1020 A TREATISE ON METAMORPHISM. 



gaseous solutions. But it would not follow that the aqueous solutions 

 precipitating the ores do not receive contributions of gases, water, and 

 metals from the contiguous igneous rock as it crystallizes and continues to 

 cool after crystallization. 



CIRCULATION IN ZONE OF ANAMORPHISM. 



In the zone of anamorphism the conditions are very different. Here 

 the openings are normally minute and disconnected, although locally and 

 for a brief time of active intrusion they may be large and continuous. 

 The amount of water in the surrounding rocks is very small, and the 

 openings are so minute that it can not make its way readily toward the 

 igneous masses. Consequently there is in this zone no condenser available 

 to transform the gaseous solutions to the liquid condition. The temperature 

 is certainly high, probably often above the critical temperature of water, 

 because of the normal increase of temperature due to depth, and because 

 of the high heat of the igneous rocks. Under these conditions it is natural 

 to suppose that adjacent to the igneous rocks gaseous solutions are produced 

 in considerable quantity, probably largelv as emanations from the igneous 

 rocks, but also to an important extent by transformation to the gaseous 

 condition of the free water of the adjacent rocks and of the water liberated 

 by the process of dehydration. Gaseous solutions would utilize the large 

 openings temporarily formed to the fullest possible extent. It has been 

 explained that the gaseous solutions, having very little viscosity and under 

 the great pressure of this zone, make their way through the minute open- 

 ings of the rocks and even between the individual mineral particles. The 

 gaseous solutions emanating- from the igneous rocks and produced from 

 the surrounding rocks may contain metallic material in considerable 

 quantity. Such gaseous solutions from various sources would deposit 

 minerals in the larger openings precisely as do aqueous solutions under 

 similar circumstances. Ores would probably be deposited even more 

 extensively as impregnations in the minute openings of the adjacent rocks. 

 The places where precipitation occurred would be controlled in part by 

 the strength of the rocks, rigid rocks furnishing openings of a larger size 

 than those which are more plastic. The localization would be very largely 

 controlled also by the composition of the rocks. If they were able to 

 take part in a reaction which would result in a precipitation, this would 



