Digital outcrop model
A digital outcrop model called a virtual outcrop model, is a digital 3D representation of the outcrop surface in a form of textured polygon mesh. DOMs allow for interpretation and reproducible measurement of different geological features, e.g. orientation of geological surfaces and thickness of layers. The quantity of identifiable and measurable geological features depends on the outcrop model resolution and accuracy. Using remote sensing techniques enables these 3D models to cover areas with difficult accessibility, e.g. several meter high cliff walls. The fact that geological interpretation can be performed on the screen in inaccessible areas where using conventional fieldwork methods may be unsafe, the large quantity of data that can be collected in short time are the key advantages of using DOMs. Georeferencing digital outcrop models allows for integration with other spatial data, e.g. results of digital geologic mapping or GIS. Alternatively to the photorealistic textured models 3D digital outcrop models may be represented by a point cloud coloured with the spectral data from the corresponding images.
Such surface model representation describes the topography of the outcrop but due to its discrete nature is difficult to interpret. Texturing digital polygonal outcrop models with images enhances the models with high resolution continuous data and therefore facilitates geological interpretation. Creation of textured DOMs can be divided into three main steps: creation of the outcrop surface model, pre-processing and registration of images covering the outcrop, texture mapping. In order to achieve the required model resolution and accuracy data are collected from the ground or from a helicopter platform. Airborne and satellite data may be integrated but as complementary datasets for the outcrop areas where close-range data are missing. Creation of the digital outcrop surface model consists of the following steps: Data acquisitionDigital data needed to create an outcrop surface model may be obtained, as in the case of digital elevation models, from laser scanning or reconstructed from multiple images taken from multiple views using structure from motion or stereo vision techniques.
An incomplete list of software packages allowing for image based modelling can be found here. Models produced with the above mentioned methods may result in comparable level of detail. Regardless of the method applied, the primary resulting data are similar: 3D coordinates of large number of points, in a form of a point cloud, describing the outcrop surface. 2. Merging point clouds and georeferencing Point clouds obtained from different perspectives need to be merged and registered into a single coordinate system. In the registration process a 3D transformation is computed between common parts of two point clouds; the 3D transformation parameters can be found on the basis of the corresponding points in the two point clouds, surface matching, in the case of mobile mapping supported by GNSS and INS, by using the direct sensor orientation methodIn the point cloud georeferencing process a 3D transformation is computed between the local project coordinate system and a geodetic coordinate system. In order to complete that action minimum three points are required, that can be located in the point cloud and their coordinates in the geodetic system are known.
3. Point cloud cleaning and decimation Regardless of the methodology of the data acquisition, the resulting point cloud is filtered and cleaned from unwanted objects, e.g. vegetation. Decrease of the overall point cloud density might be required depending on the outcrop surface complexity and size of the dataset. 4. 3D triangulation and triangle mesh optimization In order to enable the possibility of model texturing, the edited point cloud is transformed into a triangulated irregular network. Correct 3D data triangulation is a non-trivial task due to potential scan shadows, sharp topography changes and random errors; therefore additional mesh editing and optimization is required to improve equiangularity, solve topology problems or reorient inverted surface normals. Image registrationCreation of the textured 3D models requires definition of the relationship between all the triangle mesh vertices and the corresponding image points. Collinearity condition can be used in order to find that relationship, but image interior and exterior orientation parameters need to be known.
Interior camera orientation parameters are derived from the camera calibration process. When laser scanning is used during the data collection, the camera is coupled rigidly with the scanner and its orientation relative to the scanner is measured. In such cases exterior orientation parameters can be retrieved for all the images using 3D transformation. Otherwise it is possible to establish exterior camera orientation parameters on the basis of known coordinates of minimum three points on the 3D outcrop surface model and the image. In the case of a 3D outcrop surface model derived from photo modelling, the interior and exterior image orientation parameters may be computed by the modelling software.2. Image pre-selection and colour balancing Depending on the applied rendering approach a pre-selection of images most relevant for texture mapping might be needed. If the images used in the final texturing process were acquired under different illumination conditions and colours of corresponding features visible in different images differ image colour adjustment may be required.
