Glacial erratic
A glacial erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. "Erratics" take their name from the Latin word errare, are carried by glacial ice over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock in Alberta. Geologists identify erratics by studying the rocks surrounding the position of the erratic and the composition of the erratic itself. Erratics are significant because: They can be transported by glaciers, they are thereby one of a series of indicators which mark the path of prehistoric glacier movement, their lithographic origin can be traced to the parent bedrock, allowing for confirmation of the ice flow route. They can be transported by ice rafting; this allows quantification of the extent of glacial flooding resulting from ice dam failure which release the waters stored in proglacial lakes such as Lake Missoula. Erratics released by ice-rafts that were stranded and subsequently melt, dropping their load, allow characterization of the high-water marks for transient floods in areas like temporary Lake Lewis.
Erratics dropped by icebergs melting in the ocean can be used to track Antarctic and Arctic-region glacial movements for periods prior to record retention. Known as dropstones, these can be correlated with ocean temperatures and levels to better understand and calibrate models of the global climate; the term "erratic" is used to refer to erratic blocks, which Geikie describes as: "large masses of rock as big as a house, that have been transported by glacier-ice, have been lodged in a prominent position in the glacier valleys or have been scattered over hills and plains. And examination of their mineralogical character leads the identification of their sources…". In geology, an erratic is material moved by geologic forces from one location to another by a glacier. Erratics are formed by glacial ice erosion resulting from the movement of ice. Glaciers erode by multiple processes: abrasion/scouring, ice thrusting and glacially-induced spalling. Glaciers crack pieces of bedrock off in the process of producing the larger erratics.
In an abrasion process, debris in the basal ice scrapes along the bed and gouging the underlying rocks, similar to sandpaper on wood, producing smaller glacial till. In ice thrusting, the glacier freezes to its bed as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. Glacially-induced spalling occurs when ice lens formation with the rocks below the glacier spall off layers of rock, providing smaller debris, ground into the glacial basal material to become till. Evidence supports another option for creation of erratics as well, rock avalanches onto the upper surface of the glacier. Rock avalanche–supraglacial transport occurs when the glacier undercuts a rock face, which fails by avalanche onto the upper surface of the glacier; the characteristics of rock avalanche–supraglacial transport includes: Monolithologic composition – a cluster of boulders of similar composition are found in close proximity. Commingling of the multiple lithologies present throughout the glaciated basin, has not occurred.
Angularity – the supraglacially transported rocks tend to be rough and irregular, with no sign of subglacial abrasion. The sides of boulders are planar, suggesting that some surfaces may be original fracture planes. Great size – the size distribution of the boulders tends to be skewed toward larger boulders than those produced subglacially. Surficial positioning of the boulders – the boulders are positioned on the surface of glacial deposits, as opposed to or buried. Restricted areal extents – the boulder fields tend to have limited areal extent. Orientations – the boulders may be close enough that original fracture planes can be matched. Locations of the boulder trains – the boulders appear in rows, trains or clusters along the lateral moraines as opposed to being located on the terminal moraine or in the general glacial field. Erratics provide an important tool in characterizing the directions of glacier flows, which are reconstructed used on a combination of moraines, drumlins, meltwater channels, similar data.
Erratic distributions and glacial till properties allow for identification of the source rock from which they derive, which confirms the flow direction when the erratic source outcrop is unique to a limited locality. Erratic materials may be transported by multiple glacier flows prior to their deposition, which can complicate the reconstruction of the glacial flow. Glacial ice entrains debris of varying sizes from small particles to large masses of rock; this debris is transported to the coast by glacier ice and released during the production and melting of icebergs. The rate of debris release by ice depends upon the size of the ice mass in which it is carried as well as the temperature of the ocean through which the ice floe passes. Sediments from the late Pleistocene period lying on the floor of the North Atlantic show a series of layers which contain ice-rafted debris, they were formed between 70,000 years before the present. The deposited debris can be traced back to the origin by both the nature of the materials released and the continuous path of debris release.
