Amazonian (Mars)

The Amazonian is a geologic system and time period on the planet Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those on Mars today. The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 3 billion years ago, although error bars on this date are extremely large (~500 million years). The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Amazonian continues to the present day.
The Amazonian period has been dominated by impact crater formation and Aeolian processes with ongoing isolated volcanism occurring in the Tharsis and Cerberus Fossae, including signs of activity as recently as a tens of thousands of years ago in the latter and within the past few million years on Olympus Mons, implying they may still be active but dormant in the present.
Description and name origin.
The "Amazonian" System and Period is named after Amazonis Planitia, which has a sparse crater density over a wide area. Such densities are representative of many Amazonian-aged surfaces. The type area of the Amazonian System is in the Amazonis quadrangle (MC-8) around .
Amazonian chronology and stratigraphy.
Because it is the youngest of the Martian periods, the chronology of the Amazonian is comparatively well understood through traditional geological laws of superposition coupled to the relative dating technique of crater counting. The scarcity of craters characteristic of the Amazonian also means that unlike the older periods, fine scale (<100 m) surface features are preserved. This enables detailed, process-orientated study of many Amazonian-age surface features of Mars as the necessary details of form of the surface are still visible.
Furthermore, the relative youth of this period means that over the past few 100 million years it remains possible to reconstruct the statistics of the orbital mechanics of the Sun, Mars, and Jupiter without the patterns being overwhelmed by chaotic effects, and from this to reconstruct the variation of solar insolation – the amount of heat from the sun – reaching Mars through time. Climatic variations have been shown to occur in cycles not dissimilar in magnitude and duration to terrestrial Milankovich cycles.
Together, these features – good preservation, and an understanding of the imposed solar flux – mean that much research on the Amazonian of Mars has focussed on understanding its climate, and the surface processes that respond to the climate. This has included:
Good preservation has also enabled detailed studies of other geological processes on Amazonian Mars, notably volcanic processes, brittle tectonics, and cratering processes.
System vs. Period.
"System" and "Period" are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system is an idealized stratigraphic column based on the physical rock record of a type area (type section) correlated with rocks sections from many different locations planetwide. A system is bound above and below by strata with distinctly different characteristics (on Earth, usually index fossils) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (See Cretaceous–Paleogene boundary as example.)
At any location, rock sections in a given system are apt to contain gaps (unconformities) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the Cretaceous System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus, a geologic period represents the time interval over which the strata of a system were deposited, including any unknown amounts of time present in gaps. Periods are measured in years, determined by radioactive dating. On Mars, radiometric ages are not available except from Martian meteorites whose provenance and stratigraphic context are unknown. Instead, absolute ages on Mars are determined by impact crater density, which is heavily dependent upon models of crater formation over time. Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3.


York River Formation

The York River Formation is a geologic formation in Quebec. It preserves fossils dating back to the Devonian period.


Marsland Beds

The Marsland Beds is a geologic formation in Wyoming. It preserves fossils dating back to the Neogene period.


Gilmore Formation

The Gilmore Formation is a geologic formation in West Virginia. It preserves fossils dating back to the Permian period.


Macrofossil

Macrofossils, also known as megafossils, are preserved organic remains large enough to be visible without a microscope. The term "macrofossil" stands in opposition to the term microfossil. Microfossils, by contrast, require substantial magnification for evaluation by fossil-hunters or professional paleontologists. As a result, most fossils observed in the field and most "museum-quality" specimens are macrofossils.
Varieties.
Plant macrofossils.
Plant macrofossils include leaf, needle, cone, and stem debris; and can be used to identify types of plants formerly growing in the area. Such botanical macrofossil data provide a valuable complement to pollen and faunal data that can be used to reconstruct the prehistoric terrestrial environment. Algal macrofossils (for instance, brown kelp, sea lettuce and large stromatolites) are increasingly used to analyze prehistoric marine and aquatic ecosystems.
Animal macrofossils.
Animal macrofossils include the teeth, skulls, and bones of vertebrates, as well as such invertebrate remains as shells, tests, faunal armor, and exoskeletons. Fossilized dung (that is, coprolites) are also macrofossils.


Robert Helliwell

Robert A. Helliwell (September 2, 1920 – May 3, 2011) was an electrical engineer and professor at Stanford University. He was one of the pioneering scientists in the study of whistlers and related ionospheric phenomena.
Early life.
Helliwell was born in Red Wing, Minnesota, on September 2, 1920. He and his mother moved to Palo Alto, California after his father died. Helliwell and his wife, whom he knew in high school, were both undergraduates at Stanford University.
Career.
Helliwell was associated with Stanford University for his entire career, receiving all his academic credentials there and becoming a member of the electrical engineering faculty in 1946. Helliwell received his AB degree in 1942, a combined MA and electrical engineering degree in 1944, and his PhD in 1948.
Whistlers.
Helliwell's greatest discovery was accidental, as is often the case in science. Helliwell and one of his students, Jack Mallinckrodt, were investigating lightning noise at very low radio frequencies at Stanford University in 1950. Mallinckrodt heard some whistling sounds and brought them to Helliwell's attention. As Helliwell recalled in an article in the October 1982, issue of the Stanford Engineer, he thought it was an artifact, but he stood radio watch with Mallinckrodt until he heard these whistlers for himself. Helliwell described these sounds as "weird, strange and unbelievable as flying saucers" in a 1954 article in the Palo Alto Times.
Research.
In true scientific fashion, Helliwell tried to understand the mechanism involved in the production of whistlers. He conducted experiments at the VLF outpost, Siple Station in West Antarctica, which was active from 1971 to 1988. Since the wavelength of VLF radio signals is huge (a frequency of 10 kHz corresponds to a wavelength of 30 kilometers, or 18.64 miles), the Siple Station had an antenna that was thirteen miles long. The antenna was used to transmit VLF radio signals into Earth's magnetosphere, to be detected half a world away in Canada. It was possible to inject these signals into the magnetosphere, since the ionosphere is transparent to these low frequencies.
Writings.
Helliwell was the author of one book, "Whistlers and Related Ionospheric Phenomena," and more than 90 scientific papers. Three of his papers deserve special mention. One of these reported on low frequency emissions associated with the 1989 Loma Prieta earthquake. Another describes how injection of a low frequency radio signal into the magnetosphere causes a radio quieting of the natural noise that's associated with these frequencies. Another paper showed that the alternating current power grids in North America (60 Hz) and Europe (50 Hz) affect auroral chorus emissions.
Honors.
Helliwell was a fellow of the Institute of Electrical and Electronics Engineers and the American Geophysical Union, and a member of the American Association for the Advancement of Science and the United States National Academy of Sciences. The National Science Foundation named a range of hills in Antarctica, along the coast of Victoria Land on the Ross Sea, the Helliwell Hills in his honor.


Nancy Crooker

Nancy U. Crooker (born April 1, 1944) is an American physicist and professor emerita of space physics at Boston University, Massachusetts. She has made major contributions to the understanding of geomagnetism in the Earth's magnetosphere and the heliosphere, particularly through the study of interplanetary electrons and magnetic reconnection.
Early life and education.
Crooker was born in Chicago in 1944.  Her father, Michael Uss, a Lithuanian who emigrated to America as a child, was a foreman at the freight yards of the Chicago & Northwestern Railroad, and her mother, Helen Narovec, was a housewife.
Crooker holds a BA in Physics from Knox College, Illinois, and an MSc in Meteorology from the University of California, Los Angeles (UCLA). In 1972 Crooker was awarded her PhD in Atmospheric Sciences, also from UCLA, with her doctoral dissertation entitled, "The Low-Latitude Asymmetric Disturbance in the Geomagnetic Field".
Research career.
Crooker has published 207 peer-reviewed articles (as of 8 October 2019) across a range of topics within space physics. Her early career was as a postdoctoral researcher at Cornell University and then the Massachusetts Institute of Technology in the 1970s. There, together with Joan Feynman in their seminal Nature paper, she was one of the first physicists to use geomagnetic data as a way to reconstruct solar activity prior to the space age. Crooker then developed the concept of anti-parallel merging of magnetic field lines in Earth's magnetosphere published in Journal of Geophysical Research in 1979.
In 1990, she returned to UCLA as an adjunct professor before making her final move to Boston University as a research professor in 1994. Around this time, Crooker switched focus from the magnetosphere to the heliosphere, in particular the interplanetary manifestations of coronal mass ejections. In 1997, she co-edited a monograph on coronal mass ejections. In 2002, she coined the term "interchange reconnection" for describing the dynamic process by which heliospheric magnetic flux introduced by coronal mass ejections is subsequently removed, a term which has been comprehensively adopted in the field.
Crooker was president of the American Geophysical Union (AGU) Space Physics & Aeronomy Section from 2004 to 2006. She is a fellow of the American Geophysical Union, where the fellowship program recognizes AGU members who have made exceptional contributions to Earth and space science through a breakthrough, discovery, or innovation in their field. She also received the prestigious Eugene Parker Lecture award from the AGU in 2013, only the third woman to do so.
She has worked closely over decades with several other prominent space physicists, including John T. Gosling, Marcia Neugebauer, Mike Lockwood, Chris Russell and Thomas Zurbuchen.
Scientific Citizenship.
Crooker has served on numerous committees, panels and taskforces throughout her career, including:


St. John Group

The St. John Group is a geologic group in New Brunswick. It preserves fossils dating back to the Cambrian period.


Olcott Formation

The Olcott Formation is a geologic formation in Nebraska. It preserves fossils dating back to the Neogene period.


West Beckwith Mountain

West Beckwith Mountain is a prominent mountain summit in the West Elk Mountains range of the Rocky Mountains of North America. The peak is located in the West Elk Wilderness of Gunnison National Forest, about southwest of Crested Butte in Gunnison County, Colorado, United States.
West Beckwith Mountain is a laccolith, formed when magma intruded into Mancos Shale some 30 million years ago. Since then, erosion has removed the softer, overlying sedimentary rock, exposing the more resistant igneous rock. West Beckwith Mountain is one of over a dozen laccoliths in the West Elk and adjacent Elk Mountains.


