Age of the Quartzites, SchistSj Mc, of /Sauk Co. 129 



THE AGE OF THE QUARTZITES, SCHISTS AND 

 CONGLOMERATES OF SAUK CO,, WIS.* 



BY ROLAND IRVING, E. M. 

 Professor of Geology, Mining and Metallurgy. at the University of Wisconsin. 



Througli tlie central portion of the county of Sauk, Wis- 

 consin, run two ranges of hills or ridges, having an east and 

 west trend, and a height varying from a mere rise above the 

 general prairie to an altitude of five hundred feet. The width 

 from north to south never exceeds three or four miles, and in 

 places is much less than one mile. The total lengths from east 

 to west, or rather, the exact points at which the peculiar rocks 

 which make up the ridges give place to the ordinary country 

 rock, are not as yet accurately known. These lengths, however, 

 seem to be from fifteen to twenty miles. 



The rock material of the ridges is mainly a hard dark-colored 

 quartzite ; with this in some places are siliceous and talco-silice- 

 ous schists, and two or three kinds of conglomerate. The dip 

 of the strata, which, though in some places obscure, is in others 

 very marked — and can everyivhere be determined by careful 

 observation — is uniformly toward the north. The angle varies 

 from 20 deg. to 25 deg. in the south range, to 75 deg. to 80 deg. 

 in the north. 



The occurrence of these bold ridges in the midst of a prairie 

 country, together with the marked contrast between their up- 

 turned and metamorphosed layers and the entirely undisturbed 

 strata of the Potsdam and Calciferous epochs, which for miles 

 around form the country rock, has caused much speculation 

 and discussion. From time to time, during the past twenty 



* This paper has already been published, with some slight differences, In the American Jour- 

 nal of Science and Art for February, 18T2. 



