OF T H E N U R T H W E S T. 



47 



the mouth of the Wisconsin River and the Falls of St. Anthony, I have constructed 

 a series of diagrams of comparative heights, some of them above alluded to, and all 

 to be found on Sections 1 and 5. I have also made a connected Section of the 

 same,* in which the heights and distances are on such a scale as not to distort the 

 geological features of the country. 



For the sake of perspicuity, I have designated each formation by numbers, com- 

 mencing with the lowest sandstone. The subdivisions are indicated by prefixed 

 letters, beginning with the lowest layers. For the sake of reference, it may some- 

 times be convenient, in the course of this Report, to designate them by numbers 

 and letters, in conformity with the above system of annotation. 



The formations laid down in these sections extend for a considerable distance on 

 either side of the Mississippi River, the inferior members prevailing on the east 

 side, the superior on the west side. 



The Lower Sandstone and the Lower Magnesian Limestone (F. 1 and F. 2) com- 

 pose the bluffs of Hokah, of Miniskah, of Wazi Oju, and of St. Peters River. The 

 latter only shows itself on the Canon and Vermilion Rivers. It occupies, also, in 

 connexion with the overlying fossiliferous limestone (F. 3), the surface of the 

 Winnebago Reserve to near the south fork of Turkey River. Here both disappear 

 beneath the water-courses, and are replaced by the Upper Magnesian Limestone, 

 and that again, beyond the Wapsipinicon, by the Limestones of Red Cedar and 

 Wapsinonox, and which form the surface rock in the Dubuque District on the 

 lower part of those streams. Ascending the northeastern tributaries of the Mis- 

 sissippi, the strata rise, as has already been said (F. 2) ; at first forming the 

 upper hundred or two hundred feet, but gradually running out until it is replaced 

 by F. 1, which then occupies the entire thickness of the ridges, even to their very 

 summits. This change takes place, on the Wisconsin River, some forty-five miles 

 below its great bend, or a few miles east of Sauk Prairie ; on Prairie a la Crosse 

 River, about forty-five miles (by water) above its confluence with the Mississippi ; 

 on Black River, fifteen to twenty miles ; on Mountain Island River, twenty to 

 twenty-five miles ; on Buffalo River, from twenty to thirty miles ; on the Chippewa 

 River, thirty-five to forty miles, or near the mouth of its east branch, the Meno- 

 minie; on Rush River, about forty miles; on St. Croix River, about forty-eight 

 miles. Allowing for inequalities in the meanders of these rivers, the approximate 

 boundary of the Lower Magnesian Limestone will be nearly parallel with the great 

 valley through which the Mississippi flows; and about an average distance of 

 twenty miles from that river : as may be seen by reference to the geological chart 

 on which the course and bearings of the formations are laid down. 



The area over which F. 2 is the surface rock, is coloured on the chart of the 

 darkest shade of purple blue ; that over which F. 1 extends, chrome yellow ; and 

 this latter colour has been extended up the valleys of the streams where F. 1 forms 

 a considerable portion of the base of the sections. 



Towards the falls and rapids of these streams, the inferior members of F. 1 reach 

 the surface in succession, and at length are found either resting immediately upon 



* Sect. 2. 



t 



