THE LIMESTONES 163 



rangle, it is a quite pure limestone formation, with a thiclcness of some 

 75 feet. The upper 20 feet are of pure limestone of blue or clove color 

 and are exceedingly fossiliferous. Beneath follow 10 to 15 feet of thin- 

 ner, more shaly limestones, with occasional fossils, after which through 

 30 feet thickness appear alternations of these thin layers with thicker 

 beds of blue or dove limestone, with a basement of 10 feet of massive blue 

 limestone, and then the white shaly beds already noted as forming the 

 base of the formation. Ulrich suggests the probability of a slight break 

 here between the Lowville and the underlying Pamelia, but the horizon 

 is seldom exposed, the white beds are quite like those occurring lower 

 down in the Pamelia formation, and the possible break has not been 

 detected in the field. Instead tlie one formation seems to grade into the 

 other, and it is a difficult matter to draw any line between them. The 

 lower part of the Lowville formation carries mainly an ostracod fauna, 

 other forms being scarce, though they do appear. "But the lower Low- 

 ville ostracoda include species of Leperditia and Isochilina of much larger 

 size than any so far observed in the underlying Pamelia."* 



BLACK RIVER AND TRENTON LIMESTONES 



These represent formations deposited in a body of waler which nearly 

 or entirely surrounded the Adirondack region and hence have not the 

 local character of the earlier deposits. The Black Eiver limestone has 

 its type locality in the immediate region, is about 20 feet thick, is mas- 

 sive and black, and its lower half is heavily charged with black chert, so 

 that it forms an easily recognizable lithologic horizon. The Trenton is 

 thick and has many of the characteristics that it has at the type locality, 

 Trenton falls. 



HISTORICAL 



In his report, "Geology of the Second District," Emmons divides the 

 rocks concerned into the Potsdam, Calciferous (Beekmantown), Birdseye 

 (Lowville), Isle la Motte marble (Black Eiver), and Trenton.^ No 

 detailed sections are given, but his descriptions make it clear that he 

 includes in the Calciferous both the Tlieresa and Pamelia formations, 

 except for a trifling thickness of the basal Theresa which he classed with 

 the Potsdam. He especially notes the "drab-colored layers of the rock, 

 which contain calcite and celestite and which are quarried for water- 

 lime at Depauville." These form part of the light-colored, impure beds 

 of the upper portion of the Pamelia formation. Emmons missed tlie 



* Ulrich : Lettei- of March 2.5, 1908. 



' Geology of the Second District, pp. 377-886. 



