Here's why:

* Intrusions: These are igneous rocks that formed when magma (molten rock) pushed its way into existing rocks.

* Cutting across existing rock: This indicates that the magma forced its way through pre-existing rock layers. Dikes are vertical or near-vertical intrusions, often forming as magma filled cracks in the surrounding rock.

Other possibilities:

* Sills: Similar to dikes, but sills are horizontal or nearly horizontal intrusions. They form between layers of rock.

* Veins: These are narrow, mineral-filled cracks that can be quite small. While not igneous, they can also cut across existing rock.

To get a more precise identification, I'd need more information, such as:

* What kind of rock are you looking at? (Sedimentary, metamorphic, or igneous?)

* What is the size and shape of the intrusions?

* Are there any other features present, like mineral composition or textures?

Let me know if you have more details!