The post you are reporting:
Dover started it all in this area....
The Dover borehole was commenced in 1886 by the Kent Coalfields Syndicate Ltd on the site of the old Channel Tunnel works at Shakespeare Cliff, 3 miles west of Dover. It was stopped in 1893 at a depth of 2,230ft, having passed through 1,190ft of the Coal Measures and proved the existence of several coal seams. As a result of this, it was decided to sink a shaft down to mine the coal, especially a 4ft seam at a depth of 2,172ft. Shaft No. 1 (Brady Pit) was commenced near the borehole in July 1896. It was 17ft in diameter and rapidly passed through the Chalk, Chalk Marl and Gault Beds until it reached the Lower Greensand Beds in October at a depth of 366ft. At this point, so much water seeped into the shaft that it had to be abandoned.
The problem was that the Greensand Beds were pervious and contained a great amount of water which was held in position by the impervious Gault Beds above. As soon as the shaft pierced this cover, the water was released from pressure and was forced up the shaft. This is the principle of artesian wells and a similar effect can be obtained by placing an empty bucket into water and piercing a hole in the bottom — water will be forced into the bucket from below until it reaches the level of the surrounding water. Since the Greensand Beds here are at an angle, the level of the 'surrounding water' will correspond to the highest point that the Beds rise to in the area. This happens to be under the English Channel and so the Greensand will never run dry! In this case, water rose to within 40ft of the top of the shaft as it also had in the borehole.
Shortly after Shaft No. 2 (Simpson Pit) was started nearby and was slightly wider at 20ft diameter. Having experienced water problems with the first shaft, the precaution was taken of putting down 15ft boreholes from the shaft bottom as it was sunk in order to give advance warning of flooding. At 10.55pm on 6th March 1897, a team of 14 men were working in the shaft bottom when the top bed of the Lower Greensand was struck. Initially there was no sign of water and there was no indication of danger until a few minutes later, when it was found that the sand was wet. Suddenly, water shot up into the shaft from underneath and only 6 men were able to escape by climbing up the iron rings supporting the timber lining. The hoppit (large bucket) was at the surface being emptied when cries were heard from below. It could only hold 3 men at a time and was quickly lowered twice to rescue survivors clinging to the shaft walls. Two men went down in the hoppit a third time but the water had risen 80ft up the shaft and they could see no more survivors. It took over a month before workers were able to pump out the shaft and recover the 8 bodies and work was suspended. It was subsequently found that the water level in the borehole and Brady Pit had dropped 127ft at the time of the accident. The probable explanation is that, under a head of about 265ft of water from both the nearby borehole and Brady Pit, sufficient pressure was exerted on the water in the Lower Greensand to burst through the few feet of hard sandstone and clay that formed the bottom of the shaft.
Despite this disaster, sinking later continued but Dover Colliery earned a reputation for costing a lot of money with little result. It was not until 1912 that the first (and only) consignment of coal was sent from the mine and this was only 120 tons! There was a big celebration to commemorate this but there were strong rumours that the coal had actually been brought from elsewhere to impress disillusioned shareholders. Needless to say, the colliery did not last much longer although iron ore was extracted for a short time.