192 EXPLORATIONS IN TURKESTAN.
separated by warmer intervals of retreat. Three examples will now be described which seem to be explicable only on the latter theory.
(4) Moraines of the Yak Task Basin.—On the northern side of the Tian Shan
plateau, south of the eastern end of Issik Kul, lies the broad valley basin of Yak Tash, surrounded by snowy ranges whose side valleys head in little glaciers (fig. 125). Starting from one of these glaciers, that of Jukuchak, which is crossed by the road from Przhevalsk to Chadir Kul, let us examine the moraines in detail, beginning with the youngest and proceeding to the oldest, which we find half inclosing the next to oldest. The present moraine is a tiny affair, perhaps io feet high, at the foot of a valley-head glacier scarcely a quarter of a mile long and
composed largely of snow. Below this is a little pond, and then the broad, gentle slope of the side valley, which grows wider as it approaches and merges into the the main valley basin. The upper part of the side valley is floored with angular stones, but about 212 miles from the glacier these give place to a fine horizontally stratified silt, which is now dissected to a depth of 6 or 8 feet. The silt appears to be the deposit of a lake, due to the damming of the stream by a moraine lying half a mile down'the valley. This moraine is broad and flat, with few kettle-holes. It represents the last of the glacial epochs, the fifth. Below it is Arabel Lake, a sheet of water 2 or 3 miles long, hemmed in by the next moraine, and lying half in the main basin, half in the side valley. The moraine of the fourth epoch is of large size, extending 7 miles downstream, and spreading out broadly on every side so as to fill most of the Yak Tash basin. Under such circumstances the relief is naturally slight. The moraine is characterized by low bowlder-strewn hills with gentle slopes, and by broad, shallow depressions, of which twelve or fifteen were seen holding ponds from 200 to 2,000 feet in diameter (fig. 125).
The fourth moraine comes to a fairly distinct end near the point where the stream from Juuka pass turns from an eastward to a westward course. Beyond this, however, we encounter a moraine about 7 miles long which seems to be older than IV (fig. 136), but can not be sharply distinguished from it. At first sight it suggests a sand plain washed forward from the ice front, but that can not be, as it contains many bowlders 5 or 6 feet in diameter and some much larger, and in addition to this it increases in height at the lower end. It contains one or two small depressions filled with water, but otherwise its top is quite smooth, and its graded sides stretch evenly down the Jukuchak and Juuka streams, between which it lies as a long tongue. Bowlders crop out but rarely and all are well weathered, with the corners rounded off. Diagonally across the moraine runs what seems to be an abandoned channel of the Jukuchak, 5o feet deep and 400 or 500 feet wide at the top, with a string of ponds at the bottom. The other stream, the Juuka, was so far displaced to the north by the upper part of the moraine that it was caught in a rock-bound channel, where it has now cut for itself a narrow rock gorge.
The third moraine lies largely in the upper part of the typically glacial valley that connects the Yak Tash and Kara Sai valley basins. The hills above, except where they have been acted upon by glaciers, have gentle mature slopes, which form .a distinct angle with the steep and often precipitous sides of the valley. The