GEOLOGY. 289 



In the 06th Proposition of the 1st Section of the Frincipia, Theorem 26, 

 Corollary 22, Newton says: "But let there be added anyAvhere between the 

 pole and the equator a heap of new matter, like a mountain, and this by its 

 perpetual endeavor to recede from the centre of its motion will disturb the 

 motion of the globe, and cause its poles to wander about its superficies, 

 describing circles about themselves and their opposite points." Matte's 

 Translation, 1729. 



We have no evidence that within the historic period there has been an 

 elevation of any mountain mass of such a magnitude as could produce an 

 appreciable change in the position of the poles or the equator, and no records 

 of astronomical observations could, therefore, show any such changes as 

 have been adverted to. But we have undoubted evidence that in the former 

 periods of the earth's history great mountain regions, such as the Andes, the 

 Himalayas, and the Rocky Mountains, have been thrown up in well-defined 

 successive geological epochs; and knowing how vastly greater these mountain 

 masses must originally have been, from the great degradation to Avhich in the 

 lapse of ages they have been subjected, and before the degraded matter was 

 spread out to fill up the inequalities of the surface of the earth, we can see 

 a probable cause for a commencement of what Newton calls " the evagation 

 of the poles," and also the cause of a change in their position being again 

 and again produced, until even the arctic regions may have been brought 

 from a tropical position to their present position. We can see also how 

 under the hypothesis there would be a gradual progress of a peculiar climate, 

 arctic, or temperate, or tropical, over the surface of the earth, giving facil- 

 ities to the spreading of a similar flora or fauna under the necessary con- 

 ditions of light and heat for their development. 



The solution of the difficult problem under consideration obviously turns 

 upon the question of whether the geologist can show that such mountain 

 masses may have been thrown up in former periods of the earth's history as 

 would produce an "evagation" of the poles. I think we can; and that the 

 changes of climate, the spreading of similar floras and faunas, and the 

 undulations and dislocations of the strata composing the crust of the earth, 

 are the necessary corollaries. A great number of other secondary minor 

 forces, such as the eruption of igneous matter in different parts of the world, 

 have, as is well known, been in operation to produce local changes; but the 

 evagation of the poles is, as I think, the only cause of those great, wide- 

 spread changes which have been adverted to. 



The facts established by our geological investigations may be thus formu- 

 lated : 



1st. We have evidence of great changes of climate in several successive 

 periods, but with this peculiarity, that whilst the climate of the earliest peri- 

 ods was nearly uniform in all parts of the globe, this uniformity disappears 

 in the more recent periods : the uniform character of the flora of the coal- 

 measures is a proof of the one, and the very different character of the flora 

 and fauna of the arctic, temperate, and tropical zones, marks the great 

 change which has taken place. 



Now these facts, if they stood alone, might be explained on the supposi- 

 tion that, from any cause whatever, the axis of the earth was at one time 

 perpendicular to the plane of the ecliptic, and that its inclination was changed 

 at the intervals which the changes of climate indicate until the axis reached 

 its present inclination of twenty-three degrees thirty minutes. 



With the axis perpendicular to the plane of the ecliptic, we should have at 



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