231 COTTER: SODA INDUSTRY OF SIND. 



known to the Irrigation Department, who have estimated the loss 

 of water through the hanks of such canals as the Jamrao, when* 

 it passes through the sand-hills, and the almost negligible loss 

 through the canal banks where it passes through alluvial clays. It 

 seems clear that the alluvial clays beneath the desert sand hold 

 v*p the rain water, so that a moist layer is formed at the base 

 of the sand. The numerous kochur, and pools in deep hollows in 

 the sand-plateaux, I think, prove this. It is also obvious that 

 the dhands derive their water from the basal layers of the sand- 

 hills around them, since in many places there are small pools of 

 water and moist ground along the shore of the dhand, the level 

 of the water-pools being one or two feet above that of the dhand. 

 These pools are often filled with drinkable water, while the water 

 of the dhand may be unfit even for cattle. 



This moist layer of basal sand is doubtless full of organic matter, 

 due to the remains of the vegetation which formerly covered the 

 alluvial plain. It is also protected from the air and from an oxidising 

 environment by the cap of sand. Such conditions are exceptional. 

 They are very different from those prevailing below the level of 

 permanent saturation in cultivated country. Water below the level 

 of permanent saturation in ordinary alluvial plains is subject to 

 very little movement, if indeed any. Such chemical changes as 

 go on below the level of permanent saturation appear to be of the 

 type associated with a reducing environment, but the changes are 

 necessarily slow processes. Most moving water in ordinary alluvial 

 country appears to become oxidised at some time or other, and 

 the abundance of kankar nodules in the old alluvium is evidence 

 of this. But in the Sind desert there is a stratum of flowing water, 

 which is vet very well protected from the air. It appears to me 

 probable that in this circumstance is to be found the explanation 

 of the alkaline lakes of Sind. 



APPENDIX. 



ON THE ESTIMATION OF CARBONATES AND BICARBONATES 

 IN TROPICAL CLIMATES. 



It was found impossible to obtain accurate results from the us** 

 of Winkler's method, as given in the text-books. 



