The rainbow trout is a trout and species of salmonid native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead is an anadromous form of the coastal rainbow trout or Columbia River redband trout that returns to fresh water to spawn after living two to three years in the ocean. Freshwater forms that have been introduced into the Great Lakes and migrate into tributaries to spawn are called steelhead. Adult freshwater stream rainbow trout average between 1 and 5 lb, while lake-dwelling and anadromous forms may reach 20 lb. Coloration varies based on subspecies and habitat. Adult fish are distinguished by a broad reddish stripe along the lateral line, from gills to the tail, most vivid in breeding males. Wild-caught and hatchery-reared forms of this species have been transplanted and introduced for food or sport in at least 45 countries and every continent except Antarctica. Introductions to locations outside their native range in the United States, Southern Europe, New Zealand and South America have damaged native fish species.
Introduced populations may affect native species by preying on them, out-competing them, transmitting contagious diseases, or hybridizing with related species and subspecies, thus reducing genetic purity. The rainbow trout is included in the list of the top 100 globally invasive species. Nonetheless, other introductions into waters devoid of any fish species or with depleted stocks of native fish have created sport fisheries such as the Great Lakes and Wyoming's Firehole River; some local populations of specific subspecies, or in the case of steelhead, distinct population segments, are listed as either threatened or endangered under the Endangered Species Act. The steelhead is the official state fish of Washington; the scientific name of the rainbow trout is Oncorhynchus mykiss. The species was named by German naturalist and taxonomist Johann Julius Walbaum in 1792 based on type specimens from the Kamchatka Peninsula in Siberia. Walbaum's original species name, was derived from the local Kamchatkan name used for the fish, mykizha.
The name of the genus is from the Greek onkos and rynchos, in reference to the hooked jaws of males in the mating season. Sir John Richardson, a Scottish naturalist, named a specimen of this species Salmo gairdneri in 1836 to honor Meredith Gairdner, a Hudson's Bay Company surgeon at Fort Vancouver on the Columbia River who provided Richardson with specimens. In 1855, William P. Gibbons, the curator of Geology and Mineralogy at the California Academy of Sciences, found a population and named it Salmo iridia corrected to Salmo irideus; these names faded once it was determined that Walbaum's description of type specimens was conspecific and therefore had precedence. In 1989, morphological and genetic studies indicated that trout of the Pacific basin were genetically closer to Pacific salmon than to the Salmos – brown trout or Atlantic salmon of the Atlantic basin. Thus, in 1989, taxonomic authorities moved the rainbow and other Pacific basin trout into the genus Oncorhynchus. Walbaum's name had precedence, so the species name Oncorhynchus mykiss became the scientific name of the rainbow trout.
The previous species names irideus and gairdneri were adopted as subspecies names for the coastal rainbow and Columbia River redband trout, respectively. Anadromous forms of the coastal rainbow trout or redband trout are known as steelhead. Subspecies of Oncorhynchus mykiss are listed below as described by fisheries biologist Robert J. Behnke. Resident freshwater rainbow trout adults average between 1 and 5 lb in riverine environments, while lake-dwelling and anadromous forms may reach 20 lb. Coloration varies between regions and subspecies. Adult freshwater forms are blue-green or olive green with heavy black spotting over the length of the body. Adult fish have a broad reddish stripe along the lateral line, from gills to the tail, most pronounced in breeding males; the caudal fin is only mildly forked. Lake-dwelling and anadromous forms are more silvery in color with the reddish stripe completely gone. Juvenile rainbow trout display parr marks typical of most salmonid juveniles. In some redband and golden trout forms parr marks are retained into adulthood.
