32 GEOLOGY OF THE SON VALLEY, ETC. 



extension of the surface. The crust of the earth was divided into 

 plaxes, 1 separated from each other by fractures reaching deep into 

 the earth and along which differential movements of elevation take 

 place. Not only was the nature of disturbance which took place 

 utterly distinct from that of the Vindhyan epoch, but the direction of 

 the main line of disturbance is different and cuts obliquely right 

 across the area of the mountain range of Vindhyan age. 



From this it is evident that there must be a considerable differ- 



Age of the Vindhyan ence in time between the two different systems 

 system. f disturbance, and in this manner we may get a 



hint of the age of the Vindhyan system. The Gondwana system of 

 disturbance had commenced in Talchir times, that is, in the permian 

 epoch. The lapse of time from the cessation of the Vindhyan com- 

 pression must have been considerable, and we can, consequently, 

 hardly regard the age of the newest beds of the Vindhyan system as 

 of later age than devonian. How much older they may or may not 

 be there is no means of deciding. 



Recent or surface deposits are largely developed in the area 

 under consideration ; in fact, they are ordinary 

 stream deposits of sand and, gravel, which in 

 places have been compacted by a calcareous cement into sandstones 

 and conglomerates. The actual area occupied by these recent de- 

 posits at the surface is very small, even in the Son valley, where they 

 are most largely developed. Enormous areas are, however, covered 

 by a form of recent deposit which, so far as it has been noticed 

 by previous observers at all, has been described as alluvium, but to 

 which this term seems inapplicable in its proper sense. 



The deposits referred to are fine-grained and unstratified. When 

 wet they pass into a slimy and impalpable mud 



Fine-grained loam. , . .. . , , , . , ' 



when dry they indurate to the consistency of 

 rock. As seen in the sides of drainage channels they show no trace 



1 The word plax was suggested by me (Mem., Geol. Surv. Ind., Vol. XXIX., p. 167) as 

 a more satisfactory equivalent of the " scholle " of German geologists than the word " block," 

 whose use is liable to ambiguity. 

 ( 32 ) 