Some paths extend more than 3,000 kilometres distant from the point at which the ice floes broke free. The location and altitude of ice-rafted boulders r
County Kilkenny
County Kilkenny is a county in Ireland. It is part of the South-East Region, it is named after the city of Kilkenny. Kilkenny County Council is the local authority for the county; as of the 2016 census the population of the county was 99,232. The county was based on the historic Gaelic kingdom of Ossory, co-terminus with the Diocese of Ossory. Kilkenny is the 16th largest of the traditional 32 Counties of Ireland in area and the 21st largest in terms of population, it is the third largest county in the province Leinster and seventh largest in terms of population. The county is subdivided into called nine baronies which are in turn divided into civil parishes and townlands. There are about 800 townlands in Kilkenny; each barony was made up of a number of parts of parishes. Both civil parishes and baronies are now obsolete and are no longer used for local government purposes. Baronies in County Kilkenny: Callan Crannagh Fassadinin Barony of Galmoy Gowran Ida Iverk Kells Kilculliheen Kilkenny City Knocktopher Shillelogher For religious administration, the county was divided into parishes.
Every parish had at least one church. The barony boundaries and the parish boundaries were not connected. From the 17th to mid-19th centuries, civil parishes were based on early Christian and medieval monastic and church settlements; the civil parishes are divided into townlands. As the population grew, new parishes were created and the civil parish covered the same area as the established Church of Ireland; the Roman Catholic Church adapted to a new structure based on villages. There 2,508 civil parishes in Ireland, which break both barony and county boundaries; the county contains the city of Kilkenny, located at the center of the county, the towns of Ballyragget and Castlecomer to the north of the county and Graiguenamanagh, Mooncoin and Thomastown to the south. Ballyfoyle, Ballyragget, Bennettsbridge Callan, Castlecomer, Clogh, Coan Danesfort, Dunnamaggan Ferrybank, Freshford Galmoy, Gowran, Glenmore Hugginstown Inistioge Jenkinstown, Johnswell Kilkenny, Kilmacow, Knocktopher Kilmanagh Moneenroe, Mullinavat Paulstown, Piltown Redhouse, Tullogher-Rosbercon Slieverue, Stoneyford Thomastown, The Rower Urlingford Windgap The River Nore flows through the county and the River Suir forms the border with County Waterford.
Brandon Hill is the highest point with an elevation of 515 m. Most of the county has a hilly surface of moderate elevation with uplands in the north-east, the north-west and the South of the county; the county has an area of 512,222 acres. The county extends from 52 degrees 14 minutes to 52 degrees 52 minutes north latitude, from 6 degrees 56 minutes to 7 degrees 37 minutes west longitude; the north-south length of the county is 45 miles. Kilkenny extends southward from Laois to the valley of the Suir and eastward from the Munster–Leinster border to the River Barrow; the River Nore bisects the county and the River Barrow and River Suir are natural boundaries to the east and south of the county. County Kilkenny is bordered by Laois, Wexford and Tipperary; the geology of Kilkenny includes the Kiltorcan Formation, early Carboniferous in age. The Formation is located around Kiltoncan Hill near Ballyhale in the Knocktopher areas, it forms the uppermost part of the Old Red Sandstone and is the distinctive Upper Devonian–Lower Carboniferous unit in southern Ireland.
It contains non-red lithologies, green mudstones, fine sandstones and yellow sandstones. There is a fossil assemblage containing Archaeopteris and Archaeopteris hibernica. Most of the county is principally limestone of the upper and lower group, corresponding with the rest of Ireland. A large area in the north and east contains beds of coal, surrounded by limestone strata, alternated with shale, argilaceous ironstone, sandstone; this occurs eastward of the Nore around Castlecomer, along the border with Laois. It is accompanied by culm, used extensively for burning lime; the Environment of County Kilkenny contains a great variety of natural heritage, including rivers, woodlands and diverse landscapes and geological features. The main land use is grassland, dairy farming and tillage farming around Kilkenny City and in the fertile central plain of the Nore Valley. Conifer forests are found on the upland areas. Habitats of international and national importance, are designated under European Union and national legislation.
