A. N. Winchell— Great Dust fall of 1920. 359 



1. Dustfall collected at 2125 Van Hise Ave., Madison, Wis., 

 19 March, 1920. 



2. Dnstfall collected from ice on Lake Mendota, Madison, 

 Wis., 19 March, 1920. 



3. Dnstfall collected at 200 Prospect Ave., Madison, Wis., 19 

 March, 1920. 



4. Average dnstfall at Madison, Wis., 19 March, 1920. 



5. Dnstfall at Otakaia, New Zealand, 14 Nov., 1902, P. Mar- 

 shall: Nature, 68, p. 223, 1903. 



6. Dust in "red rain" at L amber hurst, Eng\, 22 Feb., 1903. 

 T. E. Thorpe: Nature, 68, p. 54, 1903. 



7. Dustfall at Naples, Italy, 10 March, 1901. P. Palmeri: 

 Rend. Accad. sci. fis. Naples. (3), 7, p. 157, 1901. 



8. Dustfall at Naples, Italy, 25 Feb., 1879. P. Palmeri : loc. 

 eit., p. 161. 



9. Dustfall at Taormina, Sicilv, 19 March, 1901. T. E. 

 Thorpe: Nature, 68, p. 222, 1903. 



This table shows even better than the chemical analyses 

 that the Madison dustfall is exceptionally rich in quartz ; 

 it contains about the same amount of total feldspar as 

 in the dustfalls at Otakaia and at Naples ; its content of 

 kaolinite is much lower than in foreign dustfalls (except 

 one at Naples) and the tenor of calcite is far lower 

 than in the European dustfalls. The Madison dust con- 

 tains more chlorite and less hematite than the others, 

 but this is at least in part due to our assumption regard- 

 ing the state of oxidation of the iron. 



In order to show how much similarity in mineral com- 

 position there is between the Madison dustfall and loess 

 of the Mississippi Valley computations of the latter made 

 in the same way as those of the dust are presented in 

 the following table. 



This tabulation shows that while the Madison dustfall 

 is quite unlike foreign dustfalls as shown by its tenor of 

 quartz, of which it contains at least twice as much as the 

 latter, it closely resembles the loess of the Mississippi 

 Valley differing no more from some samples of loess than 

 these differ from other samples of loess. It contains 

 decidedly more feldspar and less kaolinite than the loess, 

 but the high percentage of water not included in the cal- 

 culated minerals suggests that these differences are more 

 apparent than real; that is, the feldspar molecule is 

 probably already hydrated though the alkalies have not 

 been removed as thoroughly as in the loess. The only 



