Millstone Grit
Encyclopedia
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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 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"...
age which occur in the Northern England
Northern England
Northern England, also known as the North of England, the North or the North Country, is a cultural region of England. It is not an official government region, but rather an informal amalgamation of counties. The southern extent of the region is roughly the River Trent, while the North is bordered...
. The name derives from its use in earlier times as a source of millstone
Millstone
Millstones or mill stones are used in windmills and watermills, including tide mills, for grinding wheat or other grains.The type of stone most suitable for making millstones is a siliceous rock called burrstone , an open-textured, porous but tough, fine-grained sandstone, or a silicified,...
s for use principally in watermill
Watermill
A watermill is a structure that uses a water wheel or turbine to drive a mechanical process such as flour, lumber or textile production, or metal shaping .- History :...
s. Geologists refer to the whole suite of rocks which encompass both the individual sandstone beds and the intervening 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 as the Millstone Grit Group. The term Millstone Grit Series was formerly used to refer to the rocks now included within the Millstone Grit Group together with the underlying Edale Shale Group.
The term gritstone describes any sandstone composed of coarse, angular grains though, it is frequently used (with an upper case ‘G’) by British rock climbers
Rock Climbing
Rock climbing also lightly called 'The Gravity Game', is a sport in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a pre-defined route without falling...
specifically to refer to such sandstones within the Peak District
Peak District
The Peak District is an upland area in central and northern England, lying mainly in northern Derbyshire, but also covering parts of Cheshire, Greater Manchester, Staffordshire, and South and West Yorkshire....
, Pennines
Pennines
The Pennines are a low-rising mountain range, separating the North West of England from Yorkshire and the North East.Often described as the "backbone of England", they form a more-or-less continuous range stretching from the Peak District in Derbyshire, around the northern and eastern edges of...
and neighbouring areas of Northern England.
Geographical occurrence
Rocks assigned to the Millstone Grit Group occur over a wide area of Northern England where they are a hugely important landscape-forming element of the rock succession. They also occur in parts of northeast WalesWales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
. The group comprises a succession of sandstones, mudstones 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, the specifics of the sequence varying from one area to another. They give rise both to a number of ‘edges’ and a series of high plateaux throughout the region, many of which are of considerable cultural significance.
Peak District
They are the major landscape-forming rocks of the northern part of the Peak DistrictPeak District
The Peak District is an upland area in central and northern England, lying mainly in northern Derbyshire, but also covering parts of Cheshire, Greater Manchester, Staffordshire, and South and West Yorkshire....
(the Dark Peak
Dark Peak
The Dark Peak is the higher, wilder northern part of the Peak District in England.It gets its name because , the underlying limestone is covered by a cap of Millstone Grit which means that in winter the soil is almost always saturated with water...
) and of its eastern and western flanks in the counties
County
A county is a jurisdiction of local government in certain modern nations. Historically in mainland Europe, the original French term, comté, and its equivalents in other languages denoted a jurisdiction under the sovereignty of a count A county is a jurisdiction of local government in certain...
of Derbyshire
Derbyshire
Derbyshire is a county in the East Midlands of England. A substantial portion of the Peak District National Park lies within Derbyshire. The northern part of Derbyshire overlaps with the Pennines, a famous chain of hills and mountains. The county contains within its boundary of approx...
, Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...
and Cheshire
Cheshire
Cheshire is a ceremonial county in North West England. Cheshire's county town is the city of Chester, although its largest town is Warrington. Other major towns include Widnes, Congleton, Crewe, Ellesmere Port, Runcorn, Macclesfield, Winsford, Northwich, and Wilmslow...
. The great expanses of bleak moorland around Bleaklow
Bleaklow
Bleaklow is a high, largely peat covered, gritstone moorland, just north of Kinder Scout, across the Snake Pass , in the Derbyshire High Peak near the town of Glossop...
and Black Hill
Black Hill (Peak District)
Black Hill is a hill in the Peak District, England.It used to be the highest point in Cheshire, but now lies on the border between the boroughs of Kirklees in West Yorkshire and High Peak in Derbyshire, reaching above sea level....
and fringed with broken outcrops of gritstone are characteristic of the area.
