LAND AND WATER. 37 



In some cases, in low places, the process has been 

 continued further, until the peat has been petrified, or 

 converted into coal. 



Peat beds are very numerous. Some of them are of 

 very large extent. The great " Dismal Swamp " of North 

 Carolina is a vast peat bed. 



Many of the smaller muck swamps are partly com- 

 posed of ordinary soil, which has been washed in from 

 the surrounding hillsides. 



3. The Remains of Animals. The bones and shells 

 of all the great numbers and varieties of animals that 

 have lived and died on the land, and in the ocean, 

 have contributed to the formation of certain kinds of 

 soil. Limestone, and limy matter in soil, have been 

 produced from shells which have accumulated in the 

 ocean, and in lakes which have~ become dry. The rock 

 of coral reefs, and the soil formed by the crumbling of 

 such rock, are largely composed of the remains of minute 

 animals. 



The bones of land animals, when decomposed or 

 ground, add desirable elements to the soil. 



4. Substances formed by Chemical Action from the 

 three Classes mentioned. The presence of these sub- 

 stances gives fertility to the soil. Neither crumbled 

 rock, nor the remains of plants or animals, in their 

 crude original condition, would furnish any food for 

 the support of plants ; but by chemical processes in the 

 soil new combinations are gradually formed which are 

 adapted to the support of vegetable life. 



Soils are commonly classified according to the sub- 

 stances of which they appear to be largely composed, 

 as follows : 



1. Sandy. Pure sand, which is composed entirely 



