Compiled by B.M. Ellis from surveys and sketches by:-

INTRODUCTION

This report is published as a companion volume to Caving Report No. 7, “A Second Report on St. Cuthbert’s Swallet”.   It consists of a copy of the survey so far completed and a text describing the methods used in making the survey and how the surveys have been joined together.

It is now nearly nine years since St. Cuthbert’s Swallet was first entered and it maybe thought that this has been more than enough, tine in which to produce a survey of the complete system but, be that as it may, it has not been done.  Working on the idea that anything is bettor than nothing, and not knowing when the survey would be completed, it was decided to publish as comprehensive a survey as possible.  There were two possible courses that could be followed, either that part of the survey so far completed could be published or else this could be used as a basis for a survey-come-sketch of the major part of .the cave.  It was decided to took the latter course.  As more accurate surveys are made of those parts at present sketched it is intended to publish then separately so that they can be added to the present sheet if desired.  Accordingly, at the back of this Report will be found a post card and if this is completed and, returned to the given address your name will be placed on the mailing list for copies of any future additions to the survey.  As and when these become available it is intended to publish them at the sane, scale as the main sheet so that the recipient can transfer then easily, and so keep the survey up to date.  An invoice will be enclosed with each of the additions and provided that this is paid your name will be kept on the list.  Obviously it is impossible to give definite figures but it is not expected that those additions will cost more than, one shilling .each, including postage.

THE SURVEYS USED IN COMPILING THE PROVISIONAL PLAN

(1)  The Duck to the Railway Tunnel.  The late Don Coase started a high grade survey of the cave in 1955, commencing at what was then the Sump (now the Duck) and working at a Cave Research Group survey grade of 7.  This survey had reached as far as the Railway Tunnel when unfortunately he died and as yet no one has been found willing to complete the traverse.  The instruments used wore a tripod mounted. “Cave Theodolite”, and a one hundred feet long copper tape.  The cave theodolite consisted of an ex-R.A.F; astro-compass modified to take an ex-R. A. F. gun sight.  The theolodite was tested for accuracy on the surface before -use in the cave.  The horizontal scale is fitted with a vernier, and can be read to 0.2^O, while the vertical scale is graduated to 0.5^O and readings wore estimated to 0.25°.  Measurements of distance  were read to the nearest three inches.

The only closed traverse on the survey was the Fingers – Railway Tunnel – Cascade Chamber – the Fingers and at first attempt this failed to close by several feet and eleven degrees.  The next survey trip checked the observations on this traverse and the final figures failed to close by 0.2 foot and 0.02° in a total of 141 feet.  Unfortunately this was the last trip that Coase made.

(2)  Maypole Series and Line Survey to Entrance.  After the successful exploration of the Maypole Series Ron King wished to know the position of the end of the series in relation to the surface.  Therefore in 1958 he surveyed the Maypole Series and then continued a line survey from Upper Traverse Chamber to the entrance.  The instruments used in this survey were, a prismatic compass, a clinometer and a one hundred foot long copper tape.  As the compass was not calibrated a Cave Research Group grading of 5 could not be claimed, even though a clinometer had been used and is not required for a grade 4 survey.  This shows one of the failings of the C.R.G. system and a grading of 4½ seems to be appropriate in this case.  There was no closed traverse and therefore no indication of accuracy is available.

(3)  The Duck to the Entrance.  In 1960 Derek Ford was making notes for a thesis en the formation of some Mendip caves and as at that time there was no complete survey of the Old Route through the cave ho decided to plot his own.  The survey was essentially a lino survey made at C. R. G. grade 5 – 6 using a four inch diameter prismatic compass mounted on a tripod and read to 0.5°, a Watkin clinometer and steel tapes.  Distances were measured to the nearest inch.  At the time of the survey Ford also made notes on the passage width and roof height at each survey station so that a rough plan and section could be drawn.  Although the instruments were sufficiently accurate for a grading of 6 to be claimed, Ford only claims grade 5.   Again there was no closed traverse to give an indication of accuracy.

