Hence, with a low temperature, vast quantities of snow must have collected on their lofty sides; and at the same time their great height and declivity would cause the ice to move down their steeps with greater force than the glaciers which passed over New England. Writers who have given the subject considerable study think that the deep valleys of the Sierra Nevada were produced by disruptive rather than erosive agencies. This conclusion has been formed from the lack of large accumulations of débris about their lower extremities, which would not be the case if such valleys were the result of glacial erosion. But, should the coast ranges be attributed to glacial action, as has been stated, we can well account for the débris that should accumulate from the erosion of the deep valleys. The only thing that could prevent the ice from gathering on the Sierra Nevada range during an ice period in greater masses than on any mountains in the northern hemisphere would be the lack of cold; for, with a low temperature, the fall of snow would be enormous. This is shown by the great snow-fall during the short mild winters of to-day. Therefore, with ice-sheets covering a large portion of the lands of the high northern latitudes, and with the Japanese current which tempers the north Pacific waters made cold in the manner described in the foregoing pages, and while the sea along the north-west coast of America was strewn with icebergs launched from Alaska and British Columbia, it seems that California must also have obtained a frigid climate during the ice age. Therefore, on account of its exposure to the ocean winds, and the consequent heavy snow-fall, the accumulation of ice on its lands must have been immense. For, when it is considered that the glaciers of North America extended southward even into the torrid zone sufficient to cover a large portion of Central America, it is unreasonable to suppose that any portion of California could escape being covered by heavy ice-sheets during the glacial epoch. The comparatively scant fall of rain and snow over Greenland is known to form ice-sheets hundreds of feet in thickness. Therefore, what must have been the depth of ice over the high lands of the Pacific coast north of California at the culmination of a frigid period? The descriptions given by Dr. Dawson and others, of glacial phenomena along that coast, favor the impression that an immense ice-sheet at one time deeply covered the whole region from the top of the mountain range to the ocean.