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98 



BULLETIN OF THE 



origin of the entire trappean series. At this time he also regarded 

 the traps, with all the sandstone as far east as at least the Pictured 

 Ptocks, as belonging to the Quebec group. It will be seen that he 

 afterwards abandoned these views. 



Later, Prof Pumpelly in conjunction with Major T. B. Brooks pub- 

 lished a paper entitled, " On the Age of the Copper-bearing Eocks of 

 Lake Superior."* They state that their observations "demonstrate a 

 wide difference in age between the Cupriferous series of sandstones, con- 

 glomerates, and melaphyres on the one hand, and the Lower Silurian 

 sandstone, with which they have generally been considered as nearly 

 identical in age, on the other." At the western edge of the eastern 

 sandstone on Keweenaw Point " its nearly .horozontal strata abut against 

 the steep face of a wall formed by the upturned edge of beds of the 

 Cupriferous series of melaphyre and conglomerate, which dip away from 

 the sandstone at angles of 40° -60°, according to geographical position. 

 This sharply defined and often nearly vertical plane of contact, having 

 been seen by the earlier geologists at several points along a distance of 

 many miles, and having been found to be often occupied by a thick bed 

 of chloritic fluccan, which was looked upon as the product of faulting 

 motion, was considered as a dislocation. This idea seemed to gain cor- 

 roboration in the fact that, on the western side of Keweenaw Point, sand- 

 stones bearing considerable resemblance to those of the eastern horizontal 

 beds occur, apparently conformably overlying the Cupriferous series. 

 Both sandstones came to be considered as identical in age, and as form- 

 ing the upper member of the group. There were many circumstances 



■ r 



which made it difficult for us to accept this conclusion. One obstacle 

 lay in the enormous amount of dislocation required ; for instance, at 

 Portage Lake, where the strata of the Cupriferous series, with an actual 

 thickness of several miles, dip away from the supposed longitudinal fault 

 at an angle of about G0°." The Cupriferous scries is regard<.)d by them 

 as conformable to the Iluronian, wliilc the line of fault is taken to bean 

 old shore cliff, with the sandstone deposited against its base. They also 

 state that it would be difficult to account for the absence of this series 

 in localities eighteen miles from where they were found miles in thick- 

 ness, unless they represented a sinking area along whose shores the Silu- 

 rian sandstone was deposited. They also claim that this scries was worn 

 through near Lake Gogebic, and the Silurian sandstone de[)osited in the 

 trough. It is to be noticed that according to them the Cupriferous 

 series are four miles distant from the locality in which the Silurian 



* Am. Jour. Sci., (3,) TIL 428-432, 1872. 



