TRANSITIONS BETWEEN ZONES. 191 



demands expansion of volume, it would be necessary to lift the entire 

 superincumbent mass of rock, and this would require a vast amount of 

 work. This work chemical affinity is usually not sufficiently strong to 

 accomplish, therefore reactions do not take place which give increased 

 volume; but on the contrary, the pressure forces reactions in the opposite 

 sense from those in the upper zone, as a result of winch the volume of a 

 material is diminished. If the reactions diminishing volume can be of such 

 a character as to liberate heat, this will occur; but frequently, in order to 

 produce a decreased volume, chemical reactions must take place which 

 absorb heat. In this paper on metamorphism the terms zone of katamor- 

 phism and zone of anamorphism are used, as being most serviceable. In 

 structural work, however, the equivalent terms zone of fracturing and zone 

 of flowage are more serviceable and therefore will there hold their place. 

 It may be seen on page 167, also on pages 766-768, that the passage 

 from the zone of katamorphism to the zone of anamorphism is a gradation 

 and not an abrupt change. The same is true of the change from the 

 zone of fracture to the zone of flowage. (See pp. 187-189.) Therefore, 

 whether the division of the outer crust of the earth into two zones be 

 considered from the metamorphic point of view or from the structural 

 point of view, there is a transition between the two. 



