With the ever more frequent appearance of new caving publications, more and more cave surveys, surveys of diverse quality, are being published. Cave surveying presents special problems of its own, yet, since it is mainly an amateur occupation, most of those concerned with it are not surveyors by profession and often the scope of their surveying activities is limited by lack of knowledge of the full potentialities offered by this subject. Even today the subject is so young that there still remain ambiguities of technique and nomenclature peculiar to the surveying of caves, which have to be solved. The purpose of the series of articles commencing here, is to make available to the amateur cave surveyor specialist experience which may help him to improve his surveys and to broaden their scope. In the first paper Michael Rennie gives a general introduction to the subject. Subsequent contributions, each by a different author, will cover work underground, contouring, drawing up the results (by a draftsman) recording geological and archaeological information, and other aspects of cave surveying.
The writer gives an introduction to cave surveying, with special emphasis on the use of plans, elevations, and sections, on showing the relationship of a cave system to the land surface above, and on the recording of detail.
THE SURVEY of a large cave system may take months or even years to complete and often involves complex organisation. It seems a pity, therefore, that in so many instances the best results are not obtained because the surveyor, who may be conducting the survey as a side line of some other project, is not sure how to present his survey or does not realize the full potentialities of the subject.
Lest it should appear that the writer is claiming that all surveys should be carried to a uniform high standard of accuracy and detail, it should be stressed that the standard required of a survey is dependent on the purpose for which it is being prepared. Generally speaking surveys of very large cave systems, while they should be of the highest possible accuracy, must be drawn on a relatively small scale, or the results will extend over paper tens of feet long. On the other hand surveys which are intended to show scientific detail should be on a larger scale and may be limited to showing only part of a cave.
A system of grading of accuracy of cave surveys has been devised by the Cave Research Group of Great Britain (Butcher, 1950, 1962) (In light of experience, some cave surveyors are now pressing for a revision of this grading). There are seven grades, Based on the type of equipment used:
It is the practice of most cave surveyors, when carrying out a survey, to record their measurements underground and to wait until coming to the surface before commencing drawing up the results of their work. In a cave of any size, especially if it is wet, it would not be practicable for the surveyor to draw up his results underground. For all surveys where an accuracy greater than Grade 4 (C.R.G.) is required the main skeleton must be constructed on a drawing board, even if much of the detail is filled in underground at a later date. A number of very accurate surveys that by C.R.G. grading would be only Grade 4, have been drawn underground (for example, Eastern Torrs Quarry Cave, Yealmpton, Devonshire, A. J. Sutcliffe) but this method is only applicable to dry and reasonably roomy caves, and the task becomes very painstaking.
The surveyor is not able to present a true picture of a cave on paper. This could be achieved only by means of a model and he is limited to what he can achieve in two dimensions. Great ingenuity has sometimes been shown in face of this problem.
The principal Ways Of depicting a Cave System are the PLAN, ELEVATION and SECTION.
A plan is a projection of a cave into a horizontal plane (Figure 15 a). Difficulty may sometimes be experienced in deciding where a cave plan should be in relation to the actual physical structure of the cave, since the cave may expand or contract at different levels, and here it is necessary to distinguish between a simple plan, representing one horizontal level, and a complex plan representing a number of levels. One of the schemes most commonly adopted is to regard the plan as representing the limits of the cave at floor level accessible to the average human. It is of course logical to use a cave floor as a datum for a cave plan; yet such a datum can never afford anything but an ambiguous plan view of a cave. If the cave floor is sloping, the datum will not even be horizontal. On higher grade surveys, where tripods are used, the tape stretched between is sometimes taken as the datum line. In any instance the measurements must always be arbitrary. For example, in the case of a tunnel with no sediment on the floor, which closes downwards into a rift, difficulty will be experienced in deciding where to show the cave walls. In deciding, the surveyor must consider the use to which the survey is to be put.
