LAKE STREET TERRACES AND FALLSCARI' 43 



river was 30 feet deep at its head, 40 feet deep midway, and possibly 45 

 feet deep at the mouth. The original height of Minnehaha falls was 30 

 feet, whereas it is now 60 feet. Minnehaha creek has not only cut back 

 its gorge one-eighth of a mile, but has deepened it, meanwhile eroding 

 the bottom of the Lower gorge 40 to 70 feet deeper. The Deer Park 

 gorge has also deepened. Two lines of drainage from near-by swampy 

 tracts enter, one at each corner, at the head of this gorge, and those have 

 changed the outline of the original crest of the old fall, as well as deep- 

 ened the gorge. 



The Lake Street Terraces and Fallscarp 



For two miles above the mouth of Minnehaha creek the gorge of the 

 Mississippi has a north to south course, with no ancient terraces within 

 the gorge and narrow ones or none at the top. The limestone ledge on 

 either cliff is surmounted by 20 to 40 feet of shales or by glacial drift. 

 The shales appear to be continuous on the left side and to extend for the 

 greater part along the right side. These, with the included crystalline 

 limestone strata, are additional to that which the river encountered in 

 the first 2 miles above Fort Snelling. The second 2 miles of Saint An- 

 thony falls' retreat was peculiar in that respect, but as to the effect of 

 that peciiliarity we know little, since the long, straight gorge there is the 

 only record of the river. 



In the next, or fifth, mile from Fort Snelling the gorge curves toward 

 the west. Here, as a person would expect, there are some terraces on the 

 inner curve. As shown on the map (plate 1), a high terrace runs 

 across the north half of section 5. This terrace is 15 to 20 feet above the 

 top of the limestone ledge and is marked off by a well defined scarp on 

 the west side. The stream appears to have made an island on the east 

 side of the terrace. The height of the terrace rather indicates that it was 

 abandoned by the river a long time before Saint Anthony falls reached 

 that part of the gorge. I compare it to the high terrace at ]\Iinnehaha 

 creek. Also, near tlie bottom of the gorge, there is a long terrace, with a 

 remnant of a fallscarp at its northwestern end, and above this there was 

 formci'ly a sloping approach, or upper rapids, M^here a stone quarry now 

 yawns. From notes taken over 10 years ago, when the quarry was small, 

 I am al)le to describe that part also. Saint Anthony falls left a well 

 preserved record of its course, including upper rapids, fallscarp, lower 

 rapids, and river bed, here within an eighth of a mile above the west end 

 of Lake Street bridge — that is, the southwest corner of section 32. A 

 profile of the fall is shown in plate 2, figure 3. 



The scarp, which once formed the west end of the fall here, stands 



