Deux-Sèvres is a French department. Deux-Sèvres means "two Sèvres": the Sèvre Nantaise and the Sèvre Niortaise are two rivers which have their sources in the department. Deux-Sèvres was one of the 83 original départements created during the French Revolution on March 4, 1790. Departmental borders were changed in 1973 when the inhabitants of the little commune of Puy-Saint-Bonnet became formally associated with the growing adjacent commune of Cholet. Cholet is in the neighbouring department of Maine-et-Loire. In order to avoid the associated communes being administered in separate departments, Puy-Saint-Bonnet was transferred into Maine-et-Loire; the climate is mild, the annual temperature averaging 11 degrees Celsius. The département remains rural: three-quarters of the area consists of arable land. Wheat and oats are the main products grown, as well as potatoes and walnuts. Niort is the center for angelica; some beetroot is grown in the district of Melle. Vineyards are numerous in the north, there are some in the south.
The département is well known for the breeding of cattle and horses. The Parthenais breed of cattle is named after the town of Parthenay in the north of the département. Dairy products are produced in significant quantities; some quarries are in operation, as well as lime extraction operations. Textiles, leather-tanning, flour milling were the traditional industries of Niort, the capital and major city. Nowadays, with 60,000 inhabitants, is an important commercial and administrative center. In particular it is one of the main financial centers in France. Niort is the national headquarters of some of the major insurance companies in France and regional headquarters of others such as Groupama; the regional headquarters of several national banks, including Banque Populaire and Crédit Agricole, are located there. The services sector is heavily represented in Niort, in consulting, accounting and software. Chemistry and aeronautics are the main industries. Textiles and shoe making, mechanics, chemistry, food industry and food packaging are the major industries outside of the capital.
The unemployment rate in the département is low in the north-west, where many small and medium companies are developing rapidly. The south-west of the département attracts tourists with the Marais Poitevin natural area. Niort in the south of the département is connected to Paris and Bordeaux by the A10 motorway, with Nantes by the A83, with La Rochelle and Poitiers by the N11. Another important road in the north of the département is the Route nationale 149, which runs east–west from Mortagne-sur-Sèvre to Poitiers, passing through Bressuire and Parthenay; the RN149 forms part of the European route E62 from Nantes to Genoa. In Autumn 2008, the Route nationale 249 running from Nantes to Cholet, was extended, continuing towards Bressuire and on to Poitiers; this will become part of the E62 and bypass the current RN149. The north and south of the département are connected by minor roads, with the D743 and D748 linking Niort to Parthenay and Bressuire whilst the D938 connects to Thouars; the département has two railway stations on the TGV route between Paris and La Rochelle, with a journey from Niort to Paris taking 2h15.
It is served by several TER Nouvelle-Aquitaine regional railway routes, including a route from Poitiers via Niort to La Rochelle, a route from Niort to Saintes, a route from Tours to Thouars and Bressuire. A railway bus service operated as part of the TER Nouvelle-Aquitaine network follows the RN149 from Poitiers to Nantes, calling at Parthenay and Bressuire. Additionally the département provides the Réseau des Deux-Sèvres, an inter-urban bus service that connects the towns and villages of the département. There are no airports with scheduled airline service within the département, although Niort-Souche Airport is used for private movements; the nearest commercial airports are at La Rochelle and Nantes. Famous births in the département: Françoise d'Aubigné, marquise de Maintenon, second wife of Louis XIV Jacques de Liniers Louis-Marcelin, marquis de Fontanes and politician Henri-Georges Clouzot, film director Laurent Cantet, Palme d'Or at the Festival de Cannes 2008, for the movie Entre les murs Catherine Breillat, film maker and novelist Jean-Hugues Anglade, actor René Caillié explorer, the first European to return alive from the town of TimbuktuFamous people related to the département: Jean-Baptiste Baujault, French sculptor Ségolène Royal, former candidate for the 2007 French presidential election, former representative of the department at the National Assembly, former President of the Poitou-Charentes region and Minister of Ecology since 2014.
