Question 10
List four features of a geological map
This is a popular question among the candidates and the performance was fairly okay. The question requested the candidates to give the following points:
Features of a geological map
Geologic maps usually illustrate geological features such as rock units and bedding, faults, folds, intrusions, unconformities, river traces etc.
Geologic map can be super-imposed on topographic contour map.
- Formation: The fundamental unit of the geologic map is the formation. A formation is a sequence of rocks sufficiently homogeneous in composition to be regarded as constituting a rock unit. A formation may consist of one rock type e.g. sandstone or a mixture of two e.g. sandy shale, sandy limestone etc.
- On a geologic map, a formation is designated by a distinctive colour and symbol. The symbol may be a number or letter. The boundary between any two geologic formations is called geological boundary or contact line or geological interface
- Outcrop: This refers to a point on the ground surface where bedrock is exposed while still remaining in place.
- Legend: This refers to a listing of the formations of a geologic map which occur within the mapped area. For each formation, the legend indicates the distinctive colour and symbol, the nature and type of rock.
- Arrangement. For sedimentary rocks, the legend is arranged in orderly sequence with oldest formation at the bottom, the younger ones above and the youngest at the top.
- If igneous and metamorphic rocks occur within the mapped area, they are often arranged in a separate legend.