s, the
weathering of rocks by atmospheric water and carbonic acid.

Sedimentary strata must have been originally deposited in planes nearly
horizontal. Vast numbers of them have been forced, either by paroxysms
at intervals or by gradual movement, into all manner of angular
inclinations. Whatever explanations we may offer of these innumerable
and immense tilts and fractures, they would seem to demand for their
completion an inconceivable length of time.

The coal-bearing strata in Wales, by their gradual submergence, have
attained a thickness of 12,000 feet; in Nova Scotia of 14,570 feet.
So slow and so steady was this submergence, that erect trees stand one
above another on successive levels; seventeen such repetitions may be
counted in a thickness of 4,515 feet. The age of the trees is proved
by their size, some being four feet in diameter. Round them, as they
gradually went down with the subsiding soil, calamites grew, at one
level after another. In the Sydney coal-field fifty-nine fossil forests
occur in superposition.

Marine shells, found on mountain-tops far in the interior of continents,
were regarded by theological writers as an indisputable illustration of
the Deluge. But when, as geological studies became more exact, it was
proved that in the crust of the earth vast fresh-water formations are
repeatedly intercalated with vast marine ones, like the leaves of a
book, it became evident that no single cataclysm was sufficient
to account for such results; that the same region, through gradual
variations of its level and changes in its topographical surroundings,
had sometimes been dry land, sometimes covered with fresh and sometimes
with sea water. It became evident also that, for the completion of these
changes, tens of thousands of years were required.

To this evidence of a remote origin of the earth, derived from the vast
superficial extent, the enormous thickness, and the varied characters of
its strata, was added an imposing body of proof depending on its fossil
remains. The relative ages of formations having been ascertained, it
was shown that there has been an advancing physiological progression of
organic forms, both vegetable and animal, from the oldest to the most
recent; that those which inhabit the surface in our times are but an
insignificant fraction of the prodigious multitude that have inhabited
it heretofore; that for each species now living there are thousands
that have become extinct. Thoug