296 S. WEI DM AN 



996 feet, to Black River Falls, with an elevation of 812 feet, is 

 about 9 feet per mile. 



Slope of the sandstone district. — The sandstone district of south- 

 central Wisconsin south of the vicinity of Grand Rapids and 

 between the resistant Cambrian area on the north and the region 

 of hard limestone rocks of the southern part of the state is pre- 

 eminently a broad valley bottom plain dotted here and there 

 with isolated peaks and mounds of sandstone. While there is 

 considerable alluvial wash in the flat-lying sandstone district, 

 the main features of the area, the broad plain and isolated 

 peaks, are due to long-continued erosion. As stated by Salis- 

 bury and Atwood ' for the vicinity of Camp Douglas : " Here the 

 broad plain, extending in some directions as far as the eye can 

 reach, is as low as it could be reduced by the streams which 

 developed it." The sandstone district is therefore a graded val- 

 ley plain sloping upward to the north, and isolated mounds and 

 peaks are the disappearing remnants of divides of an earlier, 

 less eroded sandstone reafion. From data of elevations along- 

 the various railroads extending across the sandstone district it 

 is found that the slope of the valley plain is upward to the 

 north at the rate of about 2 feet per mile. The slope upward 

 from Kilbourn City to Grand Rapids across the entire width, 

 north and south, of the sandstone district is only about 1 00 feet 

 in about 55 miles, and thus 2 feet per mile may reasonably be 

 considered an average slope for the sandstone district (see Plate 

 I, Fig. 3). As already stated, from the vicinity of Merrill to 

 Grand Rapids the southward pitch of the peneplain slope of the 

 main pre-Cambrian area is 550 feet in 55 miles. The downward 

 slope of the sandstone district from Grand Rapids to Kilbourn 

 City is only about 100 feet for an equal distance of 55 miles. 

 Thus there is an abrupt change of slope in the main land surface 

 at the border of the sandstone and crystalline districts. The 

 surface of the dissected plateau north of Grand Rapids is there- 

 fore not continuous in slope with the surface of the sandstone 

 district south of Grand Rapids. On the other hand, as already- 

 shown, the beveled surface of the pre-Cambrian continues south- 



' Bull. V, Wis. Geol. and Nat. Hist. Survey, p. 51. 



