Purbeck Marble
Purbeck Marble is a fossiliferous limestone found in the Isle of Purbeck, a peninsula in south-east Dorset, England. It is a variety of Purbeck stone that has been quarried since at least Roman times as a decorative building stone, but this industry is no longer active.
Geology
Stratigraphically these limestone beds lie towards the top of the Durlston Formation of the Purbeck Group. They were deposited during the Berriasian age of the Early Cretaceous epoch. Purbeck Marble is not a metamorphic rock, like a true marble, but is so-called because it can take a fine polish. Its characteristic appearance comes from densely packed shells of the freshwater snail Viviparus.[1][2] Sussex Marble is similar in type. The 'marble' is properly classified as a biomicrudite, as it consists of large clasts (the snail shells) in a fine-grained limestone mud matrix.[3]
The individual marble beds (also known as 'seams'), lie between layers of softer marine clays and mudstone, laid down during repeated marine ingressions. Some of the beds contain iron oxide/hydroxide minerals, such as hematite or limonite, giving red or brown varieties, while other beds contain glauconite giving a green (or occasionally blue) colour.[3]
Occurrence
Purbeck Marble is found at outcrop, or beneath superficial cover, all the way across the Isle of Purbeck from Worbarrow Tout in the west to Peveril Point in the east. The marble beds are never more than 1.2 m thick and are often much thinner. The outcrops lie within the Purbeck Monocline, with the beds dipping moderately steeply to the north.[4]
Use
There is a single example of Purbeck Marble being used during the Bronze Age, in a cist at Langton Matravers. During the Romano-British period, Purbeck Marble was used for inscriptions, architectural mouldings and veneers, mortars and pestles, and other articles.[5]
Purbeck Marble was also quarried in medieval times and can be seen in virtually all the cathedrals of the south of England, in columns and slab panels and flooring. For example it is used in the Exeter, Ely, Norwich, Chichester, Salisbury, Lincoln, Llandaff, Southwark and Canterbury Cathedrals and in Westminster Abbey.[6]
It has been less used in modern times, but a remarkable example is the church at Kingston, Purbeck, Dorset built in 1874–1880.[7]
Though other strata of Purbeck Limestone are being quarried at the present time (2008), there are no active quarries in the Purbeck Marble. However Purbeck Marble is required from time to time for restoration work, and some was extracted in 1993.[8]
Purbeck Marble is used by a number of contemporary sculptors, such as Emily Young.[9]
References
- ↑ Arkell, W. J. (1947), Geology of the country round Weymouth, Swanage, Corfe Castle and Lulworth. London: HMSO for British Geological Survey.
- ↑ Clements, R. G. (1993), "Type-section of the Purbeck Limestone Group, Durlston Bay, Swanage, Dorset", Proceedings of the Dorset Natural History and Archaeological Society, 114, 181–206.
- ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ Beavis, John (1971), "Some aspects of the use of Purbeck Marble in Roman Britain", Proceedings of the Dorset Natural History and Archaeological Society, 92, 181–204.
- ↑ Leach, Rosemary (1978), An investigation into the use of Purbeck marble in medieval England, 2nd edition. Crediton: the author.
- ↑ Kingston (St James) Church
- ↑ Haysom, Treleven (1998), "Extracting Purbeck Marble", Hatcher Review, 5(45), 48–54.
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
