THEORY OF RECRYSTALLIZATION. . 691 



state of strain. It has been seen on pages 95-98 that state of strain is 

 very favorable to chemical action. This follows from the principle of 

 the conservation of energy. So far as minerals are in a state of strain, 

 energy is potentialized. This conclusion has been fully verified by Barus," 

 who showed experimentally that when metals are strained a large amount 

 of energy is potentialized; and, finally, Hambuechen' has shown experi- 

 mentally that strained metals are much more easily acted upon chemically 

 than unstrained metals. Therefore the experimental work of Barus and 

 Hambuechen together has completely demonstrated that a state of strain in 

 substances is favorable to chemical action. 



It has been shown (pp. 671-673) that all mineral particles in the zone of 

 anamorphism are in a high state of strain. It has been further noted that 

 the stresses may vary from equality in all directions to those so unequal as 

 to approach or surpass the elastic limit of the rock under the conditions in 

 which it exists. Therefore, the mineral particles may be strained within 

 the elastic limit or to the point of granulation; and with the latter the 

 former occurs, for even where the original mineral particles are broken the 

 individual granules ordinarily show strain shadows in polarized light. The 

 condition of unequal stress and strain is especially characteristic of mass- 

 mechanical action. (See pp. 670-672.) 



It follows from Barus's and Hambuechen's work that in this interior 

 state of strain of the mineral particles, and especially in unequal strain, 

 we have a cause for recrystallization. The simplest illustration of the 

 effect of a state of strain is perhaps furnished by glass. It is well known 

 that unannealed glass is in a strained condition. This is best illustrated by 

 Prince Rupert's drops. When a point is broken the glass explodes, break- 

 ing into powder, showing that a large amount of energy is potentialized. 

 Unannealed glass, even in the laboratory and without the presence of water, 

 slowly releases itself from strain by recrystallization. Corresponding with 

 this fact it is to be expected that ancient natural glasses, because of their 

 unannealed condition, would have released themselves from strain by 

 recrystallization; and such are the facts. 



We conclude from the above that the state of strain, and especially 

 unequal strain combined with high temperature in the presence of water, is 



"Barus, C, The mechanism of solid viscosity: Bull. U. S. Geol. Survey, No. 94, 1S92, pp. 107-108. 

 6 Hambuechen, C, An experimental study of the corrosion of iron under different conditions: Bull. 

 Univ. of Wisconsin No. 42, 1900, p. 255. 



