Crag Gill is a Site of Special Scientific Interest

Site of Special Scientific Interest

A Site of Special Scientific Interest is a conservation designation denoting a protected area in the United Kingdom. SSSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in Great Britain are based upon...

 in the Teesdale

Teesdale (district)

Teesdale was, from 1974 to 2009, a local government district in County Durham, England. Its council was based in Barnard Castle and it was named after the valley of the River Tees....

 district in south-west County Durham

County Durham

County Durham is a ceremonial county and unitary district in north east England. The county town is Durham. The largest settlement in the ceremonial county is the town of Darlington...

, 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...

. It lies about 3 km east of the village of Eggleston

Eggleston

Eggleston is a village in County Durham, in England. It is situated in Teesdale, a few miles north-west of Barnard Castle.-History:The village is first mentioned in tax records of 1196. The remains of ridge and furrow from the medieval period can still be seen. Many of the cottages date from the...

, just off the B6282 road, which separates it from the Bollihope, Pikestone, Eggleston and Woodland Fells

Bollihope, Pikestone, Eggleston and Woodland Fells

Bollihope, Pikestone, Eggleston and Woodland Fells is a Site of Special Scientific Interest in the Teesdale district of west County Durham, England...

 SSSI to the north.

Crag Gill consists of an exposure of late Namurian

Namurian

The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age...

 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....

s, 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 and 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 that form a Yoredale-type sequence. The exposure is the type locality

Type locality (geology)

Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 of the Whitestone limestone, a marker horizon

Marker horizon

Marker horizons or chronohorizons or marker beds are stratigraphic units of the same age and of such distinctive composition and appearance, that, despite their presence in separate geographic locations, there is no doubt about their being of equivalent age and of common origin...

 for Namurian stratigraphy

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

.