Millstone Grit

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The Salt Cellar, a gritstone tor on Derwent Edge in the Peak District, England Salt cellar 2 (2).jpg
The Salt Cellar, a gritstone tor on Derwent Edge in the Peak District, England

Millstone Grit is the name given to any of a number of coarse-grained sandstones of Carboniferous age which occur in the British Isles. The name derives from its use in earlier times as a source of millstones for use principally in watermills. Geologists refer to the whole suite of rocks that encompass the individual limestone beds and the intervening mudstones 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.

Contents

The term gritstone describes any sandstone composed of coarse angular grains, and specifically refers to such sandstones within the Pennines 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 Wales and northwest Ireland. The group comprises a succession of sandstones, mudstones and siltstones, the specifics of the sequence varying from one area to another. They give rise both to a number of escarpments, known locally as edges, and a series of high plateaux throughout the region, many of which are of considerable cultural significance.

Pennines

Stanage Edge in the eastern Peak district Stanage Edge.jpg
Stanage Edge in the eastern Peak district

They are the major landscape-forming rocks of the northern part of the Peak District (the Dark Peak) and of its eastern and western flanks in the counties of Derbyshire, Staffordshire and Cheshire. The great expanses of moorland around Bleaklow and Black Hill 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 in the north through Stanage Edge, Burbage Edge, Froggatt Edge, Curbar Edge, Baslow Edge, Gardom's Edge, Birchen Edge, 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 and Combs Moss to the imposing crags of the Roaches, Hen Cloud and Ramshaw Rocks in the south.

A millstone shaped from Millstone Grit quarried in the area has been adopted as the emblem of the Peak District National Park. As an image, the millstone is widely visible on literature but use is made of the objects themselves at many of the entrances to the National Park.

These rocks extend northwards through the South Pennines of Lancashire and West Yorkshire and westwards into the Forest of Rossendale and West Pennines and the Forest of Bowland, also in Lancashire. At the Yorkshire Dales they cover the south-east edge, but north of the Craven Faults, due to weathering, they form only cappings to separate hills. [1]

Northeast Wales

A small area of Millstone Grit Group rocks stretches through Flintshire and Wrexham into the northwest corner of Shropshire near Oswestry.

South Wales

The term "Millstone Grit" was also adopted in South Wales where rocks of similar age and lithology are found though the Millstone Grit Series of this region has recently been formally renamed by the British Geological Survey as the Marros Group. The thickest bed of sandstone within it was known as the Basal Grit and this has now been renamed as the Twrch Sandstone. The Farewell Rock 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.

Ireland

The term has also been adopted at Slieve Anierin in northwest Ireland, describing the series of shales, grits, and coal seams, occurring from the base of the Namurian upwards. [2] [3]

Origins

The Millstone Grit dates to the Namurian Stage of the Carboniferous Period. At this time a series of isolated uplands existed across the British Isles region. One particular east-west aligned landmass stretched from Wales through the English Midlands and East Anglia 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 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. 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. [4]

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 bands 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, Ashover Grit, 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. It is a widespread unit which attains a thickness of around 45m though is more generally 15m thick. [4] [5]

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. [6] 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. Bramley Fall stone is a notable type of Millstone Grit sourced from around the village of Bramley, near Leeds. [7]

Some of the sandstones serve as aquifers into which numerous wells and boreholes have been sunk to provide local water supplies. [8]

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 climbing developed at much the same time as access for walkers to the moors of the 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.

Related Research Articles

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. Puttrell is generally credited with starting the sport. The first climbing guidebook to the area was Some Gritstone Climbs, by John Laycock, published in 1913. There are over 10,000 routes in the Peak District. One of the most famous Peak District climbers, and a pioneer of many new routes, is Ron Fawcett. The climb known as "Master's Edge", on Millstone Edge, near Hathersage, is a testament to his skill and strength. The climb is graded E7 6c and rises 19m up the near vertical edge.

<span class="mw-page-title-main">Gritstone</span> Hard, coarse-grained, siliceous sandstone

Gritstone or grit is a hard, coarse-grained, siliceous sandstone. This term is especially applied to such sandstones that are quarried for building material. British gritstone was used for millstones to mill flour, to grind wood into pulp for paper and for grindstones to sharpen blades. "Grit" is often applied to sandstones composed of angular sand grains. It may commonly contain small pebbles.

