city in Fig. 101, applies with a sway more or less
interrupted, but always manifest, to every convex and retiring mountain
form. All banks that thus turn away from the spectator necessarily are
thrown into perspectives like that of one side of this figure; and
although not divided with equality, their irregular divisions crowd
gradually together towards the distant edge, being then less steep, and
separate themselves towards the body of the hill, being then more steep.

[Illustration: FIG. 102.]

Sec. 24. It follows, also, that not only the whole of the nearer curves,
will be steeper, but, if seen from below, the steepest parts of them
will be the more important. Supposing each, instead of a curve, divided
into a sloping line and a precipitous one, the perspective of the
precipice, raising its top continually, will give the whole cone the
shape of _a_ or _b_ in Fig. 102, in which, observe, the precipice is of
more importance, and the slope of less, precisely in proportion to the
nearness of the mass.

Sec. 25. Fig. 102, therefore, will be the general type of the form of a
convex retiring hill symmetrically constructed. The precipitous part of
it may vary in height or in slope according to original conformation;
but the heights being supposed equal along the whole flank, the contours
will be as in that figure; the various rise and fall of real height
altering the perspective appearance accordingly, as we shall see
presently, after examining the other three kinds of line.

2. Lines of Projection.

2. Lines of Projection. Produced by fragments bounding or carried
forward from the bases of hills.

Sec. 26. The fragments carried down by the torrents from the flanks of the
hill are of course deposited at the base of it. But they are deposited
in various ways, of which it is most difficult to analyze the laws; for
they are thrown down under the influence partly of flowing water, partly
of their own gravity, partly of projectile force caused by their fall
from the higher summits of the hill; while the debris itself, after it
has fallen, undergoes farther modification by surface streamlets. But in
a general way debris descending from the hill side, _a b_, Fig. 103,
will arrange itself in a form approximating to the concave line _d c_,
the larger masses remaining undisturbed at the bottom, while the smaller
are gradually carried farther and farther by surface streams.

[Illustration: FIG. 103.]

3. Lines