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Withyhill Cave Survey Notes

Notes on the recently published survey of Withyhill to be read in conjunction with that survey, by Dave Irwin.

Withyhill Cave was discovered by quarrying at Fairy Eave Quarry, near Stoke St. Michael in December 1972 - the sixth system of any size to be explored within the quarry limits.  The cave was explored by members of the Cerberus Speleological Society.  Shortly afterwards, Dr. W.I. Stanton produced a line survey to Grade 3 that indicated that the cave lay parallel with, and at certain points near to, Shatter Cave.  To determine possible sites for digging, Doug Stuckey and the author produced a survey to the obsolete C.R.G. Grade 6D (with tripod mounted instruments).

Instruments. The compass, a liquid-filled ex-W.D. prismatic and the clinometer (Japanese type) were mounted on a table together with two spirit levels, placed at right angles to each other for levelling purposes.  The whole unit - the Surveying Unit - was mounted on an ex-W.D. wooden theodolite tripod with brass fittings.  The tapes used were 30m and 10m fibron tapes.

Method of Surveying. The survey lines were produced by using the familiar 'leap-frog' technique commencing at the far end of the Glistening Pool Series and taken through to the entrance.  The West Limb of the system was surveyed on a later occasion to the same standard except where difficulties were encountered in the First and Second Boulder Chokes, when the standard was reduced to hand held equipment (B.C.R.A.5).  Offsets were marked so that extensions of this line could be made and enabling side passages to be tied on to the main survey line.

Passage detail was measured at all survey stations and at many intermediate points.  Chamber detail was collected by 'raying' from survey stations. The survey work was split between the surveyors as follows: -

Glistening Pool Series to Entrance - D. Irwin & D. Stuckey.  G.P. Junction to second boulder choke - D. Irwin.

Calibration. This proved difficult, as all field hedges were fenced additionally with barbed wire, rendering field junctions useless for calibration purposes.  After preliminary checks, the centreline of a straight portion of road was finally selected.

The calibration point lay along the southernmost section of the Fairy Cave Quarry road to the crossroads at N.G.R. 6521 4725.  It was later shown that this point was not completely free of magnetic influence, as the overall N/S distance from the entrance of the cave to the second boulder choke was in error by a little less than 10 and this error is entirely due to calibration error, as the two points, the radius location point and the same point represented on the survey coincided satisfactorily when the two were superimposed.

Survey Grading. All main survey lines were surveyed to C.R.G. Grade 6D (or B.C.R.A.6D tripod mounted).  Side passages were surveyed to B.C.R.A.5 and in two short passages; the standard was dropped to B.C.R.A.4.  This reduction of surveying standard was due entirely to the presence of stalagmite deposits.

Plotting.  The co-ordinates for each station and passage outline were plotted on to graph paper and then traced on to 'Permatrace'. The small scale at which the survey was drawn (1:400) did not permit the inclusion of floor deposits without cluttering the overall appearance.  Thick deposits of stalagmite are shown in many of the passage sections.

General Data.

Surveyed length = 766m (2,513 feet)

Vertical Range = 20m approx. (65feet 7 inches)

Number of surveying trips - line survey 3 (total 7 hours) details etc. 4 (total 7 hours)

Conclusions. The optimistic relationship of Shatter and Withyhill caves, as concluded by various people, does not exist.  The distance between East Rift in Withyhill and the Five Ways Chamber in Shatter is some 60m (197ft) apart.  The survey has been checked by radio location, an exercise carried out by Prewer et al. (6) in 1973.  Plotting of the radius location point and comparing the co-ordinate change between the entrance and the second boulder choke show the survey to be at variance by about 7m (23ft).  The reason for this has already been given and is wholly attributable to a faulty calibration site.

Acknowledgements. The surveyors would like to thank and acknowledge the help of the following, without whom the survey would not have been possible:-

Hobbs Quarries Ltd.; Cerberus Speleological Society; B. Wilton, for technical advice regarding the presentation of the survey and for photographic reduction, and the many members of the Bristol Exploration Club who held tapes and took notes.