The four categories of designated site in effect in County Kilkenny are Special Areas of Conservation, Natural Heritage Areas, Statutory Nature Reserves and Wildfowl Sanctuaries. At present there are 36 designated natural heritage sites of international and national importance in County Kilkenny, covering 4.5% of the county. County Kilkenny is comparably low compared to other mountain ranges in Ireland with the highest peak being Brandon Hill, at 515 metres above sea level; the majority of res
St Patrick's Cathedral, Melbourne
The Cathedral Church and Minor Basilica of Saint Patrick is the cathedral church of the Roman Catholic Archdiocese of Melbourne in Victoria and seat of its archbishop Peter Comensoli. In 1974 Pope Paul VI conferred the dignity of minor basilica on it. In 1986 Pope John Paul II addressed clergy during his Papal Visit; the cathedral is built on a traditional east–west axis, with the altar at the eastern end, symbolising belief in the resurrection of Christ. The plan is in the style of a Latin cross, consisting of a nave with side aisles, transepts with side aisles, a sanctuary with seven chapels, sacristies. Although its 103.6-metre length is marginally shorter than that of St Mary's Cathedral, Sydney, St Patrick's has the distinction of being both the tallest and, the largest church building in Australia. The cathedral is located on Eastern Hill in Melbourne, in an area bounded by Albert Street, Gisborne Street, Lansdowne Street and Cathedral Place. Just to the east across Gisborne Street is St Peter's Church, constructed from 1846 to 1848, the Anglican parish church of Melbourne.
In 1848, the Augustinian friar James Goold was appointed the first bishop of Melbourne and became the fourth bishop in Australia, after Sydney and Adelaide. Negotiations with the colonial government for the grant of five acres of land for a church in the Eastern Hill area began in 1848. On 1 April 1851, only 16 years after the foundation of Melbourne, the Colonial Secretary of Victoria granted the site to the Roman Catholic Church. Goold decided to build his cathedral on the Eastern Hill site. Since the Catholic community of Melbourne was at the time entirely Irish, the cathedral was dedicated to St Patrick, the patron saint of Ireland. William Wardell, Melbourne's foremost ecclesiastical architect was commissioned to prepare plans for a cathedral, but the project was delayed by severe labour shortages during the Gold Rush of 1851, which drew every able-bodied man in the colony to the goldfields, the foundation stone was not laid until 1858. An earlier building by stonemason David Mitchell was demolished for the cathedral.
The cathedral was designed in the Gothic style of early Fourteenth Century, based on the great medieval cathedrals of England, a style at the height of its popularity in the mid 19th century. The nave exhibits'curvilinear traceries' in the principal windows of circa 1300 to 1350s; the eastern arm with its chevet of chapels in the French manner is still principally in the English late Thirteenth Century style, giving the most complete essay attempted in that style during the Nineteenth Century. William Wardell was a remarkably capable architect. In 1974 Pope Paul VI conferred the dignity of minor basilica on it. In 1986 Pope John Paul II addressed clergy during his Papal Visit. In 1858 William Wardell was commissioned to plan the cathedral with a contract signed on 8 December 1858 and building commencing the same year. Although the nave was completed within 10 years, construction proceeded and was further delayed by the severe depression which hit Melbourne in 1891. Under the leadership of Archbishop Thomas Carr the cathedral was consecrated in 1897 and then it was not finished.
Given the size of the Catholic community at the time, the massive bluestone Gothic cathedral was an immense and expensive undertaking, there were long delays while funds were raised. St Patrick's was one of the two largest churches brought to substantial completion anywhere in the world in the 19th century; the other is New York, United States. Daniel Mannix, who became Archbishop of Melbourne in 1917, maintained a constant interest in the cathedral, which he was determined to see finished after the long delays during the previous 30 years, he oversaw the addition of other elements in the late 1930s. The building was completed in 1939; the cathedral is 103.6 metres long on its long axis, 56.4 metres wide across the transepts and 25.3 metres wide across the nave. The nave and transepts are 28.9 metres high. The central spire is 105 metres high and the flanking towers and spires are 61.9 metres high. The bluestone used in its construction was sourced from basalt deposits in nearby Footscray. To celebrate the centenary of its consecration in 1997, the cathedral was closed throughout 1994 to be upgraded.
