316 THE GEOLOGY OF MINNESOTA. 



[Loam. 



which is frequently black, or brown, varying to an ash-color when mingled 

 with a considerable percentage of clay from the drift, and also contains 

 gravel. The surface loam is very homogeneous over wide tracts, while that 

 in the drift area is subject to local and sudden varations. The loess loam 

 is indistinctly stratified, in valleys, but the usual appearance on the uplands 

 is that of non-stratification. This stratified arrangement is rendered the less 

 evident from the great similarity of the materials from the top to the bot- 

 tom. It does not consist, apparently, in any change from coarse to fine in 

 the sedimentation, but in a lamination of the homogeneous clayey loam, 

 and is easily obliterated by exposure, or by trickling water. This condition 

 was noted particularly in the valley at Preston, and indicates that it there 

 was deposited in still, or gently moving water. Where this loam lies over 

 the old northern drift, it passes through a gravelly stage,, the materials of 

 the loam mingling with the coarser portions of the drift, and becoming 

 finally replaced by the drift. The drift patches covered by this loam, pertain- 

 ing to the eastern and central portions of the county, and believed to be- 

 long to an earlier drift epoch, are, so far as seen, made up of gravel and 

 sand, with small stones. Very little drift clay, or till, like that which 

 covers the western part of the county, has been seen overlain by the loess 

 loam, to the east of that which pertains to the general drift-sheet of the 

 Northwest, and which occupies a narrow belt, five or six miles wide, 

 where the loam overlaps the later drift. It may be seen at several points 

 between sec. 4, Canton, and Lenora. At one point it is a light-colored, or 

 ashen, gravelly clay, which above is very irony or rusty. Over the surface 

 are numerous fragments of chert, with some small boulders of granite 

 and green-stone, and jasper and quartzitic pebbles. It is covered by several 

 feet of loam. It is seen similarly in the N. E. sec. 12, Canton. 



The pebbles that are thus mixed with the lower portion of the loam 

 are smooth and waterworn, not covered with a coating of decayed material 

 of the same nature as the pebbles themselves, as they would be expected 

 to be if the loam were derived from the decay, in situ, of the materials of 

 the drift. The thickness of the surface loam sometimes reaches twenty feet 

 in the open upland, and under favorable circumstances, where it might 

 have accumulated laterally, as well as perpendicularly, it is much .more. It 

 is thickest in the eastern part of the county. 



