444 COPPER BEARING ROCKS OF LAKE SUPERIOR. 



have merely designed to indicate by it the entire structural distinctness of the Copper- 

 Bearing Rocks from the oldest of the fossiliferous Cambrian sandstones of the region, 

 as well as from the underlying Huronian. I may also add that it appears to me very 

 unreasonable to stretch the term Cambrian over such an unconformity as subsists 

 between the last-named sandstones and the Keweenaw Series, and yet more to stretch 

 it over the unconformity between these sandstones and the Huronian. Everywhere 

 throughout the North western States, where the Cambrian sandstones come in contact 

 with the Huronian, there is evidence of an enormous time-gap between the two forma- 

 tions. As one illustration of this relation, out of many that might be cited, I may 

 mention the occurrences in the Baraboo region of Wisconsin, where a great series of 

 quartzites, including siliceous schists and immense beds of a felsitic porphyry, are 

 overlain by the fossiliferous Cambrian sandstones in such a manner as to prove beyond 

 all question that the time which elapsed between the two periods at which these forma- 

 tions were deposited was sufficiently great to cover, (1) the folding and alteration of 

 the older series, measuring upwards of 20,000 feet in thickness ; (2) the denudation of 

 the elevations of land thus produced to such an extent that ridges approaching in 

 height the highest existing mountains of the globe were entirely removed, and depres- 

 sions made in their place ; and (3) the depression of this area beneath the sea and the 

 wearing by wave action of the older rocks to supply the material for the newer. Now 

 the older of the formations in this case I take to belong, beyond question, to the same 

 horizon as that to which belong the Auimikie slates and the Huronian rocks of the 

 Lake Superior region generally. Certainly no one ever has referred or ever would refer 

 them to a lower horizon, while Winchell even regards them as the equivalent of the New 

 York Potsdam and of the Copper-Bearing Rocks of Lake Superior. Inasmuch as 

 neither the Huronian nor the Copper-Bearing Series has thus far afforded any fossils, 

 it does not seem to me reasonable to extend to them, in spite of these great unconform- 

 ities, the name of Cambrian, even though the fossiliferous rocks immediately overlying 

 them be not, as Winchell has argued from their paleontology, the equivalents of the 

 oldest of the typical Cambrian divisions of Barraude. 



But, however this may be, it seems sufficiently evident that Winchell's reference of 

 the Copper Series directly to the horizon of the New York Potsdam is untenable. If 

 I understand him correctly, he supports this reference by three kinds of evidence, 

 stratigraphical, lithological, and paleontological. The stratigraphical evidence con- 

 sists in the occurrence in the east of the following succession, in ascending order: («■) 

 A series of slates, sandstones, &c, of considerable thickness, and carrying Barrande's 

 first fauna, conformably succeeded by (b) the typical Potsdam sandstone, of very incon- 

 siderable thickness, with only a very few fossils, grading up into (c) the Calciferous 

 Sandrock, in which, and in whose continuation in Canada, is found a large fauna, cor- ' 

 responding to the second fauna of Barrande. The members of this succession he 

 parallelizes, respectively, with (a) the Auimikie Group (and hence with the Huronian 

 of the Lake Superior country generally), (b) the Keweenaw Series, and (c) the Saint 

 Croix sandstone, including the Eastern Sandstone of this volume, and the lowest 

 fossiliferous Cambrian sandstone of the Mississippi Valley. Now, not to speak of the 

 grave doubts which still hang about the relations of the older rocks in the Eastern 

 States, there are serious objections to this scheme of stratigraphical equivalence- 

 (1) It disregards the entire absence, so far as known, of fossil remains from the Aui- 



