THE GENESIS OF LOESS A PROBLEM IN PLANT ECOLOGY. 
BY B. SHIMEK. 
The question of the origin of the loess of the Mississippi valley has attracted 
the attention of the geologists of the country for two-thirds of a century. The 
consideration of the question has been left almost entirely to geologists, who 
have offered various explanations of loess-formation, all based practically on 
physical grounds. 
The biological phases of the subject have been thus far approached almost 
exclusively from the faunal side. 
It is the purpose of this paper to briefly set forth a preliminary statement 
of the relation of plants to the formation of loess, and to call attention to the 
fact that the investigation of the problem of the genesis of loess lies within the 
province of the plant ecologist, for the study of plant relations throws light on 
several important phases of the subject, and incidentally strengthens the 
aeolian hypothesis.* 
That plants play an important part in modifying the materials of the surface 
of the earth is well known. They assist in comminuting soil and rock both me- 
chanically and chemically; they form an anchorage for flne materials brought 
both by wind and water, according to location; they prevent erosion of loose 
soils; by their decay they cause changes in the amount and distribution of the 
calcium carbonate and iron constituents of the soil; and Anally, they return 
their own substance to the soil in flnely subdivided condition.** 
All this results in an increase in the amount of flne materials which may be 
removed by wind or water, or in the building up of deposits where the vegeta- 
tion is sufficient to form an anchorage for the flne materials carried by these 
agencies. 
The study of these influences of plants, and of plant-distribution as deter- 
mined by environment, throws light on the following questions related to loess- 
formation by aeolian agencies: 
I. Distrihution of loess. 
(a). It explains the greater thickness of loess on higher grounds near larger 
streams, where vegetation is more abundant because of the advantages offered 
by both the greater elevation and the more abundant plant-covering, thus form- 
ing an anchorage for the dust carried up from the adjacent bars on which the 
supply of dust is renewed by each succeeding flood. That vegetation was more 
abundant in this territory during the deposition of loess, as now, on elevations 
near the large streams is shown by the greater abundance of strictly terrestrial 
plant-feeding mollusks in the loess now occupying these elevations, the modern 
* See writer’s previous suggestions in Bull. Lab. Nat. Hist. , St. Univ. of Iowa, vol. V, 
pp. 341, 359, 360, etc.; 1904 
** See writer’s paper, Proc. la. Scad. Sci. , vol. X, pp. 41-48, 1903. 
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