692 A TREATISE ON METAMORPHISM. 



a sufficient cause to produce recrystallization of rocks. As soon as move- 

 ment begins, equilibrium is disturbed and the processes of solution and 

 deposition or recrystallization set to work rapidly to adjust the minerals. 



The amazing power of heated water in solution and deposition, or in 

 recrystallization, has already been pointed out on pages 79-81, and it 

 may be recalled that Barus has shown that above 200° C. glass and water 

 are miscible in all proportions." At temperatures as high as or higher 

 than this, which undoubtedly prevail in the deep-seated zone of deforma- 

 tion, recrystallization can go on with comparative rapidity. At any 

 moment the substances are present almost wholly as minerals. However, 

 superheated water is in the capillary and subcapillary spaces between the 

 particles, and through this as a medium adjustment by solution and deposi- 

 tion goes on continuously during the deformation. At any given moment 

 only an exceedingly small part of the material is in solution; but under the 

 molecular theory of solids all materials in a state of strain, or subject to 

 unequal pressure, or not in a compact state, will be more ready to part 

 with their molecules than the minerals not so conditioned. Thus, from all 

 mineral particles which are under one or all of these conditions, particles 

 are filed off or solution is constantly taking place. Simultaneously with 

 this, from the solutions there is deposition of material in more compact 

 molecules than those dissolved at the places where the pressure on the 

 mineral particles is less than the average. 



Two minerals that excellently illustrate the process are quartz and mica. 

 The first recrystallizes somewhat readily and the second develops on an 

 extensive scale in the schists and gneisses. That quartz occurs abundantly 

 in flat individuals in the schists is well known. Moreover, it is known in 

 some cases that the flat individuals are largely the equivalent of individual 

 crystals which have had a nearly spherical form. As illustrations of flat 

 grains of this mineral are the quartzes of the quartz-porphyries described by 

 Futterer 6 (PI. Ill, B) and of the schists from the Black Hills* (PI. XI, C), 

 which I have described. The many flat particles have exactly the appear- 

 ance they would have had if the material could have been pressed out and 



" Barus, C, Remarks on colloidal glass: Am. Jour. Sci.~, 4th ser., vol. 6, 1898, p. 270. See also 

 Am. Jour. Sci., 4th ser., vol. 9, 1900, pp. 167-168. 



''Futterer, Karl, Die " Ganggranite " von Grosssachsen, und die Quartzporphyre von Thai im 

 Thuringer Wald. Heidelberg, 1890, pp. 27-17. 



c Van Hise, C. R., The pre-Cambrian rocks of the Black Hills: Bull. Geo). Soc. America, vol. 1, 

 1890, pp. 222-226, 244. 