Nothing was added to the main building. Rather, it underwent significant conservation work, with funds contributed by the federal and Victorian governments and philanthropic donors and the community of Melbourne; the cathedral's stained glass windows had buckled and cracked and required a full year to restore to their original state. Teams of stonemasons and stained-glass craftsmen used "lime mortars and materials long-forgotten by the building trade — like medieval times"; the 1992-97 restoration works were undertaken under the guidance of Falkinger Andronas Architects and Heritage Consultants. The works were awarded the Royal Australian Institute of Architects John George Knight Award for Heritage Architecture 1996. One of the gargoyles restored by the masonry team was modelled on the then-Premier of Victoria, Jeff Kennett. There has been music at St Patrick's since 1858, but the present cathedral choir was founded in 1939 when the Vien
Old Melbourne Gaol
The Old Melbourne Gaol is a museum on Russell Street, in Melbourne, Australia. It consists of a bluestone building and courtyard, is located next to the old City Police Watch House and City Courts buildings, it was first constructed starting in 1839, during its operation as a prison between 1842 and 1929, it held and executed some of Australia's most notorious criminals, including bushranger Ned Kelly and serial killer Frederick Bailey Deeming. In total, 135 people were executed by hanging. Though it was used during World War II, it formally ceased operating as a prison in 1924; the three-storey museum displays information and memorabilia of the prisoners and staff, including death masks of the executed criminals. At one time the museum displayed what was believed at the time to be Ned Kelly's skull, before it was stolen in 1978. An allotment of scrubland to the north-east of Melbourne was selected as Port Phillips first permanent gaol. On 1 January 1838, George Wintle was appointed to be gaoler at the prison at £100 a year.
Construction of the gaol started in 1839–1840 on Collins Street West, but it was considered too small at the time. A second gaol was built between 1841 and 1844 at the corner of Russell and La Trobe Streets, adjoining the Supreme Court; the first cell block was opened for prisoners in 1845, but the facilities were considered inadequate. The gaol was crowded by 1850. With the discovery of gold in 1851, the resulting influx of population and order became more difficult to maintain. Subsequently, a new wing, with its own perimeter wall, was constructed between 1852 and 1854; the design was based on that of British prison engineer Joshua Jebb, the designs for the Pentonville Model Prison in London. The new wing was extended in between 1857 and 1859, with the boundary wall being extended during this time. In 1860, a new north wing was built. Between 1862 and 1864, a cell block was built for female prisoners on the western side – it was a replica of the present east block. In 1864, the perimeter wall, the gaol overall, was completed.
At its completion, the prison occupied an entire city block, included exercise yards, a hospital in one of the yards, a chapel, a bath house and staff accommodation. A house for the chief warders was built on the corner of Franklin and Russell streets, 17 homes were built for gaolers on Swanston street in 1860. Artefacts recovered from the area indicate that the gaolers and their families lived within the gaol walls in the 1850s and 1860s. Much of daily life inside the gaol could be gleaned from sources such as diaries written by John Castieau, governor of the gaol between 1869 and 1884. During its operation, the gaol was used to house short-term prisoners and some of the colony’s most notorious and hardened criminals, it housed up to twenty children at a time – including those imprisoned for petty theft or vagrancy, or those staying with a convicted parent. Babies under twelve months old were allowed to be with their mothers; the youngest prisoner was recorded as three-year-old Michael Crimmins, who spent 6 months in the prison in 1857 for being idle and disorderly.
In 1851, the 13 - and 14-year-old O'Dowd sisters were imprisoned. Prisoners convicted of serious crimes, such as murder, burglary and shooting, would begin their time on the ground floor with a time of solitary confinement, they were forbidden from communicating with other prisoners, enforced by the usage of a silence mask, or calico hood, when outside their cells. They would only be given a single hour of solitary exercise a day, with the remaining 23 hours spent in their cells. Inside the cells, prisoners would be able to lie on a thin mattress over the slate floors, they could only bathe and change clothes once a week, attend the chapel on Sundays. Prisoners might only have been allowed to socialise with other prisoners towards the end of their sentences; the routine for prisoners was regulated by a system of bells, enforced by punishments. Male prisoners would perform hard labour – including breaking rocks, other duties in the stone quarries, while women would sew and cook. Women would make shirts and waistcoats for male prisoners, as well as act as domestic servants for the governor and his family.
