Writhlington SSSI is a 0.5 hectare

Hectare

The hectare is a metric unit of area defined as 10,000 square metres , and primarily used in the measurement of land. In 1795, when the metric system was introduced, the are was defined as being 100 square metres and the hectare was thus 100 ares or 1/100 km2...

 geological Site of Special Scientific Interest near the town of Radstock

Radstock

Radstock is a town in Somerset, England, south west of Bath, and north west of Frome. It is within the unitary authority of Bath and North East Somerset and had a population of 5,275 according to the 2001 Census...

, Bath and North East Somerset

Bath and North East Somerset

Bath and North East Somerset is a unitary authority that was created on 1 April 1996 following the abolition of the County of Avon. It is part of the Ceremonial county of Somerset...

, notified in 1992.

This is the site of old mine workings on the Somerset coalfield

Somerset coalfield

The Somerset Coalfield included pits in the North Somerset, England, area where coal was mined from the 15th century until 1973.It is part of a wider coalfield which covered northern Somerset and southern Gloucestershire. It stretched from Cromhall in the north to the Mendip Hills in the south, and...

, including 3,000 tons of Upper Carboniferous spoil from which more than 1,400 insect fossil specimens have been recovered, including the world's earliest known Damselfly

Damselfly

Damselflies are insects in the order Odonata. Damselflies are similar to dragonflies, but the adults can be distinguished by the fact that the wings of most damselflies are held along, and parallel to, the body when at rest...

. It is a Geological Conservation Review

Geological Conservation Review

The Geological Conservation Review is produced by the UK's Joint Nature Conservation Committee and is designed to identify those sites of national and international importance needed to show all the key scientific elements of the geological and geomorphological features of Britain...

 Site, because it has yielded the largest ever collection of Carboniferous

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"...

 insects in Britain. The commonest forms belong to the order Blattodea (cockroaches) and include the extinct families Archimylacris

Archimylacris

Archimylacris is an extinct genus of cockroach-like Blattopterans, a group of insects ancestral to cockroaches, mantids and termites.Archimylacris lived on the warm swampy forest floors of North America and Europe 300 million years ago, in the Late Carboniferous times...

 and Mymarommatidae

Mymarommatidae

Mymarommatidae is a very small family of microscopic hymenopteran insects. Only 10 living species in 1 genus have currently been described but they are known from all parts of the world...

. Protorthoptera

Protorthoptera

The Protorthoptera are an extinct order of Palaeozoic insects, and represent a wastebasket taxon and paraphyletic assemblage of basal neoptera. They appear during the Middle Carboniferous , making them among the earliest known winged insects in the fossil record. Pronotal lobes may be expanded to...

 and Palaeodictyoptera

Palaeodictyoptera

The Palaeodictyoptera are an extinct order of medium-sized to very large, primitive Palaeozoic paleopterous insects.-Overview:They were characterised by beak-like mouthparts, similarity between fore- and hind wings, and an additional pair of winglets on the prothorax, in front of the first pair of...

 also occur. Frequent chelicerates (arthropods) include trace and body fossils of xiphosurid merostomes and arachnids, including Phalangiotarbi

Phalangiotarbi

Phalangiotarbi is an extinct arachnid order first recorded from the Early Devonian of Germany and most widespread in the Upper Carboniferous Coal measures of Europe and North America...

 and Trigonotarbida

Trigonotarbida

The Order Trigonotarbida is an extinct group of arachnids whose fossil record extends from the late Silurian to the early Permian . These animals are known from several localities in Europe and North America, as well as a single record from Argentina. Trigonotarbids can be envisaged as spider-like...

 and also true spiders (Araneida). Rare myriapods (millipedes) and occasional conchostracan crustaceans (clam-shrimps) also occur.