44 



PROTOZOIC ROCKS. 



the strata, by which the beds that have been rising, as one ascends the streams, dip 

 again, descending towards the river beds. While this local dip of the strata con- 

 tinues to prevail, the beds, which had nearly run out, again thicken, and constitute, 

 as before, the principal part of the hills. Thus, though opposite Winnesheik's 

 Village, and below the mouth of Bad Axe River, the Lower Magnesian Limestone 

 capping the bluffs, is only from one hundred and thirty to one hundred and fifty 

 feet thick, it again increases, five miles higher up, to one hundred and seventy-five 

 feet.* Between this and Prairie a la Crosse, the northerly rise again sets in, so 

 that at Mountain Island, the sandstone constitutes the great body of the hill, to the 

 height of four hundred and twenty-eight feet.f About this part of the Mississippi, 

 we have, in fact, what, in the language of the geologist, is termed the principal axis , 

 of the protozoic strata of the Upper Mississippi ; or the geological backbone, whence 

 the strata again decline, with local undulations, towards the Falls of St. Anthony. 



Below the outlet of Lake Pepin, the Lower Sandstone constitutes about three 

 hundred and twenty to three hundred and forty feet of the base of the hills, J while, 

 above this, the Lower Magnesian Limestone rises one hundred and sixty feet. At 

 the great bend of that lake, on the northeast side, the Lower Magnesian Limestone 

 may be seen, forming a perpendicular wall, of nearly two hundred feet ; the total 

 height above the lake being about four hundred feet.§ This conspicuous escarp- 

 ment is the spot celebrated in Indian annals as the Maiden's Rock,|| or Cap des 

 Sioux ; represented on the opposite page. 



Lake Pepin is a mere expansion of the channel of the Mississippi, produced, in a 

 great measure, by the eroding and undermining action of its waters, combined with 

 atmospheric agencies, scooping out and carrying away the inferior soft sandstones. 



* See Sect. 1, B and C. f Sec Sect. 1, No. 7, D and E. 



% See Sect. 1, I. § See Sect. 1, K. 



|| The romantic legend connected with this conspicuous point, is related in Long's Expedition. It is 

 sometimes called the Lover's Leap 



OUTLET OF LAKE PEPIN. 



