RECONNAISSANCK IN C1:NTKAL TUUKKSTAN. I99 
SUMMARY OF THE GLACIAL PERIOD. 
The facts presented in the preceding sections, together with others of a similar 
natnre not here recorded, show that in Central Turkestan there are many exidences 
of a Quaternary glacial period, although all records of glaciation are confined to 
high levels. Wherever old moraines are well developed they indicate that the glacial 
period is divisible into two or more subdivisions ; and where the valleys are large 
and reach high enough still to contain glaciers the number of these subdivisions is 
five, marked by successive moraines, each of which is smaller and at a greater alti- 
tude than its predecessor. Two 'theories present themselves as worth}- of consider- 
ation in explanation of these facts. According to one there was but a single glacial 
advance and retreat. Tiie retreat was not accomplished uniformly or rapidly, but 
by successive steps, after each of which there was a long pause that gave opportunity 
for the accumulation of a moraine ; thus five moraines were fonned by each glacier 
and those now in process of deposition belong to the sixth .step of the same long 
retreat. According to the other theor}-, each moraine represents a distinct glacial 
epoch, during which the glaciers first advanced and then retreated. Under this 
theon- the intervals of retreat were as wann as or warmer than the present and the 
ice retreated far into the mountains during each of them. 
For fifteen out of the twenty-four glaciated valleys examined the first theory' is 
sufficient, but it will not explain the other nine. In eight of these nine valleys one 
or more of the older moraines lies upon a topography different from that of to-day, so 
as to suggest that the moraines and the floor on which they rest have been trenched 
by a valley of stream erosion. In this valley lie the younger moraines, leaving the 
older moraines as terraces which extend beyond the later moraines both up-valley 
and down-valley ; the ujj-valley extension of the morainic terrace gives a minimum 
measure of the retreat of the glacier during the interglacial epoch. In the ninth 
valley a detached portion of an older moraine lies far up-valley from its successor and 
even above the main part of the modern moraine. These facts are to be explained 
only by supposing a glacial retreat and advance in each interglacial epoch, and hence 
a wanner interglacial epoch between colder glacial epochs. Another sort of evidence 
of a warmer interglacial epoch is found where one moraine lies upon its predecessor 
in an attitude which indicates that before the deposition of the younger moraine 
the older one was first an area of erosion and later of deposition. All these facts 
accord with the theory of successive advances and retreats, and thus warrant the 
division of the glacial period into several glacial and interglacial epochs. In one 
place or another signs of an interglacial retreat are found between each successive 
pair of the four earlier moraines, while the fifth moraine stands apart from the others, 
except at Kan Su, where the time during which there is evidence of retreat may be 
either between the third and fourth or fourth and fifth advances of the ice. Ever}-- 
where the climate of the successive glacial epochs seems to have grown less severe, 
and the duration of the interglacial epochs seems to have diminished in the same 
ratio. 
