332 Influence of Geological Changes on EarWs Axis. [Nov. 23, 



l°46i'; if 3° 17'; and if i, 8° 4 J' *. In each case an equal area 

 is supposed to fall simultaneously. 



Other examples are then given for continents and seas which do not 

 satisfy the maximum condition ; in some the boundaries are abrupt cliffs, 

 in others shelving. 



The conclusion is ariived at, that a single large geological change, 

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

 alteration in the position of the pole of from one to three degrees of lati- 

 tude, on the hypothesis that there is no change in the law of internal 

 density. 



6. Various hypotheses as to the nature of the internal changes accom- 

 panying the deformation of the earth are discussed. 



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

 ing 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 assumptions, too long to recapitu- 

 late, it is shown that the previous 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 msignificant amount. Even if the intumescence 

 extends right down to the centre 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 the earlier results can only be stated as a superior 

 limit to what is possible. 



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 maintained view is correct, that the earth readjusts 

 itself periodically to a new form of equilibrium, then there is a possibility 

 of a cumulative 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 cumulation is 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 brought back again to the warmth. There seems to be, how- 

 ever, certain geological objections to this view. 



* The area of Africa is about '059, and of Soutli America about 'OoS of the earth's 

 surface. 



