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27-488: A formation must be large enough that it can be mapped at the surface or traced in the subsurface. Formations are otherwise not defined by the thickness of their rock strata, which can vary widely. They are usually, but not universally, tabular in form. They may consist of a single lithology (rock type), or of alternating beds of two or more lithologies, or even a heterogeneous mixture of lithologies, so long as this distinguishes them from adjacent bodies of rock. The concept of

54-446: A facies , stratum , bed , seam , lode etc. Thickness is measured at right angles to the surface of the seam or bed and thus independently of its spatial orientation. The concept of thickness came originally from mining language, where it was used mainly to indicate the workability of seams. It has since become an established term in earth science , for example in geology, for the depth of sedimentary rocks , in hydrogeology for

81-592: A geologic formation goes back to the beginnings of modern scientific geology. The term was used by Abraham Gottlob Werner in his theory of the origin of the Earth, which was developed over the period from 1774 to his death in 1817. The concept became increasingly formalized over time and is now codified in such works as the North American Stratigraphic Code and its counterparts in other regions. Geologic maps showing where various formations are exposed at

108-525: A newly designated formation could not be named the Kaibab Formation, since the Kaibab Limestone is already established as a formation name. The first use of a name has precedence over all others, as does the first name applied to a particular formation. As with other stratigraphic units, the formal designation of a formation includes a stratotype which is usually a type section . A type section

135-594: A permanent natural or artificial feature of the geographic area in which they were first described. The name consists of the geographic name plus either "Formation" or a descriptive name. Examples include the Morrison Formation , named for the town of Morrison, Colorado , and the Kaibab Limestone , named after the Kaibab Plateau of Arizona. The names must not duplicate previous formation names, so, for example,

162-428: A specialized area within their geological discipline and are employed by universities. In Canada, National Instrument 43-101 requires reports containing estimates of mineral resources and reserves to be prepared by, or under the supervision of, a Qualified Person (QP) who has at least five years of experience with the reported minerals and is a member of a professional association. The QP accepts personal liability for

189-448: Is not a valid lithological basis for defining a formation. The contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping normally practiced in the region; the thickness of formations may range from less than a meter to several thousand meters. Geologic formations are typically named after

216-431: Is also used informally to describe the odd shapes (forms) that rocks acquire through erosional or depositional processes. Such a formation is abandoned when it is no longer affected by the geologic agent that produced it. Some well-known cave formations include stalactites and stalagmites . Thickness (geology) Thickness in geology and mining refers to the distance across a packet of rock , whether it be

243-559: Is central to the geologic discipline of stratigraphy , and the formation is the fundamental unit of stratigraphy. Formations may be combined into groups of strata or divided into members . Members differ from formations in that they need not be mappable at the same scale as formations, though they must be lithologically distinctive where present. The definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata . Formations were at first described as

270-410: Is common in the fields of geography , engineering , chemistry , urban planning , environmental studies , among others. Geologists, can be generally identified as a specialist in one or more of the various geoscience disciplines, such as a geophysicist or geochemist. Geologists may concentrate their studies or research in one or more of the following disciplines: Professional geologists may work in

297-455: Is ideally a good exposure of the formation that shows its entire thickness. If the formation is nowhere entirely exposed, or if it shows considerably lateral variation, additional reference sections may be defined. Long-established formations dating to before the modern codification of stratigraphy, or which lack tabular form (such as volcanic formations), may substitute a type locality for a type section as their stratotype. The geologist defining

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324-525: Is the deposition of lava from volcanoes, as opposed to the Neptunists , led by Abraham Werner , who believed that all rocks had settled out of a large ocean whose level gradually dropped over time. The first geological map of the United States was produced in 1809 by William Maclure . In 1807, Maclure commenced the self-imposed task of making a geological survey of the United States. Almost every state in

351-612: Is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time. For an aspiring geologist, training typically includes significant coursework in physics , mathematics , and chemistry , in addition to classes offered through the geology department; historical and physical geology, igneous and metamorphic petrology and petrography, hydrogeology , sedimentology , stratigraphy , mineralogy , palaeontology , physical geography and structural geology are among

378-409: The field and the laboratory . Geologists work in the energy and mining sectors to exploit natural resources . They monitor environmental hazards such as earthquakes , volcanoes , tsunamis and landslides . Geologists are also important contributors to climate change discussions. James Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of

