310 HISTORICAL GEOLOGY. 



gams. The two branches of the tree of life, cryptogam 

 and phenogarn, so widely separated now, when traced 

 downward, approach and almost meet here in the Coal 

 period. 



Mode of Accumulation of Coal. 



There has been much dispute on this subject, and it is 

 still obscure. There are some things, however, which 

 are reasonably certain. We shall give what is most 

 certain, in the form of three propositions : 



1. Coal has been accumulated in the presence of 

 water. This is indicated (a) by the nature of the 

 plants, which are mostly swamp-plants ; (#) by the inter- 

 stratified sands and clays, which were, of course, deposited 

 in water ; but, more than all (c) by the preservation of 

 the vegetable matter, which would have entirely disinte- 

 grated and passed off, as C0 a and H 2 0, unless completely 

 water-soaked. 



2. Coal has been formed by accumulation of 

 vegetable matter "in place" i. e., where the plants 

 grew by annual decay of generation after generation, as 

 we see now in peat-bogs and peat-swamps ; and not by 

 accumulation ly driftage, as we see in rafts. The evi- 

 dence of this is complete. We shall only mention one 

 fact, which is demonstrative : The under-day of every 

 coal is full of stumps and roots in position as they grew. 

 Every under-clay is an old fossil forest-ground, or rather 

 swamp-ground. 



Imagine, then, an old coal-swamp, with its clay bot- 

 tom full of dead stumps and roots, with its accumulation 

 many feet deep of pure peat, with its surface covered 

 with late-fallen leaves, broken branches, and prostrate 

 trunks, and the still growing vegetation shading all. 

 Now, imagine this overwhelmed and buried by sediments, 

 subjected to powerful pressure and slow change, and we 

 have all the phenomena of a coal-seam, with its under- 



