52 WISCONSIIT ACADEMY SCIENCES, ARTS, AND LETTERS. 



red sandstone. Owing to the haste with which the expedition 

 moved, the actual junction was not observed. 



The Lake Sii,perior Sijnclincd. — Foster and Whitney first painted 

 out the existence of a synclinal between Keweenaw Point and Isle 

 Royale. Professor Irving has suggested that this extends into 

 Ashland and Bayfield counties. I think it has been pretty satis- 

 factorially shown in this paper that it extends uninterruptedly 

 westward, entirely across the state of Wisconsin, and enters the state 

 of Minnesota. A general geological section across the formations 

 represented upon the upper St. Croix, is very similar to one from Le- 

 high's, on Bad River, extending southeasterly across the formations 

 to the Penokie Range. Starting from Chase's dam on the St. Croix, 

 and froDi Lehigh's, on Bad River, the formations to the south are as 

 follows: 



1. A bed of southvrard dipping sandstones. About four thou- 

 sand feet are exposed on the St. Croix, and two thousand on Bad 

 River. 



2. Trough of the synclinal; four miles across at the St. Croix, 

 and about nine, in the vicinity of Bad River. Lake Superior sand- 

 stone may fill the trough of the synclinal. At present only one 

 small exposure of horizontal red sandstone is known to occur in it. 



3. Northward dipping sandstones, shales and conglomerates. On 

 the St, Croix they are but a few feet thick; on Bad River probably 

 1,000 feet are exposed; at the mouth of the Montreal the thickness 

 is fully 10,000 feet. 



4. Amygdaloids, melaphyrs, porphyries, etc. On the St. Croix 

 ihe dip is slight to the northwest. Across the belt, the distance is 

 four and one half miles. At the Montreal River the distance across 

 the formation is about ten miles, and as the dip is nearly vertical, 

 ;the apparent thickness is, in round numbers, 50,000 feet. If the 

 rocks are of igneous origin, it is not difiicult to account for this 

 iseemingly enormous thickness. 



In Douglas and Bayfield counties, the Coppei'-Bearing strata have 

 a dip to the south, and probably conformably underlie the south- 

 ward dipping Bad river sandstone. If this is the case they are the 

 representatives, in the northern edge of the synclinal of the Ashland 

 and Burnett county copper series. The distance across the forma- 

 tion in Douglas county is about 30 miles; allowing a dip of fourteen 



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