Here's a breakdown:

* Intrusions: Magma (molten rock) that pushes its way into existing rock layers.

* Parallel to existing rock: Dikes are typically vertical or nearly vertical, cutting across pre-existing rock layers. This means they are parallel to the layering of the rock they intrude into.

Characteristics of Dikes:

* Shape: Long, thin, and often tabular (flattened).

* Composition: Can be made of a variety of igneous rocks, depending on the magma's composition.

* Size: Can range from a few inches to hundreds of feet in width.

* Formation: When magma rises through cracks or faults in the Earth's crust, it cools and solidifies.

Examples of Dikes:

* The Palisades Sill, a famous example of a dike that forms the cliffs along the Hudson River in New York.

* Dikes can be found in many areas where there is volcanic activity or where tectonic plates have moved.

Let me know if you'd like more details on dikes or have any other geological questions!