Different texture mapping algorithms exist, e.g.: single image textu
Uttara Kannada/ North Canara is a district in the Indian state of Karnataka. It is bordered by the state of Goa and Belagavi District to the north, Dharwad District and Haveri District to the east, Shivamogga District and Udupi District to the south, the Arabian Sea to the west; the city of Karwar is the administrative headquarters of the district. Sirsi and Bhatkal are other major towns in the district; the district has 2 agroclimatic divisions, namely: The coastal plain, consisting of Karwar, Kumta and Bhatkal taluks. The Malenadu, consisting of Sirsi, Yellapur, Haliyal and Mundgod taluks; the first known dynasty from Uttar Kannada District are Chutus of Banavasi. Uttara Kannada was the home of the Kadamba kingdom from the 350 to 525, they ruled from Banavasi. After the subjugation of the Kadambas by the Chalukyas, the district came under successive rule of empires like Chalukyas, Rashtrakutas and Vijayanagar empire. Famous Moroccan traveler Ibn Battuta is said to have stayed for a time in the district under the protection of Nawayath Sultan Jamal Al-Din at Hunnur.
This place is located in the town of Honnavar. Ruins of an old mosque and its minaret can still be seen in the village; the district came under the rule of Maratha Empire in the 1750s and part of Mysore Kingdom, who ceded it to the British at the conclusion of the Fourth Mysore War in 1799. It was initilally part of Kanara district in Madras Presidency; the district was divided to North and South Kanara districts in 1859. The British transferred Uttara Kannada district to Bombay Presidency in 1862. After India's independence in 1947, Bombay Presidency was reconstituted as Bombay State. In 1956 the southern portion of Bombay State was added to Mysore State, renamed Karnataka in 1972. Significant and picturesque, the Sadashivgad fort of historical importance is now a popular tourist destination located by the Kali river bridge, built at the confluence of the river and the Arabian Sea; the renowned Bengali poet and Nobel laureate Rabindranath Tagore, who visited Uttara Kannada in 1882, dedicated an entire chapter of his memoirs to this town.
The 22-year-old Rabindranath Tagore stayed with his brother, Satyendranath Tagore, the district judge in Uttara Kannada. There is a substantial amount of Chardo families in this area as they had migrated due to the persecution of the Portuguese in Goa. Cintacora known as Chitrakul and Sindpur, was known to the Portuguese as a old port; when Sadashivgad was built in this area, the village came to be known by that name. Pir fort, named for the Dargah of Shahkaramuddin, was captured and burnt by the Portuguese in 1510; the creek at the mouth of the Kali River was a trading center which came into greater prominence after Sadashivgad was built and the Portuguese realised the advantages of its sheltered harbor. In 1638 a rival English trading body, the Courteen Association, established a factory at Uttara Kannada, it was a trade port frequented by traders from Africa. Baitkhol port was famous for its natural harbour; the name Baithkhol is Bait-e-kol, meaning bay of safety. Muslin was the chief commodity purchased but Uttara Kannada was a source for pepper, cardamom and coarse blue cotton cloth.
Situated on India's west coast, 50 miles south-east of Goa, Uttara Kannada was noted for its safe harbour. In 1649 the Courteen Association united with the British East India Company and Uttara Kannada became a company factory. In the Treaty of Mangalore signed in 1784, between Tipu Sultan and the East India Company, one finds reference to Uttara Kannada and Sadashivgad written as Karwar and Sadasewgude respectively. Bhatkal and Honnavar were the chief ports of Tippu Sultan in the district; the British made Uttara Kannada their district headquarters in 1862. Since 1862, the time from which it came under Bombay Presidency, Uttara Kannada was described as a first rate harbor between Bombay and Colombo, it became a part of Maratha territory. It was a part of the Bombay Presidency until 1950; the main geographic feature of the district is the Western Ghats or Sahyadri range, which runs from north to south through the district. Between the Sahyadris and the sea is a narrow coastal strip, known as the Payanghat, which varies from 8 to 24 kilometres in width.
Behind the coastal plain are flat-topped hills from 60 to 100 meters in height, behind the hills are the ridges and peaks of the Sahyadris. East of the Sahyadris is part of the vast Deccan plateau. Moisture-bearing winds come from the west, yearly rainfall averages 3,000 millimetres on the coast, as high as 5,000 millimetres on the west-facing slopes of the Sahyadris. East of the crest is the rain shadow of the Sahyadris, which receive as little as 1,000 millimetres annually. Much of the rain falls in the June–September monsoon. Five major rivers drain westwards from the crest of the Sahyadris to the sea; these rivers form numerous waterfalls, the most famous of, Jog falls, on upper reaches of the Sharavati in neighboring Shimoga district, other famous waterfalls include Unchalli Falls, where the river Aghanashini drops 116 meters, Magod Falls, where the Bedti river plunges 180 meters in two leaps, Shivganga falls, where the river Sonda drops 74 meters, Lalguli falls and Mailmane falls on the river Kali.
