GEOLOGIC FORMATIONS OF NEW YOKK 147 



a total thickness of 200 or 300 feet. It is well seen at the ' Noses ' 

 about Fonda on the Mohawk, and also at Littlefalls; in each of 

 which places it has been raised to the surface by an uplift which 

 has brought it from its original position below the Hudson river 

 shales which are common in this region. It may also be seen 

 near Middleville on West Canada creek (where it contains in its 

 cavities many beautiful quartz crystals), and in many places in 

 the vicinity of Lake Champlain and the St Lawrence river, in 

 which latter region it has some layers so purely calcareous as to 

 be profitably burnt for lime. 



Outside of the Mohawk valley the Calciferous is a true lime- 

 stone and in parts of Columbia, Dutchess, Putnam, Westchester, 

 Orange and Rockland counties cannot be separated from the 

 Trenton. 



Trenton Group 

 Above the rocks of the Calciferous group between the Mohawk 

 valley and the Canadian border succeeds a thick series of bedded 

 limestones known as the Trenton group. This group has four 

 principal divisions, Chazy, Birdseye, Black river and Trenton. 

 These four divisions are nowhere all found together. 



Chazy Limestone 



Overlying the Calciferous sandrock in northern New York is a 

 dark, irregular, thick-bedded limestone, which derives its name 

 from the village in Clinton county where it was first studied. 



Its thickness is about 730 feet on Lake Champlain : but, in strik- 

 ing contrast with the wide extent of many other rocks, it is known 

 only in the Champlain valley, and does not appear to extend in 

 any considerable thickness into those parts of the state west or 

 south of the Adirondack region. It is not seen as a distinct or 

 separate mass in the Mohawk valley, though the rocks above and 

 below it are of well known occurrence outside of New York. 



Birdseye Limestone 



The rock which succeeds the Chazy limestone is one well known 

 in the Mohawk valley, as well known along the Black river and 



