THE PENNSYLVANIAN PERIOD 633 



the stems, branches, leaves, and fruits of the trees, shrubs, and 

 herbs which grow there, have been long accumulating, and the great 

 mass is nearly free from sediment. In various cypress and man- 

 grove swamps, too, there are considerable thicknesses of vegetable 

 matter nearly free from mud, etc. The multitude of marshes and 

 peat-bogs in the United States and Canada are further illustrations 

 of the accumulation of vegetable matter, sometimes mixed with 

 abundant sediment and sometimes nearly free from it. 



Fig. 446. Map of the Cape May peninsula, showing coastal marshes. The 

 unshaded areas inside the coast line are dry land. 



The vegetation in such situations need not be more luxuriant 

 than on moist lands which are not swampy. On fertile prairies 

 and in great forests the annual growth of vegetation is great; 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. Decay is less rapid in a cool climate 

 than in a hot one, so that in the former, there is more likely to be 

 a residuum of partially decayed organic matter. 



