WJEC A2 Geology
BGS Mapwork
I.G.Kenyon
BGS 1:50.000 scale maps
1mm on the map represents
50m on the ground
Grid squares are 1 km² and
have sides of 2cm on the map
BGS 1:25,000 scale maps
1mm on the map represents
25m on the ground
Grid squares are 1 km² and
have sides of 4cm on the map
BGS Maps are produced in solid
and solid and drift editions
Solid maps show only the
fully lithified rocks
Solid and drift maps show the
lithified rocks plus any recent
sediments deposited on top
Solid Geology – Cockermouth Sheet 23 1:50.000
Permo-Triassic Rocks
Carboniferous rocks
Recent drift deposits such as alluvium and boulder clay not shown
Solid and Drift Geology – Clitheroe Sheet 68 1:50,000
River Terrace Deposits
Alluvium
Solid Geology
Structures to Identify on BGS Maps 1
Beds – direction of dip/angle of dip
Beds – strike direction/orientation
Anticlines/synclines/monoclines
Fold axes/axial plane of folds
Domes/basins
Symmetrical/asymmetrical folds
Plunging folds
Open/tight/recumbent/overturned folds
Structures to Identify on BGS Maps 2
Normal faults/reverse faults/thrust faults
Tear faults – sinistral/dextral/step faults
Graben/rift valley/Horst/block mountain
Unconformities-angular/parallel/heterolithic
Inliers/outliers
Lava flow/sill/dyke/pluton/mineral veins
Metamorphic aureole
Inverted relief
Symbols on BGS Maps 1
Drift Symbols on BGS Maps
Generalized vertical sections are given on BGS Maps
This is a vertical log of all the rock types
present in chronological order with the oldest
at the base and the youngest at the top
On 1:50,000 maps the scale is often 1:10,000
On 1:25,000 maps the scale is often 1:4,000
However scales can vary-check carefully
on each map that you are studying
Part of generalized vertical section from Cheddar Sheet ST45 1:25,000
Part of the generalized
vertical section from Hawes
Solid and Drift 1:50,000
Note that rock types and
ages of beds are given
Unconformities are clearly
indicated in the section
It is vital that the vertical
section is studied carefully
in conjunction with the map
in order to interpret all of
the geological structures
Cross sections are also included on BGS maps and should
be studied carefully along with the vertical section and map
From Hawes Solid
and Drift 1:50,000
You do not have to construct cross sections from BGS maps at A2!
In addition to geological structures, you
will be asked questions with a GL3 bias
These could include evaluating the
suitability of certain locations for the
construction of roads, landfill sites,
housing estates, reservoirs, power
stations, dams or tunnels
Questions relating to the causes of
landslips are also a possibility
Sometimes additional maps are
included on the BGS geology maps
These may include magnetic, gravity,
radon, isostatic or mineralogical data
Questions related to this
additional data may be asked
in relation to the geological map
Okehampton/Dartmoor Map
Geology and Gravity Anomalies
Gravity anomalies (contoured in milligals). The negative gravity anomaly
is due to the granite being of lower density than the surrounding rocks
Okehampton/Dartmoor Map
Geology and Magnetic Anomalies
Aeromagnetic anomalies (contoured in nanoteslas)
Magnetic disturbances skirting the granite are due to mineralisation
in the Lower Carboniferous rocks and basic intrusions at depth
The End
Ash deposits of the Las Canadas
Volcano, Tenerife, Canary Islands