Purbeck Mineral and Mining Museum
After the closure of Eldon sidings all clay exports were via lorry. For several years the clay was carried from the mines across the A351 by trains to the "Lorry Drop". It was realised that the lorries could take the clay directly from the mines and the cost of maintaining a railway system avoided. The transhipment buildings were raised to accommodate the lorries beneath them and in the early 1970s the railway system sold partly into preservation and the rest scrapped. Use of narrow gauge railways continued underground at Norden No 6 & 7 mines until all mining operations ceased in 1999.
Clastic rock
According to Blatt, Middleton and Murray mudrocks that are composed mainly of silt particles are classified as siltstones. In turn, rocks that possess clay as the majority particle are called claystones. In geology, a mixture of both silt and clay is called mud. Rocks that possess large amounts of both clay and silt are called mudstones. In some cases the term shale is also used to refer to mudrocks and is still widely accepted by most. However, others have used the term shale to further divide mudrocks based on the percentage of clay constituents. The plate-like shape of clay allows its particles to stack up one on top of another creating laminae or beds. The more clay present in a given specimen, the more laminated a rock is. Shale, in this case, is reserved for mudrocks that are laminated, while mudstone refers those that are not.