Prisoners who had become trusted, those nearing the completion of their sentence, debtors, were housed on the third floor communal cells. These top level cells were large, held up to six prisoners at time. During its operation, the gaol was the setting for 135 hangings; the most infamous was that of bushranger Ned Kelly at the age of 25, on 11 November 1880. After a two-day trial, Kelly was convicted of killing a police officer; as st
Brunswick, Victoria
Brunswick is an inner-city suburb of Melbourne, Australia, 4 kilometres north of Melbourne's central business district. Its local government area is the City of Moreland. At the 2016 Census, Brunswick had a population of 24,473. Traditionally a working class area noted for its large Italian and Greek communities, Brunswick is known for its bohemian culture and strong arts and live music scenes, it is home to a large student population owing to its proximity to the University of Melbourne and RMIT University, the latter of which has a campus in the suburb. Brunswick's major thoroughfare is Sydney Road, one of Melbourne's major commercial and nightlife strips, it encompasses the northern section of Lygon Street, synonymous with the Italian community of Melbourne, which forms its border with Brunswick East. Brunswick takes its name from George IV and the city of Brunswick, which laid within his ancestral Kingdom of Hanover, it is bordered to the south by the suburbs of Princes Hill and Parkville, to the east by Brunswick East, to the north by Coburg and to the west by Brunswick West.
Brunswick is in the area known as Iramoo by the Aboriginal people who hunted in it. It was occupied by the Wurundjeri people. White settlement began in the 1830s, with Assistant Surveyor Darke surveying the area under the instruction of Robert Hoddle. North and south boundaries were drawn up, running in an east-west direction between Moonee Ponds Creek and Merri Creek; these boundaries would become Park Street, respectively. A narrow road was surveyed down the centre to service what were intended to be agricultural properties, which would become the major thoroughfare of Sydney Road. Ten allotments were drawn up on each side of this road, with each block of land running all the way to either Moonee Ponds Creek or Merri Creek; these wide strips of land are still reflected in the current street layout. The land was sold at auction in Sydney and attracted speculators, many of whom would never see the land they purchased. Only one original buyer, James Simpson, settled on his land. Simpson marked out two streets, Carmarthon Street and Landillo Street.
Because the land was too marshy he left the area in 1859 with much of the land unsold. In 1841 two friends, Thomas Wilkinson and Edward Stone Parker, bought land from one of the original buyers. Stone soon left but Wilkinson subdivided his land for sale or rent, he marked two roads which would become extensions of the roads marked out by Simpson. Wilkinson named the streets Albert Street. Wilkinson's office opened in 1846, taking on the name of Wilkinson's estate and thus establishing the name of the whole area. In October 1842, Miss Amelia Shaw became the licensee of the first hotel in the area, the Retreat Inn; the hotel had a weighbridge so bullock drivers could refresh themselves whilst their wagons were weighed. The establishment was renamed the Retreat Hotel. In 1842, work began on a new road along the central surveyors' division; the road was known as Pentridge Road. In 1843, William Lobb established a cattle farm on his allotment and the area became known as Lobb's Hill. A laneway down the side of his property called Lobb's Lane, would be named Stewart Street.
In 1849, one of the original land purchasers, Michael Dawson, completed work on an ivy-covered mansion on his property called Phoenix Park. The property was named after Phoenix Park near Ireland. Dawson cited his address not as Brunswick but as Philiptown, after a town in Ireland which has since reverted to its original name of Daingean. Philiptown grew into a village along the track which led from Phoenix Park to Sydney Road; this track was named Union Street. Henry Search opened a butcher's shop in 1850, on the south-west corner of Albert Street and Sydney Road; this was the first retail establishment in Brunswick. By 1851, gold diggers began making their way through the area, on their journey from the populous suburbs of Fitzroy and Collingwood. Brunswick provided a convenient place for lunch, before the diggers reached the beginnings of the roads to the goldfields, near present-day Essendon. A small village sprang up to meet the needs of the travellers, near the present day Cumberland Arms Hotel.
