EOLIAN GEOLOGY 
163 
over an area equal nearly to one-fifth of that of the United States. 
Throughout these days all work in the cities was carried on by 
gas-light just as if it were night, and street lamps remained burn¬ 
ing continuously for more than seventy hours. The dense drift¬ 
ing dusts made traveling impossible. Breathing at times became 
difficult. Neither man nor beast ventured forth except when ab¬ 
solutely compelled to do so. Impalpably fine soil sifted in through 
every crack and crany of the dwelling houses. Dust was every¬ 
where. In all respects this great gale was a typical desert simoon. 
Desert conditions were especially set for this great dust storm. 
For some weeks previously the winter snows had disappeared from 
' off the ground. There had been a long spell of exceedingly dry 
weather for this time of the year. Vegetation had not yet begun 
to spring forth. After the winter’s freezing the soil had become 
exceptionally pulverulent. All over the bared plains between the 
Rocky Mountains and the Mississippi River the same conditions 
prevailed. 
As this strong gale set in from the west, over ground thus 
especially prepared for it, prodigious quantities of fine soil were 
at once set in motion and driven eastward in a stream 600 miles 
wide and thousands of feet high. The bottom of the air current 
was as thick with sediment as a river current at flood time and 
was rushed onward ten times faster. Besides the fine soil mate¬ 
rials floated forward on the wings of the wind vast volumes of 
sand and even coarse rock-waste were propelled along the surface 
of the ground accumulating in protected places, after the manner 
of snow-drifts, in tremendous dunes. In myriads of situations on 
the bare prairies, or in the plowed fields, the soil was removed 
over many square miles to depths of three or four inches to a foot 
or more. In arid lands simoons of this description, occurring 
month in and month out throughout the year, give some slight 
conception of the vast potency of wind-scour in the favored situa¬ 
tions of the deserts. 
Aside from the great interest which such dust storms have, as 
exemplifying the efficiency of eolic powers of erosion, the imme¬ 
diate results have a direct bearing upon the rate of continental 
depletion. The measurement of the sediment carried to the 
ocean by large rivers, as the Mississippi River, utilized by Hum¬ 
phreys and Abbot, instead of being a guage of regional denuda- 
