42 



P II O T 0 Z 0 I 0 ROOKS 



Standing on the extensive plain on which Prairie du Chien is built, and looking 

 up the valley of the Mississippi, one can see this range of hills stretching away for 

 nearly four miles, and these well-defined geological terraces may be observed con- 

 verging in long lines of perspective. To the eye, these benches of rock appear 

 horizontal, but measured by the barometer, they are found gradually to rise in 

 ascending the valley ; and a still greater rise is observed in going northeast, towards 

 the Kickapoo. 



Assuming this section as a standard of comparison, the rocks constituting the 

 base of these hills are seen to rise higher and higher going north, though the hills 

 themselves retain nearly the same elevation ; the consequence is, that, one after 

 another, the superior strata run out and disappear ; and, before proceeding many 

 miles, the Lower Magnesian Limestone, which at first occupied their base, is found 

 extending even to their highest summits, while the inferior Sandstone gradually 



CLIFF or LOW Kl! MAGNESIAN LIMESTONE, PLUM CREEK, 



emerges from beneath the water-courses, and at last constitutes several hundred 

 feet of their base. Thus, at the mouth of Yellow River, this Lower Sandstone is 

 already exposed sixty feet, and at Painted Rock, one hundred and forty-five feet ; 

 showing a rise, first of thirty feet in three miles, and then of eighty-five feet in two 

 miles.* Again, eighteen to twenty miles northeast of Prairie du Chien, on the 

 Kickapoo River, a tributary of the Wisconsin, and but three or four miles in a 

 direct line from their confluence, the Lower Magnesian Limestone is already found 

 capping the tops of the adjacent hills, as depicted above, in a sketch taken on that 

 river, near the mouth of Plum Creek. 



The cliff, on the summit, is the Lower Magnesian Limestone, and in the slope 

 underneath are sandstones, with alternations of magnesian limestones. In conse- 

 quence of the softness of the sandstones, it is often difficult to get a view of them, 

 because they have crumbled away in the slope, and are hidden from view by vege- 

 tation. Occasionally they are more indurated, and then appear in a bold and 



Sect. No. 1, 2, and 3. 



est 



