Groundwork for Study of Megadiastrophism. 271 



The separation and transmission of seismic vibra- 

 tions. — My critic makes the claim that the texture of an 

 accretional earth would not be capable of transmitting 

 seismic vibrations, and that an " isotropic" medium is 

 necessary for the separation of the vibrations. Specific- 

 ally he says : 



' ' The two types of waves travel at different velocities but can 

 only become distinctly separated out in a homogeneous medium; 

 that is. homogeneous as to stress effects, or, in other words, 

 isotropic. The resultant vibrations which travel circumferen- 

 tially from the shock center pass through what we know is a 

 heterogeneous medium. The wave types are not separated in 

 the earth's surficial shell' 7 (p. 398). 



The waves here spoken of as "resultant vibrations," 

 and elsewhere .as "undifferentiated," are, as I under- 

 stand, the long waves. The medium necessary to the 

 separation is later spoken of as "a non-crystalline iso- 

 tropic material similar to 'undercooled' liquids" (p. 399). 



I understand the facts and their natural interpretations 

 to be these : 



That the seat of the earthquake, the point of origin of 

 all the seismic waves, lies within the shell not very far 

 below the surface; that the vibrations generated there 

 are very heterogeneous and mixed in the utmost confu- 

 sion; that these vibrations are propagated at different 

 speeds strictly because of their natures and their rela- 

 tions to the elasticity of the transmitting earth substance ; 

 that they are separated as a necessary effect of their dif- 

 ferent velocities; that the separation is not dependent on 

 any mysterious virtue of an isotropic medium or any 

 'undercooled' liquid; that they separate in any medium 

 that is capable of transmitting them; that there is no 

 special separation but merely a progressive separation as 

 long as they keep going; that all known types are trans- 

 mitted through the shell and undergo progressive separa- 

 tion while being so transmitted ; that nothing is known of 

 waves that cannot be transmitted through the shell ; that 

 the longest, most abundant, most conspicuous, best 

 defined, most notably organized, most far-penetrating 

 and scientifically most interesting waves, the undae longas 

 and the coda, are transmitted by the shell; that these are 

 sometimes so well transmitted that they are recorded at 



