. Soils, their properties and management . the United States is not wide, although 42 SOILS: PROPERTIES AND MANAGEMENT these soils exist along almost every stream east of theGreat Plains Region. Their best and widest develop-ment is found, as the map indicates (See Fig. 4) alongthe lower Mississippi river, where they may often showa lateral extension of one hundred miles. Extensions ofthis band are noted along the jNIissouri, Ohio, and IpperMississippi rivers. All streams flowing east exhibitareas of such soils, these areas varying with the size andvelocity of the stream. The soils of the allu
. Soils, their properties and management . the United States is not wide, although 42 SOILS: PROPERTIES AND MANAGEMENT these soils exist along almost every stream east of theGreat Plains Region. Their best and widest develop-ment is found, as the map indicates (See Fig. 4) alongthe lower Mississippi river, where they may often showa lateral extension of one hundred miles. Extensions ofthis band are noted along the jNIissouri, Ohio, and IpperMississippi rivers. All streams flowing east exhibitareas of such soils, these areas varying with the size andvelocity of the stream. The soils of the alluvial province may be divided undertwo heads because of topographic differences — (1) thefirst bottoms, or present flood plains ; and (2) the terraces,or old flood plains. These soils differ in their elevation,drainage, and age, but their general characteristics aresimilar; the surface features in both cases vary from a flatto a gently rolling topography (Fig. 6). Erosion, especiallyin the terraces, may have obliterated some of the out-. FiG. 6. — Cross-section of typical alluvial soils. (o), bed rock;(r), stream; (6), present flood plain, a recent alluvial soil; (c), floodplain terrace; (d), very old stream terrace, an old alluvial soil. standing features. Alluvial soils, being very rich, areparticularly adapted to trucking crops, although in mostcases they are utilized for more extensive farming. Whenwell drained and protected from overflow, they are therichest and most valuable of soils. GEOLOGICAL CLASSIFICATION OF SOILS 43 31. Marine soils. — The sediments which are con-tinually being carried away by rivers are eventuallydeposited in the sea, the coarser fragments near theshore, the finer particles at considerable distances. Thislayer of material, varying in thickness, consists of stratifiedgravels, sands, and clays, and is of a rather recent agecompared with the residual soils. It has not becomeconsolidated as yet, because of insufficient pressure andtime. When such
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