Anjou wine Arrondissements of the Deux-Sèvres department Cantons of the Deux-Sèvres department Communes of the Deux-Sèvres department Prefectures website
The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers 20 percent of the Earth's surface and about 29 percent of its water surface area, it separates the "Old World" from the "New World". The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, the Americas to the west; as one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, the Southern Ocean in the south. The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N. Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office; the oldest known mentions of an "Atlantic" sea come from Stesichorus around mid-sixth century BC: Atlantikoi pelágei and in The Histories of Herodotus around 450 BC: Atlantis thalassa where the name refers to "the sea beyond the pillars of Heracles", said to be part of the sea that surrounds all land.
Thus, on one hand, the name refers to Atlas, the Titan in Greek mythology, who supported the heavens and who appeared as a frontispiece in Medieval maps and lent his name to modern atlases. On the other hand, to early Greek sailors and in Ancient Greek mythological literature such as the Iliad and the Odyssey, this all-encompassing ocean was instead known as Oceanus, the gigantic river that encircled the world. In contrast, the term "Atlantic" referred to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast; the Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of millions of years ago. The term "Aethiopian Ocean", derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century. During the Age of Discovery, the Atlantic was known to English cartographers as the Great Western Ocean; the term The Pond is used by British and American speakers in context to the Atlantic Ocean, as a form of meiosis, or sarcastic understatement.
The term dates to as early as 1640, first appearing in print in pamphlet released during the reign of Charles I, reproduced in 1869 in Nehemiah Wallington's Historical Notices of Events Occurring Chiefly in The Reign of Charles I, where "great Pond" is used in reference to the Atlantic Ocean by Francis Windebank, Charles I's Secretary of State. The International Hydrographic Organization defined the limits of the oceans and seas in 1953, but some of these definitions have been revised since and some are not used by various authorities and countries, see for example the CIA World Factbook. Correspondingly, the extent and number of oceans and seas varies; the Atlantic Ocean is bounded on the west by South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe: the Strait of Africa. In the southeast, the Atlantic merges into the Indian Ocean; the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border.
In the 1953 definition it extends south to Antarctica, while in maps it is bounded at the 60° parallel by the Southern Ocean. The Atlantic has irregular coasts indented by numerous bays and seas; these include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, part of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea all of the Scotia Sea, other tributary water bodies. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23.5% of the global ocean and has a volume of 310,410,900 km3 or 23.3% of the total volume of the earth's oceans. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3; the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the Milwaukee Deep in the Puerto Rico Trench, is 8,486 m.
The bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S; the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2,000 m along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs Fracture Zone at 53°N; the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the othe
Jean Hoeufft was a French banker and arms dealer, who rose through the court of Louis XIII of France to become Treasurer to Louis XIV. Hoeufft made a fortune from his diplomatic and business ventures becoming one of the richest men in Europe outside of the royal families. Jan Hoeufft was born in 1578 in Liège in the Spanish Netherlands to a family that originated from Roermond, his father, a merchant in timber, had moved to Aachen, Liège and Heinsberg after converting to the Reformed Church. Not much is known about Jean's early life, he did not have children, he never married. Jean settled in Rouen, where there was religious freedom under Henry IV of France, he was naturalized in 1601. He developed trade and ship owner activities and from 1609 until 1616 he was involved in the salt trade from Hiers-Brouage, along with his Dordrecht-based brother Dirck. In 1620 they commissioned a ship-of-war, to be built in Amsterdam for Duke of Guise. By 1621 he was appointed chamberlain to Louis XIII. In the 1620s he was involved in arms trading for Duke of Nevers.
In 1628 he was allowed to collect taxes. In the 1630s he became a banker. Hoeufft advanced funds to the King, took part in major financial deals. In 1634 Hoeufft participated in peace talks between the Dutch and Spain, in which Jules Mazarin and Frederick Henry, Prince of Orange were involved. Hoeufft played a key part despite having no official authority to do so, his appointment as Commissioner of the States General of the Netherlands was formalized in 1637. In 1639 his house in Rouen was sacked. In 1643 he obtained a former lake near Sacy-le-Grand. Hoeufft became treasurer and Secretary to Louis XIV of France, holding those roles until his death in 1651. At the time of the Thirty Year's War, arms dealing was a lucrative business in Europe. Hoeufft, described by a contemporary as “‘a man capable of speaking and acting’ as well as ‘ money to distribute to people should there be need,’” was well-suited to the job. Hoeufft delt with Axel Oxenstierna, Johan Adler Salvius, Hugo Grotius, Abraham de Wicquefort and Adriaen Pauw on the French support for the Swedish army.
