What Stories Do Rocks Tell?
ES2903  The Principle of Cross-Cutting Relationships

Sometimes magma pushes, or intrudes, into cracks in existing rocks. When the melted rock cools and solidifies, the resulting feature is called an igneous intrusion. This image shows metamorphic rock in Death Valley, California, cut by a darker igneous intrusion.

Martin Miller, University of Oregon
A dark-colored igneous intrusion cut across metamorphic rock in Death Valley, California.

The principle of cross-cutting relationships states that an igneous intrusion is always younger than the rock it cuts across.

  !   Examine the igneous intrusion and the surrounding rock. Mentally visualize the process that formed these rocks.


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