<span class="mw-page-title-main">Stanage Edge</span> Escarpment in the Peak District, England

Stanage Edge, or simply Stanage is a gritstone escarpment in the Peak District, England, famous as a location for climbing. It lies a couple of miles to the north of Hathersage, and the northern part of the edge forms the border between the High Peak of Derbyshire and Sheffield in South Yorkshire. Its highest point is High Neb at 458 metres (1,503 ft) above sea level. Areas of Stanage were quarried in the past to produce grindstones, and some can still be seen on the hillside—carved, but never removed.

<span class="mw-page-title-main">Carboniferous Limestone</span> Limestone deposited during the Dinantian Epoch of the Carboniferous Period

Carboniferous Limestone is a collective term for the succession of limestones occurring widely throughout Great Britain and Ireland that were deposited during the Dinantian Epoch of the Carboniferous Period. These rocks formed between 363 and 325 million years ago. Within England and Wales, the entire limestone succession, which includes subordinate mudstones and some thin sandstones, is known as the Carboniferous Limestone Supergroup.

<span class="mw-page-title-main">South Pennines</span> Region of moorland and hills in northern England

The South Pennines is a region of moorland and hill country in northern England lying towards the southern end of the Pennines. In the west it includes the Rossendale Valley and the West Pennine Moors. It is bounded by the Greater Manchester conurbation in the west and the Bowland Fells and Yorkshire Dales to the north. To the east it is fringed by the towns of West Yorkshire whilst to the south it is bounded by the Peak District. The rural South Pennine Moors constitutes both a Site of Special Scientific Interest and Special Area of Conservation.

<span class="mw-page-title-main">Geology of Yorkshire</span>

The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale are Permo-Triassic. The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the south east are Cretaceous chalk uplands. The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages. The strata become gradually younger from west to east.

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. Its counterpart in the eastern part of the National Park is the Ashover Grit.

<span class="mw-page-title-main">Marros Group</span> Geological term for rock in south Wales

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 Peak District of northern England and northeast Wales by this new name.

The geology of Monmouthshire in southeast Wales largely consists of a thick series of sedimentary rocks of different types originating in the Silurian, Devonian, Carboniferous, Triassic and Jurassic periods.

The Coal Measures Group is a lithostratigraphical term coined to refer to the coal-bearing succession of rock strata which occur in the United Kingdom within the Westphalian Stage of the Carboniferous Period. Other than in Northern Ireland the term is now obsolete in formal use and is replaced by the Pennine Coal Measures Group, Scottish Coal Measures Group and the South Wales Coal Measures Group for the three distinct depositional provinces of the British mainland.

<span class="mw-page-title-main">Bosley Minn</span>

Bosley Minn is one of two names – the other being Wincle Minn – given to a prominent hill in southeast Cheshire and in the southwestern corner of the Peak District National Park in northern England. The long axis of the Minn runs NNE–SSW and its broad summit, which reaches to 386 metres (1,266 ft) at its highest point, slopes away to the valley of the Shell Brook in the east and towards Bosley Reservoir in the west. It is the western aspect of the hill, facing Bosley which is known as Bosley Minn whilst the eastern side which faces the village of Wincle is referred to as Wincle Minn.

<span class="mw-page-title-main">Coal measures</span>

In lithostratigraphy, the coal measures are the coal-bearing part of the Upper Carboniferous System. In the United Kingdom, the Coal Measures Group consists of the Upper Coal Measures Formation, the Middle Coal Measures Formation and the Lower Coal Measures Formation. The group records the deposition of fluvio-deltaic sediments which consists mainly of clastic rocks interstratified with the beds of coal. In most places, the coal measures are underlain by coarser clastic sequences known as Millstone Grit, of Namurian age. The top of the coal measures may be marked by an unconformity, the overlying rocks being Permian or later in age. In some parts of Britain, however, the coal measures grade up into mainly coal-barren red beds of late Westphalian and possibly Stephanian age. Within the Pennine Basin these barren measures are now referred to as the Warwickshire Group, from the district where they achieve their thickest development.

Some Gritstone Climbs is a rock climbing guidebook written by British lawyer John Laycock (1887–1960). The book's subtitle, included uniquely on the frontispiece, is Some Shorter Climbs . It was published in Manchester in 1913 by the Refuge Printing Department. Although focusing on rock climbing in the Peak District, it covers several adjacent cliffs outside this region, and despite its title, referring to the Millstone Grit geology of many of the cliffs, it includes several cliffs consisting of other rock types, including mountain limestone and red sandstone.

