INTERNAL FRICTION IN ROCKS 631 



In these tables there is expressed in actual values the phenomena 

 which are displayed in such a striking manner in the great exposures 

 of the Grenville series and in other terranes which have undergone 

 deformation at great depths below the surface of the earth where 

 the same force has acted on a complex of rocks of diverse character. 

 In these occurrences some of these rocks are torn to fragments, 

 which are then carried far apart in a flowing matrix formed of some 

 other and more plastic member of the complex. This is seen in a 

 striking manner where dykes of diabase or belts of granite cut 

 through a limestone, and the whole complex is then deformed under 

 conditions of deep-seated differential pressure. The diabase dyke 

 or belt of granite is torn apart into angular fragments, which are 

 floated along in sinuous curves in the plastic flowing limestone, like 

 logs or drifting timber on the surface of a flowing river (see Fig. n). 



EFFECT OF A CHANGE IN THE RAPIDITY OF THE APPLICATION OF 



PRESSURE 



In Fig. 12 there are two curves: one showing the deforma- 

 tion of alabaster, the other, the deformation of marble. These 

 also illustrate the effects of a change in the rate at which the 

 pressure is applied. 



In the former case, after a load of 36,000 pounds had been 

 gradually applied in successive increments and no movement had 

 taken place under the load for 2 minutes, the next increment of 

 load was by mistake applied suddenly, thereby submitting the 

 rock to an impact instead of to a slow increase of pressure. This, 

 as will be seen, produced at once a movement of 0.045 inch. 

 Following this, however, four increments of load, each of 1,000 

 pounds, had to be applied .before the movement was resumed, and 

 two additional increments, each of 1,000 pounds, had to be applied 

 before the movement could be re-established in its regular course, 

 after which the flow continued in the line followed by the normal 

 curve. 



In the second case — that of the marble — -the normal course of 

 the experiment was interrupted four times by postponing the time 

 of reading the deformation produced by a new increment of load 

 much longer than usual, namely, from 9 to 75 minutes. These 

 were when the load on the column of rock was 40,000, 55,000, 



