544 DEVONIAN STRATA [Oh. XXVI. 



These subdivisions are of very unequal value, whether we regard 

 the thickness of the beds or the distinctness of their fossils ; but they 

 have each some mineral or organic character to distinguish them from 

 the rest. Moreover, it has been found, on comparing the geology of 

 other North American States with the New York standard, that some 

 of the above-mentioned groups, such as Nos. 2 and 3, which are 

 respectively 1500 and 1000 feet thick in New York, are very local, and 

 thin out when followed into adjoining States; whereas others, such as 

 Nos. 8 and 9, the total thickness of which is scarcely 50 feet in New 

 York, can be traced over an area nearly as large as Europe. 



Respecting the upper limit of the above system, there has been very 

 little difference of opinion, since the Red Sandstone No. 1 contains 

 Holoptychius riohilissimus and other fish characteristic generically or 

 specifically of the European Old Red. More doubt has been enter- 

 tained in regard to the classification of Nos. 10, 11, and 12. M. de 

 Yerneuil proposed in 1847, after visiting the United States, to in- 

 clude the Oriskany sandstone in the Devonian ; and Mr. D. Sharpe, 

 after examining the fossils which I had collected in America in 1842, 

 arrived independently at the same conclusion.* The resemblance of 

 the Spirifers of this Oriskany sandstone to those of the Lower Devo- 

 nian of the Eifel was the chief motive assigned by M. de Yerneuil for 

 his view ; and the overlying Schoharie grit, No. 10, was classed as 

 Devonian because it contained a species of Asterolepis. On the other 

 hand, Prof. Hall adduces many fossils from Nos. 10 and 12 which 

 resemble more nearly the Ludlow group of Murchison than any other 

 European type ; and he thinks, therefore, that those groups may be 

 " Upper Silurian." Sir William Logan has shown that the fossils of 

 the Gaspe limestones in Eastern Canada favor the same opinion, and 

 demonstrate at least how difficult it is to draw a dividing line in that 

 country between the Devonian and Silurian systems. Although the 

 Oriskany sandstone is no more than 30 feet thick in New York, it is 

 sometimes 300 feet thick in Pennsylvania and Yirginia, where, to- 

 gether with other primary or palseozoic strata, it has been well stud- 

 ied by Professors W. B. and H. D. Rogers. 



The upper divisions (from the Catskill to the Genesee groups 

 inclusive, Nos. 1 to 4) consist of arenaceous and shaly beds, and may 

 have been of littoral origin. They vary greatly in thickness, and few 

 of them can be traced into the " far West ; " whereas the calcareous 

 groups, Nos. 8 and 9, although in New York they have seldom a 

 united thickness of more than 50 feet, are observed to constitute an 

 almost continuous coral-reef over an area of not less than 500,000 

 square miles, from the State of New York to the Mississippi, and be- 

 tween Lakes Huron and Michigan, in the north, and the Ohio River 

 and Tennessee in the south. In the Western States they are repre- 



* De Verneuil, Bulletin, 4, 678, 1847 ; D. Sharpe, Quart. Joura. Geol. Soc, vol. 

 iv. p. 145, 1847. 



