286 PHYSIOGRAPHY OF CENTRAL-ASIAN DESERTS AND OASES. 
the Tarim basin has been uptilted in Quaternary time, and it may be said that 
this tilt gradually increases mountainwards, so that a horizon nearly flat in its 
far-out extension is bent up to 10° or 15° and more near the mountains. Besides 
this general marginal tilt, there have been more local movements in the form of 
broad anticlinal arches nosed up, each with a transverse fault-scarp facing moun- 
tainwards and surmounted by its anticlinal surface sloping gently back into the 
plain. These ‘‘up-nosed’’ piedmont strata, bent behind and faulted out in front, 
some of them rising as high as 500 feet out of the plain, range about parallel to 
the bordering mountains and are found even as far out as Kashgar. 
EVIDENCE OF RECENT CHANGE TO EXTRA DRY. 
The last great change over the Tarim basin has been one of desiccation. Of 
this we have both physiographic and historic records, which tell that it became 
serious about a thousand years ago, when some hundreds of cities were over- 
whelmed by sand. Some of these ruins were excavated by Stein, and Mr. Pumpelly 
found mention of them in Chinese literature in the imperial archives of Pekin. 
It is also believed there were then expansive bodies of water of which Lob-nor 
and other shrunken lakes and brackish tarns are the withering survivals. During 
the time of greater precipitation much of the great area of dunes throughout Tarim 
was doubtless grassed over, and we may thus ascribe its burial of cities to sand 
set free when rainfall had so seriously decreased that grass failed and left the 
dunes bare and free to drift. 
TENTATIVE RECONSTRUCTION OF THE PAST IN TARIM. 
First cycle (Pliocene). 
The Tarim basin defined with high border ranges eroding to mature topography and 
building immense piedmonts of gravel, sand, and silt. 
Second cycle (Quaternary). 
Uplift of border ranges, with deep gashing of old topography and sinking of plains, 
with upbending margins worn down by streams beveling their tilting strata, with 
an erosion plain and the building of a later piedmont over that. 
Third cycle (Quaternary). 
Second uplift of border ranges, with terracing down of valleys partially alluviated 
ere the close of the second cycle, and marginal tilting up of plains with dissection 
of their second-cycle piedmonts? Shrinkage of alluviation at close of the glacial 
period and recession of silt zone over gravel zone. 
Fourth cycle (Postglacial). 
Third uplift of border ranges with stream-channeling of valley flood-plains of glacial 
alluviation during the third cycle, and more sinking of plains with tilting and 
dissection of their third-cycle piedmonts. 
Recent decrease of precipitation, shrinking of rivers and lakes, and desolation of dune 
pastures, setting free the sand that buried the cities of Tarim a thousand years 
ago, 
