\Bowl"der\, Boulder \Boul"der\, n. [Cf. Sw. bullra to
roar, rattle, Dan. buldre, dial. Sw. bullersteen larger kind
of pebbles; perh. akin to E. bellow.]
1. A large stone, worn smooth or rounded by the action of
   water; a large pebble.
2. (Geol.) A mass of any rock, whether rounded or not, that
   has been transported by natural agencies from its native
   bed. See {Drift}.
{Bowlder clay}, the unstratified clay deposit of the Glacial
   or Drift epoch, often containing large numbers of
   bowlders.
{Bowlder wall}, a wall constructed of large stones or
   bowlders.