IRRIGATION. 205 



284. What is this matter ? Is it of any agricul- 

 tural value? The answer to the first question will 

 answer both. The dissolved salts are sulphate and 

 geate of lime, and the fine deposit occurring after the 

 water has settled, is composed of one-half of geine, 

 and the remainder of salts of lime and silicates. The 

 great agricultural value is found in the clayey de- 

 posit, which occurs in the first few days. The coar- 

 ser part, that which collects about the foot of rocks, 

 and falls, and eddies, is composed, as follows : 



Geine, 3-92 



Silex, 72-70 



Oxide of iron, 9*15 



Alumina, 8*30 



Lime, 051 



Magnesia, 0*10; but consider- 



ing the elements as we have usually treated them, as 

 silicates, salts and geine, the composition of the seve- 

 ral deposits is shown in the following table : 



Geine. Sulphate Phos. of SiUrat „ 



Soluble. Insolu. of lime, lime. * uicaies - 



The coarse de- 

 posit above, 

 Freshet, 1839, 

 Freshet, July 

 7—18, '39, 



285. If the doctrine of the action of silicates, salts 



18 



