Hardpan

from WordNet (r) 3.0 (2006)

hardpan
    n 1: crust or layer of hard subsoil encrusted with calcium-
         carbonate occurring in arid or semiarid regions [syn:
         {caliche}, {hardpan}]

from The Collaborative International Dictionary of English v.0.48

Hardpan \Hard"pan`\ (h[aum]rd"p[a^]n), n.
   The hard substratum. Same as {Hard pan}, under {Hard}, a.
   [1913 Webster]

[email protected]