6 PROCEEDINGS OF THE DENVER MEETING 



The following paper was then read by the author : 



JUNCTION OF LAKE SUPERIOR SANDSTONE AND KEWEENAWAN TRAPS IN 



WISCONSIN * 



BY U. S. GRANT 



[Abstract] 



Contents 



Page 



Early investigations 6 



Results of later study 6 



Comparison of south and north side of Lake Superior syncline 7 



Features of contact .~. 7 



Contact line 7 



Topography 7 



Effect on the traps 8 



Effect on the sandstone 8 



Contact plane 8 



Conglomeratic beds 8 



Thickness of sandstone series 9 



Amount of displacement 9 



Early Investigations 



In the early days of geological investigation in the Lake Superior region two 

 sandstone series were recognized on the south shore of the lake — one a tilted 

 series, which conformably overlies the Keweenawan or copper-bearing igneous 

 rocks, and the other a fiat-lying series, found only at low altitudes on or adjacent 

 to the lake shore. The name Lake Superior sandstone was applied to the flat- 

 lying sandstones, and these were separated into two divisions, designated as the 

 Eastern and Western sandstones. These divisions were based largely on geo- 

 graphical position, the former lying on and to the east of Keweenaw point and 

 being confined to the state of Michigan, and the latter lying to the west of this 

 point in Wisconsin and Minnesota. 



Eesults of later Study 



Differences of opinion arose in regard to the relations and relative ages of the 

 Eastern sandstone and the Keweenawan traps, some holding that one and some 

 that the other was the older. This was a significant question, for on its solution 

 depended not only the age of the great copper-bearing series, but also important 

 facts in the history of a region which was destined to become, both from its eco- 

 nomic and also from its geologic features, the classic and typical pre-Cambrian 

 district for America, if not for the world. It was not until the detailed observa- 

 tions of Professors Irving and Chamberlin, made along the junction of the two 

 formations, were published in 1885 that a satisfactory solution of the problem was 

 proposed.! Their conclusions are today generally accepted by students of Lake 



* Published with the permission of Professor E. A. Birge, director of the Wisconsin Geological 

 and Natural History Survey. Local details of this junction may be found in Bulletin VI of the 

 Wisconsin Geol. and Nat. Hist. Survey, pp. 17-20, 1900. 



f Observations on the junction between the Eastern sandstone and the Keweenawan series on 

 Keweenaw point, lake Superior, U. S. Geol. Survey, Bulletin 23, 1885. Here complete references 

 to the literature of the subject may be found. 