Belsazar Hacquet

Belsazar de la Motte Hacquet (also Balthasar or Balthazar Hacquet) (c. 1739 – 10 January 1815) was a Carniolan physician of French descent in the Enlightenment Era. He was a war surgeon, a surgeon in the mining town of Idrija, and a professor of anatomy and surgery in Laibach (now Ljubljana). He researched the geology and botany of Carniola, Istria, and nearby places, and was the first explorer of the Julian Alps. He also did ethnographical work among the South Slavic peoples, particularly among the Slovene-speaking population. He self-identified primarily as a chemist and introduced the methods of chemical analysis to Carniola.
Life.
Hacquet was mysterious about the time and place of his birth and the two have remained uncertain, although sources agree that he was an illegitimate child. Most sources have cited the information from his autobiography that he was born in 1739 or 1740 in Le Conquet, Brittany to an aristocratic father. When he lived in Ljubljana, he told Sigmund Zois that he was born to a Russian grandee, but this has not been supported by any sources. In 1821, the German lexicon "Das Gelehrte Teutschland" mentioned that he had been born in Metz, Lorraine. A 2003 investigation in the town archives in Metz has given further credence to the claim that Hacquet had been born in this town or its vicinity. The author hypothesised that Balthasar Hacquet was a son of a poor mother and an unknown father, baptised on 11 August 1736 as Jean. However, the question remains unsettled pending further research.
Hacquet studied in Vienna, and was a military surgeon during the Seven Years' War (1756–1763). Since 1766 until 1773 he was the miners' surgeon and obstetrician in Idrija. In 1772 he became member of the Carniolan Agricultural Society. In 1773 he became a teacher of anatomy, physiology and obstetrics at Ljubljana Lyceum. From 1787 until 1805 he was a professor at the Lviv University (University of Lemberg). Then he worked in Krakow, where he stayed until 1809. In 1807 he became dean of the Medical Faculty. From 1810, when he retired, he lived in Vienna.
Work.
Hacquet is remembered for his scientific journeys throughout the Austrian Empire. He was a polymath, and performed research in the fields of geology, mineralogy, botany, chemistry, ethnography, petrology and karstology. He is recognized as the first scientist to perform extensive exploration of the Julian Alps. In 1777 he was the first to try to ascend to the top of Triglav (2864 m), the highest peak in Slovenia, and reached Mali Triglav (2725 m). In 1789 he published a description of the 1786 debris flow at the Slano Blato Landslide. He was the first after Carl Linnaeus to distinguish the mineral dolomite from the limestone and described it already in 1778, 13 years earlier than Déodat Gratet de Dolomieu, as the "stinking stone" (, ). He met with Dolomieu in Laibach in 1784.
Among Hacquet's written works is the four-volume "Oryctographia Carniolica", which included a geological and mineralogical study of Carniola, Istria, and surrounding districts. In this work, published in Leipzig from 1778 until 1789, he provided an in-depth report of the Idrija mercury mine, where he worked for some time with the physician and naturalist Giovanni Antonio Scopoli. He was also the author of an ethnographical study of Southern Slavic peoples called "Slavus Venedus Illyricus". From 1774 to 1787, he was the secretary of the Carniolan Agricultural Society, members of which were also other prominent members of the Enlightenment, such as Sigmund Zois, Blaž Kumerdej, Gabriel Gruber, Peter Pavel Glavar, and Anton Tomaž Linhart.
As a botanist Hacquet wrote a book on alpine flora from Carniola called "Plantae alpinae Carniolicae". The botanical genus "Hacquetia" is named after him, as well as the plant species "Pedicularis hacquetii" (Hacquet's lousewort). On one of his excursions, he discovered "on the evening, Trenta side of Triglav, a new species of scabious" and picked it for his herbarium collection, nowadays preserved in the Natural History Museum of Slovenia. He called the species "Scabiosa trenta" in the published description, and drew it. Many botanists have sought the mysterious pale yellow scabious, among them also the young Julius Kugy. He searched for the mysterious flower, and though he was not able to find it, this led him to become a great explorer and describer of the Julian Alps. The Austrian botanist, Anton Kerner von Marilaun, later proved Belsazar Hacquet had not found a new species, but a specimen of the already known submediterranean "Cephalaria leucantha".
Hacquet was a fervent collector. In Ljubljana he operated a natural history cabinet (), which was appreciated throughout Europe and was visited by the highest nobility, including the Holy Roman Emperor, Joseph II, the Russian grand duke Paul and Pope Pius VI, as well as by famous naturalists, such as and . It included a number of minerals, including specimens of mercury from the Idrija mine, a "herbarium vivum" with over 4,000 specimens of Carniolan and foreign plants, a smaller number of animal specimens, a natural history and medical library, and an anatomical theatre.
Commemoration.
A memorial relief to Belsazar Hacquet was erected in 1987 in Ljubljana at Upper Square () on the facade of the house No. 4, where he lived from 1773 to 1787 and operated his cabinet. The relief is work of the sculptor Albin Ambrožič. He has been also commemorated in a new species of fossil coral: "Aulopora hacqueti" Zapalski, 2005


Honseler Schichten Formation

The Honseler Schichten Formation is a geologic formation in Germany. It preserves fossils dating back to the Devonian period.


Alexander Halliday

Sir Alexander Norman Halliday (born 11 August 1952) is a British geochemist, an academic who is the Founding Dean of the Columbia Climate School, and Director of the Earth Institute at Columbia University. He joined the Earth Institute in April 2018, after spending more than a decade at the Department of Earth Sciences at the University of Oxford, during which time he was dean of science and engineering. He is also a Professor of Earth and Environmental Sciences at Columbia University.
Early life.
Halliday comes from Penzance, Cornwall, in the UK. He went to school at the Humphry Davy Grammar School where he studied geology. He received his undergraduate degree and PhD degree in geology from Newcastle University in 1977.
Career.
Halliday was Professor of Geochemistry at the University of Oxford from 2004-2018. Before coming to Oxford, he spent twelve years as a professor at the University of Michigan and then six years in Switzerland, where he was Head of the Department of Earth Sciences at ETH Zurich. His research involves the use of isotopic methods to study Earth and planetary processes.
Halliday is a former President of the Geochemical Society; the European Association of Geochemistry; and the Volcanology, Geochemistry and Petrology Section of the American Geophysical Union. He has experience with a range of top science boards and advisory panels including those of the Natural Environment Research Council, HEFCE, the Natural History Museum, the Max Planck Society, the Royal Society and the American Geophysical Union. At Oxford he was Head of the Division of Mathematical, Physical and Life Sciences (science and engineering) from 2007 to 2015. In 2014, he was elected Vice-President and Physical Secretary of the UK's Royal Society. He is currently a Fellow of the Royal Society and Foreign Associate of the US National Academy of Sciences.
On 14 December 2017 it was announced that Professor Halliday will be appointed as the new Director of Columbia University's Earth Institute. As a professor in Columbia's Department of Earth and Environmental Sciences, Halliday divides his time between Columbia's Morningside campus and his geochemistry lab at Lamont-Doherty Earth Observatory.
Research.
Alex Halliday is an isotope geochemist known for novel mass spectrometry techniques and their applications to the Earth and planetary sciences. An enthusiast for technological innovation, most of Halliday's recent research is in developing and using new mass spectrometry techniques to shed light on the origin and early development of the solar system and recent Earth processes, such as continental erosion and climate. However, he has also been engaged in other studies, such as the mechanisms of volcanic eruptions, and the formation of mineral and hydrocarbon deposits. Halliday has over 400 published research papers.
Accomplishments and awards.
Halliday's scientific accomplishments have been recognised with awards including the Murchison Medal of the Geological Society, the Bowen Award and Hess Medal of the American Geophysical Union, the Urey Medal of the European Association of Geochemistry and the Oxburgh Medal of the Institute of Measurement and Control. He was elected a Fellow of the Royal Society in 2000 and a Foreign Associate of the U.S. National Academy of Sciences in 2015. He was appointed a Knight Bachelor in the 2019 New Year Honours for services to Science and Innovation.


Derek Keir

Derek Keir (born 1979 Johannesburg, South Africa) has been an associate professor of geophysics at the University of Southampton since 2015. In 2013 he received the Bullerwell Lecture award from the British Geophysical Association (BGA) for significant contributions to geophysics.
Education and career.
During 1998-2002 he read geology and geophysics at Imperial College London, gaining an MSc (first class). His PhD (Tectonics and Seismology) was conducted during 2002-2006 at Royal Holloway University of London. He also held a Teaching Fellowship in Geology at Royal Holloway during this time. His thesis was on the earthquake activity of the East African rift.
In 2007 he moved to the University of Leeds as a Natural Environment Research Council (NERC) research fellow and as Teaching Fellow in Geology.
Keir was appointed Lecturer in Earth Science at University of Southampton in 2011 and became Associate Professor in Geophysics in 2015.
His major contribution to science has been to study how continents break apart by analysing the earthquake and volcanic activity of the Afar Triangle. He has researched many volcanoes in Ethiopia and Eritrea, including Corbetti, Mount Ayalu, Adwa (volcano), Erta Ale, Dabbahu Volcano, Dallol, and Nabro Volcano. He has conducted much of his research in collaboration with Kathryn Whaler and Ian Bastow.


