GEOLOGIC MAP

A 'geologic map' or 'geological map' is a special-purpose map made to show geological features.
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. 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. 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.

Contents

History

Maps and Mapping across the globe

United States

United Kingdom

See also

External links

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 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. Great Britain, the Outer Hebrides, Shetland, Orkney and the smaller surrounding isles, and also the neighbouring Isle of Man have been extensively mapped by the British Geological Survey since the early 1900s. Two 1:625000 scale maps (10 Mile Map North and 10 Mile Map South) cover the basic geology for the island group and these are then broken down into regional maps (also known as ''sheets'') which hold much more detail.
These more detailed maps fall into two categories:
:::'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.
As with the maps produced in the United States, the maps are superimposed over a topographic map, and use symbols to represent fault lines, strike and dip or geological units, boreholes etc. Colors are used to represent different geological units, however, numbers are sometimes used instead of letters.

See also

★ Geology

★ Geography

★ Cartography

External links

★ Geologic Maps'' from USGS National Park Service''

★ USGS National Geologic Map Database