PLATE XXXII. 



WABASHA COUNTY, 1888. N. H. WINCHELL. 



This county is well within the ancient pre-glacial as well as the present valley of 

 the Mississippi. The rock surface was gorged by pre-glacial erosion, and those gorges 

 were not filled by the forces of the glacial epoch, or epochs. The present streams, 

 therefore, flow between rock-walled bluffs from 200 to 400 feet below the general 

 upland. The alluvial bottom lands are broad, usually timbered and fertile, but 

 subject to floods, which are sometimes sudden and devastating. The upland country 

 is undulating, and without lakes. The bluffs of the rock-bound valleys are frequently 

 smoothed down by a great thickness of loam which everywhere covers the county, 

 and in the western part this effect is hightened by a previous overspread of till. 

 The loam and the till together are sometimes nearly a hundred feet thick, but they 

 diminish to nothing along the brow of the bluffs, where their former presence, at 

 least that of the till, is evinced by the existence of a few northern boulders on the 

 lower slopes or at the bottom of the valley. 



At a certain stage in the retreat of the ice of the last glacier, as mentioned in 

 connection with plates of Le Sueur and Rice counties (xxx and xxxi), the Zumbro 

 valley was the course of extensive drainage from the Minnesota valley. At that 

 time, while the glacial waters were bearing a gravelly detritus almost directly from 

 the glacier into all the valleys that gave escape for* its copious waters, there was 

 apparently a long tongue of ice that projected down the Mississippi valley as in a fiord. 

 This tongue dammed up the tributary streams, causing them to flow at more than 100 

 feet above their present level, forming the gravel plains from which, at a later epoch, 

 on the entire retreat of the ice, were carved the present high gravel terraces by which 

 the Zumbro and other valleys are diversified. Whether these gravel terraces were 

 formed later or earlier than the loam which widely mantles the general upland, or both, 

 is uncertain, but it is very probable that much of the upland clayey loam antedates 

 the present gravel terraces. 



Where the surface is not broken by too great ruggedness, as it is in proximity 

 to the numerous ravines and along the bluffs of the Zumbro and the Mississippi, the 

 soil is uniformly good; the loam, which spreads over the entire county, is uniformly 

 strong and fertile in all the qualities of a good soil. It is often a tenacious clay, 

 practically impervious, but sometimes is covered by sand derived from some out- 

 cropping sandstone formation, and again has thin laminae of fine sand. 



The rocks range from the Trenton to the St. Croix formation. The Trenton is 

 .found in the tops of the mounds in Mount Pleasant and Elgin townships, and the 



