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]WordNet (r) 3.0 (2006):
clunch n 1: hardened clay