324 Probable Origin and Age of the Sun. [July, 
rainfall is greater than in the temperate regions. It has been 
shown that the rate at which a country is being lowered by 
subaerial denudation is mainly determined not so much by 
the character of its rocks as by the sediment-carrying 
power of its river systems. Consequently, other things 
being equal, the greater the rainfall the greater will be the 
rate of denudation. We know that the basin of the Ganges, 
for example, is being lowered by denudation at the rate of 
about 1 foot in 2300 years ; and this is probably not very far 
from the average rate at which the equatorial regions are 
being denuded. It is therefore evident that sub-aerial denu- 
dation is lowering the Equator as rapidly as the sea-level is 
sinking from loss of rotation, and that consequently we can- 
not infer from the present form of our globe what was its 
form when it solidified. In as far as tidal retardation can 
show to the contrary, its form, when solidification took place, 
may have been as oblate as that of the planet Jupiter. 
There is another circumstance which must be taken into 
account. The lowering of the Equator, by the transference 
of materials from the Equator to the higher latitudes, must 
tend to increase the rate of rotation, or, more properly, it 
must tend to lessen the rate of tidal retardation. 
The argument may be shown to be inconclusive from 
another consideration. The question as to whether the 
earth’s axis of rotation could ever have changed to such an 
extent as to have affedted the climate of the Poles is at 
present exciting a good deal of attention. The subjedt has 
recently been investigated with great care by Professor 
Haughton,* Mr. George Darwin, t the Rev. J. F. Twisden,J 
and others, and the general result arrived at may be ex- 
pressed in the words of Mr. G. Darwin : — “ If the earth be 
quite rigid no re-distribution of matter in new continents 
could ever have caused the deviation of the Pole from its 
present position to exceed the limit of about 3 0 .” 
Mr. Darwin has shown that, in order to produce a dis° 
placement of the Pole to the extent of only i° 46', an area 
equal to one-twentieth of the entire surface of the globe 
would have to be elevated to the height of two miles. The 
entire continent of Europe elevated two miles would not 
defledt the Pole much over half a degree. Assuming the 
mean elevation of the continents of Europe and Asia to be 
1000 feet, Prof. Houghton calculates that their removal 
would displace the Pole only 199*4 miles. 
* Proc. Roy. Soc., vol. xxvi., p. 51. 
f Proc. Roy* Soc., vol. xxv. ; p. 328. 
X Paper read before the Geological Society, February iist* tBfp 
