those
superficial actions--such as those of tides, waves, rain, rivers, solar
heat, frost, vitality, vegetable and animal (passing by many others less
obvious)--which perpetually modify, alter or renew the surface of our
world, and maintain the existing regimen of the great machine, and of
its inhabitants. These last are the domain of Geology, properly so
called. No geological system can be well founded, or can completely
explain the working of the world's system as we now see it, that does
not start from Vulcanicity as thus defined; and this is equally true,
whether, as do most geologists, we include within the term Geology
everything we can know about our world as a whole, exclusive of what
Astronomy teaches as to it, dividing Geology in general into Physical
Geology--the boundaries of which are very indistinct--and
Stratigraphical Geology, whose limits are equally so.

It has been often said that Geology in this widest sense begins where
Astronomy or Cosmogony ends its information as to our globe, but this is
scarcely true.

Vulcanicity--or Geology, if we choose to make it comprehend that--must
commence its survey of our world as a nebula upon which, for unknown
ages, thermic, gravitant and chemical forces were operative, and to the
final play of which, the form, density and volume, as well as order of
deposition of the different elements in the order of their chemical
combination and deposition was due, when first our globe became a liquid
or partly liquid spheroid, and which have equally determined the
chemical nature of the materials of the outward rind of the earth that
now is, and with these some of the primary conditions that have fixed
the characters, nature and interdependence of the vegetables and animals
that inhabit it. Physical Astronomy and Physical Geology, through
Vulcanicity, thus overlap each other; the first does not end where the
second begins; and in every sure attempt to bring Geology to that
pinnacle which is the proper ideal of its completed design--namely, the
interpretation of our world's machine, as part of the universal Cosmos
(so far as that can ever become known to our limited observation and
intelligence)--we must carry with us astronomic considerations, we must
keep in view events anterior to the "_status consistentior_" of
Leibnitz, nor lose sight of the fact that the chain of causation is one
endless and unbroken; that forces first set moving, we know not when or
how, the dim remot