19II.] STEVENSON— FORMATION OF COAL BEDS. 31 



coming sediments and changed into layers of plant material. The 

 Carboniferous was not a tree and forest flora ; it was morass and 

 strand vegetation, developed on great emerging plains of marshland. 

 The prevailing forms suggest that formation of the widely extended 

 coal beds was analogous to the formation of peat bogs. 



The purity of coal substance, the continuity of the beds, their 

 regular thickness, the arrangement in benches due to clay layers 

 produced by inconsiderable inundations, the upright plant stems and 

 all the remaining relations of most coal beds appear to find sufificient 

 explanation only in this or a similar conception of the mode of their 

 formation. When at length a permanent elevation of the sea-level 

 comes, the bog is buried under sand and mud, in whose first layers, 

 just as in the last conditions of peat vegetation, a great mass of 

 plant remains is found, torn from the neighboring land ; so that it is 

 clear that the roof shale of a coal bed encloses as a rule a large 

 number of isolated plant remains. 



Newberry's^" attention was attracted to the canncls and semi- 

 cannels of Ohio at the beginning of his studies. Observations 

 made in peat bogs of this country and Europe led him to believe that 

 cannel was formed in lagoons, where completely macerated vegetable 

 tissue, probably parenchyma for the most part, accumulated as vege- 

 table mud. Among other arguments favoring his hypothesis, he 

 urges that cannel is more nearly homogeneous than cubical coal ; that 

 it contains morp volatile matter, with more hydrogen, and must have 

 been deposited .n a hydrogenous medium which prevented oxidation; 

 that it contains aquatic animals, so abundant at times, as to prove 

 that they inhabited pools in which cannel was a sediment; that the 

 plant remains in cannel are usually skeletonized ; and that in open 

 water lagoons of modern peat marshes, fine carbonaceous mud ac- 

 cumulates, which when dried is very like cannel. 



Le Conte'^^ compared the peat bog and estuary theories. The 

 arguments in favor of the peat bog theory are, the purity of the 

 coal, the fine preservation of the tender and more delicate parts 



^' J. S. Newberry, Amer. Journ. Sci., 1857. A synopsis of this paper with 

 some additional notes was given by him in Geol. Survey of Ohio, Vol. II., 

 1874, p. 125. 



'^Joseph Le Conte, "Lectures on Coal," Ann. Rep. Smithsonian Inst, for 

 1857, Washington, 1858, pp. 131-137. 



31 



