14 



TJtica Slate and 



can be taken from the Hudson River group and considered a distinct 

 formation then the Galena is to be ranked iu the same way, both on 

 account of its lithological characters and the peculiarity of its fauna. 

 To the superior formation the Galena is united by passage beds 

 and thirty species of fossils, while the Utica slate has but two more 

 species and a somewhat closer union by its lithological characters. 



Both the Thebes sandstone and the Orthis bed of Tennessee give 

 expression to the epoch following that of the Trenton and, although 

 inferior in volume and character of imbedded fossils to the Utica and 

 Galena, they unite with the Triarthrus beds of Cincinnati to estab- 

 lish the Utica horizon over the central Appalachian basin, at the 

 close of the Trenton limestone-forming epoch. 



In conclusion, it is to be considered, that, although an exact 

 equivalency in time cannot be asserted for the deposition of the 

 Utica and Galena formations, the facts presented afford strong evi- 

 dence of their belonging to the same geological epoch, and consid- 

 ered with the beds mentioned above in the central basin, they form 

 a distinct geological horizon in the Trenton period, separating and 

 distinguishing the two great divisions, the Trenton and Hudson 

 River. 



The Utica horizon will then include : 

 The Utica slate. 

 The Galena limestone. 

 The Triarthrus beds of Cincinnati. 

 The Orthis bed of Tennessee. 

 The Thebes sandstone. 



Graptolitic shales, in part, of Virginia, Tennessee and Alabama. 



We have observed that there is a well defined and distinct horizon 

 between the Trenton and Hudson River formations along the Hudson 

 and Mohawk valleys, which extends throughout the Appalachian 

 basin. With this in view there can be but one series of terras to 

 express the divisions of Prof. Dana's Trenton period. 



They are : 



Hudson Epoch. 

 Utica Epoch. 

 TpvExtox Epoch. 



The term Cincinnati epoch cannot be substituted for that of 

 Hudson River, without violence to accepted rules of nomenclature. 

 The term ^^ashville group has priority and both are synonymous 

 with the much older term Hudson River. The Hudson epoch, 

 as used above, includes the original Hudson River group of the 



