When magma forces itself across rock layers, it forms a dike.

Here's why:

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

* Dike: A tabular (flat and sheet-like) intrusion of magma that cuts across existing rock layers.

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

Essentially, the magma pushes through the existing rock layers, creating a vertical or near-vertical, wall-like structure of solidified magma.

Let me know if you have any other questions!