Rules for interpreting features on Geologic Maps

Taken from ESU ES111 class handout

Law of superposition: In a sequence of rock layers, each layer is older than the next layer above.

Principle of Horizontality: All sedimentary rock swquences 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. The older rocks are exposed in the center of eroded anticlines and domes.

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 opposite direction that the fold plunges.

5. Plunging synclines form "U" shaped outcrop belts that point in the opposite direction that the 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.

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