5IO FRANK D. ADAMS 



the lower portion of the crystal, still embedded in the alum, had been 

 much crushed, the original crystal being now represented by one 

 large fragment and a considerable quantity of fine powder. The 

 pyrite, therefore, was crushed without showing any trace of plastic 

 deformation. . 



Quartz. — A clear transparent individual of rock crystal from Hot 

 Springs, Arkansas, was selected. It was embedded in alum in the 

 usual way in a copper tube. The crystal was placed in a somewhat 

 slanting position in the tube, so that it stood approximately on a 

 pyramidal face. The pressure was raised gradually and the load used 

 was just sufficient to start and maintain a very slow bulging of the 

 tube. The pressure was continued for an hour and twenty minutes, 

 by which time the height of the tube had been reduced to i .37 inches 

 (34.8 mm.), the maximum load employed being 34,000 pounds 

 (19,404 kilos). Once only during the deformation was a faint crack- 

 ing sound heard in the tube. On removing the alum, the quartz 

 crystal was found to be still coherent with the exception of a few little 

 fragments which had broken off from one end. The crystal, however, 

 was traversed by a large number of cracks following directions 

 approximately parallel to the rhombohedral faces, many of them not 

 passing completely through the crystal, but running only a certain 

 distance and being intersected by others crossing them. It is known 

 that quartz when heated and suddenly cooled develops a tendency 

 to rhombohedral cleavage; but it is also true that when a rigid or 

 an imperfectly plastic body is submitted to pressure it tends to shear 

 along planes which cross one another at an angle approximating to 

 90°. Whether in this case a tendency to movement along rhombo- 

 hedral planes was developed, or whether the movement is one quite 

 independent of crystallographic considerations, is uncertain. There 

 was certainly, however, no indication of plastic flow. 



Garnet. — ^The last mineral examined, being also the hardest, was 

 garnet, a perfect rhombic dodecahedron of almandine from Bodo, 

 Norway, being selected. It was embedded in alum in the usual 

 manner, the whole being inclosed in a copper tube. The deformation 

 of the tube occupied 50 minutes and the maximum load required was 

 175,000 pounds (79,383 kilos). A shght cracking sound was emitted 

 at times as the experiment was going forward. On dissolving the 



