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and northwesterly out of the Adirondack region, and southerly 

 and southwesterly out of the Canadian Precambric region, and 

 these streams diverted by the large subsequent streams in the 

 Black river, St Lawrence and Ontario valleys; the Black along 

 the overlap of the sedimentaries on the crystallines, the Ontario 

 valley on the thick shales, and the St Lawrence on the limestones 

 of the depressed trough, with bordering Potsdam and Precambric 

 on both sides; hence each on a relatively weak rock belt. In 

 these positions the Tertiary successors dug out their valleys. 

 They mostly flowed as they do now, the important exception be- 

 ing in the case of the Ontario-St Lawrence drainage. The fold, 

 or warp, of the Frontenac axis crosses this drainage line in our 

 district. Even before being worn down to the Precambric this 

 would make a natural rock barrier to the drainage, since the 

 lower Ordovicic rocks are more resistant than the upper, and 

 hence form a divide or col between waters flowing northeast, 

 down the present St Lawrence valley, and waters passing west 

 through the Ontario valley, the Black river forming the chief 

 stream of the immediate region, as it now does. All writers on 

 the district have considered that, in Tertiary times, the Black 

 river turned westward into the Ontario valley. Wilson espe- 

 cially has considered the drainage of the immediate region in 

 some detail in a most excellent paper, with much of which we 

 are in entire agreement. 1 He points out that the St Lawrence 

 lacks a definite channel in the Thousand Island region, going 

 over the Frontenac axis at its most depressed point. With this 

 we agree, but we do not coincide with his view that the Black 

 river, in its course across the mapped area, is closely in its 

 preglacial channel (the river below Carthage is here referred 

 to). We are however in doubt as to where this preglacial chan- 

 nel was. Fairchild disagrees entirely with the view that the 

 preglacial waters of the Black river went westward, and turns 

 them into the St Lawrence valley below the col. His views are 

 presented on pages 141-145. I dissent somewhat, preferring the 

 view that the drainage went into the Ontario basin, but must 

 frankly admit that I have not discovered the precise route fol- 

 lowed, so that it seems to me that opinion in the matter must 

 be held in abeyance, pending discovery of the actual old channel. 

 If the Frontenac axis formed a divide here in Tertiary times 

 such divide should run across our district toward the Adiron- 

 dacks, as a divide between streams going north and those moving 



iGeol. Soc. Am. Bui. 15:236-42. 



