Chapter 2 

 ORIGIN OF SOILS 



Hans Jenny 



Division of Soils 



University of California 



Berkeley, California 



WHAT IS SOIL? 



To the geologist and the engineer Ramann's definition of soil ap- 

 pears familiar: "The soil is the upper weathering layer of the solid 

 earth crust." However, Ramann's definition fails to stress the con- 

 cept of the soil profile. Contrary to common belief, soil is not a ran- 

 domized aggregate of inorganic and organic particles. Soil is a body 

 possessing definite organization. Soil has vectorial properties. Along 

 an imaginary line extending from the surface of the soil toward the 

 center of the earth (2-axis), the sequence of soil properties differs pro- 

 foundly from that along lines parallel to the surface. Soils have a 

 profile. 



Profile characteristics of soils may be conveniently displayed by 

 soil property -depth functions as illustrated in Fig. 1. The zones of 

 maxima and minima are designated as horizons. The surface soil, 

 which has lost material to the lower strata, is labeled A horizon (A 1} 

 A 2 ), whereas the lower soil stratum, which has gained substances, is 

 denoted B horizon (B±, B 2 ). The zone underlying the B horizons is 

 called C horizon (Ci, C2). It may correspond to the original rock or 

 parent material. 



FACTORS IN SOIL FORMATION 



On the earth as a whole, there are millions of different soils or, more 

 specifically, different soil profiles. Yet, in spite of an apparent hit- 

 and-miss pattern of soil distribution, a certain regularity in the occur- 

 rence of soils is discernible. It is of two kinds. First, similar types 



41 



