EXTENSION COURSE IN SOILS. 71 
for pasture. This seriously lessens their value for such crops as sugar 
beets, cotton, or corn, which grow through the whole summer. On 
the other hand, some small grains, which make their growth very 
early in the season, are better adapted to such land. Crop rotation 
for light soil should be short. Many of the best rotations are of but 
three years' duration. 
Live-stock farming on sand. — The use of pasture is still, and prob- 
ably will long remain, an important factor in most lines of live-stock 
farming. This is partly because in grazing, stock harvest their own 
feed, and in this way greatly lessen the expense for labor. Since 
sandy soils, as we have seen, are poorly adapted to pasture grasses, 
they are not as well suited to most lines of live-stock raising as are 
heavier soils. However, it is frequently the case that considerable 
quantities of produce, grown in connection with truck raising on sandy 
soils, are not marketable and should be fed to some form of live stock. 
A small number of live stock, therefore, should usually be kept, even 
on sandy farms, the principal business of which is the growing of 
truck or vegetable crops. 
CLAY SOILS. 
Formation and location. — Clay soils are commonly formed by the 
settling out of fine sediment in standing bodies of water into which 
streams carrying the sediment have run. Such areas of standing 
water occur as lagoons along main river valleys like those of the 
Mississippi, Ohio, Missouri, and other large rivers. They were also 
formed in extensions of the Great Lakes winch existed toward the 
close of the glacial period. Broad belts of extremely heavy clay soils 
were formed in this way along the southern shore of Lake Superior, 
along Lake Michigan in Wisconsin, and on the southern borders of 
Lake Erie and Lake Ontario. Many shallow lakes existed for a 
comparatively short time at the close of the glacial period. In these 
great areas heavy clay soils were formed. Lake Agassiz in Minnesota, 
North Dakota, and Manitoba (long since dried up) is one of the best 
illustrations of the formation of heavy clay soils. The clay soil of 
the Champlain Valley in New York has its origin in the same way. 
Some areas of heavy clay soil have also been formed along the sea- 
shore as deltas and in bodies of salt water formed by shutting off the 
main portion of the ocean. As stated in Lesson I, a residual soil from 
limestone is also an extremely fine clay. This is because the soil is 
made up of the insoluble portions of the rock, the soluble portions 
having been dissolved and carried away by percolating water. 
Characteristics of clay soils (Ref. No. 7, pp. 95-99). — Clay soils owe 
their special character largely to their very fine texture. Their large 
water-holding capacity and poor underdrainage is the immediate 
result of this texture. As a secondary result they often have poor 
tilth and are liable under certain conditions to be cold during the 
