Geological
Maps
By Kari Bitler
Geologic maps can show us the absolute
ages of the rock formations that
outcrop on the surface. The maps are classified
into four time units
called Eras. Cenozoic- most recent, Mesozoic-
next older,
then Paleozic, and the last rocks on Earth are Precambrian
age,
which is the oldest. Geological structures on geologic maps
are
any features formed by deformation or movement of rocks such as a
fold
which is a bend in a rock, or a fault which is a
fracture in
rock along which displacement has occured. It also includes
the combination
of all such features of an area or region.
The different colors on
the map show the
age and outcrop pattern of the surface rocks. The rock
units are shown with
a symbol and a color. For examples check out this
site: http://www.gdsdatamaps.com/
Rules for interpreting features on Geologic Maps
Law of Superposition: In a sequence of
rock layers, each layer is older
than the next layer above.
Principle of Horizontality: All sedimentary
rock sequences were
originally laid down horizontally.
1. Layers of rock dip downward in the same
direction as that
which the youngest rock layers are exposed at the surface.
2. 
ES 111 Intro To Earth Science, Susie Aber- Class Handout
3. The younger rocks are exposed in the
center of eroded synclines
and basins.
4. Plunging
anticlines form "U"
shaped outcrop belts that point in
the same direction that the fold plunges.
5. Plunging synclines form "U"
shaped outcrop belts
that point in the opposite direction that fold plunges.
6. The steeper the dip of the layer, the
more narrow the width
of its outcrop belt.
7. In compressional faults (the two walls
are pushed together)
the hanging wall tends to move up relative to the foot
wall
8. In tensional faults (the two walls are
pulled apart) the
hanging wall tends to move down relative to the foot wall.
The Surface Features of Kansas handout from Susie Aber's Es 111 Intro to Earth Science
This page was prepared
for ES
111 Intro to Earthscience Lab
,
the instructor being Susie Aber of Emporia State University.
Return to the Student's index page