In the lowlands, these rivers form wide estuaries, extending several kilometers inland from the coast. The
India known as the Republic of India, is a country in South Asia. It is the seventh largest country by area and with more than 1.3 billion people, it is the second most populous country as well as the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives, while its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia; the Indian subcontinent was home to the urban Indus Valley Civilisation of the 3rd millennium BCE. In the following millennium, the oldest scriptures associated with Hinduism began to be composed. Social stratification, based on caste, emerged in the first millennium BCE, Buddhism and Jainism arose. Early political consolidations took place under the Gupta empires. In the medieval era, Zoroastrianism and Islam arrived, Sikhism emerged, all adding to the region's diverse culture.
Much of the north fell to the Delhi Sultanate. The economy expanded in the 17th century in the Mughal Empire. In the mid-18th century, the subcontinent came under British East India Company rule, in the mid-19th under British Crown rule. A nationalist movement emerged in the late 19th century, which under Mahatma Gandhi, was noted for nonviolent resistance and led to India's independence in 1947. In 2017, the Indian economy was the world's sixth largest by nominal GDP and third largest by purchasing power parity. Following market-based economic reforms in 1991, India became one of the fastest-growing major economies and is considered a newly industrialised country. However, it continues to face the challenges of poverty, corruption and inadequate public healthcare. A nuclear weapons state and regional power, it has the second largest standing army in the world and ranks fifth in military expenditure among nations. India is a federal republic governed under a parliamentary system and consists of 29 states and 7 union territories.
A pluralistic and multi-ethnic society, it is home to a diversity of wildlife in a variety of protected habitats. The name India is derived from Indus, which originates from the Old Persian word Hindush, equivalent to the Sanskrit word Sindhu, the historical local appellation for the Indus River; the ancient Greeks referred to the Indians as Indoi, which translates as "The people of the Indus". The geographical term Bharat, recognised by the Constitution of India as an official name for the country, is used by many Indian languages in its variations, it is a modernisation of the historical name Bharatavarsha, which traditionally referred to the Indian subcontinent and gained increasing currency from the mid-19th century as a native name for India. Hindustan is a Middle Persian name for India, it was introduced into India by the Mughals and used since then. Its meaning varied, referring to a region that encompassed northern India and Pakistan or India in its entirety; the name may refer to either the northern part of India or the entire country.
The earliest known human remains in South Asia date to about 30,000 years ago. Nearly contemporaneous human rock art sites have been found in many parts of the Indian subcontinent, including at the Bhimbetka rock shelters in Madhya Pradesh. After 6500 BCE, evidence for domestication of food crops and animals, construction of permanent structures, storage of agricultural surplus, appeared in Mehrgarh and other sites in what is now Balochistan; these developed into the Indus Valley Civilisation, the first urban culture in South Asia, which flourished during 2500–1900 BCE in what is now Pakistan and western India. Centred around cities such as Mohenjo-daro, Harappa and Kalibangan, relying on varied forms of subsistence, the civilization engaged robustly in crafts production and wide-ranging trade. During the period 2000–500 BCE, many regions of the subcontinent transitioned from the Chalcolithic cultures to the Iron Age ones; the Vedas, the oldest scriptures associated with Hinduism, were composed during this period, historians have analysed these to posit a Vedic culture in the Punjab region and the upper Gangetic Plain.
Most historians consider this period to have encompassed several waves of Indo-Aryan migration into the subcontinent from the north-west. The caste system, which created a hierarchy of priests and free peasants, but which excluded indigenous peoples by labeling their occupations impure, arose during this period. On the Deccan Plateau, archaeological evidence from this period suggests the existence of a chiefdom stage of political organisation. In South India, a progression to sedentary life is indicated by the large number of megalithic monuments dating from this period, as well as by nearby traces of agriculture, irrigation tanks, craft traditions. In the late Vedic period, around the 6th century BCE, the small states and chiefdoms of the Ganges Plain and the north-western regions had consolidated into 16 major oligarchies and monarchies that were known as the mahajanapadas; the emerging urbanisation gave rise to non-Vedic religious movements, two of which became independent religions. Jainism came into prominence during the life of Mahavira.
