around Gurney Slade and Emborough is geologically quite complex,
being located at the eastern end of the Pen Hill Pericline, one of
the four major up-folds on Mendip. To the east the Carboniferous
Limestone plunges downwards disappearing beneath the
Upper Carboniferous Quartzitic Sandstone and the Coal Measures.
South of Gurney Slade, the Carboniferous Limestone forms a down-fold
known as the Binegar syncline. To the north, the Emborough area is
located on another Syncline, sandwiched between the North Hill Pericline
and the Pen Hill Pericline. However, here, the Carboniferous Limestone
has also been thrust northwards over the younger Coal Measures along
the Emborough Thrust.
Generalised schematic geological cross-section across the northern
flank of the Beacon Hill Pericline (click to enlarge view).
Aerial view of Gurney Slade and Emborough (click to enlarge view).
The Coal Measures are exposed around Emborough Pond, a lake created
by Capability Brown. Although some thin coal seams do occur here,
the seams were relatively unproductive. To the east, these folded
Carboniferous rocks are partially covered by a blanket of younger
rocks, the oldest of which is the Triassic Dolomitic Conglomerate.
This is overlain by marine strata; the Penarth and Lias groups which
form a distinctive plateau around Ston Easton, and the silicified
strata of the Harptree Formation around Emborough. The outcrop of
the Harptree Formation is pockmarked with sinkholes formed
by dissolution and collapse of the underlying Carboniferous Limestone.
The Gurney Slade area has been a major centre for quarrying since
the mid 1800s. Several limestone quarries dot the area, the largest
being the active Gurney
Slade Quarry which works the Clifton Down Limestone and the
Oxwich Head Limestone. The limestone here
dips gently to the south-east at around 30°. A small exposure
of the horizontally bedded Jurassic Downside Stone can be seen
in the south-east corner of the quarry.
The site is a working quarry, so permission to visit should be obtained
The Clifton Down Limestone was also worked for aggregate in the disused
Binegar Quarry, which has been partially infilled with coal waste,
and in the dormant Highcroft Quarry in Binergar Bottom. The Upper
Carboniferous Quartzitic Sandstone was quarried in Gurney Slade Bottom
but the quarry is now overgrown and is on private land.
Sediment infilled fissures within the the Carboniferous Limestone
known as Neptunian dykes have been discovered in several of the quarries
in the region. The largest were discovered in Emborough Quarry.
These fissures and relict caves are infilled with Triassic and Jurassic
sediments and have yielded a wide variety of vertebrate fossil remains,
including Keuhneosaurus, an early flying lizard. Similar fissures
infilled with Jurassic sediments have been recorded in Gurney Slade