In the development of geological thought it was but natural that attention should at first be largely directed to dynamic phenomena and agents and to the structures resulting from their activity, and that geologists should be chiefly occupied with the elucidation of these structures. True, the stratified rocks of the earth’s crust have called forth speculation from the very beginning, but mainly on account of their fossil contents. Questions of classification and correlation of the formations based on superposition and on the inclosed organic remains have to a large extent engrossed the attention of the stratigrapher since the days of Lehman and William Smith. That the characters of the rocks themselves could be of any significance seems to have been realized by few, and these few considered such characters generally only from a special, often only a mineralogical, viewpoint. More recently the phenomena of alteration or metamorphism of sediments have . . .