134 Wisconsin Academy of Sciences, Arts, and Letters. 



tions have been confined chiefly to the region of Baraboo, 

 where the ranges are most separated. Their more intimate 

 association, if not direct connection, both at the east and west, 

 was shown in mj paper on the geographical distribution of 

 these rocks, and may be seen by reference to the paper of 

 Prof. Eaton, of this volume. 



The dip increases from south to north and indicates an ar- 

 rangement such as is represented in the following ideal sectioOj, 

 which also shows the nature and amount of denudation : 



Fij.l. 



S.R. 



S. R., South Range. N. R., Norlh Range. B. V., Baraboo Valley. Q., Quartzite.- 

 P. S., Potsdam Sandutone. 



That a portion at least of this erosion was sub-aerial is ne- 

 cessitated by the nature of the case, for in that way only can 

 we explain the deep excavations between and on the outside 

 of the ranges. Preceding the Potsdam period all of these- 

 rocks that are now exposed, must have stood above the ocean 

 level, and were doubtless portions of the Eozoic continent. 



3. In the earlier part of the Potsdam period, these ridges of 

 quartzites stood as islands in the seas. This is evident when 

 we consider that they exceed, in places, 500 feet in height,, 

 while at the base, sandstone, showing cross lamination and 



