MUSEUM OF COMPARATIVE ZOOLOGY. 



97 



from the fact tliat the printer placed the eastern side of their section on 

 the left hand, as was also done with that of the Copper Falls mine.* 

 Their idea then would be perfectly consonant with the presence of 

 trappean pebbles in the eastern sandstone as well as in the western, only 

 they would have been deposited prior to the faulting, instead of after itj 

 as Mr. Agassiz's view would demand. 



Mr. Robert Bellt regards the Upper Copper-bearing rocks as being of 

 Permian or Triassic age. This conclusion was based on the lithologi- 

 cal characters, and was objected to by Sir Wm. Logan in the same 



report (pp. 472-475). 



Prof K Pumpolly in 1871 published a paper on "The Paragene- 

 sia and Derivation of Copper and its Associates on Lake Superior," J a 

 subject which had been treated of before by Messrs. Whitney, Mullcr, 

 and Bauennan. 



He remarks: ''The eastern limit of the 'range* 



IS 



formed by a strongly marked and generally vertical plane of demarka- 

 tion between the highly inclined cupriferous series of rocks and the 

 sandstones which slope gently to the S. E. This sudden break is con- 

 sidered, with probably the best of reasons, by Foster and Whitney, and 

 afterwards by Rivot, to be a longitudinal fracture accompanied by a dis- 

 location of at least several thousand feet. Foster and Whitney looked 

 upon the sandstone as the equivalent of the Potsdam, while the Geol- 

 ogists of the Canadian Survey refer it to the Chazy, and both authorities 

 agree in considering it to be younger than the cupriferous rock, and of 

 the same age as the sandstone beds, which are conformably superim- 

 posed over the trappean series on the west side of Keweenaw Point,'" 



Prof. Pumpelly, it would seem, believed that the copper was de- 

 posited in the places in which it is now found by being precipitated 

 from solution through the agency of protoxide of iron. He further 

 considered that the copper was derived by concentration from the sedi- 

 mentary members of tlic scries. He remarks that " it is still an open 

 question whether the trap which formed the parent rock of the mela- 

 phyr was an eruptive or a purely metamorphic rock. If it was erup- 

 tive, it was spread over the bottom of the sea in beds of great regularity, 

 and with intervals which were occupied by the deposition of the beds 

 of conglomerate and sandstones." (/. c, p. 352.) The general tenor of 

 this and his other papers shows that at this time, and for some years 

 afterward, he leaned strongly towards the theory of the sedimentary 



* Copper LaiK^s, pp. 63, G8. 



t Geology of CEiimda, 1866-69, p. 321. 



t Am. Jour. Sci., (3,) H. 188-198, 243-258, 347-355. 



VOL. VII. — NO. 1. 7 



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