Buddhism, based on the teachings of Gautama Buddha, attracted followers from all social classes excepting the middle
In geology, bedrock is the lithified rock that lies under a loose softer material called regolith within the surface of the crust of the Earth or other terrestrial planets. Bedrock refers to the substructure composed of hard rock exposed or buried at the earths surface, an exposed portion of bedrock is called an outcrop. Bedrock may have various chemical and mineralogical compositions and can be igneous, metamorphic or sedimentary in origin; the bedrock may be overlain by weathered regolith which includes soil and the subsoil. The surface of the bedrock beneath the soil cover is known as rockhead in engineering geology, its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be thick, such that the bedrock lies hundreds of meters below the surface. Bedrock when exposed or within the subsurface may experience weathering and erosion by external factors. Weathering may be physical or chemical and alters the structure of the rock and may cause it to erode and or alter over time based on the interactions between the mineralogy and its interactions.
Bedrock may experience subsurface weathering at its upper boundary, forming saprolite. A geologic map of an area will show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed. Geology – The study of the composition, physical properties, history of Earth's components, the processes by which they are shaped. Outcrop Regolith – A layer of loose, heterogeneous superficial deposits covering solid rock Soil – mixture of organic matter, gases and organisms that together support life Weathering – Breaking down of rocks and minerals as well as artificial materials through contact with the Earth's atmosphere and waters Rafferty, John P. "Bedrock GEOLOGY". Encyclopedia Britannica. Encyclopedia Britannica. Retrieved 1 April 2019. Harris, The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Vol. 1. 5th ed. Farmington Hills, MI: Gale, 2014. P515-516. Media related to Bedrock at Wikimedia Commons
The Falkland Islands is an archipelago in the South Atlantic Ocean on the Patagonian Shelf. The principal islands are about 300 miles east of South America's southern Patagonian coast, about 752 miles from the northern tip of the Antarctic Peninsula, at a latitude of about 52°S; the archipelago, with an area of 4,700 square miles, comprises East Falkland, West Falkland and 776 smaller islands. As a British overseas territory, the Falklands have internal self-governance, the United Kingdom takes responsibility for their defence and foreign affairs; the Falkland Islands' capital is Stanley on East Falkland. Controversy exists over the Falklands' discovery and subsequent colonisation by Europeans. At various times, the islands have had French, British and Argentine settlements. Britain reasserted its rule in 1833. In April 1982, Argentine forces temporarily occupied the islands. British administration was restored two months at the end of the Falklands War. Most Falklanders favour the archipelago remaining a UK overseas territory, but its sovereignty status is part of an ongoing dispute between Argentina and the United Kingdom.
The population consists of native-born Falkland Islanders, the majority of British descent. Other ethnicities include French and Scandinavian. Immigration from the United Kingdom, the South Atlantic island of Saint Helena, Chile has reversed a population decline; the predominant language is English. Under the British Nationality Act 1983, Falkland Islanders are British citizens; the islands lie on the boundary of the subantarctic oceanic and tundra climate zones, both major islands have mountain ranges reaching 2,300 feet. They are home to large bird populations, although many no longer breed on the main islands because of competition from introduced species. Major economic activities include fishing and sheep farming, with an emphasis on high-quality wool exports. Oil exploration, licensed by the Falkland Islands Government, remains controversial as a result of maritime disputes with Argentina; the name "Falkland Islands" comes from Falkland Sound, the strait that separates the two main islands.
The name "Falkland" was applied to the channel by John Strong, captain of an English expedition which landed on the islands in 1690. Strong named the strait in honour of Anthony Cary, 5th Viscount of Falkland, the Treasurer of the Navy who sponsored his journey; the Viscount's title originates from the town of Falkland, Scotland—the town's name comes from a Gaelic term referring to an "enclosure", but it could less plausibly be from the Anglo-Saxon term "folkland". The name "Falklands" was not applied to the islands until 1765, when British captain John Byron of the Royal Navy, claimed them for King George III as "Falkland's Islands"; the term "Falklands" is a standard abbreviation used to refer to the islands. The Spanish name for the archipelago, Islas Malvinas, derives from the French Îles Malouines—the name given to the islands by French explorer Louis-Antoine de Bougainville in 1764. Bougainville, who founded the islands' first settlement, named the area after the port of Saint-Malo; the port, located in the Brittany region of western France, was in turn named after St. Malo, the Christian evangelist who founded the city.
