[Illustration: GENERAL VIEW OF THE PUMPHERSTON WORKS] The seams of shale in the Midlothian fields vary generally from 4 to 10 feet in thickness, say 7 feet as an average, and, on the whole, they are comparatively free from ribs of unproductive rock. With a thickness of 7 feet, experience has shown that the method best adapted for the efficient working of the shale is “stoop and room,” but in the case of two seams of shale, separated by a bed of foreign material of sufficient thickness for packing, the long wall method proves the more suitable. The “stoop and room” method, however, is more generally used throughout the Scottish shale district than any other, its chief characteristics being the (1) “whole” or first working, and (2) the broken or second working. The whole working consists of a series of excavations made in the shale, whereby it is divided into rectangular blocks or pillars. These excavations are called rooms, one set being driven at right angles to the dip of the shale and at regular distances from one another, and commonly called “levels”; another set, driven to the rise of these levels and at right angles to them, being usually known as “ends” or “upsets.” The latter are broken off the levels at regular intervals and driven upwards to meet the levels above. The shale miner holes as far as he can reach--probably three or more feet--and brings down the shale by blasting, the process being repeated until he penetrates a distance of from 9 to 12 feet from the face at road-head. The shale, being loosened from its natural bed, is then placed in “hutches,” which are taken to the bottom of the shaft by either horse or chain haulage (much as with coal), and then the journey to the mouth is commenced. Before leaving the question of shale mining, it should be explained that the shale miner is subject to dangers much as his colleague in the coal-pit, but the volume of gases found in the shale seams is not so great as in the coal measures. These, however, are of an explosive nature, the most common being fire-damp. Once above ground, the shale is conveyed to breaking machines by endless wire-rope haulage. Passing through the machines, it is broken into suitable sizes for distillation, and drops into hopper-shaped hutches. These hutches have a capacity of about a ton, and each in turn is conveyed to the top of the retorts on an inclined scaffold by an endless chain. The shale then falls by the operation of a lever into a hopper or magazine communicating directly with the retorts, one hopper with a storage capacity of 24 hours’ supply of shale being connected to each retort of the Pumpherston Company.