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The Virgilina Deformation

Volcanic activity ended approximately 610 million years ago. In the Hillsborough area, the volcanic islands were eroded and slowly sank beneath the sea. Approximately 600 million years ago, the volcanic arc carrying the Hillsborough Caldera smashed into another island arc. The rocks were folded and slightly metamorphized.

Known as the Virginila Deformation , the rocks were folded into a set of large anticlines and synclines. An almost vertical foliation was developed.