for the Study of M e gad last rophism. 397 



yielding can only take place by shearing or recrystal- 

 lization. This is vital to deeply pointing wedge deforma- 

 tions. 



Chamberlin deduces a noncrystalline state for the 

 earth on the basis of its rigidity, elasticity and density. 

 It is evident that both rigidity and elasticity are totally 

 independent of crystallinity. Amorphous materials, like 

 glass, or even paraffin wax, under sufficient pressure 

 become more rigid than steel under similar pressure. 

 Under differential stress of sufficient magnitude and dura- 

 tion such materials will flow because they are true liquids. 

 \A Tiile it is true that high pressure favors crystallization, 

 since for most substances the crystalline form is the most 

 dense, this is true for conditions of normal temperature. 

 High pressure experiments seem to indicate that there 

 is a limiting set of conditions as to pressure and temper- 

 ature beyond which all directional molecular arrangement 

 is destroyed. The material then becomes a highly viscous 

 liquid. There is nothing to indicate that such limiting 

 conditions may not exist at no very great depth within 

 the earth and the resulting state might, and probably 

 would, be one of ready yielding to long-imposed stresses 

 and still be a state of high rigidity and elasticity under 

 short-time stresses. For material to assume such fluid 

 properties for short-time stresses required conditions of 

 higher temperature and pressure. Seismic transmissions 

 seem to indicate that such conditions do exist at depths 

 below 0.6 of the earth's radius. 



The great depth of deformation deduced by Chamberlin 

 rests then upon conditions of rigidity and elasticity which 

 are not proved by the evidence at hand. And this is 

 vastly important, for this deduction makes it essential 

 that all earth body deformation be deep-seated and due 

 largely to tidal stress and its consequent kneading. The 

 work of Michelson'' and others does not indicate in any 

 sense that the tidal stresses are sufficient in time duration 

 or magnitude to overcome the rigidity or elasticity attrib- 

 uted to the earth. Furthermore this same evidence does 

 not prove that stress differences of diastrophic dimen- 

 sions are not competent to overcome this same rigidity 

 and elasticity and so cause plastic yielding. 



9 A. A. Michelson & H. G. Gale : The Kigiditv of the Earth. Jour. Geol- 

 ogy, vol. 22, pp. 97-130, 1914; vol. 27, pp. 585-601, 1919. 



