A. N. Winchell— Great Dustfall of 1920. 363 



1920, while analysis 10 shows that loess may even differ 

 very decidedly from the dustfall. 



This table does not show that there is any close rela- 

 tionship between dnstfall and loess; it merely shows 

 that such a relationship can not be denied on the ground 

 of differences in mechanical composition. 



Organic Constituents. — In addition to the mineral com- 

 ponents fragments of vegetation are visible; these 

 include spores and shreds, but for more accurate data 

 on the subject the samples were referred to Professor 

 R. H. Denniston of the Department of Botany of the 

 University of Wisconsin who very kindly supplied the 

 following information: Spores of fungus are present 

 which are probably to be referred to Alternaria; the 

 hypha of a fungus is also found, as well as trichomes, 

 starch grains, grass cells, and bits of charcoal. 



Finally, diatoms are found in the dust which seem to 

 be of three types including two like those found in the 

 dustfall of 1918. For the examination of these diatoms 

 samples of the dust were sent to Dr. Albert Mann, Plant 

 Morphologist of the United States Department of Agri- 

 culture, who kindly reported as follows: 



"I have examined the dust brought down by a snow- 

 storm at Madison on March 19, 1920, and find that the 

 diatoms contained are in general like those in the snow- 

 dust you collected two years ago. But there are some 

 differences. In the 1918 sample the most abundant 

 species was Nitschia (Hantschia) amphioxus (E.) W. S., 

 much outnumbering Navicula borealis (E.) K. In this 

 last sample the latter is more abundant, perhaps 3 to 1. 

 As I then stated, both these are characteristic of cool 

 sphagnum bogs and the moss on shaded tree trunks.' ' 



' 'I have found two other species in this material: — - 

 Navicula pupula K. (rather frequent) and Cymbella tur- 

 gidula Grun (very scarce). The former is often found 

 in cool and damp garden soil and on the under side of 

 leaves in damp woods. The latter is widely distributed 

 in cool fresh waters." 



Quantity of Dust Transported. — In the storm which 

 brought a heavy dustfall to Madison in 1918, we estimated 

 from meager data that at least one million tons of dust 

 were transported long distances. In 1920 the amount of 

 dust deposited at several places in Madison and at some 

 other points was determined with the following results. 



Am. Jour. Sci.— Fifth Series, Vol. Ill, No. 17.— May, 1922. 

 26 



