''For the Skiddaw group of hills, see Skiddaw Group'' The Skiddaw Group is a group of

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

rock formations named after the mountain

Skiddaw Skiddaw is a mountain in the Lake District National Park in England. Its summit is the sixth-highest in England. It lies just north of the town of Keswick, Cumbria, and dominates the skyline in this part of the northern lakes. It is the ...

in the English Lake District. The rocks are almost wholly

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

in age ( Tremadoc through

Arenig In geology, the Arenig (or Arenigian) is a time interval during the Ordovician period and also the suite of rocks which were deposited during this interval. History The term was first used by Adam Sedgwick in 1847 with reference to the "Areni ...

to Llanvirn epochs) though the lowermost beds are possibly of

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

age. This rock sequence has previously been known as the Skiddaw Slates, the Skiddaw Slates Group and the Skiddavian Series. Its base is not exposed but in its main outcrop area, it is considered to be in excess of thick though less elsewhere. It consists largely of mudstones and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, ...

s with subordinate

wacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

-type

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s. Their main occurrence is within the northern and central fells of the Lake District, either side of the major ENE-WSW aligned

Causey Pike Fault The Causey Pike Fault or Causey Pike Thrust is a major WSW-ENE trending fault within the Lower Paleozoic rocks of the English Lake District. It is named for Causey Pike, where the fault was first recognised. Extent The Causey Pike Fault has bee ...

, but inliers are found at

Black Combe Black Combe is a fell in the south-west corner of the Lake District National Park, England, just from the Irish Sea. It lies near the west coast of Cumbria in the borough of Copeland and more specifically, in the ancient district of Millom. ...

in the south of the Lake District and at Cross Fell in the

North Pennines The North Pennines is the northernmost section of the Pennine range of hills which runs north–south through northern England. It lies between Carlisle to the west and Darlington to the east. It is bounded to the north by the Tyne Valley an ...

Stratigraphy

In the

Northern Fells The Northern Fells are a mountain range in the English Lake District. Including Skiddaw, they occupy a wide area to the north of Keswick. Smooth, sweeping slopes predominate, with a minimum of tarns or crags. Blencathra in the south-east of th ...

of the Lake District, the Skiddaw Group comprises five formations of which the earliest/lowest is the Bitter Beck Formation. This is succeeded by the Watch Hill Formation, then the Hope Beck, Loweswater and Kirk Stile Formations in ascending order. The inlier at Cross Fell comprises just the Catterpallot Formation, a wacke sandstone which is the rough equivalent of the Watch Hill Formation, itself a wacke sandstone as is the Loweswater Formation. Within the

Central Fells The Central Fells are a group of hills in the English Lake District. Reaching their highest point at High Raise (2,500 ft or 762 metres), they occupy a broad area to the east of Borrowdale. The Central Fells are generally lower than the ...

are the Buttermere Formation and the overlying Tarn Moor Formation. These are matched by the Murton Formation (grey slates and thin sandstones) and the Kirkland Formation (mudstones with

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s and lavas) at Cross Fell. The Buttermere Formation is interpreted as an

olistostrome An olistostrome is a sedimentary deposit composed of a chaotic mass of heterogeneous material, such as blocks and mud, known as olistoliths, that accumulates as a semifluid body by submarine gravity sliding or slumping of the unconsolidated se ...

. The Tarn Moor and Kirkland Formations contain some volcaniclastic rocks. The inlier to the south at Black Combe contains the wackes of the Knott Hill Formation. The group underlies the Borrowdale Volcanic Group in the southern and central Lake District and the

Eycott Volcanic Group The Eycott Volcanic Group is a group of volcanic rock formations of Ordovician age (Llandeilo to Caradoc epochs) named after the locality of Eycott Hill in the English Lake District.British Geological Survey 1997 ''Cockermouth'' England and Wales ...

in the northern part of the district. The Kirkland Formation has provided fossils of '' Dichograptus octobrachiatus'' and '' Heminectere rushtoni''.Randel Crag, Skiddaw
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org

Metamorphism

The sequence was affected by low-grade regional

metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ...

and deformation associated with the Acadian Orogeny, causing the dominant fine-grained parts of the sequence to become

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. It is the finest grained foliated metamorphic ro ...

s. The resulting slaty cleavage is parallel to the axial plane of regional

fold Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure *Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Above ...

References

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Stratigraphy

Metamorphism

References

Further reading