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 county, 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. 



OUTLINE OP AN ABBA or TRENTON LIMESTONE NEAR COLUMBUS. 

 Scale 4 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 " roch.es moutonees," it being to the west of the region of 



f CT o 



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 atmospheric waters, to have received or retained the " roche 

 moutoneo " shape. 