Greenschist

Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals such as muscovite and platy serpentine. The platiness causes the tendency to split, or have schistosity. Other common minerals include quartz, orthoclase, talc, carbonate minerals and amphibole (actinolite).
Greenschist is a general field petrologic term for metamorphic or altered mafic volcanic rock. In Europe, the term prasinite is sometimes used. A greenstone is sometimes a greenschist but can also be rock types without any schistosity, especially metabasalt (spilite). The green is due to abundant green chlorite, actinolite and epidote minerals that dominate the rock. However, basalts may remain quite black if primary pyroxene does not revert to chlorite or actinolite. To qualify for the name a rock must also exhibit schistosity or some foliation or layering. The rock is derived from basalt, gabbro or similar rocks containing sodium-rich plagioclase feldspar, chlorite, epidote and quartz.
Petrology.
Greenschist, as a rock type, is defined by the presence of the minerals chlorite and actinolite and may contain albite or epidote.
Greenschist often has a lepidoblastic, nematoblastic or schistose texture defined primarily by chlorite and actinolite. Greenschists often have some foliation resulting in mineral alignment, especially of chlorite and actinolite.
Grain size is rarely coarse, due primarily to the mineral assemblage. Chlorite and to a lesser extent actinolite typically exhibit small, flat or acicular crystal habits.
Greenschist facies.
Greenschist facies is determined by the particular temperature and pressure conditions required to metamorphose basalt to form the typical greenschist facies minerals chlorite, actinolite, and albite. Greenschist facies results from low temperature, moderate pressure metamorphism. Metamorphic conditions which create typical greenschist facies assemblages are called the "Barrovian Facies Sequence", and the lower-pressure "Abukuma Facies Series". Temperatures of approximately and depths of about are the typical envelope of greenschist facies rocks.
The equilibrium mineral assemblage of rocks subjected to greenschist facies conditions depends on primary rock composition.
In greater detail the greenschist facies is subdivided into subgreenschist, lower and upper greenschist. Lower temperatures are transitional with and overlap the prehnite-pumpellyite facies and higher temperatures overlap with and include sub-amphibolite facies.
If burial continues along Barrovian Sequence metamorphic trajectories, greenschist facies gives rise to amphibolite facies assemblages, dominated by amphibole and eventually to granulite facies. Lower pressure, normally contact metamorphism produces albite-epidote hornfels while higher pressures at great depth produces eclogite.
Oceanic basalts in the vicinity of mid-ocean ridges typically exhibit sub-greenschist alteration. The greenstone belts of the various archean cratons are commonly altered to the greenschist facies. These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada.
Greenschist-like rocks can also be formed under blueschist facies conditions if the original rock (protolith) contains enough magnesium. This explains the scarcity of blueschist preserved from before the Neoproterozoic Era 1000 Ma ago when the Earth's oceanic crust contained more magnesium than today's oceanic crust.
Use.
Europe.
In Minoan Crete, greenschist and blueschist were used to pave streets and courtyards between 1650 and 1600 BC. These rocks were likely quarried in Agia Pelagia on the north coast of central Crete.
Across Europe, greenschist rocks have been used to make axes. Several sites, including Great Langdale in England, have been identified.
Eastern North America.
A form of chlorite schist was popular in prehistoric Native American communities for the production of axes and celts, as well as ornamental items. In the Middle Woodland period, greenschist was one of the many trade items that were part of the Hopewell culture exchange network, sometimes transported over thousands of kilometers.
During the time of the Mississippian culture, the polity of Moundville apparently had some control over the production and distribution of greenschist. The Moundville source has been shown to be from two localities in the Hillabee Formation of central and eastern Alabama.


