DEFORMATION OF MARBLE. 811 



such as mica, the cleavage of which often controls- the cleavage of rocks. 

 The rare existence of cleavable marbles in connection with marble forma- 

 tions, the larger parts of which lack cleavage, as in the case of the marbles of 

 the Appalachian regions just mentioned, seems to be conclusive evidence that 

 the granular character of ordinary marbles is due mainly to the processes 

 of ready solution and deposition, or recrystallization, as above explained. 



Adams and Nicolson have experimentally deformed Carrara marble." 

 Among the various reasons for selecting this marble was its evenly granular 

 character and absence of strain effects. The deformation was accomplished 

 under the conditions of pressure of the zone of anamorphism. Cylinders 

 of marble confined on their sides by strong steel bands were shortened 

 by pressure, and under these circumstances the shape of the marble was 

 changed without perceptible cracks being produced. The process was 

 carried on under various conditions. 



First, the dry marble was deformed at ordinary temperatures. The 

 rock thus deformed was found to be weaker than the original rock, but 

 sufficiently strong to show that the particles were partially welded. The 

 thin sections of the marble showed a cataclastic structure "identical with 

 that seen, in the feldspars and many gneisses."'' Many of the grains were 

 flattened, and these grains showed strain shadows and fibrous structures 

 due to minute polysynthetic twinning. 



Second, the dry marble was very slowly deformed during a period of 

 about four months at a temperature of 300° C. The deformed marble was 

 found to be strong, but not quite so strong as the original rock, showing a 

 nearer approach to perfect welding than in the case of the marble deformed 

 at ordinary temperatures. The thin sections showed a tendency toward 

 rock cleavage. "Cataclastic structure is absent, but almost every grain 

 shows an exceedingly fine fibrous structure. When examined under a 

 high power this fibrous structure resolves itself into an extremely narrow 

 polysynthetic twinning — the whole grain consisting of slightly sinuous 

 twin lamella?, extinguishing in alternate sets. Each individual is usually 

 twinned throughout, the lamella? passing from end to end, although a 

 single lamella often varies somewhat in width from place to place. The 



"Adams, F. D. and Nicolson, J. T., An experimental investigation into the flow of marbles: 

 Philos. Trans. Royal Soc. London, ser. a, vol. 195, 1901, pp. 363-101. 

 & Adams and Nicolson, cit., p. 375. 



