THE PETROLOGY OF ARCHITECTURAL FRAGMENTS
Dr. Kevin Hayward
Visiting research fellow of the University of Reading
ABOUT DR HAYWARD
Dr Hayward examines the fabric and form of stone, brick, mortar and tile - for the entire UK - for all periods (Roman-Present Day) to date not only standing buildings, but also walls and features revealed during archaeological excavation Current work involves stone by stone analysis of the Tower of London, (Bell Tower and Develin Tower) and Westminster Abbey, (Pyx Chamber and Cosmati Pavement). He assesses the geological character and source of worked stone and rubble using a variety of techniques including hand specimen, binocular microscope, thin-section petrography, mineralogical (XRD - X-Ray Diffraction) and geochemical (XRF - X-Ray Fluorescence; Stable Isotope Geochemistry (Carbon and Oxygen). His PhD sudies examined the geological source and character of early Roman tombstones and monumental architecture in southern England and was published as a British Archaeology Report no. 500.
He is the joint author on the stone sources for the recent Corpus of Roman Sculpture for London and South-East England. His work extends to chemical and thin section analysis of Victorian brick and stone in Glasgow, published as a 2015 stand alone article in the Scottish Journal of Geology, the Ecology of Crusading medieval brick from the Baltic States and the types of stone used in Roman Villa (Chedworth, Brading, Stanwick.
Kevin has been with the Hidden Abbey Stones Project from its beginnings, providing expert advice and assessment. For further information see; https://uk.linkedin.com/in/dr-kevin-hayward-326b6524
Commentary by Dr Hayward
The underlying geology of this part of the Thames Valley and through much of south-east England is devoid of stone suitable for fine carving – the rock is often too young and soft and frequently consists of clays and unconsolidated sands and gravels. This means much of the stone used in the carving of the Abbey needs to have come from afar. Fortunately, Reading’s excellent riverine links afforded to it by the River Thames allow suitable stone to easily be barged downstream from older Jurassic limestones in the Cotswolds.
Furthermore, stone can be barged upstream, via the Thames Estuary, from maritime sources as far afield as the North Downs, Lincolnshire, Dorset and even the continent.
Most of these finer rock types identified as architectural fragments or ashlar from Reading Abbey are termed freestones. Freestones are limestones or sandstones with a soft open porous texture that enables the rock to be worked or carved in any direction, and is often hard enough to withstand external weathering.
The freestones identified from Reading Abbey form part of the medieval stone package typical of many large ecclesiastical, palatial and defensive buildings in London and south-east England.
We are listing these stones, with photographic examples of the their use in the Abbey, samples of their appearance and close up microscopic fields.
In terms of frequency they are as follows:
1. TAYNTON STONE
Use: Very common stone type, both from the in-situ remains of Reading Abbey, loose blocks of architectural stone including the famous Reading altar stone and blocks reused into later post medieval walls and cellars throughout Reading.
Rock Type: Orange-brown banded shelly oolitic limestone. The surface consists of alternating bands of hard grey shelly (oyster) and ooids (small round calcite grains that often weather out, giving the rock a pitted surface)
Geological source: Burford/Taynton stone - Middle Jurassic (Bathonian) Taynton, Burford West Oxfordshire.
Example of Taynton stone as it appears in the ruins of Reading Abbey
Taynton stone—detail
Close up microscope field of view 2.4mm
2. CAEN STONE
Use: So far only identified petrologically in the large number of ornately carved capitals (the Keyser Capitals). These however were recovered from Sonning. The regal connection with Normandy resulted in large consignments of stone being supplied for use in ecclesiastical projects in London southern (Canterbury Cathedral) and eastern (Norwich Cathedral) England. However, this has inevitably led to the assumption that a lot of the stone used in Reading Abbey is made of this stone.
One may question accounts from the 16th century that Cane stone was supplied to Windsor Castle from Reading Abbey. Petrological reassessment of the Cane (Caen) stone at Windsor Castle is required because it could have easily been mistakenly for the similarly coloured Taynton stone.
