SUMMARY. 231 



It is improbable that the folding action alone has been the cause 

 of the present structure and orographical features of Central Asia 

 and the areas south of it ; for the final great changes which have 

 resulted in the draining of Central Asia of the tertiary seas, of which 

 nothing now remains but isolated salt-water lake-basins, such as the 

 Aral and the Caspian are, we must look for other causes. 



Possibly such may be found in the sinking in of large portions of 

 the southern hemisphere which caused the submergence of the Indo- 

 African area below what is now the Indian Ocean. With it the part 

 now known to us as the Peninsula of India may have partially broken 

 down, though of that we have no direct evidence, unless the impro- 

 bability that the Central Asian area could have been pushed up to its 

 present elevation above the Peninsula entirely through being folded 

 might be adduced as proof. Large tracts of Central Asia we know 

 could never have suffered folding to any but very slight extent as for 

 instance, the greater part of the tertiaries of the Turkist^n region which 

 are often in undisturbed horizontal position. On the other hand 

 these latter are but little raised above — some are even depressed 

 below — the level of India. 



In all these considerations and speculations two points seem pro- 

 bable almost beyond doubt, namely : First, that the last and main 

 disturbance of physical conditions of the Central Asian area has 

 taken place in post eocene, perhaps in middle tertiary times, and is 

 most likely still continued to the present day. 1 Secondly, that this 

 period of disturbance coincides with the sinking in of the Indo- 

 African continent, which " breaking down" caused the final draining 

 of the tertiary seas from the Central Asian area. 



Not so certain is whether the raising en bloc of the Central Asian 

 mass above the level of the Indian Peninsula is due only to the folding 

 process, or whether some movement downwards of the Peninsula, in 

 connection with the sinking in of the Indo-African region, may not 

 have Lad a share in producing the present configuration of the 



1 Manual, pp. lvi, 680, &c. 



( 231 ) 



