Plural of erratic; in geology, boulders or rock fragments carried far from their source by glaciers and left behind in different locations.
From 'erratic' used as a noun in geological terminology. Geologists borrowed the adjective to name rocks that seemed 'out of place' because glaciers had moved them.
Huge glaciers during ice ages acted like bulldozers, picking up boulders in Canada and dropping them in New York—geologists called these displaced rocks 'erratics' because they seemed in the wrong place!
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