NOTES. 443 
thought it sufficient, in order to establish their point, to show the existence of a great 
unconformity between the Copper-Bearing Rocks and the overlying sandstones. 
A; Recently, however, two writers, Messrs. Selwyn! aud N. H. Winchell,? while ad- 
mitting the existence of this unconformity, and the consequent distinctness of the 
Copper-Bearing Series from the overlying sandstones, have yet maintained the Cam- 
brian age of the former rocks. These two writers, however, differ somewhat between 
themselves, Selwyn merely maintaining that the Copper-Bearing Rocks, along with 
the overlying Cambrian sandstones and the underlying Animikie slates, “oceupy the 
geological interval elsewhere filled by those divisions of the great Paleozoic system 
which underlie the Trenton Group,” without more definitely parallelizing them with 
the older Paleozoic formations of the Eastern States. He 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, 7. ¢., the “Eastern” and “ Western” sandstones of this volume, 
and the fossiliferous Cambrian sandstone of the Mississippi Valley (his Saint Croix 
sandstone), as later than the New York Potsdam. Stated in his 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 Animikie Group of Thunder Bay, 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.”® 
Elsewhere! Winchell suggests the probability of a former continuity, in the region 
north of Lake Superior, of the Animikie slates and the schists, which in that region 
have been called Huronian, a position which I have regarded in the preceding pages 
as muck 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 Huronian and Taconic are also 
the same, which would extend Winchell’s use of the term Cambrian over the Huronian 
as well as over the Copper Series. 
Into a diseussion of the question as to how far downwards the term Cambrian should 
be stretched, I have no desire to enter at length, since I think it would be 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, &e., but 
1Science, Vol. I, pp. 11, 221. 
2Yenth Annual Report of the Geol. and Nat. Hist. Surv. of Minnesota, pp. 123-136, also Science, 
Vol. I, p. 334. 
3Tenth Annual Report of the Geol. and Nat. Hist. Surv. of Minnesota, pp. 135, 136. 
40p. cit. pp. 90, 94, 95; also Science, Vol. I, p. 834. 
