49 PROTOZOIC ROCKS 
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 OF LOWER 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. 
