i9o6.] SEE— THE CAUSE OF EARTHQUAKES. 323 



After a careful consideration of the whole question, including 

 all the forces at work, one may well doubt whether the radius of the 

 earth has shrunk a mile since the continents began to emerge from 

 the oceans. The crust could easily accommodate itself to such a 

 small shrinkage as one part in 4,000, without producing any wrink- 

 ling whatever. 



This subject of planetary wrinkles has been treated mathe- 

 matically by Professor Sir G. H. Darwin, in his researches on the 

 "Tides of a Viscous Spheroid" (Phil. Trans. Roy. Soc, Part 11, 

 1879, p. 588). And while his results are recognized to be correct, 

 on the hypothesis, they seem to me to be inapplicable to the remote 

 history of the earth, because I believe the shrinkage to have been 

 nearly insensible, and certainly much less effective than has been gen- 

 erally supposed. 



In his " Physics of the Earth's Crust," page 118, Rev. O. Fisher 

 has discussed Darwin's theory thus : 



" It may be replied to this theory, that the formation of the existing 

 continents cannot be looked at apart from their geological history, and that 

 they are evidently dependent on, and as it were, gathered round, the great 

 mountain ranges in which they culminate. Although these ranges primarily 

 originated long ago in very early geological times, their present loftiness is 

 due to quite late movements ; and, if these had not subsequently occurred, 

 they would before now have probably have been razed to the sea-level and 

 have disappeared, so that, whatever cause it was which wrinkled the conti- 

 nents, seems to have continued active to times comparatively, if not quite, 

 recent; and the moon is too far off now. The occurrence of great changes 

 of level at no very distant geological period are manifest from such instances 

 as that related by the elder Darwin." 



It has always been extremely difficult to show how contraction 

 could produce elevation of ranges, and the mechanical explanations 

 which have been put forward are admittedly unsatisfactory.^ The 

 spurs which so often jut out from the main ranges do not look like 

 wrinkles in the crust ; for they are too numerous and terminate too 

 suddenly at their extreme ends. The isolated parallel ranges so 

 often met with in Nevada and Southern California also terminate 

 too suddenly to be explained by shrinkage, or by lines of weakness. 



In his work on the " Physics of the Earth's Crust," second 

 edition, the Rev. O. Fisher has discussed with much care the inade- 



^ Fisher's " Physics of the Earth's Crust,"^ second edition, p. 123. 



