NEW-YORK FORMATIONS COMPARED WITH THOSE OF EUROPE. 
517 
Subdivisions of the Rocks of the New-York System. 
Old Red sandstone. 
1. Chemung-group. 
2. Portage group. 
3. Genesee slate. 
4. Tully limestone. 
5. Hamilton group. 
6. Marcellus shale. 
7. Corniferous limestone. 
8. Onondaga limestone. 
9. Schoharie grit. 
10. Cauda-galli grit. 
11. Oriskany sandstone. 
12. Upper Pentamerus limestone. 
13. Encrinal limestone. 
14. Delthyris shaly limestone. 
15. Pentamerus limestone. 
16. Water-lime group. 
17. Onondaga salt group. 
18. Niagara group. 
19. Clinton group. 
20. Medina sandstone. 
21. Oneida conglomerate. 
22. Grey sandstone. 
23. Hudson-river group. 
24. Utica slate. 
25. Trenton limestone. 
26. Birdseye and Black-river limestones. 
27. Chazy limestone. 
28. Calciferous sandrock. 
29. Potsdam sandstone. 
Subdivisions of the Silurian and Old Red Systems in 
Great Britain. 
Old Red sandstone. 
Upper and Lower Ludlow rocks, including the 
> Devonian System of Phillips. 
1 
Wenlock rocks. 
i 
J 
] 
y Caradoc sandstone. 
I 
J 
Llandeilo flags. 
1 
J These formations are not as fully recognized in 
Y Great Britain as in New-York. 
There are many reasons for including the Nos. 7, 8, 9 and 10 in those equivalent to the 
Ludlow formation; but in some places, the upper of these contains fossils which are charc- 
teristic of the Wenlock rocks. 
The Niagara group is evidently referable to the Dudley period, which is a part of the 
Wenlock formation. 
We are compelled to include in the rocks equivalent to the Caradoc sandstone, the Clinton 
group, from the occurrence of Pentamerus oblongus in great numbers, and in a condition pre¬ 
cisely similar to the same fossil in the impure limestones of the Caradoc formation. From 
the occurrence of large numbers of fossils in the Hudson-river group identical with those of 
the Caradoc sandstone, there remains no doubt of its equivalency with that formation. 
