191 1.] STEVEXSOX— FORMATIOX OF COAL BEDS. 3 



original plan was to arrange the synopses topically, but this separated 

 the contrasting opinions of contemporaries ; the chronological 

 arrangement is open to the objection, that it breaks up the line of 

 argument for or against an hypothesis. Yet the latter seems pre- 

 ferable as more in accord with the purpose of the summary. It 

 has been followed, except where it would fail to show an author's 

 final conclusions or where it seemed necessary to bring together 

 widely separated observations upon a special phase. 



The Hypotheses. 



There has been little diversity of opinion respecting the origin of 

 coal. Geologists and chemists, with rare exceptions, have recognized 

 that the several types consist mainly of vegetable matter which has 

 undergone chemical change. But no such consensus of opinion 

 exists respecting the mode of accumulation in beds ; geologists, for 

 about one hundred and thirty years, have been divided into two 

 opposing camps with here and there an individual warrior carrying 

 on an independent strife. 



The older hypothesis was suggested more than two centuries ago, 

 prior to the era of investigation, and it remained unchallenged until 

 the latter part of the eighteenth century, but it fell into disfavor 

 early in the nineteenth century. Thereafter, it had few, but earnest 

 defenders until within the last thirty years, during which it has been 

 urged with great energy. This, the doctrine of allochthonous origin, 

 conceives that coal beds are composed of transported vegetable 

 matter deposited in the sea or in lake basins. The conception has 

 assumed many forms but the essential feature of transport is com- 

 mon to all. 



The other hypothesis, formulated in 1778 as the result of broad 

 field observations gained general acceptance about one hundred 

 years ago ; since that time, it has been held in one form or another 

 by a majority of geologists who have studied the coal measures. It 

 is known as the doctrine of growth /;/ situ, but von Gumbel's term, 

 autochthonous, has come into general use. According to this 

 hypothesis, the plants which yielded the vegetable matter grew where 

 the coal is found, analogous conditions being found in great peat 

 accumulations, especially those of the cypress swamps of North 



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