PLANT'S GROWTH AND DECAY 



109 



rying streams accumulated in the deltas of the prehistoric 

 rivers, while the volcanic actions which marked this period 

 would often cause so great an alteration in the earth level 

 that the decomposing vegetable matter became subject to 

 the inrush of water bearing with it huge quantities of mud 

 and silt, which, depositing above the collected vegetation, 

 gradually hardened there and formed the strata which we 

 find above the coal. 



Nor were these actions confined to that particular period 

 to which we look back as the carboniferous age. We find 

 that whenever the conditions were favorable for the deposi- 

 tion of great beds of vegetable matter, actions of a similar 

 nature have led to its conversion into coal in strata of a 

 more modern character, and the formation of coal appears 

 to have been going on ever since the inception of vegetable 

 life on the earth's surface, and there is no reason to doubt 

 that the swamps and bogs of the sub-tropical forests of the 

 present day are to a minor extent carrying on the early 

 stages of the same action. 



The chemical actions that took place during the period 

 when the peat deposits, heated from below by the earth's 

 temperature and pressed on by the superincumbent deposits 

 above them, underwent those changes in composition which 

 we now recognize in our coal, can be traced by analysis, and 

 the following table indicates the way in which the gradual 



THE CONVERSION OF WOODY FIBER TO COAL 



(Butterfield) 



