E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Circles of rank or withered grass, often seen in lawns, meadows, and grass-plots. Said to be produced by the fairies dancing on the spot. In sober truth, these rings are simply an agaric or fungus below the surface, which has seeded in a circular range, as many plants do. Where the ring is brown and almost bare, the spawn is of a greyish-white colour. The grass dies because the spawn envelops the roots so as to prevent their absorbing moisture; but where the grass is rank the spawn is dead, and serves as manure to the young grass.