science which derives its name from the Greek ge, the earth, and logos, a
discourse. Previously to experience we might have imagined that investigations
of this kind would relate exclusively to the mineral kingdom, and to the various
rocks, soils, and metals, which occur upon the surface of the earth, or at
various depths beneath it. But, in pursuing such researches, we soon find
ourselves led on to consider the successive changes which have taken place in
the former state of the earth's surface and interior, and the causes which have
given rise to these changes; and, what is still more singular and unexpected, we
soon become engaged in researches into the history of the animate creation, or
of the various tribes of animals and plants which have, at different periods of
the past, inhabited the globe.

All are aware that the solid parts of the earth consist of distinct substances,
such as clay, chalk, sand, limestone, coal, slate, granite, and the like; but
previously to observation it is commonly imagined that all these had remained
from the first in the state in which we now see them-- that they were created in
their present form, and in their present position. The geologist soon comes to a
different conclusion, discovering proofs that the external parts of the earth
were not all produced in the beginning of things in the state in which we now
behold them, nor in an instant of time. On the contrary, he can show that they
have acquired their actual configuration and condition gradually, under a great
variety of circumstances, and at successive periods, during each of which
distinct races of living beings have flourished on the land and in the waters,
the remains of these creatures still lying buried in the crust of the earth.

By the "earth's crust," is meant that small portion of the exterior of our
planet which is accessible to human observation. It comprises not merely all of
which the structure is laid open in mountain precipices, or in cliffs
overhanging a river or the sea, or whatever the miner may reveal in artificial
excavations; but the whole of that outer covering of the planet on which we are