1018 A TREATISE ON METAMORPHISM. 



relative importance in gaseous and aqueous solutions. Therefore the two 

 classes are considered separately. It will be seen that in the belt of 

 cementation aqueous solutions are probably of predominating importance 

 and gaseous solutions very subordinate, and that in the zone of anamor- 

 phism gaseous solutions are of dominating importance and aqueous solu- 

 tions subordinate or unimportant. 



CIRCULATION OF GASEOUS SOLUTIONS. 



The general circulation of gaseous solutions is a function of the 

 amount of gaseous solutions, of the absolute temperature of the gaseous 

 solutions, of the amount of aqueous solutions adjacent, of gravity, and of 

 the form, continuity, size, and amount of the openings. 



The general principle which controls the movement of gaseous solu- 

 tions is that the gases move from places of high pressure to places of low 

 pressure. The expansive force of a given amount of gas in a given volume 

 is directly proportional to its absolute temperature. Other things being 

 equal, gaseous solutions tend to pass from places of high temperature to 

 places of low temperature. The higher the temperature the greater its 

 expansive power, and the more forceful its movement toward places of low 

 temperature. Therefore heat is a fundamental force in the circulation of 

 the gaseous solutions. Gravity, of the A^ery greatest importance for aqueous 

 solutions, is of importance also for gaseous solutions. So far as gravity is 

 concerned, the same principles apply to gaseous solutions and aqueous 

 solutions. The heavier column of gas pulled by gravity descends and the 

 lighter column is forced to rise. Where the columns are of equal length 

 that of lower temperature descends and that of higher temperature rises. 



The circulation of gaseous solutions in the zone of fracture and in the 

 zone of flowage is very different. Moreover, the circulation in the belt of 

 weathering 1 is different from that in the belt of cementation. 



CIRCULATION IN" BELT UK WEATHERING. 



In the belt of weathering the law of gravity practically controls the 

 circulation. Where the temperature of the gases is higher than normal 

 they rise, being driven up by the greater pressure of the adjacent cooler 

 air. Thus, above the level of the ground water, wherever heated gaseous 

 solutions are produced they rise in columns of steam, as in the case of 

 fumaroles and solfataras and in connection with volcanic action. 



