Hill is the highest point on eastern Mendip, and forms a broad
north-west-trending ridge which marks the axis of the Beacon Hill
Pericline. The Devonian Portishead Formation and older Silurian
volcanic rocks (Coalbrookdale Formation) outcrop in the core of
the pericline, with the Carboniferous Limestone flanking both sides,
although in places the limestone is buried beneath younger rocks.
At the top of Beacon Hill is a narrow strip of woodland managed by
the Woodland Trust in which are a few small outcrops of the Portishead
Formation. South of the wood, there is a prominent break of slope,
which marks the margin of the Lower Jurassic Downside Stone outcrop.
This younger rock is draped over the older Carboniferous and Devonian
rocks, and forms a gently sloping plateau between here and Shepton
Mallet. To the east, the Silurian Coalbrookdale Formation volcanic
rocks outcrop along the ridge. They consist of andesite and rhyodacite
lavas, tuffs (consolidated volcanic ash) and agglomerate (volcanic
conglomerate) sandwiched between ash-rich, fossiliferous siltstone
Fragments and pebbles of these rocks can be seen in ploughed fields
and stone walls across the outcrop.
At the eastern end of the ridge lies Cranmore Tower, a folly built
by local landowner Sir Richard Paget in 1863. The tower is not open
to the public, but there is a good view across to the Cretaceous
Upper Greensand escarpment and the conspicuous knoll of Cley Hill
from the surrounding fields. Cley Hill is an outlier of Upper Cretaceous
Chalk, with the main Chalk mass of Salisbury Plain beyond. To the
north-east, the Westbury White Horse sits just east of the conspicuous
chimney of the Westbury Cement Works.
Aerial view of Beacon Hill (click to enlarge view).
The Silurian volcanic rocks have been quarried at Moon's Hill Quarry,
south of Stoke St Michael for over 120 years. This site comprises
two clearly visible large pits situated on either side of the road.
The two quarries are now operated as a single entity by John Wainwright & Co.
Ltd.. It is a working quarry, so access is only by prior arrangement.
rocks were also quarried just south of Tadhill at Downhead Quarry.
Just over a kilometre south of Moon's Hill Quarry is the disused and
now water filled Waterlip Quarry which worked the Carboniferous Black
Rock Limestone. The rock was transported to the railway at Cranmore
Station by a tramway, which also served Moon's Hill Quarry and Downhead
Quarry, 3 km to the north-east.