Since the vertical extent of a cave can be represented on a plan to only a limited extent, cave plans are usually supplemented by sections and elevations. Even a plan, however, is not without scope for representing vertical differences of level, which can be shown by contouring, spot heights and, in the case of sloping floor deposits, by hachuring or arrows showing the direction of slope. Over seventy years ago Martel (Martel, 1894) was already making extensive use of contouring of cave floors, which method helped to give a vertical relief to the insides of some of the caves he portrayed. A method of contouring cave system maps has recently been described by D. Ford (Ford, 1965, see also Ford 1964). This is of special value in that the absolute level of the various parts of a cave system, in relation to ordnance datum, can be seen at a glance.
A Plan, Projected Elevation and True Length Elevation of part of a hypothetical cave.
The information contained in cave sections and elevations is of special value in that it provides a picture of the cave as seen from the side. This can be portrayed in a number of ways, more than one of which may be necessary in the case of high a grade survey, whereas one may suffice for a survey of small scale or lesser accuracy.
The nomenclature used by cave surveyors for vertical cave profiles of the same construction may differ. As such presentations find no parallel in other sciences this unfortunately is something we must accept for the present. Terms may be encountered such as true length elevation, projected elevation, longitudinal section, sectional elevation, section projected onto a plane and cross section. Strictly speaking the term section should be employed for part of a cave seen as if cut through in a plane at right angles to the line of sight, whereas elevation may include details projected onto a vertical plane. The following types of profile are the most important:
This is a side view of the cave projected from the plan along a given bearing, and should whenever possible be shown below the plan on the same sheet of paper and on the same scale, so that vertical lines can be dropped from each station, thus facilitating construction (Figure 15 a, b). All vertical measurements on a Projected Elevation are true to scale but there is a foreshortening of tunnels and chambers where the bearing recorded does not lie along the bearing chosen. Passages running parallel to the chosen bearing will have true representation whereas passages at right angles will appear as vertical drops equal to the fall in level of the floor. Most passages will, of course, be at some position in between. In the case of complicated caves it may be necessary to construct two or more and even subsidiary Projected Elevations. Very careful thought must therefore be given when choosing the bearing of a Projected Elevation and this must be recorded on the sheet. The main purpose of such a construction is to show the relationship between various cave passages.
A Projected Elevation in the dictionary sense should show a cave system as it might appear if it could be engraved as a model within a block of Perspex and viewed from the side. The highest and lowest points in each chamber would be visible. In fact, however, the vertical height of the various parts of a cave system, as depicted by most surveyors, is the height of the cave along the line of their traverse, and can give an untrue impression of the relative proportions of the various cave chambers. Measurements of the full vertical range of a chamber, though much to be desired, would be difficult to measure and would vary greatly between surveyors.
The present writer prefers to use the term Projected Elevation for the former type of projection. It could alternatively be called a " projection of a vertical section along a traverse line ", or simply a " Projected Section ".
A True Length Elevation shows a profile along a series of legs of a survey, set out in a straight line (Figure 15 c). All distances, both horizontal and vertical, are correct, but such a representation, which takes up more room lengthwise than a Projected Elevation, is misleading in that the distances between parts of the cave system will be shown as being further apart than is actually the case. Where a closed traverse has been carried out loop passages may occur twice on the elevation. True Length Elevations are, however, valuable for plotting scientific information and also for referencing cross sections, thus avoiding overcrowding the plan. The True Length Elevation of the present writer is the same as the Longitudinal Section of some other surveyors.
Cross Sections, taken at intervals along a passage, provide a further important guide to the shape of a cave. The length of the intervals at which they are drawn depends on the degree of accuracy and amount of detail to be shown on the survey. Cross sections should be shown as close as possible to the passage to which they refer, preferably along the True Length Elevation (Figure 16 c). In Figure 16 a, the sections are shown as being plotted on the plan of the cave, and since there is no room to show them alongside this plan, they have been numbered and grouped together nearby (Figure 16 b). This method should be avoided as the reader must make reference to two parts of the sheet to obtain the information he needs. The scale of the cross sections should of course be the same as that of the plan and elevations.
