1. I am well aware how insufficient, and, in some measure, how disputable, the account given in the preceding chapters of the cleavages of the slaty crystallines must appear to geologists. But I had several reasons, good or bad as they may be, for treating the subject in such a manner. The first was, that considering the science of the artist as eminently the science of aspects (see Vol. III. Chap. XVII. § 43), I kept myself, in all my investigations of natural objects, as much as possible in the state of an uninformed spectator of the outside of things, receiving simply what impressions the external phenomena first induce. For the natural tendency of accurate science is to make the possessor of it look for, and eminently see, the things connected with his special pieces of knowledge; and as all accurate science must be sternly limited, his sight of nature gets limited accordingly. I observe that all our young figure-painters were rendered, to all intents and purposes, blind by their knowledge of anatomy. They saw only certain muscles and bones, of which they had learned the positions by rote, but could not, on account of the very prominence in their minds of these bits of fragmentary knowledge, see the real movement, colour, rounding, or any other subtle quality of the human form. And I was quite sure that if I examined the mountain anatomy scientifically, I should go wrong, in like manner, touching the external aspects.