at high temperatures and at pressures such as prevail from the earths surface to a depth of perhaps 20 km. This impression must necessarily be marred and blurred by omissions and misinterpretations on the part. Of the authors, for it is based on data (of field association, mineralogy, chemistry-end fabric of the rocks themselves) too voluminous to be grasped and adequately handled by one or even two students. More-over, its limitations reflect the prejudices and necessarily restricted geological experience of two individuals.