405-571: The Earth to the Royal Society of Edinburgh . In his paper, he explained his theory that the Earth must be much older than had previously been supposed to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795 ( Vol. 1 , Vol. 2 ). Followers of Hutton were known as Plutonists because they believed that some rocks were formed by vulcanism , which

432-768: The Union was traversed and mapped by him; the Allegheny Mountains being crossed and recrossed some 50 times. The results of his unaided labors were submitted to the American Philosophical Society in a memoir entitled Observations on the Geology of the United States explanatory of a Geological Map , and published in the Society's Transactions , together with the nation's first geological map. This antedates William Smith 's geological map of England by six years, although it

459-646: The country. This 'wellbeing' is often in the form of greater tax revenues from new or extended mining projects or through better infrastructure and/or natural disaster planning. An engineering geologist is employed to investigate geologic hazards and geologic constraints for the planning, design and construction of public and private engineering projects, forensic and post-mortem studies, and environmental impact analysis . Exploration geologists use all aspects of geology and geophysics to locate and study natural resources. In many countries or U.S. states without specialized environmental remediation licensure programs,

486-528: The environmental remediation field is often dominated by professional geologists, particularly hydrogeologists, with professional concentrations in this aspect of the field. Petroleum and mining companies use mudloggers , and large-scale land developers use the skills of geologists and engineering geologists to help them locate oil and minerals, adapt to local features such as karst topography or earthquake risk, and comply with environmental regulations. Geologists in academia usually hold an advanced degree in

513-548: The essential geologic time markers, based on their relative ages and the law of superposition . The divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. Geologic formations can be usefully defined for sedimentary rock layers, low-grade metamorphic rocks , and volcanic rocks . Intrusive igneous rocks and highly metamorphosed rocks are generally not considered to be formations, but are described instead as lithodemes . "Formation"

540-520: The formation is expected to describe the stratotype in sufficient detail that other geologists can unequivocally recognize the formation. Although formations should not be defined by any criteria other than primary lithology, it is often useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, and chemostratigraphic units on geochemical criteria, and these are included in stratigraphic codes. The concept of formally defined layers or strata

567-487: The many required areas of study. Most geologists also need skills in GIS and other mapping techniques. Geology students often spend portions of the year, especially the summer though sometimes during a January term, living and working under field conditions with faculty members (often referred to as "field camp"). Many non-geologists often take geology courses or have expertise in geology that they find valuable to their fields; this

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594-595: The mining industry or in the associated area of mineral exploration . They may also work in oil and gas industry. Some geologists also work for a wide range of government agencies, private firms, and non-profit and academic institutions. They are usually hired on a contract basis or hold permanent positions within private firms or official agencies (such as the Geological Survey and Mineral Exploration of Iran ). Local, state, and national governments hire geologists to work on geological projects that are of interest to

621-558: The professional quality of the report and underlying work. The rules and guidelines codified in National Instrument 43-101 were introduced after a scandal in 1997 where Bre-X geologists salted drill core samples at a gold exploration property in Busang, Indonesia. The falsified drilling results misled Bre-X investors and upon discovery of the fraud, the company collapsed in the largest gold mining scam in history. In Europe exists

648-427: The public community. The investigation of a country's natural resources is often a key role when working for government institutions; the work of the geologist in this field can be made publicly available to help the community make more informed decisions related to the exploitation of resources, management of the environment and the safety of critical infrastructure - all of which is expected to bring greater wellbeing to

675-642: The surface are fundamental to such fields as structural geology , allowing geologists to infer the tectonic history of a region or predict likely locations for buried mineral resources. The boundaries of a formation are chosen to give it the greatest practical lithological consistency. Formations should not be defined by any criteria other than lithology. The lithology of a formation includes characteristics such as chemical and mineralogical composition, texture, color, primary depositional structures , fossils regarded as rock-forming particles, or other organic materials such as coal or kerogen . The taxonomy of fossils

702-425: The vertical extent of groundwater – i.e. the distance from the base of the groundwater layer to its surface – or in soil science for the vertical extent of soil horizons . Geologist A geologist is a scientist who studies the structure, composition, and history of Earth . Geologists incorporate techniques from physics , chemistry , biology , mathematics , and geography to perform research in

729-473: Was constructed using a different classification of rocks. Sir Charles Lyell first published his famous book, Principles of Geology , in 1830. This book, which influenced the thought of Charles Darwin , successfully promoted the doctrine of uniformitarianism . This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism

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