(4)  The Rabbit Warren and Extension/Catgut Series, High and Upper Traverse Chambers.  In August 1950 Chris Falshaw and Bryan Ellis started surveying in Continuation Chamber with the intention of making a survey of the Rabbit Warren and Rabbit Warren Extension.  While surveying in T-Junction Chamber another party opened Cross Leg Squeeze and the surveyors decided to survey through the Catgut Series to High Chamber before returning to the Rabbit Warren.  After four trips the survey, had been taken as far as Upper Traverse Chamber but shortly afterwards one surveyor, left the district and the other joined the army.

During the next two and a half years Ellis made a further four trips and on those completed the survey down harem Passage and then through the Rabbit Warren to the Dining Room, across to Plantation Junction and finally up to the T-Junction to complete the traverse.  The instruments used for this survey were a calibrated hand held liquid filled prismatic compass, a simple home made hand-held, clinometer and steel tapes.  Readings were taken to the nearest degree with the compass and clinometer, and to the nearest three inches for measurements of distance.  The readings for this survey were to a C.R.G. grading of 5 but due to the difficult conditions under which the survey was made and the resulting short average length of survey leg, the accuracy is probably not as high as that usually expected of this grade.

This survey contained one closed traverse of its own, that from the Railway Tunnel nearly to the Dining Room, along to Chain Chamber and T-Junction Chamber, through the Catgut Series and back to the Railway Tunnel via Upper Traverse Chamber and Harem Passage.  This traverse of 1308 feet failed to close by twenty three feet, an error of 1.8%.  There were also several further closed traverses when this survey was added to those already made in the cave, those are mentioned further in the section dealing with the joining together of the surveys.

(5)   Arête Pitch to the Choke by the New Route.  Bryan Ellis and Mike Luckwill commenced surveying the New Route in November 1961 and by the tine that this Report was being prepared they had completed a traverse from Arête Pitch to the Choke.  A line survey was also made from above the Water Shute to Upper Mud Hall so that it could be tied in with Ford’s survey.  The instruments used were a calibrated liquid filled prismatic compass and a home-made clinonotor, both mounted on a tripod.  Steel tapes were used for measurements of distances, readings being to the nearest three inches.  The “leap-frog” method of surveying was used in this the instruments are placed at alternate stations and readings are taken to the intermediate stations.  The instruments used correspond to these for a Cave Research Group grading of 6 but as they were tripod mounted for ease of use and not with the intention of gaining any accuracy a grading of 5½ would be more appropriate.  This survey does not contain any closed traverses of its own and the closed traverse with Ford’s survey is mentioned in the next section.

(6)   Sketches of those parts of the cave so far not surveyed.  To make the survey as complete as possible, those parts of the cave that have not been surveyed have been sketched by members of the B. E. C.  Roy Bennett has provided the sketch of the Rocky Boulder andCoral Series; Johnny Eatough of Cerberus Series and Dick Roberts that of the September Series.  Any other low grade sketches are by the author, either from his own know­ledge of the passages or from sketches in the Caving Log. (See page 5).

(7)  Plantation Swallet and height of the Entrance of St. Cuthbert’s Swallet.  Plantation Swallet was surveyed, for what it is worth, by Bryan Ellis.  At the same time an accurate line was plotted from the entrance of St. Cuthbert’s Swallet so that its relative position and height above Ordnance Datum could be calculated.

The height of the entrance of St. Cuthbert’s Swallet above Ordnance Datum was determined by Derek Ford who made an accurate lino from a nearby bench mark.  This line was checked part way along its length with a similar line made by Norman  Humphries ( Shepton Mallet Caving Club).  The two agreed to within 0.1 feet.

