Skiddaw Group
Encyclopedia
For the Skiddaw group of hills, see Skiddaw Group
The Skiddaw Group is a group
of sedimentary rock formations named after the mountain Skiddaw
in the English
Lake District
. The rocks are Ordovician
in age. They are largely mudstone
s and siltstone
s with subordinate wacke-type sandstone
s. Their main occurrence is within the northern and central fells of the Lake District but inliers
are found at Black Combe
in the south of the Lake District and at Cross Fell
in the North Pennines
.
In the Northern Fells
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
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
s and lavas) at Cross Fell. The Buttermere Formation is interpreted as an olistostrome
. 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 in the northern part of the district.
The Skiddaw Group is a group
Group (stratigraphy)
A group in stratigraphy is a lithostratigraphic unit, a part of the geologic record or rock column that consists of defined rock strata. Groups are divided into formations and are sometimes themselves grouped into "supergroups"....
of sedimentary rock formations named after the mountain Skiddaw
Skiddaw
Skiddaw is a mountain in the Lake District National Park in England. With a summit at 931 m above sea level it is the fourth highest mountain in England. It lies just north of the town of Keswick, Cumbria, and dominates the skyline in this part of the northern lakes...
in the English
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...
Lake District
Lake District
The Lake District, also commonly known as The Lakes or Lakeland, is a mountainous region in North West England. A popular holiday destination, it is famous not only for its lakes and its mountains but also for its associations with the early 19th century poetry and writings of William Wordsworth...
. The rocks are Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
in age. They are largely mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s and siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
s with subordinate wacke-type 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. Their main occurrence is within the northern and central fells of the Lake District but inliers
Inliers and outliers (geology)
An inlier is an area of older rocks surrounded by younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited exposure of the older underlying rocks. Faulting or folding may also contribute to the observed outcrop pattern...
are found at Black Combe
Black Combe
Black Combe is a fell in the south-west corner of the Lake District National Park, just four miles from the Irish Sea. It lies near the west coast of Cumbria in the borough of Copeland and more specifically, an area known as South Copeland...
in the south of the Lake District and at Cross Fell
Cross Fell
Cross Fell is the highest point in the Pennine Hills of northern England and the highest point in England outside of the Lake District.The summit, at , is a stony plateau, part of a long ridge running North West to South East, which also incorporates Little Dun Fell at and Great Dun Fell at...
in the North Pennines
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...
.
In the Northern Fells
Northern Fells
The Northern Fells are a group of hills 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...
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
Central Fells
The Central Fells are a group of hills in the English Lake District. Reaching their highest point at High Raise , they occupy a broad area to the east of Borrowdale. Perhaps unexpectedly the Central Fells are generally lower than the surrounding hills, the Lake District's general dome-like...
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
Tuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
s and lavas) at Cross Fell. The Buttermere Formation is interpreted as an olistostrome
Olistostrome
The term olistostrome is derived from olio - a dish of many ingredients or stew; a mixture of heterogeneous elements; hodgepodge. and stroma - a bed covering...
. The Tarn Moor and Kirkland Formations contain some volcaniclastic
Pyroclastic rock
Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed 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 in the northern part of the district.