44 SOILS: PROPERTIES AND MANAGEMENT 



found. These soils are usually low in humus, and con- 

 sequently must be handled with reference to the possi- 

 bilities of increasing their organic content. Lack of 

 humus makes the predominating color of the soil light, 

 ranging from light gray to brown and dark brown. The 

 character of these soils is governed to some extent by the 

 origin of the sediments; different rocks, particularly if 

 weathered under different climatic conditions, may give 

 rise to widely different marine soils. The climatic con- 

 ditions to which marine materials are subjected after 

 being raised above the sea may also be a considerable 

 diversifying agency. 



33. Distribution of marine soils. — Marine soils are 

 found very widely distributed in the eastern United States, 

 and make up one of our most important soil provinces. 

 Beginning at Long Island at the north (See Fig. 4), 

 they extend southward along the coast in a band ranging 

 from one hundred to two hundred miles in width. The 

 western edge of the Atlantic coastal plain is marked by 

 the great " Fall " Line, or the edge of the old continent 

 Appalachia. It is from this area that most of the sedi- 

 ments of the Atlantic marine soils were derived. Proceed- 

 ing southward, we find that Florida is practically all of 

 marine origin, together with a great area of the Gulf 

 coast extending westward to central Texas and having 

 an average width of two hundred fifty miles. This 

 gulf marine soil is considerably younger than that of 

 the Atlantic coast. It is cut into two parts by the allu- 

 vial soils of the Mississippi, and is covered by a narrow 

 band of alluvial soil on the eastern bank of that stream. 

 The sediments of the Gulf coastal plain were derived 

 from the erosion and denudation of the old lands to the 

 northward. 



