Page:Mongolia, the Tangut country, and the solitudes of northern Tibet vol 1 (1876).djvu/330

 Even on the highest summits the snow all melts in spring, although it sometimes falls in May and June, when it is raining on the neighbouring plains. The rain and snowfall on these mountains is very large, although running water is remarkably scanty; even springs are rare, and according to the Mongols only two running streams of any size occur in the whole range. This phenomenon is attributable to the wall-like steepness of these mountains, which do not retain the moisture for sufficient time to allow of the formation of rivers. The torrents, which owe their short-lived existence to the heavy rains, descend headlong to the neighbouring desert, and are lost in the sands or form temporary lakes on the clay flats ; but as soon as the rain ceases they disappear as suddenly as they were created.

The narrow, but at the same time lofty and rocky, chain of the Ala-shan mountains has been elevated by subterranean agency, and stands like a rampart in the midst of surrounding plains, exhibiting a peculiar formation, and forming quite a distinct group, as far as we could learn, unconnected with the ranges of the Upper Hoang-ho; it terminates in the sandy deserts in the south-eastern corner of Ala-shan. The chief rocks in these mountains are slates, limestone, felspar, felspathic porphyry,