110 A TREATISE ON METAMORPHISM. 



However, it will also be seen that in the zone of anamorphism, with 

 pressure as a dominant factor, reactions very generally occur with the 

 absorption of heat under the second part of van't Hoff's law. Thus, in this 

 zone the heat effect of the chemical reactions is to stay metamorphism. 

 But while the reactions which occur at depth are very generally those 

 which absorb heat, it must be remembered that in the zone of anamorphism 

 the amount of heat available, due to increase of heat with depth and to the 

 difficulty with which the heat escapes from intrusive rocks, is very great. 

 Therefore, notwithstanding the fact that the chemical reactions themselves 

 absorb heat, the temperature is much higher than in the upper zone. 

 Consequently one would expect that the chemical activity would be 

 greater in the zone of anamorphism than in the upper zone of katamorphism; 

 and with these expectations the facts correspond. (See pp. 660-661, 690- 

 692, 749-751.) 



RELATIONS OF CHEMICAL ACTION, MECHANICAL ACTION, AND HEAT. 



All transformations of material upon the earth, provided all the energy 

 factors be taken into account, involve the expenditure of energy and the 

 dissipation of part of it as heat. If this were not true it would be possible 

 to manufacture an engine by means of which an equal or greater amount 

 of energy is available for work than is expended in driving the engine, and 

 perpetual motion would be possible. In metamorphism of rocks, in order 

 that the above general statement as to the expenditure of energy shall be 

 true, it is necessary to take into account the chemical force, mechanical 

 force, and heat which promote the transformations. In those cases where a 

 transformation of material does not at first sight appear to demand the 

 expenditure and dissipation of energy, this is due to the fact that some of 

 the energy factors are overlooked. 



It has been noted that chemical actions are reversible, and it will be 

 seen subsequently that chemical reactions which take place on a large scale 

 in the zone of katamorphism are reversed in the zone of anamorphism. 

 When a chemical reaction takes place, and later that reaction is reversed 

 and the cycle is repeated, exterior energy must have been expended and 

 dissipated. To illustrate, let us consider the reversible reaction 



Fe 2 3 +3H 2 0£Fe 2 O s .3H„0. 



The reaction may advance from left to right by the expenditure of 

 chemical energy alone, and as a result of the process heat is liberated. 



