158 Evolution and Distribution of Fishes 



rlnthodont belonging to as many genera. These, like other 

 amphibians, were intolerant of saltwater. 



Ward's paper confirms and even extends the results 

 of Young. 



Papers that treat of the Northern and North-east 

 French coal-fields, of the Belgian and of the east German 

 fields, largely duplicate the conditions above revealed. 



The total thickness of the Coal Measures in Britain 

 has, by Hull, Geikie, Ward and others been estimated at 

 2,000 to as much as 12,000 feet, though 3,000-5,000 

 includes average variations. 



Over the eastern half of the North American conti- 

 nent the Coal Measures cover several widely extended 

 regions in all of which rich coal beds occur. That a nearly 

 or quite synchronous connection existed between these and 

 the above Measures of the Old World is assured from 

 many considerations, and not least from the generic or 

 even specific identity of the organic remains. The occas- 

 ional variability in species or genera probably favors the 

 view of Chamberlin, that definite and isolated centres of 

 physical as well as organismal formation existed. Thus 

 while the Michigan and Rhode Island areas may each have 

 remained distinct for a protracted period, continuity prob- 

 ably was kept up in the Pennsylvania, Ohio, Kentucky and 

 Tennessee regions. Again the Illinois-Indiana region may 

 have had at least slight connection with the Missouri-Iowa 

 area, and so on. But until very exact stratigraphic and 

 palaeontological evidence is at hand, we can only approxi- 

 mately surmise. 



Equally as suggesting the possible mode of origin of 

 coal, the great stretches that must long have remained as 

 swampy lakes, and the types of associated organisms in these 

 lakes, Newberry's account of the locality above referred to 

 may be quoted from a later publication (86). "The Linton 

 (Ohio) locality is especially interesting and instructive. 

 It has already yielded more than twenty species of fishes 

 and nearly forty species of aquatic amphibians, all inhabi- 

 tants of the same body of water. These are found in a 

 thin stratum of cannel, which, over a limited area, underlies 