The value of a cave survey depends to a considerable extent upon the amount of detail which it contains. It may consist of a simple small scale outline plan, with no detail, sufficient to enable a caver to find his way around underground, or it may be drawn on a large scale and contain detailed geological or other scientific information.
Butcher (1950), when discussing the purposes of a cave survey proposed that, in addition to having a numbered grading of accuracy for cave surveys, already outlined on pages 1 25-6, there should also be three classes A, B, and C, depending on the amount of detail to be shown upon them. Class C, based on grades 1-3, is intended for exploration and organising further work; class B, intended for such work as "the correlation of surface and underground features, study of water levels ... " is based on grades 4 and 5; and class A, for "research in geology, physics" is based on grades 6 and 7. This classification is not mentioned in Butcher's chapter on Cave Surveying in British Caving (Butcher, 1962) and has received less attention than his better known grading, though Warburton (1963) has drawn attention to the desirability of resurveying some already-surveyed caves with the intention of producing a Class A plan.
Butcher (1950, 1962, pp. 522-525) proposed a series of symbols for use in cave surveys, when plotting such features as streams, stalagmite columns, rimstone pools, rocks on the floor and avens, and these have subsequently been extensively applied by cave surveyors.
In Figure 17 the present writer shows four plan representations of the same part of hypothetical cave tunnel. In (a) only the cave walls are represented. The plan is uninteresting. In (b) some details have been added in lettering, but the result is confusing. In (e) conventional Cave Research Group symbols (Butcher, 1962) are employed and in (d) these are supplemented by short notes. In each of the latter two examples details have successfully been added without causing overcrowding. Figure 16 d shows a hypothetical cross section of a cave, employing symbols for water, sand, and stalagmite formations.
For an actual example of an easily interpreted cave plan (although the scale on which it is reproduced is too small), where the floor deposits are represented by symbols, the reader is referred to the plan of The Tunnel, a cave near W. Kimberley, Western Australia (Jennings and Sweeting, 1963).
The surface topography superimposed upon a cave plan.
One final representation, which must be mentioned, is the relationship between a cave system and the ground above. Normally this is constructed on a smaller scale than the main survey. No cave exploration is complete without an examination of the surface topography, which may reveal such features as lines of sink holes, the disposition of which may be related to the cave system below.
Attempts to superimpose surface and underground features on a single plan often lead to confusion of detail (Figure 18 d) and a cave is best represented either in solid black (Figure 18 b) or, if this will obscure important surface details, in outline only (Figure 18 a). Details of the interior of the cave should then be plotted separately on a plan where the surface topography is omitted (Figure 18 c).
In instances where a surveyor has two colour printing facilities at his disposal, surface and underground details may be superimposed in different colours. This method has been employed, for example, in Crickmay and Bendall's map of G.B. Cave, Somerset (Crickmay and Bendall, 1951), where the surface topography is printed in black, the cave plan in red.
In the same manner that the surface topography may be superimposed on a plan of a cave system, so sometimes are maps of the geological structure of the surrounding rock as was done, for example, by T. D. Ford (Ford, 1963) at Nidderdale, Yorkshire, in this instance depicting the caves as solid black. Such relationships can often be highly instructive, revealing why a cave has been formed in a particular place and providing information concerning where additional chambers are likely and unlikely to be found.
In the preceding brief account of the presentation of a cave survey the writer has attempted only to introduce the reader to the basic essentials of the subject. The paper is intended primarily for the caver who finds himself forced to produce a survey in the course of pursuing his own special branch of speleology. Cave surveying, however, is still in its infancy and unfortunately lacks the guidance of tried and proved methods or any national or international agreements of recognizable standards or terms.