614 



GEOLOGY OF CENTRAL WISCONSIN. 



adjoining towns on the east and west. A number of short parallel 

 ridges are to be seen in the same region, some of which are rock, and 

 others either altogether of drift or at least with a core only of rock. 



Roches moutonees, so characteristic of all glaciated regions where 

 the underlying formation is of the hard crystalline rocks, are not en- 

 tirely wanting in Central Wisconsin. The bald and smooth rounded 

 summits of quartzite so conspicuous on the high bluffs of Caledonia, 

 Columbia count3^ show the structure finely. These summits have a 

 direction but little south of west, coinciding with the directions of 

 of the striae upon them. The scattering knobs of granite and por- 



FiG. 52. 



COLUJSIBIA 



I TIXNRKIE. 



COLUMBUS 



)TJ]SrTY 



TlXNRXm.] 



OCfTLINE Off AN AnEA OF TrENTON LIMESTONE NKAB CoLUMBUS. 



Scale '1 miles to 1 inch. 



phyry which rise through the Potsdam sandstone in Columbia, Mar- 

 quette, Waushara and Green Lake counties are all distinctly " sheep's 

 backs." The main Archaean region of Central Wisconsin, stretching 

 westward from the Wisconsin to Black river, does not show any dis- 

 tinct "roches moutonees," it being to the west of the region of 

 greatest glaciation. Further east, in Shawano and adjoining counties, 

 these shapes would be expected. The Silurian strata of Central Wis- 

 consin are either too fragile or too susceptible to the solving action 

 of the atmosijheric waters, to have received or retained the "roche 

 moutonec " shape. ^ 



