Transported Soils

Transported soils are more numerous. Among the most important of these are the alluvial or water-made soils. These are rarely stony, are usually level, fine-grained and often very deep. Water usually leaves the soil it carries in more or less distinct layers; this "stratification" can often be seen in alluvial soils. The largest area of alluvial soil in the country is the flood plain or delta of the lower Mississippi. It reaches from the mouth of the Ohio southward for 1,100 miles. The whole area is flooded periodically and receives each time a deposit of the mud that gives the Missouri its Indian name, meaning "Big Muddy." It is exactly such conditions as this that have enabled the valley of the Nile to produce bountiful crops for 4,000 years without artificial fertilisation. The same process is responsible for thousands of meadows, swales, and swamps in northern United States, and it may be seen in action on the banks and at the mouth of every stream.

Alluvial soils are made mostly of very fine sand, and silt and clay. They vary greatly in chemical composition, but are usually very rich. Drift Soils. — Of even greater agricultural importance are "drift" soils, those that were formed by the action of the great ice sheet of the geologic past. They are distinguished from all others by having many rounded rocks or boulders, which were worn smooth and rounded by glacial action. Some drift soils are assorted or in layers, having been laid down by successive streams of water issuing from the ice; others are not in layers, having been deposited directly by the ice. The deposits of drift soil are not always spread evenly over the land. Sometimes the underlying rock comes to the surface, making patches of sedentary soil; sometimes drift soil is heaped into broad rounded knolls, from several feet to 300 feet high. These "morains" or "drumlins" are a distinctive feature in the farm landscape from eastern Massachusetts to North Dakota and north into British Columbia.

The average depth of drift soils is about 30 to 50 feet, but in some places it is 300 to 500 feet deep, and often it is merely a skim coat of seven or eight inches over the surface. As would be expected, the distribution of drift soils is very erratic. An acre may contain several wholly distinct kinds. There is a field of one acre near Lansing, Mich., in which about one-half of the soil is a stiff clay, one-fourth is gravelly loam and the balance, which was formerly a swamp, is muck. Who would try to advise the owner how to treat this field as regards tillage, fertilising, and draining ? All the variations in soils that affect the production of crops are not apparent on the surface; the character of the subsoil has a very important influence on the fertility of the surface soil. The subsoils of drift or glacial soils are extremely varied. The diversity of many of the soils of north-eastern United States may be judged from a report of James Geikie on the different kinds of soils that he found in a cut 355 feet deep, working from the surface downward:

Sandy clay 5 feet
Brown clay and stones .... 17 "
Mud 15 "
Sandy mud 31 "
Sand and gravel 28 "
Sandy clay and gravel 17 "
Sand 5 "
Mud 6 "
Gravel 30 "
Brown sandy clay and stones 30 "
Hard red gravel 4 " 6 inches
Light mud and sand 1 " 8 "
Light clay and stones 6 " 6 "
Light clay and thin block 26 "
Fine sandy mud 36 "
Brown clay, gravel, and stones 14 " 4 "
Dark clay and stones 68 "
Total 355 feet

This is probably more varied than most drift soils, but it shows the extent to which the ice, and streams of water produced by the melting of ice, have assorted and mixed the soils and soil materials of the Northeast. The value of drift soils for cropping is very variable, depending upon the material of which they are composed, and the way in which they are laid down. As a rule, however, they are fertile because they are composed of materials that have been brought together from several sources, and there is therefore greater likelihood that the essential plant foods will be present in abundance. They are apt to contain more sand or gravel and less clay than sedentary soils; hence they are usually of good texture and easily worked. But a drift clay or muck is not more valuable or manageable than a sedentary clay or muck. Those containing a fair percentage of clay are more valuable than those that consist chiefly of gravel. Wind-built Soils. — Still another type of transported soils — those built mostly by wind — is sometimes very valuable for cropping.

The wind-formed soils of Washington and Oregon are composed of fine basaltic ash. The loess and adobe soils discussed further on have been made partly by wind. More frequently, however, wind-formed soils are of little or no value, being composed mostly of fine sand ; and moreover, they may cover and ruin other soils that are valuable. On the southeast shores of Lake Michigan sand dunes 100 to 200 feet high have buried large areas of forest. The sand hills of Wyoming cover about 20,000 square miles of territory on both sides of the Niobrara River. These are a part of the "Bad Lands," a dreary waste of naked, rounded hills, composed chiefly of yellowish or grayish sand, or sandy clays blown by the wind, and extending over portions of Nebraska, Colorado, Wyoming, and Utah. The "Pine Barrens" of Michigan and of the Atlantic Coast are other illustrations of drift soils worthless for agricultural purposes.