FOSSILIFEKOUS BOOKS. 259 



Should the discussion now commenced anew in the scientific world respecting the age of 

 the Georgia Group and the Red Sandrock series, result in the establishment of their pri- 

 mordial character, the presumption will arise that the azoic rocks of New England are 

 still older perhaps even laurentian. Hence we await with much interest the develop- 

 ment of opinion on these subjects. 



LOWER SILURIAN ROCKS. 



The geologists of New York have referred to the lower silurian period, several groups 

 of rocks immediately overlying the azoic rocks in the northeastern part of their State. 

 The same terrains are continued into Vermont ; and we endeavored to trace them out, 

 and have represented them upon our Geological Map. Local names were given to 

 these groups, and they are the following, as developed in Vermont. We give them in the 

 ascending order: 



POTSDAM SANDSTONE. 



CALCIFEROUS SANDROCK. 



CHAZY LIMESTONE. 



BIRDSEYE LIMESTONE. 



BLACK RIVER LIMESTONE, OR ISLE LA MOTTE MARBLE. 



TRENTON LIMESTONE. 



UTICA SLATE. 



HUDSON RIVER GROUP. 



To these, in connection with the red sandrock series, which was supposed to overlie the 

 Hudson River Group, the general name of Champlain Group has been applied, from their 

 occurrence in the valley of Lake Champlain. 



Lithologically these lower silurian rocks may form three divisons, viz : sandstone, beds 

 of limestone and clay slates. But the more complex classification we have given, is 

 necessary only on account of the distribution of organic remains through the series. 

 Some authors have arranged these divisions into three general groups, which correspond 

 essentially to the natural lithological arrangement. On this view the smaller divisions 

 are called Epochs, and the larger divisions Periods. It regards the rocks historically, not 

 merely lithologically and palseontologically. The following is the proposed system : 



I. POTSDAM PERIOD. 



1st Epoch, Potsdam Sandstone. 

 2cl Epoch, Calciferous Sandrock. 



II. TRENTON PERIOD. 



1st Epoch, Chazy Limestone. 

 2d Epoch, Birdseye Limestone. 

 3d Epoch, Slack Eiver Limestone. 

 4th Epoch, Trenton Limestone. 



III. HUDSON PERIOD. 



1st Epoch, Utica Slate. 



2d Epoch, Hudson Biver Group. 



