uld have become the grand repositories of organic
matter, accumulated without that intermixture of earthy sediment which
so generally characterizes the subaqueous strata.

I have already stated that, in the known operation of the _igneous_
causes, a real antagonist power is found, which may counterbalance the
levelling action of running water (p. 563); and there seems no good
reason for presuming that the upheaving and depressing force of
earthquakes, together with the ejection of matter by volcanoes, may not
be fully adequate to restore that inequality of the surface which rivers
and the waves and currents of the ocean annually tend to lessen. If a
counterpoise be derived from this source, the quantity and elevation of
land above the sea may for ever remain the same, in spite of the action
of the aqueous causes, which, if thus counteracted, may never be able to
reduce the surface of the earth more nearly to a state of equilibrium
than that which it has now attained; and, on the other hand, the force
of the aqueous agents themselves might thus continue for ever
unimpaired.

_Conservative influence of vegetation._--If, then, vegetation cannot act
as an antagonist power amid the mighty agents of change which are always
modifying the surface of the globe, let us next inquire how far its
influence is conservative,--how far it may retard the levelling effects
of running water, which it cannot oppose, much less counterbalance.

It is well known that a covering of herbage and shrubs may protect a
loose soil from being carried away by rain, or even by the ordinary
action of a river, and may prevent hills of loose sand from being blown
away by the wind; for the roots bind together the separate particles
into a firm mass, and the leaves intercept the rain-water, so that it
dries up gradually, instead of flowing off in a mass and with great
velocity. The old Italian hydrographers make frequent mention of the
increased degradation which has followed the clearing away of natural
woods in several parts of Italy. A remarkable example was afforded in
the Upper Val d' Arno, in Tuscany, on the removal of the woods clothing
the steep declivities of the hills by which that valley is bounded. When
the ancient forest laws were abolished by the Grand Duke Joseph, during
the last century, a considerable tract of surface in the Cassentina (the
Clausentinium of the Romans) was denuded, and immediately the quantity
of sand and soil washed down