This text describes a new analytical approach to petrology, the study of the origins, morphology and classification of soils. It examines the chemical weathering that occurs through the interaction of rain and underground water with consolidated rocks, dealing with the subject from the microscopic scale right up to the landscape scale. The author includes an overview of major weathering processes and discusses the supergene (near the surface) alteration of rocks and minerals, structural transformations, transfers and accumulations of soils and the evolution of pedological mantles. The text arrives at a number of conclusions regarding soils as a reflection of the past and present.