The story
The term was first used by Adam Sedgwick in 1847 with reference to the "Arenig Ashes and Porphyries" in the neighbourhood of Arenig Fawr, in Merioneth, North Wales.
Etymology from Wiktionary, CC BY-SA 4.0.
Arenig
Today it means: A time interval during the Lower Ordovician period. Full definition →