Page:The Journal of geology (IA journalofgeology11893univ).pdf/235

A definite classification of glaciers does not seem to be practicable, for the reason that various types which may be selected grade one into another through many intermediate forms. It is convenient, however, especially in teaching, to recognize three generic types termed Alpine, Piedmont and Continental glaciers; and a subordinate class designated as Tidewater glaciers, to include those which reach the ocean and give origin to bergs.

Alpine glaciers occur in many mountainous regions and have their type in the Alps where they were first studied. Several divisions dependent upon size have been recognized.

Continental glaciers as their name implies are of vast extent, and at the present time are illustrated by the ice sheets of Greenland and the Antarctic continent. The Pleistocene ice sheets of America and Europe were of this class.

Piedmont glaciers are formed on comparatively level ground at the bases of mountains where the ice is unconfined by highlands in most directions and has freedom to expand. They are fed by glaciers of the Alpine type, which spread out and unite one with another on leaving the valleys through which they descend from the snow fields at higher elevations. The only known example of this class occurs in Alaska on the plain intervening between the Mt. St. Elias range and the ocean, and is the subject of this sketch.