370 THE GEOLOGY OF MINNESOTA. 



[Geological structure. 



THE GEOLOGICAL STRUCTURE OF DODGE COUNTY. 



The underlying rocks can only be seen in the valleys of the streams in 

 the northeastern portion of the county. Canisteo, Mantorville, Milton, 

 Concord and Wasioja townships include all the rocky outcrops. Over the 

 remaining seven townships the drift conceals every feature of the rock be- 

 low. All the evidence that there is indicates that to some extent, at least, 

 the rock so covered is Cretaceous, but no facts of observation can be cited 

 to demonstrate this. 



The Shakopee limestone is found in the bottom of the valley of the north 

 branch of the Zumbro but a short distance east of the county line, and the 

 characteristic arrangement of the bluffs, indicating that formation, enters 

 the county about two miles and a half. The rock has not actually been 

 seen in Dodge county, although the overlying St. Peter sandstone appears 

 in several places. It is on the strength of this evidence that the Shakopee 

 limestone is shown on the accompanying map as forming^the floor of the 

 valley in Milton township. 



St. Peter sandstone. Surrounding this valley is the bluffy outcrop of 

 this sandstone. It^is sometimes seen in digging wells or is cut by the grad- 

 ing for the highway. It preserves its characters as a white, friable sand- 

 stone, growing reddish and attaining more firmness when exposed to the 

 air. 



The Trenton limestone comprises the remaining exposures along this 

 stream. In descending the stream everything is covered by drift until 

 reaching the vicinity of the Eagle Valley mills, sec. 15, Concord. Here a 

 rock in rather thin layers is quarried, but without affording any good ex- 

 posure of the strata. Two miles farther down the stream is a quarry at 

 Concord, in the south bank N. W. J sec. 23, with the following 



Descending section at Concord. 



1. Black loam and reddish clay 4 ft. 



2. Rubble, stone 2J ft. 



3. Dolomitic rock, yellow, with fine reddish lines; layers two to eight inches 



thick 3 ft. 



4. Bluish stone, less dolomitic, in even beds from one to two feet thick 3 ft. 



5. Bluish stone, not dolomitic, in thin layers 1 ft. 



6. Heavy layers of bluish stone 3 J f t. 



Total.. 17ft. 



