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254 as soon as the restraint of the rocky walls is removed. In the case of such glaciers derived from a series of neighboring valleys their expanded extremities may coalesce laterally and form a glacier of the piedmont type. The separate alpine glaciers retain their independence so far as nourishment, structure, rate of movement and geological work are concerned and may better be termed commensal streams than tributaries. In their form, size and direction of movement they are more or less affected by their neighbors, gaining in protection and power by the union, so that a piedmont glacier is able to maintain itself at a lower level than could its separate commensals. Such glaciers are peculiarly broad and short and present a relatively great amount of frontage, which is more or less irregular or lobed by the noses of the component streams, some of which may be advancing while others are stationary or in retreat. The Wenkchemna Glacier is an interesting example of this type, having a length of one-half to one mile, a breadth of about three miles and a frontage of over three miles. About a dozen commensal streams may be recognized which originate in the minor depressions upon the protected northern slopes of the Ten Peaks. The Horseshoe Glacier at the head of the neighboring Paradise Valley is of this same type, containing some sixteen alpine, component streams.

A similar although less characteristic type of piedmont glacier may originate upon an elevated mountain slope, which is crossed by a series of sub-parallel depressions, separated by rather low divides. Each depression may at first support a small alpine glacier, which, under favorable conditions for growth, may increase in thickness until it more than fills its bed and unites laterally with its neighbors. If the supply of snow is sufficiently reduced, the loss by wind action, melting and evaporation may uncover again the divides and the piedmont glacier shrinks into its original alpine compon-