MUSEUM OF COMPAEATIVE ZOOLOGY. 77 



granite, with sandstones, amygdaloid, and secondary trap, deposited 

 around its base." * 



Dr. John J. Bigsby regarded the Lake Superior sandstone as being 

 most probably of the age of the Old Red-t Commander H. W. Bay- 

 field, in his paper entitled " Outlines of the Geology of Lake Superior," | 

 regards the hills of Keweenaw Point as formed of syenitic granite, of 

 the same character as that at Granite Point, and opposes the idea that 

 the first-mentioned point is an amygdaloid district. He regards the 

 trap and granite as the prior formed rocks, and that the sandstone is 

 composed of their debris. This sandstone, which he takes to be Old 

 Red sandstone, is said to have been tilted by a secondary upheaving, or 

 subsidence of the granite. 



In Dr. Douglas Houghton's report on the copper of Lake Superior to 

 the Secretary of War,§ we find the following statement : " After having 

 duly considered the facts which are here presented, I would not hesitate 

 to offer, as an opinion, that the trap-rock formation was the original 

 source of the masses of copper which have been observed in the country 

 bordering on Lake Superior ; and that at the present day, examinations 

 for the ores of copper could not be made in that country with hopes of 

 success, except in the trap-rock itself; which rock is not certainly known 

 to exist upon any place upon Lake Superior, other than Keweena 

 Point." The chief ore of copper that he had observed was the mala- 

 conite, although a small amount of native copper had been seen in 

 place. 



Dr. Douglas Houghton states, in his first Report on the Geology of 

 Michigan, II that the red sandstone " in the Trap regions of Lake Superior, 

 as in the vicinity of the Porcupine Mountains, .... is seen dipping 

 irregularly at a high angle from the elevated district of country, and is 

 there of a deep reddish-brown color." He evidently at that time re- 

 garded the sandstone as belonging to one formation, from the St. Mary's 

 River to the Porcupine Mountains. 



Dr. Houghton in his Fourth Annual Report on the Geology of Michi- 

 gan,^ divides the sandstones of Keweenaw Point as follows, going from 



* Am. Jour. Sci., 1824, (1,) VII. 43-49. 



t Quart. Jour. Sei., 1824, XVIII. 1-34, 228-269; Am. Jour. Sci., 1S24, (1,) 

 VIII. 60-88. 



t Trans, of the Lit. and Hist. Soc. of Quebec, 1829, I. 1-43. 



§ Nov. 14, 1831. Discovery of the Source of the Mississippi, Henry R. School- 

 craft, New York, 1834, pp. 287-292. 



II Lanman's Hist, of Mich., p. 353. 



H Joint Documents, Mich., 1841, pp. 472-607. 



