FILLMOEE COUNTY. 317 



Loam. Terraces.] 



It has already been stated that there is some reason to assign an earlier 

 date to the origin of the upland loam than to the stratified loess loam of 

 the valleys,* and it is equally true that there is some reason to assign to it 

 a different origin. Indeed, the explanation of its origin advanced by Prof. 

 J. D. Whitney,! m 1862, is applicable over a very large part of the "drift- 

 less area" in the state of Minnesota. He says: " The great mass of super- 

 ficial clay, loam and other loose materials lying on the solid rock in this 

 region, is therefore simply the residuum left after the more or less complete 

 solution and removal of the soluble portion of the rock." It is quite prob- 

 able that all the instances of lamination that have been seen in the surface 

 materials of the "driftless area" may be referred either to the agency ot 

 rivers when existing with larger volume than at present, and flowing at 

 higher levels, or to the effect of local drainage, bringing fine sediment from 

 the higher levels farther west, perhaps at the time of the last glacial epoch, 

 and depositing it both on the pre-existing drift materials and on the older 

 loam. The rotted and disintegrated condition of the surface of the older 

 rocks on the higher levels in the county, the existence throughout this de- 

 cayed interval, and sometimes extending upward in the loam, of pieces of 

 chert referable to the rock itself, the great uniformity in the character of 

 this loam, and its massive or non-stratified structure, point to this theory 

 for its origin. 



Alluvial terraces. At Preston, besides the flood-plain, the river has a 

 high terrace-plain. The Stanwix House stands on it. It consists of loess 

 loam undistinguishable from the loam that covers that portion of the 

 county. The same may be seen at Lanesboro, and at Whalan, but it is not 

 conspicuous. At Rushford fragmentary remains of this high terrace are 

 seen in the valleys of the tributary streams. Along the main valley they 

 are not well preserved. There are two terrace levels, besides the flood- 

 plain. The highest terrace-plain is from seventy to eighty feet above the 

 second, and about one hundred and thirty feet above the river. The lower 

 terrace, on which Rushford stands, is about forty feet above the river, and is 

 probably never reached by the river in even the highest water. Within 

 this lower terrace-plain, which spreads out laterally and forms the most ot 



'Report on Winona county, p. 262-3. 

 tGcology of Wisconsin, 1802, p. 126. 







