wiluams.1 TABLE OF EQUIVALENCIES. 59 



In the table the following equivalencies are given : l 



Rocks of tbo Now York systoiu. Subdivisions in Great Britain. 



Old Red sandstone Old Red sandstone. 



1. Chemung group "j 



2. Portage group. 



3. Genesee slate ! Upper and Lower Ludlow rocks including 



4. Tully limestone f the Devonian system of Phillips. 



5. Hamilton group \ 



G. Marcel 1 us shale J 



7. Corniferous limestone ) 



8. Onondaga limestone | 



9. Schoharie grit | 



10. Cauda-galli grit | 



11. Oriskauy sandstone ', , Tr , , , 



1% Upper Pentamerus limestone.... r Wenlock rocks. 



13. Encrinal limestone 



14. Delthy ris shaly limestone 



15. Pentamerus limestone 



ltf. Water-lime group 



17. Onondaga salt group 



18. Niagara group 



Correlations with the Pennsylvania and Virginia rocks and those of 

 Ohio and Michigan are expressed as follows : 



Pennsylvania and Virginia Survey. Ohio Survey. Michigan Survey. 



f Soft light-colored 

 28. Chemung group ? ^ q( Waverly sandstone | sandstones, argilla- 



27. Portage group $ ( series. I ceous slates and flag- 



26. Genesee slate No. 8 Wantiug(?) | stones of Lake llu- 



25. Tully limestone Wanting ron, sandstones of 



t Point aux Barques. 

 . „ .,. XT S Wanting or but par- \ Shales, black alumin- 



4. Hamilton group No. 8^ tially deve loped. \ ous shales. 



23. Marcellus shale No. 8 : . Black slate. 



22. Corniferous limestone j U limestone. ° f Clitf | Corniferous limestone. 



21. Onondaga limestone 



20. Schoharie grit 



( Several limestones rep- 

 19. Cauda-galli grit No. 7 < resent this andlower 



( beds. 

 18. Oriskany sandstone No. 7 - 



Some of the results thus far attained were permanently satisfactory ; 

 others have already been modified, and there are still others which 

 await correction. 



The classification of the rocks of the New York system into " system- 

 atic subdivisions, founded upon the fossil and lithological characters," 

 and the application to them of geographical names suggested by the 

 locality where the typical sections occur have stood the test of com- 

 mon use for 50 years. The classification is based upon observed facts, 

 and the nomenclature is expressive of actual facts with no mixture of 

 theory. 



The groupings of these stages into " geographical subdivisions " is 

 faulty, in that it expresses only accidental relations, and produces 

 purely artificial groups. There-are no geological reasons for drawing 



1 (ieology of New York, part iv, comprising the survey of the fourth geological district, by James 

 Hall, 1843, p. 517. 

 • Ibid., p. 61». 



