STALAGMITES AND STALACTITES

IN BANWELL CAVES

by J W Hunt

Occasional Paper No. 3

October 1998

£3

INDEX

Introduction	7
Stalagmite And Entombed Organisms	9
The Dark Peaks	18
The Axbridge Ochre Cave	23
The New Part Of The Stalactite Cave	24
Conclusions	26

PHOTOGRAPHS

J W Hunt by the Bone Stack looking at the “Pitfall” Banwell Bone Cave 1969	2
Banwell Stalactite Cave – The Great Chamber (1970)	25

DIAGRAMS

Simplified Geological Section	5
Vadose Development	5
Phreatic Development	5
Relative Elevation of the Caves	6
Banwell Bone Cave - Survey	8
Banwell Bone Cave Stalagmite On The East Side Of Beard’s Stack Of Bones	10
Growth Bands Of Ancient Fractured Stalagmite Flowstone Near “Pitfall”	11
Banwell Bone Cave Stalagmite Flowstone	13
Banwell Stalactite Cave Fractured Flowstone from The Humphrey Extension	14
Stalagmite from Cave above the Ochre Pit Cave Banwell	15
Banwell Ochre Cave Fractured Flowstone (Phase A)	17
Banwell Ochre Cave Dripstone (Phase B)	19
Phase B Continued	20
Comparison Of The 1^st “Great Dark Cycle” And The 2^nd “Irregular Dark Cycle”	21
Banwell Ochre Pit Cave Fractured Flowstone	22
Axbridge Ochre Cave Fractured Stalactite Curtain	23
Suspended Stalagmite, Stalactite Cave (New) 17^th June 1970	24
Banding Data	27 - 30

LITERARY SOURCES

Axbridge Caving Group and Archaeology Society Journal (Annual)

Axbridge Caving Group.

Banwell Archaeological Society “Search” (Annual).

Proceedings of the University of Bristol Speleological Society.

Solar Activity in the past 35000 Years from the date of Luminescence of Cave Flowstones from Bulgaria – Y Y Shopov, V Dermendjiev and G Buyukiev (1991).

INTRODUCTION

When we broke into the Ruby Chamber of Banwell Bone Cave on Wednesday 19^th November 1952 it was as though everything had been destroyed about a week ago; it was very like what we had seen in the New Chamber of the Stalactite Cavern. It seemed as if something had been running around with a great club hacking off stalagmites – but there were no signs of percussion marks. Some rocks were cracked and the mud in the Mud Passage seemed only as though it had recently been put there!

After discovery of the Galleries, also in Banwell Bone Cave, it was about 3½ months later that we dug down at the left-hand side of the 3^rd chamber on Wednesday 4^th March 1953. After passing through a fair depth of loose stones and boulders we came to a deposit of rich red iron oxide overlying grey clay, and perhaps iron below this again, then solid rock.

The great age of these deposits is indicated in that after the grey clay bed had been laid down there was a pause in which a few thin slabs from the roof fell onto it, then the iron was laid over these, then successive roof shellings of some depth accumulated over this, over a considerable time. (about 4 feet, 1.2 meters).

The water in the cave, still free of further sediments, has since had time to “eat into” and smooth over any tears in the roof where the slabs had fallen from, though these (the fallen slabs) do not show so much surface dissolution. This could be that the water, being under great pressure, had more “scouring” effect and movement along the broad expanse of roof and sides than in the floor.

A little further back, towards the 2^nd chamber of the Galleries, was the surface of the same accumulation of stones, there are several small stalagmite bosses slightly sunk sideways but not large enough to be cracked off.

On Wednesday 11^th March 1953 the Mud Passage was started to be dug out. Later on, on Wednesday 1^st April 1953 two sets of formations were discovered, one broken set of stalactites and stalagmites, and another broken set of stalactites on the surface of the mud.

It was then that the great age of the deposits in the cave was realised. They had lain there for “ages”. In the Galleries there were signs of falls from the roof but most of the scars were smoothed over, and in the Mud Passage there had been destruction of stalactites on two separate occasions with a large crack in stalagmites, between them.

