erractic being carried on a glacier
erratic (er-rat'-ic) n. A rock fragment carried by glacial ice, or by floating ice, deposited at some distance from the outcrop from which it was derived, and generally though not necessarily resting on bedrock of different lithology. Size ranges from a pebble to a house-size block. See also: perched block; exotic [struc geol]. Syn: erratic block; erratic boulder; glacial erratic. adj. Transported by a glacier from its place of origin. Syn: traveled.
Neuendorf, Klaus. Glossary of Geology, Fifth Edition, Revised (Kindle Locations 20401-20405). American Geosciences Institute. Kindle Edition.