ves or blades are arranged spirally on the shaft, and other
blades project into the interior of the cylinder from the walls of it.
The material, after being screened, is fed into this at the top, and
properly moistened. The shaft is caused to rotate, and the blades divide
and subdivide the material, forcing it always downward, so that it at
last escapes at the bottom of the pug mill in a continuous stream of
moist, well worked up clay, issuing with some force. In one type of
machine this clay stream is forced through a square orifice, from which
it comes out of the section of a brick, and by a knife or wire or some
other means it is cut into lengths.

In another type of machine there is a large revolving drum working on a
horizontal axis, with open moulds all round its edge. The clay enters
these moulds, and there is an arrangement of plungers by which it is
first compressed within the mould and then forced out on to an endless
band or some other contrivance that receives it. A third type of machine
has the moulds in the flat top of a revolving table, which, as it turns,
carries each mould in succession first to a part where it is filled from
the pug mill, next to where its contents are compressed, and lastly to
where they are pushed out for removal. However made, the brick, when
moulded, dried, and burnt, and ready for market, belongs to some one
sort, and is distinguished from other sorts by its size, color, quality,
and peculiarities.

The sorts of brick that are to be met with in the London market are very
varied. To enumerate them all would make a tedious list; to describe
them all would be equally tedious. I will endeavor, however, to give
some idea of the most conspicuous of them. We will begin with that
family of bricks of which the London stock brick is the type. It has
been said these are clamp burnt, and almost all the internal
brickwork--and not a little of the external--of the metropolis is of
stock brickwork. A good London stock brick is an excellent brick for
general purposes, but cannot be called beautiful.

Considering the vast quantity of brickwork done in the metropolis, it is
a matter for congratulation that such sound materials as good stock
bricks, stone lime, and Thames sand are so easily procurable, and can be
had at a price that puts them within the reach of all respectable
builders. When a clamp has been burnt its contents are found to have
been unequally fired, and are part of them underburn