THE KEWEENAWAN. 407 



Relations to Lotver Huronian sediments. — At a number of places which 

 may be seen by reference to the maps in the atlas (Pis. XV, XVI) the 

 gabbro is in contact with the Lower Huronian sediments, and in all cases 

 where the contacts have been studied the sediments have been found to 

 have been extremely altered as the I'esult of their proximity to the gabbro. 

 Minerals have been produced in these sediments which are in some cases 

 closely related to, in others identical with, the minerals occurring in the 

 gabbro itself. The quantity of these minerals increases as the gabbro 

 is neared, and all evidence points unquestionably to the intrusion and 

 metamorphism of the sediments by the younger gabbro. 



Relations to Giants Range granite. — The Giants Range granite and the 

 gabbro occur together in the vicinity of the Kawishiwi River, and their 

 relations are disclosed by a dike of gabbro, which is found cutting this 

 gi'anite just to the south of the falls in sec. 19, T. 64 N., R. 9 W., showing 

 that the gabbro is younger than the granite. 



Relations to Snowbank and Cacaquabic granites. — No contacts have been 

 found between the Snowbank granite and the gabbro, or between the Caca- 

 quabic granite and the gabbro. Since both of these granites are older than 

 the Upper Huronian sediments, which we know have been intruded by the 

 gabbro, the conclusion is evident that they must be older than the gabbro. 



Relations to Upper Huronian sediments. — The gabbro is in contact, at a 

 number of places, with the Upper Huronian sediments, both the Gunflint 

 formation and the Rove slates. In all cases, metamorphism, which the 

 gabbro has produced upon these sediments as the result of its contact, offers 

 conclusive evidence that it is younger than they are. 



Relations to the Keiveenawan. — Irving has placed this gabbro in the 

 Keweenawan chiefly as the result of his studies of it in Wisconsin," and 

 his later work sustained him in his views, as is shown by the fact that after 

 his studies in Minnesota'' he still retained it in its same stratigraphic position. 

 This is not the place for a detailed historical review of the various 

 opinions which have been held as to the stratigraphic position of the 

 gabbro. Reference to the annual reports of the Minnesota survey will 

 show that the opinions entertained by the members of that survey as to its 



"Geology of AVisconsin, Vol. IV, p. 171. 



''The copper-bearing rocks of Lake Superior by E. D. Irving: Third Ann. Kept. U. S. Gaol. Sur- 

 vey, 1883, pp. 93-180. Mon. U. S. Geol. Survey Vol. V. 



