The Wye Valley AONB Youth Rangers explored the landscape from St. Briavels to Clearwell caves uncovering the hidden world of geology that shapes the valley. We were led on the day by local geographer Nic Howes who is an enthusiastic interpreter of the landscape. First stop involved a descent into the Slade valley to visit the brook which has a unique geological feature. Slade Brook contains 700m of actively forming Tufa dams. Tufa or Travertine is a naturally formed precipitate of calcium carbonate rich freshwater. To protect these geological features the area has SSSI designation (site of special scientific interest).
We continued on to Clearwell and from there to Lambsquay wood. The Iron mines here have created scowles in the earth from which harts tongue ferns cling precariously and trees, their roots exposed appear to strangle the exposed rocks. It is a landscape that fires the imagination at is said to have inspired Tolkein.
We arrived at Clearwell caves in time for lunch and were able to enjoy some warm afternoon sunshine, before meeting our caving guides. John decked us out in orange boiler suits, helmets and lights and went through a few health and safety rules. We walked back towards Lambsquay wood and to the British mine entrance. The way in was marked by a veteran tree riddled with bracket fungi its roots exposed and forming a natural ladder of sorts that led to the mine door which John unbolted and let us inside….(to be continued)
Background History
The mine dates back well over 4,000 years, when early miners dug for ochre pigments to make paints. Iron ore miners later created a warren of underground passageways, by connecting the huge caverns. The iron-ore mines are part of ancient natural cave systems that began their development mainly within a bed of Carboniferous limestone known locally as the Crease Limestone, fairly soon after the rock formed, some 330 million years ago. Later, about 225 million years ago at the start of the Late Triassic Epoch, the surface of the area became a hot desert, totally unlike our modern landscape both in climate and appearance. Occasionally, torrential rain storms, far heavier and more prolonged than anything that we experience today dissolved iron minerals from the arid land surface. Massive floods of acidic, iron-rich water then entered the older cave systems, where iron-ore minerals were deposited as the water was neutralised by contact with the limestone.
Millions of years later, at about the same time that the Alps were forming elsewhere in Europe, the whole of the Forest of Dean area was uplifted again. The ancestors of major rivers, the Wye in the west and the Severn in the east, and their tributaries, eroded deep valleys through the rocks of the basin, locally cutting through the old cave systems, exposing the iron-ores that most of them now contained.
The road that now runs outside the Clearwell Caves entrance follows the now-dry valley of a former tributary to the river Wye, which probably fed underground streams until the end of the cold climatic phase associated with the last Ice Age, around 10,000 years ago.
The original source of iron mineralisation still mystifies geologists as the remaining strata above the limestone contains relatively little iron mineralisation compared to the vast quantity that became deposited into the cave systems that eventually became iron mines
Clearwell Caves are amongst the earliest and one of the last producers of ochre (natural earth pigment) in the British Isles. Ochre is now thought to have been mined here for more than 7000 years (since the Middle Stone Age). Ochre pigment is found as a soft deposit intermingled with pockets of harder crystalline iron ore.
Until the 1930's Forest of Dean mines were famous for good quality, rich pigments, particularly shades of red and purple. Purple ochre is an unusual natural earth pigment; similar colours are usually only available in synthetic forms. The mines at Clearwell were well known for the quality and wide range of ochre colours available. Yellow, orange, brown, red and purple ochre is still mined here; dug by hand, using simple tools much as the ancient miners would have done. After careful sieving, the ochre is either washed, or milled. For more information please visit: www.clearwellcaves.com
………Once inside the cave we were able to stand up to full
height before stooping forward gingerly into the first cavern. The ceiling was
covered in a white growth that flourishes where the warm and cool air mingle.
Beyond that point we began a slippery descent of 200ft, along the balcony,
where a narrow path needs to be negotiated next to a steep drop into the cavern
below, and on the rabbit hole; a passage that narrows to the point where it is
necessary to crawl and drag your body along on your belly and twist out of a
rabbit sized opening. All very challenging! Everyone did extremely well,
negotiating the terrain with courage and camaraderie. All and all a rocking
good day and one not to be forgotten in a hurry
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