272 CHAZY LIMESTONE. 



CHAZY LIMESTONE. 



Prof. Adams, in his second Annual Report upon the Geology of Vermont, p. 164, used 

 the term Isle La Motte limestone to include what we describe in this Report under the 

 names of Chazy limestone, birdseye limestone, and Black River limestone. We have 

 represented the extent of all three of these formations upon the Geological Map, Plate I, 

 by the same color, because the extent of the birdseye limestone and the Black River 

 limestone is too insignificant to deserve a separate delineation. 



The name of the Chazy limestone is derived from the town of Chazy, Clinton County, 

 New York, where it is clearly developed. 



Lithological Characters of the Chazy Limestone. 



The general character of this rock is that of a dark-colored, irregular, thick-bedded 

 limestone. The varieties of the formation in Vermont are all limestones. They are 



1. THICK-BEDDED, DUSKT-COLOBED LIMESTONE. 



2. LIMESTONE CONTAINING CHEBT AND GBAINS OF SAND. 



3. ENCBINAL LIMESTONE. 



4. CONCBETIONABT LIMESTONE. 



5. BBECCIATED LIMESTONE. 



We have an approximate section of some of these varieties as they occur upon the Isle 

 La Motte, which we will give in the descending order. First, below the Trenton Group 

 is a schistose limestone, filled with small corals. Next comes the black or Isle La Motte 

 marble (the Black River limestone), as shown at Hill's north quarry. The marble is 

 twelve feet thick. Southwest of this quarry is Hill's south quarry, known formerly as 

 Cook's quarry. Between the two quarries there is a great thickness of coarse gray lime- 

 stone containing a great many corals, fragments of trilobites, rnaclureas, etc. In many 

 places the rock is composed of nothing but fossils. Hill's south quarry is composed of 

 several layers. First, in the order of descent, is a limestone unsuitable for quarrying, 

 containing large Orthocerata ; secondly, beds of the marble, containing multitudes of 

 maclureas, and comminuted corals ; thirdly, a stratum two feet thick of compact gray 

 limestone ; fourthly, thick beds of very compact limestone, mostly consisting of com- 

 minuted fragments of corals, with encrinites, etc. Below this quarry, coarse gray thick- 

 bedded limestone extends to Fisk's quarry, in the southwest portion of the island. 

 Numerous specimens of the Maclurea magna, the characteristic fossil of this group, show 

 themselves upon almost every ledge over this interval. There are forty or fifty feet of 

 thickness of building stone in Fisk's quarry. 



These strata are all a dark gray compact limestone, ranging slightly in color, texture, 

 hardness, etc. Below the quarry we noticed before reaching the water's edge, a 

 thick black stratum, a gray tough limestone, a red encrinal limestone with occasional 

 white patches, and an unknown thickness of slaty layers passing under the lake. 

 Fleury's quarry appears to lie under Fisk's, but we did not examine its bed. Below this 

 quarry, at the water's -edge, we measured the following strata : 



