Which principle states that a fault or intrusion is younger than the rocks it cuts?

• A. Original horizontality
• B. Cross-cutting relationships
• C. Lateral continuity
• D. Inclusions

Answer: (B)

Cross-cutting relationships state that a fault or intrusion is younger than the rocks it cuts. When you see a fault displacing sedimentary layers or an igneous intrusion that cuts through existing rocks, the rocks had to be there first, and the fault or intrusion formed afterward. This lets geologists order events in time: deposition happens, then disruption or intrusion occurs, making the disruption younger than what it affects.

Original horizontality is about how sediments settle in flat layers, not about disturbances after deposition. Lateral continuity describes how layers extend until they truncate or thin, not about faults or intrusions. Inclusions refer to pieces of older material found within another rock, indicating those fragments are older than the surrounding rock, not about disruptions by faults or intrusions.