In finance, he was Cardinal Richelieu's banker for remitting subsidies during the Thirty Years War, banker to the Dukes of Saxe-Weimar.:43Hoeufft occupied a prominent place in the network of political interests that bound together France’s structure of alliances during the Thirty Years War. "In some sense, his political interests were so interwoven with his financial and mercantile interests that they are difficult to disentangle." The Hoeufft family invested over a million livres in reclamation of lakes and swamps in Picardie and other parts of France, which for the most part were carried out between 1642 and 1653 by Dutch engineers such as Jan van Ens. In 1650, Hoeufft was the director of the operation to drain the Poitou Marsh in western France. From the 1640s, one of his associates was David de la Croix, who seems to have married Hoeufft's niece, Marguerite Hoeufft; when Hoeufft died, de la Croix was among his beneficiaries and took over the Poitou marsh operation. Frédéric Otto Fabrice de Gressenich, Councillor and Maître d'hotel du Roi, the son of Jean's sister Anne, inherited the Sacy marshes along with his Hœufft cousins.
As the only cousin living in France, he administered the lands on their behalf.:169 Hoeufft died in Paris on 5 September 1651. He had two brothers and five sisters who scattered to Cologne, Dordrecht and Utrecht. Hoeufft bequeathed two million livres to the poor of the Reformed Church of Charenton. In 1736 Hoeufft's property at Petit Poitou was sold at Luçon in the Poitevin. Barthélemy Hervart – Huguenot banker Huguenots
Niort is a commune in the Deux-Sèvres department in western France. The population of Niort is 60,486 and more than 137,000 people live in the urban area. Near Niort at Maisonnay there is one of the tallest radio masts in France; the town is a centre of angelica cultivation in France. Niort has a railway station on the TGV route between La Rochelle, Gare de Niort. Direct TGV to Paris Montparnasse station takes 15 minutes. Niort is a road and motorway junction, connected to Paris and Bordeaux by the A10 motorway, with Nantes by the A83, with La Rochelle by the N11, it is the largest French city to offer free mass transit.. Niort is the French capital of mutual insurance and bank companies, with the headquarters of MAAF, MAIF, MACIF, SMACL and regional branches of national mutual companies such as Groupama, Banque Populaire. Niort is a main financial centre of France. Chemistry and aeronautics are the main industries. Niort is a major commercial centre; the football team is Chamois Niortais, which plays in the Ligue 2, the second-highest league in French football.
Rugby team Stade Niortais celebrated its 100th anniversary in 2009. The Dragons baseball team plays in the Regional League. Niort is the birthplace of the following: Achille-Félix Montaubry, tenor associated with opéra comique and operetta Gaston Chérau, writer, a member of the Académie Goncourt Aurélien Capoue, footballer Étienne Capoue, footballer Françoise d'Aubigné, marquise de Maintenon, second wife of Louis XIV Henri-Georges Clouzot, film director Paul Collomp, French hellenist and papyrologist Julien N'Da, footballer Louis-Marcelin, marquis de Fontanes and politician Mamadou Camara, footballer Mickaël Brunet, footballer Jacques Antoine Marie de Liniers et Brémond, Spanish Viceroy in the Río de la Plata Jean Sauvaget and orientalist Isabelle Druet, mezzo-soprano Niort is twinned with: Atakpamé, since 1958 Coburg, Germany, since 1974 Wellingborough, England, United Kingdom, since 1977 Springe, Lower Saxony, since 1979 Tomelloso, Ciudad Real, Castilla-La Mancha, since 1981 Gijón, Spain, since 1982 Biała Podlaska, Lublin Voivodeship, since 1995 Château de Niort Communes of the Deux-Sèvres department Pierre-Marie Poisson Niort War Memorial Sérotonine INSEE Official website Map Movies Calendar of Events Foirexpo of Niort Jobs
Charente-Maritime is a department on the southwestern coast of France named after the Charente River. A part of Saintonge and Aunis, Charente-Inférieure was one of the 83 original departments created during the French Revolution on 4 March 1790. On 4 September 1941, it was renamed Charente-Maritime; when first created, the commune of Saintes was assigned as the prefecture of the department. This changed in 1810 when Napoleon passed an imperial decree which moved the prefecture to La Rochelle. During World War II, the department was invaded by the German army and became part of occupied France. To provide defence against a possible beach landing, the Organisation Todt constructed a number of sea defences in the area. Defences such as pillboxes are noticeable on the beaches of the presqu'île d'Arvert and the island of Oléron. At the end of the war there were only two pockets of German resistance: La Rochelle, in the north and Royan in the south. Despite being completely destroyed during an RAF bombing raid on 5 January 1945, the town of Royan wasn't liberated by the French resistance until April of the same year.
