ABSTRACT
Differentiation of catenas ƒ The soils on slopes are often arranged in a typical manner from the top to the bottom and are genetically linked. Those on the upper slope supply to those of the bottom: (i) water, (ii) ions and/or (iii) solid materials. Then we have a soil chain or catena. Let us take an example. Granite is an impermeable rock, but the soils it gives rise to in temperate environments are sandy and permeable. In this situation, the lateral circulation of water and other constituents is facilitated. The soils are thus strongly differentiated laterally, a phenomenon observed as early as in 1600 by Olivier de Serres (Legros 1973). From top to bottom of the slope (Fig. 2.11) the soils get deeper and deeper, more and more moist, and also less and less acid because of lateral movement of basic cations (calcium, sodium, etc.). But the increasing thickness of the soil is not only because of transport of materials on the slope. It also results from an especially vigorous weathering in the lower slopes where the environment is wetter.
