walcott] LAKE SUPERIOR SANDSTONE. 191 



traversed by ranges of iutrusive trap, with accompanying veins of copper. * * ■ 

 To draw up in detail a comparison between these formations and those of the North- 

 west would, at this early stage of the survey of Wisconsin, be premature. 1 



In 1849 Prof. O. T. Jackson argued that the red sandstone and con- 

 glomerate rocks of Keweenaw" Poiut existed there anterior to the ele- 

 vatiou of the trap rocks, and that the eastern sandstone and the red 

 sandstone were the same in geologic age. After reviewing the mode of 

 occurrence aud the relation of the sandstone to other rocks, especially 

 a limestone from which a fragment of Pentamerus oblongus was ob- 

 tained, indicating the upper member of the Niagara, New York series, 

 he concluded that the sandstone of Keweenaw Point was not of the 

 Potsdam series,but that it was most probably the New Red, or that sys- 

 tem of sandstones which is regarded as such in New England. 2 



In their report of 1849 Messrs. Foster and Whitney color the accom- 

 panying map of Keweenaw Point so as to indicate that they consider 

 the sandstone and conglomerate superior to the trap series, forming 

 the base of the Silurian system. The same coloring and nomenclature 

 are used on the map of the district be: ween Mackinaw Bay and Choco- 

 late River, and that between Portage Lake aud Montreal River and 

 Isle Royale. 3 



In the same volume, following the report by Foster and Whitney, is 

 a general description of the region between Keweenaw Point and Mon- 

 treal River. The writer says the age of the sandstone of Lake Superior 

 could not be determined by any evidence he had been able to collect. 

 It is entirely destitute of fossils, and lies directly upon granitic rocks. 4 

 Whether it is written by Mr. Foster or Prof. Whitney is not stated. 



Mr. J. W. Foster states that he is disposed to regard the sandstone 

 of Lake Superior as resting at the base of all the fossil iferous rocks. 5 

 He evidently considered the horizontally bedded sandstone at Kewee- 

 naw Point the same as the disturbed sandstone on the opposite side. 

 Full descriptive details of the sandstones at Keweenaw Point are also 

 given by Mr. W. A. Burt. 6 In the same report Mr. Bela Hubbard 

 states that the Red sandrock is the equivalent of the Potsdam red sand- 

 rock of the New York reports, aud that on the map the geographic dis- 

 tribution skirts the trap range on both sides, but having by far its 

 broadest extension on the south side. 



1 Report of a geological reconnaissance of the Chippewa land district of Wisconsin ; and incidentally 

 of a part of Iowa and of the Minnesota Territory, 30th Congress, 1st sess., Senate Ex. Doc. No. 57, 

 1848, pp 57-58. 



2 Report on the geological and mineralogical survey of the mineral lands of the United States in the 

 State of Michigan, Ex. Doc. No. 5, House of Reps., 31st Congress, 1st sess., part 3, 1849, pp. 398, 399, 

 452. 



'Synopsis of the explorations of the geological corps in the Lake Superior land district in the north- 

 ern peninsula of Michigan, Ex. Doc. No. 5, House of Reps., 31st Congress, 1st sess., part 3, 1849, pp. 

 605-625. 



4 0p.cit.,p.655. 



5 Notes on the geology and topography of portions of the country adjacent to Lakes Superior and 

 Michigan, in the Chippewa land district, Ex.Doc. No. 5, 31st Congress, 1st sess., part 3, 1849, p. 781. 



6 Topography and geology of the survey of a district of township lines south of Lake Superior, 1845, 

 H. B. Ex. Doc. No. 5, part 3, 1849, pp. 815-839. 