Hilda mega-bonebed

The Hilda mega-bonebed is a complex of fourteen probable "Centrosaurus apertus" bonebeds discovered near the town of Hilda in Alberta, Canada. It was first described in the scientific literature by David Eberth, Donald Brinkman, and Vaia Barkas in 2010 after more than ten years of research. The Hilda mega-bonebed is significant because the behavior of the preserved dinosaurs themselves was the dominant cause of its existence, rather than the stratum's geological history like most bonebeds. It is also Canada's largest bonebed.
History of research.
In 1959, Wann Langston, Jr. recorded evidence of a "Centrosaurus" bonebed near Hilda, Alberta. Later, between 1964 and 1966 Don Taylor of the Provincial Museum of Alberta (now called the Royal Alberta Museum) oversaw the collection of fossils from yet another bonebed in the same region. These prospective bonebeds attracted the attention of scientists working for the Royal Tyrell Museum in the 1990s because Hilda was an ideal location for maintaining physical continuity across the bonebeds' expanse. Physical continuity is important, because discontinuity in the rock strata can make it harder to tell if the bones were deposited at the same time or not.
Eberth and the other researchers considered Hilda a prime site for a continuous bonebed for two reasons, one related to its history, one related to its present geography. First, during the Cretaceous the area was situated closer to the Western Interior Seaway where more sediment would have been deposited than at Dinosaur Provincial Park. Secondly, the modern Hilda area lacks the rough badland terrain that breaks up many probably equivalent deposits in Dinosaur Provincial Park.
In 1996, the Royal Tyrell Museum finally performed a preliminary survey of the area studied by Langston and Taylor and entire new bonebeds were discovered. The next year, in 1997, research at Hilda began in earnest. In only two days, researchers discovered 14 separate bonebeds in one mudstone bed that extended for at least 7 km, with 3.7 km worth of visible outcrops. By the conclusion of the research program, the scientists mapped the bonebeds and excavated the bonebed cataloged as H97-04.
They concluded that the Hilda bonebeds formed simultaneously when a herd consisting of thousands of "Centrosaurus apertus" drowned in a flood. The researchers further speculated that some of the 17 "Centrosaurus" bonebeds of Dinosaur Provincial Park likely formed simultaneously in a manner analogous to the formation of the Hilda bonebeds, which the researchers estimated to be spread over 2.3 km2. The researchers only collected fossils and taphonomic data from the bonebed H97-04, although all the others were also examined to check the quality and number of preserved bones. The research at Hilda was so complex that over ten years passed from the start of the project until David A. Eberth, Donald B. Brinkman, and Vaia Barkas published a formal description in the scientific literature.
Geographic location and extent.
The mega-bonebed is located 25 kilometers west of the town of Hilda, Alberta in a "steep-walled" valley cut into the landscape by glaciers during the Pleistocene epoch. Northward through this valley's interior runs the South Saskatchewan River. The individual bonebeds in the complex are recognizable as dense concentrations of ceratopsid bones. Research on the bonebeds of Dinosaur Provincial Park has discovered that ceratopsian bonebeds preserved in mudstone deposits tended to be circular to ovular in shape when viewed from above, so the similar Hilda bonebeds probably were as well.
H97-04 is the largest of the fourteen bonebeds, at 150 m in width. If one assumes that H97-04's 150 m width is its longest linear dimension then it had an area of about 17,671 m2. Bonebeds other than H97-04 were less than 50 m wide. These individual component bonebeds tend to have areas of only a few hundred to a few thousand square feet and would have maximum areas of somewhat less than 2,000 square meters. The individual bonebeds at Hilda were generally smaller than those at Dinosaur Provincial Park.
The researchers estimated the entire Hilda complex to be 2.3 square kilometers in area based on the length of its north-south and east-west axes. This is the size of about 280 football fields, and is one of the largest dinosaur bonebeds ever discovered. Bonebeds left by such large animals over wide areas are a rare discovery.
However, completely excavating the bonebed would be too huge and complex an undertaking to be practical.
Lithology and stratigraphy.
The Hilda mega-bonebed lies within the bottom 25 m of the Dinosaur Park Formation. Eberth, Brinkman and Barkas estimated that in the Hilda area, the Dinosaur Park Formation was almost 60 m thick between the over- and under-lying formations, but glacial activity and slumping had removed all but 43 m of this at the field site. When the researchers examined the stratigraphy of the Hilda site they found that the fourteen bonebeds occupied identical positions in the stratigraphic column. This continuity in the mudstone was what allowed them to infer that each bonebed was actually a component of a single large "mega-bonebed".
At its thinnest point the mudstone bed hosting the centrosaur fossils is 25 cm thick and it measures 1 m at its thickest. Eberth, Brinkman and Barkas observed siltstone, claystone, and abundant organic matter in the composition of the "brown-grey" mudstone. Ironstone concretions can be found scattered throughout the bed, but were most abundant where fossils were also common. Fossils are most common in the lowest parts of the bed. There are signs of deformation in the sediment composing the mudstone.
The stratum hosting the mega-bonebed has different sorts of contacts with other strata at different locations across its extent. The most distinct boundaries separate the Hilda bonebed mudstone from other mudstones above and below it. Less clear boundaries occur where the bonebed mudstone contacts the filled-in remains of an ancient body of flowing water. These contacts record where the channel cut down into the sediment now lithified as the fossil-bearing mudstone. The researchers couldn't find the bed's northern boundary, which they felt might extend north of the northernmost bonebed as part of a succession of stacked mudstone beds. An ancient channel cut all the way through the sediments now composing the mudstone, and its deposit forms the Hilda bonebed's southern boundary.
Related strata.
Eberth, Brinkman, and Barkas also noted the presence of two beds in the mudstone hosting the Hilda bonebeds that weren't ceratopsian bonebeds, but rather they contained vertebrate microfossils. The first of these was H97-09, a natural part of the same stratum that hosted the ceratopsian bonebeds, but bearing only the remains of aquatic animals like champsosaurs, crocodilians, fish, and turtles.
The second was a lens of sandstone that formed after the ceratopsian bonebeds cataloged as H97-12. This lens of sandstone penetrated down into the bed that hosted the ceratopsian bonebeds, probably deposited by a creek. Like H97-09, H97-12 contained only fragmentary remains of aquatic vertebrates like crocodiles and turtles.
Fossil content.
Centrosaur remains.
At the conclusion of their research program, Eberth, Brinkman and Barkas were unable to identify the bonebeds' ceratopsian remains to a rank more specific than the subfamily Centrosaurinae. Nevertheless, every single ceratopsian fossil that could be identified from the bonebeds had features closely resembling those of "Centrosaurus apertus". They consequently felt confident that the bonebed was mostly composed of that species.
The researchers found that the larger bones in each bonebeds tended to lie at the base of the stratum with fragments of bone becoming smaller and less concentrated at higher positions in the mudstone bed. Most of the bones were angled parallel to the plane of the bed. The researchers only found associated or articulated fossils at two of Hilda's bone beds; H97-03 had a partial "Centrosaurus" skull and H97-19 had a partial ceratopsian tail. As such, they regarded such higher quality specimens as very rare.
Eberth, Brinkman, and Barkas tried to estimate the number of bones in the mega-bonebed in order to infer the number of animals that died together during the formation of the deposit. However, the complexity of a bonebed's geologic and taphonomic history can only allow for rough estimates.
H97-04 represented the densest part of the Hilda mega-bonebed and formed the "core" of its fossil deposits. Nevertheless, the amount and quality of preserved bone was highly variable within this bed. The centrosaur fossils of H97-04 were most densely concentrated in its middle 50 m, with the 50 m on each side of this central region of the bonebed being much sparser. The researchers took the average bone density of two excavations within H97-04, 1 individual per 3 square meters, and projected it over the 2,000 square meters of the H97-04 bonebed. They estimated that this core area preserved the remains of 667 centrosaurs.
In H97-02 the researchers found that at least 6 individuals were discovered in a 20 square meter area, but suspected that this relatively high density was not uniform throughout the deposit. They concluded that the number of centrosaurs preserved at H97-02 was probably "in the low hundreds".
The remaining 15,600 square meters of the Hilda mega-bonebed contained only about 10% of the fossil density observed in the "core" of H97-04. Assuming the periphery of H97-04 had this estimated average density, there would have been about 500-600 more centrosaurs overall. Thus, the total estimated number centrosaurs preserved in the Hilda area ranged from several hundred to about 1,500 individuals. However, the presence of centrosaur bonebeds on both sides of the South Saskatchewan River suggests that the river eroded away many fossil deposits that had originally been preserved there. Therefore the original size of the centrosaur herd was probably even larger than the estimate based on still-accessible fossils would suggest and may have included up to several thousand dinosaurs.
Other fossils.
The mudstone hosting the Hilda mega-bonebed preserves large quantities of plant fossils throughout the bed as well as coal, wood debris, and root traces. The root traces come at a variety of orientations ranging from horizontal to vertical. Some of these being the roots' original life position. The researchers concluded that the abundance of preserved plant material probably reflects the great abundance of local plant life during the Cretaceous.
H97-04's excavation site Excavation A preserved shed teeth from theropods of differing size, champsosaur vertebrae, a fish scale, a pisidiid clam, and two unidentifiable coprolites in addition to its centrosaur fossils. The Excavation B site at H97-04 preserved a fish scale and two theropod teeth.
Formation.
Previous research on Albertan centrosaur bonebeds interpreted their formation in terms of a herd of dinosaurs drowning while trying to cross a swollen river. Eberth, Brinkman, and Barkas proposed a different explanation for the Hilda mega-bonebed, hypothesizing that a herd of "Centrosaurus apertus", as well as other local wildlife, were killed by a flood. The researchers concluded that all of the component bonebeds of the Hilda complex formed during the same individual flood.
The region around the Western Interior Seaway was prone to tropical storm activity, many of which could become full-scale hurricanes. Similar weather events occur today in the Gulf of Mexico and Bangladesh. These floods would have been large enough to entirely submerge the coastal lowland plains that the dinosaurs were living on, leaving nowhere to hide or escape to. Because "Centrosaurus" likely had poor swimming abilities most of the herd would have drowned during sufficiently severe flooding events. Centrosaurs not killed by the flooding would have been vulnerable to "flood-related disease" outbreaks in its aftermath. Tropical storm-induced floods were probably common sources of mass mortality for "Centrosaurus apertus". According to David Eberth, smaller local wildlife were better equipped to escape the floodwaters than centrosaurs, noting that birds could escape by flight, while mammals and reptiles could have taken shelter in trees or burrows.
After they died the dinosaurs's carcasses were deposited in clumps spread over kilometers. Variation in the location and concentration of centrosaur bones was caused by factors like force and dimensions of the flood, smoothness or roughness of local terrain, and the centrosaurs' distribution in life. These variations likely coincided with the presence of small "sub-environments" commonly found between rivers like splays, ponds or creeks.
After being deposited in their final resting places the carcasses were torn apart, had their bones trampled and chewed by scavengers. These processes left the abrasion and toothmarks seen on the bones preserved at H97-02. Chemical reactions between the decaying dinosaur flesh and floodwaters caused iron to precipitate out of the water and formed the ironstone concretions commonly found in the mudrock hosting the mega-bonebed.
Their eventful taphonomies suggests that the centrosaur carcasses were permanently buried by a later flood rather than the one that drowned them. These floods may actually have been common enough to be the primary means by which sediment was deposited in the Hilda area during the Cretaceous. Eberth Brinkman and Barkas observed evidence that the sediment was deformed and contorted near the top and bottom before it hardened into the mudstone it is today.
Comparison with other bonebeds.
The Hilda Mega-bonebed is about 76 million years old, the same age as the lower Dinosaur Park Formation outcrops of the Dinosaur Provincial Park strata. Monodominant bonebeds of horned dinosaurs like "Styracosaurus", "Pachyrhinosaurus" and "Centrosaurus" are common in late Cretaceous strata of central and southern Alberta. The close proximity of such a large number of bonebeds has fueled suspicions in some experts that some of the different bonebeds may have actually formed simultaneously in the same events.
According to Eberth, Brinkman, and Barkas, the idea that several of these bonebeds could have formed together is "difficult to test", however. This difficulty emerges from the complicated nature of local stratigraphy as individual bonebeds are difficult to track for more than a few hundred meters because they are divided by ancient channel deposits. The only certainty regarding the number of events involved in the formation of the bone beds is that more than one occurred since at least one bonebed is known to be preserved in a rock stratum directly over another bonebed. The Hilda bonebeds distinguish themselves by being preserved in a single easily traceable stratum.
In two 2005 scientific papers, Eberth, Getty, and Currie formulated a hypothesis for the formation of the centrosaur bonebeds of Dinosaur Provincial Park. They envisioned common flooding events drowning large numbers of local wildlife, including herds of "Centrosaurus" and "Styracosaurus". Flowing water would distribute these remains across the local floodplain, where they would be buried by later floods. Burial was not always permanent as some remains seem to have been uncovered again by later flood activity only to be buried again by yet more later floods. The process of reworking and reburial might have occurred over decades or millennia before the remains were buried for good in their final resting place, which was often in deposits left by channels of flowing water. Eberth, Brinkman, and Barkas thought that the above scenario "appl[ied] particularly well" so the Hilda bonebeds formed as a result of similar processes to those of Dinosaur Provincial Park.
The bonebeds at Hilda and in Dinosaur Provincial Park also preserve similar quantities and types of plant fossils. The two areas differed, however, in that all of the component bonebeds of the Hilda mega-bonebed, apart from H97-04, were smaller and preserved lower numbers of dinosaurs than those of the park. The centrosaur bonebeds of Dinosaur Provincial Park were often more than 10,000 square meters in area. These bonebeds tended to preserve centrosaurs in the "hundreds to low thousands" apiece.
Implications.
Although not the first "Centrosaurus" bonebed, the study of the fossils preserved in the Hilda mega-bonebed provides additional data that will help scientists estimate the size of ceratopsid herds and therefore better understand ceratopsid social behavior. Hilda increases the evidence for herding in "Centrosaurus" and that centrosaur herds were sometimes significantly larger than previously thought, possibly containing numbers in the high hundreds to low thousands. The abundant mudstone beds in the Hilda area may imply that floods like the one drowned the centrosaurs at Hilda were common. The researchers contended that the existence of a single mega-bonebed with 14 individual components at Hilda may imply that some of the bonebeds of Dinosaur Provincial Park may themselves be components of larger mega-bonebeds.
The Hilda mega-bonebed may also support the previously suggested notion that some kinds of centrosaurines participated in seasonal migrations, travelling from east to west. Brinkman and others proposed this hypothesis in 1998 to explain why ceratopsians represented a greater portion of ornithischian biodiversity at sites like Unity, Saskatchewan or Onefour, Alberta near the ancient coast, while the famous centrosaur bonebeds of Dinosaur Provincial Park were all preserved in more inland habitats.
The migration hypothesis proposed by Brinkman and the others was that centrosaurs bred near the coast and reared their young in small family groups. These groups would then migrate toward the west in order to avoid seasonal hazards like storms or to exploit seasonally available resources in that direction. As the migration progressed the family groups would gradually merge, becoming large herds, which may have protected them from predators on the journey. Eberth, Brinkman, and Barkas noted that Hilda is located roughly halfway between the ancient coast and the Dinosaur Provincial Park bonebeds.


Natural (archaeology)

In archaeology, natural is a term to denote a layer (stratum) in the stratigraphic record where there is no evidence of anthropogenic activity. While there may be "natural" layers interbedded with archaeologically interesting layers, such as when a site was abandoned for long periods of time between occupations by man, the top (the horizon) of the natural layer below which there is no anthropogenic activity on site, and thus where the archaeological record chronologically begins, is the sought-for point to terminate digging. This final natural layer is often the underlying geological makeup of the site that was formed by geological processes. It is the goal of complete excavation to remove the entirety of the archaeological record all the way to the final "natural", thus leaving only the natural deposits of pre-human activity on site. If the excavation is related to development, the impact assessment may stipulate excavation will cease at a certain depth, because the nature of the development will not disturb remains below a certain level; such an excavation may not reach a natural or sterile layer. Thus one always has to overdig a site (dig past the top of the natural) in order to establish the natural.
Issues of definition.
Natural can be a relative term. On urban sites where research interests may make a detailed examination of the earliest part of the record impractical, prehistoric or rudimentary human activity may go unrecorded, as opposed to an equivalent horizon on a rural site for which the study team's agenda is to look for prehistoric evidence. Chemical and soil process over time often obscure and cause decomposition of cultural materials, and thus a human-occupied layer may look natural. Additionally, early prehistoric tools were manufactured from natural materials, such as bone, stone and fiber; they do not stand out as clearly as metal, glass and plastic. The effect of decompositional processes is that the older an archaeological deposit is, the more it will appear similar to the underlying geology. For some archaeologists, a basic rule of thumb is "the greater the contrast a context has with the natural, the younger it is." Similarly, United States prehistoric archaeologists often rely on significantly diminished counts of lithic flake debitage to assess the excavation unit's trend toward natural stratigraphy. While a trend may be recognized, a stratum is not called natural or sterile, unless it is void of cultural materials.
Geoarchaeology.
Natural is becoming a blurred term in archaeology due to an increased understanding by researchers of natural processes. In addition, through the development of geoarchaeology, scholars believe the natural landscape has a bearing on interpretation of subsequent human activity on any given site. As geoarchaeology continues to influence the interpretation of processes that occur within the archaeological record, the term "natural" has become less useful.