The geology of Lancashire in northwest England consists in the main of Carboniferous age rocks but with Triassic sandstones and mudstones at or near the surface of the lowlands bordering the Irish Sea though these are largely obscured by Quaternary deposits.

The geology of Merseyside in northwest England largely consists of a faulted sequence of Carboniferous Coal Measures rocks overlain in the west by younger Triassic and Permian age sandstones and mudstones. Glaciation during the present Quaternary Period has left widespread glacial till as well as erosional landforms. Other post-glacial superficial deposits such as river and estuarine alluvium, peat and blown sand are abundant.

The Pennine Coal Measures Group is a lithostratigraphical term referring to the coal-bearing succession of rock strata which occur in the United Kingdom within the Westphalian Stage of the Carboniferous Period. In formal use, the term replaces the Coal Measures Group as applied to the succession of coal-bearing strata within the Pennine Basin which includes all of the coalfields of northern England and the English Midlands. It includes the largely concealed Canonbie Coalfield of southern Scotland and the coalfields of northeast Wales and the minor Anglesey coalfield. The sequence consists in the main of mudstones and siltstones together with numerous sandstones, the more significant ones of which are individually named. Some are laterally extensive, others are more restricted in their range. There are numerous coal seams, again with some being more laterally continuous than others. Those which were economically valuable were named though any individual seam may have attracted different names in different pits and different districts. Marine bands preserving distinctive and dateable marine fossils such as goniatites and brachiopods are widespread within the sequence and enable correlation to be made between sequences in one part of the basin and another and with other basins

The geology of County Durham in northeast England consists of a basement of Lower Palaeozoic rocks overlain by a varying thickness of Carboniferous and Permo-Triassic sedimentary rocks which dip generally eastwards towards the North Sea. These have been intruded by a pluton, sills and dykes at various times from the Devonian Period to the Palaeogene. The whole is overlain by a suite of unconsolidated deposits of Quaternary age arising from glaciation and from other processes operating during the post-glacial period to the present. The geological interest of the west of the county was recognised by the designation in 2003 of the North Pennines Area of Outstanding Natural Beauty as a European Geopark.

The geology of national parks in Britain strongly influences the landscape character of each of the fifteen such areas which have been designated. There are ten national parks in England, three in Wales and two in Scotland. Ten of these were established in England and Wales in the 1950s under the provisions of the National Parks and Access to the Countryside Act 1949. With one exception, all of these first ten, together with the two Scottish parks were centred on upland or coastal areas formed from Palaeozoic rocks. The exception is the North York Moors National Park which is formed from sedimentary rocks of Jurassic age.

The geology of the Yorkshire Dales National Park in northern England largely consists of a sequence of sedimentary rocks of Ordovician to Permian age. The core area of the Yorkshire Dales is formed from a layer-cake of limestones, sandstones and mudstones laid down during the Carboniferous period. It is noted for its karst landscape which includes extensive areas of limestone pavement and large numbers of caves including Britain's longest cave network.

The geology of the Peak District National Park in England is dominated by a thick succession of faulted and folded sedimentary rocks of Carboniferous age. The Peak District is often divided into a southerly White Peak where Carboniferous Limestone outcrops and a northerly Dark Peak where the overlying succession of sandstones and mudstones dominate the landscape. The scarp and dip slope landscape which characterises the Dark Peak also extends along the eastern and western margins of the park. Although older rocks are present at depth, the oldest rocks which are to be found at the surface in the national park are dolomitic limestones of the Woo Dale Limestone Formation seen where Woo Dale enters Wye Dale east of Buxton.

References

  1. ↑ Wilson, Alfred (1992). Geology of the Yorkshire Dales National Park. Grassington: Yorkshire Dales National Park Committee. ISBN   0-905455-34-7.
  2. ↑ Yates 1957, pp. 356–357.
  3. ↑ Geological Survey Ireland 1878, p. 188.
  4. 1 2 Aitkenhead, N. et al 2002 British Regional Geology: the Pennines and adjacent areas (4th Edn) (BGS, Nottingham)
  5. ↑ Various of BGS 1:50,000 scale geological map sheets
  6. ↑ "Black Rock". Archived from the original on 2009-11-11. Retrieved 2009-12-20.
  7. ↑ "Bramley Fall Stone". Stone in Archaeology Database. University of Southampton. Retrieved 13 January 2023.
  8. ↑ "Archived copy" (PDF). Archived from the original (PDF) on 2009-11-12. Retrieved 2009-12-20.{{cite web}}: CS1 maint: archived copy as title (link)

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