THE GROWTH OF COAL 235 



fragments of tissues. Still later, some local facts in a French 

 coal field have induced an eminent observer of that country to 

 revive the drift theory of coal, in opposition to that of growth 

 in situ. Views of this kind have also recently been advanced 

 in England by some of those younger men who would earn dis- 

 tinction rather by overthrowing the work of their seniors than 

 by building on it. These writers base their conclusions on a 

 few exceptional facts, as the occasional occurrence of seams of 

 coal without distinct underlays, and the occurrence of clay 

 partings showing aquatic conditions in the substance of thick 

 coals ; and they fail to discern the broader facts which these ex- 

 ceptions confirm. Let us consider shortly the essential nature 

 of coal, and some of the conditions necessary to its forma- 

 tion. 



A block of the useful mineral which is so important an element 

 in national wealth, and so essential to the comfort of our winter 

 homes, may tell us much as to its history if properly interro- 

 gated, and what we cannot learn from it alone we may be taught 

 by studying it in the mine whence it is obtained, and in the 

 cliffs and cuttings where the edges of the coaly beds and their 

 accompaniments are exposed. 



Our block of coal, if anthracite, is almost pure carbon. If 

 bituminous coal, it contains also a certain amount of hydrogen, 

 which in combination with carbon enables it to yield gas and 

 coal tar, and which causes it to burn with flame. If, again, we 

 examine some of the more imperfect and more recent coals, the 

 brown coals, so called, we shall find that in composition and 

 texture they are intermediate between coal proper and hardened 

 or compressed peat. Now such coaly rocks can, under the 

 present constitution of nature, be produced only in one way, 

 namely, by the accumulation of vegetable matter, for vegetation 

 alone has the power of decomposing the carbonic acid of the 

 atmosphere, and accumulating it as carbon. This we see in 

 modern times in the vegetable soil, in peaty beds, and in 



