_ On the Physical Geology of the United States, §c. 293 
had before its elevation. Inertia, therefore, would cause the mass 
at the top, to press to the westward with a force. proportional to 
its mass, and the above mentioned velocity, and at intermediate 
heights with a proportionably less momentum. If the strata be 
capable of yielding, they must, when elevated in highly curved 
wrinkles, tend to fall over to the westward, as a consequence of 
the influence of inertia and the revolution af the earth from 
to E. on its axis. 
We have reason to believe, both from the action of natural 
laws and from observation, that the aggregate amount of subsi- 
dence, or of contraction of the mass of the earth, at least equals, 
if it does not exceed the amount of elevation above former water 
levels. 'The evidences above adduced of variable currents de- 
positing strata of various textures and composition ; of conform- 
able and unconformable strata of the same ages; and the influ- 
ence of inertia and the rotation of the earth producing the fold- 
ed axes with an eastwardly dip, all tend to render it more than 
probable, that the secondary causes of the phenomena were parox- 
ysmal rather than secular, and that they occurred at distant in- 
tervals of time, with long periods of comparative repose. 
It has already been remarked, there are no evidences known, 
that there has been more water upon the surface of the earth at 
any preceding time than at present.* It follows from the various 
facts known, that the relative levels of the land and water have 
changed and the land must have been elevated, or the bed of the 
ocean must have sunk, or that both these effects have been more 
or less extensively produced. toe$ 
The only causes to which we can ascribe such relative chan- 
ges of level that have not yet been considered, are. 
Ist. Some subterranean force tending to ara parts of the 
earth’s surface. : 
2d. The collapse of the crust of the globe by a secular refrige- 
ration upon its contracted nucleus, causing depression In some parts 
and elevation in others.t The powerful lateral thrust, that would 
be caused by a subsidence of the solidified crust upon a contracted 
nucleus which it is too’large to envelope closely, would cause 
an elevation of some parts, with wrinkles and plications of the 
strata, and may be supposed to be amply sufficient to elevate 
* See p. 284, ante. t See p. 287. 
Vol. xx1x, No. 2.—July-Sept. 1845. 38 
