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Stock Hill Mine Cave

Some observations after a year of digging.

An initial description of this site was given in B.B. 461 (Oct. 1991).  It is now a suitable time for an update, being just over a year since the dig commenced and also the temporary shutting down of operations due to flooding.  (This article was received in the autumn of '92 - the cave is still flooded!  Ed.).

During the year a total of 3203 loads of spoil have been hauled out of the entrance shaft - around 50 tons!!!  This has been tipped in adjacent depressions and landscaped.  On 2nd September all digging kit and ladders were brought to the base of the entrance shaft to escape the gradually rising water levels in the lower mineshaft and natural sections.

Since the last report a tremendous amount of work has been done clearing out the completely in-filled natural passage intercepted by the Old Man halfway down the mine­shaft. This is a steeply descending and amply proportioned phreatic tube dropping vertically to the present dig. The infill is a red/brown sticky clay in a partly mineralized joint.  Apart from the clay there are also patches of fine silt and water worn pebbles of sandstone up to 2" across.  Variously coloured clays, sands, iron ores and tiny pieces of galena were also found - as were hundreds of six-sided calcite "dogtooth" crystals up to 1" long and christened "Stock Hill Diamonds".

Tiny (c. 2" diameter) roof tubes have formed on top of the infill and eroded the limestone ceiling. These tubes are lined with fish-scale like tiny calcite crystals the like of which are unknown to the writer. Larger, in-filled roof tubes or anastomoses have also been uncovered - these pre-date the clay infill.  No bones or organic remains of any type have been found and there are no formations or calcite deposits on the cave walls (though a large lump of stalagmite was found in the debris halfway down the mineshaft). This would suggest that most of the cave was either water or sediment filled but never air filled.  All limestone surfaces have a dusty grey patina when exposed and are smoothly eroded with phreatic pocketing but no scalloping.

The size of the passage and angle of dip would, if projected back to the surface at c. 856' A.O.D., indicate the existence of a major catchment area at one time, predating the St. Cuthbert's valley (and cave system) and being at least 75' above the present bottom of the St. Cuthbert’s depression.  It is thus likely to have been an early drainage route of the original St. Cuthbert's stream - this may have been fed by water from the once higher ground to the north of Priddy.

Now emptied of infill the dimensions of this passage are impressive and indicate an extensive phreatic system, though undoubtedly choked for some distance.  A draught issues from small open fissures in the lower mineshaft giving some encouragement to the possibilities of open passage.  Unfortunately these cracks are not conducive to digging.

The cave is on the boundary of the Lower Limestone Shales and Black Rock Limestone and heading towards the nearby Stock Hill Fault.

Drainage is presumably to Wookey Hole Cave and/or Rodney Stoke Rising, though if the system is as ancient as suspected it could have fed springs now buried by alluvial deposits. It is possible that the cave formed in early Pleistocene times.

The writer would welcome any more enlightened thoughts on his theories!

The lower part of the mineshaft has also been cleared to an apparently solid floor with a small choked rift below, The blocked level has been partly excavated and may be worth more work. Mining artefacts discovered while digging are illustrated on the next page and will be presented to Wells Museum.

The list of diggers over the last year is too long to publish but suffice it to say that many members and friends have taken part.  Special mention must be made of Martin Riddell who provided the magnificent scaffolding head frame.  Trevor "Mr. Enthusiasm" Hughes and bang man Tony Boycott.  It is hoped to resume work, here when conditions are drier or a heavy duty pump is obtained.  In the meantime do not despair ­there are lots of other digs which need your help!

Tony Jarratt

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With reference to mining artefacts (see next page) I have following abstract - Ed.

THE GENTLEMAN'S MAGAZINE

NOVEMBER 1816

Country News

Among the public benefits produced by the Royal Geological Society of Cornwall, is the introduction of an alloyed Tamping-bar, instead of the common iron bar formerly employed by the Miners, which promises to be as efficacious in preventing explosions in the Mines of that County, as Sir Humphrey Davy's safety lamp in those of the North.