1883. | Geological Effects of a Varying Rotation of the Earth. 19 
level would remain approximately stationary, would be near thirty 
degrees of latitude. It would describe a see-saw movement, as 
it were, around those parallels. The variation in altitude at the 
equator would be about one-half as much as at the poles, in any 
change in which the volume of the earth remained the same. 
A decrease of velocity of rotation would, in this way, eventu- 
ally lift the tropical lands so high above the sea, that their weight 
would become a force sufficient to cause their depression, which, 
in time, would either lift the tropical sea-beds, or the higher lati- 
tudes of both land and sea-bottom. 
The former would have little effect to accelerate the earth’s 
rotation, because the average altitude of equatorial continents and 
seas would remain the same. It would, however, have the effect 
to drive the waters still more toward the poles. Eventually, how- 
ever, if not at first, equatorial lands would sink, at the expense of 
raising higher latitudes, and acceleration would result. This de- 
. pression, when begun, would probably go beyond the point just 
sufficient to establish equilibrium in the earth’s crust, and would 
continue, even while the rotation was being accelerated by the 
depressions. For momentum, in all known cases of vibration, 
carries the vibratory body beyond the point of rest. Any increase 
of acceleration would be closely followed by a rise of the sea- 
level, within the tropics, and a lowering of the sea-level outside, 
increasing in amount toward the poles. This, with the extra fall 
of the tropical crust, would turn the tide, eventually, to such an 
acceleration, that the polar regions would be much elevated above 
the sea, and in time they would begin-to sink from their weight. 
This would become a retarding influence, which, with the con- 
tinued retarding influence of the sun and moon, would produce a 
transfer of water to the higher latitudes, and so the cycle of one 
vibration would be complete. Now, if these two forces alone 
should act upon sea and land, there would be, on the whole, a run- 
ning down, a graduation of vibrations into rest, only to be occa- 
sionally broken, perhaps, by varying astronomical relations; but 
| -another feature comes in to keep the great double pendulum 
swinging. The contraction of the earth will accelerate, by the 
depression of the tropical regions, and retard by depression of 
higher latitudes. This, therefore, would be a force to keep this 
vibration continued. The efficiency of this force can scarcely be 
questioned, at least for the earlier geological epochs, when we 
