Page:Popular Science Monthly Volume 3.djvu/300

288 advantage of allowing the continent to stand still instead of sinking it several thousand feet below the ocean-level.

Mr. De Kay claimed that the bowlders originated at or near the places in which they now lie, that they are the remains of ancient peaks of primitive rock that have since been demolished by earthquakes and by atmospheric forces, the sites covered by detritus, and concealed from the observer. This was announced in 1828, but it made no headway, probably from the fact that these bowlders lie on the surface not only where primitive rocks abound, but also over broad areas where the primitive rocks are buried thousands of feet below later sedimentary formations, such formations being intact over the whole area.

In 1837 Prof. Louis Agassiz propounded that theory known as the glacier theory in a paper read before the Helvetic Society of Natural History in his native country, Switzerland. It is thus concisely stated by Mr. Charles McLaren: "It was deduced from a careful study of the phenomena attending glaciers. . . . The Swiss philosopher advanced step by step. He satisfied himself that in the Alpine valleys, where glaciers still exist, they once rose to a higher level, and extended farther down into the low country than they now do. Next he discovered indications of their former existence on Mont Jura and over the whole Swiss valley; and, connecting these with similar indications found in the Vosges, the Scandinavian mountains, and elsewhere, and with the well-known fact of sheets of ice covering the northern shores of Siberia, and entombing the remains of extinct species of animals, he came to the conclusion that, at a period, geologically speaking, very recent, all the Old World north of the 35th or 36th parallel had been enveloped in a crust of ice. Whence the cold came which produced this effect, and why it afterward disappeared, are questions he did not feel himself bound to answer." This theory had been suggested before by Venetz, but had been applied by him only to the region of the Alps. Prof. Agassiz afterward more fully worked out his theory, giving facts, and careful measurements, and calculations, in his famous work entitled "Études sur les Glaciers."

Prof. Agassiz supposes that the eastern Alps were upheaved when the coating of ice was on the surface, this being the last cataclysm that has visited Europe. By this upheaval of the Alps the ice was disturbed, like the rocky formations. This was accompanied or followed by a higher temperature, and the thawing of the ice, which produced torrents and consequent valleys of erosion. The floods which followed the upheaval of the Alps were sufficient to float icebergs containing blocks of rock that might be deposited in different places, the water being at least 300 feet deep, and the agent that carried and deposited the fine drift in the valleys below. The catastrophe which enveloped the northern regions in ice was sudden, according to Prof. Agassiz, but the retreat of the glacier was slow.