No I BS. 



I !:; 



thought it sufficient, in order to establish their point, to sho* the existence of a greal 

 unconformity between the Copper-Bearing Rocks and the overlying sandstones. 



Recently, however, two writers, Messrs. ^»-l\\ \ n ' and N. II. Winchell, 1 while ad 

 oiittiug the existence of this unconformity, and the consequeul distinctness of the 

 Copper-Bearing Series from tl verlying sandstones, have yel maintained the Cam- 

 brian age of the former rocks. These two writers, however, differ somewhal between 

 themselves, Selwyn merely maintaining that the Copper-Bearing Rocks, along with 



the overlying Cambrian sandstones and the underlying A.nimikie slates, icupy the 



geological interval elsewhere tilled by those divisions of the greal Paleozoic system 

 which underlie the Trenton Group," without more definitelj parallelizing them with 

 the older Paleozoic formations of the Eastern States. Be also says that he prefers "to 

 call them all Lower Cambrian, which includes the Potsdam sandstone and the Primor- 

 dial Silurian." 



Winchell, on the other hand, would make the Copper-Bearing Rocks the direct 

 equivalent of the New York Potsdam, while regarding the sandstones which uncon- 

 formably overlie them, i. e., the "Eastern" and '-Western" sandstones of this volume. 

 and the fossiliferous Cambrian .sandstone of the Mississippi Valley (hiB Saint Croix 

 sandstone), as later than the New York Potsdam. Stated in Ins own words, the follow- 

 ing are Winchell's conclusions: 



1. " The Taconic Group was correctly established by Professor Emmons, though its 

 limits, stratigraphically and geographically, were at first wrongly defined by him. 



2. "The Georgia Group of Vermont, and the Aniinikie Group of Thunder lias, and 

 the Acadian of New Brunswick are the equivalent of the Taconic of Emmons. 



3. "The Taconic has the true Primordial fauna of Barrande. 



4. "The Potsdam, which lies conformably above it in the east, is represented by the 

 rocks of the Copper-Bearing Series in the west. 



5. "No fossils, representing the true Primordial fauna, have yet been discovered 

 in the west, nor have any been found in the western representative of the Potsdam. 



6. "The 'second fauna' of Barrande is found in the Quebec Group of Canada, and 

 in the Saint Croix sandstone of the west, lying in each case above the Potsdam sand- 

 stone." 8 



Elsewhere 4 Winched suggests the probability of a former continuity, in the region 

 north of Lake Superior, of the Aniinikie slates and the schists, which in that region 

 have heen called Hurouian. a position which 1 have regarded in the preceding pages 

 as much more than probably true. If it is so. and Winchell's reference of the Ani- 

 mikie to the Taconic of Emmons is correct, then the Hurouian and Taconic are also 

 the same, which would extend Winchell's use of the term Cambrian over the Hurouian 

 as well as over the Copper Series. 



Into a discussion of the question as to how far downwards the term Cambrian should 

 be stretched, I have no desire to enter at length, since 1 think it would he a profitless 

 one. I will only say that, in using the word Keweenawan, I have never designed to 

 give to this term a scope equivalent to that of the terms Cambrian, Silurian, &c., hut 



'Science, Vol. I, pp. 11,221. 



2 Tenth Annual Report of the Geol. and Nat. Ili*t. Surv. of .Minnesota, pp. 123-136, also - 

 Vol. I, ]i. 334. 



3 Tenth Annual Report of the Geol. and Nit. Hist. Surv. of Minnesota, pp.135, 130. 

 *Op. eit. pp. 'J", 94, 95; also Science, Vol. I, i>. B34. 



