I38 NEW YORK STATE MUSEUM 



.east in the New England States, nor to the west as far as Michigan 

 and Indiana. The}' seem to be absent also in the Appalachian folds 

 north of Virginia. Evidently New York formed part of a very 

 large land area during the Cambric ages. The first important 

 and unquestionable Paleozoic submergence of the southern 

 flanks of this land occurred in the early part of the succeeding 

 Ozarkic period. This was the Potsdam or Saratogan sub- 

 mergence. 



Potsdam deposition commenced in the Champlain trough, 

 toward its northern end, working southward in that trough, and 

 also working westward up the St Lawrence trough. In its 

 lower portion it was probably a continental deposit, but the 

 upper portion carries a marine fauna, and this continues on 

 through the passage beds into the Little Falls dolomite which 

 lies directly above. The deposition was continuous and un- 

 broken, so far as we know, from the one formation into the 

 other. The subsidence in the St Lawrence trough reached as 

 far west as Kingston during the Potsdam and probably but little 

 farther. From Kingston it extended southward at least to some 

 point in the valley of Black river. To how large an extent 

 western New York was submerged we do not know positively. 

 It seems likely, however, that a considerable expansion of the 

 upper St Lawrence trough occupied the north central part of the 

 State and probably covered also the western part of New York 

 and the central part of Pennsylvania. For various reasons which 

 can not be discussed at this time, it seems unlikely that this 

 western lobe of the Saratoga sea connected with the eastern 

 or Champlain lobe across the southern part of New York prior 

 to the closing stage of the Potsdam. In this and the transition 

 stage the highly emergent parts of the Adirondack uplift which 

 now became an island, had been much reduced by erosion and gen- 

 eral subsidence; and the supply of clastic matter consequently 

 was much less during the succeeding Little Falls dolomite stage. 

 However, just preceding the latter, warping occurred which 

 caused reemergenee of the northern and western flanks of the 

 island and restriction of the sea to the Champlain trough on 

 the east and the Mohawk basin on the south. The latter ex- 

 tended southward to northern New Jersey where its deposits 

 are recognized in the lower part of the Kittatiny dolomite ; and 

 thence in a southwesterly direction through central Pennsylvania. 

 Gastropod faunas found at Beauharnois near Montreal, near White- 



