The
Culm Measures are a geological formation of the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
period that occur in south-west
EnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west and the North Sea to the east, with the English Channel to the south separating it from continental...
, principally in
DevonDevon is a large county in England. The county is also referred to as Devonshire, although that is an unofficial name, rarely used inside of the county itself and often indicating a traditional or historical context. The county shares borders with Cornwall to the west and Dorset and Somerset to...
and
CornwallCornwall is a county of England in the United Kingdom, forming the tip of the south-western peninsula of Great Britain. It is bordered to the north and west by the Atlantic Ocean, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Taken with the...
. They are so called because of the occasional presence of a soft, sooty coal, which is known in Devon as
culm.
The majority of the formation consists of
shaleShale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable...
s and thin
sandstoneSandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow,...
s, but there are also occurrences of
slateSlate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary...
,
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
and
chertChert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
.
"Culm grassland" on the formation's slates and shales is composed of purple
moorMoorland or moor is a type of habitat found in upland areas, characterised by low growing vegetation on acidic soils. Moorland nowadays generally means uncultivated hill land , but the Old English mōr also refers to low-lying wetlands...
grass and rush pasture.
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The
Culm Measures are a geological formation of the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
period that occur in south-west
EnglandEngland is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west and the North Sea to the east, with the English Channel to the south separating it from continental...
, principally in
DevonDevon is a large county in England. The county is also referred to as Devonshire, although that is an unofficial name, rarely used inside of the county itself and often indicating a traditional or historical context. The county shares borders with Cornwall to the west and Dorset and Somerset to...
and
CornwallCornwall is a county of England in the United Kingdom, forming the tip of the south-western peninsula of Great Britain. It is bordered to the north and west by the Atlantic Ocean, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Taken with the...
. They are so called because of the occasional presence of a soft, sooty coal, which is known in Devon as
culm.
The majority of the formation consists of
shaleShale is a fine-grained, clastic sedimentary rock composed of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable...
s and thin
sandstoneSandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains. Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow,...
s, but there are also occurrences of
slateSlate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. The result is a foliated rock in which the foliation may not correspond to the original sedimentary...
,
limestoneLimestone is a sedimentary rock composed largely of the mineral calcite . The deposition of limestone strata is often a by-product and indicator of biological activity in the geologic record...
and
chertChert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
.
"Culm grassland" on the formation's slates and shales is composed of purple
moorMoorland or moor is a type of habitat found in upland areas, characterised by low growing vegetation on acidic soils. Moorland nowadays generally means uncultivated hill land , but the Old English mōr also refers to low-lying wetlands...
grass and rush pasture. It is noted for a wide diversity of species, some extremely rare including the
Marsh FritillaryThe Marsh Fritillary is a butterfly of the Nymphalidae family.The Marsh Fritillary is in decline in Europe and one of 11 butterflies covered by the United Kingdom Biodiversity Action Plan. The UK distribution can be seen on the National Biodiversity Network. The adult butterflies are marked in...
butterfly. Some 92 percent of culm grassland has been lost in the past 100 years, 48 percent being lost between 1984 and 1991 alone. There are a number of organisations trying to halt the decline including
Devon Wildlife TrustThe Devon Wildlife Trust is a member of The Wildlife Trusts partnership covering the county of Devon, England. It is a registered charity, established in 1962 as the Devon Naturalists Trust, and its aim is to safeguard the future of the county's urban, rural and marine wildlife and its...
with its Culm Natural Networks project, Butterfly Conservation, and
Natural EnglandNatural England is a non-departmental public body of the UK government. It was formed on 1 October 2006. It is responsible for ensuring that England's natural environment, including its land, flora and fauna, freshwater and marine environments, geology and soils, are protected and improved...
with its
Environmental StewardshipEnvironmental Stewardship is an agri-environment scheme run by the Department for Environment, Food and Rural Affairs in England. It was formally launched on 18 March 2005, although the first agreements did not start until 1 August 2005....
Scheme.