and atmospheric agencies, we see the like ever growing complications of
effects. The denuding actions of air and water have, from the beginning,
been modifying every exposed surface; everywhere causing many different
changes. Oxidation, heat, wind, frost, rain, glaciers, rivers, tides,
waves, have been unceasingly producing disintegration; varying in kind
and amount according to local circumstances. Acting upon a tract of
granite, they here work scarcely an appreciable effect; there cause
exfoliations of the surface, and a resulting heap of _debris_ and
boulders; and elsewhere, after decomposing the feldspar into a white
clay, carry away this and the accompanying quartz and mica, and deposit
them in separate beds, fluviatile and marine. When the exposed land
consists of several unlike formations, sedimentary and igneous, the
denudation produces changes proportionably more heterogeneous. The
formations being disintegrable in different degrees, there follows an
increased irregularity of surface. The areas drained by different rivers
being differently constituted, these rivers carry down to the sea
different combinations of ingredients; and so sundry new strata of
distinct composition are formed.

And here indeed we may see very simply illustrated, the truth, which we
shall presently have to trace out in more involved cases, that in
proportion to the heterogeneity of the object or objects on which any
force expends itself, is the heterogeneity of the results. A continent
of complex structure, exposing many strata irregularly distributed,
raised to various levels, tilted up at all angles, must, under the same
denuding agencies, give origin to immensely multiplied results; each
district must be differently modified; each river must carry down a
different kind of detritus; each deposit must be differently distributed
by the entangled currents, tidal and other, which wash the contorted
shores; and this multiplication of results must manifestly be greatest
where the complexity of the surface is greatest.

It is out of the question here to trace in detail the genesis of those
endless complications described by Geology and Physical Geography: else
we might show how the general truth, that every active force produces
more than one change, is exemplified in the highly involved flow of the
tides, in the ocean currents, in the winds, in the distribution of rain,
in the distribution of heat, and so forth. But not to dwell upon these