Wigmore re-visited.
Some further thoughts.
Trevor Hughes
Belfry Bulletin No 391/392, November/December
1980
Tony Jarratt's article in B.B. No. 371 marked the end of a
lively series of articles about this interesting conglomerate
cave. This, I hope, will redress the situation and inspire some
thoughts, and even probably some work underground.
At the time of Tony's article Wigmore was being dug
virtually every day; I was on leave and Tony was on holiday. The
latest event in his article was the pushing on past the Smoke
Room to where a large slab blocked the passage (30th Nov.
'78). What follows continues from there.
The weekend of 2nd/3rd December saw a large party of
Belfryites attacking the offending slab by means of a rope winch.
This slab, the result of roof block fall, was removed and broken
up by hammer and chisel. Approximately four feet of new passage
leading to a choked right hand corner was entered.
An unreachable left hand bend, after a further two feet, could
be seen. A major setback occurred on that Saturday, the
substantial mud and stone collapse from the Smoke Room. This
slump increased during the following days and completely blocked
the way on.
Attention now turned to the large, black hole, through
boulders, revealed by this collapse. Some stabilization was
required but on 9th December '78 the upper section of the
Smoke Room was entered. The chamber was found to consist of tiny
rift inlets and wedged boulders.
On the following weekend a large B.E.C. team dug at the debris
which blocked the way along the lower passage. This flowing
stream made spoil hauling a wet and miserable task. It was
decided to leave the dig until the following spring. The final
comment in my caving log entry for that trip summed up the
situation: "Much more work still to be done."
After this trip the cave appears to have been left alone - no
entries were recorded in the hut log. I was at sea, enjoying only
infrequent trips to Mendip; other digs found favour; the sun
shone; the Hunter's was open; etc. As a result, for twenty
months Wheal Wigmore heard only the lonely knocker's chisel.
No curse ridden digger's breath nor shovel on rock.
Silence.
I could not allow this to continue. A weekend on Mendip at the
end of August this year found me with an itchy digging arm and
two volunteers for their first ever trip down Wigmore; Ian
(Wormhole) Caldwell and (Quiet) John Watson. Deluded by promises
of me digging in their recent extensions in the deepest reaches
of Manor Farm Swallet they agreed on an exploratory trip.
The entrance pitch, Hesitation Chamber and the two climbs were
unchanged apart from accumulations of vegetable debris and
oddments of the capping formers. However the winter streams of
78/79 and 79/80 had not been idle. The start of Christmas Crawl
had been scoured out and now seems quite sizeable. The entry to
Santa's Grotto had to be dug open - easily removable gravel
choked the low section of passage to within four inches of the
roof.
A large boulder and several smaller rocks had slumped into the
entrance of Pinks and Posies. These were moved or demolished and
an entry made. The first section of Pinks and Posies was
unchanged. However the remains of the Smoke Room collapse and
allowed gravel to accumulate behind it. The last section of
passage was fairly heavily choked to within six inches of the
roof. Ian's and John's moans of inactivity forced a
retreat before I could come to grips with this choke. The Smoke
Room collapse, however, did seem to have largely vanished.
The next visit was a post AGM trip (good conglomerate mud is
excellent for clearing the mind of such politics) by Chris Smart,
'Quackers', Nigel Dibben and 'Mac (I don't feel
well) anus'. Chris dug into the Smoke Room, passed the now
non-existent collapse and reached a point some ten feet beyond
the Smoke Room where a boulder obstructed the way. The passage
could be seen to continue. This represents 2/3 of the original
distance from the Smoke Room to the end of the cave as it stood
on 2/12/78.
Inspired by the success of this trip Ross White and I ventured
to the end on 11/10/80, armed with an array of digging gear. A
week of continuous rain had produced a fine stream flowing down
the entrance shaft. This was diverted to a secondary sink in the
clearing to the south-west of the entrance, where the water
disappears through the Rhaetic Marl. The cave remained very wet
despite our efforts. Ross put his talents to good use and rapidly
moved aside the boulder that had stopped Chris. The original end
of the cave was quickly reached. Loose gravel now chokes the
passage at the left hand bend completely to the roof. We both dug
at this choke for a while. However, having little convenient
dumping space and no spoil hauling gear we decided to call it a
day. We returned, wet and filthy, to the surface.
