RELATIONS OF ZONES. 171 



importance of this factor steadily increases with depth. This is more 

 broadly true in the case of increase of volume than in. that of decrease 

 of volume ; for in the latter case in the zone of katamorphism the strength 

 of the rocks near the surface may prevent subsidence, and the decrease of 

 volume simply produce porosity. A common illustration of that is vesicu- 

 lar dolomite. However, in the zone of anamorphism, when the reactions 

 result in decrease of volume, subsidence occurs and energy is dissipated. 

 The importance of the necessity of lifting the overlying' material in order 

 to find more room in the case of increase of volume is well illustrated by 

 the frequent rapid hydration or slacking, with great expansion and rapid 

 disintegration, which follows when a partly hydrated rock, buried but a 

 few feet, is brought to the surface." Apparently when buried the tendency 

 for hydration and necessary expansion with liberation of heat was not 

 sufficient to lift the superjacent material. When the necessity of elevat- 

 ing the superjacent material was removed by transfer to the surface the 

 process of hydration and expansion went on to completion with great 

 rapidity. 



I conclude from the foregoing that in so far as energy is concerned 

 there are four cases. Chemical reaction may (1) release energy and result 

 in the liberation of heat, or (2) may consume energy and result in the 

 absorption of heat. The change of volume may be (3) by decrease of 

 volume, and result in the release of energy and the liberation of heat, or 

 (4) by increase of volume, and result in the consumption of energy and 

 in the absorption of heat. (1) and (3) will be called plus, and when they 

 are combined the heat developed is equal to their sum; (2) and (4) will 

 be called minus, and when they are combined the heat absorbed is equal 

 to their sum. When (1) and (4) or (2) and (3) are combined heat may 

 be liberated or absorbed, and consequently energy dissipated or stored, 

 depending upon the relative values of the opposing factors. 



It has been noted that the three important reactions in the zone of 

 katamorphism are oxidation, carbonation, and hydration; and in the zone 

 of anamorphism are deoxidation, silication, and dehydration. 



Since all of the abundant metallic elements except iron are completely 

 oxidized as they occur in the original rocks, the important inorganic com- 

 pounds which are oxidized in the zone of katamorphism are mainly those 



a Merrill, G. P., Disintegration of the granitic rocks of the District of Columbia: Bull. Geol. Soc. 

 America, vol. 6, 1895, p. 332. 