The ‘eastern edges’ of the Peak District’ comprise a broadly north-south arranged series of west-facing cliffs from Bamford Edge
Bamford Edge
Bamford Edge is an overhang of gritstone rock that sticks out north of the village of Bamford, Hope Valley, in the English county of Derbyshire....
in the north through Stanage Edge, Burbage Edge, Froggatt Edge
Froggatt Edge
Froggatt Edge is a gritstone escarpment in the Dark Peak area of the Peak District National Park, in Derbyshire, England and situated in close proximity to the villages of Froggatt, Calver, Curbar, Baslow and Grindleford...
, Curbar Edge, Baslow Edge, Gardom's Edge
Gardom's Edge
Gardom's Edge is located near Baslow in Derbyshire, England.The shelf between Gardom's Edge and Birchen Edge is now moorland used for grazing sheep, but was inhabited and arably farmed duringthe Bronze Age...
, Birchen Edge
Birchen Edge
Birchen Edge is a rock face in the Peak District, United Kingdom, popular with walkers and with novice climbers as most of the climbing routes are in the lower grades.-Nelson's Monument:...
, Dobb/Chatsworth Edge, Harland Edge and Fallinge Edge in the south. To the east of these edges is a broad band of relatively flat moorland known as the Eastern Moors.
Towards the western margins of the Peak District are a rather more broken series of edges, facing in a variety of directions, from those surrounding the high plateaux of Kinder Scout
Kinder Scout
Kinder Scout is a moorland plateau in the Dark Peak of the Derbyshire Peak District in England. Part of the moor, at 636 m above sea level, is the highest point in the Peak District, the highest point in Derbyshire, and the highest point in the East Midlands. It is accessible from the villages of...
and Combs Moss to the imposing crags of the Roaches
The Roaches
The Roaches is the name given to a prominent rocky ridge situated above Leek and Tittesworth Reservoir in the Peak District of England...
, Hen Cloud
The Roaches
The Roaches is the name given to a prominent rocky ridge situated above Leek and Tittesworth Reservoir in the Peak District of England...
and Ramshaw Rocks
The Roaches
The Roaches is the name given to a prominent rocky ridge situated above Leek and Tittesworth Reservoir in the Peak District of England...
in the south.
Pennines
These rocks extend northwards through the South PenninesSouth Pennines
South Pennines is a region of moorland and hill country in northern England lying towards the southern end of the Pennines. It is bounded to the west by the Forest of Rossendale and the Yorkshire Dales to the north...
of Lancashire
Lancashire
Lancashire is a non-metropolitan county of historic origin in the North West of England. It takes its name from the city of Lancaster, and is sometimes known as the County of Lancaster. Although Lancaster is still considered to be the county town, Lancashire County Council is based in Preston...
and West Yorkshire
West Yorkshire
West Yorkshire is a metropolitan county within the Yorkshire and the Humber region of England with a population of 2.2 million. West Yorkshire came into existence as a metropolitan county in 1974 after the passage of the Local Government Act 1972....
and westwards into the Forest of Rossendale and West Pennines
West Pennine Moors
The West Pennine Moors cover an area of approximately of moorland and reservoirs in Lancashire and Greater Manchester, England.The West Pennine Moors are separated from the main Pennine range by the Irwell Valley. The moorland includes Withnell, Anglezarke and Rivington Moors in the extreme west,...
and the Forest of Bowland
Forest of Bowland
The Forest of Bowland, also known as the Bowland Fells, is an area of barren gritstone fells, deep valleys and peat moorland, mostly in north-east Lancashire, England. A small part lies in North Yorkshire, and much of the area was historically part of the West Riding of Yorkshire...
, also in Lancashire. At the Yorkshire Dales
Yorkshire Dales
The Yorkshire Dales is the name given to an upland area in Northern England.The area lies within the historic county boundaries of Yorkshire, though it spans the ceremonial counties of North Yorkshire, West Yorkshire and Cumbria...
they cover the south-east edge, but north of the Craven Fault
Craven Fault
The Craven Fault is the name applied by geologists to the group of crustal faults in the Pennines that form the south edge of the Askrigg Block. It is evident at the surface in the contrast of limestone with millstone grit. It is coincident with the south edge of the Yorkshire Dales National Park...
s, due to weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
, they form only cappings to separate hills.
