ABSTRACT
Although there are many areas where the original rocks appear on the surface, a great part of the land surface is covered by rock particles in a superficial layer of varying thickness, which forms the skeleton of the soil. Soil is a complex structure and the range of living organisms, including micro-organisms, varies considerably. All soils possess a profile, often described in terms of ‘horizons’. Horizon A is the upper layer and hence the most weathered, horizon B is less weathered but contains fine soil particles and soluble substances washed in from above, while horizon C is practically unweathered. Weathering is a continual process, important in providing a supply of neutralizing bases and stabilizing the soil pH value. Very hard rocks, such as granite, weather very slowly and the supply of bases is inadequate to prevent acidification.
