Divergence of opinion.—Probably there is no subject in geology on which the divergence of opinion is so great while at the same time the observational material is so ample as that of glacial erosion. A few geologists believe that glaciers have excavated valleys and basins thousands of feet deep in solid rock, while others think that ice erosion has been inconsequential. There was a time when Joseph Le Conte and John Muir held the opinion that Yosemite valley had been excavated by Sierran glaciers, while J. D. Whitney was not convinced that glacier ice had ever even occupied the valley. Today most students of living glaciers and glacial work deny that glaciers possess great erosive power, while a group of physiographers claim that the peculiar features of Norwegian, Alaskan, and other deep valleys, including those of the New York “Finger” lakes, are due to great . . .