256 GEOLOGY OF EASTERN WISCONSIN. 



in great thickness their truncated edges and dip at a high angle in a 

 common direction northeast. (6) That there was a vast lapse of 

 time in which the erosion might take place. These rocks are un- 

 doubtedly a portion of the Baraboo quartzite series which has been 

 proven to be pre-Potsdam, and since the Portland and Waterloo 

 quartzites rise at their highest points into the Trenton horizon, there 

 must at least have elapsed time enough for the deposit of 1,200 feet 

 of sandstone and limestone before they were finally covered in the 

 Trenton period. 



