MATTER IN SOLUTION. 59 



Rhone, and Elbe, would, in the course of 8,000 years, have 

 conveyed away in solution an amount of mineral matter 

 equal in weight to the whole quantity of water discharged by 

 them in a year. 



In India the various dissolved carbonates contained in 

 the river-water are a source of some perplexity to the culti- 

 vators of the soil ; for as rain falls only at certain seasons, 

 and there are often long periods of drought, large sums have 

 been expended in conveying water to the fields by means of 

 a system of irrigation, and now that this has been done, it 

 is found that the land in some parts has been rendered 

 actually unfit for cultivation by the large amount of mineral 

 matter conveyed in the water, and the question is how to 

 get rid of it again. 



When considering the dissolved minerals carried away by 

 water, we must bear in mind that they are not, like the sedi- 

 ment, taken only, or even chiefly, from the bed of the river 

 and the banks between which it flows. On the contrary, 

 they are drawn from far and wide, from the whole area, in 

 fact, which the river drains. For the rain, as it soaks through 

 the earth, dissolves something of every bed through which 

 it passes* : the springs, as they flow under ground, often by 

 very complicated channels, do the same ; and, in fact, the 

 whole network of streams, large and small, above or below 

 ground, by which every river of any size is fed, all con- 

 tribute their share of dissolved mineral matter, and are 

 most strongly impregnated just when their waters are most 



* About 100 tons of mineral matter are said to be annually dissolved 

 per square mile, all over the world ; of this about half is carbonate of 

 lime. 



