Notes upon the Geology of the Western /States. 61 



New York. This mass is the "blue limestone," of Prof. Locke, 

 in the Ohio reports, but not, as has been supposed, a member of 

 the Mohawk group, but a limestone and shale series, represent- 

 ing what in New York is a shale and sandstone group. The 

 fossils are essentially the same. Pterinea carinata, Cyrtolites or- 



natus, Bellerophon bilobatus, Leptasna ? Trinucleus, and 



Graptolites, are the fossils which characterize equally rocks holding 

 the same place in New York. Two or more species of Isotelus are 

 frequently found in the same rocks. The Isotelus in New York 

 is a characteristic fossil of the Trenton limestone. This group 

 is well developed, forming high, abrupt cliffs on the Ohio below 

 Portsmouth, and at Cincinnati ; also at Maysville, Ky. and Mad- 

 ison, Ind. At either of these places many other fossils are found 

 besides those enumerated. In the higher beds are Delthyris and 

 Orthis, one species of the latter genus the same as occurs in the 

 Niagara group in New York. 



At Newport, Ky. opposite to Cincinnati, and at one or two 

 other places in this vicinity, there is a green shale with the Tri- 

 arthrus, Graptolites, and a few encrinal joints, shewing the same 

 assemblage of fossils and in the same position as the " Utica 

 slate" of New York. The rock below this, which is seen in 

 place only during low water of the Ohio, is a shaly limestone, 

 with shells and great numbers of the fragments, with sometimes 

 perfect specimens of the Isotelus ; Dr. Locke of Cincinnati has 

 a very large individual of this genus. This rock is probably the 

 equivalent of the Trenton limestone of New York. 



The Ontario and Mohawk groups are both seen on the Missis- 

 sippi above Dubuque, containing as elsewhere, a large number of 

 fossils.* At the same place and below these rocks, there is a mass 

 of sandstone, but I have not been able to identify it with any 

 mass farther east. 



My examinations were not extended far enough to the north 

 to discover the lower members of the transition or Silurian sys- 

 tem, which doubtless would be found there. I have sufficient 

 data to feel entirely satisfied of the results of these examinations 

 as here given. These may be of some use, particularly as re- 

 gards the readers of the geological reports, where it is not only 

 desirable to give extended views, but also to explain, as far as 

 possible, the rocks now known by diff'erent names. * 



At this place the mass appears much thinner than farther eastward. 



