The principle of inclusions which states that the source of rock fragments found in a unit must be older than the unit with the fragments is important because

Explanation: The principle of inclusion explains that if a rock fragment is enclosed within another rock(larger rock), the enclosed fragment is called an intrusion. The enclosed rock fragment must have been present before the enclosing rock. Therefore the enclosed rock fragment (inclusion) is older than the enclosing rock.

In igneous formations foreign bodies may carried along with magma flows which cool alongside the matrix. Such bodies are called inclusions enclosed within the enclosing formation and are called xenolith. This xenolith are older than the formation enclosing them. Xenoliths are inclusions in igneous formations.

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