112 A TREATISE ON METAMORPHISM. 



factors are taken into account the reactions take place in such a way as to 

 demand the expenditure of energy and the loss of a part of it. 



Whei-e chemical force, mechanical force, and high temperature work 

 together, with an abundance of water, as an agent of metamorphism, the 

 speed of rock metamorphism is very great as compared with the slow 

 alterations which occur at the surface of the earth. For instance, Barus 

 finds that water at temperatures above 185° C. and under high pressure is 

 capable of very rapidly uniting with glass, forming a new compound, which 

 at these temperatures is liquid, and which he calls water glass. In a retort 

 he combined 210 grams of glass and 50 grams of water in twelve hours 

 at a temperature of 210° C. into water glass, which was liquid at that 

 temperature, but became a clear solid at ordinary temperatures." 



Not only amorphous compounds but crystalline minerals also are acted 

 upon rapidly at such temperatures and pressures. At 180° C, with 

 pressure sufficient to keep the water in the liquid form, Lemberg 6 has 

 completely dissolved zeolites in pure water. Under similar conditions 

 it has also been shown that pure water acts rapidly upon powdered 

 anhydrous silicates. For instance, Forchhammer showed that water under 

 these conditions dissolves potassium silicate from powdered orthoclase." 



Within the zone of rock flowage temperatures and pressures higher 

 than those with which these experiments have been made are available, and 

 it is therefore to be supposed that in the zone of anamorphism there is rapid 

 transformation of the minerals to forms which are relatively stable under 

 the conditions obtaining at any given time and place. So far as substances 

 have not a compact state of aggregation energy is potentialized. Pressure 

 being a very potent factor, the transformations would of course be into 

 condensed systems, or into minerals having high specific gravity and 

 probably complex molecular structure. It is evident that in the forces of 

 chemical action, mechanical action, and heat, and the agent, water, we have 

 adequate causes for the crystallization of amorphous compounds, for the 

 recrystallization of strained minerals, and for the recrystallization of highly 



« Barus, G, The compressibility of liquids: Bull. U. S. Geol. Survey No. 92, 1892, pp. 78-84. 

 Hot water and soft glass in their thermo-dynanric relations: Am. Jour. Sci., 4th ser., vol. 9, 1900, 

 pp. 164-65. 



!l Doelter, C, Allgemeine chemische Mineralogie, Wilhelm Engelmann, Leipzig, 1890, p. 189. 



o Forchhammer, G., Ueber die Zusammensetzung der Porcellanerde und ihre Entstehung aua 

 dem Feldspath: Poggendorff, Annalen, vol. 35, 1835, p. 354. 



