Pollination
Pollination is the transfer of pollen from a male part of a plant to a female part of a plant enabling fertilisation and the production of seeds, most by an animal or by wind. Pollinating agents are animals such as insects and bats. Pollination occurs within a species; when pollination occurs between species it can produce hybrid offspring in nature and in plant breeding work. In angiosperms, after the pollen grain has landed on the stigma, it develops a pollen tube which grows down the style until it reaches an ovary. Sperm cells from the pollen grain move along the pollen tube, enter an ovum cell through the micropyle and fertilise it, resulting in the production of a seed. A successful angiosperm pollen grain containing the male gametes is transported to the stigma, where it germinates and its pollen tube grows down the style to the ovary, its two gametes travel down the tube to where the gametophyte containing the female gametes are held within the carpel. One nucleus fuses with the polar bodies to produce the endosperm tissues, the other with the ovule to produce the embryo Hence the term: "double fertilization".
In gymnosperms, the ovule is not contained in a carpel, but exposed on the surface of a dedicated support organ, such as the scale of a cone, so that the penetration of carpel tissue is unnecessary. Details of the process vary according to the division of gymnosperms in question. Two main modes of fertilization are found in gymnosperms. Cycads and Ginkgo have motile sperm that swim directly to the egg inside the ovule, whereas conifers and gnetophytes have sperm that are unable to swim but are conveyed to the egg along a pollen tube; the study of pollination brings together many disciplines, such as botany, horticulture and ecology. The pollination process as an interaction between flower and pollen vector was first addressed in the 18th century by Christian Konrad Sprengel, it is important in horticulture and agriculture, because fruiting is dependent on fertilization: the result of pollination. The study of pollination by insects is known as anthecology. Pollen germination has three stages; the pollen grain is dehydrated so that its mass is reduced enabling it to be more transported from flower to flower.
Germination only takes place after rehydration, ensuring that premature germination does not take place in the anther. Hydration allows the plasma membrane of the pollen grain to reform into its normal bilayer organization providing an effective osmotic membrane. Activation involves the development of actin filaments throughout the cytoplasm of the cell, which become concentrated at the point from which the pollen tube will emerge. Hydration and activation continue. In conifers, the reproductive structures are borne on cones; the cones are either pollen cones or ovulate cones, but some species are monoecious and others dioecious. A pollen cone contains hundreds of microsporangia carried on reproductive structures called sporophylls. Spore mother cells in the microsporangia divide by meiosis to form haploid microspores that develop further by two mitotic divisions into immature male gametophytes; the four resulting cells consist of a large tube cell that forms the pollen tube, a generative cell that will produce two sperm by mitosis, two prothallial cells that degenerate.
These cells comprise a reduced microgametophyte, contained within the resistant wall of the pollen grain. The pollen grains are dispersed by the wind to the female, ovulate cone, made up of many overlapping scales, each protecting two ovules, each of which consists of a megasporangium wrapped in two layers of tissue, the integument and the cupule, that were derived from modified branches of ancestral gymnosperms; when a pollen grain lands close enough to the tip of an ovule, it is drawn in through the micropyle by means of a drop of liquid known as a pollination drop. The pollen enters a pollen chamber close to the nucellus, there it may wait for a year before it germinates and forms a pollen tube that grows through the wall of the megasporangium where fertilisation takes place. During this time, the megaspore mother cell divides by meiosis to form four haploid cells, three of which degenerate; the surviving one develops as a megaspore and divides to form an immature female gametophyte. Two or three archegonia containing an egg develop inside the gametophyte.
