UPPER HURONIAN. 395 



RELATIONS TO ADJACENT FORMATIONS. 



The relations of the Rove slates to the other formations of the district 

 are easily determined. The oldest rock with which they are in contact is 

 that which has been described as the Gunflint formation. The slates are a 

 conformable series of sediments overlying this formation, and consequently 

 younger than it. In previous pages the relations of the Gunflint formation 

 to the other older rocks of the district have been described, and it is not 

 necessary to add anything to the statement concerning the age of the Rove 

 slates other than that they are younger than all of the rocks below the 

 G-unflint formation. 



Relations to Keweenaivaii dolerite. — In places the Rove slates are found 

 in contact with great masses of dolerite. Near the contact the sediments 

 are found to be harder than elsewhere, and in some places to have had 

 produced in them minerals which are evidently of secondary origin, corre- 

 sponding to the products of contact metamorphism, which have been 

 studied in other districts. This induration is undoubtedly due to the 

 metamorphic action of the dolerite. This alone is proof of the fact that the 

 dolerite is younger than the sediments. In addition to this proof, however, 

 we have the further evidence of the contortion of the slates, which has been 

 noticed in a number of places where the beds were in contact with the 

 dolerites, having been intruded by them. Moreover, the dolei'ites them- 

 selves are much finer grained at the edge than elsewhere. These three 

 facts — ^the fine-grained character of the edges of the dolerite masses, the 

 induration of the slates along this contact, and the contortion of the beds — 

 form indubitable evidence that the dolerites are younger than and intrusive 

 in the slates. 



Belations to Keweenaivan {Didutli) gabhro. — The only place where a good 

 contact between the gabbro and the slates was observed is that mentioned 

 above, on the southwest side of Loon Lake. Here the gabbro overlies the 

 slates, and produced considerable changes as the result of its contact with 

 them. The superposition of the gabbro and the contact zone in the slates 

 afford conclusive proof of the relative ages of the two, the Duluth gabbro 

 being very clearly younger than the Rove slate. 



