No. 3.] ROBB — GEOLOGY OP ST. IGNACE ISLAND. 179 



Huronian series, occur in pebbles in the conglomerates of the Upper 

 Copper-Bearing series. Besides the locality already mentioned," (the 

 Albany and Boston Mines) "the great cupriferous bed of the Calumet 

 and Hecla Mine is a remarkable example of a rock made up almost 

 wholly of the ruins of these peculiar petro-silexes. In 1872, as already 

 described, he found these rocks in situ on the north shore of Lake 

 Superior." 



Referring to the small island, Ijinu* a little to the south of St. 

 Ignace, lie further states at page 232 : 



" These rocks, from the lithological descriptions given, including 

 the microscopic characters, and the results of chemical analysis, are 

 evidently identical with the orthofelsites or petro-silex poryphyries 

 previously described by the writer as characteristic of the Huronian 

 series along the Atlantic coast, etc. They are the same with those 

 discovered by him on the north shore of Lake Superior, and which 

 enter so largely into the cupriferous conglomerates of the Keeweenian 

 series, on the south shore of the lake." 



My inference from Dr. Hunt's remarks is, that he undoubtedly 

 regarded these poipliyries, even where they occur "on a small 

 island Ivinii; a little to the south of St. lunace," as beloii2;in<r to 

 the Huronian formation, and even to the ba.se of that series. The 

 island referred to obviously occupies the same geological position 

 and may even be iu the same area as that described by me, but 

 I think we have positive and conclusive proof in the facts which 

 I have adduced, that the latter are associated with and overlie 

 the great Upper Copper-B( aring or Keeweenian group, winch, 

 according to Dr. Hunt's determinations, overlies his Taconiaa 

 and Montalbm terrains. And if this peculiar rock can be 

 shown not to be exclusively characteristic of the Huronian, we 

 need not, perhaps, go so fur down in tlie geoloiiical series as to 

 that horizon to seek for tlie origin of the pebbles in the Calumet 

 and Hecla conulomer.ites ; and. if my deductions are correct, 

 they may similarly affect many determinations cited on the 

 highest authority. Even if we had no direct evidence of the 

 superposition of the porphyries on the amygdaloids and con- 

 glomtrates, the fact that the latter, at this place, contain no 

 pebbles of the porphyiy is, in my view, a .>-trong corroborative 

 proof of the more recent age of the porphyry. If these rocks are 

 Huronian, there must be an interval, according to Dr. Hunt's 

 own figures, of at least 50,000 or 60,000 feet of strata between 

 them and the rocks with which they are so intimately associated. 

 This could hardly be accounted for by a fault, even if the rela- 

 tive Conditions of the rucks could lend any countenance to such 



