Purbeck, ISLE OF, a peninsular district of Dorsetshire, 12 miles long and 5 to 9 broad, is bounded N. by the river Frome and Poole Harbour, E. and S. by the English Channel, and W. by the little stream of Luckford Lake, which runs from Lulworth Park to the Frome. The coast is bold and precipitous, with St Albans Head, 360 feet high; inland a range of chalk downs curves east and west, attaining a maximum height of 655 feet. The geology of the 'isle' is very interesting. The Purbeck Beds are a group of strata forming the upper members of the Jurassic System (q.v.); the Purbeck Marble, belonging to the upper section of these, is an impure fresh-water limestone, composed almost wholly of the shells of Paludina carinifera (see DIRT-BEDS). Nearly a hundred quarries are worked; and the quarrymen still form a curious kind of trades' guild. Of old the 'isle' was a royal deer-forest. Swanage and Corfe Castle are the chief places.
See Robinson's A Royal Warren, or Rambles in the Isle of Purbeck (1882), and J. Bray's Swanage (1890).