GEOLOGY OP THE NORTHERN ADIRONDACK REGION 373 



extends along it unbroken, with the Lowville beneath. Hence 

 the BUick River sea surrounded the regiion on all three sides 

 with apparently unbroken connections, much diminishing the 

 siize of the former land areas of the region, even that of Beek- 

 mantown times, which was the smallest of those that preceded 

 it. The present outcrops of the Mohawk valley are near the 

 old shore line, and the irregular, ridgy character of the bottom 

 was the cause of the variations in thickness of the formation 

 there. Had erosion cut somewhat deeper, in other words, were 

 the exposures of the formation on a line somewhat south of 

 the present, it would undoubtedly extend east and west un- 

 broken. The Beekmantown pebbles in the Black River, in the 

 Tribes Hi 11- Amsterdam region, reported by Vanuxem and by 

 Prosser, are very significant as showiing the near vicinity of 

 the shore line.^ 



Trenton formation. The Trenton formation may be said to 

 show a general uniformity in lithologic character all about the 

 Adirondack region, though wdth much variation in detail from 

 place to place. Instead of the quite pure, massive limesitones 

 of the Chazy and Lowville formations, the major portion of the 

 Trenton is found to consist of thin bedded, black, shaly lime- 

 stones, often with partings of black, calcareous shales, the en- 

 tire formation being thus contaminated with a certain amount 

 of land wash in the shape of fine mud. The limestones are 

 usualh' havd and brittle, with conchordal fracture, though be- 

 coming thin bedded and shaly, and even the heavier beds split 

 thinl}' on weathering. 



In all sections there is considerable gray, rather coarsely 

 crystalline, fairly pure, very fossiliferous limestone, usually 

 thin bedded though sometimes becoming fairly massive. While 

 sometimes fairly persistent for considerable distances, such 

 beds are usually lens-shaped masses of restricted lateral extent, 

 entirely surrounded by the black calcareous muds of the ordinary 

 character. Beds of this sort seem less local and more persistent 

 in the ^lohawk than in the Champlain valley, as has been pointed 

 out by White, and constitute a larger portion of the formation 

 in the former situation, indicating less local variation in the 



iGeol. N. Y. 3d Dist. p. 44; 15th An. Rep't State Geol. 1 : 653. 



