Start Relative dating unconformities

Relative dating unconformities

In contrast, rock units such as groups, formations, and members are localized subsets of systems.

The first principle is the Principle of Superposition which states that in an undisturbed succession of sedimentary rock, the oldest layers are on the bottom.

Geologists use several principles to find the relative age of geologic layers. Remember, contact metamorphism is changes in a rock due to contact with magma or lava.

- The principle of superposition is simply the fact that the lowest layer of a rock formation is the oldest layer while the youngest layer is towards the top. Think of it as a boundary layer between igneous rocks and sedimentary rocks.

For example, rocks named Juras (for the Juras Mountains) in France and Switzerland were traced northward and found to overlie a group of rocks in Germany named Trias.