450 



PENNSYLVANIAN PERIOD 



have been long accumulating, and little sediment is mixed with 

 them. In cypress and mangrove swamps, too, there are consider- 

 able thicknesses of vegetable matter nearly free from mud, etc. 

 The multitude of marshes and peat-bogs in the United States and 



Canada are fur- 

 ther illustrations 

 of the accumula- 

 tion of vegetable 

 matter, in some 

 cases mixed with 

 abundant sedi- 

 ment and in 

 some nearly free 

 from it. 



The vegetation 

 in swamps need 

 not be more 

 luxuriant than 

 that on moist 

 lands which are 

 not swampy. On 

 fertile prairies 

 and in some for- 

 ests the annual 

 growth of vege- 

 tation is great; 



Fig. 394. Map of the Cape May peninsula, showing 

 coastal marshes. The unshaded areas inside the coast line 

 are dry land. 



but since the leaves, fruits, twigs, and trunks decay as they fall, 

 the larger part of their substance is returned to the atmosphere. 

 In a moist region there is more growth (and therefore more death) 

 of vegetation than in a dry one, and a better chance that decay will 

 not keep pace with death. 



Preservation of vegetable matter. Where vegetation falls 

 into water, as in marshes, it undergoes slow change different from 

 the decay suffered by vegetation on dry land. It is the partial 

 preservation of organic matter in the water of marshes and ponds 

 which converts them into peat-bogs, for peat is nothing more than 

 accumulated vegetable matter undergoing those changes to which 

 vegetable matter in water is subject. Under favorable conditions, 

 the peat of a bog may become very deep, as in the Dismal Swamp. 

 In and about marshes and swamps, therefore, we find the conditions 



