42 NATURE AND PROPERTIES OF SOILS 



areas are found in the West as well. A glance at the soil 

 map of this country shows four great eastern and central 

 provinces — the Piedmont Plateau, the Appalachian Moun- 

 tains and Plateaus, the Limestone Valleys and Uplands, and 

 the Great Plains Region. The first three groups alone oc- 

 cupy 10 per cent, of the area of the United States. The age 

 of these soils varies in the order named, showing that, while 

 they are very old as compared with other soils yet to be dis- 

 cussed, there may be vast periods of geologic time between 

 their beginnings. As a matter of fact, there is probably a 

 greater difference in age between the soils of the Piedmont 

 Plateau and those of the Great Plains Region than has elapsed 

 since the latter were formed. (See Fig. 9.) 



26. Cumulose soils. — At relatively recent periods shal- 

 low lakes, ponds, and basins have been formed, partly by 

 stream action, partly by marsh conditions along sea or lake 

 coasts, or by glaciation, a common origin in northern United 

 States and Canada. The highly favorable moisture rela- 

 tions along the banks of such standing water has encouraged 

 the growth of many plants, such as algae, mosses, reeds, flags, 

 grass, and even larger types of vegetation. These plants 

 thrive, die and fall down to be covered by the water in which 

 they grew. The water shuts out the air, prohibits rapid 

 oxidation, and thus acts as a partial preservative. The decay 

 that does go on is largely through the agency of fungi and 

 anaerobic bacteria, that break down the tissue, and liberate 

 certain gaseous constituents. As the process continues the 

 organic mass becomes dark or even black in color. 



Accumulations of this nature are dotted over the entire 

 country. Their size may vary from a few acres to several 

 thousand. Along streams the old abandoned beds offer ready 

 opportunity for the beginning of such accumulations. 

 Marshes either salt or fresh often contain such deposits. 

 Shallow basins produced by the scraping or damming action 

 of glaciers are frequently occupied by such material. In the 



