20 NEW YORK STATE MUSEUM 



Over the entire area explored, no contacts approaching the hori- 

 zontal have actually been seen between the Potsdam and the Pre- 

 cambrian. Everywhere the former is found resting upon steeply 

 sloping hillsides of the latter and thus is rapidly cut out, often 

 along the strike. Such relations, if the contact were not visible, 

 would readily suggest a faulted condition, but no actual faults, 

 other than the microfaulting, have been seen anywhere in the 

 quadrangle.^ The Potsdam outlier at locality 83 dips inward under 

 the north face of Waterman Hill, whereas Mr Bullis's well on 

 the top of the hill (locality 87) entered gneiss (overlaid by till) 

 at 96 feet depth, which is over 140 feet higher, while gneiss also 

 outcrops in the summit due south of the outlier, 250 feet above it. 

 A fault was suspected here, and again in the exposures northwest 

 of West Potsdam (localities 44 to 50) there are some puzzles 

 possibly due to a minor slip; but in view of all the other evidence, 

 especially Doctor Martin's Precambrian investigations, any consid- 

 erable faulting in our region appears to be out of the question.^ 

 We may safely look upon Waterman hill, then, as indicating a pre- 

 Potsdam or sub-Potsdam relief of at least 250 feet magnitude. 

 The presence of a deep pre- Potsdam valley to the north of this hill, 

 thus denoted, ties in with other facts to be presented. 



The Concealed Zone 



In contrast with the outliers, when we turn to the northern embed 

 for the main mass of the Potsdam strata we find, clear across the 

 quadrangle, a mile and one-half wide zone without outcrops between 

 the outposts of the Precambrian rocks and the nearest Paleozoic 

 ledges. The first outcrops are invariably well up in the Theresa 

 formation or higher. 



It is within this concealed zone that the main belt of Potsdam 

 must lie, if it exists across our map area. Eastward from the Oswe- 

 gatchie Professor Gushing maps a narrowing w^edge of Potsdam 



^ Cushing's belief in major faulting at Hannawa, just east of our map, 

 (i6th Rep't N. Y. State Geol. (1898), p. 14, 24), seems to be purely infer- 

 ential, with another explanation equally plausible. 



' Dr R. W. Ells, who studied and mapped the faults in the Paleozoics 

 about Ottawa, specifically remarks their absence in these sa;me rocks 

 along the Canadian side of the St Lawrence, a district also mapped by 

 him. Trans. Roy. Soc. Can., 6, (no. 4), p. 118, (1900). 



• Since the above was written a masterly treatment of the whole prob- 

 lem of pre-Potsdam topography has appeared in Mus. Bui. 18, Canada 

 Dep't of Mines, by Kindle and Burling (1915). 