Summary of surveys used in Compiling Plan

THE PLOTTING OF THE PROVISIONAL PLAN

For all the surveys used in preparing the plan the surveyor’s readings were obtained, the exception to this being for Ford’s survey between the Wire Rift and the Entrance.  From this information the latitude, departure and height of each station was calculated using three figure trigonometrical tables and a calculating machine.  All the calculations were made to the nearest 0.1 foot and then the co-ordinates were adjusted to the nearest foot.  All the readings from tables and all calculations were then repeat­ed as a check.  From the co-ordinates so obtained it was possible to  attempt plotting the surveys on one sheet.

As soon as the plotting was attempted – it immediately became obvious that there was a serious discrepancy between the surveys of Ford and Coase for that part of the Main Stream between the bottom of Everest Passage and the Duck.  Theoretically Coase’s survey -was the more accurate but for several reasons it was decided to use Ford’s.  As this choice will surprise many people I must explain my reasons.

1. 1. If an error is made in a theodolite traverse the error is amplified as the traverse proceeds; an error of bearing on a compass traverse only affects the direction of the leg on which the error was made, the error does not(if anyone doubts the validity of this state­ment, a few minutes exercise on an imaginary traverse with a protractor and ruler should prove the point.).
   2. Ford did not make a closed traverse and therefore no check on accuracy is available, but at the first attempt Coase’s traverse failed to close by “several feet and eleven degrees”.  Admittedly the traverse closed extremely well on the second attempt but this does show that errors possibly exist in Coase’s survey.
   3. Both Ford and myself have taken compass bearings along suitable passages such as the Main Stream near the bottom of Everest Passage, along Sewer Passage and down GoarWe did not use each others survey stations but in none of these places did we differ by more than two degrees.  However, not only did the surveys of Ford and Cease differ in detail but the difference in bearing between Gour Rift and Sewer Passage measured by theodolite by Coase disagreed with the difference measured magnetically by Ford and myself.  The same applies between Sewer Passage, and the Main Stream near Everest Passage where the difference between the two sets of readings was over thirty degrees.  There is the possibility of magnetic abnormalities and this will have to be checked before a complete plan is published.
   4. Finally there is my own survey through the Rabbit Warren between the Main Stream near the Dining Room and PlantationAlthough this survey was of a lower grade it failed to close on Ford’s survey between those points by three foot, an error of 0.5% but it failed to close on the survey as madeby Coase by a considerably greater figure, 10.8%  in fact.

The only other part of the cave where there was a choice of surveys was from Kanohenjunga to the Entrance.  Here there was the line survey made by King after completing his survey of the Maypole Series, and there was Ford’ s survey.  These two disagreed by thirteen foot when plotted together but as the exact location of   King’s survey station at Kanchenjunga was not known this discrepancy could be plus or minus ten feet.  In this case it was decided again to use Ford’s survey because not only was it made to a greater potential accuracy but also, because it included passage detail.

Having made a decision on which surveys to use where there wasa choice, then came the task of joining all the surveys together.  The positions of the stations for Ford’s survey through the cave were plotted on gridded paper at a scale of forty foot to the inch.  To this basic line passage detail was added and here Coase’s survey was used to a large extent because he had surveyed the features in greater detail.  To this survey of the Old Route was added that part of Coase’s survey from the bottom of Everest Passage to the Cascade.  Ford did not survey this area and Coase’s survey is almost certainly accurate – the final closure error after re-surveying being extremely small.

The Rabbit Warren survey was taken next and fitted across the Coase -Ford survey from the Railway Tunnel to Plantation Junction.  From the Railway Tunnel to the Dining Room the closure error was fairly high, 2.5%, and the Warren traverse should have been repeated.  However, this was not done and instead the error was distributed along the traverse, the Main Stream survey being taken as correct.  When this had been done, all the various smaller closed traverses in this section, those between the Rabbit Warren and the Main Stream, closed to within three feet.

As already mentioned the closed traverse between the Dining Room and Plantation Junction failed to close by 0.5% (three foot) and this error was distributed along the Rabbit barren, traverse.

