earth occurs mainly in England. It has been mined in the Lower Greensand Group and the Vale of White Horse, Oxfordshire. The Combe Hay Mine was a fuller's earth mine operating to the south of Bath, Somerset, until 1979. Other sites south of Bath included Frome, Lonsdale, Englishcombe, Tucking Mill, and Duncorn Hill. Although these sites had been used since Roman times, William Smith developed new methods for the identification of deposits of fuller's earth to the south of Bath. Other English sources include a mine near Redhill, Surrey (worked until 2000), and Woburn, Bedfordshire, where production ceased in 2004. Hills, cliffs, and slopes that contain fuller's earth can be unstable, since this material can be thixotropic when saturated by heavy rainfall. Historical significance Fulling is an important step in the production of woolen garments, and can be traced back to ancient times. Cuneiform texts from Mesopotamia mention a raw material, (, : 'gypsum, plaster'), literally "white earth", which was delivered to fullers for the finishing of cloth. There are several Biblical references to fulling (2 Kings 18:17; Isaiah 7:3 and 36:2; Malachi 3:2; Mark 9:3), but the materials used to whiten the fabric are not specified. Pliny the Elder mentions several types of fuller's earth ( in Latin) from a variety of locations, each with different properties and therefore different uses. The first references to fulling mills are from Persia, and by the time of the Crusades in the late eleventh century, fulling mills were active throughout the medieval world. The use of fuller's earth across the Indian subcontinent dates back to at least 1879. While its household use and transportation by local carts in the Sindh region predates the 1800s, export by rail was first recorded in 1929 in British India. The prospective value of Fuller's earth is a significant plot point in the Sherlock Holmes story, The Adventure of the Engineer's Thumb by Arthur Conan Doyle. In the tale, the titular engineer undertakes a seemingly spurious repair commission for an outlandish sum, accepting his client's explanation that the potential profit from Fuller's earth warrants both the expense and total secrecy. The adventure is set in 1889, implying that the Fuller's earth was then well-known as a lucrative commodity, 'only found in one or two places in England.' Uses In addition to its original use in the fulling of raw fibers, fuller's earth is now utilized in a