Some coastal rainbow trout and Columbia River redband trout populations and cutbow hybrids may display reddish or pink throat markings similar to cutthroat trout. In many regions, hatchery-bred trout can be distinguished from native trout via fin clips. Fin clipping the adipose fin is a management tool used to identify hatchery-reared fish. Rainbow trout, including steelhead forms spawn in early to late spring when water temperatures reach at least 42 to 44 °F; the maximum recorded lifespan for a rainbow trout is 11 years. Freshwater resident rainbow trout inhabit and spawn in small to moderately large, well oxygenated, shallow rivers with gravel bottoms, they are native to the alluvial or freestone streams that are typical tributaries of the Pacific basin, but introduced rainbow trout have established wild, self-sustaining populations in other river types such as bedrock and spring creeks. Lake resident rainbow trout are found in moderately deep, cool lakes with
National monument (United States)
In the United States, a national monument is a protected area, similar to a national park, but can be created from any land owned or controlled by the federal government by proclamation of the President of the United States. National monuments can be managed by one of several federal agencies: the National Park Service, United States Forest Service, United States Fish and Wildlife Service, the Bureau of Land Management, or the National Oceanic and Atmospheric Administration; some national monuments were managed by the War Department. National monuments can be so designated through the power of the Antiquities Act of 1906. President Theodore Roosevelt used the act to declare Devils Tower in Wyoming as the first U. S. national monument. The Antiquities Act of 1906 resulted from concerns about protecting prehistoric Native American ruins and artifacts on federal lands in the American West; the Act authorized permits for legitimate archaeological investigations and penalties for taking or destroying antiquities without permission.
Additionally, it authorized the president to proclaim "historic landmarks and prehistoric structures, other objects of historic or scientific interest" on federal lands as national monuments, "the limits of which in all cases shall be confined to the smallest area compatible with the proper care and management of the objects to be protected."The reference in the act to "objects of...scientific interest" enabled President Theodore Roosevelt to make a natural geological feature, Devils Tower in Wyoming, the first national monument three months later. Among the next three monuments he proclaimed in 1906 was Petrified Forest in Arizona, another natural feature. In 1908, Roosevelt used the act to proclaim more than 800,000 acres of the Grand Canyon as a national monument. In 1918, President Woodrow Wilson proclaimed Katmai National Monument in Alaska, comprising more than 1,000,000 acres. Katmai was enlarged to nearly 2,800,000 acres by subsequent Antiquities Act proclamations and for many years was the largest national park system unit.
Petrified Forest, Grand Canyon, Great Sand Dunes were originally proclaimed as national monuments and designated as national parks by Congress. In response to Roosevelt's declaration of the Grand Canyon monument, a putative mining claimant sued in federal court, claiming that Roosevelt had overstepped the Antiquities Act authority by protecting an entire canyon. In 1920, the United States Supreme Court ruled unanimously that the Grand Canyon was indeed "an object of historic or scientific interest" and could be protected by proclamation, setting a precedent for the use of the Antiquities Act to preserve large areas. Federal courts have since rejected every challenge to the president's use of Antiquities Act preservation authority, ruling that the law gives the president exclusive discretion over the determination of the size and nature of the objects protected. Substantial opposition did not materialize until 1943, when President Franklin D. Roosevelt proclaimed Jackson Hole National Monument in Wyoming.
He did this to accept a donation of lands acquired by John D. Rockefeller, Jr. for addition to Grand Teton National Park after Congress had declined to authorize this park expansion. Roosevelt's proclamation unleashed a storm of criticism about use of the Antiquities Act to circumvent Congress. A bill abolishing Jackson Hole National Monument passed Congress but was vetoed by Roosevelt, Congressional and court challenges to the proclamation authority were mounted. In 1950, Congress incorporated most of the monument into Grand Teton National Park, but the act doing so barred further use of the proclamation authority in Wyoming except for areas of 5,000 acres or less; the most substantial use of the proclamation authority came in 1978, when President Jimmy Carter proclaimed 15 new national monuments in Alaska after Congress had adjourned without passing a major Alaska lands bill opposed in that state. Congress passed a revised version of the bill in 1980 incorporating most of these national monuments into national parks and preserves, but the act curtailed further use of the proclamation authority in Alaska.
The proclamation authority was not used again anywhere until 1996, when President Bill Clinton proclaimed the Grand Staircase-Escalante National Monument in Utah. This action was unpopular in Utah, bills were introduced to further restrict the president's authority. None of which have been enacted. Most of the 16 national monuments created by President Clinton are managed not by the National Park Service, but by the Bureau of Land Management as part of the National Landscape Conservation System. Presidents have used the Antiquities Act's proclamation authority not only to create new national monuments but to enlarge existing ones. For example, Franklin D. Roosevelt enlarged Dinosaur National Monument in 1938. Lyndon B. Johnson added Ellis Island to Statue of Liberty National Monument in 1965, Jimmy Carter made major additions to Glacier Bay and Katmai National Monuments in 1978. On June 24, 2016, President Barack Obama designated the Stonewall Inn and surrounding areas in Greenwich Village, New York as the Stonewall National Monument, the first national monument commemorating the struggle for LGBT rights in the United States.
