484 Adams <& Coker — Investigation into the Flow of Bocks. 



In these experiments, as in the case of those on page 479, 

 the deformation was carried out at comparatively low pressures. 

 The marble after deformation was hard and solid. Tested in 

 compression it was found to be nearly as strong as the original 

 marble. When sliced and examined under the microscope, the 

 rock showed no trace of cataclastic structure, but the grains 

 were seen to be distinctly flattened, giving to the rock a folia- 

 tion which in some places was very pronounced. The calcite 

 individuals showed the very narrow polysynthetic twinning 

 producing the fibrous appearance before described. The twin 

 lamellse were in some cases twisted, the twisting being accom- 

 panied by strain shadows, which phenomenon, however, in 

 this rock was neither very common nor very striking. The 

 individual grains had to all appearance acted as plastic bodies. 

 A very pronounced movement along gliding planes, coincid- 

 ing in direction with the course of twin lamellse, is undoubted. 

 This movement, induced by comparatively low pressures at this 

 elevated temperature, is identical in character with that pro- 

 duced by very high pressures at the ordinary temperatures. 

 In both the movement is due to translation and twinning ; 

 breaking or cataclastic structure is absent. 



The increased temperature evidently gives the calcite a freer 

 movement on its planes of translation and twinning, — the rise 

 in temperature increases its plasticity. In the case of ice 

 crystals, as is well known, a rise in temperature develops simi- 

 larly a greater ease of movement along the gliding planes. 



3. Deformation of the marble when heated to 300 C. in the 

 presence of water. 



In the series of experiments formerly made, in addition to 

 heat and pressure a third factor, viz., the presence of moisture, 

 was introduced. A column of Carrara marble enclosed in its 

 iron tube was slowly deformed while at a temperature of 

 300° C, but in the presence of water vapor under a pressure 

 of 460 lbs. to the square inch (32*33 kilos, per square cm.). 

 The apparatus used for the purpose of this deformation is 

 described in the paper to which reference has already been 

 made. This deformation was carried on very slowly, and at 

 as uniform a rate as possible, the experiment extending over a 

 period of 54 days or nearly two months. Tested in compres- 

 sion, the rock after deformation was slightly stronger than the 

 original rock. Its structure was found to be identical in char- 

 acter with that seen in the case of the marble which had been 

 deformed at 300° C. or 400° C. while dry. A distinct folia- 

 tion was induced, some of the calcite individuals being three 

 or even four times as long as they were wide. Some few of 

 these flattened grains displayed strain shadows, but no twin- 

 ning, while the grains in their immediate vicinity showed well- 



