ON THE ORIGIN OF COAL. 185 



the upper Coal measures, has been considered 

 indicative of the fresh water origin of those strata ; 

 but when these fossils are found in company 

 with remains of the Megalichthys, Holoptychius, 

 Cselacanthus, Platysomus, Palseoniscus, and other 

 genera, heretofore considered as of decidedly 

 marine origin, their diagnostic value ceases, 

 even if all these genera were confined to fresh 

 water ; but it is well known that such is not the 

 case, but that many are found in salt water. 



Independently of this, we must take into con- 

 sideration the vast extent of the true Coal-fields 

 of Europe, all of which have, most probably, been 

 once united and formed under similar conditions ; 

 and the evidence they present of the action of 

 currents of water, is very diff'erent from what we 

 now witness at the mouths of estuaries or on 

 beaches, for we find no deposits in them resembling 

 those of the latter. Professor H. D Rogers, in his 

 admirable paper on the origin of the Appalachian 

 Coal strata, at p. 469, states " that it may fairly 

 be questioned whether any sensible proportion of 

 river silt could spread itself to the distance of one 

 hundred and fifty or two hundred miles seawards." 

 The extent of this immense Coal deposit, as well 

 as its accompanying strata and organic remains, 

 B b 



