DESERTS. 267 
Physiographically, the great features of this spacious valley arise from its 
ancient terraces and grade-plains. In general, there are three past erosion stages 
represented and these with the present river channel make four erosion cycles. 
But for over 30 miles, midway between Obu-garm and Katta Kara Muk, the 
third and fourth stages merge into one; or rather the third-cycle flood-plain warps 
under present alluviation and the river spreads out with no channel. Often 
the second-stage terrace is found obliterated and the valley becomes a simple 
wide gorge with tributaries cut into the old topography of its first stage, the pene- 
plain stage of these regions. 




gee ee SO ee 
Ist cycle 
Grade plains flanking 
Limestone 
the Peter The Great mts. 




SECTION THREE MILES BELOW THE ALAI VALLEY. 
29 cycle terrace 
J 
| 
Pe and 4th cycles (Present flood plain) ase Yi} 
FIVE MILE SECTION NEAR HAUI. 


1st cycle 1St cycle 
Y Y 
> 
2nd cycle 
//j 

5 4theycle x= 
TYPE FIVE MILE SECTION WHERE THIRD CYCLE FLOOD-PLAIN IS NOT WARPED UNDER THE PRESENT FLOOD-PLAIN-~ 
Fig. 444.—Terraces of the Kizil Su in Karategin. 
As the first-stage topography has been uplifted and dissected by this great 
gorge and all its tributary systems to a depth of from 3,000 to 4,000 feet, only 
limited areas of its original slopes now remain. It is to be inferred from a con- 
formity of grade-plains and flat-topped spurs flanking the Peter-the-Great Range 
and dissected remnants of a one-time half-peneplained belt of the Alai Mountains 
north. When uplift began, it was by no means a peneplain, but rather a mature 
topography grading into the wide, shallow valley of the Kizil Su and peaked here 
