32 A TREATISE ON METAMORPHISM. 



reasonably full and satisfactory knowledge, not only of the known principles 

 of geology, but of the observed phenomena in the parts of the world which 

 had been studied. While by many years of work a geologist may still be 

 able to learn the important facts concerning various provinces, it is no 

 longer possible for one man to have anything like complete information as 

 to the local geology of many parts of the world. Not only is this so, but 

 no one geologist can know all the important discovered facts concerning a 

 particular branch of geology. Moreover, in recent years the accumulation 

 of facts has gone on much faster than the development of geological theory. 

 Nowhere is this more true than in the branch of geology known as 

 petrology, and in petrology it is perhaps more true of the phenomena of the 

 alterations of rocks than of any other. Scarcely a paper on petrology 

 appears that does not contain some account of the alterations of minerals or 

 of rocks, but in most cases there is no serious attempt to arrange the observed 

 phenomena in order under recognized principles. Indeed, there is no 

 general set of recognized principles under which the phenomena can be 

 reduced to order. 



Some years ago, finding myself lost in the vast accumulation of data, 

 I began to formulate principles applicable to the alterations of rocks. The 

 result of this work is the present treatise, which is an attempt to reduce the 

 phenomena of metamorphism to order under the principles of physics and 

 chemistry, or, more simply, under the laws of energy. It is but a part of 

 the larger task of reducing to order under the same laws the entire subject 

 of physical geology. 



As a result of the development of the science of petrology, especially 

 microscopical petrology, it has been ascertained that changes are continu- 

 ally occurring within the rocks constituting the outer part of the earth. 

 This statement is equally applicable to the most porous rocks at the surface 

 of the earth and to the densest rocks as deep below the surface as observa- 

 tion gives exact knowledge. All changes, by whatever forces, agents, and 

 processes caused, and in whatever classes of rocks occurring, whether 

 solidified magmas, chemical precipitates, organic deposits, or mechanical 

 deposits, may be called metamorphism. 



Metamorphism, as here used, means any change in the constitution of 

 any kind of rock. 



It will be shown that at any given time and place, under any given 



