Soils 33 



lose. They are found in areas varying from a fraction of an 

 acre to thousands of acres. Any basin that contains standing 

 water throughout the year is a favorable place for the formation 

 of cumulose soil. The vegetation grows, dies, and is covered 

 by the water. The water, shutting out the air, prevents rapid 

 oxidation and, as a result, the organic matter is largely pre- 

 served and collects from year to year. The soil that eventually 

 forms is very high in organic matter. Muck soil is in a more 

 advanced stage of decomposition than peat. When drained, 

 areas of muck soil often are of immense value for certain crops, 

 especially celery, onions, and lettuce. 



Colluvial soils. Fragments of rocks and soil that are car- 

 ried to the base of cliffs by the force of gravity make up the 

 colluvial soils. Their area is small and the soil is usually 

 shallow and unproductive. They are found only in mountain- 

 ous or very hilly regions and as farm soils are not important. 



Alluvial soils. Along nearly every stream water-deposited 

 soil can be found. This is alluvial. The power of a stream 

 to carry sediment varies with the rate of flow, the more rapid 

 the flow, the larger the particles that can be carried. If the 

 flow of the stream that is carrying sediment is checked, some 

 of the sediment is deposited. When the river-beds are rela- 

 tively steep, deposits are usually narrow ribbons of coarse sand 

 or gravel. When the bed becomes less steep, the deposits are 

 wider and of finer material. Much humus is washed into 

 alluvial deposits and soils of this type are usually rich, of good 

 depth, and valuable for farming. 



Marine soils. Along the seashore, deposits of varying 

 thickness are made. When such deposits are elevated above 

 the sea, a condition that is often found, they are given the 

 name, marine soils. Most of these are sandy and are largely 

 used for vegetable-growing. Marine soils in the United States 

 extend along the Atlantic and Gulf Coastal Plains. 



Lacustrine soils. Sediment which has been deposited in 

 lakes may later, by the drying up of the lake, become soil. 



