!4 LA TOUCHE : GEOLOGY OF WESTERN RAJPUTANA, 



It seems not improbable that the depression -in which the salt 

 deposits of Pachpadra are collected is a portion of an old bed of the 

 Luni. Near the town of Pachpadra and again lower down where the 

 Luni makes a sudden bend to the south there are traces of the bed of 

 a large river indicated on the one-inch map, 1 and even now when 

 the river is in flood it spills over the northern bank above Tilw^ara and 

 flows towards the Pachpadra depression, but is prevented from flood- 

 ing it by sandhills. 



There seems little doubt that within quite recent times the flow 

 of water down these rivers must have been much greater than it is 

 now, and that the change is due to an alteration in the climate. 

 Nearly all the rivers contain masses of subrecent conglomerate, formed 

 of well rolled pebbles and boulders of various crystalline rocks em- 

 bedded in a calcareous sandy matrix. The conglomerate is always in 

 horizontal layers, exposed in the banks and beds of the rivers and 

 sometimes filling cracks and fissures in the older rocks. These pebbles 

 and boulders must have been transported at a time when the flow of 

 water was much greater than it is now, for the present rivers, even in 

 times of flood, are able to move little more than fine sand and gravel, 

 and only just round off the corners of such fragments of rock as do 

 find their way into them. 



If the sand that now chokes the lower courses of the rivers were 

 cleared out, the velocity of the water in the rivers would no doubt be 

 increased, and its power of erosion and of rounding pebbles and trans- 

 porting them would be proportionally enhanced. At the same time the 

 sea would occupy a large portion of the valleys, the Runn of Cutch, 

 for instance, even without any subsidence of the valley floor. This 

 change would no doubt have a great effect on the climate and the 

 rainfall inland would be greatly increased. A gradual silting up of 

 the river valleys, combined with the progressive encroachment of the 

 blown sand, would account for the change to the present arid condi- 

 tion of the country. 



1 Rajputana Survey. Sheet 71. 

 ( M ) 