Having made these adjustments to the Rabbit Warren survey it was found that the complete Rabbit Warren traverse failed to close by 1.4%.  Again this error was distributed along the traverse, for this purpose it being assumed that the likelihood of error was the sane throughout the length.  This, was not a very fair assumption because it was much more likely that errors would be made in the more constricted sections of the survey, that is in the Rabbit Warren Extension and particularly in the Catgut Series.  However, a satisfactory method of weighting the corrections could not be found and it was thought that it would be safer to distribute the error throughout the survey in proportion to the length of each leg.

The most difficult survey to tie in was that of the Maypole Series by King.  A tie-bearing had to be taken from his station at Maypole Pitch to one of the Rabbit Warren traverse stations, and by using this and his line survey from Upper Traverse Chamber to the entrance, the survey was tied-in to the satisfaction of the author.

For the final survey, that of the New Route, there was a closed trav­erse through the bedding plane from above the Water Shute Upper Mud Hall and also the position of Traverse Chamber Pitch to give an additional check.  The closure error on the traverse from Arête Pitch to Upper Mud Hall Pitch was 1.8% and it is thought that most of this lies between the Water Shute and Mud Hall because not only does the position of Traverse Chamber Pitch agree well with that obtained from the Rabbit Warren and Maypole Series surveys, but also tripods were not used on this section.  Some of this error may be “lost” when accurate co-ordinates for Ford’s survey stations above the Wire Rift are available.  At present the traverse has boon closed using co-ordinates taken from Ford’s drawing of his survey results and not those obtained by calculation.  However, the surveyor feels that at least part of the error may be at Pulpit Pitch because he considers that insufficient care was taken over the readings at this point.  A more accurate method of carrying the survey down the pitch will have to be used as a check.

The connection between the stream sinking in Plantation Swallet and that joining the main stream at Plantation Junction was proved by the author, during 1961;details are given in Belfry Bulletin No.166, Dec­ember 1961.  At the same time the connection was proved between various streams found on the eastern side of the cave; these connections are shown on the survey.

It will be seen that there is still plenty of work to be done with regard to surveying in the cave, not only the surveying of parts not pre­viously done but also checking certain parts that have been.  Whenand if, this is completed it is intended to publish a survey of the complete cave, together with sections.

B.M Ellis

December 1961

ADDENDUM

Since the remainder of the Report was typed the following information has become available on the “sketches” mentioned on page 3.

Rocky Boulder and Coral Series.  Roy Bennett provided a sketch of this part of the cave and this has been used on the survey.  Although the sketch is from memory and therefore technically of C.R.G. Grade 1, the series tie in with the survey of the cave in so many places that the accuracy is thought to be equivalent at least to that of a normal Grade 2.

Cerberus Series.  This survey has been made by C.A. Marriott and not by John Eatough as mentioned on page 3.  A C.R.G. Grade 6 survey was made from the Dining Room to the Rat Run, then trouble was found with the tri­pod and the survey was completed at C.R.G. Grade 1 for the last few feet to Everest Passage.  There was not sufficient time for the co-ordinates of the stations to be calculated and the small closure error was closed by eye.  The sketch of Lake Chamber is by the author and is a very hazy Grade 1.  It is hoped that a complete survey of Cerberus Series will be published as one of the Additions in the near future.

September Series.  Dick Roberts has started a Grade 4 survey of this series but it was not completed in time for publication on this survey.  His line has been used for the route through the boulder ruckle so that Illusion and Cone Chambers could be sketched in to show the known course of Plantation Stream.  The completed survey of this series is another that it  hoped to publish as an Addition in the near future.

The Choke to Everest Passage.  The Main Stream from the lower side of The Choke to the bottom of Everest Passage was surveyed atG.R.G. Grade 3 by the author.  Measurements were made with a prismatic compass read to the nearest 5°, and by pacing.

B.M.E.     Feb. 1962.