Northeast Wales
A small area of Millstone Grit Group rocks stretches through FlintshireFlintshire
Flintshire is a county in north-east Wales. It borders Denbighshire, Wrexham and the English county of Cheshire. It is named after the historic county of Flintshire, which had notably different borders...
and Wrexham
Wrexham
Wrexham is a town in Wales. It is the administrative centre of the wider Wrexham County Borough, and the largest town in North Wales, located in the east of the region. It is situated between the Welsh mountains and the lower Dee Valley close to the border with Cheshire, England...
into the northwest corner of Shropshire
Shropshire
Shropshire is a county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. It borders Wales to the west...
near Oswestry
Oswestry
Oswestry is a town and civil parish in Shropshire, England, close to the Welsh border. It is at the junction of the A5, A483, and A495 roads....
.
South Wales
The term 'Millstone Grit' was also adopted in South WalesSouth Wales
South Wales is an area of Wales bordered by England and the Bristol Channel to the east and south, and Mid Wales and West Wales to the north and west. The most densely populated region in the south-west of the United Kingdom, it is home to around 2.1 million people and includes the capital city of...
where rocks of similar age and lithology
Lithology
The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...
are found though the Millstone Grit series of this region has recently been formally re-named by the British Geological Survey
British Geological Survey
The British Geological Survey is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS headquarters are in Keyworth, Nottinghamshire, but other centres...
as the Marros Group
Marros Group
The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geographically separate rock sequences of the Pennines and...
. The thickest bed of sandstone within it was known as the Basal Grit. This has now been renamed as the Twrch Sandstone. The Farewell Rock
Farewell Rock
The Farewell Rock is the name given to a series of sandstones which lie at the boundary of the Coal Measures with the underlying Marros Group in South Wales. Once thought to be a single sandstone, it is now accepted that the same name has been applied to several different sandstones of similar age...
was formerly considered to be the uppermost unit of the Millstone Grit series of South Wales though it is now included within the overlying South Wales Coal Measures
Coal Measures Group
The Coal Measures Group is a lithostratigraphical term coined to refer to the coal-bearing succession of rock strata which occur in Great Britain within the Westphalian Stage of the Carboniferous Period. The Coal Measures Group is preceded by the Millstone Grit Group which is of Namurian age...
.
Main article: Marros Group
Marros Group
The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geographically separate rock sequences of the Pennines and...
Origins
The Millstone Grit dates from the NamurianNamurian
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...
Stage of the 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"...
Period. At this time a series of isolated uplands existed across the British Isles
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
region. One particular east-west aligned landmass stretched from Wales through the English Midlands
English Midlands
The Midlands, or the English Midlands, is the traditional name for the area comprising central England that broadly corresponds to the early medieval Kingdom of Mercia. It borders Southern England, Northern England, East Anglia and Wales. Its largest city is Birmingham, and it was an important...
and East Anglia
East Anglia
East Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...
to the continent and is now known as the Wales-Brabant High though was formerly referred to as St George’s Land. Other uplands the erosion of which would provide the source material for the Millstone Grit lay to the north and northeast of the region. The Pennine Basin
Pennine Basin
The Pennine Basin is a sedimentary basin which was active during the Carboniferous Period and which reached from the Southern Uplands of Scotland in the north to the former Wales-London-Brabant Massif in the English Midlands to the south...
received input of sand and mud largely from southerly directed rivers from these northern landmasses.
Rivers running north off the Wales-Brabant High deposited material in the southern parts of the Pennine basin from northeast Wales to the Peak District. Southerly flowing rivers from this same landmass were responsible for the Millstone Grit/Marros Group succession in South Wales.
