"888 N. H. WINCHELL ON THE RECESSION 



has really been thus changed by infiltration to varying depths, yet 

 its lower portion, where it has its full development, is blue. 

 Another noticeable difference between the red and grey deposits is 

 the presence of a laminated, or often non-laminated, loam, which 

 reaches sometimes fifteen feet in thickness, over the red hardpan 

 towards the east and south, especially in the valley of the Mississippi, 

 and its absence over the grey hardpan towards the west, or its 

 occurrence only in very thin and small low patches round its mar- 

 gins. The grey hardpan disappears towards' the east gradually, 

 extending further in the valleys than in the uplands ; and where 

 the hardpan itself is not seen, sometimes the gravel from it is dis- 

 tributed several miles further, often mingled with a gravel derived 

 from the denudation of the red hardpan. The most easterly portion 

 of the grey hardpan, in the vicinity of the Falls of St. Anthony, not 

 in the valley of the Mississippi, lies within the limits of the city of 

 Minneapolis, on the west side of the river, and there marks the limit 

 of the moving ice which deposited it. This is a remarkable inci- 

 dent of itself. This is the furthest limit to which the ice could 

 move the drift in this neighbourhood. More to the west its force 

 extended much further south, and its boundary seems to mark 

 out roughly the limit of the Big "Woods of Minnesota, at least in 

 their southern and eastern portions. The following general section 

 will express the arrangement and natural sequence of the different 

 parts of the drift, when they are all considered, as represented in 

 the vicinity of the Falls of St. Anthony : — 



1. Loam 3 to 6 feet. 



[ 2 (a). Grey sand and gravel to 20 feet. 



2 (b). Brick-clay to 25 feet. 



2 (c). Grey sand and gravel with boulders . . 1 to 20 feet. 



2. Grey hardpan to 12 feet. 



3 (a). Red gravel and sand to 10 feet. 



3 (6). Eed fine sand or laminated clay to 10 feet. 



3 (c). Eed gravel with stones and boulders . . to 6 feet. 



3. Eed hardpan to 25 feet. 



3. 



The foregoing Table summarizes and brings into one view the 

 details derived from a great many separate sections. There are 

 three distinct parts or members of the drift, namely, loess, grey 

 hardpan, and red hardpan ; but the separate subdivisions of each 

 member are not all seen at any single point. The subdivisions 

 a, b, c represent modified conditions of the main members or parts, 

 (2 and 3), and are accumulations derived from the washing and rede- 

 position of the finer and coarser constituents of these main members. 

 Nos. 2 (6) and 3 (6) are very apt to be entirely wanting, No. 2, 

 with perhaps a thin deposit of No. 2 (a), being the only represen- 

 tative of the later drift. There are places also where the only 

 representative of the later drift is a heterogeneous mingling of 

 coarse gravel and boulders belonging to No. 2(c). This is more 

 frequently the case near the margin of the later drifts, and beyond 



