5 NEW YORK STATE MUSEUM 



that direction. In short, whereas the Paleozoic frontier corresponds 

 with the margin of the St Lawrence valley as far west as the 

 Raquette river, there these two suddenly part company, the Pre- 

 cambrian exposures extending down into and becoming a part of 

 the valley floor but preserving many Paleozoic remnants in their 

 hollows. At the same time, as noted by Gushing,^ a folded group 

 of weaker Grenville metasediments appears intercalated in the 

 massive Saranac gneisses that have alone formed the Precambrian 

 on the east ; and it is probably these weaker crystalline zones yield- 

 ing more readily to compression that have occasioned the undula- 

 tions in the overlying strata.^ Smooth zones of outcrop with incon- 

 spicuous dips therefore give way to vigorous zigzags and visible 

 tiltings while both outliers and inliers become frequent. With the 

 more nearly complete substitution of Grenville rocks for gneiss as 

 we pass southwestward into the town of Gouverneur the Paleozoic 

 embed is again offset toward the St Lawrence and the archipelago 

 of outliers reaches its fullest development. It will be seen that 

 the transition span accordingly includes also the Ogdensburg quad- 

 rangle next west, recently mapped by Professor Gushing.^ 



THE GEOLOGIGAL FORMATIONS 



General Statements 



Five divisions are recognized in the Paleozoic rocks of the Can- 

 ton quadrangle as colored on the map.* These are, in ascending 

 order :^ the Potsdam sandstones, the Theresa mixed beds, the 

 Heuvelton white sandstone, the Bucks Bridge mixed beds, the 

 Ogdensburg dolomite. 



In age, these rocks range from Cambrian (Ozarkian of Doctor 



^ On p. 6 of the i6th report, before cited. 

 *Geol. Soc. of Amer. Bui. 26, p. 290-94. 



• N. Y. State Mus. Bui. 191. 



* Two other possible formations are suggested in the text, one the 

 upper or white Potsdam, which may require separate recognition, the 

 other the mass of Trenton shaly liniestone at locality 4, recorded on 

 page 39- 



° Geol. Soc. of Amer. Bui. '^, p. 289. For convenience of the reader 

 the position of these divisions in the standard time-scale is indicated bj- 

 the italics below: 



Precambrian time (Rocks described in Bulletin 185) 

 Paleozoic time 



Cambrian period: Georgian epoch 

 Acadian epoch 



