GEOLOGICAL CLASSIFICATION OF SOILS 35 



of fact, there is probably a greater difference in age be- 

 tween the soils of the Piedmont Plateau and those of 

 the Great Plains Region than has elapsed since the latter 

 were formed. The soils of the Piedmont Plateau have 

 been formed mostly from gneiss and schist. In fact, 

 the Piedmont Plateau is the remnant of the old continent, 

 Appalachia, wliich was in existence in early Cambrian 

 times. The rocks of the Appalachian Mountains and 

 Plateaus are limestone, sandstone, and shales. The Great 

 Plains Region presents limestone, sandstone, and shale 

 of the Cretaceous, Permian, and Carboniferous ages, be- 

 sides much unconsolidated material. The soils of these 

 provinces, extending as they do over great areas, vary 

 within wide limits due to rock formation, climatic con- 

 ditions, and ag^; yet certain common characteristics, 

 as already pointed out, are exhibited by all. 



27. Cumulose soils. — This type of soil is of a very 

 different character from the one just imder discussion, 

 beinff made up largely of organic matter with the mineral 

 constituents of secondary importance. At relatively 

 recent periods shallow lakes, ponds, and basins were 

 formed, partly by stream action, partly by marsh con- 

 ditions along sea or lake coasts, or, what is commoner in 

 the northern part of the United States, by glaciation. 

 Any basin that contains water throughout the year serves 

 as a place for the formation of cumulose soil. The highly 

 favorable moisture relations along the banks and shores 

 of such standing water encourage the growth of many 

 plants such as algse, moss, reeds, flags, grass, and the like. 

 These plants thrive, die, and fall down only to be covered 

 by the water in which they were growing. The water 

 shuts out the air to a large extent, prohibits rapid oxida- 

 tion, and thus acts as a preservative for the rapidly collect- 



