Derg, Lough, an expansion of the waters of the Shannon, Ireland, 24 m. long, from 2 to 6 broad; also a small lake in the S. of Donegal, with small islands, one of which, Station Island, was, as the reputed entrance to St. Patrick's Purgatory, a place of pilgrimage to thousands at one time.
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Derbyshire * Dervishes