Inverted arch

from The Collaborative International Dictionary of English v.0.48

Inverted \In*vert"ed\, a.
   [1913 Webster]
   1. Changed to a contrary or counterchanged order; reversed;
      characterized by inversion.
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   2. (Geol.) Situated apparently in reverse order, as strata
      when folded back upon themselves by upheaval.
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   {Inverted arch} (Arch.), an arch placed with crown downward;
      -- much used in foundations.
      [1913 Webster]