194 THE CAMBRIAN. mu.x.si. 



sandstone west of the Montreal Biver is colored the same as the sand- 

 stones of the central portion of Wisconsin referred to the Potsdam. In 

 the legend the Lake Superior sandstone is included with the lower 

 sandstones of Wisconsin and Minnesota as the equivalent of the Pots- 

 dam sandstone of New York. 



Mr. J. O. Norwood calls attention to the resemblance of the sandstone 

 on the south shore of Lake Superior, west of Montreal River, to the 

 sandstones of the Chippewa, St. Croix, and Kettle Rivers. A section 

 is given that occurs above the mouth of Cranberry River. 1 



In some remarks connected with the geology of the north shore of 

 Lake Superior Prof. J. D. Whitney states that from Sault Ste. Marie, 

 following the south shore in its whole extent, and along the north side 

 as far east as the northeastern extremity of Neepigon Bay, we find ex- 

 posed on the lake shore only shales, sandstones, and conglomerates, 

 the equivalent of the Potsdam sandstone and the accompanying trap- 

 pean rocks. 2 



In speaking of the red sandstone of Lake Superior Mr. II. R. School- 

 craft states that in his expedition of 1820 he recognized a sandstone at 

 the Sault of St. Mary's. He says: 



That this is the Old Red sandstone may be inferred simply from tho fact that, al- 

 though deposited originally in horizontal beds, its position has been disturbed in 

 many localities. 3 



In his report as State geologist of Michigan Dr. A. Winchell describes 

 the sandstone at the Falls of the St. Mary's River, where it has a 

 measured thickness of at least 18 feet. On some of the surfaces he ob- 

 served obscure traces of Alga3. On some specimens from the Montreal 

 River not less than three species of fossil plants have been discovered. 

 He favors the view that the sandstones of the south shore of Lake Su- 

 perior are of the age of the Potsdam. 4 



When commenting upon the fact that Prof. Jules Marcou had re- 

 ferred the red sandstone of Lake Superior to the Trias Prof. J. S. 

 Newberry states : 



No American geologist will need to be informed that the sandstones of Lake Supe- 

 rior are of the age of the Potsdam of New York and lie at the base of the Silurian 

 series. It is true that there is considerable lithological resemblance between the 

 Potsdam sandstones of Lake Superior and those overlying the Carboniferous series in 

 New Mexico ; but that fact serves simply to show how fallacious are the inferences 

 derived alone from lithological characters. 5 



description of the geology of middle and western Minn., including the country adjacent to the 

 northwest and part of the southwest shore of Lake Superior. Rep. Geol. Surv. of Wis., Iowa, and . 

 Minn., and, incidentally, of a portion of Nebraska Territory. Philadelphia, 1852, p. 269. 



2 Remarks on some points connected with the geology of the north shore of Lake Superior. Am. 

 Assoc. Proc, vol. 9, 1855, p. 205. 



3 Observations on the geology and mineralogy of the region embracing tho sources of the Mississippi 

 River and the Great Lake basins during the expedition of 1820. Schoolcraft's Mississippi River. 

 Phila., 1855, pp. 316, 317. 



4 Geology, general sketch. Geol. Surv. Michigan, 1st Biennial Rep. of Prog. Lansing, 1861, pp. 

 49-51. 



6 Geological report. Report upon the Colorado River of the West, expl. in 1857-58 by Lieut. J. C. Ives, 

 Part in, 1861, p. 75. 



