Though, therefore, the subject sketched on this page is sufficiently
trifling in itself, it is important as a perfect general type of the
overhanging of that kind of precipices, and of the mode in which they
are connected with the banks above. Fig. 88 shows its abstract leading
lines, consisting of one great parabolic line _x y_ falling to the brow,
curved aqueous lines down the precipice face, and the springing lines of
its vegetation, opposed by contrary curves on the farther cliff. Such an
arrangement, with or without vegetation, may take place on a small or
large scale; but a bolder projection than this, except by rare accident,
and on a small scale, cannot. If the reader will glance back to Plate
+37+, and observe the arrangement of the precipices on the right hand,
he will now better understand what Turner means by them. But the whole
question of the beauty of this form, or mode of its development, rests
on the nature of the bank above the cliffs, and of the aqueous forces
that carved it; and this discussion of the nature of banks, as it will
take some time, had better be referred to next chapter. One or two more
points are, however, to be stated here.
Sec. 39. For the reader has probably been already considering how it is
that these overhanging cliffs are formed at all, and why they appear
thus to be consumed away at the bottom. Sometimes if of soft material
they actually _are_ so consumed by the quicker trickling of streamlets
at the base than at the summit, or by the general action of damp in
decomposing the rock. But in the noblest instances, such cliffs are
constructed as at c in Fig. 73, above, and the inward retirement of the
precipice is the result of their tendency to break at right angles to
the beds, modified according to the power of the rock to support itself,
and the aqueous action from above or below.
I have before alluded (in p. 157) to this somewhat perilous arrangement
permitted in the secondary strata. The danger, be it observed, is not of
the fall of the _brow_ of the precipice, which never takes place on a
large scale in rocks of this kind (compare Sec. 3 of this chapter), but of
the sliding of one bed completely away from another, and the whole mass
coming down together. But even this, though it has several times
occurred in Switzerland, is not a whit more likely to happen when the
precipice is terrific than when it is insignificant. The danger results
from the imperfect adhesion of the mountain beds; not at all from the
external form of them. A cliff, which is in aspect absolutely awful, may
hardly, in the part of it that overhangs, add one thousandth part to the
gravitating power of the entire mass of the rocks above; and, for the
comfort of nervous travellers, they may be assured that they are often
in more danger under the gentle slopes of a pleasantly wooded hill, than
under the most terrific cliffs of the Eiger or Jungfrau.
[Illustration: FIG. 89.]
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