PENEPLAINS IN THE TIAN SHAN. 8l 
plateau, known to the Kirghiz as the " Arpa," 3,000 meters in altitude, overlooked 
by serrated ranges and traversed by low hills (1900, 125). Alinasy, who traveled 
somewhat farther east in 1900, gives "syrt" as the Kirghiz name of the plateau, 
which he describes as occupied by highland meadows (1901, 254). In Friedrich- 
sen's thorough review of all that has been written about these mountains, there 
is no clear statement concerning the plateau-like quality of the inner region ; but 
it may be inferred from the statement that the general law of vertical relief in 
the Tian Shan is an increase of absolute height accompanied by a decrease of 
relative height in passing from north to south (1899, 209). In Friedrich sen's 
account of his own exploration, however, there is an explicit statement. He trav- 
ersed the syrt or highland southeast of Issik Kul at an altitude of 3,000 meters, and 
found it to be an extended, gently inclined plain in which the granite, gneiss, and 
steep clay slates are broadh- tnmcated, above which the snowy ranges (4,000 meters) 
rise with relatively small relief, and below which deep, canyon-like valleys are eroded 
by the Sary-jass River and its tributaries. He recognized it to be a " Denudations- 
flache" or peneplain (1903, 99). 
The deformation that the great peneplain has suffered in that part of its area 
which is now mountainous seems to have involved late or post-TertiarA- movements 
of relativel)- local uplift, as in the Bural-bas-tau ; or of much broader uplift, as south 
of Issik Kul ; or of moderate warping, as in the branch of the Dsungarian Ala-tan ; 
or of block faulting and tilting, as about the west end of Issik Kul. This is consistent 
with the account of the Tian Shan furnished to Suess by Mushketof, in which it is 
stated that the earlier deformation of these mountains was not before the Trias, and 
that the final configuration of the ranges was given in post-Tertiary- time. The 
latter statement is based on the occurrence of Tertiar}- strata at great altittides, no 
mention being made of the evidence from peneplanation (Suess, 1897, i, 619). 
It is noteworthy that there is no general evidence of crustal compression in the 
later defonnation that the Tian Shan seems to have suffered. True, the vertical 
strata and the \-ertical cleavage of slates impl\- that the region suffered a strong 
compression in some time previous to peneplanation ; but the existing Tian Shan 
ranges, so far as they are described, are not the result of that ancient compression. 
They are due to a later system of defonnation that gives little evidence of com- 
pression. The contrast between the earlier Tian Shan s)stem and the present 
ranges is similar to that pointed out by Ciilbert between the Appalachians and the 
Basin ranges of Utah and Nevada : 
In the Appalachians corrugation 'has been produced commonly by folding, exceptionally by 
faulting; in the Basin ranges, commonly by faulting, exceptionally by flexure. The regular alter- 
nation of curved synclinals and anticlinals is contrasted with rigid lx)dies of inclined strata, bounded 
by faults. The former demand the assumption of great horizontal diminution of the space covered 
by the .disturbed strata, and suggest lateral pressure as the immediate force concerned; the latter 
involve little horizontal diminution, and suggest the application of vertical pressure from below. 
* * * In the case of the Appalachians the primary phenomena are superficial; in that of the Basin 
ranges they are deep-seated, the superficial being secondary; that sucJi a force as has crowded 
together the strata of the Appalachians — whatever may have been its source — ^lias acted in the 
ranges on some portion of the earth's crust beneath the immediate surface ; and the upper strata, 
continually adapting tliemselves, under gravity, to the inequalities of the lower, have assumed the 
forms we see (1875, 61, 62). 
