are able to subdue the land.] As streams grow old they approach
more and more closely to baselevel, although they are never able
to attain it. Some slight slope is needed that water may flow and
waste be transported over the land. Meanwhile the relief of the
land has ever lessened. The master streams and their main
tributaries now wander with sluggish currents over the broad
valley floors which they have planed away; while under the erosion
of their innumerable branches and the wear of the weather the
divides everywhere are lowered and subdued to more and more gentle
slopes. Mountains and high plateaus are thus reduced to rolling
hills, and at last to plains, surmounted only by such hills as may
still be unreduced to the common level, because of the harder
rocks of which they are composed or because of their distance from
the main erosion channels. Such regions of faint relief, worn down
to near base level by subaerial agencies, are known as PENEPLAINS
(almost plains). Any residual masses which rise above them are
called MONADNOCKS, from the name of a conical peak of New
Hampshire which overlooks the now uplifted peneplain of southern
New England.

In its old age a region becomes mantled with thick sheets of fine
and weathered waste, slowly moving over the faint slopes toward
the water ways and unbroken by ledges of bare rock. In other
words, the waste mantle also is now graded, and as waterfalls have
been effaced in the river beds, so now any ledges in the wide
streams of waste are worn away and covered beneath smooth slopes
of fine soil. Ground water stands high and may exude in areas of
swamp. In youth the land mass was roughhewn and cut deep by stream
erosion. In old age the faint reliefs of the land dissolve away,
chiefly under the action of the weather, beneath their cloak of