nnot give us rocks which shall be either granite or slate, nor
which shall be both granite and slate. Every attempt to produce that
which shall be _any_ rock, ends in the production of that which is _no_
rock.

It is true that the distinctions of rocks and plants and clouds are less
conspicuous, and less constantly subjects of observation than those of
the animal creation; but the difficulty of observing them proves not
the merit of overlooking them. It only accounts for the singular fact,
that the world has never yet seen anything like a perfect school of
landscape. For just as the highest historical painting is based on
perfect knowledge of the workings of the human form, and human mind, so
must the highest landscape painting be based on perfect cognizance of
the form, functions, and system of every organic or definitely
structured existence which it has to represent. This proposition is
self-evident to every thinking mind; and every principle which appears
to contradict it is either misstated or misunderstood. For instance, the
Athenaeum critic calls the right statement of generic difference
"_Denner_-like portraiture." If he can find anything like Denner in what
I have advanced as the utmost perfection of landscape art--the recent
works of Turner--he is welcome to his discovery and his theory. No;
Denner-like portraiture would be the endeavor to paint the separate
crystals of quartz and felspar in the granite, and the separate flakes
of mica in the mica slate,--an attempt just as far removed from what I
assert to be great art, (the bold rendering of the generic characters of
form in both rocks,) as modern sculpture of lace and button-holes is
from the Elgin marbles. Martin has attempted this Denner-like
portraiture of sea-foam with the assistance of an acre of canvas--with
what success, I believe the critics of his last year's Canute had, for
once, sense enough to decide.

Again, it does not follow that because such accurate knowledge is
_necessary_ to the painter that it should constitute the painter, nor
that such knowledge is valuable in itself, and without reference to high
ends. Every kind of knowledge may be sought from ignoble motives, and
for ignoble ends; and in those who so possess it, it is ignoble
knowledge; while the very same knowledge is in another mind an
attainment of the highest dignity, and conveying the greatest blessing.
This is the difference between the mere botanist's knowledge of plants,
a