Meanwhile, in the spring of the second year two sperm cells are produced by mitosis of the body cell of the male gametophyte. The pollen tube elongates and pierces and grows through the megasporangium wall and delivers the sperm cells to the female gametophyte inside. Fertilisation takes place when the nucleus of one of the sperm cells enters the egg cell in the megagametophyte’s archegonium. In flowering plants, the anthers of the flower produce microspores by meiosis; these undergo mitosis to form male gametophytes. Meanwhile, the ovules produce megaspores by meiosis, further division of these form the female gametophytes, which are strongly reduced, each consisting only of a few cells, one of, the egg; when a pollen grain adheres to the stigma of a carpel it germinates, developing a pollen tube that grows through the tissues of the style, entering the ovule through the micropyle. When the tube reaches the egg sac, two sperm cells pass through it into the female gametophyte and fertil
Latin America
Latin America is a group of countries and dependencies in the Western Hemisphere where Romance languages such as Spanish and French are predominantly spoken. The term "Latin America" was first used in an 1856 conference with the title "Initiative of the America. Idea for a Federal Congress of the Republics", by the Chilean politician Francisco Bilbao; the term was used by Napoleon III's French government in the 1860s as Amérique latine to consider French-speaking territories in the Americas, along with the larger group of countries where Spanish and Portuguese languages prevailed, including the Spanish-speaking portions of the United States Today, areas of Canada and the United States where Spanish and French are predominant are not included in definitions of Latin America. Latin America consists of 13 dependencies and 20 countries which cover an area that stretches from the northern border of Mexico to the southern tip of South America, including the Caribbean, it has an area of 19,197,000 km2 13% of the Earth's land surface area.
As of 2016, its population was estimated at more than 639 million and in 2014, Latin America had a combined nominal GDP of US$5,573,397 million and a GDP PPP of 7,531,585 million USD. The idea that a part of the Americas has a linguistic affinity with the Romance cultures as a whole can be traced back to the 1830s, in the writing of the French Saint-Simonian Michel Chevalier, who postulated that this part of the Americas was inhabited by people of a "Latin race", that it could, ally itself with "Latin Europe" overlapping the Latin Church, in a struggle with "Teutonic Europe", "Anglo-Saxon America" and "Slavic Europe". Further investigations of the concept of Latin America are by Michel Gobat in the American Historical Review, the studies of Leslie Bethell, the monograph by Mauricio Tenorio-Trillo, Latin America: The Allure and Power of an Idea. Historian John Leddy Phelan (located the origins of “Latin America” in the French occupation of Mexico, his argument is that French imperialists used the concept of "Latin" America as a way to counter British imperialism, as well as to challenge the German threat to France.
The idea of a "Latin race" was taken up by Latin American intellectuals and political leaders of the mid- and late-nineteenth century, who no longer looked to Spain or Portugal as cultural models, but rather to France. French ruler Napoleon III had a strong interest in extending French commercial and political power in the region he and his business promoter Felix Belly called “Latin America” to emphasize the shared Latin background of France with the former colonies of Spain and Portugal; this led to Napoleon's failed attempt to take military control of Mexico in the 1860s. However, though Phelan thesis is still mentioned in the U. S. academy, two Latin American historians, the Uruguayan Arturo Ardao and the Chilean Miguel Rojas Mix proved decades ago that the term "Latin America" was used earlier than Phelan claimed, the first use of the term was opposite to support imperialist projects in the Americas. Ardao wrote about this subject in his book Génesis de la idea y el nombre de América latina, Miguel Rojas Mix in his article "Bilbao y el hallazgo de América latina: Unión continental, socialista y libertaria".
As Michel Gobat reminds in his article "The Invention of Latin America: A Transnational History of Anti-Imperialism and Race", "Arturo Ardao, Miguel Rojas Mix, Aims McGuinness have revealed the term'Latin America' had been used in 1856 by Central and South Americans protesting U. S. expansion into the Southern Hemisphere". Edward Shawcross summarizes Ardao's and Rojas Mix's findings in the following way: "Ardao identified the term in a poem by a Colombian diplomat and intellectual resident in France, José María Torres Caicedo, published on 15 February 1857 in a French based Spanish-language newspaper, while Rojas Mix located it in a speech delivered in France by the radical liberal Chilean politician Francisco Bilbao in June 1856". So, regarding when the words "Latin" and "America" were combined for the first time in a printed work, the term "Latin America" was first used in 1856 in a conference by the Chilean politician Francisco Bilbao in Paris; the conference had the title "Initiative of the America.
