VOLUME XXV NUMBER 7 



THE 



JOURNAL OF GEOLOGY 



OCTOBER-NOVEMBER igij 



ON THE AMOUNT OF INTERNAL FRICTION DEVELOPED 

 IN ROCKS DURING DEFORMATION AND ON THE 

 RELATIVE PLASTICITY OF DIFFERENT TYPES OF 

 ROCKS 



FRANK D. ADAMS, D.Sc, F.R.S., and J. AUSTEN BANCROFT, M.A., Ph.D. 



McGill University, Montreal 



INTRODUCTION 



At the meeting of the Geological Society of America held in 

 Albany in the year 1900, a brief resume of the experimental work 

 on the flow of marble carried out by Adams and Nicolson was pre- 

 sented to the Society, and in the discussion which followed the 

 reading of this paper a number of interesting points were suggested 

 by various speakers as worthy of experimental investigation. 

 Among these was one put forward by Dr. G. K. Gilbert, 

 which, in a letter to the authors, he subsequently formulated as 

 follows : 



It has been thought that great pressure breaks down the structure called 

 solidity and so reduces viscosity that very little differential stress is necessary 

 to produce flow. It is thought that the strength of rocks is practically un- 

 affected by pressure, in which case flow should begin only when differential 

 stress equals the crushing strength of the material as conditioned by the 

 temperature. It is certainly conceivable also that the strength of rocks is 

 increased by pressure, so that the production of flow requires differential stress 

 greater than the crushing stress as conditioned by the temperature. I hope 

 your experimentation may be brought to throw light upon this point. 



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