clunch

from WordNet (r) 3.0 (2006)

clunch
    n 1: hardened clay

from The Collaborative International Dictionary of English v.0.48

Clunch \Clunch\, n. [Perh. fr. clinch to make fast]
   1. (Mining) Indurated clay. See {Bind}, n., 3.
      [1913 Webster]

   2. One of the hard beds of the lower chalk. --Dana.
      [1913 Webster]