Bath Stone (lead authors WGT/PS)
The term Bath Stone refers to Middle Jurassic bioclastic oolitic limestones (bio-oosparite) of the Great Oolite Group, deposited in shallow seas 168 to 166 million years ago (Bathonian). The outcrop between Bath (Somerset) and Corsham (Wilts) has been extensively quarried above and below ground since the 1700s. These limestones are not present in Dorset, their lateral equivalent being the Fuller’s Earth, Frome Clay and Forest Marble (qv) Formations.
Due to its strength, Bath Stone is commonly seen as window dressings and quoins, especially in Victorian churches. Bath Stone has been used in Dorset since the railways were built in the mid-19th century. Most Bournemouth churches and the 19th century ones in Poole, plus the cemetery chapels in Blandford (qv) have dressings of Bath Stone with walls of more local materials. Those churches which required extensive renovation in the late 19th century have interior work also – an example being Upwey church. A distinctive weathering characteristic is that the upper part of exterior arches in Bath Stone tends to turn a dark orange/brown. However, Bath Stone used in Dorchester (Agriculture House, Trinity Church in the High Street) remains a muddy cream colour and has quite a high shell fragment content.
Text by WGT, JT & PS March 2017
Two levels are used as building stone: the Combe Down Oolite and the higher Bath Oolite & Corsham Limestone. In both cases the stone is cream-coloured with a sparry calcite cement which is harder than the ooids. The latter often weather out leaving moulds with the cement standing proud of the surface. Weathering and the addition of fungal/algal films can result in a honey-coloured or reddish-looking stone.
Similar Middle Jurassic limestone is quarried in Lincolnshire
and sometimes used as a Bath Stone substitute.