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 .
23-651: Bleaklow is a high, largely peat-covered, gritstone moorland in the Derbyshire High Peak near the town of Glossop . It is north of Kinder Scout , across the Snake Pass ( A57 ), and south of the A628 Woodhead Pass . Much of it is nearly 2,000 feet (610 m) above sea level and the shallow bowl of Swains Greave on its eastern side is the source of the River Derwent . Bleaklow Head (633 m), marked by
46-457: A huge cairn of stones, the high point at the western side of the moor, is a Hewitt and is crossed by the Pennine Way . It is one of three summits on this plateau above 2,000 feet, the others being Bleaklow Stones , some 1.9 miles (3.1 km) to the east along an indefinite ridge, and Higher Shelf Stones , 0.9 miles (1.4 km) south of Bleaklow Head. At 633 metres (2,077 feet), Bleaklow
69-436: A section. The samples are analyzed to determine their detrital remanent magnetism (DRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. For sedimentary rocks this is possible because, as they fall through the water column, very fine-grained magnetic minerals (< 17 μm ) behave like tiny compasses , orienting themselves with Earth's magnetic field . Upon burial, that orientation
92-509: Is a stub . You can help Misplaced Pages by expanding it . Stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata ) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks . Stratigraphy has three related subfields: lithostratigraphy (lithologic stratigraphy), biostratigraphy (biologic stratigraphy), and chronostratigraphy (stratigraphy by age). Catholic priest Nicholas Steno established
115-498: Is a formal stratigraphic term for this sequence of rocks. The gritstone edges of the Peak District are an important climbing area and the rock is much relished by English climbers , among whom it has almost cult status and is often referred to as "God's own rock". The rough surface provides outstanding friction, enabling climbers to stand on or grip the subtlest of features in the rock. This article related to petrology
138-431: Is also commonly used to delineate the nature and extent of hydrocarbon -bearing reservoir rocks, seals, and traps of petroleum geology . Chronostratigraphy is the branch of stratigraphy that places an absolute age, rather than a relative age on rock strata . The branch is concerned with deriving geochronological data for rock units, both directly and inferentially, so that a sequence of time-relative events that created
161-534: Is due to physical contrasts in rock type ( lithology ). This variation can occur vertically as layering (bedding), or laterally, and reflects changes in environments of deposition (known as facies change). These variations provide a lithostratigraphy or lithologic stratigraphy of the rock unit. Key concepts in stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries imply about their original depositional environment. The basic concept in stratigraphy, called
184-411: Is preserved. For volcanic rocks, magnetic minerals, which form in the melt, orient themselves with the ambient magnetic field, and are fixed in place upon crystallization of the lava. Oriented paleomagnetic core samples are collected in the field; mudstones , siltstones , and very fine-grained sandstones are the preferred lithologies because the magnetic grains are finer and more likely to orient with
207-529: Is the second-highest point in Derbyshire and the area includes the most easterly point in the British Isles over 2,000 feet, near Bleaklow Stones. Much of the main plateau of Bleaklow is a boggy peat moorland, seamed by 'groughs' (pronounced 'gruffs', water-eroded channels in the peat) and lacking strong changes in elevation – in poor conditions its traverse is probably the most navigationally challenging in
230-616: The Bleaklow Bomber is still visible. A memorial was erected at the site in 1988. There is public access to the area. Gritstone " Millstone Grit " is an informal term for a succession of gritstones which are to be found in the Pennines (including the Peak District ) of northern England. These sediments were laid down in the late (upper) Paleozoic era, in the Carboniferous period, in deltaic conditions. The Millstone Grit Group
253-534: The Moors for the Future Partnership, funded by EU LIFE+ programme between 2010 and 2015. This involved laying 52 kilometres (32 mi) of geotextiles to stabilise eroded peat, creating 4,000 mini-dams to retain water, introducing 150,000 moorland plants and spreading 807 million Sphagnum fragments across the whole Bleaklow Project site. The summit affords views across Manchester , Lancashire and Cheshire to
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#1733105514297276-502: The Peak District . Bleaklow is part of the National Trust's High Peak Estate . There has been considerable investment of resources in recent years to block many of the eroded peat gulleys as part of major schemes to re-wet and restore healthy Sphagnum moss communities which are essential for peat formation, carbon capture, and reduction in dissolved carbon which contaminates water supplies. Much of this work has been coordinated by
