of Wells is dominated by its superb cathedral and the springs which
rise around its walls. However, the area is also interesting for
its geology. The city is overlooked by the sandstone massif of Pen
Hill and flanked by ridges of Carboniferous Limestone which are partially
buried by younger Triassic strata and gravel deposits upon which
most of the city is built.
The Carboniferous Clifton Down Limestone is well exposed in many
small pits and quarries on Tor Hill to the west of the city. This
ridge forms the axis of an upfold or anticline which can be seen
in the adjacent concrete block-works. The ridge is flanked on either
side by Triassic rocks. The Clifton Down Limestone is also exposed
in several quarries around Stoberry Park north of the city and in
the entrance to Stoberry Park tunnel. One of the old quarries is
now a private garden.
The unconformity between the limestone and the overlying Dolomitic
Conglomerate can be seen in a field just west of the A39 near Stoberry.
The conglomerate can also be seen in Milton Lane and in the lower
parts of Biddlecombe.
The topmost Triassic and basal Jurassic rocks outcrop around Milton,
north of Wells and can be seen in the New Cut, Milton.
The cathedral was started in the 12th century using mostly local
stone and is an excellent place to examine the local geology. Much
of the cathedral, including the nave and the west front is built
from the Inferior Oolite. Also known as 'Doulting Stone' this beautiful
yellow rock was obtained from quarries around Doulting, near Shepton
Mallet. Later in the 12th century, local 'Chilcote Stone', a local
variation of the Lower Jurassic Downside Stone, was used as a replacement
when the Doulting quarries were under the control of Glastonbury
Abbey and unavailable. It was obtained from small quarries between
West Horrington and Shepton Mallet and can be seen in walls around
The west wall of the west cloister is formed of rubble blocks of
the Triassic Dolomitic Conglomerate. The Jurassic Blue Lias has been
used extensively for paving slabs and tombstones. This greyish blue
rock can be split easily and is often used for flagstones, but suffers
from frost heaving. Dark reddish brown Carboniferous Coal Measure
'Pennant' Sandstone slabs have also been used for paving and in some
of the gravestones.
The grey columns on the West Front are of 'Kilkenny Marble', actually
a fine-grained Carboniferous limestone shipped in from Ireland in
1872. This rock was chosen because it could be easily worked to produce
the columns. If the surface is wetted crinoid fragments and algal
patches can be seen. Inside the cathedral, the Jurassic Great Oolite
Limestone, a golden-yellow oolitic limestone better known as Bath
Stone, was used for fine carved work such as the font and the pulpit.
However, the vaults were made from tufa, a very light rock formed
of calcium carbonate deposited by lime-rich springs and streams,
principally because of its lightweight porous nature.
|Wells and springs
Wells, as its name suggests, grew up around a series of springs known
as St Andrews Risings. These rise up in the floor of an ornamental
lake in the grounds of the Bishops Palace. One of these, the Scotland
Spring supplies the water that feeds the conduit in the Market
Place, from where water flows down the High Street in stone gutters
made from the Jurassic Blue Lias Formation. Dye tracing proves
that all these springs are fed by a single underground conduit
in the underlying Carboniferous Limestone, which bursts up through
the overlying Triassic strata. These springs are fed by stream
sinks on the slopes of Beacon Hill to the north-east of Wells.
and Mendip Museum
Adjacent to the cathedral on Cathedral Green is the Wells and Mendip
Museum Founded in 1893, it houses a fine collection of local rocks,
fossils and minerals, as well as displays about the history of cave
diving. It is a good starting point to learn about the geology of
the region. The museums founder, Herbert Balch (1869–1958) was a
pioneering caver and amateur archaeologist who held a lifelong interest
in the geomorphology and history of Mendip.
South-east of Wells is Dulcote Quarry, a working aggregate quarry
formerly run by Foster Yeoman Ltd. The Clifton Down Limestone here
is folded so much it is now vertical or even overturned; spectacular
testament to the enormous geological forces operating at the end
of the Carboniferous.
Overlying the Carboniferous Limestone are beds of the Triassic Mercia
Mudstone and Dolomitic Conglomerate which contained concretionary
nodules and geodes infilled with quartz crystals known locally
as 'potato stones' or 'Bristol diamonds'.