THE IOW AN LOESS. 159 



noted were of a flattened form, man}' of them being mica scales. The 

 extreme size noted was 0.1139 by 0.0285 millimeter. A prominent charac- 

 teristic of the loess grains is their angularity and their irregularity. "Sharp 

 corners and rough surfaces are the rule and any approach to regularity or 

 smoothness the exception." The mineralogical examination shows that 

 quartz greatly preponderates, while particles of feldspar, mica, hornblende, 

 augite, magnetite, dolomite, and calcite are present, the mineral constitution 

 being not greatly different from that of the glacial deposits from which the 

 loess is probably largely derived. It is found that loess in the Driftless Area 

 has been modified by the introduction of residuary material, and is therefore 

 formed in part of true loess material and in part of wash from the residuary 

 soil of the surrounding country. 1 



Samples of the several grades of loess were collected in 1892 by the 

 writer in various parts of western, central, and southern Illinois and sent to 

 Prof. Milton Whitney, of the United States Department of Agriculture, for 

 mechanical analysis. Several samples were analyzed under Professor 

 Whitney's direction by Prof. J. A. Udden. The separations were made 

 substantially after Johnson and Osborn's "beaker method." The results 

 have been published by Whitney in a report to the Illinois Board of World's 

 Fair Commissioners. 2 The following tables, taken from Whitney's report, 

 are rearranged to bring out the distinction between loess supposed to have 

 been wind deposited and that which ma)' have been deposited bv water. 

 Other changes in the grouping of the analyses have also been made. The 

 analyses of bowlder clays are introduced, in order that their physical con- 

 stitution may be compared with that of the loess and white clay. It will be 

 observed that in the bowlder clay -the percentage of fine material (0.005 

 millimeter or less) is greater than in typical loess, thus suggesting the partial 

 removal of such material from the loess. The tables bring out clearly the 

 fact that the pervious loess contains a smaller percentage of fine particles 

 than the compact, but that it contains no coarse particles. They also show 

 that in the pervious loess the soil contains a larger percentage of fine particles 

 than the subsoil. Whitney remarks that the loess soil and subsoil show the 

 reverse of the rule in agricultural lands, it being the rule that the subsoil 



1 Sixth Ann. Eept. U. S. Geol. Survey, pp. 278-285. 



: Report on the examination of some soils from Illinois, by 'Milton Whitney. Final Report of 

 Illinois Board of World's Fair Commissioners, 1893, pp. 93-114. Published at Springfield, Illinois, in 

 1895. H. W. Eokker Printing Company. 



