II P. Gushing — Lower Paleozoic Hocks of -New York. 137 



in the dove limestones of division B; but up to the present 

 these have furnished no fossils and precise correlation cannot 

 be made until these are forthcoming. We greatly doubt its 

 presence; we doubt if the Beekmantown of the Champlain 

 valley has a single member in common with that of the Mohawk. 

 And certainly, with the exception of the Tribes Hill, Beek- 

 mantown deposition in New York was confined to the Cham- 

 plain trough and to its prolongation southward ; and to a 

 branch trough extending up the St. Lawrence valley. The 

 Mohawk and Black river valleys were unsubmerged. And, 

 during Tribes Hill time on the other hand the Mohawk and 

 lower Black river valleys were submerged, the Champlain 

 valley probably not. This contrasted distribution might seem 

 to support the recent suggestion of Raymond that the Tribes 

 Hill should be classed with the Little Falls dolomite beneath 

 rather than with the Beekmantown.* Raymond's argument 

 is wholly paleontologic, and must be answered by a paleontolo- 

 gist. There was oscillation both preceding and succeeding the 

 Tribes Hill, and the relative importance of the two breaks can- 

 not be determined in New York. To be able to class the 

 Tribes Hill with the Little Falls would much simplify areal 

 mapping in the Watertown region, where the Saratogan has 

 comparatively meager representation. The thinned western 

 edge of the Fotsdam is present, followed by some 25 feet of 

 passage beds (Theresa). These are directly overlaid by a simi- 

 lar small thickness of impure limestones with the Tribes Hill 

 fauna. The Tribes Hill beds are so like the calcareous mem- 

 bers of the passage beds beneath that Cushing was constrained 

 to map the two together as a single lithologic unit. And yet, 

 according to our results, the boundary between two systems 

 must lie midway in that thin, lithologic unit. But Ulrich is 

 positive in his correlation of the faunas and, in reply to the 

 incongruity of distribution between the Tribes liill and the 

 remainder of the Beekmantown, points out that the early 

 Devonian was characterized by similar incongruity, the distri- 

 bution of the Helderberg and Oriskany rocks contrasting 

 sharply with that of the Onondaga and its successors. 



The Chazy Group. 



There is an unconformity between the Beekmantown and 

 Chazy groups which marks a time of extensive withdrawal of 

 the sea from the New York region. Like their Beekmantown 

 predecessors the Chazy rocks in New York are chiefly restricted 

 to the Champlain trough. They do not however' run south- 

 ward along that trough as the Beekmantown rocks do, but 



* This Journal, Nov., 1910. 



