GEOLOGY OF Is'ORTHERN" WISCON'SIK. 49 



Triassic, others to the Potsdam, we may regard the question as defi- 

 nitely settled by the investigations of Dr. Rominger, of the Mich- 

 igan Geological Survey, and others, that the:y are the downward 

 continuation of the light colored Potsdam sandstones of the Mis- 

 sissippi valiey. iSTo fosils have ever been obtained from these sand- 

 stones. In the eastern part of the upper peninsula of Michigan 

 they are found directly underlying light colored sandstones and 

 Calciferous strata. A large area of Lake Superior sandstone ex- 

 tends southwesterly from Keweenaw Bay nearly to the Montreal 

 River. The distance from the western end of this area to the ex- 

 posures of horizontal red sandstone on the Wisconsin shore of 

 Lake Superior is about 30 miles. From their proximity to each 

 other, and also from a similarity in lithological characters, and in 

 stratigraphical relations to the underlying formations, it may be 

 asserted that the red sandstones skirting the lake shore from near 

 Ashland to the St. Louis River, at the western end of the lake, and 

 those of the Apostle Islands, are of the same age as those east of 

 Keweenaw Point. 



Upon the St. Croix River the Lake Superior sanestone does not 

 occur. Only the light colored Potsdam and Bad River sandstones 

 are represented upon that stream. It has been shown by Professor 

 Irving that the dipping sandstones, shales, and conglomerates, as- 

 sociated with the Cupriferous rocks, very much ante-date the hori- 

 zontal sandstones of Lake Superior in age. This being the case 

 no satisfactory evidence can be drawn of the age of the horizontal 

 sandstones from the stratigraphical relations which occur in the 

 vicinity of the St. Croix River. The conclusions of Dr. Owen 

 upon the "Age of the Lake Superior Sandstones," are based mainly 

 upon the fact that the Bad River sandstones dip beneath, and are 

 overlaid by light colored Potsdam sandstones. He did not realize that 

 there is a vast difference in age between these and the true Lake 

 Superior sandstone. There is no known locality west of Kewee- 

 naw Point, where the Lake Superior sandstone and Potsdam of the 

 Mississippi valley are not separated by many miles. 



The Lake Superior sandstones usually contain a large per cent., of 

 alumina and sesquioxide of iron, which it has been observed were 

 derived from the wearing down of the highly aluminous and ferrug- 

 inous Copper-Bearing rocks. 

 4 W A s 



