14 STEVENSON— FORMATION OF COAL BEDS. [April 21. 



tion. He objects further that the theory does not account for the 

 alternation of calcareous with argillaceous and siliceous beds, and 

 asks on what principle one may expect that beds of earth, spread out 

 by the floods, should be periodically calcareous, argillaceous or sili- 

 ceous, and how can it account for the alternations of clay beds with 

 numerous coal beds ; why should a second flood in its blind fury 

 deposit a second series of beds on exactly the same spot where the 

 first series is deposited? 



Conybeare-° adhered to the belief that vegetable matter alone 

 was the source of coal and accepted Sternberg's suggestion that 

 torrents tore oiT the vegetation from scattered primitive islands 

 to deposit at the bottom of adjacent basins. He conceived at this 

 early date a theory having not a few of the features characterizing 

 one offered at a much later date. He thinks that the coal measures 

 were deposited in estuaries and that the partial filling up of lakes 

 and estuaries oft'ers us the only analogies in the actual order of 

 things with which the coal deposits can be compared. Respecting 

 the deposit at Bovey Tracy, he says : 



We must here suppose the wintry torrents to liave swept away a great 

 part of the vegetation of the neighboring hills and buried them in the estu- 

 ary with the alluvial detritus collected in its course : tlie latter would, from 

 its gravity, have sunk first and formed tlie floor ; tlie wood would have 

 floated till, having lost its more volatile parts by decomposition and become 

 saturated with water moisture, it likewise subsided upon them, being per- 

 haps loaded by fresh alluvium drifted down upon its surface; the re-iterated 

 devastations of successive seasons must have produced the repetition and 

 alternation of the beds . . . and if we suppose a like order of things to have 

 operated more extensively and for a longer period during the formation of 

 the coal strata, we shall find sucli an hypothesis sufficiently in accordance 

 with their general ])hcnomena. 



Ad. Brongniart,-^ after long study of the fossil plants, concluded 

 that in the Carboniferotis time the dr}- land was confined to islands 

 on which grew the ])lants who>e remains are in the coal formation. 

 Numerous proofs established that the plants grew in the very places 

 where they are found or, at most, within only a little distance away. 



"" \V. 1). Conybearc. "Outlines of Geology of Enghuid and Wales," 

 London, 1822, pp. 334, 345. 347. 



■' Adolphe Brongniart. "" Prodromme d'une histoirc des vegetaux fos- 

 siles," Paris, 1828, pp. 183, 184. 



14 



