UPPER INDIA. 71 



lation of saline matters on their surface is the residue of 

 evaporation, the greater part being due to the rising, by 

 capillary attraction, of the salts brought down to them from 

 the higher lands in former times. The beds of all lakes must 

 in the same way be gradually rising, from the amount of 

 earthy matter brought to them with the water from higher 

 lands. Should, by any convulsion of nature, the outlets of 

 the Ked Sea become closed, and it be converted into an inland 

 lake, it is easy to suppose its level would be reduced to below 

 the ocean-level, from the amount of evaporation from its sur- 

 face exceeding the amount of water supplied to it by rivers 

 and springs. This lowering of the surface would go on till in 

 the course of time the surface area was contracted and an 

 equilibrium established between the amount received from 

 rivers and springs (i. e. surface and underground drainage) 

 and the amount lost by evaporation. 



In the case of land irrigated from canals the same causes 

 are at work; the rain which falls on the hills and other 

 elevated lands is diverted into the canals and distributed over 

 the land, carrying with it what amount of salts it may con- 

 tain. The percentage of salts in the water may be small, 

 but if it is in excess of the amount required and taken up by 

 the crops grown on the land, it will continue increasing 

 until from its excess it becomes injurious. 



The fact, however, remains that lands subjected to irriga- 

 tion in Upper India, more especially to irrigation from canals, 

 become after some time covered with reh. On analysis it is 

 found that reh may be composed 



1st. Entirely of carbonate of soda ; or, 



2nd. Of carbonate and sulphate of soda; or, 



3rd. Of carbonate and sulphate of soda and chloride of 



sodium. 

 All these salts are more or less useful to vegetation ; it is only 



