Adams <& Coker—The Flow of Marble. 475 



Thin sections of the deformed column passing vertically 

 through the unaltered cone and deformed portion of the rock 

 were readily made and when examined under the microscope 

 clearly showed the nature of the movement which had taken 

 place. Under the microscope the deformed portion of the 

 rock can be distinguished at once by a turbid appearance dif- 

 fering in a marked manner from the clear, transparent mosaic 

 of the unaltered cone. In that portion of the rock which has 

 suffered deformation the calcite individuals have been squeezed 

 against one another in such a manner that a distinct flattening 

 of the grains has resulted. The individuals are not only flat- 

 tened, but in some cases distinctly twisted, these movements 

 being effected by the development in the calcite, first of 

 marked strain shadows, and then, where the movement is more 

 intense, by the appearance in each calcite grain of a series of 

 fine parallel lines or very narrow bands giving to it a fibrous 

 appearance, which bands become more numerous as the distor- 

 tion of the grain becomes more pronounced, the calcite as these 

 bands increase in number displaying a progressive decrease in 

 transparency. When highly magnified, these lines are seen to 

 be due to an extremely minute polysynthetic twinning. The 

 chalky aspect of the deformed rock on the surface of fracture 

 is chiefly due to the destruction by this repeated twinning of the 

 continuity of the even cleavage surfaces of the calcite indi- 

 viduals, thus making the reflecting surfaces much smaller. 



By this twinning the calcite individuals are enabled under 

 pressure to alter their shape somewhat, while the flattening of 

 the grains is evidently due to movements along the gliding 

 planes of the crystals. 



In the paper by Adams and Nicolson describing the results 

 formerly obtained in the deformation of marble at ordinary 

 temperatures, it was stated that a microscopic examination of 

 the deformed rock revealed the presence of an " anastomozing 

 meshwork of curved and branching lines " of minutely granu- 

 lated calcite running through the rock, these being lines of 

 cataclastic structure similar to those obtained when marble is 

 deformed by Kick's process. In our more recent experiments, 

 however, this cataclastic structure is seldom found and in 

 many cases is entirely absent. This is probably due to the 

 fact that in this latter work the grinding and fitting of the 

 columns to the tubes has been carried out with the utmost 

 accuracy, while in the former experiments mechanical work 

 was less perfect and the column probably did not in all cases 

 fit its tube perfectly. It is probable that the little lines along 

 which cataclastic structure is developed may have been largely 

 due to a slight shearing of the column before perfect adjust- 

 ment of the tube had been effected by the pressure to which it 

 was subjected. 



