ses--besides finding that the
evidence permits us to assume such commencement to have been
inconceivably remote, as compared even with the vast eras of geology; we
are not without positive grounds for inferring the inconceivable
remoteness of such commencement. Modern geology has established truths
which are irreconcilable with the belief that the formation and
destruction of strata began when the Cambrian rocks were formed; or at
anything like so recent a time. One fact from _Siluria_ will suffice.
Sir R. Murchison estimates the vertical thickness of Silurian strata in
Wales, at from 26,000 to 27,000 feet, or about five miles; and if to
this we add the vertical depth of the Cambrian strata, on which the
Silurians lie conformably, there results, on the lowest computation, a
total depth of some seven miles. Now it is held by geologists, that this
vast series of formations must have been deposited in an area of gradual
subsidence. These beds could not have been thus laid one on another in
regular order, unless the Earth's crust had been at that place sinking,
either continuously or by small steps. Such an immense subsidence,
however, must have been impossible without a crust of great thickness.
The Earth's molten nucleus tends ever, with enormous force, to assume
the form of a regular oblate spheroid. Any depression of its crust below
the surface of equilibrium, and any elevation of its crust above that
surface, have to withstand immense resistances. It follows inevitably
that, with a thin crust, nothing but small elevations and subsidences
would have been possible; and that, conversely, a subsidence of seven
miles implies a crust of great strength, or, in other words, of great
thickness. Indeed, if we compare this inferred subsidence in the
Silurian period, with such elevations and depressions as our existing
continents and oceans display, we see no evidence that the Earth's crust
was appreciably thinner then than now. What are the implications? If, as
geologists generally admit, the Earth's crust has resulted from that
slow cooling which is even still going on--if we see no sign that at the
time when the earliest Cambrian strata were formed, this crust was
appreciably thinner than now; we are forced to conclude that the era
during which it acquired that great thickness possessed in the Cambrian
period, was enormous as compared with the interval between the Cambrian
period and our own. But during the incalculable series of