Idea for a Federal Congress of Republics." The following year the Colombian writer José María Torres Caicedo used the term in his poem "The Two Americas". Two events related with the U. S. played a central role in both works. The first event happened less than a decade before the publication of Bilbao's and Torres Caicedo works: the Mexican–American War, after which Mexico lost a third of its territory; the second event, the Walker affair, happened the same year both works were written: the decision by U. S. president Franklin Pierce to recognize the regime established in Nicaragua by American William Walker and his band of filibusters who ruled Nicaragua for nearly a year and attempted to reinstate slavery there, where it had been abolished for three decades In both Bilbao's and Torres Caicedo's works, the Mexican-American War and Walker's expedition to Nicaragua are explicitly mentioned as examples of dangers for the region. For Bilbao, "Latin America" w
Mexico
Mexico the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States. Covering 2,000,000 square kilometres, the nation is the fifth largest country in the Americas by total area and the 13th largest independent state in the world. With an estimated population of over 120 million people, the country is the eleventh most populous state and the most populous Spanish-speaking state in the world, while being the second most populous nation in Latin America after Brazil. Mexico is a federation comprising 31 states and Mexico City, a special federal entity, the capital city and its most populous city. Other metropolises in the state include Guadalajara, Puebla, Tijuana and León. Pre-Columbian Mexico dates to about 8000 BC and is identified as one of five cradles of civilization and was home to many advanced Mesoamerican civilizations such as the Olmec, Teotihuacan, Zapotec and Aztec before first contact with Europeans. In 1521, the Spanish Empire conquered and colonized the territory from its politically powerful base in Mexico-Tenochtitlan, administered as the viceroyalty of New Spain.
Three centuries the territory became a nation state following its recognition in 1821 after the Mexican War of Independence. The post-independence period was tumultuous, characterized by economic inequality and many contrasting political changes; the Mexican–American War led to a territorial cession of the extant northern territories to the United States. The Pastry War, the Franco-Mexican War, a civil war, two empires, the Porfiriato occurred in the 19th century; the Porfiriato was ended by the start of the Mexican Revolution in 1910, which culminated with the promulgation of the 1917 Constitution and the emergence of the country's current political system as a federal, democratic republic. Mexico has the 11th largest by purchasing power parity; the Mexican economy is linked to those of its 1994 North American Free Trade Agreement partners the United States. In 1994, Mexico became the first Latin American member of the Organisation for Economic Co-operation and Development, it is classified as an upper-middle income country by the World Bank and a newly industrialized country by several analysts.
The country is considered both a regional power and a middle power, is identified as an emerging global power. Due to its rich culture and history, Mexico ranks first in the Americas and seventh in the world for number of UNESCO World Heritage Sites. Mexico is an ecologically megadiverse country, ranking fourth in the world for its biodiversity. Mexico receives a huge number of tourists every year: in 2018, it was the sixth most-visited country in the world, with 39 million international arrivals. Mexico is a member of the United Nations, the World Trade Organization, the G8+5, the G20, the Uniting for Consensus group of the UN, the Pacific Alliance trade bloc. Mēxihco is the Nahuatl term for the heartland of the Aztec Empire, namely the Valley of Mexico and surrounding territories, with its people being known as the Mexica, it is believed to be a toponym for the valley which became the primary ethnonym for the Aztec Triple Alliance as a result, although it could have been the other way around.
In the colonial era, back when Mexico was called New Spain this territory became the Intendency of Mexico and after New Spain achieved independence from the Spanish Empire it came to be known as the State of Mexico with the new country being named after its capital: the City of Mexico, which itself was founded in 1524 on top of the ancient Mexica capital of Mexico-Tenochtitlan. Traditionally, the name Tenochtitlan was thought to come from Nahuatl tetl and nōchtli and is thought to mean "Among the prickly pears rocks". However, one attestation in the late 16th-century manuscript known as "the Bancroft dialogues" suggests the second vowel was short, so that the true etymology remains uncertain; the suffix -co is the Nahuatl locative, making the word a place name. Beyond that, the etymology is uncertain, it has been suggested that it is derived from Mextli or Mēxihtli, a secret name for the god of war and patron of the Mexica, Huitzilopochtli, in which case Mēxihco means "place where Huitzilopochtli lives".
