304 
ME. GEORGE H. DARWIN ON THE INFLUENCE OE 
deformation, the forms of continent and depression which produce the greatest deflection 
of the poles, for the transport of a given quantity of matter from one part of the earth’s 
surface to another, are then investigated. These forms are shown, projected stereo- 
graphically, in fig. 2 (p. 293). 
Part IV. gives what evidence I have been able to collect of the areas and amounts of 
deformation to which the earth may have been subjected in geological history ; but as 
the discussion is not mathematical, it seems unnecessary to give an abstract thereof. 
Part V. gives numerical applications of the preceding theorems to the case of the earth, 
on the assumption that the internal density is unaltered by the deformation. From this 
it appears that the poles may have been deflected from 1° to 3° in any one geological 
period ; but the reader is referred back to that part for details. 
If upheaval and subsidence of the surface are due to a shrinking of the earth as a 
whole, but to a more rapid shrinking in some regions than others, the deflection of the 
poles is the same as that found where there is no disturbance of the strata of equal 
density. 
But if the upheaval and subsidence are due to local intumescence and contraction of 
the strata underneath the rising or falling areas, the previous numerical estimates must 
be largely reduced ; for the extent of this reduction the reader is referred to the Table 
in Section 23 (p. 302). 
It thus appears that the deflection of the poles first given is a superior limit to that 
which is possible. 
25. Conclusion. 
There remain, in conclusion, one or two miscellaneous points to be referred to. 
In a letter to Sir C. Lyell read before the Geological Society*, Sir John Herschel 
has pointed out that the isothermal strata near the surface of the earth must approxi- 
mately follow the solid surface. Therefore, when a thick stratum is deposited at the 
bottom of the ocean, the primitive bottom is gradually warmed and expands. There 
is thus a tendency for the upheaval of sea-beds, on which a large amount of matter has 
been deposited ; but this kind of upheaval certainly falls within the case of superficial 
intumescence, and could therefore affect the geographical position of the poles but little 
more than would be due merely to the weight of the deposited stratum. It must be 
noticed, moreover, that the weight of the deposited stratum would tend to compress the 
primitive sea-bed, and might counteract the expansion due to rise of temperature. 
If the earth were absolutely rigid the pole could never have wandered more than 
from 1° to 3° from its primitive position, whatever geological changes were successively 
to take place ; because the new pole could never be brought to a greater distance from 
its original position, by any fresh distribution of the matter forming the continents, than 
the maximum for this amount of matter arranged in continents of a like height. 
But it was maintained in Part I. that from time to time the earth makes a kind of 
* Proc. Geol. Soc. vol. ii. p. 549. 
