A geologic map or geological map is a special-purpose map made to show geological features. A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, Regions, and Themes Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit
The stratigraphic contour lines are drawn on the surface of a selected deep stratum, so that they can show the topographic trends of the strata under the ground. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes It is not always possible to properly show this when the strata are extremely fractured, mixed, in some discontinuities, or where they are otherwise disturbed.
Strike and dip symbols consist of (at minimum) a long line, a number, and a short line which are used to indicate tilted beds. Strike and dip refer to the orientation or attitude of a Geologic feature The long line is the strike line, which shows the true horizontal direction along the bed, the number is the dip or number of degrees of tilt above horizontal, and the short line is the dip line, which shows the direction of tilt.
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History
The oldest preserved geologic map is the Turin papyrus, made around 1150 BCE for gold deposits in Egypt. The Turin Papyrus is an ancient Egyptian Map, generally considered the oldest surviving map of topographical interest from the ancient world Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79
A fascinating story of the first modern geologic map is told in The Map that Changed the World, by Simon Winchester. The Map that Changed the World is a book by Simon Winchester. It's the story of William Smith, a canal digger who created the first geologic map of Great Britain in 1819, but ended up in debtor's prison and lived homeless for 10 years until he was recognized for his work by King William IV in 1831. William Smith ( March 23 1769 &ndash August 28 1839) was an English Geologist, credited with creating the first nationwide (Harper-Collins publishers, 2202. ISBN 0-06-093180-9)
Maps and Mapping across the globe
United States
In the United States, geologic maps are usually superimposed over a topographic map (and at times over other base maps) with the addition of a color mask with letter symbols to represent the kind of geologic unit. The United States of America —commonly referred to as the A topographic map is a type of Map characterized by large-scale detail and quantitative representation of relief, usually using Contour lines in modern A geological unit is a volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant easily mapped and recognizable The color mask denotes the exposure of the immediate bedrock, even if obscured by soil or other cover. Bedrock is the native consolidated rock underlying the surface of a terrestrial planet usually the Earth. Each area of color denotes a geologic unit or particular rock formation (as more information is gathered new geologic units may be defined). In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere However, in areas where the bedrock is overlain by a significantly thick unconsolidated burden of till, terrace deposits, loess deposits, or other important feature, these are shown instead. Compaction (geology refers to the process by which a Sediment progressively loses its Porosity due to the effects of loading Till is unsorted glacial sediment Glacial drift is a general term for the coarsely graded and extremely heterogeneous Sediments of glacial origin A terrace deposit is geological term for a flat platform of land created alongside of a River or sea where at some time in the past the river has cut itself a deeper Loess is a homogeneous typically non stratified porous Friable,slightly coherent often calcareous fine-grained Silty pale yellow or buff windblown ( aeolian Stratigraphic contour lines, fault lines, strike and dip symbols, are represented with various symbols as indicated by the map key. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement Whereas topographic maps are produced by the United States Geological Survey in conjunction with the states, geologic maps are usually produced by the individual states. The United States Geological Survey ( USGS) is a scientific agency of the United States government. A US state is any one of the fifty subnational entities of the United States of America that share Sovereignty with the federal government There are almost no geologic map resources for some states, while a few states, such as Kentucky, are extensively mapped geologically. The Commonwealth of Kentucky ( is a state located in the East Central United States of America.
United Kingdom
In the United Kingdom the term geological map is used. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located The UK and Isle of Man have been extensively mapped by the British Geological Survey since 1835; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947. The Isle of Man (Ellan Vannin ˈɛlʲən ˈvanɪn or Mann (Mannin) is a self-governing Crown dependency, located in the Irish Sea at the geographical The British Geological Survey (BGS is a partly publicly-funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its Continental
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 (the 1:250,000 series covers the entire UK continental shelf), whilst other scales generally cover exposures on land only. The continental shelf is the extended perimeter of each Continent and associated Coastal plain, which is covered during interglacial periods such
Sheets of all scales (though not for all areas) fall into two categories:
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- Superficial deposit maps (previously known as solid and drift maps) show both bedrock and the deposits on top of it.
- Bedrock maps (previously known as solid maps) show the underlying rock, without superficial deposits.
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The maps are superimposed over a topographic map base produced by Ordnance Survey, and use symbols to represent fault lines, strike and dip or geological units, boreholes etc. Ordnance Survey (OS is an Executive agency of the United Kingdom government A borehole is the generalised term for any narrow shaft drilled in the ground either vertically or horizontally Colors are used to represent different geological units. Explanatory booklets (memoirs) are produced for many sheets at the 1:50,000 scale.
Small scale thematic maps (1:1,000,000 to 1:100,000) are also produced covering geochemistry, gravity anomaly, magnetic anomaly, groundwater, etc. The field of geochemistry involves study of the chemical composition of the Earth and other Planets chemical processes and reactions that govern the composition A gravity anomaly is the difference between the observed Gravity and a value predicted from a model A magnetic anomaly ( Geophysics) is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations
See also
External links
- Geologic Maps from USGS National Park Service
- USGS National Geologic Map Database
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