BLACK RIVER SECTIONS 169 



the formation shoiild thicken westward and thin out to zero in the oppo- 

 site direction. Its presence in force to the west is no donl)t indicated by 

 the great thickness of limestone underneath the Utica, which is reported 

 .in all the deep wells of that general area. The prolongation of this line 

 northward l)eyond Carthage would lie about 5 miles east of Leraysville 

 on the east edge of the Theresa sheet. About Leraysville the Pamelia 

 thickness is some 50 feet, which is increased to about 125 feet on the 

 western edge of the quadrangle. This rate of change in thickness would 

 just about reduce the 50 feet thickness at Leraysville to the assumed 25 

 •feet thickness shown along the river valley in the distance of 5 miles east 

 .from Leraysville to the prolongation of this line. 



Age op the Theresa and Pamelia Formations 



It has been argued that the Potsdam of this district is necessarily of 

 more recent date than the Potsdam of the Champlain region, since the 

 Potsdam deposits progressively encroached from east to west on a slowly 

 sinking floor; hence that, while the Potsdam of the immediate region 

 was being laid down, Beekmantown dolomites were forming on the 

 Champlain meridian. While within certain limits this is no doubt true, 

 it is quite possible to unduly emphasize the difference in age. The Pots- 

 dam is a continuous formation from one district to the other and carries 

 the same fauna throughout in its upper portion. Tt is everywhere over- 

 aid by the passage beds of the Theresa formation, up into which some of 

 its fossil forms run. To the writer it has long seemed that the universal 

 |)\\'ard gradation of the Potsdam into the Beekmantown rendered it ex- 

 ceedingly improbable that the line between the Cambrian and Lower 

 Silurian systems was properly drawn at this horizon, and this view has 

 been emphasized for some time in correspondence with the State Geolo- 

 gist's office. The same omnipresent relations between the two formations 

 in Canada forced Ells to a similar conclusion, though his method of 

 avoiding the difficulty was by moving the Potsdam up into the Lower 

 Silurian. ^- 



The writer's argument has been that at least some portion of the Beek- 

 mantown should be classed with the Potsdam as Saratogan or Upper 

 Caml)rian. It was realized that in those portions of basins of subsidence 

 remote from shorelines lack of breaks between systems might well occur ; 

 but the deposits in question in northern Xew York were all laid down 

 at the edges of basins and near shorelines, and it seemed that in such 

 ;ituations breaks between formations should be the rule. 



^- Transactions of the Royal Society of Canada, 1894, section iv, pp. 21-.S0. 



