124 Wisconsin Academy of Sciences, Arts, and Letters. 



KEPOET ON THE GEOLOGY OF THE REGION 

 ABOUT DEVIL'S LAKE. 



BY PROFESSOR JAMES H. EATOU, A. M., 

 Of Beloit College. 



Topography. — The formation of Sauk county is the Pots- 

 dam sandstone. (Potsdam epoch of the N. Y. Survey.) It 

 lies nearly horizontal, with a gentle dip to the southeast. The 

 higher elevations, especially in the southern part of the county, 

 are capped with conformable layers of the lower magnesian 

 limestone. (Calcareous epoch of the N. Y. surveys.) Run- 

 ning east and west through the center of the county are two 

 parallel ridges, with an average elevation of 400 to 500 feet, 

 and a base of two to four miles. The distance between them is 

 three to four miles. The Baraboo river runs in this valley 

 and empties east into the Wisconsin. A north and south val- 

 ley cuts half way through the eastern end of the southern 

 ridge, and then trends east towards the valley of the Wiscon- 

 sin. In the north end of this valley lies Devil's Lake. 



LiTHOLOGY OF THE RiDGES. — They are a comjmct, crystal- 

 ine sandstone, without cement, or quartzite. The predominant 

 colors are pink and red, often banded with straight or con- 

 torted parallel lines of lighter and darker colors. In some 

 places the rock is an homogeneous white quartz, with distinct 

 and well formed crystals. 



Origin of the Quartzite. — Both the nature of the rock 

 and its position give evidence that it is metamorphic Potsdam 

 sandstone. The rock presents all gradations from the simple 

 sandstone to the perfectly crystallized quartz. The Potsdam 



