Coal as a recorder of incipient rock metamorphismy

If the evidence presented in the body of this paper is accepted, there seems to be no question that eight stages in the metamorph-ism of coal can be recognized and explained by the processes that have been active in the earth coincident with the development of plant life on the land; and that at least six of these stages have left few if any marks on the composition or physical appearance of the sediments associated with the coal, therefore, they may be classed as incipient stages of rock metamorphism.