denehole

An old excavation in chalk consisting of one or more chambers at the base of a vertical shaft. The shaft passed through overlying strata and about 1m of chalk, often many metres in total, before the chambers were excavated. According to the Kent Underground Research Group, deneholes were mines for chalk (lime), primarily to be spread on adjacent fields to improve soil fertility.

This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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