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IOWA ACADEMY OF SCIENCE 
In other words, the term in question refers not to the origin of the de- 
posit, but to the nature of the material deposited. As a matter of fact, 
the nature" of the material indicates an aeolian origin for it; but not all 
aeolian material is loess. Unless it possess certain well-defined and 
easily recognized physical characteristics it cannot be defined by that 
term. What are the characteristics that must be present in order to 
constitute true loess ? 
1. The material is fine-grained and, with two exceptions to be noted, 
absolutely homogeneous. It is so fine-grained that, to quote the late 
Dr. Calvin, when crushed between the thumb and finger it has a 
“greasy” feeling. In other words, the individual particles are so small 
and so uniform that they produce no separate effect on the touch 
nerves. The material is a perfect powder. It has no grit. 
2. Because of its fineness, it is so light as to be readily transported 
by the wind; forming in fact an impalpable dust that! even in still 
air remains in suspension for a long period of time. 
3. Because of its homogeneous and uniform texture it is, when 
in mass, easily compacted. When so compacted it resists the action 
of erosion more perfectly than does the ordinary clay or sand of the 
glacial drift. This is shown especially well in the case of the Mis- 
souri valley loess, but is measurably true of all loess. 
4. The color is not an invariable factor, since it depends upon the 
source of the material, and the sources in different localities will vary. 
It is usually yellow, yellow-brown or brown, but the grey and grey- 
brown tints are not unknown. 
5. When in mass the loess is likely to contain lime nodules, or ‘ ‘ loess- 
kindchen.” These are often Jacking. Similar nodules are sometimes 
found in joint clay. Their presence does not prove the material to be 
loess. 
6. The loess is fossiliferous. It is this fact that first led to the now 
somewhat archaic theory of an aqueous origin. Since it has been shown 
that many of these fossils are land forms, and the others are such as 
frequent shallow prairie brooks and pools, or even “sloughs” and 
“draws” where the soil is perpetually damp, the aqueous theory has 
been largely abandoned in favor of the aeolian. An absolutely non- 
fossiliferous loess can be imagined, though the writer cannot find that 
such a loess has ever been found. 
7. The loess is often, but not always, stratified. The strata are 
seldom horizontal, but are irregular, or else are inclined to follow the 
contours of the pre-loessian hills. 