List of U. S. National Forests List of areas in the United States National Park System List of U. S. wilderness areas Protected areas of the United States List of proposed national monuments of the United States National monument proclamations under the Antiquities Act Congressional Research Service reports regar
Deer are the hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk, the fallow deer, the chital. Female reindeer, male deer of all species except the Chinese water deer and shed new antlers each year. In this they differ from permanently horned antelope, which are part of a different family within the same order of even-toed ungulates; the musk deer of Asia and chevrotains of tropical African and Asian forests are separate families within the ruminant clade. They are no more related to deer than are other even-toed ungulates. Deer appear in art from Paleolithic cave paintings onwards, they have played a role in mythology and literature throughout history, as well as in heraldry, their economic importance includes the use of their meat as venison, their skins as soft, strong buckskin, their antlers as handles for knives. Deer hunting has been a popular activity since at least the Middle Ages and remains a resource for many families today.
Deer live in a variety of biomes. While associated with forests, many deer are ecotone species that live in transitional areas between forests and thickets and prairie and savanna; the majority of large deer species inhabit temperate mixed deciduous forest, mountain mixed coniferous forest, tropical seasonal/dry forest, savanna habitats around the world. Clearing open areas within forests to some extent may benefit deer populations by exposing the understory and allowing the types of grasses and herbs to grow that deer like to eat. Additionally, access to adjacent croplands may benefit deer. However, adequate forest or brush cover must still be provided for populations to thrive. Deer are distributed, with indigenous representatives in all continents except Antarctica and Australia, though Africa has only one native deer, the Barbary stag, a subspecies of red deer, confined to the Atlas Mountains in the northwest of the continent. However, fallow deer have been introduced to South Africa. Small species of brocket deer and pudús of Central and South America, muntjacs of Asia occupy dense forests and are less seen in open spaces, with the possible exception of the Indian muntjac.
There are several species of deer that are specialized, live exclusively in mountains, swamps, "wet" savannas, or riparian corridors surrounded by deserts. Some deer have a circumpolar distribution in Eurasia. Examples include the caribou that live in Arctic tundra and taiga and moose that inhabit taiga and adjacent areas. Huemul deer of South America's Andes fill the ecological niches of the ibex and wild goat, with the fawns behaving more like goat kids; the highest concentration of large deer species in temperate North America lies in the Canadian Rocky Mountain and Columbia Mountain regions between Alberta and British Columbia where all five North American deer species can be found. This region has several clusters of national parks including Mount Revelstoke National Park, Glacier National Park, Yoho National Park, Kootenay National Park on the British Columbia side, Banff National Park, Jasper National Park, Glacier National Park on the Alberta and Montana sides. Mountain slope habitats vary from moist coniferous/mixed forested habitats to dry subalpine/pine forests with alpine meadows higher up.
The foothills and river valleys between the mountain ranges provide a mosaic of cropland and deciduous parklands. The rare woodland caribou have the most restricted range living at higher altitudes in the subalpine meadows and alpine tundra areas of some of the mountain ranges. Elk and mule deer both migrate between the alpine meadows and lower coniferous forests and tend to be most common in this region. Elk inhabit river valley bottomlands, which they share with White-tailed deer; the White-tailed deer have expanded their range within the foothills and river valley bottoms of the Canadian Rockies owing to conversion of land to cropland and the clearing of coniferous forests allowing more deciduous vegetation to grow up the mountain slopes. They live in the aspen parklands north of Calgary and Edmonton, where they share habitat with the moose; the adjacent Great Plains grassland habitats are left to herds of elk, American bison, pronghorn antelope. The Eurasian Continent boasts the most species of deer in the world, with most species being found in Asia.
