Devonian Shales of Northern Ohio. 209 



land the easterly thickening of the shale series proceeds at a 

 more rapid rate than the easterly dip of the limestone, and a 

 westerly declination of from 6 to 7 feet per mile results. 



Age of the Huron shale. — In testing the overlap hypothesis 

 we are concerned more directly with the age of the Huron or 

 basal shale of the Ohio group than with the age of the Cleve- 

 land. For this reason, and because of the limitations of space 

 the present discussion of faunal evidence is confined chiefly to 

 the Huron. The upper Devonian age of the Chagrin shale is 

 generally conceded, and more detailed consideration of its 

 correlation is not essential to the present discussion. 



It has been pointed out elsewhere in this paper that the 

 black shales in the Huron River section known as the Huron 

 and Cleveland, while synchronous in part with the Chagrin 

 shale to the east, represent, in the writer's opinion, a distinct 

 bathymetric facies from it. The latter represents the shallower 

 inshore facies, and the former the deeper water and more 

 pelagic facies of the same sea, just as the upper part of the 

 Hamilton of eastern New York and the Genesee shale represent 

 distinct bathymetric conditions and equally unlike faunas. 

 For this reason there is but little in common between the 

 faunas of the dark colored members of the Ohio and the light 

 colored Chagrin. The paleontologic evidence of the age of the 

 Huron is of prime interest in this connection because of its 

 bearing on the overlap theory. Since this hypothesis assumes 

 the Carboniferous age of the Huron, the discovery in it of Car- 

 boniferous fossils is essential to its demonstration, or of Devo- 

 nian fossils for its rejection. The report of David White on 

 some well-preserved plant remains collected from beds within 

 10 feet of the lowest exposures of the Huron shale on the 

 Huron River are of considerable interest in this connection. It 

 is as follows :* 



" I have examined with great care and interest the fossil plant 

 from the Huron shale, near Milan in northern Ohio. The fossil 

 comprises a long fragment of the trunk of the type described by 

 Sir William Dawson as Catamites inornatns. On examination I 

 find the species to present the essential characters of Nathorst's 

 genus JPseudobornia, which is typical of the Pseucloborniales — 

 an order that probably is ancestral to both the Sphenophjdlales 

 and Calamariales. 



The specimens, as originally described by Dawson, are said to 

 have been obtained from the Genesee shale along the shore of 

 Cayuga Lake in New York. I have examined similar material 

 collected by Prof. C. S. Prosser from the upper part of the Gene- 

 see shale at Blacksmith's Gully, near Bristol Center, Ontario 

 County, New York, and from Seneca Point on the west shore 



* Letter to the writer Dee. 18, 1911. 



