u may turn it, as you choose, into either a ridge or an incision,
into either a boss or a cavity. If you put the dark touch on the side of
it nearest the sun, or rather, nearest the place that the light comes
from, you will make it a cut or cavity; if you put it on the opposite
side, you will make it a ridge or mound; and the complete success of the
effect depends less on depth of shade than on the rightness of the
drawing; that is to say, on the evident correspondence of the form of
the shadow with the form that casts it. In drawing rocks, or wood, or
anything irregularly shaped, you will gain far more by a little patience
in following the forms carefully, though with slight touches, than by
labored finishing of texture of surface and transparencies of shadow.

59. When you have got the whole well into shape, proceed to lay on the
stains and spots with great care, quite as much as you gave to the
forms. Very often, spots or bars of local color do more to express form
than even the light and shade, and they are always interesting as the
means by which Nature carries light into her shadows, and shade into her
lights; an art of which we shall have more to say hereafter, in speaking
of composition. _a_, in Fig. 5, is a rough sketch of a fossil
sea-urchin, in which the projections of the shell are of black flint,
coming through a chalky surface. These projections form dark spots in
the light; and their sides, rising out of the shadow, form smaller
whiter spots in the dark. You may take such scattered lights as these
out with the penknife, provided you are just as careful to place them
rightly as if you got them by a more laborious process.

60. When you have once got the feeling of the way in which gradation
expresses roundness and projection, you may try your strength on
anything natural or artificial that happens to take your fancy, provided
it be not too complicated in form. I have asked you to draw a stone
first, because any irregularities and failures in your shading will be
less offensive to you, as being partly characteristic of the rough stone
surface, than they would be in a more delicate subject; and you may as
well go on drawing rounded stones of different shapes for a little
while, till you find you can really shade delicately. You may then take
up folds of thick white drapery, a napkin or towel thrown carelessly on
the table is as good as anything, and try to express them in the same
way; only now you will find