Medieval Denehole at Northfleet

In October 2008, Kent Underground Research Group members were asked to investigate a denehole found on a housing development site to the west of Springhead Road, Northfleet.

The local geology is Thanet Sand overlying loose-jointed Upper Chalk with the usual layer of Bull-Head Flints at the boundary.

Two other deneholes had previously been recorded by the Group on the same site in March 2006 and September 2007.

The latest find at TQ 6191 7304 was located when ground probing revealed underground voids. A mechanical excavator was used to dig a deep trench that intercepted the side of a small chalk chamber, thus gaining access for the KURG team to enter the site on 13th October.

ABOVE TOP: An unconventional but easy way to explore a denehole!

The exposed chalk cavity was found to be the remains of a small double-trefoil denehole, the digger having broken into a primary chamber. This chamber had suffered both roof failure and severe flaking from the walls so that very little of the original structure could be observed. A few tool marks were seen on the end wall made by the usual short-headed iron picks. The collapse of this chamber was due to the loose-jointed nature of the chalk in this area and probably accelerated by vibrations caused by the process of probing and excavating the access.

The two small lateral chambers of the trefoil were found to be intact but of a diminutive size compared with similar deneholes. It is probable that the miners knew of the poor structural quality of the chalk and excavated smaller chambers to minimise collapse.

ABOVE: Plan and section of the denehole.

The shaft of the denehole was found to have been sealed with chalk blocks and it was not possible to gain access into the other three chambers beyond the blockage.

It was usual in this type of small chalk mine to make a dangerous pit fall safe by sealing off the shaft. This was often achieved by simply throwing down a bush or tree-stump and backfilling on top. In some cases, especially around the Gravesham area, the entrances of the two primary chambers were sealed off with roughly built flint walls before the shaft was backfilled. To seal the shaft with chalk blocks was most unusual but may be because the excavators did not encounter enough flints during the mining operations to make this material practicable.

The plan and excavation techniques show that the denehole is a typical, although small, Medieval type probably dug around the 12th century.

Rod LeGear