224: F. F. Wright — Schistosity by Crystallization. 



Art. XX. — Schistosity by Crystallization. A Qualitative 

 Proof ; by Feed. Eugene Weight. 



In the general theory of the metamorphism of rocks, pres- 

 sure, especially stress applied in one direction, has long been 

 considered an important factor ; and in recent years sufficient 

 evidence has been accumulated by geologists from observa- 

 tions in the field to demonstrate practically its influence on the 

 textures of rocks during their formation. Investigations of 

 the behavior of a body or chemical system under stress have 

 also been made by chemists and physicists, and fundamental 

 laws of equilibrium deduced therefrom which have a direct 

 bearing on the broader problems of metamorphism. 



Le Chatelier* discovered a number of years ago, that in a 

 chemical system " any change in its factors of equilibrium 

 from outside is followed by a reverse change within the sys- 

 tem." At constant temperatures, therefore, an increase of 

 external pressure tends to produce those changes which are 

 attended by diminution of volume. In the words of Bancroft,+ 

 " the system in equilibrium tends to return to equilibrium by 

 elimination of the disturbing element." Most solids dissolve 

 with decrease in volume : when this is the case, the solubility 

 is increased. Kiecke and also Hambuechen^: have proved ex- 

 perimentally an important deduction from this general law, 

 that a body under unequal strain dissolves most rapidly along 

 the line of greatest stress. 



In accord with this law of physical chemistry, Yan Hise,§ 

 reasoning from the standpoint of geology, has shown that in 

 the deep-seated zone or zone of anamorphism " the deforma- 

 tion in connection with mass mechanical action is mainly 

 accomplished not by mechanical subdivision but by the chemi- 

 cal action of recrystallization ;" that " under strains with a 

 stress difference an exceedingly small amount of water at the 

 high temperature is capable of dissolving particles of substance 

 under the greatest stress and depositing them along lines of 

 less resistance, the movement of the solution being slight and 



* Comptes Rendus, xcix, 786, 1884 ; quoted in W. D. Bancroft's "The 

 Phase Rule," Ithaca, 1897, p. 4. Van't Hoff has also derived the same law 

 from the second principle of thermodynamics and expressed it in mathe- 

 matical terms. Studien zur Chemischen Dynamik, Van't Hoff and Cohen, 

 p. 223. 



f " The Phase Rule," Ithaca, 1897, p. 4. 



X Riecke, E., Nachr. v. d. K. Ges. d. Wissensch. zu Gottingen, Math.- 

 phys. Klasse 1894, iv, 278-284 ; Hambuechen, C, "An Experimental Study 

 of the Corrosion of Iron under Different Conditions," Bull. Univ. of Wiscon- 

 sin, No. 42, 1900, p. 255. 



§ " Metamorphism of Rocks and Rock Flo wage," Bull. Geol. Soc. America, 

 vol. 9, May, 1898; also " Treatise on Metamorphism," U. S. Geol. Survey, 

 Mon. 47, Chap, vii: vm (1904). 



