90 BULLETIN OF THE 



a member of the Upper Silurian.* Later, Mr. Jules Marcou advocated 

 the view that this sandstone was of the age of the New Ked, and opposed 

 the ideas of Messrs. Foster and Whitney.f At the meeting of the Brit- 

 ish Association for the Advancement of Science, July, 1851, Sir W. E. 

 Logan t advanced the idea that the sandstone and its associated traps 

 were older than the Potsdam, and of Cambrian age. This view was 

 based on the idea that the azoic rocks north of Lake Huron were the same 

 as the traps of Keweenaw Point. § Dr. D. D. Owen, as mentioned before, 

 in his " Geological Survey of Wisconsin, Iowa, and Minnesota " (pp. 187- 

 196) regarded the sandstone as of the same age as the Potsdam of Wis- 

 consin, but Col. Chas. Whittlesey (Ibid., pp. 459-4G1) was inclined 

 to think it was older. Dr. J. J. Bigsby || believed the sandstone to be 

 Cambrian (or Silurian). Later, Dr. C. T. Jackson advocated the igneous 

 origin of the calcite veins in this region. U Mr. Jules Marcou, in his 

 " Geological Map of the United States, with Text," held that the sand- 

 stone was of the age of the New Red, and apparently regards the trap as 

 having been injected in the form of dikes. The copper veins were also 

 thought to be dikes, with the copper of like igneous origin. This work 

 gave rise to a long controversy, in which the age of the sandstone was 

 quite thoroughly discussed ; but in only a few cases shall we refer to the 

 various articles elicited by it. Those interested in the literature of the 

 Marcou -Anon.- Agassiz - Barrande -Blake - Dana - Hall - Hunt - Logan - jNIur- 

 chison-Whitney controversy will find the principal articles, that have 

 any bearing on the geology of Lake Superior, given under the names of 

 the different authors in the list of articles at the end of this paper. 



The same views regai'ding this district that were given in Messrs. 

 Foster and Whitney's Report on the Copper Lands were again pre- 

 sented in brief in Professor Whitney's " Metallic W^ealth of the United 

 States." * * Dec. 5th, 1855, Dr. Jackson explained the deposition of 

 the copper in the veins " as the result of the chemical action of 

 protoxide of iron in the trap-rock, which decomposed the vapor of 

 chloride of copper, as it rushed from the interior of the earth through 

 the crevices ; if, as is probable, these wonderful native copper lodes, are 



* Proc. Bost. Soc. Nat. Hist., Oct. 2 and 16, 1850, IIL 335-339. See also Bull 

 Soc. GeoL France, (2,) 1849-50, VII. 209, Elie de Beaumont. 

 t Bull. Soc. Geol. France, 1850-51, (21) VIII. 101-105. 



I Trans, of the Sections, pp. 59-62. 



§ See Am. Jour. Sci., (2,) 1857, XXIII. 305-314. 



II Edinburgh Kew Phil. Jour., 1852, LIII. 55-62. 

 H Proc. Bost. Soc. Nat. Hist., 1853, IV. 308, 309. 



** Philadelphia, 1854, pp. 247-305. Am. Jour. Sci., (2,) 1857, XXIII. 305-314. 



