OLMSTED COUNTY. 37 



St. Peler sandstone.] 



Limestone and sandstone are minified with occasional strips of light-green shale. In general the 

 face presents the appearance of an alternation of horizontal layers of thin and more shaly beds, 

 with heavy, coarse and rough limestone beds. Some green-shale layers alternate with dark, 

 nmber-colored (ochreous) shale, neither being more than two inches thick. They are tortuous and 

 not continuous. This phase appears like the tops of the bluffs at Winona. but is at a considerably 



higher horizon 30 ft. 



No. 2. Persistent white sandstone (Jordan) seen 10 ft. 



Total exposure : 40 ft. 



This rock, in connection with the underlying Jordan, produces charac- 

 teristic surface features. When worn deeply into by erosion it presents bold 

 cliffs and craggy, rounded, hills. When not covered thickly by drift, or by 

 the loess loam, it makes a poor surface for agriculture, as may be seen in 

 some parts of Oronoco. Its area is nearly barren, or covered with scant 

 grass, with hazel and scrub oak (in this case a dwarfed growth of Quercus 

 macrocarpa), or with small paper birch, and other wood-growth not large 

 enough to be of importance economically. When this floor is covered by 

 drift, as in the beautiful prairie township of Farmington, the soil may be 

 unsurpassed. The most of this township is devoted to wheat, and at the 

 proper season it seems to be one continuous wheatfield. 



This rock does not furnish much good building material in this county. 

 It is not of even bedding and homogeneous texture generally. Pieces are 

 sometimes employed at Rochester for window-caps and water-tables. These 

 pieces are found only in the uppermost layers. No general use is made 

 of them. 



The St. Peter sandstone. The area of this rock is difficult to represent on 

 a map. It is so friable that it will not endure erosion when left to itself. 

 It is only where it is capped by the lower layers of the Trenton that it 

 successfully resists the attacks of water. By itself, uncovered by other 

 formations, it occupies but little space. It juts out beneath the cap of lime- 

 stone only a few feet or rods. From a projecting spur of limestone it may 

 extend further, as is illustrated in the city of Rochester. A spur of Trenton 

 comes in from the west, and ends "near the city limits. The sandstone, 

 however, can be struck in'sinking wells almost anywhere in the western 

 portion of the city. Occasionally, where erosion was incomplete, an outlier 

 of crumbling sandstone can be seen not capped by limestone. Such out- 

 liers may be found in the southwestern'part of Farmington, and in other 

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