8 BULLETIN 355, U. S. DEPARTMENT OE AGRICULTURE. 
and frequently filling valleys beyond the ice border with gravel, sand, 
and finer sediment to a depth of from 50 to 200 feet. 
Glacial soils, as would be supposed, vary widely in their productive 
capacity, and the management of soils within the glacial area is often 
difficult because of the wide differences in soil types which may occur 
even within the boundaries of a single farm. 
Wind-formed soils — Loess (Ref. Nos. 2, pp. 68-69; 3, pp. 59-61). — 
It is a familiar fact that the atmosphere carries suspended a consid- 
erable quantity of fine dust particles and that after rains and snows 
the air is left clearer because much of the dust has been carried to the 
earth by the falling raindrops or snowflakes. During high winds, 
when the land surface is dry and not covered by vegetation, the air 
frequently becomes so laden with fine soil that one can see for only 
a short distance. Where windbreaks occur these soil grains are often 
deposited in large quantities, forming soil drifts of varying character. 
The sand dunes bordering the shores of the Great Lakes are of wind 
formation. On the Great Plains of the western United States, where 
the soil is dry and heavy winds are common, considerable damage is 
often done to farms by the transportation and drift of soil from 
place to place. 
Loess is a type of soil of a fine, silty composition, which commonly 
contains a considerable amount of calcareous materials. Loess has a 
peculiar ability to stand in nearly vertical walls when eroded by wind or 
stream. Such soils are unusually uniform, both in physical and mineral 
composition, and possess high natural fertility. An extensive area 
of typical loess soil is found in the Chinese Empire, where the material, 
as above described, extends to the depth of 1,000 feet or more. This 
immense deposit is generally believed to have been transported by the 
wind. The so-called loess soil of the United States, however, extending 
over much of the Mississippi Valley, is commonly believed to have 
been transported largely by water. Its depth varies from a few feet 
in the outer edges of the area to 150 feet, or more, in the more central 
portions. 
EXERCISES, LESSON I. 
Materials needed. — Samples of typical soils found in the community, including marsh 
soil, if any; hand lens; long pickle bottles with corks; a few pieces of rock candy 
(this can be secured at the local store); specimens of common rock, such as granite, 
trap rock, schist, shale, slate, limestone, marble, sandstone, and quartzite; specimens 
of common rock-forming minerals — feldspar, hornblende, quartz, black and white 
mica, calcite, and gypsum. 
ROCKS AND MINERALS. 
(a) Examine carefully the rock-forming minerals — feldspar, quartz, hornblende, 
mica, and calcite. Compare relatively their weight, then note color and plane or 
direction of cleavage of each, after which determine their relative degree of hardness. 
The relative hardness can be determined by scratching each with the others. 
