448 G. H. Darwin—Influence of Geological Changes, etc. 



produce an alteration in the position of the pole of from one to 

 change, such as those which obtain on the earth, is competent to 

 three degrees of latitude, on the hypothesis that there is no 

 change in the law of internal density. 



6. Yarious hypotheses as to the nature of the internal changes 

 accompanying the deformation of the earth are discussed. 



First, it is shown that if upheaval and subsidence are due to 

 a shrinking of the earth as a whole, but to the shrinking being 

 quicker than the mean in some regions and slower in others, 

 the results are the same as those previously attained. 



Second, the increase of surface matter due to the deposit of 

 marine strata also gives the same results. 



Third, the hypothesis that upheaval and subsidence are due 

 to the intumescence or contraction immediately under the 

 regions in question is considered. Under certain special as- 

 sumptions, too long to recapitulate, it is shown that the previ- 

 ous results must be largely reduced. A table of the values of 

 the reducing factor for various thicknesses of the intumescent 

 strata is given ; from which it appears that if the stratum is 

 tolerably thin and at all near the surface, the deflection of the 

 pole is reduced to quite an insignificant amount. Even if the 

 ds right down to the center of the earth in a 

 cone bounded by the elevated region, the results would be only 

 about § of the former ones. Hence it appears that tfa 

 results can only be stated as a superior limit to what is 



7. In conclusion it is pointed out that if the earth be quite 

 rigid, no redistribution of matter in new continents could ever 

 cause the deviation of the pole from its primitive position to 

 exceed the limit of about 3°. But if the previously kw 



view is correct, that the earth r< aeally to a 



new form of equilibrium, then there is possibility of a cumula- 

 tive effect; and the pole may have wandered some 10° or 15° 

 from its primitive position, or have made a smaller excursion 

 and returned to near its old place. No such cum 

 possible, however, with respect to the obliquity of the ecliptic. 

 It is suggested that possibly the glacial period may not have 

 been really one of great cold, but that Europe and North 

 America may have been then in a much higher latitude, and 

 that on the pole retreating they were brongl 

 warmth. There seem to be, however, certain geological objec- 