At the twentieth session of the United Nations General Assembly, the Fourth Committee determined that, in all languages other than Spanish, all UN documentation would designate the territory as Falkland Islands. In Spanish, the territory was designated as Islas Malvinas; the nomenclature used by the United Nations for statistical processing purposes is Falkland Islands. Although Fuegians from Patagonia may have visited the Falkland Islands in prehistoric times, the islands were uninhabited when Europeans first discovered them. Claims of discovery date back to the 16th century, but no consensus exists on whether early explorers discovered the Falklands or other islands in the South Atlantic; the first recorded landing on the islands is attributed to English captain John Strong, who, en route to Peru's and Chile's littoral in 1690, discovered the Falkland Sound and noted the islands' water and game. The Falklands remained uninhabited until the 1764 establishment of Port Louis on East Falkland by French captain Louis Antoine de Bougainville, the 1766 foundation of Port Egmont on Saunders Island by British captain John MacBride.
Whether or not the settlements were aware of each other's existence is debated by historians. In 1766, France surrendered its claim on the Falklands to Spain, which renamed the French colony Puerto Soledad the following year. Problems began when Spain discovered and captured Port Egmont in 1770. War was narrowly avoided by its restitution to Britain in 1771. Both the British and Spanish settlements coexisted in the archipelago until 1774, when Britain's new economic and strategic considerations led it to voluntarily withdraw from the islands, leaving a plaque claiming the Falklands for King George III. Spain's Viceroyalty of the Río de la Plata became the only governmental presence in the territory. West Falkland was left abandoned, Puerto Soledad became a prison camp. Amid the British invasions of the Río de la Plata during the Napoleonic Wars in Europe, the islands' governor evacuated the archipelago in 1806. Thereafter, the archipelago was visited only
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, to understand the stress field that resulted in the observed strain and geometries; this understanding of the dynamics of the stress field can be linked to important events in the geologic past. The study of geologic structures has been of prime importance in economic geology, both petroleum geology and mining geology. Folded and faulted rock strata form traps that accumulate and concentrate fluids such as petroleum and natural gas. Faulted and structurally complex areas are notable as permeable zones for hydrothermal fluids, resulting in concentrated areas of base and precious metal ore deposits. Veins of minerals containing various metals occupy faults and fractures in structurally complex areas; these structurally fractured and faulted zones occur in association with intrusive igneous rocks.
They also occur around geologic reef complexes and collapse features such as ancient sinkholes. Deposits of gold, copper, lead and other metals, are located in structurally complex areas. Structural geology is a critical part of engineering geology, concerned with the physical and mechanical properties of natural rocks. Structural fabrics and defects such as faults, folds and joints are internal weaknesses of rocks which may affect the stability of human engineered structures such as dams, road cuts, open pit mines and underground mines or road tunnels. Geotechnical risk, including earthquake risk can only be investigated by inspecting a combination of structural geology and geomorphology. In addition, areas of karst landscapes which reside atop underground caverns, potential sinkholes, or other collapse features are of particular importance for these scientists. In addition, areas of steep slopes are potential landslide hazards. Environmental geologists and hydrogeologists need to apply the tenets of structural geology to understand how geologic sites impact groundwater flow and penetration.
For instance, a hydrogeologist may need to determine if seepage of toxic substances from waste dumps is occurring in a residential area or if salty water is seeping into an aquifer. Plate tectonics is a theory developed during the 1960s which describes the movement of continents by way of the separation and collision of crustal plates, it is in a sense structural geology on a planet scale, is used throughout structural geology as a framework to analyze and understand global and local scale features. Structural geologists use a variety of methods to measure rock geometries, reconstruct their deformational histories, estimate the stress field that resulted in that deformation. Primary data sets for structural geology are collected in the field. Structural geologists measure a variety of planar features, linear features; the inclination of a planar structure in geology is measured by dip. The strike is the line of intersection between the planar feature and a horizontal plane, taken according to the right hand convention, the dip is the magnitude of the inclination, below horizontal, at right angles to strike.
For example. Alternatively and dip direction may be used as this is absolute. Dip direction is measured in 360 degrees clockwise from North. For example, a dip of 45 degrees towards 115 degrees azimuth, recorded as 45/115. Note that this is the same as above; the term hade is used and is the deviation of a plane from vertical i.e.. Fold axis plunge is measured in dip direction; the orientation of a fold axial plane is dip and dip direction. Lineations are measured in terms of dip direction, if possible. Lineations occur expressed on a planar surface and can be difficult to measure directly. In this case, the lineation may be measured from the horizontal as a pitch upon the surface. Rake is measured by placing a protractor flat on the planar surface, with the flat edge horizontal and measuring the angle of the lineation clockwise from horizontal; the orientation of the lineation can be calculated from the rake and strike-dip information of the plane it was measured from, using a stereographic projection.
