126 NEW YORK STATE MUSEUM 



the north Atlantic basin, just as the former, perhaps more insulated 

 but of wider extent, stretched across the south Atlantic from south- 

 west northeasterly. 



Problem of the black shales. The Upper Devonic of Appalachia 

 is eminently characterized by its abundance, often preponderance, 

 of black shale beds. These are thickest in Michigan, Ohio, Ten- 

 nessee and Kentucky and seem to thin continuously eastward into 

 New York. Not all students have agreed in construing the entire 

 heavy mass of these bituminous shales as Devonic, but the upper 

 divisions (Chattanooga shales) have been, with some reason, as- 

 signed to the opening stage of the Carbonic. It is probably true 

 that these shale bands have been studied most closely in New York 

 where it is evident that they represent the thinning edge of the body 

 of this sediment. Here the upper black shales of the Genesee and 

 Portage groups have caught more abundantly than elsewhere the 

 characteristic marine fauna of the intercalated deep water marine. 

 A customary interpretation of the origin of these black Devonic 

 shales was that of shallow water origin. This conception assumed, 

 largely on the basis of the plant remains in which the rocks abound 

 and especially the accumulations of sporiferous deposits occurring 

 in the Ohio beds, that they were near-shore beds formed in shallow 

 basins with choked outlets. Another popular explanation was to 

 refer them to the accumulation of fat muds beneath a Sargasso sea. 

 Both interpretations, twenty years ago, were accepted alternatively 

 without special scrutiny. At a later date the writer had occasion to 

 give attention to the problem and in seeking a solution brought out 

 the very evident fact that the known seaward sweep of terrestrial 

 vegetation by rivers of the land into the rivers of the ocean, the 

 abundance of such distant flotsam observed by oceanographers, 

 failed to compel any such interpretation as the first, while the 

 Sargasso sea conception is entirely eliminated by the nature of the 

 flora of these shales, which is wholly terrestrial. The Genesee and 

 Portage black shales, furthermore, were shown to carry a highly 

 characteristic marine fauna, whose elements show a deep water 

 habitus. 



These older conceptions have the merit of the obvious and 

 specious. There are, however, deeper considerations which have 

 been brought out with some degree of analytical force and which 

 are not in harmony with this interpretation of a shallow water 

 origin for these extensive deposits. If I am not mistaken, it was 

 Professor Williams who first directed attention to the fact that in 

 all the bituminous shale beds of the Appalachian Paleozoic succes- 



