bowlder

{ } n. [ Cf. Sw. bullra to roar, rattle, Dan. buldre, dial. Sw. bullersteen larger kind of pebbles; perh. akin to E. bellow. ] [ 1913 Webster ]

1. A large stone, worn smooth or rounded by the action of water; a large pebble. [ 1913 Webster ]

2. (Geol.) A mass of any rock, whether rounded or not, that has been transported by natural agencies from its native bed. See Drift. [ 1913 Webster ]

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. [ 1913 Webster ]