Variability of the Earth’s climate - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 97

Figure 2.43. Erratic stone (Geike, 1894).

Figure 2.44. Scratched stone (Geike, 1894).

stiff semi-fluid causes the stony fragments to move in a nearly uniform direction,
so that they grate over the underlying rocks like a rasp ... . From the stability of

the motion of such a substance as ice there would result grooves and striation

both on the rocks beneath and on the boulders and pebbles that, like iron
plowshares, are forced over them. Scratched surfaces of rock and scratched
stones are therefore, in ordinary cases, most trustworthy indications of glacial

...