Page:Popular Science Monthly Volume 4.djvu/661



ILL within a comparatively recent time, geologists regarded the climate of the prehistoric periods as tropical or warm temperate. Those who first sought to explain the presence of certain scratches upon ledges, by the action of moving ice in continental masses scouring the surface, were met by ridicule and skepticism. The writer has now before him a caricature devised to illustrate the notions of the literary world upon this subject thirty years since in England. The excellent Dr. Buckland appears clad in furs, such as are required in Greenland, with a map of ancient glaciers under his arm, showing markings made on the rocks 33,333 years ago. On one side is represented a bridge with a scratched paving-stone at the entrance, and an inscription like this: "Scratches made day before yesterday by a cart-wheel passing over Waterloo Bridge." It is said that the learned doctor was greatly amused by the sketch, and sent copies of it to all his scientific friends. The one before us bears his autograph.

But within the last three decades numerous observers have carried out the suggestions of the earlier geologists to a very extensive application. Forbes and Agassiz explored the glaciers of Switzerland in order to learn the laws of ice-motion; Lyell, Murchison, Ramsay, and others, have ransacked the fields of Great Britain in search of facts from which to generalize; and, in our country, Hitchcock, Mather, Whittlesey, Newberry, Dana, and a score of younger men, have made the investigation of the drift period a matter of enthusiasm. The existence of an immense era when all of Northern America and Europe was enveloped by enormous thicknesses of solid ice, crunching fragments of rocks beneath its massive tread, and transporting square miles of moraine rubbish upon its back, is now universally accepted. Some have gone so far as to believe that the entire globe was encircled