U4: 



SILUEIAN STEATA OF UNITED STATES. [Ch. XXVIL 



SheUe qf the lowest known Fossiliferous Beds in Russia. 



Fig. 605. 





Sii)7ionot)'eta nnguicrdata, Eicliwald. 



From the lowest Silurian Sandstone, "Obelus 



grits," of Petersburg. 



a. Outside of perforated valve. 



b. Interior of same, showing the termination of 



the foramen within. 



Oholus Apollinis, Eichwald. 

 From the same locality. 

 o. Interior of the larger or ventral valve. 

 &. Exterior of the upper (dorsal) valve. 

 (Davidson.) 



Among the green grains of the sanely strata above mentioned, Pro- 

 fessor Ehrenberg has recently (1854) announced his discovery of remains 

 of foraminifera. 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., Hotalia^ 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 iu the section, fig. 505, p. 388. 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 iu Russia, 

 nearly iu 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 inost 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 JVew York. (^Strata below the 

 Oriskany Sandstone, see Table, p. 426.) 



New York Names. 



1. Upper Pentameriis Limestoue 



2. Enciinal Limestone 



3. Delthyris Shaly Limestone 



4. Pentameriis Limestone 



5. Tentaculite Limestone 



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 



14. Trenton Limestone 



15. Black-River Limestone 



16. Bird's-Eye Limestone 



17. Chazy Limestone. 



18. Calcit'erous Sandstone 



19. Potsdam Sandstone 



British Equivalents. 



Upper Silurian (or Ludlow and 

 Wenlock formations). 



Middle Silurian (or Caradoc Sand- 

 stone). 



}- Lower Silurian (or Llandeilo beds). 



' Cambrian ? (or Lingula flags and 

 beds, older than " the Llandeilo.") 



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

 British equivalents. All paleontologists, European and American, such 



