SUPERPOSITION AND THE LAW OF REGULARITY IN STRATAL ORDER—KEYS TO THE PRACTICE AND THEORY OF GLOBAL STRATIGMPHY

Abstract

In petroleum geology, the widespread practice of mapping lateral variations of lithology within the confines of general formations instead of time‐zones inevitably provokes differences of opinion over the scope and definition of stratigraphy. These differences can be traced back to a blending together of the separate concepts of two founders of geology, William Smith and Abraham Gottlob Werner. Werner originated a lithologic definition of rock formations; also, he taught the concept that the relative ages of formations could be determined by fossils. Smith contributed to the development of stratigraphy with his invention of the term ‘stratigraphical’, which referred to the occurrence of specific fossils and rock types within units of strata.The outcome of reconciling these different concepts has been that geologists have used Smith's basic terminology, the principle of superposition, and the formational units of stratigraphy, but have redefined them to accord with Werner's theory of Earth history. These changes in definition have confused the concept of stratigraphy, because they misrepresent its spatial form evident from ‘regularity in stratal order’. This general law was accepted by William Smith as the basis for his stratigraphical arrangement of rocks and fossils, which in the practice of correlating rocks by superposition led to a stratigraphic system of strata and the economy of a single stratigraphic scale.