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 underburnt, part well burnt, part overburnt.  They are sorted accordingly into shuffs, grizzles, stocks of two or three qualities, shippers, and burrs.  Several sorts of malm stocks, which are superior in color and texture, are made, and are used for facing bricks and for cutting; and what are called paviors, which are dark and strong bricks, are also made.  The London stock is erroneously, but usually, described as gray.  It is really of a pie crust yellow of various tones.  Sometimes it is the same color when cut, but the hardest stocks are of a dark, dirty purple or brown, or sometimes nearly black inside.  A stock brick is rarely quite square or quite true; its surface is often disfigured