DIFFERENTIAL PRESSURE ON MINERALS AND ROCKS 499 



was taken. This measured i .378 inches X i . 18 inches X i . 38 to i . 389 

 inches (35 mm. X 30. 05 mm. X35.05 to 35.3 mm.). It was inclosed 

 in paraffine wax in a copper tube in the usual way. This was squeezed 

 down until it showed signs of rupture when the salt crystal, now 

 considerably flattened, was removed and placed in paraffine in 

 another shorter but wider tube, which was in its turn squeezed down 

 until rupture threatened, when the crystal was removed to a third 

 and still wider piece of copper tube, in which the deformation was 

 completed, the maximum load employed being 157,000 pounds. 



The salt when removed was found to have the form of a continuous 

 flat cake, nearly square in section. It now measured o . 56 inch 

 (14.2 mm.) in thickness and was 2.215 inches to 2.25 inches (53.97 

 mm. to 57.15 mm.) by 2 inches to 2.125 inches (50.8 to 53.975 mm.) 

 in diameter. Photographs of the crystal as it appeared before and after 

 deformation are shown in Plate I, Figs, h and c. Although a solid 

 mass, quite firm and hard, it had developed a series of fissures 

 extending from both the lower and upper surfaces into the mass, 

 these being wedge shaped in form and following the direction of the 

 faces of the cube, i.e., running parallel to the longer sides of the 

 flattened crystal. These fissures did not pass completely through 

 the crystal from top to bottom, but often penetrated into it deeply. 

 Neither were they continuous from side to side, but were interrupted 

 and crossed each other at right angles. They were not seen on the 

 narrow edges of the mass. 



The deformed crystal of salt was brightly translucent but not 

 actually transparent, and the sides of the flattened crystal were in 

 several places beautifully curved. The remarkable plasticity of the 

 salt not only is shown by the manner in which the crystal was flattened 

 out, but is seen in a striking way where the cube, having been carried 

 against the sharp incurving edge of the spreading end of the tube in 

 one place, took an impression of the latter in the form of a deep, sharp- 

 angled, and smooth-faced groove crossing the corner of the salt cube, 

 the impression being as sharp as if it had been taken in wax. 



In the present case it was found inadvisable to carry the deforma- 

 tion of the salt any farther, singg the little fissures mentioned above 

 having once formed, the downward pressure forced the paraffine 

 into them, and thus tended to divide up the salt crystal by a series of 



