FORMATION OF COAL. .183 



eighteen feet, while the surface of the huge quagmire is in 

 many places covered by a layer of moss four or five inches 

 thick. The black, spongy soil beneath is made by the decay 

 of countless generations of these various forms of vegetable 

 life, but it has advanced beyond what is strictly speaking the 

 peat stage, for almost all trace of fibre has disappeared and 

 the whole has been converted into mud, which again is 

 dissolved and gives its colour to the clear, brown-tinted 

 water of the pools. 



The whole delta of the Mississippi (14,000 square miles) 

 is for the most part covered by a series of similar swamps and 

 similar vegetation growing with the utmost luxuriance, both 

 in the water and in the black soil. In 1812 a large extent 

 of " cypress swamp " in the Mississippi valley was disturbed 

 by earthquake, and sank below the level of the water, peat, 

 ferns, tree- stumps, fallen trunks, and standing trunks being 

 covered with the river-mud or alluvium, which is brought 

 down in such abundance. In the course of time the mud 

 would so accumulate as to rise to the surface, and would 

 speedily be covered with a fresh growth ; another mass of 

 peaty mud would accumulate on the top of the old one with 

 a layer of hardened mud or sand between. This alluvium 

 being, however, more or less porous, would not prevent 

 the buried peat from parting with more and more of its 

 gases ; but as the hydrogen, oxygen, and nitrogen, would 

 pass away more rapidly than the carbon, the proportion 

 of this latter would continually increase, until there might 

 be perhaps as much as eighty-two per cent, of carbon, 

 with five and a half of hydrogen, and scarcely twelve and a 

 half of oxygen and nitrogen together. 