J W Hunt

1998

The sequence of the Mud Passage deposition is best charted in the table, much of it is confirmed by things found in the Galleries stalagmites.

MUD PASSAGE DEPOSITS	GALLERIES DEPOSITS
Small calcite lined holes in brown-mixed clay	Cave Pearls
Straws and stalactites broken	Straws and stalactites broken
Brown-mixed clay (Water-borne deposits)	Brown-mixed clay (Water-borne deposits)
Large stalagmites broken	Large stalagmites broken
Stalactites broken, one sealed in stalagmite	Stalactites broken, one sealed in stalagmite
Stalactites and stalagmites forming	Stalactites and stalagmites forming
More fallen flakes	Black and ochreous deposits on loose stones
Fallen pieces of stone with Dog-Tooth Spar underneath
Grey clay

The discovery of a large piece of stalagmite in 1950, in the Banwell Ochre Cavern led to experiments in drawing up of depositions. In 1990 I attempted to chart Banwell stalagmites and also an Axbridge stalactite (1951). There is no harm done regarding deposition drawings.

Many years ago Ray Gilson reasoned that percolating water, which built the formations, started by water falling on the vegetation and so stalactites and stalagmites were influenced by what was happening outside the caves. Many of the influences concern solar activity of some 11 years or more duration.

From the Eastern Branch of the Banwell Bone Cave I showed that the cave had once been covered with stalactite and stalagmite formations, before the bone deposits came into the cave. Many of these formations were decaying, most of them fell presumably from eroding entrances and recesses.

I sorted out the breakages of formations are best shown in the Mud Passage (off the Ruby Chamber) which I detailed in the 1966 ACG&AS Journal. The later ones are confirmed by the large stalagmites in the Galleries. It happens that the Galleries stalagmite is evidently “dead” and rolled away. The smaller stalagmite in the Mud Passage was also broken off but it was soon covered by mud and remained in fresher condition. See also the drawings in the “Baker Extension, Banwell Bone Cave”, Axbridge Caving Group Occasional Publication Number 1 (1991).

STALAGMITE AND ENTOMBED ORGANISMS

In a small alcove between the Eastern Branch and the main stack of bones, constructed by Mr Beard, and below the East Side of the Pitfall, are remains of a spread of flowstone. It is shown in the photograph, to the left of the standing figure but the formation has been so stained from earth, bones and other organic materials what could have been “sparkling white” is now dirty and black, so does not show up.

Collecting samples of formations in 1966 with a small hammer and chisel, the writer made a “lucky strike”, obtaining a complete flake from the broken edge of this stalagmite deposit. It is quite “dead”, of a crystalline nature turning to spar, and the piece struck off was just over 50mm thick (almost 2 inches). The stalagmite is briefly described by John Tucker in Search No. 19, Journal of the Banwell Society of Archaeology 1983.

BANWELL BONE CAVE

STALAGMITE ON THE EAST SIDE OF BEARD’S STACK OF

In 1990, opportunity occurred to carefully (and successfully) saw down through this brittle specimen and polish it as far as practical without disintegration. It could then be examined with a strong magnifying glass. The dead, crystalline nature made examination difficult, but, by marking it with a pencil line, then estimating the thickness of visible light and dark growth bands, the graph-like enlarged drawing could be constructed, the light and dark deposits being offset either side of a vertical line equal to their thickness. Diagonal lines from the centres of these offsets could be linked to give “trace pen-like” oscillations.

Examination revealed this to be an anciently shattered stalagmite. It had not been broken by early 19^th century investigations, as continued seepage had “healed over” the broken surface.

