A flood plain, where alluvial soil has been deposited by the river.
Long ago the northern part of our country was covered with a sheet of ice. This ice crept slowly southward, and as it moved along it tore off all the soil and loose rocks on the surface of the earth over which it passed. When it melted it left them spread roughly over the country. Such material forms glacial soil. It is often deep but not very rich.
U. S. Geological Survey
Soil brought by a glacier and deposited as the ice melted.
There is another kind of soil, formed by the wind. If you have ever been in a dust storm you have seen the fine, powdery substance that settles over everything and creeps into the smallest cracks. In some countries where there are strong winds and not much rain there is little vegetation on the surface to hold the soil. Year after year the winds pick up particles of the dusty soil, whirl them high in the air, and do not let them down again until they have been carried many miles. In some far-off land where the winds go down the dust particles settle again to the earth. After a long, long time, enough dust collects to form a thick layer of the richest soil. This is called æolian soil, from the word Æolus, meaning the "wind."
There is one more kind of soil which we ought to know about; that is peat soil. It is found in marshy or swampy lowlands and is formed largely of plant remains. When lands with such soil are drained, they prove very rich.