WALcorr.l LAKE SUPERIOR SANDSTONE. 197 



ity, is of the same age as the eastern sandstone, along the shore of 

 Lake Superior, east of Keweenaw Point. 



A description of the Lake Superior sandstone is given by Dr. Irving 

 in his account of the geological structure of northern Wisconsin that is 

 very full and complete, and it will be referred to again in the summary 

 of our present knowledge of that formation. 1 In the account of the 

 geology of the eastern Lake Superior district in the same volume Dr. 

 Irving described the Lake Superior or Potsdam sandstone of the 

 Apostle Islands and adjoining shore. 2 An account of the sandstone 

 as it occurs in the western Lake Superior district is given by Mr. E. T. 

 Sweet in 18S0. 3 



Dr. M. E. Wadsworth notes that the sandstone at Marquette rests 

 upon the Azoic schists. That south of the Carp River, iu the locality 

 figured by Messrs. Foster and Whitney, the sandstone strata are seen 

 to abut against and overlie the vertical edges of the quartzite. 4 



A general account of the Potsdam sandstone series is given by Dr. 

 R. D. Irving in his article on the mineral resources of Wisconsin. Of 

 the Lake Superior sandstone he says: 



The horizontal sandstone of the south shore of Lake Superior belongs unquestion- 

 ably to this formation, though it is a matter of doubt whether the two sandstones do 

 or ever did connect. The Lake Superior rock differs from its more southern equiva- 

 lent in its red color. 5 



The sandstones at the eastern end of Lake Superior, on the St. Mary's 

 River, were referred to the Oliazy formation by Sir W. E. Logan. Dr. 

 T. S. Hunt calls this view a speculation, which was shown to be unten- 

 able by the establishment of the Potsdam age of the sandstones over- 

 lying the quartzites of Wisconsin and in northern Michigan, where 

 Rominger finds the upper sandstone to be overlaid by Galciferous-Ohazy 

 beds." 



Tin* Eastern sandstone, or that between the Keweenaw Ridge and 

 eastward along the south shore of Lake Superior, is well described by 

 Dr. R. D. Irving in his account of the copper- bearing rocks of Lake 

 Superior. 7 This is followed by a description of the western sandstone, 

 or that occurring on the south shore of the lake, west of Keweenaw 

 Pqint. Au abstract of this report also appeared in the third annual 

 feport of the U. S. Geological Survey, 1883, pp. 89-188. 



Iu an article on the age of the rocks ef the northern shore of Lake 

 Superior Dr. A. R. 0. Selwyn states that he considers the trap and 

 sandstone to be of Lower Cambrian age. He calls them all Lower 

 Cambrian, which includes Potsdam and Primordial Silurian. He holds 



Geological structure of northern Wisconsin. Geol. Wise. Surv. of 1873-'79, vol. 3, 1880, pp. 1-25. 



2 Op. (it., pp. 207-210. 



3 Lake Superior Sandstone. Geol. Wise. Surv. of 1873-1879, vol. 3, 1880, pp. 350-352. 



4 Notes on tho geology of the iron and copper districts of Lake Superior. Camb. Mus. Comp. Zool. 

 Bull., vol. 7, 1880, p. 60. 



6 The mineral resources of Wisconsin. Am. Inst. Mining Eng. Trans., vol. 8, 1880, p. 489. 

 6 The Geology of Lake Superior. Science, vol. 1, 1883, p. 219. 

 T U. S. Geol. Survey, Monograph, vol. 5, 1883, pp. 351-365. 



