finally consumed.

Monuments are smaller masses and may be but partially detached
from the cliff face. In the breaking down of sheets of horizontal
strata, outliers grow smaller and smaller and are reduced to
massive rectangular monuments resembling castles (Fig. 17). The
rock castle falls into ruin, leaving here and there an isolated
tower; the tower crumbles to a lonely pillar, soon to be
overthrown. The various and often picturesque shapes of monuments
depend on the kind of rock, the attitude of the strata, and the
agent by which they are chiefly carved. Thus pillars may have a
capital formed of a resistant stratum. Monuments may be undercut
and come to rest on narrow pedestals, wherever they weather more
rapidly near the ground, either because of the greater moisture
there, or--in arid climates--because worn at their base by
drifting sands.

Stony clays disintegrating under the rain often contain bowlders
which protect the softer material beneath from the vertical blows
of raindrops, and thus come to stand on pedestals of some height.
One may sometimes see on the ground beneath dripping eaves pebbles
left in the same way, protecting tiny pedestals of sand.

MOUNTAIN PEAKS AND RIDGES. Most mountains have been carved out of
great broadly uplifted folds and blocks of the earth's crust.
Running water and glacier ice have cut these folds and blocks into
masses divided by deep valleys; but it is by the weather, for the
most part, that the masses thus separated have been sculptured to
the present forms of the individual peaks and ridges.