28 LA TOUCHE : GEOLOGY OF WESTERN RAJPUTANA. 



Vindhyans there is no doubt that an entire change of conditions took 

 place during it, and that from this time onwards this region, which 

 had in former times been the scene of intense volcanic activity, became 

 subjected only to those slow changes of level which have resulted in 

 the gradual accumulation of a series of sedimentary rocks. The oldest 

 of these are sandstones, passing upwards into impure cherty lime- 

 stones, and the whole group from its resemblance to the Vindhyan 

 sandstones and limestones on the eastern side of the Aravalli range 

 has been referred to that period. The position of the group with 

 reference to the undoubted Talchir boulder beds of Bap and Pokaran 

 renders it impossible that it can be other than Vindhyan. 



At Jodhpur the thickness of the sandstones does not exceed 200 

 feet, but they have been subjected to great denudation, and the upper 

 portion of the beds has been everywhere removed. In this neighbour- 

 hood they dip very gently towards the north, and gradually disappear 

 beneath the plain, and the isolated groups of hills further north 

 probably consist of higher beds of the same series. At Pokaran, 

 where they are exposed close to the Talchirs, but not visibly in 

 contact with them, the boundary is probably a faulted one. 



The sandstones consist of rapid alternations of more or less fine 

 grained gritty material, generally tinged with red, but sometimes 

 grey or white. Strings of waterworn pebbles of quartz, none of 

 which are of large size, frequently occur, especially in the higher 

 portion of the beds, and with the presence of current or false 

 bedding, which is very conspicuous in the artificially scarped 

 cliffs near Jodhpur, and the numerous examples of ripple marking, 

 which is beautifully developed on the surface of some of the finer 

 beds, indicate that the sandstones were laid down in shallow 

 water. Some of the finer beds make a most excellent building 

 stone, universally employed in Jodhpur and the neighbourhood. 

 Not only are the walls of the houses built of it, but pieces of 

 sufficient length in proportion to their thickness are obtained and 

 used as beams for the roof, while thinner slabs are used for the 

 ( 38 ) 



