able to proceed simultaneously without interfering with each other. In rich lodes and in the case of thick masses, the system of working in large chambers or extensive excavations, or by transverse attacks, is employed. Superficial deposits are worked like open quarries. In British practice, coal is generally worked on the post (or pillar and stall) system, or on the long-wall system. The pillar and stall principle is carried out in the working away of a certain portion of the coal as a first measure, and in leaving the remainder in pillars, which are either to serve permanently for the support of the roof, or to be at some future time partially or totally removed. In the North of England, where this system has been brought to perfection, it is also named panel-work, because the whole area is divided into quadrangular panels, each panel containing an area of from eight to twelve acres, and round each panel is at first left a solid wall of coal of from forty to fifty yards thick. Through the panel walls roads and air-courses are driven in order to work the coal contained within these walls. Thus all the panels are connected together with the shaft as to roads and ventilation, and each district or panel has a particular name, so that any circumstance relating to the details of the colliery can be readily referred to a specified place. [Illustration: PART OF A COLLIERY LAID OUT IN FOUR PANELS.] A. Engine shaft: divided F, G. Two panels completed as into three compartments, to the first work. an engine pit and two coal pits. B, C. Dip head level. D. Panel, with the rooms a a in regular progress to the rise. A, E. The rise or crop gallery. H. Panel fully worked out. K, K. Panel walls. By this plan, of which the above illustration gives a distinct idea, the pillars of a panel may be worked out at any time most suitable for the economy of the mine, and the loss of coal amounts to no more than about a tenth, instead of a third or a half by the old methods.