1. Gorges and Troughs.—Gullies, gorges and basins which retain snow and ice are fairly numerous in mountain districts. They are generally ravines, or rock fissures, or hollows, in positions below the snow line where snow and ice are sufficiently protected, from sun and wind, to remain long after snow in the surrounding open country, at the same altitude, has melted away. Some of these gorges are small, some big. As a rule, they are deep and narrow.
In north-eastern Siberia, a form of permanent surface ice is found, which the Tungusses speak of as tarinnen, which means “ice troughs” or “ice valleys.”[15] These tarinnen are broad valleys, with either a horizontal floor or one sloping gently in the form of a trough, over which the ice is spread in the form of a sheet. The Tungusses assert that the ice in some of these troughs never wholly melts away, although it lessens in quantity from the beginning of May till the end of August, after which it once more increases.
[15] Bulletin de la classe physico-mathématique de l’Académie Impériale des Sciences de St. Pétersbourg. 1853. Vol. XI, pages 305-316.
Subterranean Ice Sheets.—In several places in different parts of the world there are underground ice sheets which extend over large spaces; they are common under the tundras of Alaska; and there are fine examples on Kotzebue Sound,[16] on the Kowak River,[17] and along the Yukon River.[18] The “Ice Spring” in Oregon seems to be a formation of the same kind. Several examples of these subterranean ice sheets are reported also from different parts of the Russian Empire.
[16] See Part III: [page 167].
[17] See Part III: [page 167].
[18] See Part III: [page 166].
A somewhat different kind of ice sheet was observed on Mount Etna. Sir Charles Lyell[19] speaks of it as a “glacier preserved by a covering of lava.” He says Signor Mario Gemmellaro satisfied himself that nothing but a flowing of lava over snow could account for the position of the glacier. Ice sheets somewhat similar to these are reported from Tierra del Fuego,[20] and probably also such sheets occur in Iceland; and enormous heaps of ice covered with sand are found on Mount Chimborazo.[21] On the northwestern coast of Greenland, glaciers, whose flow has stopped, were observed buried under an accumulation of moss and grass.[22]
[19] Principles of Geology, 11th Edition, Chap. XXVI.
[20] See Part III: [page 190].