299-431: The law of superposition , states: in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence. Chemostratigraphy studies the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time, and researchers can use those to map subtle changes that occurred in the paleoenvironment. This has led to
322-547: The natural remanent magnetization (NRM) to reveal the DRM. Following statistical analysis, the results are used to generate a local magnetostratigraphic column that can then be compared against the Global Magnetic Polarity Time Scale. This technique is used to date sequences that generally lack fossils or interbedded igneous rocks. The continuous nature of the sampling means that it is also a powerful technique for
345-588: The ambient field during deposition. If the ancient magnetic field were oriented similar to today's field ( North Magnetic Pole near the North Rotational Pole ), the strata would retain a normal polarity. If the data indicate that the North Magnetic Pole were near the South Rotational Pole , the strata would exhibit reversed polarity. Results of the individual samples are analyzed by removing
368-512: The gap may be due to removal by erosion, in which case it may be called a stratigraphic vacuity. It is called a hiatus because deposition was on hold for a period of time. A physical gap may represent both a period of non-deposition and a period of erosion. A geologic fault may cause the appearance of a hiatus. Magnetostratigraphy is a chronostratigraphic technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout
391-437: The rock layers. Strata from widespread locations containing the same fossil fauna and flora are said to be correlatable in time. Biologic stratigraphy was based on William Smith's principle of faunal succession , which predated, and was one of the first and most powerful lines of evidence for, biological evolution . It provides strong evidence for the formation ( speciation ) and extinction of species . The geologic time scale
414-480: The rocks formation can be derived. The ultimate aim of chronostratigraphy is to place dates on the sequence of deposition of all rocks within a geological region, and then to every region, and by extension to provide an entire geologic record of the Earth. A gap or missing strata in the geological record of an area is called a stratigraphic hiatus. This may be the result of a halt in the deposition of sediment. Alternatively,
437-405: The significance of strata or rock layering and the importance of fossil markers for correlating strata; he created the first geologic map of England. Other influential applications of stratigraphy in the early 19th century were by Georges Cuvier and Alexandre Brongniart , who studied the geology of the region around Paris. Variation in rock units, most obviously displayed as visible layering,
460-406: The specialized field of isotopic stratigraphy. Cyclostratigraphy documents the often cyclic changes in the relative proportions of minerals (particularly carbonates ), grain size, thickness of sediment layers ( varves ) and fossil diversity with time, related to seasonal or longer term changes in palaeoclimates . Biostratigraphy or paleontologic stratigraphy is based on fossil evidence in
483-429: The theoretical basis for stratigraphy when he introduced the law of superposition , the principle of original horizontality and the principle of lateral continuity in a 1669 work on the fossilization of organic remains in layers of sediment. The first practical large-scale application of stratigraphy was by William Smith in the 1790s and early 19th century. Known as the "Father of English geology", Smith recognized
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#1733105514297506-810: The west and towards the Hope Valley , Holme Moss , Emley Moor and Yorkshire to the east. In exceptional weather conditions it is possible to see Snowdonia in North Wales . There are a number of aircraft crash sites on Bleaklow. On 3 November 1948, USAF Boeing RB-29A Superfortress 44–61999, of the 16th Photographic Reconnaissance Squadron, 91st Reconnaissance Group, 311th Air Division, Strategic Air Command , crashed at Higher Shelf Stones, Bleaklow ( 53°27′2.12″N 1°51′54.03″W / 53.4505889°N 1.8650083°W / 53.4505889; -1.8650083 ), en route from Scampton to Burtonwood . All 13 crew members were killed. A large amount of wreckage of
529-525: Was developed during the 19th century, based on the evidence of biologic stratigraphy and faunal succession. This timescale remained a relative scale until the development of radiometric dating , which was based on an absolute time framework, leading to the development of chronostratigraphy. One important development is the Vail curve , which attempts to define a global historical sea-level curve according to inferences from worldwide stratigraphic patterns. Stratigraphy
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