Answer: According to the principle of cross-cutting relationships, an intrusive rock body is younger than the rocks into which it intrudes.
Explanation:
To understand this answer you need to know what cross-cutting relationship of rocks is. Lets take an example of the volcano surrounded with volcanic rocks. Whenever, Magma from volcanoes flows down, they intrudes into the spaces or cracks present between the already existing rocks. After some time, when this magma cools down it becomes a rock, but this rock remains within those already existing rocks. This also explains that the newly made rocks within the already existing rocks are younger than the later. This is what we call a cross-cutting relationship.
