Intrusions of igneous rock are younger than the layers beneath and surrounding them. Here's why:

* Igneous Intrusions: These form when molten rock (magma) pushes its way into existing rock layers.

* Principle of Superposition: In undisturbed rock layers, the oldest layers are at the bottom, and the youngest layers are at the top.

* Cross-Cutting Relationships: Igneous intrusions cut across existing rock layers, indicating they formed after the layers were already in place.

Therefore, the intrusion itself is younger than the rocks it cuts through.