Europe, in comparison, has lower diversity in animal species. However, many national parks and protected reserves in Europe do have populations of red deer, roe deer, fallow deer; these species have long been associated with the continent of Europe, but inhabit Asia Minor, the Caucasus Mountains, Northwestern Iran. "European" fallow deer lived over much of Europe during the Ice Ages, but afterwards became restricted to the Anatolian Peninsula, in present-day Turkey. Present-day fallow deer populations in Europe are a result of historic man-made introductions of this species, first to the Mediterranean regions of Europe eventually to the rest of Europe, they were park animals that escaped and reestablished themselves in the wild. Europe's deer species shared their deciduous forest habitat with other herbivores, such as the extinct tarpan, extinct aurochs (fo
International Union for Conservation of Nature
The International Union for Conservation of Nature is an international organization working in the field of nature conservation and sustainable use of natural resources. It is involved in data gathering and analysis, field projects and education. IUCN's mission is to "influence and assist societies throughout the world to conserve nature and to ensure that any use of natural resources is equitable and ecologically sustainable". Over the past decades, IUCN has widened its focus beyond conservation ecology and now incorporates issues related to sustainable development in its projects. Unlike many other international environmental organisations, IUCN does not itself aim to mobilize the public in support of nature conservation, it tries to influence the actions of governments and other stakeholders by providing information and advice, through building partnerships. The organization is best known to the wider public for compiling and publishing the IUCN Red List of Threatened Species, which assesses the conservation status of species worldwide.
IUCN has a membership of over 1400 non-governmental organizations. Some 16,000 scientists and experts participate in the work of IUCN commissions on a voluntary basis, it employs 1000 full-time staff in more than 50 countries. Its headquarters are in Switzerland. IUCN has observer and consultative status at the United Nations, plays a role in the implementation of several international conventions on nature conservation and biodiversity, it was involved in establishing the World Wide Fund for Nature and the World Conservation Monitoring Centre. In the past, IUCN has been criticized for placing the interests of nature over those of indigenous peoples. In recent years, its closer relations with the business sector have caused controversy. IUCN was established in 1948, it was called the International Union for the Protection of Nature and the World Conservation Union. Establishment IUCN was established on 5 October 1948, in Fontainebleau, when representatives of governments and conservation organizations signed a formal act constituting the International Union for the Protection of Nature.
The initiative to set up the new organisation came from UNESCO and from its first Director General, the British biologist Julian Huxley. The objectives of the new Union were to encourage international cooperation in the protection of nature, to promote national and international action and to compile and distribute information. At the time of its founding IUPN was the only international organisation focusing on the entire spectrum of nature conservation Early years: 1948–1956 IUPN started out with 65 members, its secretariat was located in Brussels. Its first work program focused on saving species and habitats and applying knowledge, advancing education, promoting international agreements and promoting conservation. Providing a solid scientific base for conservation action was the heart of all activities. IUPN and UNESCO were associated, they jointly organized the 1949 Conference on Protection of Nature. In preparation for this conference a list of gravely endangered species was drawn up for the first time, a precursor of the IUCN Red List of Threatened Species.
In the early years of its existence IUCN depended entirely on UNESCO funding and was forced to temporarily scale down activities when this ended unexpectedly in 1954. IUPN was successful in engaging prominent scientists and identifying important issues such as the harmful effects of pesticides on wildlife but not many of the ideas it developed were turned into action; this was caused by unwillingness to act on the part of governments, uncertainty about the IUPN mandate and lack of resources. In 1956, IUPN changed its name to International Union for Conservation of Nature and Natural Resources. Increased profile and recognition: 1956–1965 In the 1950s and 1960s Europe entered a period of economic growth and formal colonies became independent. Both developments had impact on the work of IUCN. Through the voluntary involvement of experts in its Commissions IUCN was able to get a lot of work done while still operating on a low budget, it established links with the Council of Europe. In 1961, at the request of United Nations Economic and Social Council, the United Nations Economic and Social Council, IUCN published the first global list of national parks and protected areas which it has updated since.
