l68 EXPLORATIONS IN TURKESTAN. 
and its residual mouulaiiis, and in order that the weak Tertiary strata should still 
exist in the warped and uplifted plains, its deformation nuist have been compara- 
tively recent. 
Numerous other examples of this kind might be cited, but one will suffice. 
At Giilcha, about 30 miles southeast of Osli, on the border between the Fergana 
basin on the north and the Alai Mountains on the south, the Gulcha River flows 
in a valley 2,000 feet deep. Between this valley and the next there is an upland 
which in a general view appears to slope smoothly and gently to the north, although 
it is somewhat notched here and there. The surface of the upland truncates 
inclined strata which vary in hardness from the resistant oyster-bearing limestone 
to the soft, shaly sandstones of the Tertiar)-. It is still well preserved, in .spite of 
the fact that there is in some places a descent of 2,000 feet in 3 miles. The sloping 
upland plain nuist have been formed as a peneplain, and must have been given its 
present inclination at a somewhat recent date. In the western part of the Tian 
Shan range, where the plateau character is less marked, and in the main range of 
the Alai Mountains, the old peneplain is shown chiefly in the level crests of the 
ridges. Kven in the lofty Pamir there are certain ranges where the snowy peaks 
are smoothly truncated, as though by the old peneplain, in spite of the fact that 
they are from 15,000 to 20,000 feet high. The fragments of old surfaces are indeed 
so numerous that it seems safe to conclude that much of the country was once 
reduced to a peneplain, and the rest of it at least to the stage of late maturity- 
The extent of this degraded region was fully 100,000 square miles — that is, at least 
400 miles east and west and 250 miles north and south, and probably much more. 
Although the age of the peneplain is not closely fixed by the evidence of fossils, it 
may be referred to the end of the Tertiary, because its erosion was completed after 
practically the whole Tertiary series of the region had been laid down and warped. 
For the present we shall consider that the erosion of the peneplain marks the close 
of the Tertiary era and that the Quaternaiy is introduced by the succeeding changes 
of elevation. 
