gate effects of innumerable eruptions, each of which may have been
comparable in violence to those now experienced in volcanic regions.

It may indeed be said that we have as yet no data for estimating the
relative volume of matter simultaneously in a state of fusion at two
given periods, as if we were to compare the columnar basalt of Staffa
and its environs with the lava poured out in Iceland in 1783; but for
this very reason it would be rash and unphilosophical to assume an
excess of ancient as contrasted with modern outpourings of melted matter
at particular periods of time.[240] It would be still more presumptuous
to take for granted that the more deep-seated effects of subterranean
heat surpassed at remote eras the corresponding effects of internal heat
in our own times. Certain porphyries and granites, and all the rocks
commonly called plutonic, are now generally supposed to have resulted
from the slow cooling of materials fused and solidified under great
pressure; and we cannot doubt that beneath existing volcanoes there are
large spaces filled with melted stone, which must for centuries remain
in an incandescent state, and then cool and become hard and crystalline
when the subterranean heat shall be exhausted. That lakes of lava are
continuous for hundreds of miles beneath the Chilian Andes, seems
established by observations made in the year 1835.[241]

Now, wherever the fluid contents of such reservoirs are poured out
successively from craters in the open air, or at the bottom of the sea,
the matter so ejected may afford evidence by its arrangement of having
originated at different periods; but if the subterranean residue after
the withdrawal of the heat be converted into crystalline or plutonic
rock, the entire mass may seem to have been formed at once, however
countless the ages required for its fusion and subsequent refrigeration.
As the idea that all the granite in the earth's crust was produced
simultaneously, and in a primitive state of the planet, has now been
universally abandoned; so the suggestion above adverted to, may put us
on our guard against too readily adopting another opinion, namely, that
each large mass of granite was generated in a brief period of time.

Modern writers indeed, of authority, seem more and more agreed that in
the case of granitic rocks, the passage from a liquid or pasty to a
solid and crystalline state must have been an extremely gradual process.

The doctrine so much ins