gist, and consequently arriving at grand and comprehensive views
in geology. He communicated the results of his observations
unreservedly, and with the fearless spirit of one who was conscious that
love of truth was the sole stimulus of his exertions. When at length he
had matured his views, he published, in 1788, his "Theory of the
Earth,"[104] and the same, afterwards more fully developed in a separate
work, in 1795. This treatise was the first in which geology was declared
to be in no way concerned about "questions as to the origin of things;"
the first in which an attempt was made to dispense entirely with all
hypothetical causes, and to explain the former changes of the earth's
crust by reference exclusively to natural agents. Hutton labored to
give fixed principles to geology, as Newton had succeeded in doing to
astronomy; but, in the former science, too little progress had been made
towards furnishing the necessary data, to enable any philosopher,
however great his genius, to realize so noble a project.

_Huttonian theory._--"The ruins of an older world," said Hutton, "are
visible in the present structure of our planet; and the strata which now
compose our continents have been once beneath the sea, and were formed
out of the waste of pre-existing continents. The same forces are still
destroying, by chemical decomposition or mechanical violence, even the
hardest rocks, and transporting the materials to the sea, where they are
spread out, and form strata analogous to those of more ancient date.
Although loosely deposited along the bottom of the ocean, they become
afterwards altered and consolidated by volcanic heat, and then heaved
up, fractured, and contorted."

Although Hutton had never explored any region of active volcanoes, he
had convinced himself that basalt and many other trap-rocks were of
igneous origin, and that many of them had been injected in a melted
state through fissures in the older strata. The compactness of these
rocks, and their different aspect from that of ordinary lava, he
attributed to their having cooled down under the pressure of the sea;
and in order to remove the objections started against this theory, his
friend, Sir James Hall, instituted a most curious and instructive series
of chemical experiments, illustrating the crystalline arrangement and
texture assumed by melted matter cooled under high pressure.

The absence of stratification in granite, and its analogy, in mineral
characte