But if little is known about the beginning of the salt-mining industry in Cheshire, there is not much more to be learnt about its development and ultimate decay. To-day, only the Adelaide Marston Mine at Northwich is working, and of the nineteen mines that were open in Cheshire in 1881, only nine were at work, while from an undated plan and key showing the rock-salt mines in the Northwich district, which was probably published a few years earlier, we learn that of the fifty rock-salt mines that had been abandoned, twelve had been sunk to the bottom bed and the rest had been worked as top-bed mines. [Illustration: INTERIOR PENNY’S LANE MINE, NORTHWICH] The story of the exploitation of the top and bottom beds is one that is soon told. The top bed was worked until the mines began to fall in and the subsequent breaking in of fresh water converted the old workings into brine reservoirs. In 1779, the discovery of the lower bed of rock-salt at Lawton prompted the owners of the Marston Mine at Northwich to sink below the top bed in which they were working, and, in 1781, a trial shaft which was sunk from the top mine by means of a horse gin, demonstrated the existence of the bottom deposit in that district. Other owners transferred their operations from the top to the bottom bed, and for the next fifty years practically all the rock-salt was excavated from that source. In 1830 the roofs in these workings began to crack, and attention was directed to the insufficiency of the pillars by which they were supported. A competent surveyor, who did not hesitate to declare that the workings were in a dangerously insecure condition, was regarded as an alarmist by the old salt proprietors, who commissioned other “experts” to examine the pits, and were satisfied with their assurance that they considered each pit to be entirely free from any danger, and that they should not hesitate to work in any of them. Three years later the roof of the first bottom-bed mine fell in, others collapsed in rapid succession, and by 1840 some twenty mines had collapsed, let in water, and become filled with brine. In 1881, only nine rock-salt mines were at work, and eight of these had a combined area of 123 acres.