Industrial Archeology and clay mines

[watervole]

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)

Comments

[watervole.livejournal.com]

Actually, post-glacial effects are much greater than global warming as far as sea levels in Poole go. Think of England as a see-saw. The north got loaded down with glaciers and sank, pushing the south upwards. With the glaciers gone, the south is still rising in what's called isostatic rebound.

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.