Another hypothesis suggests that Mēxihco derives from a portmanteau of the Nahuatl words for "moon" and navel. This meaning might refer to Tenochtitlan's position in the middle of Lake Texcoco; the system of interconnected lakes, of which Texcoco formed the center, had the form of a rabbit, which the Mesoamericans pareidolically associated with the moon rabbit. Still another hypothesis suggests that the word is derived from Mēctli, the name of the goddess of maguey; the name of the city-state was transliterated to Spanish as México with the phonetic value of the letter x in Medieval Spanish, which represented the voiceless postalveolar fricative. This sound, as well as the voiced postalveolar fricative, represented by a j, evolved into a voiceless velar fricative during the 16th century; this led to the use of the variant Méjico in many publications in Spanish, most notably in Spain, whereas in Mexico and most other Spanish–speaking countries, México was the preferred spelling. In recent years, the Real Academia Española, which regulates the Spanish l
Guatemala
Guatemala the Republic of Guatemala, is a country in Central America bordered by Mexico to the north and west and the Caribbean to the northeast, Honduras to the east, El Salvador to the southeast and the Pacific Ocean to the south. With an estimated population of around 16.6 million, it is the most populated country in Central America. Guatemala is a representative democracy; the territory of modern Guatemala once formed the core of the Maya civilization, which extended across Mesoamerica. Most of the country was conquered by the Spanish in the 16th century, becoming part of the viceroyalty of New Spain. Guatemala attained independence in 1821 as part of the Federal Republic of Central America, which dissolved by 1841. From the mid to late 19th century, Guatemala experienced civil strife. Beginning in the early 20th century, it was ruled by a series of dictators backed by the United Fruit Company and the United States government. In 1944, authoritarian leader Jorge Ubico was overthrown by a pro-democratic military coup, initiating a decade-long revolution that led to sweeping social and economic reforms.
A U. S.-backed military coup in 1954 installed a dictatorship. From 1960 to 1996, Guatemala endured a bloody civil war fought between the US-backed government and leftist rebels, including genocidal massacres of the Maya population perpetrated by the military. Since a United Nations-negotiated peace accord, Guatemala has witnessed both economic growth and successful democratic elections, though it continues to struggle with high rates of poverty, drug trade, instability; as of 2014, Guatemala ranks 31st of 33 Latin American and Caribbean countries in terms of the Human Development Index. Guatemala's abundance of biologically significant and unique ecosystems includes a large number of endemic species and contributes to Mesoamerica's designation as a biodiversity hotspot; the name "Guatemala" comes from the Nahuatl word Cuauhtēmallān, or "place of many trees", a derivative of the K'iche' Mayan word for "many trees" or more for the Cuate/Cuatli tree Eysenhardtia. This was the name the Tlaxcaltecan soldiers who accompanied Pedro de Alvarado during the Spanish Conquest gave to this territory.
The first evidence of human habitation in Guatemala dates back to 12,000 BC. Evidence, such as obsidian arrowheads found in various parts of the country, suggests a human presence as early as 18,000 BC. There is archaeological proof. Pollen samples from Petén and the Pacific coast indicate that maize cultivation had developed by 3500 BC. Sites dating back to 6500 BC have been found in the Quiché region in the Highlands, Sipacate and Escuintla on the central Pacific coast. Archaeologists divide the pre-Columbian history of Mesoamerica into the Preclassic period, the Classic period, the Postclassic period; until the Preclassic was regarded as a formative period, with small villages of farmers who lived in huts, few permanent buildings. However, this notion has been challenged by recent discoveries of monumental architecture from that period, such as an altar in La Blanca, San Marcos, from 1000 BC; the Classic period of Mesoamerican civilization corresponds to the height of the Maya civilization, is represented by countless sites throughout Guatemala, although the largest concentration is in Petén.
This period is characterized by urbanisation, the emergence of independent city-states, contact with other Mesoamerican cultures. This lasted until 900 AD, when the Classic Maya civilization collapsed; the Maya abandoned many of the cities of the central lowlands or were killed off by a drought-induced famine. The cause of the collapse is debated, but the drought theory is gaining currency, supported by evidence such as lakebeds, ancient pollen, others. A series of prolonged droughts, among other reasons such as overpopulation, in what is otherwise a seasonal desert is thought to have decimated the Maya, who relied on regular rainfall; the Post-Classic period is represented by regional kingdoms, such as the Itza, Kowoj and Kejache in Petén, the Mam, Ki'che', Chajoma, Tz'utujil, Poqomchi', Q'eqchi' and Ch'orti' in the highlands. Their cities preserved many aspects of Maya culture; the Maya civilization shares many features with other Mesoamerican civilizations due to the high degree of interaction and cultural diffusion that characterized the region.
