7 ON THE FORMATION OF COAL 151 



action of air and rain ; the leaves and stems would 

 gradually be reduced to little but their carbon, or, 

 in other words, to the condition of mineral char- 

 coal in which we find them ; while the spores and 

 sporangia remained as a comparatively unaltered 

 and compact residuum. 



There is, indeed, tolerably clear evidence that 

 the coal must, under some circumstances, have 

 been converted into a substance hard enough to 

 be rolled into pebbles, while it yet lay at the 

 surface of the earth ; for in some seams of coal, 

 the courses of rivulets, which must have been 

 living water, while the stratum in which their 

 remains are found was still at the surface, have 

 been observed to contain rolled pebbles of the 

 very coal through which the stream has cut its 

 way. 



The structural facts are such as to leave no 

 alternative but to adopt the view of the origin 

 of such coal as I have described, which has just 

 been stated; but, happily, the process is not 

 without analogy at the present day. I possess a 

 specimen of what is called " white coal " from 

 Australia. It is an inflammable material, burning 

 with a bright flame, and having much the con- 

 sistence and appearance of oat-cake, which, I am 

 informed, covers a considerable area. It consists, 

 almost entirely, of a compacted mass of spores and 

 spore-cases. But the fine particles of blown sand 

 which are scattered through it, show that it must 



