Culm Measures
Encyclopedia
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
period that occur in south-west England
England
England 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, with the North Sea to the east and the English Channel to the south separating it from continental...
, principally in Devon
Devon
Devon is a large county in southwestern England. The county is sometimes referred to as Devonshire, although the term is rarely used inside the county itself as the county has never been officially "shired", it often indicates a traditional or historical context.The county shares borders with...
and Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
. 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 shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
s and thin sandstone
Sandstone
Sandstone 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 colour, but the most common colours are tan, brown, yellow,...
s, but there are also occurrences of slate
Slate
Slate 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 layering...
, limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and chert
Chert
Chert 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 moor
Moorland
Moorland or moor is a type of habitat, in the temperate grasslands, savannas, and shrublands biome, found in upland areas, characterised by low-growing vegetation on acidic soils and heavy fog...
grass and rush pasture. It is noted for a wide diversity of species, some extremely rare including the Marsh Fritillary
Marsh Fritillary
The Marsh Fritillary, Euphydryas aurinia, is a butterfly of the Nymphalidae family.It is widespread in the Palaearctic region from Ireland in the West to Yakutia in the East, and to North-west China and Mongolia in the South.E. aurinia is represented by many subspecies.The most widely accepted...
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 Trust
Devon Wildlife Trust
The 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 England
Natural England
Natural England is the non-departmental public body of the UK government 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 Stewardship
Environmental Stewardship
Environmental 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.