A. N. Winchell— Great Dust fall of 1920. 349 



Aet. XXXIV.— The Great Dustfall of March 19,1920; by 

 Alexander N. Whstchell, Professor of Mineralogy and 

 Petrology, University of Wisconsin, and Eric R. 

 Miller, Meteorologist, TJ. S. Weather Bureau. 



Object of the Investigation. — Since the dustfalls of 

 March, 1918, that we reported in this Journal 1 and the 

 Monthly Weather Bevieiv, 2 we have collected the solid 

 precipitates from all storms, with the object of throwing 

 light on (a) the probable origin of the dust, (b) the con- 

 tribution of plant food to the soils of the Eastern States, 

 and (c) the chemical relationships between American and 

 European dustfalls. During the interval of more than 

 three and a half years there has been only one unusually 

 heavy deposit of atmospheric dust at Madison, Wis- 

 consin, namely that of March 19, 1920. 



Sources of Material and Information. — The dust was 

 first noticed by us in the upper layers of a fall of 0.4 

 inch of snow and sleet, to which it gave a grayish tinge, 

 on the morning of March 19, while the last of the fall 

 was still coming down. We immediately collected 

 samples from measured areas in various places, in 

 Madison. 



Professor Charles F. Marvin, Chief of the Weather 

 Bureau, upon our request, very kindly sent a telegraphic 

 request to the officials in charge of seven offices, to collect 

 samples of the dust and send them to us. The places 

 from which these samples were received, and the officials 

 to whom we are indebted for material, and descriptions 

 of the precipitate in situ are 



Charles City, Iowa. H. P. Hardin. 



Dubuque, Iowa. J. H. Spencer. 



Green Bay, Wis. F. W. Conrad. 



La Crosse, Wis. E. C. Thompson. 



Ludington, Mich. C. H. Eshleman. 



Saginaw, Mich. F. H. Coleman. 



St. Paul, Minn. J. N. Ryker. 



At Charles City, Dubuque, and La Crosse the dustfall 

 was noticed by the observers. At Dubuque it was 



1 Vol. 46, p. 599, 1918, and vol. 47, p. 133, 1919. 



2 Vol. 46, p. 502, 1918. 



