74 EXPLORATIONS IN TURKESTAN. 
There can be no question that the highland of the Bural-bas-taii was once part 
of a well-finished lowland of erosion, presumabh- a peneplain of subaerial degrada- 
tion. It must ha\e gained its present altitude with comparative rapidity, and in 
geologically modern time ; otherwise it would be more dissected to-day. When it 
still lay low, the lowland of which it was a part must have been much more 
extensive than the present area of the highland ; for lowlands can not be worn down 
on resistant crystalline rocks without the very general reduction of all neighboring 
and quiescent structures. It thus becomes probable, from the consideration of this 
range alone, that many neighboring ranges have shared its historj-, and if they do 
not all to-day imitate its plateau-like fonn, it must be that they were somewhat less 
worn down in the previous cycle of erosion, or, like the Dongus-tau, already more 
consumed (owing to greater uplift or to weaker structure) in the present cycle, or 
both. This conclusion did not long remain a matter of speculation only, for at Son 
Kul and around Issik Kul we found many other ranges that sujjported it. 
THE KOK-TAI. RANGE AND THE SON KUL BASIN. 
The steep-sided glacial troughs that we examined in the Kok-tal range north- 
east of Son Kid are eroded in a granitic upland of moderate relief that slopes 
toward the lake basin. The sloping tipland was continued east of the lake, where 
it gradtially descended to a broad granite floor, across \\liich the lake outlet has cut 
an open trench, 75 or 100 feet deep. All this granite surface is to-day suffering 
dissection and gaining stronger relief The lake outlet must fall rapidly in 
descending 3,000 feet to the Narin Ri\-er, and a deep gorge will in time be cut 
along its course. The side streams from the north will, therefore, intrench them- 
selves deeply, and the granite .slope between them will be converted into a series of 
.sharp spurs in the mature stage of the present cycle of erosion. The simple surface 
in which the glacial troughs and stream valleys have already been eroded is itself a 
surface of erosion, but it could not have been produced in its present attitude ; it 
must have long stood lower and more nearly level. Its present elevated and inclined 
attitude must have been gained by a warping uplift in modern geological time. We 
are, therefore, disposed to look upon the sloping upland as once having made part 
of the peneplain that is more clearly proclaimed in the highland of the Bural-bas- 
tau. The basin of Son Kid is probably the result of warping or faulting the same 
peneplain. The northern slope of the Kok-tal range descends rapidly into the 
valley of the Tuluk, and its slope is sharply dissected by man}- side streams. When 
seen from the moraines in the Chalai range, north of the Tuluk, the crest of the 
Kok-tal has a rather even crest line, much more even than the serrate crest of the 
Chalai range itself 
THE RANGES NEAR ISSIK KUL. 
The road through the gorges of the Juvan-arik gave us no sight of the 
mountain crests ; but when we entered the open Kach-kar basin, the long slope of 
the Alexander range ascended northward from the farther side of the basin, and 
its general appearance at once suggested block-faulting. This suggestion was con- 
