* Magma: Molten rock found beneath the Earth's surface.

* Intrusion: When magma forces its way into existing layers of rock.

* Hardening: As magma cools and solidifies, it forms igneous rock.

There are different types of intrusions:

* Batholiths: Massive, irregularly shaped intrusions that cover large areas.

* Stocks: Smaller, similar to batholiths, but with a smaller surface area.

* Dikes: Tabular, sheet-like intrusions that cut across existing rock layers.

* Sills: Tabular, sheet-like intrusions that are parallel to existing rock layers.

These intrusions can form a variety of landforms and are responsible for many of the features we see in mountainous regions.