THE STRUCTURE OF THE FORMATION
331. Since all the structures exhibited by formations, such as zones, layers, consocies, etc., are to be referred to zonation or alternation, these principles are first considered in detail. This, then, constitutes the basis for a consideration of the structure of a normal formation, with special reference to the different parts that compose it. The investigation of formational structure, since the latter is the result of aggregation, invasion, and succession, is accomplished by instruments, quadrats, etc., in the manner already indicated under development, and no further discussion of it is necessary here.