GEOLOGICAL CHANGES ON THE EARTH’S AXIS OE ROTATION. 
305 
rough adjustment to a figure of equilibrium. If this adjustment is, as seems probable, 
by an earthquake, it will take place with reference to the axis of rotation at the instant 
of the earthquake. Now there exists in erosion and marine deposits a cause of terres- 
trial deformation which is certainly independent of such adjustments; and it seems 
probable that the causes of geological upheaval and subsidence are so also. We have 
therefore clearly a state of things in which the pole may wander indefinitely from its 
primitive position. On this hypothesis, as in successive periods the continents have 
risen and fallen, the pole may have worked its way, in a devious course, some 10° or 15° 
away from its geographical position at consolidation, or may have made an excursion 
of smaller amount and have returned to near its old position. May not the Glacial 
Period, then, have been only apparently a period of great cold 1 If at that period the 
N. pole stood somewhere where Greenland now stands, would not the whole of Europe 
and a large part of N. America have been glaciated % And if the N. pole retreated to 
its present position, would it not leave behind it the appearance of a very cold climate 
having prevailed in those regions \ 
But although such a cumulative effect is possible with respect to the geographical 
position of the pole, none such is possible with respect to the obliquity of the ecliptic. 
Now this kind of wandering of the poles would of course require extensive and 
numerous deformations, and it is hard to see how there can have been a shifting of the 
surface weights sufficient to produce it, without frequent changes in the geographical 
distribution of land and water. If, then, geologists are right in supposing that where 
the continents now stand they have always stood, would it not be almost necessary to 
give up any hypothesis which involved a very wide excursion of the poles \ 
Appendix A. (See p. 279.) 
To calculate 5h and in a supposed case of elevation and subsidence. 
Take the case of sec. 21 (fig. 3), where the elevation is given by lit sin 20 cos 2 cp, from 
$=0 to 5r, and from <p = — ^ to and zero over the rest of the sphere. Suppose that 
the internal motion is entirely confined to the quarter of the sphere defined by the 
above limits of 0 and cp , that radial particles are always radial, and that the motion is 
entirely meridional. 
Let 9+S be the disturbed colatitude of the point 9, <p. Then the equation of conti- 
nuity, which expresses that the volume of the elementary pyramid ^c 3 sin 0 db dtp remains 
constant, when 0 becomes 0+S-, is 
^ (3- sin 9) + ~ sin 9 sin 29 cos 2<p = 0, 
the integral of which is 
2 h 
^ sin 9+qy t cos 2<p sin 3 9=a constant ; 
2 u 2 
