The necessity which controls the form and construction of the breaker building is that the unbroken and unscreened coal must first be taken to a point in the building sufficiently high to allow of its passage, by gradual descent, with slow movement, through successive rolls, screens, shutes, and troughs until, thoroughly broken and fully cleaned and separated, it reaches the railroad cars, standing under the pockets, and is loaded into them for shipment. It is sometimes possible, as has already been intimated, to locate a breaker on the side of a hill so that the coal may be run into the head of it from the mine by a surface track without the necessity of hoisting. In this case the building will hug the hill, extending for a long distance down the slope of it, but without rising at any point to a great height from the surface of the ground. In these days, however, the breaker is more frequently erected in the valley. The general results are thought to be better, and the special convenience to railroad outlets to market is certainly greater. Besides this, the necessities of the case in shaft mining seem to demand it. A peculiar and characteristic feature of a breaker so built is the great vertical height to which one portion of the building is run up. This is the portion that contains the shaft up which the coal is hoisted, and from the top of which it starts on its long descending route to the surface again. From one hundred to one hundred and fifty feet is not an unusual height for this portion of the building. From this topmost part of the structure the roof slopes down by stages, on one or two sides, widening out, running off at an angle to cover a wing, spreading by a projection here and there until, by the time the last ten feet in height are reached, the ground space covered by the building has come to be very great. Under the last or lowest portion of the structure are the railroad sidings on which the cars stand to be loaded from the many pockets in which the shutes have terminated. Two engines are necessary at the breaker, one a winding engine to hoist coal from the surface to the top of the breaker, and the other a breaker engine to move the rolls, screens, and other breaker machinery. The winding engine is usually put on the opposite side of the shaft tower from the rolls and screens, and the ropes from it, either exposed or under cover of a long sloping roof, reach up to the sheaves in the head frame. The breaker engine is usually housed in a wing at one side of the main building, while the several nests of boilers, under a separate cover, are required by the act of 1885 to be at least one hundred feet away from the breaker.