Geography of Sheffield county, from bituminous (ideal for domestic heating) to "Thick Coal", of a semi-anthracitic quality, appropriate for use in iron-smelting and in engine furnaces. Associated with the Upper Coal Measures were valuable iron ore deposits, occurring in the form of nodules. Large quantities of locally occurring fireclay were also exploited, as well as ganister (a clay used to make refractory furnace linings). The city of Sheffield derives its name from the River Sheaf which Until the 17th century was written as "Scheth" or "Sheath". Sidney Oldall Addy equates the origins of this word with the Old English "shed" (as in "water-shed")
Sheffield City Centre of the city centre, is host to numerous national and international sporting events, notably swimming and Basketball. The Crucible Theatre, in Tudor Square, is host to the World Snooker Championships which have been held there since 1977. Sheffield is home to the greatest concentration of theatres in the UK outside London. These include the Crucible, Lyceum, Montogomery and Studio theatres. The city centre is home to numerous venues which attract many well-known musicians, comedians, theatre groups and so on. Examples include the City Hall, O2 Academy, Plug, and the Lyceum and Crucible theatres. Sheffield city centre is host to its