50 R. Irving—Copper-bearing Rocks of Lake Superior. 
rounded boulders and pe of erratic rocks, and which 
appears to be overlaid by the regular boulder drift wherever 
the two come into contact. e rivers and their branches cut 
deep valleys into these clays, often showing banks as much as 
100 feet high; but only in four places have any rocks in place 
been seen within this area in Ashland County. t A, ona 
small stream called Silver Creek, there is an exposure of hori- 
zontal red sandstone and shale, having the usual appearance of 
the sandstone and shale of the Apostle Islands. This locality 
of horizontal sandstone is only three-quarters of a mile north 
of the trap exposures on the same stream. e dipping sand- 
stones and shales do not show in this vicinity ; but four miles east 
they are apparent in great force, having a dip of ninety degrees, 
and a thickness of hundreds of feet in sight. No other exposure 
of horizontal sandstone has yet been seen on the mainland of 
Ashland County, either on its coast or inland. On the coast 
of Bayfield County, however, ee its entire length, expo- 
arated by rocks of the Copper-bearing Group.* That they are, 
however, the same, is extremely probably for the following 
reaso 
westward and soutl d to the St. Croix River in western Wis- 
* The distance between the western end ne eastern area, near the Montreal 
of the 
River, and the easternmost outcrop of the western, is about thirty-six miles. 
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