8 /. IV. POWELL 



Contraction does not seem to be an explanation of all or even 

 the chief phenomena which we have briefly set forth. When 

 this hypothesis was considered, flexion seemed to be the chief 

 method of displacement ; now we know that fracturing and 

 faulting is the chief method in regions of maximum action. 

 When inclined rocks are studied they seem to have been 

 stretched, as evidenced in the elongation of particles transverse 

 to the strike, and they seem further to have been stretched by 

 the opening of fissures and joints. Altogether it may be 

 affirmed that displacement does not teach the doctrine of a con- 

 tracting earth, or, if that statement is too strong, it does not give 

 evidence of a sufficient contraction necessary to the hypothesis, 

 and it also fails to explain the concomitant phenomena. 



With this hypothesis another is associated, namely, that 

 the centrosphere of the earth is metallic, for which no vestige of 

 inductive evidence has yet appeared ; and the stupendous fact 

 remains that the centrosphere has more than twice the density 

 of the crust. All eruptive rocks which come into the purview 

 of science are found to have an average constitution which is 

 about the same as that of the sedimentary rocks. It is found by 

 experiment in the industrial arts that under pressure metallic and 

 other substances flow ; and geology teaches that all of the other 

 rocks are secularly deformed under differential pressures, so that 

 rocks highly metamorphosed in this manner are twisted, con- 

 torted, and kneaded into new shapes. Finally, there is now 

 abundant geologic evidence to show that the faulting near the 

 surface appears as flexure at greater depths, and finally that 

 flexure appears as molecular readjustment at still greater depths, 

 expressed in slaty structure where the particles of the rocks are 

 rearranged in parallel planes. 



The metals of the normal condition have .great density, but 

 in a pure condition are found only in exceedingly minute quanti- 

 ties ; all the other rocks have a small density. If now we assume 

 that all rocks flow under pressure, that the critical point is vari- 

 able and that the modulus of compression is also variable, being 

 greater for the lighter rocks and less for the heavier, and that 



