ABSTRACT
The main objective here is to understand why soils are stratified into horizons and why they retain this structure during their development. For this we shall develop what we call the weathering-front model. It forms the central and unifying principle of this entire work. Then we will study the fine mechanisms that can explain this vertical structuration. This chapter could have been titled ‘modelling’. It is particularly difficult compared to the others that are illustrated with many observations made in the natural environment. But it is essential to devote the necessary time to it because it facilitates understanding of the rest of the volume.
