A window, especially in geology, a hole or opening in a mountain range through which younger rocks are visible beneath older ones.
From German Fenster meaning 'window,' derived from Latin fenestra. In geological terminology, it refers to a 'window' through which you can see layers beneath.
Geologists borrowed the German word 'fenster' because it perfectly describes what a window does—it lets you see through to what's beyond. A fenster in the Alps or Appalachians reveals ancient rock sequences and tells the story of how mountains were formed and later eroded.
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