Ashlar and Internal Structural Stones
Ashlar is the name given to stones which can be cut and shaped by a stonemason. They can be found externally used for the quoins at the corners of the building, windows frames and mullions, door frames and the drip stones of buttresses. They are also used internally for architectural, supporting structures such as pillars, capitals and arches. Only one or two churches on the northern borders of Hertfordshire are completely made of Clunch, the most notable example being St. Mary’s, Ashwell.
Clunch
This is a hard variety of chalk quarried from the Totternhoe Stone, Melbourne Rock and Chalk Rock beds within the Chalk. It can generally be seen as crumbly white blocks in walls although it was most often used for quoins, window frames and doorways. The colour varies from the pale cream of the Totternhoe Stone to the hard white of the Chalk Rock. Both varieties can be readily compared at Pirton church. Being relatively soft clunch is prone to graffiti. Over time the clunch begins to disintegrate and the surface texture becomes distinctly flakey . Very rotten blocks are sometime replaced piecemeal. If money is available however an entire door or window might be replaced by a more resilient Jurassic limestones as at North Mymms.
Internally clunch has often been used for pillars and arches, where it has survived the ravages of time much better than when used outside. Even very early medieval capitals retain their crisp, newly cut appearance. However being relatively soft the walls and pillars have often been defaced by graffiti, some of which is of great historical interest. See particularly the medieval graffiti in Ashwell church.
Barnack Stone
This is a tough oolitic limestone of Middle Jurassic age, with lots of shell debris within it. It was quarried in the village of Barnack, north of Peterborough, from Roman times to the late medieval period when the quarries became exhausted. The stone was expensive, mainly due to transportation costs and so was used sparingly, mainly for quoins and the pillars of doorways, holy water stoops and fonts
Two rock types that have been used extensively for repairing or replacing blocks of the decaying clunch of external quoins, window frames and mullions, and the doorways of medieval churches are :
Portland Stone
This Upper Jurassic limestone is a glaring white and often stands out like a sore thumb when used on old medieval churches as it does not weather-in easily. Different stages of weathering can however often be picked out when it has been used piecemeal to patch up quoins or buttresses over several decades. Thin wavy sections through oyster shells can often be seen in the more weathered blocks as can the distinctive ooliths. It is still being quarried on the Isle of Portland and near Swanage on the Isle of Purbeck.
Cotswold Limestones
These creamy coloured Middle Jurassic oolitic limestones were, and still are, extensively quarried along the ‘Cotswold’ escarpment from Somerset to Lincolnshire. Varieties such as Bath stone, Taynton stone and Lincolnshire limestone can be distinguished by the specialist. Using a hand lens you can pick out the spherical ooliths and angular flakes of shell debris which make up this rock.
