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IOWA ACADEMY OF SCIENCE 
fine soil that it is often impossible to see objects more than very short distances. 
The sun is frequently obscured as by a heavy rain-cloud. The dust floats up- 
wards thousands of feet above the surface of the ground and remains suspended 
for many days. The amounts of fine materials that are thus carried away must 
be enormous. 
The tremendous effects of the dust-storm, or sand-storm, on the Sahara and 
Arabian deserts have been known since earliest historic times; but they have 
been looked upon as merely those of idle, shifting sands, rather than as a power- 
ful and persistent geologic force. Some of the geologic effects of the wind as a 
denuding power have been recently ably discussed by Walther,^ whose observa- 
tions were made on the northern African deserts. Similar wind effects on hare 
sand-bars of the Missouri river reproduce on a small scale in a humid climate 
the conditions of the great desert regions.^ 
Dust alone is not transported by the winds. Sands and pebbles are swept 
along with considerable force. On the bare rocks these act as a sand-blast, 
polishing the harder ledges until their exposed surfaces appear as if they were 
actually fused. Under the influence of streaming sands all rock-outcrops are 
worn rapidly away, at a rate many times faster than when corroded by running 
waters. During a single “storm” large areas of hare rock may be uncovered, 
exposed to the triturating action of the moving sands, and become again cov- 
ered before the winds die down. Shallow basins from a few hundred yards to 
several miles across may be hollowed out of the surface of the plains that may 
afterwards fill with storm-waters, producing lakes of temporary character. To 
some such cause Gilbert^ has ascribed the origin of certain ponds in western 
Kansas. In desert regions tne eolian genesis of minor lake basins is very much 
more prevalent than is commonly supposed. 
The formation of lake basins by means of the wind must be regarded after 
all only a special phase of a more general process. Among the larger effects 
of eolian action is general planation, a process holding in the arid region the 
same position as base-levelling does in the normal humid region. Under condi- 
tions of an arid climate shallow rock-floors could be expected in the basin- 
plains. Under conditions of a humid climate the interment plains would be 
deeply filled with detritus. In perfect accordance with this suggestion the sur- 
faces of the interment deserts are actually found to be worn out on the bevelled 
edges of the strata composing the substructure, in the same way that the 
peneplain is formed by water near sea-level. The process of general levelling 
without base-levelling in the arid country is probably more rapid on the whole 
than that producing penplanation. Much of the supposed leveling effect in 
the arid districts ascribed to sheet-flood erosion is doubtless more properly the 
result of eolian action. 
General levelling without base-levelling of elevated regions under conditions 
of an arid climate has been recently widely recognized. In southwestern 
United States the vast plains of New Mexico and Arizona, especially the Jornada 
del Muerto and neighboring deserts, were lately described in some detail.* 
1. Abhand. Konigl. f. Sach. Gesellsch. d. Wissensch., XVI Bd., 1901. 
2. Am. Jour. Sci. (4), Vol. VI, pp. 299-304, 1898; also Bull, de la Soc. Beige de geol., du 
pale., et hyd. , t. XII, pp. 14-21, 1901. 
3. Journal Geology, Vol. Ill, pp. 47-49, 1895. 
4. Am. Jour. Sci. (4), Vol. XV, pp. 207-210, 1903. 
