5o8 FRANK D. ADAMS 



It is evident in this case that while there may have been some slight 

 plastic deformation in portions of the cube, the movement has been 

 essentially one which has taken place along planes of fracture. 



Orthoclase. — The crystals used in this experiment were from Good 

 Springs, Lincoln County, Nevada. They were of simple form and 

 very symmetrical development, being bounded by the clinopinacoids, 

 the basal faces, and the unit prisms. 



Three of the crystals were placed together in the same copper tube, 

 one lying on a clinopinacoid, one on a prismatic face, and one on its 

 basal plane. The experiment occupied one hour and forty-five 

 minutes. Alum was used as the embedding material and the maxi- 

 mum load — which was of course that reached at the conclusion of the 

 experiment — was 195,000 pounds (88,455 kilos). As the compres- 

 sion slowly proceeded, faint cracking sounds were frequently heard 

 from the interior of the tube. On removing the brass plate, the out- 

 lines of the crystals could be seen in the alum at either end. At one 

 end they were for the most part still covered by a thin film of alum, 

 while at the other end they had been forced into the brass plate, 

 deeply indenting it; while one of the crystals, in which a sharp edge 

 came against the brass plate, had forced its way through this plate, 

 tearing it completely open. These portions of the crystal in contact 

 with the brass plates showed no signs of fracture. On dissolving 

 away the alum, however, all three crystals were found to have been 

 much crushed in places. 



The crystal which lay upon the prismatic face still held together 

 but was traversed by several little fissures which had their courses 

 chiefly parallel to the base and to the clinopinacoid, that is, in the 

 direction of the normal cleavage of the mineral. They did not, how- 

 ever, invariably follow these planes, but in some cases ran irregularly 

 across the crystal. The individual which lay upon its clinopinacoid 

 had crumbled to pieces. The largest of these pieces showed little 

 cracks parallel to the base and to the clinopinacoid and others running 

 in the direction of the orthopinacoid. The crystal which rested upon 

 its basal plane was reduced to a mass of little fragments without 

 definite form. 



Two thin sections were prepared from the first and second of the 

 crystals respectively, in order to ascertain whether any further evi- 



