Reconstitution processes in shales, slates, and phyllites

Abstract

It is the author's good fortune to collaborate with Dr. J. W. Evans in describing the rock specimens which he collected on the expedition to Caupoliean in Bolivia during 1901-2. These specimens contain a very large proportion of shales, slates, and phyllites, and in their investigation certain petrographic methods devised for a detailed study of the slates of North Wales, Devon, and Skiddaw were followed. The present paper is intended primarily to describe these methods as applied particularly r the Bolivian rocks and to a Skiddaw slate facies which, for purposes of comparison and contrast, is of special interest. It is not suggested that between groups of rocks from places so widely separated as Bolivia and Skiddaw close correlation is possible; the products of the reconstitution processes which the two groups record differ considerably in detail; but as providing data for the study of the mechanism of these processes the two groups can be conveniently examined together.