West Harptree are located at the mouth of Harptree Combe, a narrow
gorge cut into the Dolomitic Conglomerate down which a small stream
flows. The gorge is a SSSI for its flora and fauna, and contains
several distinct wildlife habitats including old ash woodland, rough
grassland, marshy grassland and rocky crags. Half way down the combe,
an aqueduct crosses the valley. This is part of network of aqueducts
and tunnels feeding spring water from Chewton Mendip to the Barrow
Gurney reservoirs. The top end of Harptree Combe leads up onto Smitham
Hill and East Harptree Woods, an area of woodland and heath developed
on the Harptree Formation.
This rock is relatively impermeable and gives rise to a very boggy
acidic soil with a characteristic heathland flora.
Aerial view of Harptree and Smitham Hill (click to enlarge view).
The Harptree area was an important lead and zinc mining area. Lead
ore was mined from veins in the Carboniferous Limestone around
Gibbets Brow and Lamb Leer, and manganese and zinc from veins in
the Dolomitic Conglomerate around Harptree Combe.
This has left a legacy of old pits, spoil heaps and shafts creating
areas of pockmarked 'gruffy ground'. The lead-rich spoil heaps are
home to several rare plant species. Much of the ore was processed
and smelted on Smitham Hill where ore dressing and smelting works
were built by the East Harptree Lead Works Company in 1867. The Smitham
Chimney dates from this time and is the last old lead-smelting chimney
still standing on Mendip.
Caves and karst
There are relatively few known caves in the Harptree area, but the
largest, Lamb Leer Cavern was discovered in about 1674 by lead miners.
The cave is 67 m deep and contains one of the largest chambers on
Mendip. The area is also pockmarked with large sinkholes, particularly
around the margins of the Harptree Formation. The largest is the
Devil's Punch-Bowl, an impressive depression over 50 m in diameter
and almost 20 m deep. These have been formed by the dissolution of
Carboniferous Limestone and Dolomitic Conglomerate at depth, followed
by collapse and subsidence of the cover rocks.