CHAPTER III. 



THE AGENTS OF METAMORPHISM. 



GENERAL STATEMENT. 



The agents through which the alterations of rocks take place are 

 gaseous and liquid solutions and organisms. Solutions are the special 

 subject of this chapter. Organisms are influential only in the belt ot 

 weathering, and their action is therefore considered in connection with that 

 belt. (See Chapter VI.) 



The circulation and work of solutions involve a consideration of the 

 circulation and work of the gases of the earth, of which the atmosphere is 

 the dominant portion, and a consideration of the circulation and work of the 

 water of the earth, of which the ocean is the dominant portion. While the 

 circulation and work of the atmosphere and of overground water may from 

 a purely theoretical point of view be considered as a part of a treatise on 

 metamorphism, the work of these epigene agents is the subject of that 

 division of geology which has been named physiography, and as the work 

 of the atmosphere and overground water is so fully dealt with in connection 

 with that subject, this branch of metamorphism will not be discussed here 

 at all. But the circulation and work of underground gas and water solu- 

 tions are of fundamental importance in metamorphism and must be some- 

 what fully considered. 



Gas and water below the surface in the openings of the rocks will be 

 called ground gas and ground water, to discriminate them from gas and 

 water above the lithosphere. 



Solutions ' ' are homogeneous mixtures which can not be separated into 

 their constituent parts by mechanical means.'" 1 The properties of solutions 

 vary continuously and regularly with the concentration. 6 Under the 



f'Ostwald, W., Solutions, translated by M. M. Pattison Muir; Longmans, Green & Co., London, 

 1891, p. 1. 



'^Cameron, F. K., Application of the theory of solutions to the study of soils: Rept. No. 64, Field 

 Operations of the Division of Soils, 1899, U. S. Dept. of Agric, 1900, pp. 142-143. 



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