Some Points in the Geology of Northern Wisconsin. 117 



spread out in horizontal layers on the bottom of the sea, whilst 

 the sedimentation of the sandstones was still in progress. 

 Hence the present tilted position of these sandstones and traps 

 was produced by a movement entirely subsequent to the solid- 

 ification of the latter ; and, therefore^ the tilted position of the 

 sandsfones of the Montreal and Bad rivers, those of the former 

 reaching a thickness of nearly ten thousand feet, is not due to the 

 protrusion of igneous rock, hut to an ordinary regional disloca- 

 tion, in which the trap-pean beds themselves partook. Moreover 

 the strong indications of conf or mobility between the whole of the cop- 

 per bearing series, and underlying Huronian, goes to show that this 

 disturbance was due in part, at least, to the same causes that ele- 

 vated and folded the beds of the latter series. We have then in 

 this case horizontal sandstones found in immediate proximity 

 to sandstones which have undergone regional disturbance. The 

 vertical sandstones^ then, belong to a period far antecedent to that of 

 the horizontal sandstone. 



The conclusions, then, that I would draw are these : 



1. The Copper Bearing and Huronian Series were once 

 spread out horizontally one over the other and owe their pres- 

 ent highly tilted position to one and the same disturbance. 



2. That subsequently — alter a long period of erosion — the 

 horizontal Silurian sandstones were laid down over, and against 

 the upturned edges of the Copper Bearing Series, filling also 

 the synclinal, in Ashland county, which lies between the north- 

 ward and southward dipping sandstones. 



3. That hence the Copper Bearing Series is more nearly 

 allied to the Archaean, than to the Silurian rocks. 



One fact observed, however, seems at first difficult of explan- 

 ation on this hypothesis. In Douglas county, as already said, the 

 horizontal sandstones can be traced to their exact junction with 

 the southward-dipping traps. But, in several places, these sand- 

 stones present a very remarkable change as the trap is ap- 

 proached. On passing up the gorge of Black River, whose 

 sides are perpendicular exposures of rock over one hundred 



