426 DEVOisriAN strata [Cm. XX VL 



whole, no less than forty species of placoid and ganoid fish have been 

 already collected in Russia, some of the placoids being of enormous size, 

 as before stated, p. 419. 



Devonian Strata in the United States. 



In no country hitherto explored is there so complete a series of strata 

 intervening between the Carboniferous and Silurian as in the United 

 States. This intermediate or Devonian group was first studied in all its 

 details, and with due attention to its fossil remains, by the Government 

 Surveyors of New York. In its geographical extent, that State, taken 

 singly, is about equal in size to Great Britain ; and the geologist has the 

 advantage of finding the Devonian rocks there in a nearly horizontal and 

 undisturbed condition, so that the relative position of each formation can 

 be ascertained with certainty. 



Subdivisions of the Neiu York Devonian Strata^ in the Reports of the 

 Government Surveyors. 



Names of Groups. Thickness in Feet. 



1. Catskill group or Old Red Sandstone - . . - 2000 



2. Chemung group - .-.-.„. 1500 



3. Portao^e 



ligr4 '" 



4. Genesee 



6. TuUy -... = .. ... 15 



6. Hamilton ..... ... looO 



Y. Marcellus --.-.--.-50 



8. Corniferous ) ;-„ 



9. Onondaga f -------- ou 



10. Schoharie 



11. Cauda-Galli 



12. Orislvany sandstone - - - - - - 5 to 30 



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 60 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 nohilissimus and other fish characteristic generically or 

 specifically of the European Old Red. More doubt has been entertained 

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

 proposed in 1847, after visiting the United States, to include the Oriskany 

 sandstone in the Devonian ; and Mr. D. Sharpe, after examining the fossik 

 which I had collected in America in 1842, arrived independently at the 