During much of the Carboniferous Period, world sea-levels were fluctuating in response to the growth and decline of a series of major ice-caps over the continents then clustered around the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
. Britain lay in the equatorial region. At times of high sea-level, silt and mud accumulated within the Pennine basin whilst at times of low sea-level, major deltas prograded across the region, their legacy being the thick sandstone beds of the Millstone Grit Group.
Stratigraphy
The Millstone Grit Group comprises over thirty individually named sandstones, some of regional extent, others more local in their occurrence. The intervening mudstones and siltstones are not generally named though important marine bandsMarine band (geology)
Marine band is a geological term for a bed of rock, commonly black or dark grey shale, containing an abundance of fossils of marine organisms. These strata represent episodes of flooding by seawater and are important in enabling the comparison or correlation of rock sequences in different localities....
within them are named.
The oldest, and hence lowermost in the succession is the thick Pendle Grit of central Lancashire. It is succeeded by the sandstone known variously as the Brennand Grit, Warley Wise Grit and Grassington Grit. These are all of Pendleian (E1) age – the lowermost sub-stage of the Namurian.
The Lower Follifoot Grit, Silver Hills Sandstone, Nottage Crag Grit, Marchup Grit, Red Scar Grit, Ward’s Stone Sandstone, Cocklett Scar Sandstones and Dure Clough Sandstones are all assigned to the following Arnsbergian sub-stage. The Kinderscoutian includes the Kinder Grit, Longnor Sandstones, Shale Grit, Todmorden Grit, Parsonage Sandstone, Heysham Harbour Sandstone, Eldroth Grit and Ellel Crag Sandstone.
The next sub-stage of the Namurian succession is the Marsdenian and it is to this that the Chatsworth Grit, Huddersfield White Rock, Holcombe Brook Grit, Greta Grits, Roaches Grit
Roaches Grit
Roaches Grit is a coarse sandstone which outcrops widely throughout the western part of the Peak District of northern England and gives rise to several significant landscape features in the area...
, Ashover Grit
Roaches Grit
Roaches Grit is a coarse sandstone which outcrops widely throughout the western part of the Peak District of northern England and gives rise to several significant landscape features in the area...
, Gorpley Grit, Pule Hill Grit, Fletcher Bank Grit, Brooksbottom Grit, Five Clouds Sandstones and Sheen Sandstones are assigned.
The closing sub-stage of the Namurian, the Yeadonian includes the Lower Haslingden Flags and the last sandstone in the entire Millstone Grit succession known as the Rough Rock
Rough Rock
The Rough Rock is a widespread unit of coarse sandstone which is a prominent landscape-forming feature in the Peak District and Pennines of northern England...
. It is a widespread unit which attains a thickness of around 45m though is more generally 15m thick.
Economic importance
Various of the sandstone beds of the Millstone Grit have been quarried for building stone, paving flags and roofing material. Its use in the construction of dry stone walls across the areas where it outcrops is considerable. In neighbouring limestone areas, gritstone has often been preferred in the past for use as gateposts and lintels. The very name of the rock derives from its widespread use within cornmills where it proved suitable for grinding stones. It also found agricultural use as drinking troughs for animals. The majority of the quarrying for such use took place along the eastern edges of the Peak District. Millstone Edge was a significant source whilst abandoned millstones can be seen below the edges at Stanage, Froggatt and Baslow.Some of the sandstones serve as aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
s into which numerous wells and boreholes have been sunk to provide local water supplies.
Crushed gritstone is also used as aggregate in path and road construction.
Rock climbing
The gritstone edges of West Yorkshire and the Peak District provide one of the classic areas in Britain for rock climbing. Public access to these edges for climbingRock climbing in the Peak District
Rock climbing is a popular activity in the Peak District; particularly on edges such as Stanage or Froggatt. Generally the climbing style is free climbing and the rock is either gritstone or limestone. Climbing has been practised in the Peak District since the late 19th century; James W...
developed at much the same time as access for walkers to the moors of the Peak District and Pennines was established during the first half of the twentieth century. Their proximity to large centres of population resulted in their rapid development as climbing venues. Today many thousands of climbers are found throughout the year enjoying the several thousand recorded rock climbs on the dozens of individual gritstone crags in the region.