er·rat·ic / iˈratik/ • adj. not even or regular in pattern or movement; unpredictable: her breathing was erratic. ∎  deviating from the normal or conventional in behavior or opinions: neighbors were alarmed by increasingly erratic behavior.• n. (also erratic block or boulder) Geol. a rock or boulder that differs from the surrounding rock and is believed to have been brought from a distance by glacial action.DERIVATIVES: er·rat·i·cal·ly / -(ə)lē/ adv.

erratic Glacially transported rock whose lithology shows that it could not have been eroded from the local country rock. An example is the occurrence near Snowdonia, Wales, of granites derived from Scotland. An ‘indicator’ is an erratic whose origin can be located precisely.

erratic A glacially transported rock whose lithology shows that it could not have been derived from the local country rock. An example is the occurrence near Snowdonia, Wales, of granites derived from Scotland. An ‘indicator’ is an erratic whose origin can be located precisely.

erratic In geology, a rock that has been transported some distance from its source by glacial action, and is therefore of a different type to the surrounding rocks. The tracing of erratics can give important information about the movement of ice.