SANDSTONES. 115 



titles in all soils. Most spring and river waters 

 contain it, and in hard waters it is often abund- 

 ant, rendering them unfit for washing and culi- 

 nary purposes. 



Phosphorite is a mineral phosphate of lime. 

 The presence of phosphoric acid in all cultivated 

 soils may be traced to this substance. Without 

 it no cultivated plants can come to perfection. 

 The source of this substance in soils must be 

 from the many generations of animals that have 

 lived on the earth, and whose bones have be- 

 come scattered and mixed with the soil. It is 

 also found in the ancient unstratified rocks, such 

 as the apatites of Canada and Northern New 

 York, the phosphatic guano beds of South Caro 

 lina, and other places. Many of these rocks 

 contain a larger amount of phosphoric acid than 

 the same weight of bones. As these rocks slow- 

 ly crumble down in the soil ; the phosphates, if 

 they become soluble, are taken up. by plants. 



Sandstones are a great source of the inorganic 

 materials in soils. They are of various formations, 

 and their composition is not at all arbitrary; 

 alumina, silica, carbonate of lime, oxide of iron, 

 and other substances, are found in various 

 proportions in the different varieties. The co- 

 hesion of the particles is sometimes caused by a 

 sort of semi-fusion, as in the common grit or 

 burr stones, while in other varieties the cohesion 



