'composition o* soils 85 



result of the decay of rocks containing some form of 

 calcium. The compounds of calcium found in soils 

 are popularly called i.i.mf. In regions where lime-tone 

 rocks are abundant the soil is well supplied with lime; 

 but where the soil has been formed by the decay of 

 Mich rocks as sandstone l>ut little lime wil! be found. 

 The amount of lime in the soils is, of course, depend- 

 ent on the amount of lime in the rocks from which 

 they are formed, and for this reason the supply of lime 

 in various soils is very different. As already men- 

 tioned, the soils of limestone regions are well supplied, 

 and are, as a rule, very fertile. The soils of the fa- 

 mous bluegrass regions of Virginia, Tennessee, and 

 Kentucky are formed from limestone rocks, and are 

 noted for their fertility. Besides forming plant food, 

 lime has a decided influence on the supply of nitrogen 

 in the soils and also on their mechanical condition. . 



The quantity of lime in soils varies greatly; in 

 rich limestone Mill it may reach 2 to 3 per cent, and 

 in poor, sandy soils fall as low as .1 per cent. The 

 calcium in soils is usually combined with carbon and 

 oxygen to form ;i carbonate, or with phosphorus and 

 oxygen to form phosphates. Sometimes it is com- 

 bined with sulphur and oxygen to form a sulphate. 



87. Iron in Soils. — This element occurs abundantly 

 in all soils, however poor. It is usually found com- 

 bined with oxygen, forming an oxide, or with oxygen 

 ami water to form a hydrate; at times it is combined 

 with phosphorus ami aluminum. Nearly all rocks con- 

 tain iron, which becomes a part of the ><>il when the 

 rocks decay. Iron gives to soils their \arious colors 



