Page:Popular Science Monthly Volume 35.djvu/579

Rh universe had an animating soul, which was diffused through every form of material existence, giving to each the powers and properties it was found to possess. He was a warm upholder of the Copernican system of philosophy; for adherence to which Galileo also suffered at a later date. He believed that the universe was of infinite extent and embraced an endless multitude of worlds. In a word, he had broken the fetters of ecclesiastical dogma, and had entered on a career of original speculation and research. No wonder he was considered a dangerous man, and that first the prison, and finally the stake, were his portion. Times, however, have greatly changed; and he who was led as a criminal to death for having dared to think for himself and uttered his thought, is now placed high on the honor-roll of the forerunners of modern liberty and civilization, and is gratefully remembered by thousands of intelligent men and women the world over.



publication of "The Great Ice Age," by James Geikie, fifteen years ago, and of its second edition, revised, two or three years later, presented to the general reader a comprehensive and very interesting account of the Glacial period, the latest completed chapter of geologic history. In this, as in so many other portions of the geologic record, the most important recent contributions to knowledge have been gathered on this continent; and Prof. Wright, widely known for his extensive observations and fruitful investigations in glacial geology, has here set forth, in an attractive popular style, the vast array of evidence that an ice-sheet formerly overspread the northern half of North America, stretching southward to Nantucket, Martha's Vineyard, and Long Island, to the cities of New York, Cincinnati, and St. Louis, and on the Pacific coast to Seattle and Vancouver Island.

Conclusive proof that the drift deposits, bowlders, and striæ found upon all the country farther north are due to the agency of land-ice seems to be supplied by the terminal moraines which were recognized only about a dozen years ago by Clarence King in the Elizabeth Islands on the south coast of New England, by Cook and Smock in New Jersey, and by Chamberlin in Wisconsin. Since then Prof. Wright has devoted every vacation and leisure day to the fascinating study of the drift, and has personally examined and mapped large portions of the glacial boundary along its extent across the eastern half of the United States, from Nantucket and Cape Cod through New Jersey, Pennsylvania, Ohio, Indiana, Illinois, Missouri, Kansas, Nebraska, and South and North Dakota. This boundary traverses valleys, hills, and mountains, with surprising disregard of the contour, often rising or falling one thousand feet or more within short distances in crossing the Alleghany ranges.

Not content with these investigations, Prof. Wright went three years ago to Alaska, and there spent a month in observations of the Muir Glacier, which enters the sea at the head of Glacier Bay, terminating in water about six hundred feet deep, and rising above the water in a vertical cliff of ice a mile long and two hundred and fifty to three hundred feet high. The author's measurements showed that this glacier is pushed out into the bay at an average rate of forty feet per day, moving thus many times faster than the comparatively small glaciers of the Alps, though not surpassing the motion of Greenland glaciers, which similarly end in the sea, being there broken into icebergs and floated away.

Portions of Prof. Wright's exploration of the glacial boundary were done for the Geological Surveys of Pennsylvania and of the United States, the terminal moraine through Pennsylvania being traced by him in company with the late Prof. Henry Carvill Lewis. During these surveys, and in the visit to the Muir Glacier, many very instructive photographs were taken, which appear 