GEOLOGICAL CHANGES ON THE EAETH’S AXIS OE EOTATION. 
293 
fractions of the whole surface : a and v are indicated on one of the continents. The 
other hemisphere is the same as this figure, 
when seen in a looking-glass. It will be 
observed that the limiting case is when the 
two continents fill up two quarters of the 
earth, and the two seas the other two. 
It is clear that the greatest deflection 
of the polar axis which can be produced 
by the elevation of continents of height Jc 
and having a total area and the de- 
pression of similar seas, will be PK. 
A numerical Table of results will be given 
below, formed by interpolation in the above 
Table. 
Eig. 2. 
N.POLE 
IV. ON GEOLOGICAL CHANGES ON THE EAETH’S SUEEACE. 
16. The jpomts to be considered. 
It is now necessary to consider what kind and amount of superficial changes are 
brought about in the earth’s shape by such geological changes as are believed to have 
taken place. The points to be determined are : — 
i. Over what extent of the earth’s surface is there evidence of consentaneous subsi- 
dence, or upheaval, during any one period. 
ii. What is the extreme vertical amount of that subsidence or upheaval. 
iii. How the sea affects the local excesses and deficiencies of matter on the earth’s 
surface. 
iv. How marine and aerial erosion affect the distribution of the excess or deficiency 
of matter. 
v. The possibility of wide-spread deformations of the earth, which approximately 
carry the level surfaces with them. 
The object of this discussion is to find what areas and amounts of elevation and 
subsidence on a sealess and rainless globe are equivalent, as far as moving the principal 
axis, to those which obtain on the earth. These areas and effects will be referred to as 
“ effective areas and amounts of elevation or subsidence.” 
It is probable that during the elevation or subsidence of any large area, the change 
proceeds at unequal rates in different parts ; probably one part falls or rises more quickly 
than another, and then the latter gains on the former. But it has been shown, in the 
dynamical part of this paper, that the axis of rotation sensibly follows the axis of figure. 
Hence it is immaterial by what course the earth changes its configuration, provided the 
changes do not proceed by large impulses, a supposition which may be certainly excluded. 
