syncline

/ˈsɪŋklaɪn/
noun
  1. A fold in rock layers that bends downward, forming a trough or U-shape, with the youngest rocks at the center.
    • The hikers walked along the bottom of a syncline, surrounded by steep rock walls.
    • In the diagram, the syncline is shown as a downward curve in the layers of earth.
    • The valley was actually a large syncline formed millions of years ago.
Antonyms