continental; and when we consider the great frequency of slight
movements in certain districts, we can hardly suppose that a day, if,
indeed, an hour, ever passes without one or more shocks being
experienced in some part of the globe. We have also seen that in Sweden,
and other countries, changes in the relative level of sea and land may
take place without commotion, and these perhaps produce the most
important geographical and geological changes; for the position of land
may be altered to a greater amount by an elevation or depression of one
inch over a vast area, than by the sinking of a more limited tract, such
as the forest of Aripao, to the depth of many fathoms at once.[789]

It must be evident, from the historical details above given, that the
force of subterranean movement, whether intermittent or continuous,
whether with or without disturbance, does not operate at random, but is
developed in certain regions only; and although the alterations produced
during the time required for the occurrence of a few volcanic eruptions
may be inconsiderable, we can hardly doubt that, during the ages
necessary for the formation of large volcanic cones, composed of
thousands of lava currents, shoals might be converted into lofty
mountains, and low lands into deep seas.

In a former chapter (p. 198), I have stated that aqueous and igneous
agents may be regarded as antagonist forces; the aqueous laboring
incessantly to reduce the inequalities of the earth's surface to a
level, while the igneous are equally active in renewing the unevenness
of the surface. By some geologists it has been thought that the
levelling power of running water was opposed rather to the _elevating_
force of earthquakes than to their action generally. This opinion is,
however, untenable; for the sinking down of the bed of the ocean is one
of the means by which the gradual submersion of land is prevented. The
depth of the sea cannot be increased at any one point without a
universal fall of the waters, nor can any partial deposition of sediment
occur without the displacement of a quantity of water of equal volume,
which will raise the sea, though in an imperceptible degree, even to the
antipodes. The preservation, therefore, of the dry land may sometimes be
effected by the subsidence of part of the earth's crust (that part,
namely, which is covered by the ocean), and in like manner an upheaving
movement must often tend to destroy land; for if it render the b