380 TJic American Geologist. June, 1^599 
OBSERVATIONS ON DI RTSTORMS. 
By E. O. Hershey, Freejiort, 111. 
Note. — The following paper was written three years ago. It was communicated 
to the undersigned, who had intended to publish it elsewhere. Observations on the 
geological work of the wind are not often recorded and this paper is too valuable to 
escape publication, even if it has been delayed. It evidences the usual keen obser- 
vation and penetration of an author whose ability I highly appreciate. 
J. A. Udden. 
The recent "dirtstorm" which spread a thin sheet of wind- 
carried silt, derived from the dry soil of the great plains over a 
large part of the state of Illinois and contiguous areas, has 
aroused general interest in the subject. A few observations 
on this and several similar storms, which have occurred in parts 
of the great central basin of our country during the past few 
\ tars, may not be devoid of value in aiding in the final solution 
of the problems which these wide-spread distributions of dust 
present. 
Dirtstorms and sandstorms are of frequent occurrence at 
all seasons of the year on the great plains, and during the 
summer are by no means uncommon in Illinois. But the 
conditions are exceptional under which these clouds of dust are 
carried as far east as lake Michigan in mid-winter, when the 
greater portion of the Northwest is under a more or less con- 
tinuous covering of snow^ During several years residence in 
the city of Freeport in the northwestern portion of the state, 
only two storms of this character have been observed by the 
writer. The first occurred a little more than a week before 
the great storm and lasted only a few hours. It was accom- 
panied by a slight fall of snow of the blizzard variety and was 
brought by a moderately strong wind from a due westerly di- 
rection. The dust in the atmosphere presented the appear- 
ance of a haze or very thin fog of a light brown color. The 
color always distinguishes the presence of dust. When the 
haze is white it consists of water particles; when of a bluish 
tint, of carbon particles or smoke; and when of a distinctly 
brownish tint, the constituent particles are invariably an im- 
palpable dust. 
The great storm which has attracted so much attention, 
reached the city of Freeport shortly after noon on February 
18, 1896. During the forenoon there had beeen light flurries 
of snow, but by noon all snow clouds had disappeared from 