Rock Type: Fine condensed cream, yellow or yellow brown limestone (packstone). In thin section (see below) the rock is made of tiny black snail pellets (peloids). Fine surface can be conducive to the application of pigment (paint)
Geological source: Caen stone Middle Jurassic (Bathonian) Caen, Departement Calvados (Normandy France)
Close up microscope field of view 2.4mm
Caen stone detail
Capital in Reading Museum
3. BARNACK STONE
Use: So far only identified in a reused fragment in the wall alongside St James’s Church. Outside Cambridgeshire this rock is used in the production of sarcophagi. The example (below) from Westminster Abbey probably dates from the 12th century. The quarrying and supply of this rock goes into disuse after the 13th century, as the quarry largely runs out of stone.
Rock Type: Very hard sparry shelly limestone with occasional ooids.
Geological source: Barnack stone Middle Jurassic (Bajocian) Barnack Village, Cambridgeshire near Peterborough (extensive use in Peterborough Cathedral)
Barnack stone used for a sarcophagus
Barnack stone detail
Close up microscope field of view 2.4mm
4. PURBECK MARBLE
Use: So far only identified petrologically in in a reused column shaft column in the wall alongside St James’s Church (see below). The rock is polished black forming striking column bases, shafts within an abbey or cathedral in contrast to yellow rocks e.g. in Salisbury Cathedral.
Rock Type: Fine dark grey sparry limestone packed full of small 10mm complete freshwater snails Paludina carinifera Shelly Wackestone
Geological source: Purbeck marble, Purbeck Group, Durlston Formation (Lower Cretaceous), Swanage-Langton Matravers, Isle of Purbeck, Dorset.
Polished Purbeck marble
Cross section of Purbeck marble in the Abbey Ruins
Close up microscope field of view 2.4mm
5. REIGATE STONE / MALMSTONE
Use: So far only identified petrologically in an ashlar block in the arch leading from St James' to Abbots Walk . In medieval London this is the most common rock type, used not only as ashlar (e.g. Westminster Abbey Refectory Wall) but also in window mullion (tracery) mouldings.
Rock Type: Very low density fine-grained lime-green (glauconitic) limestone). Fine surface can be conducive to the application of pigment (paint)
Geological source: Reigate-Mertsham stone Upper Greensand, Upper Cretaceous, Reigate-Mertsham (East Surrey). or Malmstone Upper Greensand (Farnham District).
Reigate stone in Abbey ruins
Close up microscope field of view 2.4mm
6. HARD CHALK / CLUNCH
Use: So far only identified petrologically in ashlar blocks in the arch (below). Identified in ashlar blocks from 11th and 12th century Westminster Abbey.
Rock Type: Condensed white very powdery limestone full of tiny microfossils
Geological source: Chalk Rock/Clunch/Totternhoe stone/Stockbridge stone. Possibly from the immediate environs of Reading, or via boat (River Kennet) from outcrops in West Berkshire.
Example of clunch
Close up microscope field of view 2.4mm
For more information about the above stones, their quarries and how to interpret their use, especially in the Abbey, see the section The Stones, under the HASP heading.
SOME OTHER STONE TYPES
Examples of the next two types of stone have not been positively identified at Reading. However Sir Henry Englefield, writing in his famous survey of the Abbey of 1779, mentioned the existence of tufa. He pointed out that it was used in stone vaulting owing to its lighter weight, thereby creating less downward thrust on the supporting walls and pillars.
Look out for Tufa
Use: Not identified so far in Reading Abbey (other than a fragment that may possibly have come from the Chapter House). Elsewhere e.g. Westminster Abbey associated with vaulting e.g. 11th century Pyx Chamber.
Rock Type: Tufa – Low Density Hard calcareous spring water deposit full of voids.
Geological source: Holocene river/spring water deposit - many possible sources along the Thames and Kennet Valley e.g. Woolhampton.
Samples of tufa
Look out for Quarr stone
Use: Not identified so far in Reading Abbey Elsewhere e.g. Westminster Abbey, Tower of London, Winchester associated with 11th to early 12th century vaulting and ashlar. Quarry supplies run out in the 13th century.
Rock Type: Hard white skeletal limestone (Featherstone) full of small, elongate hollowed out shell
Geological source: Quarr stone, Tertiary; Quarr (Quarr Abbey), north coast of Isle of Wight.
SEARCHING FOR ABBEY STONE
The above provides a guide for anyone trying to identify a stone that they believe may have its origins in Reading Abbey.
If you think you have found something of interest please do get in touch (see the Contact Us section) - we shall be most pleased to hear from you.