Page:Popular Science Monthly Volume 12.djvu/339

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THE ICE AGE.

In the West the same tale is repeated. Throughout Ohio, bowlders are found which are composed of rock utterly foreign to their present surroundings; indeed, of material not known within the limits of the State. These are found perched over declivities, buried in the soil with their exposed edges showing above the surface, or else lying unencumbered in slight depressions of the ground. In Indiana, Michigan, Illinois, Wisconsin, etc., they are omnipresent, and the streets of Cincinnati are paved with the smaller specimens that crowd in exhaustless trains upon the footsteps of their larger companions. In short, we gather the irrefragable testimony, wherever we look for it, through our Northern States, through Europe and Asia, and even along the western coast of South America, that some immense force has been exerted in times past, not only to dislocate and shatter the rocky barriers which opposed it, but also to carry away the evidences of its ravages, and scatter them in its southward movement far removed from their place of origin. Further, let it be remarked that, though one class of these erratics is composed of angular and unworn stones, another yields bowlders that have undergone severe attrition, and along their larger axes are striated and polished; bearing in mind, moreover, that the direction of their transit coincides with that of the furrows and flutings in the same region, we may strictly conclude that they are a feature also of the same excessive and gigantic system of erosion.

But there is another appearance which we believe vitally connected with these, and one of a yet broader and more significant character in its general relations than they are. Over Scotland, England, Ireland, Scandinavia, Denmark, Central Europe, Switzerland, Russia, France, Spain, and in North and South America, in short, wherever we discover bowlders and grooved surfaces, we find a deep and characteristic deposit, not the work of alluvial formations or recent detritus, for it underlies these, but the record of a vast disintegration which, having planed and corroded the continents, has covered the land with sheets of gravel, clay, silt, and sand, all intermixed with stones and bowlders, variously combined in their order of succession, and ranging in depth to over 300 feet. These immense beds furnish gravel for roads and ballast, sand for glass-making and mortars, and clay for pottery; their included stones and fragments are scored and embroidered with fine and interlacing striæ, and they cover the furrowed surfaces of either hemisphere for miles.

They represent the accumulated wear and tear of continents, under some extraordinary agent of erosion and denudation, whose teeth have resistlessly ground upon the solid rocks of the hills and highlands, hiding disfigured surfaces beneath a covering of ruin. Long Island is itself but one long dirt-heap: an accumulated pile of continental débris, sand, clay, gravel, intermixed and overlaid by bowlders, is here gathered together into a more or less stratified state,