RECENT DEPOSITS. 41 



between them while in the air very slight, accounts for the small 

 amount of attrition that they undergo. The persistence of the parti- 

 cles of carbonate of lime and foraminifera among grains of hard 

 material like quartz to such great distances as I have indicated also 

 shows that the amount of attrition that goes on must be very small. 



2. Kunkur. 



I have already mentioned 1 the almost universal occurrence of 

 thicks bed of calcareous tufa or kunkur among the desert sands, and 

 shown how they are apt to collect round the bases of the isolated 

 rocky knolls scattered over the country. At first sight the source 

 of the lime in these deposits was not at all obvious, for the lavas 

 granites, and other crystalline rocks round which they collect do not 

 contain lime in any appreciable quantity. But the discovery of the 

 particles of carbonate of lime and foraminifera in the sand at once 

 afforded an explanation of the origin of these deposits. Occasional 

 showers of rain falling upon the sand dissolve these particles and 

 since the moisture is quickly evaporated, the lime is soon re-deposited 

 as tufa. Naturally this process goes on most rapidlv where the rain 

 water is collected on a rocky surface and flows off into the surround- 

 ing sand ; and thus the gently sloping " glacis" at the bases of the 

 knolls, described in Chapter II, are formed. 



3. Origin of the Salt. 



It is a well known fact that the sand and alluvium of the Rajputana 

 desert is more or less impregnated with salt. Except after heavy 

 rain the water that lingers in a few pools here and there along the 

 course of the Luni is intensely salt, and large quantities of it of 

 immense commercial value, are obtained from brine pits situated in 

 various depressions in the general surface of the plain, the largest 

 of which occurs near Pachpadra, or from salt lakes like those at 



1 Supra, p. 12. 



( 41 ) 



