UPPER HURONIAN. 391 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



Distribution. — In the Mesabi district south and west of the VermiUon 

 range these slates cover a large area. The Rove slates, which are found 

 in the Vermilion district, represent merely a 2)ortion of the slates that cut 

 across the east end of the district and that are not cut out by the Duluth 

 gabbro. 



The westernmost exposures of these slates in the Vermilion district are 

 found in sec. 26, T. 65 N., R. 4 W. The formation underlies a very narrow 

 area in the south-central part of the above section, but rapidly widens to 

 the east. The northern boundary of the slates extends northeastward, and 

 is limited by the Gunflint formation and a great dolerite sill. The southern 

 boundary trends east-southeast and the Duluth gabbro everywhere marks 

 their southern extent. At the eastern limit of the map the extreme width 

 of the Rove slate area in the United States is only about 2 miles, and a 

 great deal of this width is taken up by intrusive sills of dolerite, which very 

 materially reduce the areal distribution of the sediments. Beyond the 

 limits of the map the slates have an enormous development in Minnesota 

 and in the adjacent portion of Canada. They may be seen especially well 

 along the Canadian shore of Lake Superior and on the islands in the lake 

 from Pigeon River northeastward to Thunder Cajje. 



Exposures. — The exposures are usually very good along the lake and 

 wherever steep escarpments occur, which is usually immediately along the 

 lake shores. When the hills stand some distance back of the lakes it is not 

 uncommonh" found that although the northern slope is fairly steep, a heavy 

 talus conceals the greater portion of the slates. The slates rarely show any 

 exposures at all, or but very poor ones, on the gentle southern slope of the 

 hills. 



Topography. — The topography is that which is usually developed in 

 areas of monoclinal dipping rocks. Ridges haA^e been formed whose trend 

 corresponds approximately to the strike of the slates, here about east and 

 west. These ridges have very steep escarpments on their north faces, 

 where the rocks have been cut directly across the dip, and very gentle 

 slopes to the south which agree in general with the dip. Tlie depressions 

 between the ridges are occupied by lakes, or if not by lakes then by low 

 ground with a stream which eventually flows into a lake. Seen in profile 