Advances such as writing and the calendar did not originate with the Maya. Maya influence can be detected from Honduras, Northern El Salvador to as far north as central Mexico, more than 1,000 km from the Maya area. Many outside influences are found in Maya art and architecture, which are thought to be the result of trade and cultural exchange rather than direct external conquest. After they arrived in the New World, the Spanish started several expeditions to Guatemala, beginning in 1519. Before long, Spanish contact resulted in an epidemic. Hernán Cortés, who had led the Spanish conquest of Mexico, granted a permit to Captains Gonzalo de Alvarado and his brother, Pedro de Alvarado, to conquer this land. Alvarado at first allied himself with the Kaqchikel nation to fight against their traditional rivals the K'iche' nation
New Zealand
New Zealand is a sovereign island country in the southwestern Pacific Ocean. The country geographically comprises two main landmasses—the North Island, the South Island —and around 600 smaller islands. New Zealand is situated some 2,000 kilometres east of Australia across the Tasman Sea and 1,000 kilometres south of the Pacific island areas of New Caledonia and Tonga; because of its remoteness, it was one of the last lands to be settled by humans. During its long period of isolation, New Zealand developed a distinct biodiversity of animal and plant life; the country's varied topography and its sharp mountain peaks, such as the Southern Alps, owe much to the tectonic uplift of land and volcanic eruptions. New Zealand's capital city is Wellington. Sometime between 1250 and 1300, Polynesians settled in the islands that were named New Zealand and developed a distinctive Māori culture. In 1642, Dutch explorer Abel Tasman became the first European to sight New Zealand. In 1840, representatives of the United Kingdom and Māori chiefs signed the Treaty of Waitangi, which declared British sovereignty over the islands.
In 1841, New Zealand became a colony within the British Empire and in 1907 it became a dominion. Today, the majority of New Zealand's population of 4.9 million is of European descent. Reflecting this, New Zealand's culture is derived from Māori and early British settlers, with recent broadening arising from increased immigration; the official languages are English, Māori, NZ Sign Language, with English being dominant. A developed country, New Zealand ranks in international comparisons of national performance, such as quality of life, education, protection of civil liberties, economic freedom. New Zealand underwent major economic changes during the 1980s, which transformed it from a protectionist to a liberalised free-trade economy; the service sector dominates the national economy, followed by the industrial sector, agriculture. Nationally, legislative authority is vested in an elected, unicameral Parliament, while executive political power is exercised by the Cabinet, led by the prime minister Jacinda Ardern.
Queen Elizabeth II is the country's monarch and is represented by a governor-general Dame Patsy Reddy. In addition, New Zealand is organised into 11 regional councils and 67 territorial authorities for local government purposes; the Realm of New Zealand includes Tokelau. New Zealand is a member of the United Nations, Commonwealth of Nations, ANZUS, Organisation for Economic Co-operation and Development, ASEAN Plus Six, Asia-Pacific Economic Cooperation, the Pacific Community and the Pacific Islands Forum. Dutch explorer Abel Tasman sighted New Zealand in 1642 and named it Staten Land "in honour of the States General", he wrote, "it is possible that this land joins to the Staten Land but it is uncertain", referring to a landmass of the same name at the southern tip of South America, discovered by Jacob Le Maire in 1616. In 1645, Dutch cartographers renamed the land Nova Zeelandia after the Dutch province of Zeeland. British explorer James Cook subsequently anglicised the name to New Zealand. Aotearoa is the current Māori name for New Zealand.
It is unknown whether Māori had a name for the whole country before the arrival of Europeans, with Aotearoa referring to just the North Island. Māori had several traditional names for the two main islands, including Te Ika-a-Māui for the North Island and Te Waipounamu or Te Waka o Aoraki for the South Island. Early European maps labelled the islands North and South. In 1830, maps began to use North and South to distinguish the two largest islands and by 1907 this was the accepted norm; the New Zealand Geographic Board discovered in 2009 that the names of the North Island and South Island had never been formalised, names and alternative names were formalised in 2013. This set the names as North Island or Te Ika-a-Māui, South Island or Te Waipounamu. For each island, either its English or Māori name can be used. New Zealand was one of the last major landmasses settled by humans. Radiocarbon dating, evidence of deforestation and mitochondrial DNA variability within Māori populations suggest New Zealand was first settled by Eastern Polynesians between 1250 and 1300, concluding a long series of voyages through the southern Pacific islands.
