THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE \J 



GRENVILLE SERIES 

 GRENVILLE LIMESTONE 



Grenville limestone in its various phases is found in narrow belts 

 and patches with a general northeast-southwest trend, and in irregu- 

 lar masses, filling the areas between the various contorted igneous 

 gneisses and more competent members of the Grenville sediments. 

 The longest of these strips, with a maximum breadth of about 2 

 miles, extends diagonally from the southwest corner of the quad- 

 rangle to the vicinity east of Slab City, where it passes under the 

 Paleozoic overlap. Its local distribution corresponds essentially 

 with that surmised by Professor Smyth as early as 1895 (Smyth, 

 1898, pages 481-82 ; cf. also beyond, page 18). Its course is m^arked 

 by the valley of Harrison creek, that of the Grass river, and the 

 low^er course of Little river and Tracey brook ; thence northward it 

 is obscured by drift, and the probability of its extension to the point 

 indicated is based solely upon an outcrop on the left bank of a brook 

 about 2^ miles northeast of the Canton-Potsdam town line. If, as 

 is doubtless the case, this limestone belt is continuous with that 

 traced by Professor Smyth from Antwerp through Gouverneurto a 

 point *' about two miles south of Canton village," it is the northeast 

 extremity of the largest mass of limestone yet observed in the north- 

 west Adirondacks. 



Its narrowest portion, two-tenths of a mile broad, is found in the 

 valley of Harrison creek where it crosses the road running north- 

 west to Eddy. Southwestward from this point the formation 

 broadens to a little over one-half of a mile at the margin of the 

 quadrangle; northeastward a similar breadth is attained about six- 

 tenths of a mile beyond the railroad bridge, where, however, allow- 

 ance should be made for the thick mass of vitreous quartzite incor- 

 porated in the middle of the belt. Another lesser constriction oc- 

 curs a short distance beyond, at a point locally known as Woodcock's 

 rapids, w^here the narrow belt of gabbro-amphibolite, which there 

 approaches the river, begins to swing eastward through an arc of 90 

 degrees. From this point northeastward the limestone rapidly 

 broadens and attains its greatest breadth of 234 miles in the vicinity 

 of the Canton-Russell road, where it shows a tendency to bifurcate 

 round a mass of intercalated gneisses and schists. Both branches, 

 if such they may be considered, disappear farther on under the 

 heavy cover of drift, which for the rest of the distance northeast- 

 ward effectively conceals their separate boundaries and their rela- 

 tions with the associated Precambrian formations. 



