182 A TREATISE ON METAMORPHISM. 



both by the chemical reactions and by the volume change in both zones may 

 be mentioned the devitrification of glass. (See Chapter V, pp. 251-252.) 

 The chemical reaction is presumably under the first part of van't Hoff's 

 law, and the, volume is decreased. Another instance of chemical reaction 

 with the liberation of heat and condensation of volume is the replacement 

 of calcium by magnesium in limestone, thus transforming the rock into 

 dolomite." 



It is thought to be certain that the total of all the changes taking place 

 in the whole of the mass of rocks concerned in any given modification of 

 the lithosphere results in the dissipation of energy, and it is believed that 

 such is the fact for each of the physical-chemical zones separately. In the 

 zone of katamorphism the chemical reactions result in liberation of heat; 

 the average volume reaction results in absorption of heat. It is, however, 

 thought certain that the residual is in favor of the former. In the zone 

 of anamorphism the average of the chemical reactions results in absorption 

 of heat; the average of the volume reactions results in the liberation of 

 heat. It has already been seen (pp. 170-171) that the amount of energy 

 required for the volume change rapidly increases with depth, and in the 

 lower zone it is thought that the heat liberated from the volume changes is 

 greater than the heat absorbed by the chemical reactions, and therefore 

 that the residual is in favor of the liberation of heat. 



Hence, it is concluded that the changes which take place in each of 

 the zones are under the g-eneral law of the running- down of energy into 

 the form of heat which is dissipated, and this accords with the apparent 

 order of the universe. 



A corollary to the foregoing pages is the conclusion that in the upper 

 zone, where pressure is relatively unimportant, on the average, alterations 

 result in the expansion of the volume of the rocks; and that in the 

 deeper-seated zone, where pressure is important or dominant, on the averag-e 

 the alterations result iu the contraction of the volume of the rocks. It 

 follows as a further conclusion from this that the tendency of the alterations 



"■ The verification from authorities of the heat of the chemical reactions and the volume relations 

 for the majority of the changes above mentioned have been very kindly made for me by Mr. A. T. 

 Lincoln. Mr. Lincoln either has found the results used in the works of Thomsen, Ostwald, Mendeleeff, 

 or other standard authorities, or from the data there found has been able to calculate results which 

 answer the specific questions I gave to him. 



