Rocks and the Velocity of Seismic Waves. 63 



Some of the specimens which have been examined are 

 nearly isotropic. Most of these rocks are of recent formation. 

 For these I have calculated the velocities of propagation of 

 longitudinal waves in unlimited medium 



y = yA + W = */ k + $ n , using Lord Kelvin's notation), 

 which are placed under the following table. 



1 



Rock. Age. 



Density. 



v _ N A+2 / * /kilmA 

 p \ sec. / 



t P 



Peridotite Serpentine. 



Marble j 



Weathered Clayslate. 



Tuff Sandstone 



Algonkian. 

 Paleozoic. 



Mesozoic. 



Tertiary. 



Diluvium. 



2-786 

 2-654 

 2-490 

 2-236 

 2-223 

 2-321 

 2-305 

 2-316 

 2-346 

 1-944 

 2-454 

 2-228 

 2-198 

 2-263 

 2-557 

 2167 

 2-222 

 2-283 

 2-397 

 1-838 

 2-014 

 2-547 

 1-943 

 2- 4 00 

 2435 

 2-039 

 2-022 



5-86 

 4-09 

 2-25 

 2-93 

 2-76 

 3-35 

 316 

 3-18 

 . 311 

 3-02 

 2-78 

 2-25 

 2-14 

 1-88 

 4-44 

 402 

 3-77 

 3-38 

 306 

 2-75 

 2-58 

 2-57 

 2-54 

 2-50 

 2-35 

 2-32 

 2-21 



2-68 

 3-37 

 1-63 

 104 

 110 

 1-91 

 1-95 

 1-86 

 1-99 

 1-74 

 1-93 

 1-51 

 1-67 

 1-26 

 2-69 

 2-25 

 1-96 

 217 

 206 

 1-58 

 1-56 

 1-77 

 1-46 

 1-52 

 1-54 

 1-65 

 1-72 





Rbyolite Tuff 







EbyoliteTuff 





J 



, Tuff 





" 



" 





Tuff 



Andesifce Tuff 



AndesiteTuff 





j Tuff 







I did not think it necessary to calculate the velocity of 

 surface-waves, which according to Lord Bayleigh amounts to 



0-9554 



v> 



— , as the difference of rigidity in different spe- 

 cimens is so great that the presence of the factor 0*9554 will 

 not materially affect the result. 



General Result. — In examining the elastic constants of 

 rocks classified according to the age of formation,, we find a 

 distinct gradation as we pass from those of recent for- 

 mation to the oldest. The increase of density, as well as the 

 quasi-crystalline behaviour of rocks, is the most important 

 characteristic of rocks which are deeply embedded in the 



