124 A TREATISE ON METAMOEPHISM. 



The water in rocks may completely or partly fill the openings. Where 

 the openings of a rock are completely filled, the rock is saturated. Unless 

 all the openings in a rock are subcapillary it will remain saturated only 

 so long as it is surrounded or partly surrounded by the saturating liquid. 

 If withdrawn from the saturating liquid, all the water may be drawn 

 off by ordinary physical means except that adhering to the walls of the 

 openings. This residual amount of water is called the water of imbibition. 

 The difference between the water of saturation and that of imbibition, 

 which, as will be seen, is the water which may flow somewhat readily, may 

 be called the water of hygrometricity. In the rocks having subcapillary 

 openings (see pp. 143-146) the attraction extends from wall to wall, and 

 therefore the entire film of water in the spaces adheres to the rock particles, 

 or is water of imbibition. In the rocks having subcapillary pores only, the 

 water of imbibition and saturation is the same. 



The next question which arises is as to the source of the ground water. 

 On pages 661-668 reasons are given for the belief that the circulation in the 

 zone of anamorphism, which corresponds to the zone of rock flowage, is 

 very slow indeed. In this deep-seated zone decarbonation, dehydration, 

 and to some extent deoxidation of the rocks take place. It is shown (see 

 pp. 764-766) that with these exceptions, excluding igneous rocks, the compo- 

 sition of the rocks metamorphosed in the zone of anamorphism closely 

 corresponds with their original composition, contrasting greatly in this 

 respect with the rocks metamorphosed in the zone of fracture. From these 

 and other facts it is certain that the circulation of water in the zone of 

 anamorphism is very slow. However, it is probable that a large portion of 

 the carbon dioxide and water liberated slowly makes its way into the zone 

 of fracture. It is also explained that some water may join the zone 

 of fracture through the agency of igneous rocks which enter this zone. 

 But the amount of these supplies of water at any one time is small — indeed, 

 insignificant compared with the amount required to keep up the active 

 circulation which we know exists in the zone of fracture. Since, then, it can 

 not be shown that any considerable fraction of the water of circulation of 

 the zone of fracture is derived from the zone of rock flowage, we can only 

 suppose that this water is derived from precipitation. The subterranean 

 water is therefore predominantly of meteoric origin. 



