GEOLOGICAL CHANGES ON THE EAETH’S AXIS OE EOLATION. 
297 
with respect to the equator, would alter the position of the principal axis, without 
leaving any trace whatever of elevation or depression for geologists to discover. 
The discrepancy which is found between the ellipticity of the earth, as deduced from 
various arcs of meridian, is, I presume, attributable to real inequalities in the earth’s 
form, and not entirely to errors of observation and to the elliptical form of the equatorial 
section. It seems, moreover, quite possible that these wide-spread inequalities may have 
varied from time to time. 
Hence, even if the deposit of strata in the sea did not produce a continual shifting of 
the weights on the earth’s surface, and even if geologists should ultimately come to the 
conclusion that there has never been any consentaneous elevation and depression of very 
large continents relative to the sea-level, but that the oscillations of level have always 
been local, it would by no means follow that the earth’s axis has remained geographi- 
cally fixed. 
V. NUMEEICAL APPLICATION TO THE CASE OE THE EAETH. 
20. Continents and Seas of Maximum Effect. 
As far as I can learn, geologists are not of opinion that there is any more reason why 
upheavals and subsidences should take place at one part of the earth’s surface than at 
another. It is accordingly of interest to suppose the elevations and depressions to take 
place in the most favourable places for shifting the axis of figure. The area over which 
a consentaneous change may take place is also a matter of opinion. 
The theorem in maxima and minima in Part III. makes it easy to construct a table 
from which that area may be selected which seems most probable to geologists. The 
following Table is formed by interpolation in the Table in sec. 14 ; the first column gives 
the fraction of the earth’s surface over which an elevation is supposed to take place, a 
depression over an equal area taking place simultaneously. The second column gives 
the angular shift in the earth’s axis of figure, due to 10,000 feet of effective elevation; 
as was shown in Part IV., this would convert a deep ocean into a continent. If 
10,000 feet be thought too high an estimate, the last column may be reduced in any 
desired proportion. Lastly, fig. 2 shows the forms of these continents and seas of 
maximum effect. 
Area of elevation 
or subsidence, as 
fraction of Earth’s 
surface. 
Deflection of pole 
for 10,000 feet 
effective elevation. 
•001 
H' 
•005 
nf 
•01 
22 f 
•05 
l 0 46f 
•1 
3° 17' 
•15 
4° 33|' 
•2 
5° 36|' 
•5 
8° 4 1' 
N.B. The area of Africa is about *059, and of S. America about -033 of the Earth’s surface. 
2 t 2 
