nappe

noun

1. Geology. a large mass of rock thrust a considerable distance along a nearly horizontal fault plane or in an overturned anticlinal fold.
2. Geometry. one of the two equal sections of a cone.

noun

1. a large sheet or mass of rock, commonly a recumbent fold, that has been thrust from its original position by earth movements
2. the sheet of water that flows over a dam or weir
3. geometry either of the two parts into which a cone (sense 2) is divided by the vertex