Wave-formed ripple

In sedimentology, wave-formed ripples or wave-formed ripple marks are a feature of sediments (sandstones, limestones, siltstones) and dunes. These ripple marks are often characterised (and thus distinguished from current ripples) by symmetric cross sections and long relatively straight crests, which may commonly bifurcate. Commonly, these crests can be truncated by subsequent flows. Their wavelength (periodicity) depends on the sediment grain size, water depth and water-particle orbits in the waves. On tidal flats the pattern of wave-formed ripples may be complicated, as a product of changing depth and wind and tidal runoff directions. Symmetrical ripples are commonly found in shallow waters. Beaches are a good place to find these ripples.
While wave-formed ripples are traditionally described as symmetrical, asymmetric wave ripples are common in shallow waters along sandy shores. They are produced by bottom oscillations generated by passing breaker waves, which have unequal intensity in opposite directions.
Wave-formed ripples indicate an environment with weak currents where water motion is dominated by wave oscillations.
Although symmetrical ripples are also called bi-directional ripples there is a difference between them. Bi-directional ripples are rarely symmetrical due to the difference in force of the two directions, where as the wave formed or oscillation ripples form from the circular water movement pattern of water molecules. These ripples form parallel to the shore line. They usually display rounded troughs and rounded crests.
Ripples.
Ripples are relatively small, elongated ridges that form on bed surfaces perpendicular to current flow. With continuous current flow in one direction, asymmetrical ripples form. Asymmetrical ripples contain a steeper slope downstream. With an alternation in current flow from one direction to the opposite symmetrical ripples form. Symmetrical ripples tend to have the same slope on both sides of the crest.
Formation.
Symmetrical ripples form as water molecules oscillate in small circles. A particle of water within a wave does not move with the wave but rather it moves in a small circle between the wave crest and wave trough. This movement of water molecules is the same for all water molecules effected by the wave. The water molecules continue to do this to a depth equal to 1/2 the wavelength. The water molecule traveling in a circular pattern interacts with the sediment on the floor and moves the sediment into symmetrical ripples. These ripples can be either straight crested or sinuous crested ripples.


Bridwell Formation

The Bridwell Formation is a geologic formation in Texas. It preserves fossils dating back to the Neogene period.


Ooid

Ooids are small (commonly ≤2 mm in diameter), spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, most commonly in shallow tropical seas (around the Bahamas, for example, or in the Persian Gulf). After being buried under additional sediment, these ooid grains can be cemented together to form a sedimentary rock called an "oolite". Oolites usually consist of calcium carbonate; these belong to the limestone rock family. Pisoids are similar to ooids, but are larger than 2 mm in diameter, often considerably larger, as with the pisoids in the hot springs at Carlsbad (Karlovy Vary) in the Czech Republic.
Formation.
An ooid forms as a series of concentric layers around a nucleus. The layers contain crystals arranged radially, tangentially or randomly. The nucleus can be a shell fragment, quartz grain or any other small fragment. Most modern ooids are aragonite, a polymorph of calcium carbonate; some are composed of high-magnesium calcite, and some are bimineralic (layers of calcite and aragonite). Ancient ooids can be calcitic, either originally precipitated as calcite (as in calcite seas), or formed by alteration (neomorphic replacement) of aragonitic ooids (or the aragonite layers in originally bimineralic ooids). Moldic ooids (or molds later filled in by calcite cement) occur in both young and ancient rocks, indicating the removal of a soluble polymorph (usually aragonite).
Variation.
Whether ooids become calcitic or aragonitic can be linked to strontium/calcium substitution within the crystalline structure. This has been shown in some examples to be due to temperature fluctuations in marine environments, which affects salinity levels, which in turn facilitate the substitution. Marine calcitic ooids were typically formed during calcite sea intervals, especially during the Ordovician and the Jurassic Periods. The geochemistry of these seas was a function of seafloor spreading and fluctuating Mg/Ca ratios. Low Mg/Ca ratios favor the precipitation of low-magnesium calcite.
Growth mode.
Ooids with radial crystals (such as the aragonitic ooids in the Great Salt Lake, Utah, US) grow by ions extending the lattices of the radial crystals. The mode of growth of ooids with tangential (usually minute needle-like) crystals is less clear. They may be accumulated in a "snowball" fashion from tiny crystals in the sediment or water, or they may crystallize in place on the ooid surface. A hypothesis of growth by accretion (like a snowball) from the polymineralic sediment of fine aragonite, high-magnesium calcite (HMC) and low-magnesium calcite (LMC), must explain how only aragonite needles are added to the ooid cortex. Both in tangential and in radial ooids, the cortex is composed of many very fine increments of growth. Some modern (and ancient) ooids partially or totally lack clear layering and have a micritic (very fine grained) texture. Examination of such micritic ooids by scanning electron microscopy often shows evidence of microbial borings later filled by fine cement.
Growth factors.
There are several factors that affect ooid growth: supersaturation of the water with respect to calcium carbonate, the availability of nuclei, agitation of the ooids, water depth, and the role of microbes.
References.
Flügel, Erik (2010), "Microfacies of Carbonate Rocks: Analysis, Interpretation and Application", 2nd ed., Springer, pp. 242–244. . Accessed 2014-06-23.


Dunderberg Shale

The Dunderberg Shale is a geologic formation in Nevada and Utah.
It preserves fossils dating back to the Cambrian period.


Fossil Creek Volcanics

The Fossil Creek Volcanics is a geologic formation in Alaska. It preserves fossils dating back to the Ordovician period.


Heath Shale

The Heath Shale is a geologic formation in Montana. It preserves fossils dating back to the Carboniferous period.


Challis Volcanics

The Challis Volcanics is a geologic formation in Idaho. It preserves fossils dating back to the Paleogene period.


Gazzi-Dickinson method

The Gazzi-Dickinson method is a point-counting technique used in geology to statistically measure the components of a sedimentary rock, chiefly sandstone. The main focus (and most controversial) part of the technique is counting all sand-sized components as separate grains, regardless of what they are connected to. Gazzi-Dickinson point counting is used in the creation of ternary diagrams, such as QFL diagrams.
Technique.
To perform a point count using the Gazzi-Dickinson method, a randomly selected thin section from a sedimentary rock is needed, with a slide advance mechanism that will randomly select points on the slide with a petrographic microscope. A minimum of 300 representative points (preferably 500 points) should be used to perform the count. On each randomly selected point that lands on a sand grain, the operator must determine the make-up of the area chosen, i.e. whether it is a mineral grain that is sand sized (larger than 62.5 micrometers) or a finer-grained fragment of another rock type, called a lithic fragment (e.g. a sand-sized piece of shale). These counts are then converted to percentages and used for compositional comparisons in provenance studies. Typically, only framework (non-matrix) grains are counted, or non-framework grains are counted and then excluded from percentages when using descriptive devices such as QFL triangles. This can create problems with pseudomatrix, which are lithic grains that have been deformed and thus blend in with (or have become) matrix.
History.
The Gazzi-Dickinson method came out of separate work by P. Gazzi in 1966 and William R. Dickinson, starting in 1970. Dickinson and his students (most notably Raymond Ingersoll, Steven Graham, and Chris Suczek) at Stanford University in the 1970s established the method and its use to use the composition of sandstones to infer tectonic processes. This was in contrast to ideas presented by sedimentary geologists at Indiana University at the time, who used the more traditional "QFR" or "rock fragment" method of Robert Folk (1974) (which later grew into the Folk classification scheme), in which all grains that are connected are considered rock fragments, and the individual components are disregarded.
The best way to explain the differences in these two schools of thought is with an example: A sand rich in grus, or a granitic sand, when point counted with these two methods would yield drastically different results. A QFR-style count would be rich in rock fragments, whereas a Gazzi-Dickinson point count would show the sand rich in quartz and feldspar. Proponents of the Indiana University method would say that information is lost by not counting rock fragments. Proponents of Gazzi-Dickinson point counting would say that small changes in erosional transport would change the composition of the sand.


Leonard Series

The Leonard Series is a geologic group in Oklahoma. It preserves fossils dating back to the Permian period.


Bert Formation

The Bert Formation is a geologic formation in France. It preserves fossils dating back to the Permian period.


Kollerkogel Formation

The Kollerkogel Formation is a geologic formation in Austria. It preserves fossils dating back to the Devonian period.


Cut (gems)

When a gemstone is desired to be used in jewelry, it is cut depending on the size and shape of the rough stone, as well as the desired piece of jewelry to be made. As a general rule, a cut gemstone will reduce the mass (described in the carat) by about 50 percent.
There are several techniques available to work with gemstones; among them are sawing, grinding, sanding, lapping, polishing, grilling, and tumbling. The diamond cut planning stage is a complex process that requires the cutter to work with unique rough stones. Very often, the location of the inclusions in a rough stone will determine the type of shape to which a diamond may be cut. For economic reasons, most diamonds are cut to retain weight instead of maximizing brilliance.
Types.
A list of cuts:


Delorme Formation

The Delorme Formation is a geologic formation in Northwest Territories. It preserves fossils dating back to the Silurian period.


