Wherever snow falls in large quantity and lies from year to year, there glaciers are formed in the ravines and valleys. Although made up of snow, they are almost as compact as ice, and pressed upon by the frequent accumulations at their head, they move downward, even over ground that is for considerable distances nearly level, though the movement may be only a foot or two in a year. With a great depth, sometimes more than a quarter of a mile, they have immense momentum, and they sweep the earth and stones before them, and they polish the general surface of the bed-rock and scratch deep parallel ruts in it. Where they stop, either with the end or side, they leave a ridge of their stones, called a moraine.

Glaciers were once abundant in the higher portion of the Sierra Nevada, as numerous moraines, ruts and polished surfaces testify. That was in some remote age, when the climate was much colder than it is at present. The Yosemite valley had its glacier, and Mr. King, of the State Geological Survey, thought it was a thousand feet deep. The glacial polish and grooving are found in all the cañons leading into Yosemite valley, and especially in the little Yosemite cañon at the lowest place where it can be crossed, and also on the rocks at the Nevada Fall. One moraine runs from the base of the South Dome to the Washington Column, extending from each side in a curve down the valley. Another begins at the western end of the South Dome and runs down the valley. A third marks the boundary between the glaciers that come down from the Little Yosemite valley and Toloolewack cañon. A fourth starts just below the Bridal Veil Fall, on one side, and a quarter of a mile below the Capitan on the other, and runs down to a point in the middle of the valley.

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