A number of irregularities, the writer observed, and small cavities, resembled sections of stalagmite from an Australian cave where record had revealed distortions due to the effect of organic growths. Free air circulation and some directional influence from light-sensitive organisms seemed to be contributory factors[1]

The Bone Cave specimen had the appearance of a white “fossil cheese”. A scale of percentage has been introduced to give reference points irrespective of any varying rates of deposits. Organic growths at 1% (perhaps even ab. inito), striving to persist up through the slowly growing bands, received fresh nourishment, that left a cavity. In 10% - 20% of deposition greatest activity of organic growth is evident with a number of cavities evident, some organisms struggling up from earlier bands. Some continue up to 60% but then seem to die away. At 78%, activity resumed until shattering of the formation. Further growth covering the breakage eventually became heavily invaded, contaminated and stained, presumably from bones, fur and earth, and stalagmite growth was terminated.

It will be seen from the Drawing (x3) that the organisms strove to extend upwards against entombment by the growing stalagmite, inclining north-westwards. This could be the effect of water flow, as it is not certain if light-sensitivity was involved. If it was, then light (however low lux) from the present entrance archway could have exerted an influence as well as the Pitfall. Hitherto, the earliest discovery of sealed organic remains were what appeared to be the remains of flies on the side of the Ruby Chamber opposite the Mud Passage, which were discovered by John Chapman on 5^th May 1954. (Compare Sandford Levy)

The Bone Cave stalagmite may be of similar age to those ancient formations on the boulder floor of the Eastern Branch – it may also be compared with the slumped stalagmite floor (also “dead”) in the alcove by the Frozen Rivers Grotto (that is the subject of further investigation).

As will be explained the Mud Passage and Galleries testify to three breakages. Which of these the Bone Cave stalagmite relates to is uncertain, but it is not far from the Pitfall and it probably records what was happening there and in what most probably was the remnants of another chamber high above, extending eastwards, now eroded away. Some bats could have come in, hung up, and fouled the stalagmite.

Examination of a similar piece of shattered stalagmite from the Humphrey Extension of the Stalactite Cave, Banwell, suggested a like sequence of banding before fracturing. The stalagmite was however, not “dead” or crystalline but the piece examined had a band of powdery, decomposed material in it. This did not seem of equal thickness throughout and might have been a localised fall of decomposed limestone?

The testimony of a series of breakages in the Galleries and Mud Passage, recorded by the writer in the ACG&AS Journal for 1966 pp 31 – 43, is that there was

1. A long period of growth

2. Shattering of stalactites

3. Some continued growth (sealing a few of these in)

4. Major breakage of large stalagmites

5. An influx of waterborne clays

6. Drainage

7. Some growth and a further breakage of stalactite straws

8. Some further slight growth to the present day (often to one side, from stalactite stumps, and of quite white deposit appearance)

The impression gained is that item 4 was the occasion of greatest destruction – was it a seismic effect or effects of Ice Age “deep freezes”? Examination of one stalagmite near the Tapestry, certainly suggested the latter, but a random crack-up would be expected. Instead fracturing occurs in a way suggestive of major jarring action (earthquake?) cracking off anything that would have a “swing” to it, so thick stalagmites have been cracked clean across near their base or lifted off. It could be that deep-freezing exerted a weakening of the structures, (such as has been observed), making it easier for them to succumb in earthquake action. As regards to item 7, there were few stalactites left or only small ones formed, so the strength of any third shock involved is not certain. (See also Axbridge Caving Group Occasional Publication Number 2 –Banwell Bone Cave – Researches in the Eastern Branch (1997) pp 41 – 42)

Comparison of the various breakages has been mainly in relation to bands of white, lighter or “transparent” deposits, but peaking of coloured or darker bands give other “readings”. In the Banwell Ochre Cave Stalagmite three great cycles of “dark” banding are evident, into the present century. Fracture occurred near the end of the first cycle, and in the dripstone continuation a very regular “dark” cycle follows, but in the third cycle there is more white banding, reminiscent of the first. The Bone Cave flowstone might contain record of two dark cycles.

It may be suggested that the Bone Cave stalagmite was fractured in the first breakage, with some regrowth, it survived the second breakage and became, eventually, buried under bone deposits. It could be argued that the first breakage was not severe enough, that the second breakage was responsible and, since deposition was by seepage and not dependent on overhead stalactites (which were shattered) regrowth proceeded independently whereas that of true stalagmites in other parts of the system was halted. Such is the uncertainty of present knowledge.