If a fault has lineations formed by movement on the plane, e.g.. It is easier to record strike and dip information of planar structures in dip/dip direction format as this will match all the other structural information you may be recording about folds, etc. although there is an advantage to using different formats that discriminate between planar and linear data. The convention for analysing structural geology is to identify the planar structures called planar fabrics because this implies a textural formation, the linear structures and, from analysis of these, unravel deformations. Planar structures a
A geologic map or geological map is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface. Bedding planes and structural features such as faults, folds and lineations are shown with strike and dip or trend and plunge symbols which give these features' three-dimensional orientations. Stratigraphic contour lines may be used to illustrate the surface of a selected stratum illustrating the subsurface topographic trends of the strata. Isopach maps detail the variations in thickness of stratigraphic units, it is not always possible to properly show this when the strata are fractured, mixed, in some discontinuities, or where they are otherwise disturbed. Rock units are represented by colors. Instead of colors, certain symbols can be used. Different geologic mapping agencies and authorities have different standards for the colors and symbols to be used for rocks of differing types and ages. Geologists take two major types of orientation measurements: orientations of planes and orientations of lines.
Orientations of planes are measured as a "strike" and "dip", while orientations of lines are measured as a "trend" and "plunge". Strike and dip symbols consist of a long "strike" line, perpendicular to the direction of greatest slope along the surface of the bed, a shorter "dip" line on side of the strike line where the bed is going downwards; the angle that the bed makes with the horizontal, along the dip direction, is written next to the dip line. In the azimuthal system and dip are given as "strike/dip". Trend and plunge are used for linear features, their symbol is a single arrow on the map; the arrow is oriented in the downgoing direction of the linear feature and at the end of the arrow, the number of degrees that the feature lies below the horizontal is noted. Trend and plunge are notated as PLUNGE → TREND; the oldest preserved geologic map is the Turin papyrus, which shows the location of building stone and gold deposits in Egypt. The earliest geologic map of the modern era is the 1771 "Map of Part of Auvergne, or figures of, The Current of Lava in which Prisms, Etc. are Made from Basalt.
To be used with Mr. Demarest's theories of this hard basalt. Engraved by Messr. Pasumot and Daily, Geological Engineers of the King." This map is based on Nicolas Desmarest's 1768 detailed study of the geology and eruptive history of the Auvergne volcanoes and a comparison with the columns of the Giant's Causeway of Ireland. He identified both landmarks as features of extinct volcanoes; the 1798 report was incorporated in the 1771 Royal Academy of Science compendium. The first geological map of the U. S. was produced in 1809 by William Maclure. In 1807, Maclure undertook the self-imposed task of making a geological survey of the United States, he mapped nearly every state in the Union. During the rigorous two-year period of his survey, he crossed and recrossed the Allegheny Mountains some 50 times. Maclure's map shows the distribution of five classes of rock in what are now only the eastern states of the present-day US; the first geologic map of Great Britain was created by William Smith in 1815 using principles first formulated by Smith.
In the United States, geologic maps are superimposed over a topographic map with the addition of a color mask with letter symbols to represent the kind of geologic unit. The color mask denotes the exposure of the immediate bedrock if obscured by soil or other cover; each area of color denotes a geologic unit or particular rock formation. However, in areas where the bedrock is overlain by a thick unconsolidated burden of till, terrace sediments, loess deposits, or other important feature, these are shown instead. Stratigraphic contour lines, fault lines and dip symbols, are represented with various symbols as indicated by the map key. Whereas topographic maps are produced by the United States Geological Survey in conjunction with the states, geologic maps are produced by the individual states. There are no geologic map resources for some states, while a few states, such as Kentucky and Georgia, are extensively mapped geologically. In the United Kingdom the term geological map is used; the UK and Isle of Man have been extensively mapped by the British Geological Survey since 1835.
Two 1:625,000 scale maps cover the basic geology for the UK. More detailed sheets are available at scales of 1:250,000, 1:50,000 and 1:10,000; the 1:625,000 and 1:250,000 scales show both onshore and offshore geology, whilst other scales cover exposures on land only. Sheets of all scales fall into two categories: Superficial deposit maps show both bedrock and the deposits on top of it. Bedrock maps show the underlying rock, without superficial deposits; the maps are superimposed over a topographic map base produced by Ordnance Survey, use symbols to represent fault lines and dip or geological units, boreholes etc. Colors are used to represent different geological units. Explanatory booklets (