214 EXPLORATIONS IN TURKESTAN. 
Although we do not find in the historj' of Shor Kul a complete series of records 
to match all the changes of climate inferred from the stud\- of the old moraines, we 
find no records inconsistent with such changes and many confinnator)- of them. 
The essential features of our glacial theorj- are that a number of cold or glacial 
epochs were separated by wanner interglacial epochs, when the climate was approxi- 
mately like that of to-day, and that these epochs decreased in severity and length 
from fust to last. The retreat of the lake between the two epochs of unequal 
expansion supports this most clearly. Further study will probably show that the 
past oscillations of the lake agree even more perfectly with those of the glaciers. 
.\t present only a tentative correlation of lacustrine and glacial epochs is possible. 
The silts of the upper lake level may represent either or l:)oth of the first two 
glacial epochs ; the cutting of the deepest valle}- in them represents the succeeding 
wanner interglacial epoch ; the third and fourth epochs, glacial and interglacial, are 
perhaps represented by the gravel filling and the terraces, respectively, which lie in 
the deep valley. The fifth glacial epoch seems to correspond to the rise of the lake 
to the lOO-foot level, and the present retreat of the ice to the present retreat of the 
water. 
SUMMARY. 
In our review of the history of Central Turkestan, from Paleozoic times down 
to the present, we have found that the greater changes ha\-e on the whole affected 
the entire country rather than small areas. Uniformity has been the rule. During 
the Paleozoic era the entire region was submerged beneath the sea and the deposi- 
tion of calcareous strata was long-continued. After the latter had attained a great 
thickness tectonic movements began on a large scale and continued until the lime- 
stones had been closely folded and mountains had been fonned, which were worn 
away during the first part of the succeeding era. The Mesozoic and Tertiary eras 
are not sharply separated and must be considered together. Throughout the greater 
part of these eras tenestrial conditions prevailed, with the deposition of strata 
characteristic of interior basins, namely, conglomerates, cross-bedded sandstones, 
and silts, which appear to be vast playa deposits. Most of the strata are without 
fossils, and in this and other ways suggest that the climate was dr)- and that desert 
conditions prevailed more or less extensively. Only once during this long period 
did the sea encroach on the land. This was at the end of the Mesozoic era, when 
limestones and marls were laid down in what seems to have been a sea of somewhat 
fluctuating depth. It is not impossible that between the Mesozoic and Tertiary 
eras there were world-wide movements which elsewhere caused uplift and erosion, 
followed by unconfonnable deposition ; but here the movements of this time caused 
encroachment of the sea and deposition. In the basin region of America the 
Mesozoic and Tertiary eras present a succession of strata notably similar to those of 
Central Asia. The resemblance is so marked and extends so far into details that 
it can scarcely be the result of chance. It suggests that interior arid basins which 
to<lay resemble one another have long resembled one another and have passed 
through a similar succession of changes. 