The village included a tent market, described as being like a bazaar, where miners could buy goods needed for the goldfields. Brunswick Post Office opened on 1 January 1854. In 1859, Wilkinson established the area's first newspaper, The Brunswick Record, which changed its name in 1858 to The Brunswick & Pentridge Press. By 1857, the local population was estimated at 5000; the Brunswick Municipal Council was established in that year at the Cornish Arms Hotel, which still stands. The first municipal chambers were established in 1859 on Sydney Road at Lobb's Hill, between Stewart and Albion Streets; the present Brunswick Town Hall is an imposing Victorian edifice built in 1876 on the corner of Dawson Street and Sydney Road, near the centre of Brunswick. In the 1850s, quarries and a large brickworks established in Brunswick using the local clay and bluestone became the largest industry in the area. In 1884 the first Brunswick railway line opened, running from North Melbourne to Brunswick and Coburg.
The line ran directly into the Hoffmans Brickworks, reflecting the importance of the brick-making industry to the local community. Prior to World War I, Brunswick was the "brickyard capital of Victoria". Remnants of the brickyards are still visible in some
Slate
Slate is a fine-grained, 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 rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression; the foliation in slate is called "slaty cleavage". It is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression; when expertly "cut" by striking parallel to the foliation, with a specialized tool in the quarry, many slates will display a property called fissility, forming smooth flat sheets of stone which have long been used for roofing, floor tiles, other purposes. Slate is grey in color when seen, en masse, covering roofs. However, slate occurs in a variety of colors from a single locality. Slate is not to schist; the word "slate" is used for certain types of object made from slate rock.
It may mean a writing slate. They were traditionally a small, smooth piece of the rock framed in wood, used with chalk as a notepad or noticeboard, for recording charges in pubs and inns; the phrases "clean slate" and "blank slate" come from this usage. Before the mid-19th century, the terms slate and schist were not distinguished. In the context of underground coal mining in the United States, the term slate was used to refer to shale well into the 20th century. For example, roof slate referred to shale above a coal seam, draw slate referred to shale that fell from the mine roof as the coal was removed. Slate is composed of the minerals quartz and muscovite or illite along with biotite, chlorite and pyrite and, less apatite, kaolinite, tourmaline, or zircon as well as feldspar; as in the purple slates of North Wales, ferrous reduction spheres form around iron nuclei, leaving a light green spotted texture. These spheres are sometimes deformed by a subsequent applied stress field to ovoids, which appear as ellipses when viewed on a cleavage plane of the specimen.
Slate can be made into roofing slates, a type of roof shingle, or more a type of roof tile, which are installed by a slater. Slate has two lines of breakability – cleavage and grain – which make it possible to split the stone into thin sheets; when broken, slate retains a natural appearance while remaining flat and easy to stack. A "slate boom" occurred in Europe from the 1870s until the first world war, allowed by the use of the steam engine in manufacturing slate tiles and improvements in road and waterway transportation systems. Slate is suitable as a roofing material as it has an low water absorption index of less than 0.4%, making the material waterproof. In fact, this natural slate, which requires only minimal processing, has the lowest embodied energy of all roofing materials. Natural slate is used by building professionals as a result of its durability. Slate is durable and can last several hundred years with little or no maintenance, its low water absorption makes it resistant to frost damage and breakage due to freezing.
Natural slate is fire resistant and energy efficient. Slate roof tiles are fixed either with nails, or with hooks as is common with Spanish slate. In the UK, fixing is with double nails onto timber battens or nailed directly onto timber sarking boards. Nails were traditionally of copper, although there are modern alloy and stainless steel alternatives. Both these methods, if used properly, provide a long-lasting weathertight roof with a lifespan of around 80–100 years; some mainland European slate suppliers suggest that using hook fixing means that: Areas of weakness on the tile are fewer since no holes have to be drilled Roofing features such as valleys and domes are easier to create since narrow tiles can be used Hook fixing is suitable in regions subject to severe weather conditions, since there is greater resistance to wind uplift, as the lower edge of the slate is secured. The metal hooks are, however and may be unsuitable for historic properties. Slate tiles are used for interior and exterior flooring, stairs and wall cladding.
