It will be remembered that the design was to sink the shaft so that its foot should be nearly to the bottom of the synclinal valley or basin. If this has been done, then it is possible that the passage below the foot of the shaft parallel to the gangway actually runs along the synclinal axis. But if the bottom of the valley is still lower, the cross-headings will be driven farther down and a new parallel passage made, and, if necessary, still another. These openings now slope from the foot of the shaft downward, and in them is collected not only the water that may fall from the shaft, but, as the work advances, all the water that comes from all parts of the mine. This basin which is thus made to receive the mine water is called the “sump,” and from it the water is pumped up through the shaft and discharged at the surface. If the mine happens to be a very wet one it will require the constant labor of the most powerful pumping engine to keep the level of the water in the sump lower than the foot of the shaft. In some cases, in older workings, a section of the mine which has been worked out and abandoned is used for a sump, and then the water may cover an area many acres in extent. When a shaft has been newly sunk, the openings for the sump are the only ones that are made below the level of the foot of the shaft or below the level of the gangway. Henceforth all the workings will be made on the upper side of the gangway, extending up the slope of the seam, until such time as it may be deemed advisable to sink an inside slope to open a new set of workings on a lower level. The main gangway on one side of the shaft and the airway above it are now carried along simultaneously, and parallel with each other, and are united at distances of from forty to sixty feet by cross-headings. As soon as the last cross-heading is opened the one which immediately preceded it is walled up as tightly as possible. This is to insure ventilation. A current of air comes down the hoisting-way of the shaft, passes into the gangway and along it to the last cross-heading, where it crosses up into the airway and traverses the airway back to the cross-heading that was driven up from the upper end of the foot of the shaft. Passing down this cross-heading it comes to the air compartment of the shaft, and is drawn out to the surface by a powerful fan. This is the ventilating system of the mine in its simplest form. It is apparent that if any of the cross-headings nearer to the shaft than the last one should be left open, the air current would take a short course through it up to the airway, and so back to the shaft, without going to the extremity of the gangway at all. This gangway is the main artery of the mine; it is the highway by which all the empty cars go in to the working faces, and by which all the loaded cars come out to the foot of the shaft; it is the general watercourse by which the entire mine above it is drained, and by which the water is carried to the sump. In