LAND AND WATER. 37 



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

 continued further, initil the peat has been petrified, or 

 converted into coal. 



Peat beds arc very numerous. Some of them are of 

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

 Car(jlina is a vast peat bed. 



Many of the smaller muck swam})s are partly com- 

 posed of ordinary soil, which has been washed in from 

 the surrounding hillsides. 



3. The Remains of Auimdh. — 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 nuitter in soil, have been 

 produced from shells which have accumulated in the 

 ocean, and in lakes which have beconu^ dry. The rock 

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

 such rock, are largely composed of the remains of minute 

 animals. 



Tlie 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 s<jil. Neither crumbled 

 rock, nor the remains of ])lauts or animals, in their 

 crude original condition, would furnish any food for 

 the su])poi't of plants ; but by chemical ])rocesses in the 

 soil new combinations are gradually foi-med Mhich are 

 adapted to the support of vegetal)le life. 



Soils are commonly classified according to the sul)- 

 stances of which they a])])ear to be largely composed, 

 as follows : — 



1. Sandy. — Pure sand, which is composed entirely 



