Culm Measures

The Culm Measures are a geological formation of the Carboniferous period that occur in south-west England, principally in Devon and Cornwall. They are so called because of the occasional presence of a soft, sooty coal, which is known in Devon as culm.

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The majority of the formation consists of shales and thin sandstones, but there are also occurrences of slate, limestone and chert.

"Culm grassland" in the formation's slates and shales is composed of purple moor grass and rush pasture. It is noted for a wide diversity of species, some extremely rare including the Marsh Fritillary 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 looking to halt the decline including Devon Wildlife Trust with its Culm Natural Networks project and Butterfly Conservation.