44 



jenny. ORIGIN OF SOILS 



[Ch. 2 



probably correct provided that very resistant rocks such as granite, 

 porphyry, quartzite are considered. Softer rocks, like certain sand- 

 stones and shales, weather much more rapidly. In unconsolidated 

 materials such as loess, sand dunes, moraines, alluvial deposits, and 

 volcanic ash layers, visible profile development may take place in a 

 few centuries or even decades. 

 Examples of the chronofunction 



s = f(time)ci, , r , p 



are given in Fig. 2 for the s-property calcium carbonate (CaC0 3 ). The 

 curves refer to the leaching of CaC0 3 from the surface layer of English 



'1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 



J-*. 



100 150 200 250 300 350 400 

 Age of soil in years 



Fig. 2. Time functions of leaching of calcium carbonate in English sand dunes 

 (Salisbury) and Dutch clay polders (Hissink). 



sand dunes and Dutch clay polders (Jenny, 1946). In the cool, humid 

 climates of England and Holland, about 300 years are required to free 

 the surface soil of lime. 



An example of a chronosequence of depth functions 



E (s) = f(time)ci,o,r, P 



is presented in Fig. 3. The three soils Yolo, Zamora, and Hillgate 

 were formed on alluvial material derived from sedimentary rocks, in a 

 climate having mild, humid winters and hot and dry summers (Cali- 

 fornia). The vegetation is grass. The relative age of these soils is in- 

 ferred from the physiographic positions of the alluvial fans and ter- 

 races. Yolo is the youngest soil; Hillgate the oldest. It may be no- 

 ticed that the density of the subsoil {B horizon) increases as the soils 

 become older. 



