182 



GEOLOGY OF THE SECOND DISTRICT. 



This marble is of a jet black color, of a close fine grain, and slightly crystalline. In one 

 direction it is rather brittle, and requires to be handled with care when cut in thin tables ; 

 but these are so placed when employed for mantels and other purposes, that the strain and 

 weight does not bear upon them in this direction so as to endanger their breaking. The 

 planes of deposition of this marble often exhibit an interesting surface ; thus, it is usually 

 studded with projections from both the upper and under side, which interlock with each other 

 as represented in fig. 39. Generally these projections are composed of a fibrous substance, 

 similar in color and structure to fibrous sulphate of strontian. In the direction of those jagged 

 places, the layers will often separate and expose a surface of several square feet. Sometimes 

 there is interposed an extremely fine slaty matter, in which the most delicate impressions of 

 fucoidal markings are preserved, and occasionally a small encrinite which has not yet been 

 particularly examined. 



Trenton Limestone. 



The rock succeeding the black marble, is the Trenton limestone, which is well marked by 

 its fossils, and by its lithological characters at the Falls. It has put on here its usual forms, 

 a limestone in thin beds, with shaly layers intervening, containing the Orthis testudinaria and 

 alternata, Isotelus gigas, Strophomena deltoidea and Trinucleus tessellatus, figures of which 

 may be seen by turning to the geology of Jefierson county. 



In Warren county, this rock can be examined only to advantage on the rocky gorge of the 

 Hudson, and more particularly about the Falls. Passing down the river towards Baker's 

 falls, it soon disappears beneath the Utica slate. If traced to the west, or up the river, it is 

 also soon concealed beneath the same rock. The dip of the Trenton, therefore, above the 

 falls, is west ; while for a short distance below, it is east, an arrangement produced by a 

 fracture and uplift which crosses the river at or near the falls, forming thereby a slight anti- 

 clinal ridge, and by which the fall is made at this place. The following section or diagram 



a Falls. 



b b Utica slate. 



is offered in explanation of this peculiar feature in the disposition of the rocks. It was at this 

 place that I was enabled, several years since, to determine the true position of the slates of 

 the Hudson river series. 



The uplift at Glen's-Falls is a phenomenon of some interest, when taken in connection with 

 he changes of the same character to the cast of it. Here the rocks arc really but little dis- 



