444 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
The rapid rise of velocity after the 
passing of the storm center was pro¬ 
duced by the steep barometric gradient 
between Low IV and High VIII which 
followed closely. These strong follow¬ 
ing winds characterized this storm all 
the way across the western half of the 
continent. The closed loop in Figure 1 
shows the area within which the wind 
attained velocities exceeding 40 miles 
per hour at all stations. These veloci¬ 
ties occurred west of the dividing line 
on February 12, and east of that line 
on February 13. The winds apparently 
blew the dust up into the air, where it 
was carried forward into and around 
the storm center, and there precipated 
with rain and snow. Air trajectories 
of this type have been traced by Shaw 
and Lempfert ( 9 , figs. 84 K and 86 B ). 
Snow covered most of the region 
within the area of high winds, except 
the Missouri valley (fig 1). Trees and 
by the analyses. The dust-bearing 
snow was so badly drifted that no 
attempt was made to ascertain the 
weight of the dust per unit area. The 
samples used in the analyses were col¬ 
lected in the country west of Madison 
by W. S. Fusch and Dr. J. G. Dickson. 
Director Edwin B. Frost, of the Yerkes 
Observatory, also forwarded large 
samples obtained by sweeping the 
terrazzo floor of the observatory, into 
which the wind had blown dust through 
crevices. 
PHYSICAL COMPOSITION 
Prof. H. W. Stewart, of the Soils 
Department of the University of Wis¬ 
consin, made a mechanical analysis of 
the dust. His results are given in 
Table I. 
The breaking of a tube prevented 
completion of the duplicate on the clay 
and silt separates. The “fine gravel, ,, 
Table I.— Size of constituents of dustfalls in a 10-gm. sample of air-dried material 
Separates 
Size 
Per cent in dupli¬ 
cate parts 
Average 
A 
B 
Fine gravel .. 
2.0-1.0 
0.15 
0.40 
1.10 
4.37 
33.17 
14.15 
33. 76 
3.79 
10.60 
0.10 
0.41 
0.98 
3.74 
33.36 
0.12 
0.41 
1.04 
4.06 
33.26 
14.15 
33. 76 
3. 79 
10.60 
Coarse sand__ 
1.0-0.5__ 
Medium sand..__ 
0.5-0.25 ... 
Fine sand... 
0.25-0.1.. 
"Very fine sand__ 
0.1-0.05 ... 
Coarse silt_____ 
0.05-0.025.. 
Medium silt _ _ 
0.025-0.01 ___ 
Fine silt ..... 
0.01-0.0005_ 
Clay___ . 
Less than 0.005. 
Total___ 
101.49 
101.19 
Table II.— Size of constituents of dustfalls compared with that of loess 
Size 
Percentages 
A 
B 
C 
D 
E 
<0.005_____ 
10.60 
25. 46 
11.15 
24.5 
28.9 
0.005-0.010____ 
3.79 
12.04 
22.01 
) 
0.010-0.025____ 
33. 76 
44.60 
56.17 
> 66.5 
63.9 
0.025-0.050___ 
14.15 
11. 47 
5.99 
1 
0.05-0.10_____ 
33.26 
4.96 
1. 22 
5.8 
4.6 
0.10-0.25_ 
4.06 
.82 
1.04 
1.0 
1.3 
0.25-0.50___ 
1.04 
.04 
0.58 
0.4 
0.4 
0.50-1.0_______ 
0.41 
.02 
0.29 
1.2 
0.6 
1.0-2.0_ 
0.12 
.00 
1.08 
0.6 
0.2 
Total...__ 
101.19 
99. 41 
99.53 
100.0 
99.9 
A—Dust from snowfall at Madison, Wis., Feb. 13, 1923. 
B.—Average of three samples of dustfall at Madison, Wis., Mar. 19,1920 (I#, p. 849). 
C—Dustfall at Madison, Wis., Mar. 9, 1918 (11, p. 602). 
D. —Loess, 3 feet below surface, Muscatine Co., Iowa (8, p. 1848). 
E. —Loess, 3 feet below surface, Ringgold Co., Iowa (2, p. 1918). 
other tall vegetation exposed to the “coarse sand,” and “medium sand” 
wind throughout the area doubtless are practically all plant tissues and not 
contributed to the organic matter shown mineral matter. There is some organic 
