* Faults are breaks in the Earth's crust. They occur when stress builds up in the rocks and causes them to fracture.
* Rock layers form over time. Sedimentary rocks, for example, are formed by layers of sediment accumulating and being compressed over millions of years.
* The fault must cut through the existing rock layers. This means the rock layers were already there before the fault developed.
Therefore, the process goes:
1. Rock layers form.
2. Stress builds up in the Earth's crust.
3. A fault develops, cutting through the existing rock layers.
This is a key principle in geology known as the principle of cross-cutting relationships. It helps geologists determine the relative ages of different geological features.
