INDIAN GEOLOGY. 139 



o-reat fault. The Siwaliks were laid down to the south of 

 the fault, while the hills to the north were still rising ; and 

 probably in part while the fault was still forming. Subse- 

 quently, the Siwaliks themselves became involved and 

 were raised to form the present Sub- Himalayan Chain ; and 

 now they bear the same relation to the alluvial deposits 

 of the Gangetic plain that the older rocks to the north of 

 the fault bore to them at the time of their deposition. Pro- 

 bably, too, there is now a boundary fault between the Sub- 

 Himalayas and the Gangetic plain itself. 



In Kumaun and Gahrwal, where the structure is well 

 known, there is not merely one of these faults, but a whole 

 series of parallel faults which divide the hills into a number 

 of belts ; and in each belt the newest beds are older than 

 the newest beds in the belt to the south and newer than 

 the newest in the belt to the north. In each case the 

 fault practically marks the northern boundary of the newest 

 rocks in the belt to the south of it, and the age of these 

 newest beds probably gives us the period at which the 

 fault was completed. 



Thus the Himalayas gradually grew outwards from 

 north to south, slowly encroaching on the area of deposition to 

 the south ; and each of these great reversed faults marks a 

 stage in the process. Oldham goes on to show how this 

 mode of growth agrees with Fischer's theory of the formation 

 of mountains ; but for this discussion I must refer to the 

 account given in the Man// a/. 



The question of the age of the Himalayas also is too 

 large a one to be dealt with here. It depends mainly on 

 what is meant by the term Himalayan Chain ; and it must 

 suffice here to point out that the presence of Nummulitic 

 rocks at a height of 1 8, 500 feet above the sea ] clearly proves 

 that at least a very large part of the elevation has taken 

 place since the commencement of the Tertiary era. 



Philip Lake. 



1 La Touche. " Re-discovery of Nummulites in Zanskar." Rec. Geo/. 

 Surv. India, xxi. (1888), p. 160. 



