These parallel lines are carved into hard rock surfaces when abrasive debris, like boulders or gravel, is dragged across them under immense pressure. In glacial geology, they indicate the exact direction of past ice flow. In structural geology, similar marks on a fault plane indicate the vector of slip between two blocks of crust.
Heard on the job
The striation on this outcrop clearly shows the ice sheet was moving due south.
Related terms
Bedrock
The solid, intact rock layer that lies beneath soil, gravel, and other loose surface materials.
Fault
A planar fracture in a rock volume across which there has been significant displacement.
Country rock
The pre-existing, non-mineralized rock that surrounds and encloses an orebody or igneous intrusion.