Batesland Formation

The Batesland Formation is a geologic formation in South Dakota. It preserves fossils dating back to the Neogene period.


Bala Group

The Bala Group is a geologic group in Wales. It preserves fossils dating back to the Ordovician period.


Petrography

Petrography is a branch of petrology that focuses on detailed descriptions of rocks. Someone who studies petrography is called a petrographer. The mineral content and the textural relationships within the rock are described in detail. The classification of rocks is based on the information acquired during the petrographic analysis. Petrographic descriptions start with the field notes at the outcrop and include macroscopic description of hand specimens. However, the most important tool for the petrographer is the petrographic microscope. The detailed analysis of minerals by optical mineralogy in thin section and the micro-texture and structure are critical to understanding the origin of the rock. Electron microprobe or atom probe tomography analysis of individual grains as well as whole rock chemical analysis by atomic absorption, X-ray fluorescence, and laser-induced breakdown spectroscopy are used in a modern petrographic lab. Individual mineral grains from a rock sample may also be analyzed by X-ray diffraction when optical means are insufficient. Analysis of microscopic fluid inclusions within mineral grains with a heating stage on a petrographic microscope provides clues to the temperature and pressure conditions existent during the mineral formation.
History.
Petrography as a science began in 1828 when Scottish physicist William Nicol invented the technique for producing polarized light by cutting a crystal of Iceland spar, a variety of calcite, into a special prism which became known as the Nicol prism. The addition of two such prisms to the ordinary microscope converted the instrument into a polarizing, or petrographic microscope. Using transmitted light and Nicol prisms, it was possible to determine the internal crystallographic character of very tiny mineral grains, greatly advancing the knowledge of a rock's constituents.
During the 1840s, a development by Henry C. Sorby and others firmly laid the foundation of petrography. This was a technique to study very thin slices of rock. A slice of rock was affixed to a microscope slide and then ground so thin that light could be transmitted through mineral grains that otherwise appeared opaque. The position of adjoining grains was not disturbed, thus permitting analysis of rock texture. Thin section petrography became the standard method of rock study. Since textural details contribute greatly to knowledge of the sequence of crystallization of the various mineral constituents in a rock, petrography progressed into petrogenesis and ultimately into petrology.
It was in Europe, principally in Germany, that petrography advanced in the last half of the nineteenth century.
Methods of investigation.
Macroscopic characters.
The macroscopic characters of rocks, those visible in hand-specimens without the aid of the microscope, are very varied and difficult to describe accurately and fully. The geologist in the field depends principally on them and on a few rough chemical and physical tests; and to the practical engineer, architect and quarry-master they are all-important. Although frequently insufficient in themselves to determine the true nature of a rock, they usually serve for a preliminary classification, and often give all the information needed.
With a small bottle of acid to test for carbonate of lime, a knife to ascertain the hardness of rocks and minerals, and a pocket lens to magnify their structure, the field geologist is rarely at a loss to what group a rock belongs. The fine grained species are often indeterminable in this way, and the minute mineral components of all rocks can usually be ascertained only by microscopic examination. But it is easy to see that a sandstone or grit consists of more or less rounded, water-worn sand grains and if it contains dull, weathered particles of feldspar, shining scales of mica or small crystals of calcite these also rarely escape observation. Shales and clay rocks generally are soft, fine grained, often laminated and not infrequently contain minute organisms or fragments of plants. Limestones are easily marked with a knife-blade, effervesce readily with weak cold acid and often contain entire or broken shells or other fossils. The crystalline nature of a granite or basalt is obvious at a glance, and while the former contains white or pink feldspar, clear vitreous quartz and glancing flakes of mica, the other shows yellow-green olivine, black augite, and gray stratiated plagioclase.
Other simple tools include the blowpipe (to test the fusibility of detached crystals), the goniometer, the magnet, the magnifying glass and the specific gravity balance.
Microscopic characteristics.
When dealing with unfamiliar types or with rocks so fine grained that their component minerals cannot be determined with the aid of a hand lens, a microscope is used. Characteristics observed under the microscope include colour, colour variation under plane polarised light (pleochroism, produced by the lower Nicol prism, or more recently polarising films), fracture characteristics of the grains, refractive index (in comparison to the mounting adhesive, typically Canada balsam), and optical symmetry (birefringent or isotropic). "In toto", these characteristics are sufficient to identify the mineral, and often to quite tightly estimate its major element composition.
The process of identifying minerals under the microscope is fairly subtle, but also mechanistic - it would be possible to develop an identification key that would allow a computer to do it. The more difficult and skilful part of optical petrography is identifying the interrelationships between grains and relating them to features seen in hand specimen, at outcrop, or in mapping.
Separation of components.
Separation of the ingredients of a crushed rock powder to obtain pure samples for analysis is a common approach. It may
be performed with a powerful, adjustable-strength electromagnet. A weak magnetic field attracts magnetite, then haematite and other iron ores. Silicates that contain iron follow in definite order—biotite, enstatite, augite, hornblende, garnet, and similar ferro-magnesian minerals are successively abstracted. Finally, only the colorless, non-magnetic compounds, such as muscovite, calcite, quartz, and feldspar remain. Chemical methods also are useful.
A weak acid dissolves calcite from crushed limestone, leaving only dolomite, silicates, or quartz. Hydrofluoric acid attacks feldspar before quartz and, if used cautiously, dissolves these and any glassy material in a rock powder before it dissolves augite or hypersthene.
Methods of separation by specific gravity have a still wider application. The simplest of these is levigation, which is extensively employed in mechanical analysis of soils and treatment of ores, but is not so successful with rocks, as their components do not, as a rule, differ greatly in specific gravity. Fluids are used that do not attack most rock-forming minerals, but have a high specific gravity. Solutions of potassium mercuric iodide (sp. gr. 3.196), cadmium borotungstate (sp. gr. 3.30), methylene iodide (sp. gr. 3.32), bromoform (sp. gr. 2.86), or acetylene bromide (sp. gr. 3.00) are the principal fluids employed. They may be diluted (with water, benzene, etc.) or concentrated by evaporation.
If the rock is granite consisting of biotite (sp. gr. 3.1), muscovite (sp. gr. 2.85), quartz (sp. gr. 2.65), oligoclase (sp. gr. 2.64), and orthoclase (sp. gr. 2.56), the crushed minerals float in methylene iodide. On gradual dilution with benzene they precipitate in the order above. Simple in theory, these methods are tedious in practice, especially as it is common for one rock-making mineral to enclose another. However, expert handling of fresh and suitable rocks yields excellent results.
Chemical analysis.
In addition to naked-eye and microscopic investigation, chemical research methods are of great practical importance to the petrographer. Crushed and separated powders, obtained by the processes above, may be analyzed to determine chemical composition of minerals in the rock qualitatively or quantitatively. Chemical testing, and microscopic examination of minute
grains is an elegant and valuable means of discriminating between mineral components of fine-grained rocks.
Thus, the presence of apatite in rock-sections is established by covering a bare rock-section with ammonium molybdate solution. A turbid yellow precipitate forms over the crystals of the mineral in question (indicating the presence of phosphates). Many
silicates are insoluble in acids and cannot be tested in this way, but others are partly dissolved, leaving a film of gelatinous
silica that can be stained with coloring matters, such as the aniline dyes (nepheline, analcite, zeolites, etc.).
Complete chemical analysis of rocks are also widely used and important, especially in describing new species. Rock analysis has of late years (largely under the influence of the chemical laboratory of the United States Geological Survey) reached a high pitch of refinement and complexity. As many as twenty or twenty-five components may be determined, but for practical purposes a knowledge of the relative proportions of silica, alumina, ferrous and ferric oxides, magnesia, lime, potash, soda and water carry us a long way in determining a rock's position in the conventional classifications.
A chemical analysis is usually sufficient to indicate whether a rock is igneous or sedimentary, and in either case to accurately show what subdivision of these classes it
belongs to. In the case of metamorphic rocks it often establishes whether the original mass was a sediment or of volcanic origin.
Specific gravity.
Specific gravity of rocks is determined by use of a balance and pycnometer. It is greatest in rocks containing the most magnesia, iron, and heavy metal while least in rocks rich in alkalis, silica, and water.
It diminishes with weathering. Generally, the specific gravity of rocks with the same chemical composition is higher if highly crystalline and lower if wholly or partly vitreous. The specific gravity of the more common rocks range from about 2.5 to 3.2.
Archaeological applications.
Archaeologists use petrography to identify mineral components in pottery. This information ties the artifacts to geological areas where the raw materials for the pottery were obtained. In addition to clay, potters often used rock fragments, usually called "temper" or "aplastics", to modify the clay's properties. The geological information obtained from the pottery components provides insight into how potters selected and used local and non-local resources. Archaeologists are able to determine whether pottery found in a particular location was locally produced or traded from elsewhere. This kind of information, along with other evidence, can support conclusions about settlement patterns, group and individual mobility, social contacts, and trade networks. In addition, an understanding of how certain minerals are altered at specific temperatures can allow archaeological petrographers to infer aspects of the ceramic production process itself, such as minimum and maximum temperatures reached during the original firing of the pot.


Nittany Arch

The Nittany Arch or Nittany anticline is an anticline geologic formation in the western part of the Ridge-and-Valley physiographic province of the Appalachian Mountains of Central Pennsylvania, United States. The Nitany Arch is more than 100 miles (160 kilometers) long, stretching from Muncy to Hollidaysburg, with a maximum width of approximately 9 miles (15 kilometers).
During the Appalachian orogeny, the sedimentary rock layers in this area folded up, forming the Nittany Arch. The arch was an ancient Himalayan scale mountain that towered above what is now Nittany Valley. It has since eroded leaving its many rock layers exposed with the youngest rock layers at the foot of the Allegheny Front. The more durable rock layers have left the surrounding sandstone ridges above the limestone valleys.


