DIFFERENTIAL PRESSURE ON MINERALS AND ROCKS 525 



4. Under the differential pressure fluorspar not only changed its 

 form but also its color. 



5. The softer rocks, such as Carrara marble, are readily deformed, 

 the shapes assumed varying somewhat with the character of the 

 material in which the rock is embedded during deformation. The 

 movement takes place in part by distortion of the calcite grains and 

 in part by the development of a cataclastic structure in the rock. 



6. Crystalline dolomite is more resistant. The movement induced 

 in it resembles that produced in a very stiff paste. This movement 

 takes place chiefly through the development of cataclastic structure. 



7. Very fine-grained massive limestones display a movement in 

 which flowing and fracture are combined. 



8. The harder rocks, like granite, crumble under the pressure, 

 although in those places where the movement is very slight, the rocks 

 develop an indistinct foliated structure owing to the granulation 

 (cataclastic structure), with movements in the granulated portion of 

 the rock. 



9. For the development of a flow structure in the harder rocks, 

 much higher differential pressures are required than are obtained 

 by this process — such differential pressures, for instance, as may be 

 secured when the rocks are inclosed in steel before being submitted 

 to the deforming load. . 



