RECONNAISSANCE IN CENTRAL TURKESTAN. I7I 
the border of the Kashgar basin was 15 or 20 miles north of its present location, and 
was a place of heavy gravel deposition. Then a small fold de\-eloped along the 
border, lifting up part of the gravels and causing the accelerated streams to deposit 
their load of pebbles farther toward the center of the basin, where playas had formerly 
deposited silt. Later another fold was developed and the gravels once more ad\-anced, 
and so on by steps which were perhaps too slow to be noticed. The older gravels 
were compressed and hardened into conglomerates and their upper portions were 
woni down to the smooth grade of the Tertiary peneplain. A similar experience 
befell all the underlying fonnations. Each of them, and the peneplain as well, 
represents not a certain time, but a stage in development, and some of the stages 
are not yet completed. 
PHYSIOGR.\PHIC PROVINCES. 
THE TIAN SHAN PLATEAD. 
The part of Central Turkestan traversed by the writer divides itself naturally 
into four provinces — namely, the Tian Shan plateau, the Alai Mountains, the 
Kashgar basin, and the Fergana basin. The first of these is generalh- tenned the 
Tian Shan ^Mountains, but as far as the province was seen, it is not strictly a 
mountain range according to a scientific definition, nor is it strictly a plateau. It is 
a region of mountainous structure, and once of truly mountainous form, but it 
long ago reached old age, and has since been uplifted to its present height with 
relati\-ely little renewed folding of the strata. In structure it is still mountainous, 
but its present form and altitude are due to an uplift of the unifonn kind which 
is usually associated with the formation of plateaus. To-day it may best be 
described as a plateau; to-morrow, geologically speaking, when all the remnants 
of the uplifted peneplain surface and the last of the post-Paleozoic strata have 
been removed and dissection has gone far enough to produce strong relief, it will 
again become a typical mountain region of highly folded limestones. The general 
structure is shown in the accompanying section (fig. 124), which is about 200 miles 
long and extends south-southwest from the mouth of the Juuka Su, 25 miles 
west of the east end of Issik Kul, to the Kashgar desert at Sugun, 30 miles west of 
Shor Kul. The section represents the general character of the plateau in its least 
dissected portion. Farther east and farther west the surface is more deeply trenched 
by the main streams. Along the section the profile is essentially a ver\- broad anti- 
cline of the Uinta type, as defined by Powell, where the sides are monoclines and the 
top is flat. The fact that the component strata were already highly folded does not 
alter the character of the last uplift, although it makes it less evident in the cross- 
section. If the line representing the surface is looked at alone, the true nature of 
the deformation is evident. The anticline is not strictly flat on top, but undulating. 
The troughs form broad basins at an altitude of from 10,000 to 12,000 feet, while the 
crests fonn broad ridges which reach a height of from 13,000 to 15,000 feet. 
On the steep northern slope of the broad anticline the valleys are fairh- open 
at the base where the>- reach the Tertian- strata of the Issik Kul basin, but the\- 
are for the most part narrow canyons with inaccessible walls of naked rocks 
