COMPRESSIBILITY AND DEFORMATION OF CERTAIN ROCKS 565 



square inch. The question of the amount of pressure required to deform rocks 

 was then investigated. This investigation was directed to obtain an answer to a 

 problem stated by Mr G. K. Gilbert 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 unaffected by pressure. 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." 



The rocks investigated were Cockeysville (Maryland) dolomite, Carrara marble 

 Belgian marble ( " Noir Fin "), and Baveno granite. The investigation shows that 

 when a rock is submitted to differential stress after the elastic limit has been ex- 

 ceeded and the texture of the rock has been broken down, owing to the internal , 

 friction of the mass, the differential stress required to produce movement in the 

 deformed rock is much greater than the pressure required to start deformation by 

 breaking down the original texture] of the rock. Certain figures are presented in 

 the case of each of the rocks and their mathematical significance described. It is 

 shown that this work opens up a very extended field for investigation. 



The results of a series of experiments on the deformation of rock-making min- 

 erals is then described. 



The deformation of Carrara marble under much higher pressures than those em- 

 ployed in a former investigation on the flow of marble was then studied, the rock 

 being inclosed in tubes of nickel steel, for which the authors are indebted to the 

 Bethlehem Steel Company. Under the very high pressures employed a perfect 

 plastic flow was developed in the marble at the ordinary temperature. Carrara 

 marble was also deformed very quickly under a high pressure and a comparison 

 made between the deformed marble and overstrained metals in respect of the in- 

 fluence of time and of heat in increasing the strength of the deformed rock. As in 

 the case of steel, it was found to become stronger by simple lapse of time. The 

 influence of rate of deformation upon the strength and character of the marble 

 was also studied. 



The work was then extended to the deformation of limestones containing various 

 impurities, such as sand, clay, bituminous matter, etcetera, some of them being 

 highly fossiliferous. 



The paper concludes by presenting the results of the study of the deformation 

 of series of dolomites that from the Beaver Dam quarries, Cockeysville, Maryland, 

 being most thoroughly studied, and with a description of some preliminary expe- 

 riments on the deformation of granite. 



The paper was discussed by J. F. Kemp, C. K. Leith, and A. P. 

 Coleman. 



Skssion of Thursday Evening, December 29 



At 6.30 o'clock the annual dinner was served at the Hotel Walton, 

 with ladies and other guests present. 



At 8.30 o'clock the Society met in formal session in a parlor of the 