Charleston Sandstone

The Charleston Sandstone is a geologic formation in West Virginia. It preserves fossils dating back to the Carboniferous period.


Newlands Group

The Newlands Group is a geologic group in Scotland. It preserves fossils dating back to the Silurian period.


Davis Spring Formation

The Davis Spring Formation is a geologic formation in Nevada. It preserves fossils dating back to the Carboniferous period.


Brad Formation

The Brad Formation is a geologic formation in Texas. It preserves fossils dating back to the Carboniferous period.


Descon Formation

The Descon Formation is a geologic formation in Alaska. It preserves fossils dating back to the Silurian period.


Liming (soil)

Liming is the application (to soil) of calcium- and magnesium-rich materials in various forms, including marl, chalk, limestone, burnt lime or hydrated lime. In acid soils, these materials react as a base and neutralize soil acidity. This often improves plant growth and increases the activity of soil bacteria, but oversupply may result in harm to plant life.
Liming can also improve aggregate stability on clay soils. For this purpose structure lime, products containing calcium oxide (CaO) or hydroxide (Ca(OH)2) in mixes with calcium carbonate (CaCO3), are often used. Structure liming can reduce losses of clay and nutrients from soil aggregates.
The degree to which a given amount of lime per unit of soil volume will increase soil pH depends on the buffer capacity of the soil (this is generally related to soil cation exchange capacity or CEC). Soils with low CEC will usually show a more marked pH increase than soils with high CEC. But the low-CEC soils will witness more rapid leaching of the added bases, and so will see a quicker return to original acidity unless additional liming is done.
Over-liming is most likely to occur on soil which has low CEC, such as sand which is deficient in buffering agents such as organic matter and clay.
Most acid soils are saturated with aluminium rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminium. This concept of "corrected lime potential" to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the "lime requirement" of soils.
An agricultural study at the Faculty of Forestry in Freising, Germany that compared tree stocks 2 and 20 years after liming found that liming promotes nitrate leaching and decreases the phosphorus content of some leaves.


Timeline of Cambrian research

This timeline of Cambrian research is a chronological listing of events in the history of geology and paleontology focused on the study of earth during the span of time lasting from 541 to 485.4 million years ago and the legacies of this period in the rock and fossil records.
19th century.
1892
20th century.
1911
1912
1977


Phoenix Plate

The Phoenix Plate (also known as the Aluk Plate or Drake Plate) was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as early as 410 million years ago, during which time the Phoenix Plate was subducting under eastern Gondwana.
By the Late Jurassic–Early Cretaceous 150–130 million years ago, the Pacific Plate arose from the Izanagi-Farallon-Phoenix triple junction, resulting in the creation of the Izanagi-Pacific-Phoenix and Farallon-Pacific-Phoenix triple junctions. Subduction ceased east of Australia about 120 million years ago, during which time a transform/transpressional boundary formed. This transform/transpressional boundary with the Phoenix Plate lasted until about 80 million years ago as the plate continued to descend southwards as a result of Late Cretaceous subduction under the Antarctic Peninsula.
During the Late Cretaceous or early Cenozoic, the southwestern part of the Phoenix Plate fragmented into the Charcot Plate, much in the same way in which the Rivera and Cocos plates were formed by the fragmentation of the Farallon Plate.
The Antarctic-Phoenix Ridge, a mid-oceanic ridge between the Antarctic and Phoenix plates, initiated following Late Cretaceous to early Cenozoic times when the Phoenix Plate had divergent boundaries with the Bellingshausen and Pacific plates in the southwestern Pacific Ocean. A major decrease in spreading rate of the Antarctic-Phoenix Ridge and the convergence rate of the Phoenix Plate with the Antarctic Plate occurred around 52.3 million years ago, followed by subduction of a segment of the Antarctic-Phoenix Ridge between 50 and 43 million years ago.
Although active subduction occurred for over 100 million years, it stopped or slowed dramatically about 3.3 million years ago when seafloor spreading on the Antarctic-Phoenix Ridge ceased, leaving a small remnant of the former Phoenix Plate incorporated in the Antarctic Plate. This remnant underlies the southwest Drake Passage and is surrounded by the Shackleton Fracture Zone in the northeast, the Hero Fracture Zone in the southwest, the South Shetland Trough in the southeast and the extinct Antarctic-Phoenix Ridge in the northwest.


Vegetation-induced sedimentary structures

Vegetation-induced sedimentary structures (VISS) are primary sedimentary structures formed by the interaction of detrital sediment with "in situ" plants. VISS provide physical evidence of vegetation's fundamental role in mediating sediment accumulation and erosion in clastic depositional environments. VISS can be broken into seven types, five being hydrodynamic and two being decay-related. The simple hydrodynamic VISS are categorized by centroclinal cross strata, scratch semicircles and upturned beds. The complex hydrodynamic VISS are categorized by coalesced scour fills and scour-and-mound beds. The decay-related VISS are categorized by mudstone-filled hollows and downturned beds.
Hydrodynamic structures.
Upturned beds (vegetation shadow).
Upturned beds are mounds of elongated sediment that are deposited on the lee (downflow) side of an obstruction, containing form-concordant stratification. These may also be described as tongue shaped. These beds are formed where plants were once standing and caused a decrease in bed shear, allowing sediment to deposit near their base. This commonly occurs with meandering flow that deposits sediment on the lee side of a plant. Sediment is also accumulated on the front and sides of an obstruction when deposition is high. The presence of upturned beds in cross-section is consistent with modern vegetation shadows.
Scratch circles.
Sets of concentric grooves that form in sand or mud by the action of sharp objects anchored at the center of a curvature set. Most likely formed from some sort of free moving plant under water. Plants are bent by the current, causing them to scratch concentric grooves into the adjacent substrate. The grooves are most likely formed in a muddy substrate, which preserved them during deposition of the overlying sediment. These scratch semicircles can record currents in wind or water during ancient deposition.
Centroclinal cross strata.
Bodies of fine to very fine grained sand that fill symmetrical, cone shaped, depressions centered on tree trunks by swirling flood water. The fill is generally organized into form-concordant, concentric laminae that dip towards the tree. Centroclinal cross strata form from the infilling of scours created around trees by swirling flood water. Studies and piers show us just how the scouring process works. In front of these piers, decelerating flow and friction with the bed material causes a downward pressure gradient that leads to erosive downflow. Downflow is accompanied by horseshoe shaped sediment deposits that generate a U-shaped scour around the front and sides of the obstruction.
Scour-and-mound beds.
Diffuse sandy lenses associated with standing vegetation at numerous horizons, within the poorly drained floodplain assemblage containing heterolithic bedding. These typically occur above rooted horizons. Scour-and-mound beds that are between sand and heterolithic bedding would suggests that they are formed in forested areas with standing water. Where sand charged flows rapidly decelerated and deposited large amounts of sediment with only minimal scour.
Coalesced scour fills.
Large, internally complex sandstone bodies in well-drained floodplain strata, which superficially resemble small channel bodies. These discrete, locally thickened accumulations are laterally equivalent to thin sheet (crevasse splay) sandstones and are strongly incised into red mudstones. Coalesced scour fills are strongly erosional structures formed where interconnected scours between trees are infilled with sandy sediment during waning flow. Strong incision into underlying strata and downflow tapering suggests that the precursor scours formed in response to vigorous floods across the well-drained floodplain. These essentially are unconstrained by channels and vegetation. The current flow carried only enough sand to fill the scour and blanket the floodplain with a thin sand layer.
Decay-related structures.
Downturned beds and mudstone-filled hollows.
Sedimentary structures that appear to "protrude" into underlying strata.
Most likely from the decay of entombed plants. These may have a "pothole-like" form. They reflect a prominent component of soft-sediment deformation in overlying and adjacent strata, but may also represent hydrodynamic activity around a plant that was not preserved.


List of fossil species in the London Clay

A list of prehistoric and extant species whose fossils have been found in the London Clay, which underlies large areas of southeast England.
Plant fossils, especially seeds and fruits, are found in abundance and have been collected from the London Clay for almost 300 years. Some 350 named species of plant have been found, making the London Clay flora one of the world's most diverse for fossil seeds and fruits. The flora includes plant types found today in tropical forests of Asia and demonstrates the much warmer climate of the Eocene epoch, with plants such as "Nypa" (Nipah palms) and other palms being frequently encountered. The following plants list is incomplete and is based on the research by Marjorie Chandler. and research works done by the paleobotanist Steven R. Manchester and by professor of plant palaeobiology Margaret Collinson.
Animals.
Animal fossils include bivalves, gastropods, nautilus, worm tubes, brittle stars and starfish, crabs, lobsters, fish (including shark and ray teeth), reptiles (particularly turtles), and a large diversity of birds. A few mammal remains have also been recorded. Preservation varies; articulated skeletons are generally rare. Of fish, isolated teeth are very frequent. Bird bones are not infrequently encountered compared to other "lagerstätten", but usually occur as single bones and are often broken.
The following fauna species list follows Clouter (2007).
Vertebrates.
Reptiles.
Crocodylians
Snakes
Turtles and tortoises
Molluscs.
Bivalves.
Anomiidae
Astartidae


Dunbar Creek Formation

The Dunbar Creek Formation is a geologic formation in Montana. It preserves fossils dating back to the Paleogene period.


Claudine Stirling

Claudine Helen Stirling is a New Zealand isotope geochemistry academic. As of 2018, she is a full professor at the University of Otago.
Academic career.
After a 1996 PhD titled " 'High-precision U-series dating of corals from Western Australia : implication for last interglacial sea-levels' " at the Australian National University, Stirling worked at University of Michigan and ETH Zürich before moving to the University of Otago in 2006, rising to full professor in 2018.


