for the Study of Megadiastrophism. 101 



duration, and Knott 19 states that: "Within this nucleus 

 of radius .4 the material of the earth has lost its elastic- 

 solid character and can transmit only compressional 

 (primary) waves" and "as the nucleus is approached the 

 material of the earth is becoming less of an elastic-solid 

 and more of an elastic, highly compressed liquid." 



The evidence of a breakdown of rigidity in the earth's 

 central portions is difficult to reconcile with Chamberlin's 

 statement 20 that rigidity increases "towards the center 



faster than density all the way to the center." 



"This evidence is thus directly opposed to the conception 

 of an earth core which is dense and rigid." The core is 

 undoubtedly dense but its rigidity has vanished. 



Xow if rigidity breaks down no matter what the depth 

 for the stress differences of such short duration and 

 small amplitude as seismic waves impose, then the rigidity 

 and elasticity for stress differences of diastrophic dimen- 

 sions in time duration and magnitude must break down at 

 much more superficial depths. At least no experimental 

 evidence has yet been submitted which proves or eA^en 

 implies that the material within the earth cannot yield, 

 under the long time differential stresses imposed by dias- 

 trophic movements, under the conditions of temperature 

 and pressure which exist at not a great depth. 



Earth Yielding. — An earth composed of crystalline 

 material could apparently only yield through the dynamic 

 influences of condensation. The adequacy of tidal 

 stresses is questionable. In such an earth the major 

 features of surface relief, such as continents and ocean 

 basins, could hardly be the direct result of diastrophism 

 but could exist only because of differences in density 

 extending to great depths as a result in turn of selective 

 growth with a less volume of dense material falling, 

 during growth, per unit area on the oceanic areas than 

 of less dense material on the continental areas. 



It would seem evident that mere surficial loading or 

 underloading of any possible dimensions could not, in a 

 crystalline rigid earth, cause sinking or rising of the 

 earth's surface. It is not even apparent how peneplana- 

 tion would be followed by uplift and yet without excep- 



19 Op. cit., p. 136. 



- T. C. <;hamberlin: Jour. Geologv, vol. 29, p. 395, 1921, and Bull. Geol. 

 Soc. Am., vol. 32, p. 221, 1921. 



