570 SILURIAN STRATA OF UNITED STATES. [Ch. XXVII. 



brachiopods consist of the Oholus or Tlngulite of Pander, and a 

 Siphonotreta (figs. 657, 658). Notwithstanding the antiquity of this 

 Kussian formation, it should be stated that both of these genera of 

 brachiopods have been also found in the Upper Silurian of England, 

 i. e. in the Dudley limestone. 



Among the green grains of the sandy strata above mentioned, Prof. 

 Ehrenberg has announced (1854) his discovery of remains of foram- 

 inifera. These are casts of the cells ; and amongst five or six forms 

 three are considered by him as referable to existing genera (e. g. 

 Textularia, Rotalia, and Guttulina). 



SILURIAN STRATA OF THE UNITED STATES. 



The position of some of these strata, where they are bent and highly 

 inclined in the Appalachian chain, or where they are nearly horizontal 

 to the west of that chain, is shown in the section, fig. 552, p. 497. 

 But these formations can be studied still more advantageously north 

 of the same line of section, in the States of New York, Ohio, and other 

 regions north and south of the great Canadian lakes. Here they are 

 found, as in Russia, nearly in horizontal position, and are more rich in 

 well-preserved fossils than in almost any spot in Europe. In the State 

 of New York, where the succession of the beds and their fossils have 

 been most carefully worked out by the Government surveyors, the 

 subdivisions given in the first column of the annexed list have been 

 adopted. 



Subdivisions of the Silurian Strata of New York. (Strata below 

 the Oriskany Sandstone, see Table, p. 543.) 



New York Names. British Equivalents. 



1. Upper Pentamerus Limestone. 



2. Encrinal Limestone. 



3. Delthyris Shaly Limestone. 



4. Pentamerus and Tentaculite 



Limestones. Wenlock Formations). 



5. Water Lime Group. 



6. Onondaga Salt Group. 



7. Niagara Group. 

 . 8. Clinton Group. 



9. Medina Sandstone. 



10. Oneida Conglomerate. 



11. Gray Sandstone. 



12. Hudson River Group. 



13. Utica Slate. 

 it' TreMon Limestone , ^ m ini (or Caradoc and 



\i M^£££r i Upper and Lower LlandeUo) - 



17. Chazy Limestone. 



18. Calciferous Sandstone. J 



19. Potsdam Sandstone. Upper Cambrian. 



In the second column of the same table I have added the supposed 

 British equivalents. All palaeontologists, European and American. 



Upper Silurian (or Ludlow and 



Middle Silurian (or May-Hill and 

 Llandovery Groups). 



