ago, those who believed icebergs would explain glaciation triumphantly asked the glacialists, Where are the terminal moraines which must have accumulated at the lower edge of the great ice-sheet? It is very strange their existence was not suspected by the early glacialists; and, as we now show their lines of distribution upon our maps, we remove another obstacle to the acceptance of the glacial theory.

Writers now generally employ the word till to denominate the materials accumulated by the ice, including the moraines and bowlder clays. The ground-moraine is that form of the till least noticed in the examination of active glaciers, because situated in the nearly impenetrable abysses between ice and earth. In the continental glacier, where the surface had the unbroken white snow for its covering, this form of moraine accumulation must have been the most abundant. In middle New England the ground-moraine is developed into the lenticular hill—an oblong rounded hummock, sometimes two hundred feet high, mostly composed of lower till, with a trend corresponding to the direction of the ice-current in the neighborhood, varying from nearly southeast near Newburyport to south 10° west in the Connecticut Valley. This lower till is compact, sometimes clayey, full of small, scratched, far-traveled stones in a forced position, with the iron coloring matter in the ferrous or protoxide condition. The capping of the hill or upper till is loose, the fragments are rough, not far removed from their source, commonly lying naturally, and the color is yellowish red from the presence of ferric oxide. These characteristics suggest the derivation of the upper till from the materials held in the ice at the time of its melting; they falling promiscuously upon the surface of the ground-moraine, compacted by the great weight of the glacier.

The moraines regarded by us as terminal are in all respects like