192 EXPLORATIONS IN TURKESTAN. 
separated by wanner intervals of retreat. Tliree examples wU\ 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 
platean, south of the ea.stern 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 Jnknchak, 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 10 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 jiond, 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 2 ]/> miles from the glacier these give place to a fme 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, dtie 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 dej^ressions, 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 
manv 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 Jnknchak 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, 50 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 Ta.sh and Kara Sai valley basins. The hills above, except 
where they have been acted upon b)- glaciers, have gentle mature slopes, which 
form a distinct angle with the steep and often precipitous sides of the valley. The 
