X906.J SEE— THE CAUSE OF EARTHQUAKES. 341 



inevitable incident in distributing more equably the accumulating stresses. 

 So, also the first great readjustments probably left many local strains and 

 unequal stresses which gradually eased themselves by warpings, minor fault- 

 ings, etc., so that some minor movements were a natural sequence of the 

 great movements." 



From these citations one gets a good idea of the explanations 

 heretofore considered most plausible. 



Let us now examine this reasoning a little more closely. Is it 

 mechanically conceivable that large segments of the lithosphere should 

 thus act together as units? Would not such action imply that the 

 the earth is cut deep down into the lithosphere and free to move 

 along the boundaries of these severed segments ? If the lithosphere 

 were thus cut up into pieces, and all the segments could be regarded 

 as solid, with abundant lubricating oil between them, they might 

 by their mutual gravity crowd towards the center, and possibly the 

 small ones would be squeezed between the larger. But when we 

 recall that the earth is not cut up in this way, with oil between the 

 pieces, but is one unbroken mass, it is clear that the greatest resis- 

 tance would arise to relative motion of the parts. The friction of 

 one part against the other would be so amazingly great that no 

 motion would take place at the supposed joint. Even if motion oc- 

 curred it is impossible to see how the crust could be crumpled without 

 producing a corresponding condensation of the matter underlying 

 the folded area, the density of which would thus be greatly increased, 

 in some cases by 50 per cent. Now geodetic observations show that 

 the density of the matter under the mountains not only is not greater 

 than the average, but actually less ; and thus we see that the folds 

 of the crust could not be produced in this way. For in the first 

 place, motion could not take place on account of friction ; and in 

 the second place, if it took place, the resulting condensation of the 

 underlying matter would become sensible to geodetic measurement, 

 which is contrary to observation. 



Is it not therefore impossible to entertain the doctrine of large seg- 

 ments of the lithosphere moving together and squeezing others 

 between them? Should not this whole theory, along with the hy- 

 pothesis of contraction in general, be entirely given up? 



