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Industrial Archeology and clay mines
Does anyone know much about clay mining?
On Brownsea Island in Poole Harbour, we're currently clearing rhododendron from
an area that used to be dug for clay. The clay was pretty low grade, used for
drainage pipes and the like, but we've uncovered a lot of ventilation shafts.
They look like giant well heads, about ten feet in diameter and are made of
brick. We've found six or seven now - and the top of all of them is very close
to sea level. The rim is maybe five or six feet above the sea.
If they were ventilation for a mine, then the mine would have been entirely
below sea level. I find it hard to believe that a mine for clay would have been
econimic, especially as the surrounding 'rock' seems to be a loose sand.
Shoring it up would have been difficult and dangerous.
A lot of clay was dug from the surface; an old map of the island shows a pool
called 'clay pit' which we rediscovered around three years ago (it was
completely hidden by rhododendron and eventually turned out to be a hundred
metres or so in length).
Why mine underground? Perhaps digging the pit deeper and deeper risked
subsidence or too much incursion of sea water. The pit is effectively at sea
level with a barrier of only a few feet between it and the sea. (It may have
been higher in earlier times as there are some steep slopes close to the area
that could have been cut back by digging)
On Brownsea Island in Poole Harbour, we're currently clearing rhododendron from
an area that used to be dug for clay. The clay was pretty low grade, used for
drainage pipes and the like, but we've uncovered a lot of ventilation shafts.
They look like giant well heads, about ten feet in diameter and are made of
brick. We've found six or seven now - and the top of all of them is very close
to sea level. The rim is maybe five or six feet above the sea.
If they were ventilation for a mine, then the mine would have been entirely
below sea level. I find it hard to believe that a mine for clay would have been
econimic, especially as the surrounding 'rock' seems to be a loose sand.
Shoring it up would have been difficult and dangerous.
A lot of clay was dug from the surface; an old map of the island shows a pool
called 'clay pit' which we rediscovered around three years ago (it was
completely hidden by rhododendron and eventually turned out to be a hundred
metres or so in length).
Why mine underground? Perhaps digging the pit deeper and deeper risked
subsidence or too much incursion of sea water. The pit is effectively at sea
level with a barrier of only a few feet between it and the sea. (It may have
been higher in earlier times as there are some steep slopes close to the area
that could have been cut back by digging)
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It all sounds fascinating, though I can't shed light on anything.
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But neither of these should have any significant impact in the time since clay-mining stopped as it was probably only in the last century.
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I guess they must have mined it underground, but it sounds a very risky and low-profit operation.
I don't think it lasted that long, so I guess that's probably why. I shall have to see if I can find any local history books relating to it.
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The type of brick used should give clues as to when these shafts were constructed, e.g. Roman bricks very different from Victorian ones, again diff from modern bricks.
There has been ongoing oil extraction from the Poole Harbour area from some decades, but can't see why this would necessitate sinking such big shafts, drilling more like. However pre-oil, a lot of mineral lines built around the Isle of Purbeck, just south of Poole Harbour, maps published in Railway magazine, 6/77, and OS maps, eg the 1:25,000 one of 1966, show old rly lines/tramways.
PS there is a feature shown about 1 km south of Slepe Farm, looks like a short old rly, but sep from more published old rlys, this feature consists of a cutting and an embankment aligned, running southwest to northeast, about 600 m long, not sure what this is.
The sae around Poole Harbour is currently retreating, as the bay fills up with silt, but was once flooded by sea, but long before man would have constructed brick shafts there. (or maybe as Brownsea island is a well known haven for the red squirrel, there are just some very large squirrels there, burying very big nuts)
Hillary Shaw
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Could these holes have been to with this?
http://www.geog.port.ac.uk/webmap/hantsmap/hantsmap/copperas.htm
The china works were connected by a mile long tramway -
http://www.soton.ac.uk/~imw/brownsea.htm
IIRC Brownsea Island was used for Anti-Aircraft purposes during WW2.
Nick P
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It has to be over 70 years old simply because of the age of the rhododendron.
There was a small tramway here at some point. The only trace left now is a short ridge all of three feet high where it ran along the shore close by all these shafts.
The island was used as a decoy for Poole during the war. The resulting bomb craters are now used to store water in.
Gun emplacments would logically be at the end of the island facing the harbour mouth (nearly a mile away from the clay pits). There have been guns there at some points in the island's history. There's some old canon down that end.
The red squirrels are doing well. As the rhodendron is reduced, the amount of pine increases. More pine = more squirrels.
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I see the owner went bankrupt! Not surprising given the poor quality of the clay. I can't help wondering if the mines were safe and if anyone died there. We're looking at an area now where we wonder if there's been subsidence.
BTW, your icon reminds me of Brownsea Villa, the Wildlife Trust's HQ on the island. Hardly surprising as it used to be the vicarage for St Mary's church.
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Could they be containers for the Q-sites to divert bombers from Poole and Holton Heath
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I would think10ft would be too small for anti-aircraft. If it was a Bren or such like they would surly have been about 4 to 6ft anything larger then 20ft or so. It was and still is a practise to test air bottles and such like underwater. could it be possible they were for testing explosives?
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sounds like WW2 anti-aircraft position foundations. what gives the impression that they are wellheads/vent shafts? do they go down a great distance? if not, then likely to be foundations of AA posts, or similar.
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Just found a book MILITARY DORSET TODAY by Colin A Pomeroy
COASTAL DEFENCE GUN BATTERY
Eastern End of Island in grounds of Brownsea Castle.
2 x 4.7" naval guns installed in 1940.
Underground gun control room.
40mm bofors added on run up to Overlord, on open ground to rear of battery.
Today both gun positions visible including one with gun mounting ring.
Two searchlight buildings remain.
STARFISH DECOY SITE OS: SZ 012881
Western end of island, built 1941
Concrete contriol bunker located 200 yrads from tanks of inflammable
liquids.
Today control bunker invisible beneath heavy growth, but air raid shleter
at SZ 016877 and ancillary building (ammo store?) at SZ 016881
Regds Ian
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Ours isn't the decoy site either (doesn't match description and is in the wrong place). However, I suspect we may end up clearing there eventually - if it's hidden under heavy growth, then the growth is probably rhododendron. We might get there in five or six years...