most reasonable in their arrangement,
is most probable in their invention. I have theoretically deduced shafts
from walls, but shafts were never so reasoned out in architectural
practice. The man who first propped a thatched roof with poles was the
discoverer of their principle; and he who first hewed a long stone into
a cylinder, the perfecter of their practice.

Sec. II. It is clearly necessary that shafts of this kind (we will call
them, for convenience, _block_ shafts) should be composed of stone not
liable to flaws or fissures; and therefore that we must no longer
continue our argument as if it were always possible to do what is to be
done in the best way; for the style of a national architecture may
evidently depend, in great measure, upon the nature of the rocks of the
country.

Our own English rocks, which supply excellent building stone from their
thin and easily divisible beds, are for the most part entirely incapable
of being worked into shafts of any size, except only the granites and
whinstones, whose hardness renders them intractable for ordinary
purposes;--and English architecture therefore supplies no instances of
the block shaft applied on an extensive scale; while the facility of
obtaining large masses of marble has in Greece and Italy been partly the
cause of the adoption of certain noble types of architectural form
peculiar to those countries, or, when occurring elsewhere, derived from
them.

We have not, however, in reducing our walls to shafts, calculated on the
probabilities of our obtaining better materials than those of which the
walls were built; and we shall therefore first consider the form of
shaft which will be best when we have the best materials; and then
consider how far we can imitate, or how far it will be wise to imitate,
this form with any materials we can obtain.

Sec. III. Now as I gave the reader the ground, and the stones, that he
might for himself find out how to build his wall, I shall give him the
block of marble, and the chisel, that he may himself find out how to
shape his column. Let him suppose the elongated mass, so given him,
rudely hewn to the thickness which he has calculated will be
proportioned to the weight it has to carry. The conditions of stability
will require that some allowance be made in finishing it for any chance
of slight disturbance or subsidence of the ground below, and that, as
everything must depend on the uprightness of the shaft, as little chanc