La Rochelle was captured on 9 May 1945. Charente-Maritime is part of the Nouvelle-Aquitaine administrative region, it has a land area of 6864 km² and 628,733 inhabitants as of 2012. The important rivers are the Charente and its tributaries, the Boutonne and the Seugne, along with the Sèvre Niortaise, the Seudre, the Garonne, in its downstream part, the estuary of the Gironde; the department includes the islands of Île de Ré, Île d'Aix, Ile d'Oléron, Île Madame. The department forms the northern part of the Aquitaine Basin, it is separated from the Massif Armoricain by the Marais Poitevin to the north-west and from the Parisian basin by the Seuil du Poitou to the north-east. The highest point in the department is in the woods of Chantemerlière, near the commune of Contré in the north-east, rises to 173 m. Charente-Maritime is surrounded by the departments of Gironde, Deux-Sèvres and Vendée; the climate is mild and sunny, with less than 900 mm of precipitation per year and with insolation being remarkably high, in fact, the highest in Western France including southernmost sea resorts such as Biarritz.
Average extreme temperatures vary from 38 °C in summer to−5 °C in winter. The economy of Charente-Maritime is based on three major sectors: tourism, maritime industry, manufacturing. Cognac and pineau are two of the major agricultural products with maize and sunflowers being the others. During the summer months, families flock from all over Europe to bask in the sun and enjoy the local seafood. Royan, popular for its extensive beaches and attractions, is one of the most famous seaside resort of atlantic coast. Charente-Maritime is the headquarters of the major oyster producer Marennes-Oléron. Oysters cultivated here are shipped across Europe. Rochefort is a shipbuilding site and has been a major French naval base since 1665. La Rochelle is a seat of major French industry. Just outside the city is a factory for the French engineering giant Alstom, where the TGV, the cars for the Paris and other metros are manufactured, it is a popular venue for tourism, with its picturesque medieval city walls. The inhabitants of the department are called Charentais-Maritimes.
The President of the General Council is Dominique Bussereau of the Union for a Popular Movement. Popular destinations include, La Rochelle, Saintes, St Jean d'Angely, Rochefort, Île d'Aix, Île de Ré and Île d'Oléron; the department is served by the TGV at La Rochelle. It can be reached by motorway by the A10 and A837. Cantons of the Charente-Maritime department Communes of the Charente-Maritime department Arrondissements of the Charente-Maritime department Éclade des Moules "Charente-Inférieure". Encyclopædia Britannica. 5. 1911. Charente Maritime website News Charente Maritime Official Tourism Guide of Charente-Maritime Official Tourism Guide of Charente-Maritime Charente Maritime News Zoo de la Palmyre Ile d'Oléron Ile de ré Tourisme Ile de re
Duckweeds, or water lenses, are flowering aquatic plants which float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Known as "bayroot", they arose from within the arum or aroid family, so are classified as the subfamily Lemnoideae within the Araceae. Other classifications those created prior to the end of the 20th century, place them as a separate family, Lemnaceae; these plants leaves. The greater part of each plant is a small organized "thallus" or "frond" structure only a few cells thick with air pockets that allow it to float on or just under the water surface. Depending on the species, each plant may have one or more simple rootlets. Reproduction is by asexual budding, which occurs from a meristem enclosed at the base of the frond. Three tiny "flowers" consisting of two stamens and a pistil are produced, by which sexual reproduction occurs; some view this "flower" as a pseudanthium, or reduced inflorescence, with three flowers that are distinctly either female or male and which are derived from the spadix in the Araceae.
