6 3 6 



FRANK D. ADAMS AND J. AUSTEN BANCROFT 



In these measurements it must again be noted that the factor 

 of pressure alone was considered, no account being taken of the 

 element of heat in the crust, which would undoubtedly tend to 

 increase the ease of movement. 



In the experiments it has been shown, as mentioned, that the 

 resistance to deformation exerted by the wall of the steel tube 

 gradually increases as the experiment progresses. If, however, the 

 value of the resistance is taken at a point where the regular column 

 shows a diametral increase of 0.05 inch (or 6.35 per cent), i.e., when 

 the deformation is well under way and after which it becomes pro- 

 portional to the increased tangential pressure, this resistance, in the 

 case of the experiment with the steel wall 0.25 centimeter thick, 

 would be equivalent to 26,685 pounds to the square inch, or 1,815 

 atmospheres, that is, to a depth of 4. 2 miles below the surface. 



In the case of our experiment with a steel wall o . 33 centimeter 

 thick it would be equivalent to 37,359 pounds per square inch, or 

 2,542 atmospheres, that is, to a depth of 5 . 8 miles below the surface. 



Thus at these respective depths the additional tangential thrust 

 required to induce a pronounced movement in the case of marble 

 and granite, respectively, would be as shown in Table V. 



TABLE V 



CONCLUSIONS 



i. All the rocks employed in the present investigation can be 

 deformed under differential pressure at ordinary temperatures. 



2. In order to effect an equal deformation, it is necessary to 

 employ differential pressures having different values in the case of 

 the several rocks. 



3. The ease with which these rocks are deformed has as one of 

 its functions the hardness of the rock (or of the minerals compos- 

 ing it). 



