PALEOZOIC ROCKS OF THE CANTON QUADRANGLE 21 



(the upper white portion alone present), with its last exposure 

 at " The Ledges " in the Indian Creek swamp, about a mile west 

 of our borders. Here these sandstones vanish under glacial drift 

 together with a large part of the thickness of the Theresa, of which, 

 with one possible exception, not more than the top 20 feet have 

 been positively seen on the quadrangle. At locality 42, southwest 

 of West Potsdam, in the bottom of a small brook valley, among a 

 great mass of stream-washed boulders, is a disrupted ledge about 

 a rod long of white sandstone, varied buffy and reddish, that is 

 quite massive and with brilliantly glittering surfaces due to 

 recrystallization of quartz, like the higher Potsdam; but its south- 

 erly dip and proximity to extensive Heuvelton and even Bucks 

 Bridge outcrops favor a reference to one of the lower hard sand- 

 stones in the Theresa west of our district. 



It would seem that if present, so resistant a formation as the 

 Potsdam ought to outcrop, as it does both east and west. At 

 Rensselaer Falls it is extensively displayed in the bed of the Oswe- 

 gatchie, making rapids, whereas both the Grass and the Raquette 

 cross from the Precambrian to the Theresa without a ripple. On 

 the Raquette moreover there is scant room for any Potsdam 

 between the gneiss at Potsdam village and the topmost Theresa 

 beds above Sissonville (localit)^ t,3)- Cushing^ noted this fact but 

 invoked faulting and considered the gneiss at Potsdam an isolated 

 knob or " inlier " with the main belt of Potsdam sandstone passing 

 behind (south of) it. This is conjectural, for the nearest outcrops 

 to the southwest, though remote, are of Grenville tied up with 

 numerous Precambrian. masses beyond, while the accumulating 

 evidence is contrary to major faulting in our area. 



Just at the point where the Potsdam belt enters the east edge of 

 the Canton sheet, the Precambrian outcrops begin to protrude far 

 to the north (see the key map, figure i), narrowing the space 

 between them and the Beekmantown across the Canton quadrangle, 

 while the space between the Heuvelton and the Beekmantovi'n is 

 not similarly compressed. That this great Precambrian promon- 

 tory cuts out the Potsdam for a few miles is therefore not incred- 

 ible. There is no question that the lower part of the sandstone 

 series, including at least the entire thickness of the typical red 

 beds, is thus interrupted, since the white layers of the upper division 



^ i6th Rep't N. Y. State Geol., p. 24. Cushing's observations along the 

 Raquette were of the pioneer type, just at the close of the field season. 

 See page 55. 



