isted upon formerly, that crystalline rocks,
such as granite, gneiss, mica-schist, quartzite, and others were
produced in the greatest abundance in the earlier ages of the planet,
and that their formation has ceased altogether in our own times, will be
controverted in the next chapter.

_Gradual development of subterranean movements._--The extreme violence
of the subterranean forces in remote ages has been often inferred from
the facts that the older rocks are more fractured and dislocated than
the newer. But what other result could we have anticipated if the
quantity of movement had been always equal in equal periods of time?
Time must, in that case, multiply the derangement of strata in the ratio
of their antiquity. Indeed the numerous exceptions to the above rule
which we find in nature, present at first sight the only objection to
the hypothesis of uniformity. For the more ancient formations remain in
many places horizontal, while in others much newer strata are curved and
vertical. This apparent anomaly, however, will be seen in the next
chapter to depend on the irregular manner in which the volcanic and
subterranean agency affect different parts of the earth in succession,
being often renewed again and again in certain areas, while others
remain during the whole time at rest.

That the more impressive effects of subterranean power, such as the
upheaval of mountain-chains, may have been due to multiplied convulsions
of moderate intensity rather than to a few paroxysmal explosions, will
appear the less improbable when the gradual and intermittent development
of volcanic eruptions in times past is once established. It is now very
generally conceded that these eruptions have their source in the same
causes as those which give rise to the permanent elevation and sinking
of land; the admission, therefore, that one of the two volcanic or
subterranean processes has gone on gradually, draws with it the
conclusion that the effects of the other have been elaborated by
successive and gradual efforts.

_Faults._--The same reasoning is applicable to great _faults_, or those
striking instances of the upthrow or downthrow of large masses of rock,
which have been thought by some to imply tremendous catastrophes wholly
foreign to the ordinary course of nature. Thus we have in England
faults, in which the vertical displacement is between 600 and 3000 feet,
and the horizontal extent thirty miles or more, the width of the
fissures