Over the centuries that followed, these settlers developed a distinct culture now known as Māori. The population was divided into iwi and hapū who would sometimes cooperate, sometimes compete and sometimes fight against each other. At some point a group of Māori migrated to Rēkohu, now known as the Chatham Islands, where they developed their distinct Moriori culture; the Moriori population was all but wiped out between 1835 and 1862 because of Taranaki Māori invasion and enslavement in the 1830s, although European diseases contributed. In 1862 only 101 survived, the last known full-blooded Moriori died in 1933; the first Europeans known to have reached New Zeala
Mountain
A mountain is a large landform that rises above the surrounding land in a limited area in the form of a peak. A mountain is steeper than a hill. Mountains are formed through tectonic forces or volcanism; these forces can locally raise the surface of the earth. Mountains erode through the action of rivers, weather conditions, glaciers. A few mountains are isolated summits. High elevations on mountains produce colder climates than at sea level; these colder climates affect the ecosystems of mountains: different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, such as mountain climbing; the highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m. There is no universally accepted definition of a mountain.
Elevation, relief, steepness and continuity have been used as criteria for defining a mountain. In the Oxford English Dictionary a mountain is defined as "a natural elevation of the earth surface rising more or less abruptly from the surrounding level and attaining an altitude which to the adjacent elevation, is impressive or notable."Whether a landform is called a mountain may depend on local usage. Mount Scott outside Lawton, Oklahoma, USA, is only 251 m from its base to its highest point. Whittow's Dictionary of Physical Geography states "Some authorities regard eminences above 600 metres as mountains, those below being referred to as hills." In the United Kingdom and the Republic of Ireland, a mountain is defined as any summit at least 2,000 feet high, whilst the official UK government's definition of a mountain, for the purposes of access, is a summit of 600 metres or higher. In addition, some definitions include a topographical prominence requirement 100 or 500 feet. At one time the U.
S. Board on Geographic Names defined a mountain as being 1,000 feet or taller, but has abandoned the definition since the 1970s. Any similar landform lower. However, the United States Geological Survey concludes that these terms do not have technical definitions in the US; the UN Environmental Programme's definition of "mountainous environment" includes any of the following: Elevation of at least 2,500 m. Using these definitions, mountains cover 33% of Eurasia, 19% of South America, 24% of North America, 14% of Africa; as a whole, 24% of the Earth's land mass is mountainous. There are three main types of mountains: volcanic and block. All three types are formed from plate tectonics: when portions of the Earth's crust move and dive. Compressional forces, isostatic uplift and intrusion of igneous matter forces surface rock upward, creating a landform higher than the surrounding features; the height of the feature makes it either a hill or, if steeper, a mountain. Major mountains tend to occur in long linear arcs, indicating tectonic plate boundaries and activity.
Volcanoes are formed when a plate is pushed at a mid-ocean ridge or hotspot. At a depth of around 100 km, melting occurs in rock above the slab, forms magma that reaches the surface; when the magma reaches the surface, it builds a volcanic mountain, such as a shield volcano or a stratovolcano. Examples of volcanoes include Mount Pinatubo in the Philippines; the magma does not have to reach the surface in order to create a mountain: magma that solidifies below ground can still form dome mountains, such as Navajo Mountain in the US. Fold mountains occur when two plates collide: shortening occurs along thrust faults and the crust is overthickened. Since the less dense continental crust "floats" on the denser mantle rocks beneath, the weight of any crustal material forced upward to form hills, plateaus or mountains must be balanced by the buoyancy force of a much greater volume forced downward into the mantle, thus the continental crust is much thicker under mountains, compared to lower lying areas.
Rock can fold either asymmetrically. The upfolds are anticlines and the downfolds are synclines: in asymmetric folding there may be recumbent and overturned folds; the Balkan Mountains and the Jura Mountains are examples of fold mountains. Block mountains are caused by faults in the crust: a plane; when rocks on one side of a fault rise relative to the other, it can form a mountain. The uplifted blocks are block horsts; the intervening dropped blocks are termed graben: these can be small or form extensive rift valley systems. This form of landscape can be seen in East Africa, the Vosges, the Basin and Range Province of Western North America and the Rhine valley; these areas occur when the regional stress is extensional and the crust is thinned. During and following uplift, mountains are subjected to the agents of erosion which wear the uplifted area down. Erosion causes the surface of mountains to be younger than the rocks that form the mountains themselves. Glacial processes produce characteristic landforms, such as pyramidal peaks, knife-edge arêtes, bowl-shaped cirques that can contai
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The dictionary definition of Yucca at Wiktionary
. Encyclopædia Britannica (11th ed.). 1911.
