112 Wviconsin Academy of Sciences^ Arls^ and Letters. 



ness never less than four miles, and in places on the east 

 much more than this. This enormous thickness may be due 

 to some extent to folding and faulting, although no evidences 

 of this have been seen. Of course, if portions of the group 

 are of igneous origin, as they are supposed to be, the great 

 thickness may be readily explained by the rapid formation of 

 molten masses. Still, the upper portions of this series are, 

 beyond all doubt, the results of sedimentation exclusively, 

 and in one portion of Ashland county, one can walk over the 

 edges of upturned sandstones, which show no sign of fault or 

 fold whose actual thickness, after making the trigonometrical 

 correction for dip, falls but little short of 10,000 feet. 



The rocks of this copper-bearing series, form in Ashland 

 county a broad belt, which is widest at its eastern end, where 

 the rocks reach the shore of the lake, and narrows toward 

 the west, at the same time receding toward the southward. 

 The most westerly known portion of this belt is at Long Lake, 

 in the southern end of Bayfield county. East of the Mon- 

 treal river the series continues without break to the end of 

 Keweenau Point. The Wisconsin belt, however, is the re- 

 sult of the fusion of two distinct belts in Michigan, which 

 come together just east of the Montreal river, and which, east- 

 ward of the point of junction, are separated by an area under- 

 laid by horizontal Silurian sandstones. 



Northward of the belt of copper-bearing rocks in Ashland 

 county, and removed from it as much as eight or ten 

 miles, are two or three isolated outcrops of sandstones and 

 traps, along a line some twenty-five or thirty miles in length, 

 which I have regarded as forming the northeasterly edge of a 

 synclinal of which those already mentioned, to the southward, 

 form the southerly edge. 



In Douglas county, the Copper Bearing Series is largely rep- 

 resented, and forms a broad belt curving southwestward across 

 the county from one side to the other, and extending on the 

 east into Bayfield county, whose peninsular form is doubtless 

 due to this continuance, as indicated further on. 



