EROSIOXAL HISTORY OF DRIFTLESS AREA 57 



Frank Leverett, who spent several days in northeastern 

 Iowa with Mr. Williams and the writer in 1915, going over 

 some of their data and listening with interest to some of 

 their interpretations. For these interpretations, however, 

 the writer assumes full responsibility. 



The previous work of Grant and Burchard in the Lan- 

 caster and Mineral Point quadrangles, resulting in Folio 

 No. 145 of the U. S. Geological Survey, were particularly 

 useful. 



Finally to R. D. Salisbury. M. M. Leighton and Leroy 

 Patton, thanks are offered for thorough criticism of the 

 manuscript of Part II as well as Part I of this paper. 



ROCK FORMATIONS 



The rock formations of the Driftless Area range from 

 Huronian to Silurian in age. Hard pre-Cambrian quartzite 

 and igneous rocks outcrop in various places in Wisconsin, 

 as at Baraboo, Wausau, Necedah, and Black River Falls 

 and appear to underlie Paleozoic sediments throughout the 

 area. The Paleozoic group consists of Cambrian, Ordovi- 

 cian, and Silurian formations, the names, thicknesses and 

 relative resistance of which are shown in the accompany- 

 ing table. The Decorah shale is variable in thickness but 



TABLE SHOWING THE ROCK FORMATION OF THE DRIFTLESS AREA 



