ent shores, before the species of European
forest-trees will die out, he would reply that such alterations in the
inanimate world might be multiplied indefinitely before he should have
reason to anticipate, by reference to any known data, that the existing
species of trees in our forests would disappear and give place to
others. In a word, the movement of the inorganic world is obvious and
palpable, and might be likened to the minute-hand of a clock, the
progress of which can be seen and heard, whereas the fluctuations of the
living creation are nearly invisible, and resemble the motion of the
hour-hand of a timepiece. It is only by watching it attentively for some
time, and comparing its relative position after an interval, that we can
prove the reality of its motion.[255]

CHAPTER XII.

DIFFERENCE IN TEXTURE OF THE OLDER AND NEWER ROCKS.

Consolidation of fossiliferous strata--Some deposits originally
solid--Transition and slaty texture--Crystalline character of
Plutonic and Metamorphic rocks--Theory of their origin--Essentially
subterranean--No proofs that they were produced more abundantly at
remote periods.

Another argument in favor of the dissimilarity of the causes operating
at remote and recent eras has been derived by many geologists from the
more compact, stony, and crystalline texture of the older as compared
with the newer rocks.

_Consolidation of strata._--This subject may be considered, first in
reference to the fossiliferous strata; and, secondly, in reference to
those crystalline and stratified rocks which contain no organic remains,
such as gneiss and mica-schist. There can be no doubt that the former of
these classes, or the fossiliferous, are generally more compact and
stony in proportion as they are more ancient. It is also certain that a
great part of them were originally in a soft and incoherent state, and
that they have been since consolidated. Thus we find occasionally that
shingle and sand have been agglutinated firmly together by a ferruginous
or siliceous cement, or that lime in solution has been introduced, so as
to bind together materials previously incoherent. Organic remains have
sometimes suffered a singular transformation, as for example,] where
shells, corals, and wood are silicified, their calcareous or ligneous
matter having been replaced by nearly pure silica. The constituents of
some beds have probably set and become hard for the first time when th