the south side of the Beacon Hill pericline, this region covers the
area between Downhead,
Leighton and Chantry, including the delightful Asham Wood. Most
of the area is underlain by the Carboniferous Limestone on the southern
limb of the Beacon Hill Pericline which dips at around 20º–50º to
the south and south-south-east. The Carboniferous Limestone is bounded
along its southern margin by the Cranmore Fault which almost follows
the A361. The fault is marked by a change in slope between the hard
Carboniferous rocks and the softer Jurassic strata.
Another fault, the Downhead Fault bounds the Carboniferous Limestone
to the west and juxtaposes it against the Portishead Formation. Streams
draining the sandstone slopes of Cranmore Hill sink underground into
the limestone along the line of the fault. Water-tracing experiments
have shown that the water originally flowed to springs in the Leighton
valley and Holwell but some of the groundwater flow has been intercepted
by the quarrying.
Aerial view of Torr Works and Asham Wood (click to enlarge view).
In places, particularly to the south-east, younger Jurassic rocks
overlie the Carboniferous Limestone. The contact between the limestone
and the Inferior Oolite is marked by a well-developed unconformity
which is best seen at Tedbury Camp Quarry and Vallis Vale.
The area is probably best known for the huge Torr Works
quarry. One of the two 'superquarries' located on east Mendip,
Torr Works was operated by Foster Yeoman Ltd., but is now owned
by Aggregate Industries. The quarry was previously known as Merehead
Quarry, but it was purchased by the Yeoman family who redeveloped
and renamed the site in the early 1970s. The site is a working
quarry, but visits can be arranged by contacting the company in
The disused Asham Wood and Westdown Quarries in the Leighton valley
clearly expose the lower part of the Black Rock Limestone. The thinly
bedded, muddy limestones here are weak and easily folded, and several
excellent, highly contorted, fold structures can be seen in Asham
Wood Quarry. The stronger, thicker limestone beds farther south are
less well folded and dip around 20°–30° to the south.
The hydrogeology of the Torr Works to Asham Wood area, showing
the movement of groundwater proved by tracer testing using fluorescent
dyes. Adapted from University of Bristol Spelaeological Society Proceedings,
Vol. 19(1), 1991 (click to enlarge view).
Asham Wood is one of the finest, and largest, examples of ancient
semi-natural woodland in the Mendips with a diverse range of woodland
communities, reflecting marked differences in the underlying soil.
The site is owned and managed as a nature reserve by Hanson Aggregates,
who operate Whatley Quarry.