IUCN's best known publication, the Red Data Book on the conservation status of species, was first published in 1964. IUCN began to play a part in the development of international treaties and conventions, starting with the African Convention on the Conservation of Nature and Natural Resources. Environmental law and policy making became a new area of expertise. Africa was the focus of many of the early IUCN conservation field projects. IUCN supported the ‘Yellowstone model’ of protected area management, which restricted human presence and activity in order to protect nature. IUCN and other conservation organisations were criticized for protecting nature against people rather than with people; this model was also applied in Africa and played a role in the decision to remove the Maasai people from Serengeti National Park and the Ngorongoro Conservation Area. To establish a stable financial basis for its work, IUCN participated in setting up the World Wildlife Fund
The elk or wapiti is one of the largest species within the deer family and one of the largest terrestrial mammals in North America and Northeast Asia. This animal should not be confused with the still larger moose to which the name "elk" applies in British English and in reference to populations in Eurasia. Elk range in forest and forest-edge habitat, feeding on grasses, plants and bark. Male elk have large antlers. Males engage in ritualized mating behaviors during the rut, including posturing, antler wrestling, bugling, a loud series of vocalizations that establishes dominance over other males and attracts females. Although they are native to North America and eastern Asia, they have adapted well to countries in which they have been introduced, including Argentina and New Zealand, their great adaptability may threaten endemic species and ecosystems into which they have been introduced. Elk are susceptible to a number of infectious diseases, some of which can be transmitted to livestock. Efforts to eliminate infectious diseases from elk populations by vaccination, have had mixed success.
Some cultures revere the elk as a spiritual force. In parts of Asia and their velvet are used in traditional medicines. Elk are hunted as a game species; the meat is higher in protein than beef or chicken. Elk were long believed to belong to a subspecies of the European red deer, but evidence from many mitochondrial DNA genetic studies beginning in 1998 shows that the two are distinct species. Key morphological differences that distinguish C. canadensis from C. elaphus are the former's wider rump patch and paler-hued antlers. Early European explorers in North America, who were familiar with the smaller red deer of Europe, thought that the larger North American animal resembled a moose, gave it the name elk, the common European name for moose; the word elk is related to the Latin alces, Old Norse elgr, Scandinavian elg/älg and German Elch, all of which refer to the animal known in North America as the moose. The name wapiti is from the Shawnee and Cree word waapiti, meaning "white rump"; this name is used in particular for the Asian subspecies, because in Eurasia the name elk continues to be used for the moose.
Wapiti is the preferred name for the species in New Zealand. Asian subspecies are sometimes referred to as the maral, but this name applies to the Caspian red deer, a subspecies of red deer. There is a subspecies of elk in Mongolia called the Altai wapiti known as the Altai maral. Members of the genus Cervus first appear in the fossil record 25 million years ago, during the Oligocene in Eurasia, but do not appear in the North American fossil record until the early Miocene; the extinct Irish elk was not a member of the genus Cervus, but rather the largest member of the wider deer family known from the fossil record. Until red deer and elk were considered to be one species, Cervus elaphus. However, mitochondrial DNA studies, conducted on hundreds of samples in 2004 from red deer and elk subspecies as well as other species of the Cervus deer family indicate that elk, or wapiti, should be a distinct species, namely Cervus canadensis; the previous classification had over a dozen subspecies under the C. elaphus species designation.
Elk and red deer produce fertile offspring in captivity, the two species have inter-bred in New Zealand's Fiordland National Park, where the cross-bred animals have all but removed the pure elk blood from the area. There are numerous subspecies of elk described, with six from North America and four from Asia, although some taxonomists consider them different ecotypes or races of the same species. Populations vary as to antler shape and size, body size and mating behavior. DNA investigations of the Eurasian subspecies revealed that phenotypic variation in antlers and rump patch development are based on "climatic-related lifestyle factors". Of the six subspecies of elk known to have inhabited North America in historical times, four remain, including the Roosevelt, Tule and Rocky Mountain; the Eastern elk and Merriam's elk subspecies have been extinct for at least a century. Four subspecies described in Asia include the Tianshan wapiti. Two distinct subspecies found in China and Korea are the Alashan wapitis.
The Manchurian wapiti is more reddish in coloration than the other populations. The Alashan wapiti of north central China is the smallest of all subspecies, has the lightest coloration and is the least studied. Biologist Valerius Geist, who has written on the world's various deer species, holds that there are only three subspecies of elk. Geist recognizes the Manchurian and Alashan wapiti but places all other elk into C. canadensis canadensis, claiming that classification of the four surviving North American groups as subspecies is driven, at least for political purposes to secure individualized conservation and protective measures for each of the surviving populations. Recent DNA studies suggest
Malheur National Forest
The Malheur National Forest is a National Forest in the U. S. state of Oregon. It contains more than 1.4 million acres in the Blue Mountains of eastern Oregon. The forest consists of high desert grasslands, juniper, pine and other tree species. Elevations vary from about 4,000 feet to the 9,038-foot peak of Strawberry Mountain; the Strawberry Mountains extend east to west through the center of the forest. U. S. Route 395 runs south to north through the forest, while U. S. Route 26 runs east to west; the forest was established by President Theodore Roosevelt on June 13, 1908, is named after the Malheur River, from the French, meaning "misfortune". It is managed by the United States Forest Service for timber extraction, cattle grazing, gold mining and wilderness use. A 1993 Forest Service study estimated. In descending order of land area, the forest is located in parts of Grant, Harney and Malheur counties. There are three ranger districts in the forest, with offices in John Day, Prairie City, Hines.
