HOUSTON COUNTY. 209 



Topography.] 



not so narrow as in much of the western and central parts of Fillmore 

 county, but are of the same character as those in the Shakopee and St. Croix 

 areas broader and smoother, allowing the loam, when deposited, to enter 

 their deepest recesses and to spread itself evenly over the whole. While 

 the loam itself becomes thicker and more clayey toward the Mississippi 

 river, it has so effectually and so deeply covered the whole country that 

 generally a rolling or undulating surface has resulted which is almost 

 free from the familiar sink-holes so common in the Trenton area, but 

 is characterized by deep, wide valleys and long ridges. The bluffs that 

 enclose the valleys are sometimes tillable, or at least turfed over from top 

 to bottom. They are of all bights from the mere shallow depression suf- 

 ficient for ready drainage, to valley lines over five hundred feet deep. The 

 whole of Root river valley, which is in the St. Croix sandstone, is over five 

 hundred feet in depth, with limestone capping the bluffs. Some of its 

 tributary valleys are equally deep and wide, but the smaller tributary val- 

 leys become shallower and more rocky as the gorges ascend in the St. Law- 

 rence limestone the whole system making a series of deep valleys along 

 the river and of alternating vales and ridges at greater distance from the 

 main valley. The county is nowhere destitute of excellent natural drain- 

 age. There are very few of the characteristic sink-holes of the Trenton, 

 that formation having but a small superficies in the county, and that not 

 within the reach of important drainage courses which were capable of 

 producing the pre-glacial gorges. Within the Shakopee area have been 

 seen three or four similar sink-holes, but they differ from the Trenton sink- 

 holes in being more plainly a part of continuous ravines and in being 

 broader in comparison to their depth. 



If the valleys excavated by drainage were filled up the county would 

 be very nearly flat, the highest part being in the southwestern corner, in 

 the area of the Trenton limestone. The great diversity of surface that 

 appears, arises entirely from the effect of erosion by streams and atmos- 

 pheric forces, on the rocks, which consist of alternating sandstones and 

 limestones. This effect would be still greater, or rather would be still 

 more apparent, were it not that the loess-loam, which is very thick in this 

 part of the state, tones down with its overspreading canopy, the roughness 

 which the rocky surface really possesses, leaving it actually one of an undu- 



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