Geological Map (Basic Introduction)



What are geological maps?

A geological map shows the distribution of different types of rock in an area. It usually consists of a topographic map (a map that gives information about the shape of the earth's surface) that is shaded or colored to indicate where various rocks are located. Units occur on or just below the surface of the earth. Figure 1.1 shows a geological map of an area in the Cotswolds. It tells us, for example, that clays form the bedrock at Childswickham and Broadway, but if we move east up the Cotswold Escarpment up to Broadway Hill we can find oolithic limestones. Lines are drawn on the map to show the boundaries between each rock unit.


How do you create such a geological map?

The geologist on site first records the nature of the rock where it is visible on the surface. Rock outcrops are examined and features such as rock composition, internal structure and fossil content are recorded. They can be distinguished and shown separately on the basemap. The rocks are of course notexposed everywhere on the surface. In fact, much of the area in Fig. 1 is covered by soil and alluvial debris deposited by younger rivers. Soil type, land surface shapes (geomorphology) and borehole information. Enable geophysical methods the properties of rocks (such as their magnetism and density) need to be measured remotely and are therefore useful for mapping rocks in poorly exposed regions. This additional information is taken into account when the geologist determines the position of the boundaries of the rock units to be drawn on the map. However, there are always parts of the map where there is more uncertainty about the nature of the bedrock, and it is important that the card reader realize that there is a lot of interpretation used in the mapping process.

Geological Map

What is a geological map used for?

The maximum apparent use of a geological map is to signify the nature of the near-floor bedrock. This is simply of great significance to civil engineers who, for example, have to suggest at the excavation of avenue cuttings or at the siting of bridges; to geographers reading using land and to agencies exploiting minerals. The skilled geologist can, however, extract extra from the geological map. To the skilled observer the capabilities on a geological map reveal crucial clues approximately the geological records of an area. Furthermore, the bands of coloration on a geological map are the expression at the floor of layers or sheets of rock which expand and slant downwards into the crust of the earth. The regularly complex sample on a map, like the graininess of a refined timber desk top, affords tell-tale proof of the shape of the layers below the floor. To make those deductions first calls for know-how of the feature shape of not unusual place geological systems such as faults and folds.


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