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History
The oldest preserved geologic map is the Turin papyrus, made around 1150 BCE for gold deposits in Egypt.
A fascinating story of the first modern geologic map is told in The Map that Changed the World, 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. (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 color mask denotes the exposure of the immediate bedrock, even if obscured by soil or other cover. Each area of color denotes a geologic unit or particular rock formation (as more information is gathered new geologic units may be defined). 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. Stratigraphic contour lines, fault lines, strike 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 usually produced by the individual states. There are almost no geologic map resources for some states, while a few states, such as Kentucky, are extensively mapped geologically.
United Kingdom
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; a separate Geological Survey of Northern Ireland (drawing on BGS staff) has operated since 1947.
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.
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. 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.
See also
External links
- Geologic Maps from USGS National Park Service
- USGS National Geologic Map Database