The Malheur National Forest contains the largest known organism in the world: an Armillaria solidipes that spans 2,200 acres. There are two wilderness areas in the Malheur National Forest. Strawberry Mountain Wilderness at 68,700 acres Monument Rock Wilderness at 19,620 acres, located within the Wallowa–Whitman National Forest Vinegar Hill-Indian Rock Scenic Area, a high-elevation scenic area in the northeast portion of the forest Malheur National Wildlife Refuge, a federally protected refuge to the south of the forest Malheur National Forest home page Cedar Grove Botanical Area
Basalt is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows. By definition, basalt is an aphanitic igneous rock with 45–53% silica and less than 10% feldspathoid by volume, where at least 65% of the rock is feldspar in the form of plagioclase; this is as per definition of the International Union of Geological Sciences classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaiʻi. Basalt features a fine-grained or glassy matrix interspersed with visible mineral grains.
The average density is 3.0 g/cm3. Basalt is defined by its mineral content and texture, physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is grey to black in colour, but weathers to brown or rust-red due to oxidation of its mafic minerals into hematite and other iron oxides and hydroxides. Although characterized as "dark", basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured, superficially resembling andesite to untrained eyes. Basalt has a fine-grained mineral texture due to the molten rock cooling too for large mineral crystals to grow; these phenocrysts are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a vesicular texture is called vesicular basalt, when the bulk of the rock is solid; this texture forms when dissolved gases come out of solution and form bubbles as the magma decompresses as it reaches the surface, yet are trapped as the erupted lava hardens before the gases can escape.
The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic groundmass are referred to as diabase or, when more coarse-grained, as gabbro. Gabbro is marketed commercially as "black granite." In the Hadean and early Proterozoic eras of Earth's history, the chemistry of erupted magmas was different from today's, due to immature crustal and asthenosphere differentiation. These ultramafic volcanic rocks, with silica contents below 45% are classified as komatiites; the word "basalt" is derived from Late Latin basaltes, a misspelling of Latin basanites "very hard stone", imported from Ancient Greek βασανίτης, from βάσανος and originated in Egyptian bauhun "slate". The modern petrological term basalt describing a particular composition of lava-derived rock originates from its use by Georgius Agricola in 1556 in his famous work of mining and mineralogy De re metallica, libri XII. Agricola applied "basalt" to the volcanic black rock of the Schloßberg at Stolpen, believing it to be the same as the "very hard stone" described by Pliny the Elder in Naturalis Historiae.
Tholeiitic basalt is rich in silica and poor in sodium. Included in this category are most basalts of the ocean floor, most large oceanic islands, continental flood basalts such as the Columbia River Plateau. High and low titanium basalts. Basalt rocks are in some cases classified after their titanium content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and the Emeishan Traps. Mid-ocean ridge basalt is a tholeiitic basalt erupted only at ocean ridges and is characteristically low in incompatible elements. E-MORB, enriched MORB N-MORB, normal MORB D-MORB, depleted MORB High-alumina basalt may be silica-undersaturated or -oversaturated, it has greater than 17% alumina and is intermediate in composition between tholeiitic basalt and alkali basalt. Alkali basalt is poor in silica and rich in sodium, it may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a high-magnesium form of basalt, erupted in back-arc basins, distinguished by its low titanium content and trace-element composition.
Ocean island basalt Lunar basalt The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene. Olivine can be a significant constituent. Accessory minerals present in minor amounts include iron oxides and iron-titanium oxides, such as magnetite and ilmenite; because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, paleomagnetic studies have made extensive use of basalt. In tholeiitic basalt and calcium-rich plagioclase are common phenocryst minerals. Olivine may be a phenocryst, when