for the Study of Megadiastrophism. 399 



the waves arriving there must, for part of their journey, 

 have traversed some homogeneous material situated 

 below a comparatively thin layer. ' ' In fact, the rays of 

 these vibrations which emerge at the arc distance of 10° 

 or 700 miles actually penetrate to a depth of only 100 

 kilometers. Here then is apparently direct proof of a 

 transmitting medium which is isotropically homogeneous 

 at a comparatively shallow depth beneath the surface. 



Now Chamberlin interprets this necessary and demon- 

 strated homogeneity as a medium possessing an average 

 homogeneity but a minute heterogeneity. 11 Such an 

 interpretation becomes, of course, essential under the 

 hypothesis of deep crystallinity for the earth. If such 

 a minutely heterogeneous medium would have the identi- 

 cal transmitting properties as an actually isotropic one, 

 then one obstacle in the way of acceptance of the postulate 

 is removed, but are there not other obstacles? 



The necessary confinement of large heterogeneity to 

 such a comparatively thin outer shell would seem to 

 present a formidable difficulty in the way of Chamberlin 's 

 postulated process of the introduction of tongue melts 

 from the deep interior to the more surficial portions of 

 the earth, for certainly these introduced heterogeneities 

 would not all insinuate themselves above such a shallow 

 depth as the transmitted seismic waves make necessary. 



The important point deserving special emphasis is that 

 the splitting up of the two vibration phases at such 

 shallow depths as are penetrated by rays emerging at a 

 distance of 700 miles from the shock center indicate a 

 profound change in physical state at a very shallow depth 

 beneath the earth's surface. The suddenness of this 

 change is further indicated by the apparent reflection of 

 transmitted waves against the surface of demarkation. 

 The most reasonable conclusion to be drawn is that this 

 sudden change is from a heterogeneous outer shell to a 

 non-crystalline isotropic material similar to "under- 

 cooled" liquids. Chamberlin 's statement 12 that "the hot 

 interior of the earth is not a suitable environment for 

 under-cooled liquids," does not take into account that 

 this physical state is the combined result of temperature 

 and pressure rather than of temperature alone. 



11 T. C. Chamberlin: Jour. Geology, vol. 29, p. 395, 1921. 



12 T. C. Chamberlin: The Origin of the Earth, Chicago, 1916, p. 181. 



