

walcott.] LAKE SUPERIOR SANDSTONE. 195 



Of the sandstone at the base of the fossiliferous series Dr. T. S. Hunt 



says: 



Along the northern rim of the great Paleozoic basin of North America the Potsdam 

 sandstone of the New York geologists is unquestionably the lowest rock from below 

 Quebec to the Island of Montreal, and thence passiug up the valley of Lake Champlain 

 and sweeping round the Adirondack Mountains until it reenters Canada and soon dis- 

 appears to the north of Lake Ontario, where the Birdseye and Black River limestones 

 repose directly upon the Lanrentian rocks, and furthermore overlie the great Lake 

 Superior group of slates and sandstones, which, reposing on the unconformable Hu- 

 ronian system, constitute the upper copper-bearing rocks of this region. This Lake 

 Superior group, as Sir William Logan remarks, may then iuclude the Potsdam, Cal- 

 ciferous, and Chazy, and thus be equivalent in part to the Quebec group, hereafter to 

 be described. 1 



The section on the Montreal Eiver, including 11,850 feet of strata, 

 according to Mr. Charles Whittlesey, is referred by him to the Potsdam 

 sandstone, with a statement that this is not the entire thickness of the 

 Potsdam at the mouth of the Montreal. 2 He states that some foreign 

 geologists have essayed to place this formation nearly at the summit 

 of the geological system, not only without evidence but against the most 

 conclusive proof. He correlates the sandstone at the Falls of the St. 

 Croix, with its abundance of fossils, with the sandstone of the section 

 mentioned, and states that it has been traced strati graphically beneath 

 the Trenton and Calciferous strata of the New York survey, on the 

 St. Mary's Eiver, at the Pictured Eocks, on the Escanawba, the Menom- 

 inee, Ocouto, Wolf, Wisconsin, and St. Croix Eivers. 3 



The view that the sandstones and superjacent .rocks of the south 

 shore of Lake Superior were deposited within the lake's basin when 

 the lake stood at a higher level has been held only, as far as known to 

 me, by Mr. Thomas Macfarlane. In a report on the geological forma- 

 tions of Lake Superior he says : 



On the other hand, the Upper rocks and St. Mary sandstones are never found far 

 inland, but occur close to the shore in comparatively low-lying land and rocks. They 

 seem to have had, as the theater of their eruption and deposition, the bottom of the 

 lake, at a time when its surface was at a higher level than it is at present, although 

 not so high as the general surface of the surrounding Laureutian and Huronian hills. 4 



In a paper on the position of the sandstone of the southern slope of 

 a portion of Keweenaw Point, Lake Superior, Prof. Alexander Agassiz 

 states that the sandstone of the southern side of the mineral range in 

 the vicinity of Torch Lake is plainly of a different age, lying, as it does, 

 unconformably upon the former (i. e., the trap). This view agrees with 

 that held by the geologists who refer the sandstone of the southern por- 

 tion of Keweenaw Point to the Potsdam, and that of the northern 

 coast to a pre-Potsdam formation. 5 



1 On some points in American geology. Am. Jonr. Sci., 3d ser., vol. 31, 1861, p. 397. 



2 The Penokie Mineral Range, Wisconsin. Bost. Soc. Nat. Hist. Proc, vol. 9, 1863, p. 238. 

 3 0p.cit,p.239. 



4 On the geological formation of Lake Superior. Canad. Naturalist, new ser., vol. 3, 1867, p. 178. 

 •On the position of the sandstone of the southern slope of a portion of Keweeuaw Point, Lake 

 Superior. Boston Soc. Nat. Hist., Proc, vol. 11, 1868, p. 245. 



