lO NEW YORK STATE MUSEUAI 



As for the northerly branch, it is more than probable, as above 

 intimated, that it continues to flank the southeast side of the broad 

 belt of the Canton granite gneiss till both are overlapped by the 

 Paleozoic series near Slab City. The east branch also, in all likeli- 

 hood, continues on under cover to the Crary Mills ledges, as sug- 

 gested by Professor Smyth (1898, page 482), and perhaps beyond, 

 though direct evidence for or against this view is lacking on 

 account of the intervening thick cover of Quaternary material. 



The only other limestone occurrence of pronounced linear extent 

 and. conforming to the average (northeast) trend of the formations, 

 is that which presumably occupies the depression in the west central 

 ninth of the quadrangle, that is. Upper Lake valley and its swampy 

 northeastward continuation in the adjacent angle of Grass river. 

 Though even the identity of the crystalline bedrock of this valley 

 is doubtful owing to the total lack of outcrops within the Canton 

 quadrangle, the meager evidence at hand favors the belief that this 

 topographic feature occupies the site of a belt of Grenville limcsLv:)ne 

 or other easily eroded calcareous formation. This is suggested by 

 the outcropping of limestone ledges a short distance west of the 

 edge of the quadrangle on the southeast edge of the valley, bor- 

 dered on the northwest by remnants of the Potsdam sandstone, and 

 on the southeast edge by the knoll of granite which reaches over a 

 short distance into the Canton quadrangle at latitude 44" 35^ What- 

 ever view be taken as to the age of this physiographic feature, and 

 as to the presence or absence of Paleozoic deposits beneath the 

 Quaternary, the evidence available is distinctly in favor of regarding 

 the excavation as having been effected, at least in large measure, 

 in Grenville limestone. This interpretation is supported by the only 

 testimony given on the Canton sheet, namely, that the main tributary 

 to Upper lake on the southeast side, Church brook, has cut 

 its valley in a narrow strip of limestone which borders the south 

 and west sides of the large club-shaped boss of granite gneiss west 

 of Canton. There is hardly reason to suppose that this strip oi 

 limestone, which can be traced to within several hundred yards of 

 the edge of the Upper lake depression, abruptly terminates as soon 

 as the brook enters the broad flat valley. On the other hand, it 

 seems more than likely that the Church Brook limestone connects 

 with that known to occur just over the border on the Ogdensburg 

 sheet, through the pinching out of the intervening rusty gneisses by 

 stratigraphic or tectonic cause, and that their combined masses fill 

 the entire swampy depression adjacent to the granite boss. 



