Final answer:
The principle of inclusions explains the occurrence of older rocks trapped within younger rocks.
Step-by-step explanation:
The principle of inclusions explains the occurrence of older rocks trapped within younger rocks. According to this principle, a clast or a different-looking rock that is contained inside another rock is older than the rock that contains it.
For example, if a mafic rock is surrounded by a coarse-grained granite, the mafic rock formed first and then the granite formed around it. This principle helps geologists determine the relative ages of different rock layers.