Bowlder
BOWLDER, noun [from bowl.] A small stone of a roundish form, and of no determinate size, found on the sea shore and on the banks or in the channels of rivers, etc., worn smooth or rounded by the action of water; a pebble.
The term bowlder is now used in Geology for rounded masses of any rock, found out of place, and apparently transported from their original bed by water. Bowlders of Granite, often of great size, are very common on the surface of the most recent formations.