76 



PltOTOZOIC ROCKS OF 



T H E 



NORTHWEST. 



times ; but Dr. Shumard, who was instructed to collect evidence of any ancient 

 river deposits at a higher level, observed, over the limestone at the Falls, a bed of 

 drift of about eleven feet in thickness, and, resting thereon, a bed of sand containing 

 Cyclas, Limnea, Physa, and Planorbis, and this deposit he traced on to the same 

 level for nearly half a mile below the present position of the Falls. 



The same gentleman also observed, half a mile below the Falls, and about a 

 quarter of a mile east of the gorge, on rising ground, over which runs the trail to 

 St. Paul's, a white marl charged with the same genera of shells, but of different 

 species. 



The former of these deposits is doubtless of fluviatile origin, and affords evidence 

 of the river having flowed, at one time, for a short distance, at least, above the 

 gorge ; the latter seems to be a lacustrine deposit, the bottom of some drained lake, 

 of which there are numerous instances in the Chippewa Land District. 



If we except these beds and the underlying drift, no formations of more recent 

 date than the shell limestones of St. Peter's were observed along the Mississippi, 

 from the Wisconsin River to the Falls of St. Anthony. This statement will apply 

 also to the country east of the Mississippi, as far as the water-shed between that 

 stream and Lake Superior, except along the valley of the St. Croix above the Falls. 



SECTION V. 



ITS RANGE, EXTENT, AND BEARING. 



Of this formation, together with its associated member, F. 2 c, the southern 

 portion is confined to a belt, narrow, but of considerable length, ranging nearly 

 west, on both sides of the lower portion of the Wisconsin River, but chiefly south 

 of that stream, together with a continuation of the same belt west of the Mississippi, 

 and ranging towards and beyond the forks of Turkey River. 



Its appearance, in the north, is still more limited ; being restricted to a few miles 

 in the immediate vicinity of the Falls of St. Anthony. 



In the high lands lying on both sides of the Lower St. Croix, near the Kinni- 

 kinick, also between Yellow River and the Upper Iowa, this formation occurs in 

 outliers, assuming much the same symmetrical, mound-like forms as described and 

 represented in the preceding section. 



