310 



GEOLOGY. 



Most of the above names are derived from localities where the 

 rocks representing the several epochs are exposed. It is not to be 

 understood that these epochs were of equal duration, or that the cor- 

 responding formations are equally thick or equally distinct. The first 

 two formations have sometimes been grouped under the name Cana- 

 dian, and the last three under the name Trenton, though this grouping 

 has little significance. 



Recently it has been proposed 1 to substitute the following classifica- 

 tion for that hitherto in use: 



3. Cincinnatian(Neo-J? ichmon ? ^eds » (Ohio and Indiana) 

 nv,„™~i„™„\ 1 -Lorraine beds 



Champlainic) [ Ut ic a shales 



2. Mohawkian (Meso- { ^enton limestone 

 ruTnnininin^ i Black River limestone 



Champlainic) | Lowvil i e l imes tone 



1. Canadian (Paleo- / Chazy limestone 



Champlainic) \ Beekmantown limestone 



With reference to this classification, it may be said that there seems 

 no adequate reason for supplanting the term Ordovician. The sub- 

 division of the system into three main series, a lower, a middle, and 

 an upper, is certainly to be commended on the basis of convenience. 

 So much of the classification is applicable universally. The subdi- 

 visions in the right-hand column above are based on the detailed work 

 of recent years, and must be accepted as best expressing present knowl- 

 edge of the system in New York. The relations of the old and the 

 new classifications to each other are evident on inspection. 



Perhaps the following may be accepted for the present as the most 

 satisfactory compromise : 



Champlainic 2 (Lower 

 Silurian or Ordovi- 

 cian) 



Upper Ordovician 

 (or Cincinnatian) 



Ordovician -i Middle Ordovician 



Richmond beds (Ohio and Indiana) 

 Lorraine beds 

 Utica shales 



f Trenton limestone 

 i Black River limestone 



(or Mohawkian) 1 LowviUe limestone 



Lower Ordovician / Chazv limestone 

 (or Canadian) \ Beekmantown limestone ( = Calcif erous) 



1 Clark and Schuchert, Science, Vol. X, 1899, p. 876; and Am. Geol., Vol. XXV. 

 1900, p. 118. 



2 The term Champlainic was proposed b}^ Hall, Vanuxem, Mather, and Emmons, 

 in 1842, to include what is now known as Ordovician and the Potsdam 



3 Winchell and Ulrich, Geol. of Minn., Vol. Ill, Pt. 2, p. ciii; and Nickles, Am 

 Geol., Vol. XXXII, p. 202. 



