198 BULLETIN OF THE NEW YORK STATE MUSEUM. 



of localities. It gives us, as it were, the provinces of occur- 

 rence in the greater classes. In New York, the lithological 

 characteristics of some of the geological formations have 

 been studied so carefully, and are so persistent and well- 

 known that their rocks have become types. The typical 

 Potsdam sandstone, the Medina sandstone, the Trenton 

 limestone, are recognized by practical quarrymen as well as 

 by geological experts. The geographical limits of some of 

 these varieties coincide with the geological boundaries of 

 the outcropping formations. And hence a geological map 

 of the state shows their respective areas of occurrence. 



The arrangement in this report is in accordance with the 

 geological order under the several classes of rocks, which 

 are as follows : 



I. Crystalline Rocks. 



1. Granites, gneisses, syenites, etc., etc. 



2. Trap-rocks. 



3. Limestones and marbles. 



IL Fragmental Rocks. 



1. Sandstones and conglomerates. 



2. Slates. 



In the general notes on the geological relations of the 

 building stone of the state, and in the description of the 

 quarry districts and localities the subdivisions under the 

 head of Limestones are : 



Calciferous 



Chazy 



Trenton 



Niagara 



Lower Helderberg 



Upper Helderberg 



TULLY 