On first glance at the terminal choke it is credible to
suggest that the conglomerate passage bifurcates at this point,
but this is not my belief. Having viewed the end in December
'78 when the present gravel choke was not there I wish to put
forward the view that this choke is the result of stream
deposition behind roof block fall, the material coming largely
from the Smoke Room collapse. Digging at the end is very feasible
- the gravel is loose, mud free and easily dug. The most
convenient way of removing the spoil would be in 'poly'
sacks which could easily be hauled along the low passages. A team
of four or five diggers would be required. The removal of the
loose material will allow the block fall to be attacked either
chemically of mechanically. What could follow? Open passage would
most probably be of the same pattern as before: low bedding
modified by block fall. But what of the limestone? Where is it?
When will it be met? Only by digging will the truth be known but
here are the geomorphological details of the area: -
1) All Eights Mineshaft (55965291) elevation 925 ft is only
1410ft north of Wigmore, the shaft cap being 45ft higher.
Limestone is met at a depth of 80ft. The water in the shaft is
said to emerge at Sherbourne Spring.
2) The underlying limestone dips at 30° to the north-east
- it is on NE slopes of the North Hill pericline. The limestone
surface can be assumed to rise in a SW direction.
3) The unconforming conglomerate has in lower Wigmore,
produced a bedding passage dipping to the south at 2-3°, most
noticeably in Christmas Crawl. (Incidentally, the average surface
gradient between All Eights and Wigmore is 2° to the
SSE).
4) Wigmore Swallet is 78 ft deep at the end.
Personally I think the limestone is very close despite the
fact that a groundwater divide separates the water flow routes of
the two sites.
But what of Wigmore's subterranean flow to Cheddar? I
would like to propound that there exists an as yet unknown major
drainage passage heading east-west that transits the Wigmore
area. The head of this catchment is the Tor Hole Swallet area.
This watershed is quite sizable and, as demonstrated by Tor Hole
Swallet, bears little relation to the surface landform.
The passage of water through this system is extensively
controlled by the layer of Harptree Beds, Marl and Rhaetic Shales
which cover the area. Rainwater collects at discrete points on
this impervious layer before flowing underground, giving rise to
the large number of sinkholes in the area. As the sinkholes
develop they are choked by slumping bf the surface clays leading
to slow flow rates by percolation action in the upper regions of
these poorly developed caves. The solutional power at depth is
consequently proportionally greater due to the absence of
calcareous matter in these clays. The amalgamation of water from
these many, small, choked passages would lead to the formation of
a master passage by preferential solution. The depth of this
initially phreatic passage would be just below the water table
pertinent to the time of its formation. This passage would be
largely strike controlled, in the limestone, and would contour
around the northern side of the North Hill pericline.
The major development of this passage would have begun at an
elevation of about 650 ft a.o.d. This development is supported by
the existence of a large cavity, found by boring, at a depth of
approximately 200ft in the fields immediately to the east of
Wigmore Swallet. A passage at this depth would correspond to a
period when the water table was such that Great Oones Hole acted
as the Cheddar resurgence, some 300ft higher than today. This
indicates the great age of the proposed passage.
The height of the lowest sinks (690ft) indicate that the large
cavity most probably represents a fossil section of passage or
even possible a chamber of a similar nature to those above the
active streamway in Stoke II.
After the initial section of slow flow the flow in the main
passage to Cheddar would be of a more rapid nature. Examples of
this flow structure are: -
1) Tor Hole, Long Wrangle and Minery Cottage Swallets, 1 mile
to the east of Wigmore. Flow travel time to Cheddar: 72 - 87
hours.
2) Red Quar Swallet, 0.5 mile SSE of Wigmore. Flow travel
time: 5 days.
3) Bowery Corner Swallet, 1.5 miles west of Wigmore. Flow
time: 50 hrs.
Castle Farm Swallet, a B.E.C. dig in 1963/65, produced a
draughting, choked passage at 20ft depth. This project has, I
hear, been re-opened. A dye test here would be of immense
value.
The rapid travel time (11 hours) of the Wigmore water is
highly significant. I believe that it indicates the close
proximity of the master passage and the relatively open nature of
the passage to it. The presence of the nearby cavity supports
this proposition.
For Wigmore Swallet to reach the depth of the master passage a
steeply descending passage is required. In the limestone a dip
passage would rapidly reach the required depth. Whether this
passage is a low bedding or a vadose trench only direct
exploration will tell. The limestone passage may be well
developed, of course, for the reasons stated earlier. I also
predict that the Wigmore stream will be augmented at the obvious
line of weakness - the conglomerate / limestone boundary.
Wigmore Swallet, with a length to date of 237 ft, is the only
cave in the area whose underground course has been followed for
any distance. It must represent a potential key to this proposed
system. The terminal choke cannot be left alone. Digging there is
not easy but the reward will surely repay the effort and could be
of major significance. The challenge should not be ignored.
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