This article appeared in the Winter 1971 (Issue #27) edition of the Kent Archaeological Review.
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The Bexley Deneholes.
In the 1920's, when Bexley was still a rural area, there were no less than 120 deneholes to be seen in Joyden's Wood and the two adjacent woods, which were known as Stankey Wood and Cavey Springs. Other deneholes could be found on Dartford Heath where it borders on to Crayford. The greater number of these were, even at that time, partly fallen in or existed only as depressions in the ground. Today there are very few to be seen. Stankey Wood and Cavey Springs were both of quite small acreage but contained between them about 75 deneholes. The shafts were sunk close together as if the excavators' wishes were to concentrate as many deneholes as possible in the smallest area of land. As these shafts constituted a danger to both men and plough teams it was probably considered necessary to confine them to an isolated area set aside for mining operations. An interesting point regarding this particular group of dencholes is that their excavators took great care to avoid one set of underground chambers breaking into others already formed from an adjacent shaft. When the excavators saw that there was a possibility of a breakthrough, that part of the working was abandoned, or alternatively, the course of the heading was altered to avoid piercing an adjoining chamber. It is apparent that the miners' main objective was to obtain a maximum amount of chalk from each fresh sinking whilst at the same time taking care not to extract too much chalk and so endanger the stability of the vaulting. Doubtless, through a period of trial and error, the excavation shape, now recognised as the double trefoil, was evolved which allowed a maximum chalk yield with a minimum risk of roof collapse.
Most of the Cavey Springs and Stankey Wood deneholes have been examined during the past 90 years and in some cases plans have been published. They show, in the main, an extraordinary similarity of construction and are mostly of the double-trefoil pattern, i.e., with six chambers; three radiating out on each side of the base of the shaft. (See plan and elevation of a Cavey Springs denehole). In Joyden's Wood, however, there were departures from this standard form of construction. Some of those which have been examined had three chambers only, spaced out radially from the shaft. Deneholes with four or five chambers are known but must be regarded as being most exceptional. Deneholes always have an enormous cone of sand at the bottom of the shaft, far in excess of that which natural attrition of the sides of the shaft or sand falling in from ground level might produce. It would appear that when sinking a new denehole shaft, miners frequently dumped freshly excavated soil down the shaft of any nearby one which had been worked out.
Since 1935, the continual spread of building development has caused a great number of open deneholes to be destroyed by deliberate attempts to fill them in or by sealing the shafts at the top. In the past, these attempts were clumsily done and were far from permanent. Due to the very large volume of cavern space it was virtually impossible to fill them completely, so many of the shafts were just choked up with tossed in tree trunks and brushwood. Naturally, when the timber ultimately rotted away at its extremities the plug of soil and rotting wood fell down the shaft into the void below leaving the denehole once again open and dangerous. F C J Spurrell, who explored so many of the Bexley deneholes in the 1870s, states that during this period shafts were being inexpertly filled in by labourers unfamiliar with the large subterranean chambers below. Cavey Springs once had about 34 deneholes sunk in an area of less than five acres. These sinkings had been roughly set out in three lines and as closely spaced as possible in so small an area. Today, no trace remains of these deneholes, for in March, 1967, planning permission was granted to the CEGB to erect a power plant on this heavily undermined piece of woodland. Before building operations were commenced each set of underground chambers were carefully located and fully sealed with a slurry of Thanet Sand.'Most of the deneholes in Joyden's Wood have also been disposed of in the same manner. An exception to this pattern of destruction is in the southern part of the wood where a deep denehole has been incorporated into the drainage system of a nearby housing estate and serves as a huge soakaway. This particular denehole is 53 feet deep and has only three chambers, each being 47 feet long, 20 feet high and 10 feet wide. The shaft has been lined with brickwork and stormwater is conducted off the roadways and is passed into the chambers through ports left in the brickwork of the shaft.
William Lambarde, when describing Crayford in his Perambulation of Kent (1570) states:
"There are, to be scene, as well in the open Heath neare to this Towne, as also in the closed grounds about it, sundry artificiall Caves, or holes, in the earth, whereof some have ten, some fifteene, and some twenty fathoms in depth: at the mouth (and thence downward) narrow, like to the Tonnell of a chimney, or passage of a well: but in the bottome large, and of great receipt: insomuch as some of them have sundry roomes (or partitions) one within another, strongly vaulted, and supported with pillars of chalke." This sixteenth century description of pillared dene. holes on the open heath and the closed grounds about it exactly fits the deneholes
in Stankey Wood, an area which has now been absorbed into the modern residential estate of Baldwyns Park, Bexley. It is here that the final phase of Bexley's denehole excavations could be seen. Although the usual double-trefoil denehole is present in this area several deneholes existed which represented an evolution in the design of the underground chambers. When the chalk miners had completed the customary double-trefoil pattern they discovered a practical, safe and economical method of enlarging each successive working, thus obtaining more chalk from each new denehole they sunk. This was achieved by driving a secondary heading at right angles between pairs of primary chambers. Care was taken to leave a stout pillar of chalk between the newly hewn opening. This evolved form of chalk mining transformed the double-trefoil pattern of chambers into a single cavern, its vault supported by six massive pillars of chalk. One such denehole is known with this elaborate plan and until 1964, was still open and accessible. Nearby, are others unfinished, but showing that they, too, were in the transitional stage of being enlarged into pillared caverns. For some unknown reason, all mining work ceased and the deneholes were abandoned in varying stages of completion. Although their shafts are now sealed it is testimony to their shape and the miners' skill in forming them, that some of these chambers are still extant today and in relatively sound condition despite the passing of so many centuries since their excavation.