Law of included fragments

The law of included fragments is a method of relative dating in geology.

[1] One example of this is a xenolith, which is a fragment of country rock that fell into passing magma as a result of stoping.

For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer.

A similar situation with igneous rocks occurs when xenoliths are found.

These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix.