8 BULLETIN 355^ U. S. DEPARTME]SI"T OF AGEICULTURE. 



and frequently filling valleys beyond the ice border witb 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 famihar fact that the atmosphere carries suspended a consid- 

 erable quantity of fime 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-caUed loess soil of the United States, however, extending 

 over much of the Mississippi VaUey, 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 

 Boil, 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, quai'tz, black and "white 

 mica, calcite, and gypsum. 



BOCKS 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 determiue their relative degree of hardness. 

 The relative hardness can be determined by scratching each ^Tith the others. 



