Glacial Erratics: Marker Rocks from Distant Places (RM-01)
Erratics are water- and ice-worn rocks transported from distant sources by glacial ice. They are made up of rock types different from the bedrock. Glacial drift of northern Indiana contains tons of cobbles and boulders of granite, gneiss, marble, quartzite, basalt, and other rocks. Many stream valleys contain minute traces of gold, diamonds, quartz, garnet, and other unusual minerals.

Erratics are generally considered to be a nuisance, especially by farmers who must clear their fields of rocks that frost forces to the surface. But some gravel pit operators have found a ready market for "fieldstone" cobbles and larger erratic boulders for architectual and specialty construction.

Our Hoosier State Beneath Us: Rocks and Minerals