but in places
the old dry cliff-lines can be discerned beneath like a skeleton.
The precipitation there has not been great enough to destroy the old
lines--only enough to mask them.

* There could be a balance of precipitation and still very little
snow- or rainfall, or they might be very great.

The "inner gorge" of the Grand Canyon appears to have been cut far more
rapidly than the outer one, and at a much later period; were this not
the case there would be no inner gorge. It is a singular fact that some
side canyons, the Kanab, for example, while now possessing no running
water, or at best a puny rivulet, and depending for their corrasion on
intermittent floods, meet on equal terms the great Colorado, the giant
that never for a second ceases its ferocious attack. Admitting that the
sharper declivity of the Kanab would enhance its power of corrasion,
nevertheless we should expect to see it approach the Grand Canyon by
leaps and bounds, like the Havasupai farther down, but, on the contrary,
there are parts that appear to be at a standstill in corrasion, or even
filling up, and its floor is a regular descent, except for the last
three or four miles where the canyon is clogged by huge rocks that
seem to have fallen from above. The maximum height of its present
flood-waters is about six feet, proved by a fern-covered calcareous
deposit, projecting some fifteen feet, caused by a spring (Shower-Bath
Spring) on the side of the wall, seven or eight miles above the mouth,
which is never permitted by the floods to build nearer the floor of
the canyon. A suspicion arises, on contemplating some of these apparent
discrepancies, that the prevailing conditions of corrasion are not
what they were at some earlier period, when they were such that it was
rendered more rapid and violent; that there was perhaps an epoch when
these deep-cut tributary canyons carried perennial streams, and when
the volume of the Colorado itself was many times greater, possessing a
multiplied corrasive power, while the adjacent areas were about as arid
as now. At such a time, perhaps, the Colorado performed the main work of
the inner gorge, the Kanab, and similar affluents, their deep now rather
evenly graded canyons. Such an increase of volume, if we suppose the
aridity to remain as now, could have come about only by an increase of
precipitation on the mountain summits. During the Glacial Epoch, the
Rocky Mountain summits were considerably glaciate