CHANGES IN THE LEVEL OF ISSIK KUL. 10/ 
of cross-bedded sands and gravels, with occasional silty layers, sloping toward the 
lake. Here and there low hills rise over the plain. The hills are chiefly made of 
silt, but contain also certain laj-ers of rough gravel with broken shells of land 
snails. The bod}- of the plain is about 200 feet above the lake. During the 
formation of the plain, the local baselevel at the eastern end of the lake may have 
been relatively higher than now, but whether the strata of the plain are fluviatile 
or lacustrine does not clearly appear. Semenof noted the marginal conglomerates 
in 1856, and inferred from them that "the lake in former times occupied a far 
more extensive basin" (1869, 331). The same explorer states that the mountains 
on the north of the lake are named from the Kirghiz word "kungei,'' meaning 
"toward noon," and those on the south from "terskei," meaning "toward midnight," 
thus referring to the opposite aspects of the two piedmont slopes (1858, 359). 
Severtzof noted in his journey of 1867 that the Ak-su, entering Issik Kul at the 
southeastern corner, had cut its \-alley through 200 feet of sands and conglomerates, 
and inferred from this that the lake was once higher than now (1875, 21 J. Capus 
(1892, 56) and Schwarz (1900, 581) probably base their statements that Issik Kul 
once stood 60 meters higher than now on Severtzofs obser\'ations. All estimates 
of the fonner higher stand of Issik Kul based on the distribution of sands and con- 
glomerates seem untrustworth}', because such deposits are more likely of fluviatile 
than of lacustrine origin. 
The piedmont slopes and the eastern plain are not now in their original condition. 
They are more or less dissected by open \alle}s and branching gullies. The valleys 
are not distinct near the western end of the lake. They are from 50 to 70 feet 
deep where we crossed many of them on the northern piedmont slope a few miles 
back from the midlake shore, but tlie\- decrease to less and less depth toward the 
present shoreline. The eastern plain is well dissected b}- branching terraced valleys 
with open straths. Even at the shoreline the valleys at the middle, and still more 
at the eastern end of the lake, are eroded distinctly beneath the piedmont and the 
eastern plains ; and, as will be more fully stated below, the lake waters now invade 
the valley mouths, the invasion being of increasing measure eastward. It is 
inferred from this that the sloping plains were not graded with reference to the 
present level of the lake, but with reference to a lake surface that descended gently 
eastward with respect to the present lake surface. 
The valleys emphasize this conclusion. It has just been mentioned that they 
increase in depth as one passes from west to east, along the north side of the lake. 
The>- were not noticed at the west end. They became serious obstacles in road 
building near the middle of the lake, and at its eastern end the road winds about 
on tlie plain to avoid them ; hence it is probable that the cause of the valle\' 
erosion should be associated with a tilting of the lake basin, whereb\- the eastern 
end was raised more than the western, after the piedmont slopes and the eastern 
plain had been fonned. Climatic change is also to be considered as a cause of the 
valley erosion, because the depth of the valleys below the piedmont slopes increases 
toward the mountains. This indicates a change in the regime of the streams, such 
as a change of climate commonly produces, and such as is commoidy associated with 
