170 A TREATISE ON METAMORPHISM. 



simple ones. The zone of anamorphism may be defined as the zone in 

 which alterations of rocks result in the production of complex compounds 

 from more simple ones. 



Summarizing the energy factors in the zone of anamorphism, so far 

 as the volume change is concerned, the result is to liberate heat; so far 

 as the chemical reactions are concerned, heat may be liberated or absorbed, 

 but the latter reaction is more common. In the latter case the heat 

 absorbed is almost certainly much greater than that liberated by decrease of 

 volume. If it were not that a considerable number of the chemical reactions 

 liberate heat, it would be certain that heat is absorbed in the zone of 

 anamorphism But the heat liberated by some chemical reactions must 

 be added to that liberated by decrease of volume. Whether this sum is as 

 great as the heat absorbed by the preponderating chemical reactions is 

 somewhat uncertain; but it is thought to be rather probable, for the com- 

 pounds immediately concerned in the reactions, that the total effect is to 

 absorb heat and store energy. However, in order to accomplish this, energy 

 must be derived from an outside source, and when all the factors which in 

 any way affect the reactions are taken into account, including the movement 

 of the superincumbent material, heat is dissipated and energy lost. (See 

 p. 182.) 



RELATIONS OF ZONES OF KATAMORPHISM AND ANAMORPHISM. 



We shall now consider the zones of metamorphism together with 

 reference to the energy factors. So far as the chemical reactions are 

 concerned, it has been seen that they msij take place with liberation or 

 absorption of heat. So far as heat is liberated energy is dissipated. So 

 far as heat is absorbed energy is stored. The change in volume may also 

 result in the dissipation or storage of energy. Where increase of volume 

 is preponderant energy may be stored (1) by increasing the volume of the 

 rocks affected by the reaction or (2) by elevating the overlying rocks in 

 order that the space shall be available for the expenditure. In a given 

 case the energy may be stored by (1) or (2) or a combination of them. 

 Where decrease of volume is preponderant energy is dissipated (1) by the 

 decrease of volume of the rock affected by the reaction or (2) by subsid- 

 ence of the overlying material, or by both. Below the extreme outer film 

 of the earth the factor of elevation or subsidence of the overlying rocks is 

 of vastly greater importance than the volume change, and the relative 



