360 A. N. Winchell— Great Dust fall of 1920. " 



Table V. Calculated mineral composition of Mississippi Valley 

 loess compared with that of the Madison dustfall. 



12 3 4 5 6 



Quartz 36.47 39.66 43.52 45.56 48.89 49.50 



Albite 17.89 11.42 9.24 14.22 14.30 12.10 



Orthoclase 13.69 12.20 12.03 12.62 6.98 10.86 



Anorthite 7.64 .... 7.60 2.19 .... 4.74 



Kaolinite 7.94 15.62 17.15 14.83 12.29 14.12 



Chlorite 9.26 3.65 1.55 3.10 



Enstatite 3.24 



Calcite 9.39 



Magnesite 4.57 



Apatite 35 .14 



Gypsum .22 



Ilmenite 1.01 .76 



Hematite 2.17 4.02 2.71 2.97 3.25 



Magnetite .64 1.19 



Water, etc 7.03 3.12 .10 .58 



1.37 3.17 



.88 6.43 1.11 



3.56 

 .53 .94 .21 



1.10 



1.37 1.12 .26 



Total 101.28 100.03 100.33 100.22 100.65 99.83 



1. Average Madison dustfall of March 19, 1920. 



2. Loess, Galena, Illinois. Chamberlin and Salisbury: 6th 

 Ann. Rep. U. S. Geol. Survey, 1885, p. 282. 



3. Loess, Kansas City, Mo. W. E. McCourt : Missouri Bureau 

 Geol. & Mines, 14, p. 94, 1917. 



4. Loess, Dubuque, la. Chamberlin and Salisbury: loc. cit. 



5. Loess, Mt. Vernon, la. N. Knight : Am. Geol., 29, 1902, 

 p. 189, 1902. 



6. Loess, Kansas City, Mo. Chamberlin and Salisbury: loc. 

 cit. 



other difference between the dustfall and the loess that 

 requires comment is the scarcity of carbonate in the 

 former. But this scarcity is matched by the condition 

 found by McCourt in the loess from Kansas City, and 

 the other sample from that locality as well as the loess 

 from Dubuque contain very little carbonate. It is note- 

 worthy that four samples of European dustfalls are rich 

 in carbonate as shown by numbers 6-9 in table IV. It 

 seems very probable that the amount of carbonate in a 

 dustfall would vary through wide limits depending largely 

 upon the type of chief country rocks in the area of origin 

 of the dust. 



Accordingly, we find no fundamental distinctions in 

 chemical or mineral composition between the Madison 

 dustfall and the Mississippi loess ; on the contrary, the 

 two are more alike than Madison dust and foreign dust. 

 The chief differences which exist are such as would be 

 produced by weathering of the dust. 



