. Elements of geology : a text-book for colleges and for the general reader. Geology. 50 AQUEOUS AGENCIES. be even above it—Dana), but diverges as we pass toward the pole, and finally touches the sea-level at about 66° north and south latitude, at ~b b. Below this, again, is the line of lower limit of glaciers, which, commencing again nearly coincident with the two preceding, at the equator, approach- es and touches the sea- level at about 50° lati- tude, or, under favor- able circumstances, at even lower latitudes. The difference be- tween these lines is often several thousand feet. In the Al
. Elements of geology : a text-book for colleges and for the general reader. Geology. 50 AQUEOUS AGENCIES. be even above it—Dana), but diverges as we pass toward the pole, and finally touches the sea-level at about 66° north and south latitude, at ~b b. Below this, again, is the line of lower limit of glaciers, which, commencing again nearly coincident with the two preceding, at the equator, approach- es and touches the sea- level at about 50° lati- tude, or, under favor- able circumstances, at even lower latitudes. The difference be- tween these lines is often several thousand feet. In the Alps, the line of 32° is 2,000 feet, and the line of lower limit of glaciers 5,000 feet, below the snow- line. In some parts of the arctic region, the line of 32° is 3,500 feet below the snow-line, and in Norway the lower limit of glaciers is 4,000 feet below the line of 32° (Dana). For the sake of simplicity we have represented the surfaces, of which these lines are the sections, as regular spheroids ; but, in fact, they are very irregular, being much influenced by climate. Their intersection, with the sea-level will, therefore, not be along lines of latitude, but will be irregular, like iso- therms. As the line a c marks the lower limit of glaciers in different latitudes, it is evident that at c glaciers will touch the sea, and beyond this point will run far into the sea. It is in this manner, as we will see hereafter, that icebergs are formed. In Chili, glaciers touch the sea- level at 46° 40' south latitude.* General Description.—In glacial regions a mountain-valley is occu- pied in its highest part by perpetual snow; below this, farther down the valley, by neve—a granular snow, intermediate between snow and ice; still farther down, by true glacier-ice; and, finally, by a river (Fig. 44). This river is formed partly by the melting of the whole surface of the glacier, both above and below, and partly by the natural drain- age of the valley. The glacier, however, is
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