Evolution of the duckweed inflorescence remains ambiguous due to the considerable evolutionary reduction of these plants from their earlier relatives. The flower of the duckweed genus Wolffia is the smallest known, measuring 0.3 mm long. The fruit produced through this occasional reproduction is a utricle, a seed is produced in a bag containing air that facilitates flotation. One of the more important factors influencing the distribution of wetland plants, aquatic plants in particular, is nutrient availability. Duckweeds tend to be associated with fertile eutrophic conditions, they can be spread by waterfowl and small mammals, transported inadvertently on their feet and bodies, as well as by moving water. In water bodies with constant currents or overflow, the plants are carried down the water channels and do not proliferate greatly. In some locations, a cyclical pattern driven by weather patterns exists in which the plants proliferate during low water-flow periods are carried away as rainy periods ensue.
Duckweed is an important high-protein food source for waterfowl. The tiny plants provide cover for fry of many aquatic species; the plants are used as shelter by pond-water species such as bullfrogs and fish such as bluegills. They provide shade and, although confused with them, can reduce certain light-generated growths of photoautotrophic algae. Duckweed is eaten by humans in some parts of Southeast Asia; as it contains more protein than soybeans, it is sometimes cited as a significant potential food source. Some initial investigations to what extent duckweed could be introduced in European markets show little consumer objection to the idea; the plants can provide nitrate removal, if cropped, the duckweeds are important in the process of bioremediation because they grow absorbing excess mineral nutrients nitrogen and phosphates. For these reasons, they are touted as water purifiers of untapped value; the Swiss Department of Water and Sanitation in Developing Countries, associated with the Swiss Federal Institute for Environmental Science and Technology, asserts that as well as the food and agricultural values, duckweed may be used for wastewater treatment to capture toxins and for odor control, that if a mat of duckweed is maintained during harvesting for removal of the toxins captured thereby, it prevents the development of algae and controls the breeding of mosquitoes.
The same publication provides an extensive list of references for many duckweed-related topics. These plants may play a role in conservation of water because a cover of duckweed will reduce evaporation of water when compared to the rate of a sized water body with a clear surface. Despite some of these benefits, because duckweed thrives in high-nutrient wetland environments, they can be seen as a nuisance species when conditions allow them to excessively proliferate in environments that are traditionally low in nutrients; this is the case within the Everglades, where surface runoff and agricultural pollution have introduced increased levels of nutrients into an otherwise low-nutrient wetland system, which allows fast growing species such as duckweed to establish themselves and displace other native species such as sawgrass. The duckweeds have long been a taxonomic mystery, have been considered to be their own family, the Lemnaceae, they reproduce asexually. Flowers, if present at all, are small.
Roots are either much reduced, or absent entirely. They were suspected of being related to the Araceae as long ago as 1876, but until the advent of molecular phylogeny, testing this hypothesis was difficult. Starting in 1995, studies began to confirm their placement in the Araceae and since most systematists consider them to be part of that family, their position within their family has been less clear, but several 21st-century studies place them in the position shown below. They are not related to Pistia, an aquatic plant in the family Araceae; the genera of duckweeds are: Spirodela, Lemna and Wolffia. Duckweed genome sizes have a 10-fold range representing diploids to octaploids; the ancestral genus of Spirodela has the smallest genome size, while the most derived genus, contains plants with the largest genome size. DNA sequencing has shown that Wolffiella and Wolffia are more related than the others. Spirodela is at the basal position of the taxon, followed by Lemna, Wo
Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known