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CHAP. VI.
FLUVIATILE DEPOSITS.
17
bination, just as we see to have been determined by many travellers on the plains of North Germany, Russia, North America, and the regions west and north of the Alps.
The height of the origin of a glacier depends, as already observed, on the elevation of the line of perpetual snow; and this varies, not only with latitude, but by the influence of local causes and peculiarities of climate. In all the northern zone's it is above the isothermal lines of 32, and is so much the more above this line, as the difference between winter cold and
