Page:Popular Science Monthly Volume 12.djvu/334

320 scattered their burden of débris far and wide over its plains. The conception was a bold, almost a terrifying one; and, because the actual history and nature of glaciers was so little known, it was regarded with aversion and spoken of with contempt. Agassiz had laboriously studied the glaciers of the Alps, he had conned the lesson they taught with eager apprehension of its great significance, and he knew so well every characteristic of their work that he instantly recognized abroad the same indelible evidence of their past presence.

Venetz, Rendu, and Charpentier, had preceded him in glacial study, and had insisted upon an extension of the Alpine glaciers far beyond their present beds in past ages, but had not realized the immense utility of these views in explaining the glaciated surfaces of Europe. Forbes, Hopkins, and Tyndall, succeeded him in the investigation of glacial physics, and by their close scrutiny into the constitution of ice, and the laws of ice-making and glacial motion, fairly established a new department of physical science, and added confirmation to the views of Agassiz.

Now, let us examine some of these singular and hitherto inexplicable records, which elicited Agassiz's theory, and which, long before they were harmonized by that assumption, had been attentively examined by geologists and explained upon other grounds. Furthermore, we will review them without reference to the theory of glacial action, and only subsequently compare them with the effects now being produced wherever glaciers and icebergs are at work.

The rocks as they lie in place, the flanks and summits of mountains to heights of 5,000 and 10,000 feet, and the surfaces of outcropping masses over immense areas of the world, are all gauged in long, straight channels, sometimes a foot deep, sometimes eight feet deep, with widths from two to three feet. These grooves, of all dimensions, pass over the rock in groups like mouldings, and the rocks they occur upon are polished and oftentimes lustrous. The channels diminish in size to the faintest striæ, which, like sharp scratches, cover the surface, running along at times in parallel series, or diverging in different directions, as though the great primitive plane had varied its course over them, scouring with exquisite fineness.

These lines and runnels score the rocks over the Northern United States and Canada, throughout Europe, in Asia, and over the shores of South America. We discover almost instantly that in the same region they have the same direction; that they seem, as it were, to stream with us from the north; and that, wherever other scores contravene this, these secondary markings are themselves harmonious, indicating some subsequent action upon the rock, in character similar to the first, though varying in its motion, and probably restricted in its extent and importance. Thus the scores upon the rocks of New England point northwest and southeast, and only local derangements disturb this prevalent direction. The easting increases as we progress