Before mining operations are begun a complete survey is made of all outcroppings, and their differences in level are obtained. From this data a comparatively accurate knowledge may be had of the position of the coal bed under ground, as the dip of the seams is very moderate and uniform, and but few faults and other irregularities are encountered. It is then decided where to locate the mouth of the drift so that the entry can be driven in on the rise of the coal and the mine become self-draining. It is important, however, to have the opening at a convenient point near the river or railroad, and it is usually so made if possible, even though the dip should be away from the opening. The inclination is always so slight as not to interfere greatly with the hauling of cars, and it is not much of a task to make a separate opening for drainage. The coal seam is divided by vertical cleavage planes, running at right angles to each other, one of which is known as the _butt_ cleavage and the other as the _face_ cleavage. The main entries are driven in, if possible, on the face cleavage, as are also the chambers, or “rooms” as they are called here; while the entries from which the rooms are turned are always driven on the butt cleavage. The drift, or main entry, has an airway running parallel with it; sometimes it has one on each side of it. It is driven eight or nine feet in width, except where two tracks are necessary, in which case it is made from twelve to fifteen feet wide. These double or treble entries are parallel to each other, and are separated by a wall of coal from twenty-five to forty feet in width. Through this wall, at about every thirty yards, entrances, or, as they are called here, “break-throughs,” are made, having the same width as the entry. The height of roof in the entries of the Pittsburgh seam is usually five and one half or six feet in the clear. At right angles to the main entry butt entries are driven in pairs, parallel to each other and about thirty or forty feet apart, with break-throughs or cross-cuts for the passage of air, as on the main entries. From each of these butt entries, at right angles to them, and in opposite directions, the rooms are driven. They are made about twenty-one feet wide, with pillars between them twelve feet thick, and are not often more than eighty yards in length. They are usually driven to meet the faces of the rooms which are being worked from the next parallel butt entry, or are extended to that butt entry itself. At the point where the room turns off from the butt entry it is made only seven feet wide for a distance of from fifteen to twenty-one feet, then the room is widened out to its full width of twenty-one feet. The track on which the mine wagon runs is laid straight up the side of the room from the opening at the entry, occupying a clear space about seven feet wide. The rest of the room is well filled with the refuse which has been separated