68o PAUL MacCLINTOCK 



neighboring regions, it seems well to note it here, and by so doing 

 possibly to fix the date of the warping — after the first ice invasion 

 at the east of the area and before the second invasion on the west. 



Additional evidence of such a displacement of the Mississippi 

 might be expected in old channels. In the eastern part of the 

 valley, Wisconsin glaciation has destroyed any possible trace, 

 while at the west the river was either displaced for so short a time, 

 or subsequent erosion has been so great that there is no evidence 

 of a chaimel occupied during the displacement. No channel is found 

 in Jo Daviess County, Illinois, where a similar tongue of ice pushed 

 across the Mississippi Valley from Iowa and left drift near Hanover.^ 



h) Age. — Two drift sheets, the Kansan and the pre-Kansan, 

 are thought to be present in Iowa near the mouth of the Wiscon- 

 sin River.^ The western drift in the Wisconsin VaUey must be 

 correlated in age with one of these. The former drift sheet is less 

 weathered than the latter, which is represented, according to present 

 determinations, only by scattered and very much weathered errat- 

 ics. Judging from the thickness (20 to 50 feet), and from the large 

 content of limestone and dolomite, it seems most probable that 

 the Bridgeport and Wauzeka drift is of Kansan age. 



PART n. WISCONSIN DRIFT 



I. The terminal moraine of the last glacial invasion extends 

 southward from the Baraboo Range, crossing the Wisconsin River 

 i\ miles northeast of Prairie du Sac. On the south side of the 

 river it maintains a southerly direction to Black Earth Creek which 

 it crosses ij miles east of Cross Plains. North of the river this 

 moraine is a belt showing morainic topography, while south of the 

 river it is in most places a narrow distinct ridge strewn with 

 bowlders. Where it crosses the river the section shows 60 feet of 

 cross-bedded sand with smaU lenses of fine gravel, overlain, with 

 a sharp contact, by 30 feet of till. The sharp contact shows no 

 weathering. This sand may be outwash from an early Wisconsin 

 moraine farther east or may be the outwash deposited in front of 

 the advancing late Wisconsin ice. 



» E. W. Shaw and A. C. Trowbridge, III. State Geol. Sun. Bull, 26 (1916), p. 87. 

 * A. C. Trowbridge, Bull. Geol, Soc, America, Vol. XXVI (1914), P- 76. 