Bear Rock Formation

The Bear Rock Formation is a geologic formation in Northwest Territories. It preserves fossils dating back to the Devonian period.


Grande Coupe Beds

The Grande Coupe Beds is a geologic formation in Quebec. It preserves fossils dating back to the Ordovician period.


Montgomery Creek Formation

The Montgomery Creek Formation is a geologic formation in California. It preserves fossils dating back to the Paleogene period.


Vunta Formation

The Vunta Formation is a geologic formation in Northwest Territories. It preserves fossils dating back to the Silurian period.


Milk Creek Formation

The Milk Creek Formation is a geologic formation in Arizona. It preserves fossils dating back to the Neogene period.


Neumann lines

Neumann lines, or Neumann bands, are fine patterns of parallel lines seen in cross-sections of many hexahedrite iron meteorites in the kamacite phase, although they may appear also in octahedrites provided the kamacite phase is about 30 micrometres wide. They can be seen after a polished meteorite cross-section is treated with acid. The lines are indicative of a shock-induced deformation of the kamacite crystal, and are thought to be due to impact events on the parent body of the meteorite.
The lines are named after Johann G. Neumann, who discovered them in 1848 in the iron meteorite Braunau, a hexahedrite, which fell in 1847.


Crychan Formation

The Crychan Formation is a geologic formation in Wales. It preserves fossils dating back to the Silurian period.


Hook Head Formation

The Hook Head Formation is a geologic formation in Ireland. It preserves fossils dating back to the Carboniferous period.


Gypsum des Camoins

The Gypsum des Camoins is a geologic formation in France. It preserves fossils dating back to the Paleogene period.


Sericitic alteration

Sericitic alteration or sericitization is a process of mineral alteration caused by hydrothermal fluids invading permeable country rock. Plagioclase feldspar within the rock is converted to sericite (sericite is not a mineral; it is a term that is used to describe any fine-grained white phyllosilicate when a distinction cannot be determined), which typically consists of fine-grained white mica and related minerals. Sericitic alteration occurs within the phyllic alteration zone.


Neidr Facula

Neidr Facula is a bright, irregular depression on the surface of Mercury, located at 35.9° N, 302.7° W. It was named by the IAU in 2018. "Neidr" is the Welsh word for snake.
Neidr Facula is located north of the prominent Rachmaninoff crater and west of the bright Nathair Facula.


Creechbarrow Limestone

The Creechbarrow Limestone is a geologic formation in England. It preserves fossils dating back to the Paleogene period.


Paramecia (alga)

Paramecia is a non-mineralized Ediacaran alga with a differentiated, compartmentalized thallus. This alga probably had multiple phases in its lifecycle, as possible reproductive structures have been identified.


Hohe Warte Limestone

The Hohe Warte Limestone is a geologic formation in Austria. It preserves fossils dating back to the Devonian period.


Chelsea filter

In gemmology, a Chelsea filter is a dichromatic optical filter used for identifying coloured stones.
History.
The "chelsea" filter was originally devised by Anderson and Payne in 1934 of the Gem testing Laboratory of the London Chamber of Commerce & Industry. The filter was devised with the collaboration of gemmology students of the Chelsea College of Science and Technology where Basil Anderson was an instructor for the Gemmological Association of Great Britain. Since this filter allows transmission of both deep-red wavelengths around 690 nanometres and yellow-green wavelengths, around 570 nanometres, that matched emerald's emission and absorption characteristics, this filter was initially recommended to assist the discrimination between natural emerald and its simulants such as green glass, tourmaline, peridot, etc. This discrimination is possible because chromium (containing iron) and vanadium-free emeralds emit a red fluorescence when illuminated by white light that also has a content of ultraviolet wavelengths.
Synthetic emeralds were commercially introduced around 1940. These produce the same pink-red response as some emeralds through the Chelsea filter. However, although this filter is unable to predictably discriminate between natural and synthetic emerald, it has been subsequently found capable of distinguishing aquamarine, blue topaz, and their blue synthetic spinel simulants, because unlike natural gemstones, blue cobalt-containing synthetic spinels emit a red fluorescence under white light.
"Chelsea Colour Filter" is a UK Trademark held by The Gemmological Association of Great Britain (UK Trademark Registration No. 1473951).
Use.
Hold the filter an inch or two from the eye. Light the stone with a strong incandescent light bulb or torch, not LED. The stone may appear to change colour. The filter must be held near to the eye but there is no need to hold the filter close to the stone, even items in showcases can be examined providing they are lit by strong lights.
Chelsea Filters were also used to help separate aquamarine and natural zircon from synthetic flame-fusion spinel (used extensively in "birthstone" jewelry), as both of the former absorb the red portion of the spectrum and the synthetic spinel did not.


Carbon Peak

Carbon Peak, elevation , is a summit in the West Elk Mountains of Colorado. The peak is southwest of Crested Butte in the Gunnison National Forest. Carbon peak is a laccolith formed during the mid-Tertiary period, and is part of the “laccolith triangle” as described by the Colorado Geological Survey.


Danny Bridge Formation

The Danny Bridge Formation is a geologic formation in England. It preserves fossils dating back to the Carboniferous period.


Brasso Clay

The Brasso Clay is a geologic formation in Trinidad and Tobago. It preserves fossils dating back to the Neogene period.


Lech (river)

The Lech (, "Licca") is a river in Austria and Germany. It is a right tributary of the Danube in length with a drainage basin of .
Its source is located in the Austrian state of Vorarlberg, where the river rises from lake Formarinsee in the Alps at an altitude of . It flows in a north-north-easterly direction and crosses the German border, forming the Lechfall, a waterfall; afterwards the river enters a narrow gorge (the Lechschlucht). Leaving the Alps, it enters the plains of the Allgäu at Füssen at an elevation of in the German state of Bavaria, where it used to be the location of the boundary with Swabia. The river runs through the city of Füssen and through the Forggensee, a man-made lake which is drained in winter. Here, it forms rapids and a waterfall.
The river flows further northwards through a region called the Lechrain, and passes the cities of Schongau, Landsberg, Augsburg (where it receives the Wertach) and Rain before entering the Danube just below Donauwörth at an elevation of . It is not navigable, owing to its torrential character and the gravel beds which choke its channel. There are extensive views of the Lech valley from Neuschwanstein Castle, near Füssen.
Etymology.
Inscriptions from 8/7 B. C. prove that the river name is first mentioned in the Celtic tribe name "Licates". The river itself is called "Likios" or "Likias" in the 2nd century. Around the year 570 the name "Licca" is found in records. In the 8th century, names such as "Lecha" and "Lech" appeared. The term "Licus" is still used in 1059.
The name stands in analogy to the Welsh word "llech" ("stone slab") and the Breton word "lec'h" ("gravestone"). In this context, the meaning of the word "Lech" is explained as "the stony".
History.
On more than one occasion, historic events have been decided on the banks of this river.
Hydroelectric power plants.
Currently, there are 33 hydroelectric power plants on the Lech. The power plants are listed beginning at the headwaters:
 |
 | Lechstaustufe 8a – Kinsau || 9.2 || 1992 ||
 |
 | Lechstaustufe 9 – Apfeldorf || 7.2 || 1944 ||
 |
 | Lechstaustufe 10 – Epfach || 8.3 || 1948 ||
 |
 | Lechstaustufe 11 – Lechblick || 8.1 || 1943 ||
 |
 | Lechstaustufe 12 – Lechmühlen || 7.9 || 1943 ||
 |
 | Lechstaustufe 13 – Dornstetten || 8.2 || 1943 ||
 |
 | Lechstaustufe 14 – Pitzling || 7.9 || 1944 ||
 |
 | Lechstaustufe 15 – Landsberg || 8.0 || 1944 ||
 |
 | Lechstaustufe 18 – Kaufering || 16.7 || 1975 ||
 |
 | Lechstaustufe 19 – Schwabstadl || 12.0 || 1981 ||
 |
 | Lechstaustufe 20 – Scheuring || 12.2 || 1980 ||
 |
 | Lechstaustufe 21 – Prittriching || 12.1 || 1983 ||
 |
 | Lechstaustufe 22 – Unterbergen || 12.4 || 1982 ||
 |
 | Lechstaustufe 23 – Mandichosee || 12.0 || 1978 ||
 |
 | Hochablass || 3.1 || 2013 ||
 |
 | Eisenbahnerwehr || 3.2 || 2006 ||
 |
 | Wolfzahnauwehr || 2.0 || 2010 ||
 |
 | Kraftwerk Gersthofen || 9.9 || 1901 ||
 |
 | Kraftwerk Langweid || 7.0 || 1908 ||
 |
 | Kraftwerk Meitingen || 11.6 || 1922 ||
 |
 | Staustufe Ellgau || 10.0 || 1952 ||
 |
 | Staustufe Oberpeiching || 12.3 || 1954 ||
 |
 | Staustufe Rain || 11.2 || 1955 ||
 |
 | Staustufe Feldheim || 8.5 || 1960 ||


Moydart Formation

The Moydart Formation is a geologic formation in Nova Scotia. It preserves fossils dating back to the Silurian period.


East Beckwith Mountain

East Beckwith Mountain is a prominent mountain summit in the West Elk Mountains range of the Rocky Mountains of North America. The peak is located in the West Elk Wilderness of Gunnison National Forest, west by south (bearing 264°) of the Town of Crested Butte in Gunnison County, Colorado, United States.
Geology.
East Beckwith Mountain is a laccolith, formed when magma intruded into Mancos Shale approximately 30 million years ago. Subsequently the softer, overlying sedimentary rock has eroded away, exposing the more resistant igneous rock. East Beckwith Mountain is one of over a dozen laccoliths in the West Elk and adjacent Elk Mountains. Of these laccoliths, East Beckwith Mountain is noted for its distinctive glacial landforms. On the north side of this elongated, east-west oriented mountain, there are five glacially carved cirques with intervening arêtes, and moraines fan out from the mountain's base.