COMPARISON OF SECTIONS 173 



As in the case of the Chazy, much of the Beekmantown formation is 

 confined to the Chazy basin and its southward extension, and did not 

 reach westward into the Mohawk and Black Eiver districts; so that 

 through this time also there was land extension in both these directions. 

 The Beekmantown basin did, however, extend up the Saint Lawrence 

 valley for a distance, though it never reached the Theresa district. Until 

 the Beekmantown of the Saint Lawrence valley receives more detailed 

 study, a definite comparison of it with the Champlain-Beekmantown is 

 not possible. It is clear that it thins westward to complete disappear- 

 ance and that the entire formation is not represented. The writer has 

 been over the ground, but the work was of hurried character and done 

 twelve years ago, and the drift cover is so heavy that outcrops are few. 

 He is decidedly of the opinion, however, that it is the base which disap- 

 pears westward instead of the summit. Such sections as that doAvn the 

 Eaquette from Potsdam to below Norwood show Potsdam sandstone fol- 

 lowed by the passage beds of the Theresa formation, above which quite 

 fossiliferous limestones come in after a very short vertical interval. The 

 fauna has never been studied, but it is certainly much more like the 

 rather abundant fauna of the upper divisions of the Beekmantown than 

 like that of Division C. This means that uplift took place after the de- 

 posit of the Theresa formation, and that the break in the Champlain 

 valley between Divisions A and B is the same break as that in the Theresa 

 district between Theresa and Pamelia formations, though of much less 

 magnitude; hence that the uplift involved both the Saint Lawrence and 

 Champlain valleys, and that the renewed depression which inaugurated 

 the Beekmantown was at first confined to the Champlain trough and its 

 southward extension, and later sent a- bay up the Saint Lawrence trough 

 with progressive encroachment westward. The unconformity in the 

 Champlain valley is of less magnitude than that about Theresa by at 

 least 2,200 feet thickness of Beekmantown and lower and middle Chazy 

 rocks which are present in the one and absent in the other district. It is 

 to be noted that this reexpanded Beekmantown basin had somewhat dif- 

 ferent outlines from its upper Cambrian predecessor, probably not reach- 

 ing the Theresa region at all, while in Canada the Beekmantown overlaps 

 the Potsdam onto the pre-Cambrian. The Chazy sea also had a bay in 

 this direction whose extent is unknown, but which in Canada overlapped 

 the Potsdam and Beekmantown onto the pre-Cambrian. Grabau argues 

 that the basal sandstones of these sections are of Beekmantown and Chazy 

 age instead of being Potsdam, this view being based on the supposed con- 

 tinuity of the section.^* While it is quite possible that there may be 



"Bull. Geol. Soc. Am., vol. 17, pp. 584-585. 



