362 A. N. Winchell— Great Dust fall of 1920. 



was between .02 and .001 mm. ; that is, most of the mate- 

 rial would be classed as silt or clay. The largest parti- 

 cles carried long distances by the wind are thought to 

 be only .07 to .08 mm. 



There are many mechanical analyses of loess from this 

 country with which these analyses of dustfalls may be 

 compared, as illustrated iii the following table. 



Table VII. — Size of constituents of dustfalls compared 

 with loess. 





1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



^.005 mm. 



11.15 



10.7 



. 25.57 



24.5 



26.7 



28.9 



26.4 



32.0 



17.1 



10.5 



*\005- .010 



22.01 ] 



| 



11.91 1 

















.010- .025 



56.17 



► 85.0 



44.09 



>66.5 



64.8 



63.9 



56.4 



63.4 



67.5 



42.3 



.025- .050 



5.19 



1 



11.35 J 

















.05 - .10 



1.22 



3.2 



5.04 



5.8 



3.6 



4.6 



14.5 



1.4 



15.0 



42.9 



.10 - .25 



1.04 



0.2 



0.87 



1.0 



1.8 



1.3 



1.4 



1.1 



0.3 



3.6 



.25 - .50 



0.58 



0.1 



0.05 



0.4 



1.8 



0.4 



0.5 



0.6 



0.1 



Tr. 



.50 -1.00 



0.29 



0.0 



0.03 



1.2 



1.4 



0.6 



0.1 



1.1 



0.1 



0.1 



1.00 -2.00 



1.08 



0.0 



0.00 



0.6 



0.0 



0.2 



0.0 



0.3 



0.0 



0.0 



99.53 99.2 98.91 100.0 99.9 99.9 99.8 99.9 100.1 99.8 



1. Dustfall at Madison, 1918. 



2. Loess, 6 ft. below surface at Edwards, Miss. E. W. Shaw: U. S. Geol. 

 Survey, Prof. Pp. 108, 135, 1918. 



3. Dustfall at Madison, 1920. 



4. Loess, 3 feet below surface, Muscatine Co., la. Field Oper. U. S. 

 Bur. Soils, 1914, p. 1848. 



5. Loess, 3 feet below surface, Harrison Co., Mo. Field Oper. U. S. Bur. 

 Soils, 1914, p. 1960. 



6. Loess, 3 feet below surface, Binggold Co., la. Field Oper. U. S. Bur. 

 Soils, 1916, p. 1918. 



7. Loess, 3 feet below surface, Callaway Co., Mo. Field Oper. U. S. Bur. 

 Soils, 1916, p. 1933. 



8. Loess, 3 feet below surface, Grundy Co., Mo. Field Oper. U. S. Bur. 

 Soils, 1914, p. 1991. 



9. Loess, 6 feet below surface at Weeping Water, Neb. Alway & Eost: 

 Soil Science I, 1916, p. 407. 



10. Loess, 3 feet below surface at North Platte, Neb. W. W. Burr: 

 Kes. Bull. 5, Agr. Exp. Sta. Neb., 1914, p. 12. 



The mechanical analyses of loess show that it varies 

 considerably in percentage distribution of sizes present. 

 The analysis of the loess from Edwards, Miss. (No. 2) 

 is very similar to the Madison dustfall of 1918, while 

 analyses 4, 5, and 6 are closely like the dustfall of 1920. 

 These have been selected to show that loess may be of 

 the same types as these dustfalls, but it is also commonly 

 found of other types. Analyses 7, 8, and 9 illustrate loess 

 differing distinctly, but not greatly, from the dustfall of 



