120 Adams and Coher — Elastic Constants of Rocks. 



Summary of Results. 



In the table on the following page a summary is shown of the 

 average values obtained for E, o-, C and D in the case of all 

 the rocks examined in this investigation. Together with these 

 are placed for purposes of comparison the results obtained for 

 these constants in the case of wrought iron, cast iron and glass. 

 In the second table these values are again presented, recal- 

 culated into C.G.S. units. 



The rocks fall naturally into three groups differing from one 

 another in compressibility, but the several members of each 

 group agreeing fairly closely among themselves. 



9000 



^J 7000 



o 



vj 5000 



3000 



IOOO 











'u 



/\ 













• 



























40 80 120 160 ZOO 240 



STRAIN 



Fig. 12. Plate glass, stress-strain curves. 



These three groups show a corresponding difference in com- 

 position. 



The first group consists of the marbles and limestones. 

 These have an average value for D of 6,345,000. One of 

 these, however, the Black Belgian marble, which is very much 

 finer in grain than the others, and breaks almost like a piece of 

 glass, has a very much higher value for D than that possessed 

 by the other rocks, which among themselves are nearly identi- 

 cal. If we omit this Belgian marble, the average of D for the 

 other limestones and marbles is 5,855,000. 



The second group comprises the granites. These again show 

 a close agreement of values among themselves, except in the 

 case of the Stanstead granite, which rock as already mentioned 

 shows a defective elasticity. The average value of D for the 

 granites is 4,399,000. 



The third group embraces the basic intrusives (gabbro, 

 anorthosite, essexite and diabase). These show greater dif- 

 ferences, but have an average value for D of 8,825,000. The 

 nepheline syenite, although higher in silica and therefore 

 properly speaking an acid rock, in its freedom from quartz 

 and its richness in feldspar (although the feldspar is largely 

 orthoclase instead of plagioclase), in mineralogical composition 



