this was formerly thought unlikely as it was reasoned that chalk could have been obtained outcropping close by. j.e.l. caiger worked in kent excavating, surveying and researching deneholes and concluded that they were excavated in prehistoric, roman, medieval and even post-medieval times in order to produce a supply of unpolluted chalk to spread on fields for the purposes of marling. by excavating a narrow shaft, the miners used up as little of the productive agricultural land as possible. he suggested various other practical issues which supported his ideas including that open cast chalk extraction would require moving the material further than necessary and that shallower chalk deposits have much of their minor mineral content leached out by groundwater.