BACTERIA IN NATURAL PROCESSES. 127 



at the bottom it is commonly of a hard consist- 

 ence, brownish in colour, and with only slight 

 traces of the original woody structure. Such 

 material is called lignite. It contains a higher 

 percentage of carbon than peat, but a lower per- 

 centage than coal, and is plainly a step in coal for- 

 mation. But the process goes on, the hydrogen 

 and oxygen loss continuing until there is finally 

 produced true coal. 



If this is the correct understanding of the for- 

 mation of coal, we see that we have plainly a pro- 

 cess in which bacterial life has had a large and 

 important share. We are, of course, densely 

 ignorant of the exact processes going on. We 

 know nothing positively as to the kind of micro- 

 organisms which produce this slow, peculiar fer- 

 mentation. As yet, the fermentation going on in 

 the formation of the peat has not been studied 

 by the bacteriologists, and we do not know from 

 direct experiment that it is a matter of bacterial 

 action. It has been commonly regarded as sim- 

 ply a slow chemical change, but its general simi- 

 larity to other fermentative processes is so great 

 that we can have little hesitation in attributing it 

 to micro-organisms, and doubtless to some forms 

 of plants allied to bacteria. There is no reason 

 for doubting that bacteria existed in the geologi- 

 cal ages with essentially the same powers as 

 they now possess, and to some forms of bacteria 

 which grow in the absence of oxygen can we 

 probably attribute the slow change which has 

 produced coal. Here, then, is another great 

 source of wealth in Nature for which we are de- 

 pendent upon bacteria. While, of course, water 

 and pressure were very essential factors in the 

 deposition of coal, it was a peculiar kind of fer- 

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