. Principles of agricultural chemistry [microform] . cago. At the end of the glacier is deposited a mixture of earth androcks of all sizes, which is known as a moraine. When thecoming of a higher yearly temperature causes the front of aglacier to retreat, it leaves the surface of the earth covered withthe mixed deposit characteristic of glaciers. The deposit beneaththe glacier, which is called till, is sometimes an extremely dense,stony clay, having been compacted under the pressure of themoving ice. 70 PRINCIPLES OF AGRICULTURAL CHEMISTRY The northern part of the United States was once covere
. Principles of agricultural chemistry [microform] . cago. At the end of the glacier is deposited a mixture of earth androcks of all sizes, which is known as a moraine. When thecoming of a higher yearly temperature causes the front of aglacier to retreat, it leaves the surface of the earth covered withthe mixed deposit characteristic of glaciers. The deposit beneaththe glacier, which is called till, is sometimes an extremely dense,stony clay, having been compacted under the pressure of themoving ice. 70 PRINCIPLES OF AGRICULTURAL CHEMISTRY The northern part of the United States was once covered by agreat glacier sheet, stretching down from Canada. Glacial soilsare accordingly found in New York, Ohio, and other NorthernStates. Some of these deposits have been reworked by riversuntil their glacial characteristics are no longer easily soils are especially important in New York and statesnorth of it, and in the states north of the Ohio and Missouririvers. They frequently contain considerable amounts of car-bonate of Fig. 20.—Hypothetical map of glacial sheets of NorthAmerica. Salisbury. The waters from the melting of the glacial sheet also carriedground-up material. Though this was sorted by the water, it isdifferent from ordinary alluvial soils. These soils are found inthe area adjacent to the glacial regions. Loess, finely ground material derived from glacial drift andtransported by winds or flowing water, consists of grains ofquartz, feldspar, mica, hornblende, with some limestone and clay. ORIGIN O? SOIIvS 7r Wind Blown Soils.—In any region where the soil becomes verydry and is not covered with vegetation, as in deserts or aridsections, the soil particles may be taken up by wind, and perhapscarried considerable distances. The attrition of the wind-borneparticles reduces the softer minerals rapidly to dust, and harderminerals, such as quartz, more slowly. The dust and sand areseparated, as the dust is carried farther. Wind-borne desertsa
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