294 TH GEOLOGY OF MINNESOTA. 



[Galena timeitooe. 



feet, toward the upper portion. They contain but little shale in Fillmore 

 county, and that is near the base and near the top. 



This rock forms a great many precipitous bluffs. It appears in the 

 form of mural faces along a great many creeks and canons in the central 

 portion of the county. It generally rises nearly perpendicularly from the 

 top of a short talus to the summit, exhibiting a continuous section of the 

 bedding. Its area is pre-eminently the region of sink-holes. The canons 

 that are so frequent in it run out in ascending the valleys, and disappear in 

 a succession of sink-holes which become smaller and smaller, and more and 

 more distant, till the general prairie level is reached. While in general its 

 ithological characters are quite uniform, near the top the layers begin to 

 alternate with layers that exhibit the characteristic lithology of the Galena, 

 and are accompanied with some thin layers of green shale. It seems to 

 pass gradually into the Galena, or rather to assume the features that have 

 ben ascribed to that formation. 



"VIEW ON T>EZR CREEK raEARWEISBACHJS MILIJ 

 FIG. 20. 



The accompanying views represent the manner ot weathering of the 

 Galena and Upper Trenton. At Weisbach's dam, on Deer creek, S. E. \ sec. 11, 

 Spring Valley, the face of the bluff which rises perpendicularly about a 

 hundred feet, is wrought into a series of majestic pilasters running from 

 the bottom to the top of the escarpment, as shown in figure 21. 