The Banwell caves are formed in very steep rock strata (70° and more dip North) and some movement might be expected. This could affect the caves elsewhere and the writer found an ancient “dead” broken piece of stalactite curtain in the Pool Chamber of Axbridge Ochre Cave in 1951, comparable in size to the Banwell formations.

At the Banwell Ochre Mines, 2.5 km eastward of the Bone Cave, the writer, in 1950, then a member of the Mendip Geological Club (later absorbed, in September 1950, by the ACG rescued a 4 inch thick slab of stalagmite which had been blasted by the miners around 1937 – 1940 AD. It is of great significance, the greatest contribution to Science of this short-lived Club, and appears to bear silent witness to changes over a very great period, until its destruction. It had formed on a great mass of iron ore.

The first section is of flowstone, from seepage, like the Bone Cave example, and crystallisation is evident. Also like the Bone Cave example, it has been shattered. The fracture “healed” but continued growth was dripstone, water was dripping from points above, so eventually two small stalagmite bosses formed on its rippling surface.

Superficially (and by similarly plotting the banding) this stalagmite seems to equate with the Bone Cave example. In the later growth, traces of possible organic growth occurs, but only one small area can be directly compared with the Bone Cave examples. The cave it came from (approximately 50m OD) is not far below the surface and such intrusions must relate to gradual erosion and unroofing of former extensions. Vide ACG&AS Journal Vol 3, No 1, p 42 (November 1956) regarding this stalagmite and the chamber it was found in.

THE DARK PEAKS

The plates of stalagmite bandings are only what can be visually determined, there are doubtless many more subtle fluctuations within or even between them. The Bone Cave flowstone was a poor specimen for such a study; it had crystallised and was affected by organic growths is of rather white appearance and so difficult to discern “dark banding”. Nevertheless it was noted that two dark peaks seemed evident, one at about 9.75 – 19.5% and another at 76 – 78%. To gain an insight into the dark banding, at this level of study there is no better example than “The Great Dark Cycle” in the Ochre Cave dripstone (B) section. The first part, commencing around the fracturing and infilling of the underlying flowstone, is incomplete, but, from then on, there is gradual increase in “dark” peaks and the interval between, to the major dark peak at around 20% then nearly equal a decline. The difference between the peaks is 51% of B.

Where the sequence is clearest, light and dark bands are also of equal number when a dark peak is added in. It is noticeable too, that there is a general increase/decrease of the lesser dark bands between the dark peaks. This is not as constant a feature as the peaks – but indicates that another little dark peak at around 49 – 50% must be regarded as the “tail end” of “The Great Dark Cycle”. To offset deficiencies at the commencement of the first half of the Cycle, the whole data of the second half is available for study.

What if the banding was at fairly constant rate in time (if related to cycles of the Sun) and the apparent increase/decrease of the banding was due to rate of deposition? In other words, are the dark peaks to be regarded as of equal duration, and likewise. Is the smallest interval between to be compared with the greater?

The next “Irregular Dark Cycle” is of comparable size with Dark peaks at 51.8% to 53.0% to 55.2% to 56.5%. The major Dark peak is at 69.5% to 72.5% with others 81.2% to 83.5% and 85.8% to 87.6%.

Next to the Ochre Cave was the Ochre Pit Cave. It is a collapsed cave with a bed of ancient animal remains, which the miners dug out in 1937. Among items were a piece of a foot bone of Bison which had an area hollowed out and is exhibited in Wells Museum. Details of the bones are given in ACG & AS Journal Volume 3, Number 1 (1956) pp 40 – 45 and p 25.

Along the southern side of the Pit are ancient stalagmites. One near the animal deposits was found to be loose. I found that the loose structure was due to its being shaken and part of it was fractured. This was the cause of its being loose, and pieces were grated together. It was rather too cloudy and not much could be done about it. A drawing is given but not sure how it fits in with the others

<