d
of the same mineral ingredients. As the hardest crystals produced
artificially in the laboratory require the longest time for their
formation, so we must suppose that where the cooling down of melted
matter takes place by insensible degrees, in the course of ages, a
variety of minerals will be produced far harder than any formed by
natural processes within the short period of human observation.

These subterranean volcanic rocks, moreover, cannot be stratified in the
same manner as sedimentary deposits from water, although it is evident
that when great masses consolidate from a state of fusion, they may
separate into natural divisions; for this is seen to be the case in
many lava-currents. We may also expect that the rocks in question will
often be rent by earthquakes, since these are common in volcanic
regions; and the fissures will be often injected with similar matter, so
that dikes of crystalline rock will traverse masses of similar
composition. It is also clear, that no organic remains can be included
in such masses, as also that these deep-seated igneous formations
considered in mass must underlie all the strata containing organic
remains, because the heat proceeds from below upwards, and the intensity
required to reduce the mineral ingredients to a fluid state must destroy
all organic bodies in rocks included in the midst of them.

If by a continued series of elevatory movements, such masses shall
hereafter be brought up to the surface, in the same manner as
sedimentary marine strata have, in the course of ages, been upheaved to
the summit of the loftiest mountains, it is not difficult to foresee
what perplexing problems may be presented to the geologist. He may then,
perhaps, study in some mountain-chain the very rocks produced at the
depth of several miles beneath the Andes, Iceland, or Java, in the time
of Leibnitz, and draw from them the same conclusion which that
philosopher derived from certain igneous products of high antiquity; for
he conceived our globe to have been, for an indefinite period, in the
state of a comet, without an ocean, and uninhabitable alike by aquatic
or terrestrial animals.

CHAPTER XXVII.

EARTHQUAKES AND THEIR EFFECTS.

Earthquakes and their effects--Deficiency of ancient
accounts--Ordinary atmospheric phenomena--Changes produced by
earthquakes in modern times considered in chronological
order--Earthquake in Syria, 1837--Earthquakes in Chili in 1837 and