EXPOSURE ON UNIVERSITY CAMPUS 357 



On the campus of the University of Minnesota 20 years ago dunes of 

 sand drifted about to such an extent that the driveways were contin- 

 ually changed during the summer season by the efforts of the teamsters 

 to drive around the accumulating sand piles. On the opposite side of 

 the street, along the south side of the campus, a railway cut was made 

 some years ago. Professor N. H. Winchell has published quite a de- 

 tailed description of the glacial drift profiled at that time.* From this 

 description it would appear that the dune sand reached a thickness in 

 one spot of 5 feet. This was 650 feet east of the brink of the river gorge 

 (see figure 1). At 550 feet from the river the " loam, sandy, not dis- 

 tinctly stratified, alluvial " deposit was 4 feet, and at 350 feet from the 

 river the "alluvial, sandy loam " was only 3 feet in thickness. Figure 

 2, plate 33, shows this same deposit in a neighboring exposure. 



The process of dune-making is apparently the same now as it was 

 hundreds of years ago, before the Minneapolis peat bed began to form. 



RELATION OF DUNE SANDS TO TERRACE GRA VELS 



It has been possible also to establish another line of proof of the nature 

 of the dune sands based on a discovered relation between them and 

 Mississippi river sands and gravels. As has just been described, the 

 campus of the University of Minnesota is underlaid by several feet of 

 fine, loose, unstratified sand. This sand rests upon gravel, and this in 

 turn upon the till.f The uppermost layer in this section is dune sand. 

 Its relation to the post-Glacial river gravels of the Mississippi can be 

 seen near b}^ in a way to furnish proof of the eolian nature of the sand 

 deposit. At the foot of Pleasant street, southeast Minneapolis, only a few 

 blocks away from the campus, is the spot referred to. This is opposite, 

 the old landing which marks the exact head of navigation of the river. 

 Here still remains a part of the river channel, which was formed before 

 Saint Anthony falls existed at this point. The position of the falls is 

 now one and one-half miles above this point. The old channel and the 

 gravel deposit now lying within it must be several thousand years old ; 

 at all events, older than the time when the falls had reached this point 

 in their retreat. The old channel mentioned is cut a little into the blue 

 limestone layer, which in south Minneapolis is about 12 feet thick. It 

 is probable that this channel was abandoned by the river while the falls 

 were yet some distance fartherclown the stream. ' The now existing Saint 

 Anthony fails are approached through a channel cut into this same bed 

 of blue limestone, and the crest of the falls is over the underlying socalled 



♦Geological and Natural History Survey of Minnesota, Final Report, vol. ii, 1888, chap. xi. The 

 geology of Hennepin county, pp. 297-299, figs. 17, 18, 19, and their descriptions, 

 t Compare also N. H. Winchell's figures, loc. cit, 



LI— Bull. Geol. Soc. Am., Vol. 10, 1898 



