1907.1 AND MOUNTAIN FORMATION. 397 



sector beneath the ocean is represented as having crowded slightly upon the 

 sectors beneath the continents on either hand, this crowding being repre- 

 sented by the short arrows b, b'. By comparing bb' with aa the reason for 

 the shear zone will be made apparent. On the right-hand side the outer part 

 of the sub-oceanic sector is represented as crowding upon the continental 

 sector an exceptional amount, as represented by the deflection of the line 

 b'b". This gives rise to the plateau at the right. The proportions of most 

 of the significant parts are necessarily exaggerated relatively." 



Let US now analyse this explanation a little more closely. These 

 authors remark that '' that part of the outer shell which is beneath 

 the ocean is supposed to descend without much compression, while 

 the necessary folding is concentrated on the borders of the conti- 

 nent." Is not this a purely gratuitous assumption, simply begging 

 the question, and wholly unjustifiable? Why should the oceans 

 descend without compression, while the continents are squeezed up 

 at their edges? Obviously one has as much right to assume that 

 the oceans are compressed by the sinking of the continents, as that 

 the continents are compressed by the sinking of the oceans. Again, 

 they say that " the portions on each side preserve their length by 

 thrusting laterally and hence descend along paths represented by the 

 arrow-headed lines, etc." But does not the assumption that '* the 

 portions preserve their length " imply that the ocean segment has 

 not shrunk at all in respect to surface area, while the continent has 

 been squeezed up at the edge to let it go down? 



What right have we to assume a similar shrinkage in the radius 

 of these sectors, and admit a shrinkage in one surface area (the con- 

 tinental) but deny it in another (the oceanic), which is much the 

 larger of the two ? 



Could one imagine a more improbable effect of secular cooling? 



Moreover the above figure corresponds to a shrinkage of about 

 one tenth of the radius, or 400 miles. In view of the fact which has 

 been shown in the paper on the " Temperature of the Earth " that 

 our globe is not shrinking at all, it is unnecessary to make further 

 comment on this unauthorized procedure. 



But we may remark that in this *' Geology," Vol. II., p. 131, we 

 find a direct contradiction of the above explanation. It runs as 

 follows : 



