BLACK RIVER LIMESTONE. 281 



The same variety of rocks is also found in the northwest part of Ferrisburgh, where 

 it has been quarried ; at Larrabee's Point in Shoreham, where it is twenty feet thick ; 

 and in the northwest part of Benson, upon the land of Mr. Orrin Benson. A careful 

 examination of the region would perhaps bring to light the existence of this valuable 

 rock through the towns of Panton, Addison and Bridport. 



The characteristic fossils of the Black River limestone occur also in a grayish blue 

 limestone, not very different from the common Chazy limestone. 



The Columnaria alveolata (Gold) has been found at a locality a few rods east of Highgate 

 mineral spring ; at Hill's north quarry of black marble on Isle La Motte ; upon an island 

 in Button Bay in Ferrisburgh ; and at McNeil's Point in Charlotte. Upon the island in 

 Button Bay is a very profuse display of fossils, particularly of coralline forms. 



Upon Plate VIII, Fig. 3, will be found a geological map of Isle La Motte, in which the 

 amount of surface of the Black River limestone is represented. When the apparently 

 smooth faces of the joints in the black marble at Hill's north quarry are examined with 

 a microscope, they will be seen to be studded over with projecting points, a section of 

 which presents a very rough appearance. Many of these projections are composed of 

 crystals of sulphate of strontian. 



The fossils of the Black River limestone are more numerous, in proportion to its 

 thickness, than those of any preceding group of lower silurian strata. Some interesting 

 results have been derived by the comparison of catalogues of species obtained from it in 

 Canada, New York, and Tennessee ; to which we should have been glad to contribute, had 

 our opportunities for the examination of the Vermont strata been sufficiently extensive. 

 The following species have been found in this rock in Vermont, which will, for convenience, 

 be described under Trenton Limestone: Columnaria alveolata (Gold.) Stromatocerium 

 rugosum (Hall), an undetermined species of Chcetetes, Streptoplasma profunda (Hall), S. 

 cornicuhim (Hall), Tetradium columnar i e (Hall), crinoidal columns, an undetermined 

 species of Pkytopsis, Orthoceras annellmn (Con.) 0. vertebrale (Hall), and Orthis pectin- 

 ella, (Con.) All these species except Streptoplasma profunda, and the two species of cham- 

 bered shells, are from the island in Button Bay, in Ferrisburgh. 



TRENTON LIMESTONE. 



We use this term to include the Trenton limestone of the New York Reports. 



Lithological characters. 



One very soon learns to distinguish this rock in Vermont, from all others, by its com- 

 mon characters of black schistose layers, associated with slaty seams of limestone and 

 occasionally argillaceous matter. There are other varieties, however, that can be assigned 

 to this formation only by their fossils. Certain layers, for example, in Benson, cannot be 

 distinguished lithologically from the coarse thick-bedded limestones of the calciferous 

 sandrock. The following are the chief varieties : 



1. Shaly black limestone, scarcely differing from Utica slate. 



2. Black compact schistose limestone, the layers of which are separated from one another. 



3. Slaty layers, sometimes argillaceous. 



4. Gray thick-bedded strata. 



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