Tiles are grouted along the edges. Chemical sealants are used on tiles to improve durability and appearance, increase stain resistance, reduce efflorescence, increase or reduce surface smoothness. Tiles are sold gauged, meaning that the back surface is ground for ease of installation. Slate flooring can be slippery. Slate tiles were used in 19th century UK building construction and in slate quarrying areas such as Blaenau Ffestiniog and Bethesda, Wales there are still many buildings wholly constructed of slate. Slates can be set into walls to provide a rudimentary damp-proof membrane. Small offcuts are used as shims to level floor joists. In areas where slate is plentiful it is used in pieces of various sizes for building walls and hedges, sometimes combined with other kinds of stone. In modern homes slate is used as table coasters; because it is a good electrical insulator and fireproof, it was used to construct early-20th-century electric switchboards and relay controls for large electric motors.
Fine slate can be used as a whe
Sandstone
Sandstone is a clastic sedimentary rock composed of sand-sized mineral particles or rock fragments. Most sandstone is composed of quartz or feldspar because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in Bowen's reaction series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, yellow, grey, pink and black. Since sandstone beds form visible cliffs and other topographic features, certain colors of sandstone have been identified with certain regions. Rock formations that are composed of sandstone allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity. Quartz-bearing sandstone can be changed into quartzite through metamorphism related to tectonic compression within orogenic belts.
Sandstones are clastic in origin. They are formed from cemented grains that may either be fragments of a pre-existing rock or be mono-minerallic crystals; the cements binding these grains together are calcite and silica. Grain sizes in sands are defined within the range of 0.0625 mm to 2 mm. Clays and sediments with smaller grain sizes not visible with the naked eye, including siltstones and shales, are called argillaceous sediments; the formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water or from air. Sedimentation occurs by the sand settling out from suspension. Once it has accumulated, the sand becomes sandstone when it is compacted by the pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains; the most common cementing materials are silica and calcium carbonate, which are derived either from dissolution or from alteration of the sand after it was buried.
Colors will be tan or yellow. A predominant additional colourant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red, with additional manganese imparting a purplish hue. Red sandstones are seen in the Southwest and West of Britain, as well as central Europe and Mongolia; the regularity of the latter favours use as a source for masonry, either as a primary building material or as a facing stone, over other forms of construction. The environment where it is deposited is crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size and composition and, in more general detail, include the rock geometry and sedimentary structures. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings: Terrestrial environmentsRivers Alluvial fans Glacial outwash Lakes Deserts Marine environmentsDeltas Beach and shoreface sands Tidal flats Offshore bars and sand waves Storm deposits Turbidites Framework grains are sand-sized detrital fragments that make up the bulk of a sandstone.
These grains can be classified into several different categories based on their mineral composition: Quartz framework grains are the dominant minerals in most clastic sedimentary rocks. These physical properties allow the quartz grains to survive multiple recycling events, while allowing the grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in origin and from older sandstones that have been recycled. Feldspathic framework grains are the second most abundant mineral in sandstones. Feldspar can be divided into two smaller subdivisions: plagioclase feldspars; the different types of feldspar can be distinguished under a petrographic microscope. Below is a description of the different types of feldspar. Alkali feldspar is a group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8, this represents a complete solid solution. Plagioclase feldspar is a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.
Lithic framework grains are pieces of ancient source rock that have yet to weather away to individual mineral grains, called lithic fragments or clasts. Lithic fragments can be any fine-grained or coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments found in sedimentary rocks are clasts of volcanic rocks. Accessory minerals are all other mineral grains in a sandstone. Common accessory minerals include micas, olivine and corundum. Many of these accessory grains are more dense than the silicates that
