CUSHING — GrEOUQGY OF CLINTON Col X I V. 



513 



Calciferous of the Champlain valley,* and their section at Shoreham, Vt., gives 

 to the formation, which they separate into five subdivisions, a thickness of 

 1,800 feet. How large a part of this thickness the Calciferous possesses in 

 Clinton county, can not be determined, but commonly the different exposures 

 are correlated without difficulty with the various members of Brainard and 

 Seely's section. The basal layers of the formation arc shown in Champlain 

 township, conformably overlying the Potsdam. In Pern and Beekmantown 

 are good exposures of the higher and more fossiliferous members. The lower 

 half or two-thirds is made up largely of grey, often sandy dolomites, quite 

 barren of fossils. In the upper third, beds of limestone are mingled with the 

 dolomite, and some sandy beds, weathering with thick yellow sandy crusts, 

 also oecur. 



Chazy limestone. At Chazy village is the type section of this group 

 which follows the Calciferous in ascending order. Brainard and Seely have, 

 however, shown that the lower one hundred feet is lacking here and that the 

 Valcour Island section is more complete, f Besides the excellent exposures in 

 Chazy township the rocks of this group are also well shown in part just north 

 of Plattsburgh, and on Bluff Point, two miles south of Plattsburgh, extending 

 thence to the south into Peru, where the lower part of the formation is better 

 shown than at any other point in the county on the mainland. 



Brainard and Seely have recognized three subdivisions of the Chazy 

 rocks, and their detailed section at Chazy village is reproduced on a later 

 page. The lower subdivision is largely constituted of quite crystalline lime- 

 stones of grey color, often full of crinoidal fragments and with Orthis costaUs 

 the most abundant fossil; the middle division is of blue-black fine-<rrained 

 limestone and contains Mucin rea magna at nearly all horizons ; the upper 

 division is quite variable in character, but is largely composed of somewhat 

 impure blue limestones, carrying Khynchonella plena abundantly. 



The aggregate thickness of the Chazy limestone at Chazy village is 74<» 

 feet, with the base not shown. On Valcour Island, Brainard and Seely give 

 it a thickness of 890 feet, and there it seems to reach its maximum. 



For the most part these rocks are easy of recognition, and even small 

 exposures may be assigned to their proper position without great trouble. 

 There is a considerable quarry enterprise engaged in working the rocks of this 

 group, some beds furnishing an ornamental marble, some a rough building 

 stone, and some being burned for lime. 



* Bulletin American Museum of Natural History, Vol III., No. 1, p. 3. 

 t Bulletin Geological Society of America, Vol II, pp. 293 to 300. 



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