Principles oh Structural Geology is designed to be a concise introduction to the deformation of the earth's crust, encompassing the wide-ranging subject matter of introductory courses in structural geology. Three principal aspects of structural geology are emphasized: The basic principles of natural rock deformation are presented in Part II, Principles of Deformation (Chapters 3,4, and 5), including stress, strain, and the physical processes of elastic, plastic, and brittle deformation of rock. These chapters present the basic principles of solid-state deformation to the level necessary to comprehend the main phenomena of structural geology