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show, distinctly recognizes the chief physical oscillation of the 

 region. 



It would, therefore, appear that some marked but well defined 

 change of level occurred in the area south of the Kingston-Brock- 

 ville Archaean axis at the close of the Potsdam, which was also 

 materially reduced in thickness. This is in marked contrast to the 

 conditions which prevailed north of that axis throughout the Ottawa 

 basin; and it may, be supposed that, at a certain stage in. the de- 

 position of the sandstone formation, the surface was raised above 

 the level of the sea, and so remained till the beginning of Black 

 River time throughout the whole extent of Lake Ontario. 1 



Age of the Pamelia formation. Our section here shows the. 

 Pamelia formation to lie between the Theresa and Lowville forma- 

 tions, separated from each by an unconformity, the lower of which 

 is much more important than the upper. In the Champlain valley 

 two great formations, the Beekmantown and the Chazy, with a 

 combined thickness of 2000 feet, occupy this same interval, yet the 

 Pamelia formation is unlike either. On the basis of its position 

 and fauna, Ulrich correlates it with the upper part of the Stones 

 River formation, a formation of Chazy age, but laid down in a 

 separate basin from the Chazy, so that faun-ally and lithologically 

 the two are quite distinct. The Stones River basin lay to the west 

 and southwest of the Chazy trough, and was much larger. The 

 barrier between the two in New York comprised the Mohawk val- 

 ley region, much of the Adirondack district, and at least the west- 

 erly portion of the St Lawrence trough. 2 



Curiously too, although much sedimentation occurred in the 

 Champlain trough during Beekmantown-Chazy time, and only 

 Pamelia deposit in our district here, yet this is practically un- 



1 Roy. Soc. Can. Trans, ser. 2, v. 9, § iv, p. 106. 



It is to be noted that Black River is here used in a general sense as 

 including the whole body of limestone. 



2 Since the above was written another paper by Professor Grabau has 

 appeared which presents more definitely his interpretation of the rock suc- 

 cession and age in this district [Jour. Geol. 17:211-26]. The fundamental 

 difference between us seems to be that he regards the break between the 

 Theresa and Pamelia formations as representing the somewhat expanded 

 westward continuation of the break in the Champlain valley between the 

 Beekmantown and Chazy, and recognizes no break there between the Cam- 

 bric and Beekmantown. We regard it as representing most of Beekman- 

 town and all of lower and middle Chazy time and think that, to the east 

 in the St Lawrence valley, it splits into two breaks with a wedge of later 

 Beekmantown inserted between. He thinks there is no Cambric here, and 

 that the Potsdam and Theresa are of Beekmantown age; and he recog- 

 nizes no break between the Cambric and Ordovicic. We find evidence of 

 a considerable series of oscillations of level in the general region, while he 

 argues, if we correctly understand him, for a slow, progressive subsidence 

 of the region during Potsdam and Beekmantown time. 



