CHAP IX.
To know the temperature of the interior parts of the
globe at the present period, and the effects depending
on its condition in this respect, is important, as furnishing
one, and that, perhaps, the most instructive, of the
elements for computing the changes which have, in
earlier times, affected its structure and configuration, and
varied its adaptations for organic life. By combining
such knowledge of the subterranean parts of the earth
as they now are, with inferences concerning more ancient
periods, we are to seek the laws of action and variation
of terrestrial heat, and, with the help of chemical and
mechanical philosophy, to arrive at a general contemplation
or "theory" of this part of geological science.
Once well established, such a "theory" will be fertile
of deductions bearing on all the known phenomena of
organic and inorganic action: the recorded facts of
geology form, on the other hand, a parallel series of
terms, which involve the same elements: by comparison
of these two scales, the progress made in the interpretation
of nature will readily appear, and the lines of
further research will be clearly indicated.
The phenomena indicative of the presence and degree of heat below the surface of the earth, are either such as mark its ordinary and regular state, as HOT SPRINGS, which, with a few exceptions, are not known to vary in their temperature, and VOLCANOS, which mark, in their epochs of critical action and their periods of repose, the measure of the intermitting agencies connected with their origin, growth, and decay. The conclusions which arise from these cognate phenomena may
