GEOLOGY OF THE PHILIPSBURG REGION OF QUEBEC 331 



In 1 9 10, Ulrich and Gushing^ in studying the age and relations 

 of the Little Falls dolomite, which they correlate with Division A 

 and the part of B below the dove-grey limestone horizon at East 

 Shoreham, found evidence of an important break between the Little 

 Falls dolomite and the Tribes Hill limestone above. Commencing 

 at Ticonderoga on Lake Champlain and passing from there to 

 Whitehall, 20 miles south, thence to Saratoga, 35 miles farther 

 south-southwest from Whitehall, thence into the Mohawk valley, 

 20 miles southwest of Saratoga, and from there west to Little Falls, 

 Middleville, and Newport, about 40 miles farther, they found evi- 

 dence of this important unconformity. They state that the Tribes 

 Hill and Little Falls formations seem unconformable everywhere 

 in New York and they make this unconformity the dividing line 

 between the proposed Ozarkic and the Beekmantown. 



Since the Division A and B at East Shoreham, which Ulrich 

 and Gushing have correlated with the New York Little Falls dolo- 

 mite and Tribes Hill limestone respectively, can be correlated so 

 closely on lithological grounds with Logan's Division Ai and A2 

 at Philipsburg, an unconformity might be expected between these 

 two members. It is true that an abrupt change in the deposition 

 did occur, but there appears to be no evidence of a diastrophic 

 movement of importance. It is the opinion of the writer that the 

 line between the Upper Gambrian and the Beekmantown in the 

 Ghamplain Valley cannot as yet be definitely drawn. With more 

 careful study of available sections, it becomes clearer that no impor- 

 tant break occurred until the end of the Beekmantown. It is 

 generally agreed that the stratigraphic relations of the Potsdam 

 to the overlying Theresa and Little Falls dolomite indicate a 

 sequence of sedimentation interrupted by no important break. 



Wherever the line is drawn in the Ghamplain Valley, it does 

 not seem logical on any ground to separate the Little Falls dolomite 

 (Division Ai) from the pure dove-colored limestone of Division 

 A2 (Tribes Hill) at Philipsburg. Although faunal evidence is 

 almost entirely lacking, it is apparent that the dolomites above and 

 below the Tribes HiU limestone were deposited under essentially 



^ E. O. Ulrich and H. P. Gushing, New York State Mus., Bull. 140 (1910), pp. 

 97-140. 



