114 AMERICAN MANURES. 



carbonate of lime, sulphate of lime (lime and 

 sulphuric acid), and phosphate of lime. 



Gabon ate of Lime (common limestone) is the 

 chief constituent of the shells of fishes and egg 

 shells ; corals also consist of carbonate of lime, 

 derived from the skeletons of innumerable min- 

 ute insects. 



The origin of the common limestones is very 

 remarkable. They are built up from deposits 

 of the remains of shell-fish and coral insects, 

 which lived in ancient seas, and which having 

 been raised above the surface by submarine 

 forces, have hardened into a rock by the slow 

 infiltration of water holding carbonate of lime 

 in solution, or by the rapid and more powerful 

 effect of volcanic heat. 



There are few limestones, in which the shells 

 and corals cannot yet be seen in form, more or 

 less perfect. They are not found in the purest 

 and most crystalline marbles, because these 

 have clearly been subjected to the action of heat 

 with great pressure, which has obliterated the 

 forms. 



Sulphate of Lime, or Gypsum, is an important 

 ingredient of fertile soils, as it furnishes two 

 elements necessary to plants. In some localities, 

 gypsum is found in immense beds or rocks, some- 

 what similar in appearance to limestone. 



It is very generally distributed in small quan- 



