GLACIATED PEBBLES (16)
GLACIATED PEBBLES are small stones whose shapes have been altered by the grinding action of a glacier. Such pebbles commonly have at least one flattened side that shows scratches (called striae). The striae were produced when the pebbles were pushed over bedrock or ground against other pieces of rock.
Glaciers tore fragments from the bedrock over which they moved and the fragments accumulated in, on, and under the mass of ice. The rock fragments were transported, some of them far from their source, and were deposited as the glacier moved along or when the ice melted.
Soft rocks like limestone and dolomite are easily scratched, but soft rocks cannot make grooves in hard igneous and metamorphic rocks. Therefore soft rocks have more striae.
Glaciated pebbles can be found in deposits in many parts of the state, especially in northeastern and east-central Illinois. However, many deposits near the surface have been weathered and striae have been destroyed. An especially good place to look for striated pebbles is in quarries and strip mines where glacial drift overburden has been removed. Pebbles found in such deposits show good striae for they are but little weathered.