WINONA COUNTY. 239 



Topography.] 



ern and southern, but this difference is owing simply to the fact that the 

 larger drainage valleys are in the eastern and northern portions. The 

 inequalities of surface are wholly due to the excavation by streams into 

 the rocky strata, forming deep valleys and even rocky gorges. The rugged- 

 ness which these valleys must have presented originally, has been relieved 

 by the heavy mantle of loam which now covers the whole county, amount- 

 ing to a thickness of fifty or sixty feet. This mantle serves not only to 

 smooth off the roughness by filling the valleys, but it constitutes an imper- 

 vious sheet through which waters percolate with slowness, and which con- 

 stitutes the subsoil of the county. 



Although the strata are thus canoned, the surface materials are so 

 abundant that the bluffs do not everywhere show the rock, but they are 

 rounded over and generally turfed from top to bottom. It is only along 

 the deepest gorges, and there chiefly near the tops of those bluffs that face 

 the prevailing winds, that the rocky structure is prominently and con- 

 stantly exposed. The east bluffs of the Whitewater river, and the north 

 bluffs of the Rollingstone, and especially the bluffs of the Mississippi on the 

 Wisconsin side, illustrate the effect of the strong and prevailing winds in 

 keeping the rock uncovered, and in producing precipitous and picturesque 

 headlands and pinnacles. Such bold and picturesque bluffs are uniformly 

 composed of the St. Lawrence limestone, at least in their upper portions, 

 but along the deeper valleys occasional precipitous portions of the under- 

 lying sandstone strata are also included. Figure 7, showing such pinna- 

 cled cliffs near Homer, overlooking the Mississippi river, are composed of 

 the upper, brecciated, strata of the St. Lawrence limestone. Numerous 

 similar towers of the same rock are to be seen in the county, particularly 

 in the valley of the South Rollingstone creek above Stockton. 



Within the broad valleys are good farming lands. They slope toward 

 the creeks which drain them, but are frequently diversified with terraces 

 of alluvium which maintain a plateau-like outline, gradually descending, 

 for, sometimes, several successive miles. Toward the upper portions of the 

 valleys these terraces are more broken away, and there constitute simply a 

 thickened mantle of surface loam around the bases of the bluffs. The up- 

 lands are undulating. They constitute the greater portion of the area 

 of the county. Their general level is pretty constant, when dependent on 



