St. Mary’s Church, Sturminster Marshall ST95121 00402, 395121 100402, 50.8032 -2.0706
Lead authors: JT and PJB

The church was originally built in the 12th century, when it belonged to a hospital in France, but Henry VI granted it to Eton College, who remain the patrons today. It was considerably rebuilt in 1859, using much of the old stone, and some surprisingly far-fetched new ones.

Invariably as here, the oldest, most repaired and improved east chancel church walls and windows reveal very mixed individual stone types. Here, variously coursed stone, with butted-on vestry. PB

Mixed with the Heathstone in the exterior walls are small blocks of Purbeck limestones from the Intermarine Beds, with the string course at waist height being from the Broken Shell Limestone known as Burr. The string courses above the windows could not be identified due to the height.

Flat in a photo but three dimensional to the naked eye, the massed heaping of broken bivalve shell can be well seen. The metric scale is usefully marked in 40 divisions of 0.25 mm and of more use measuring grain size or to view microscopic textures. PB

The ooidal grain size of most Bath Stone averages twice the size of much north Dorset oolitic limestone. The larger grains are 0.5mm in diameter, (in and around a fossil shell) as seen here. PB

Unmatched repairs and lichens characterise the north walling and windows of the same historic stones and even more flint. The eastern two windows are of Upper Greensand, the western ones of Purbeck Burr and the roof is clay tiled. Photo: PB

Here the finer grained orange sand of the Poole Formation’s Heathstone is less evident amongst the even harder dark stone that was nevertheless hewn into dimensional ashlar. Photo:PB

Again in the tower's west face, a combination of fine grained greensand porosity with a very high percentage of glauconite grains, seen black in x10 magnification above, accounts for this severe weathering. Image: PB

Interior. The north arcade dates from the 12th century, and is partly Heathstone partly Burr (Upper Purbeck Broken Shell Limestone). The pillars of the arcade were squared off in the 19th century in order to strengthen them.

The Upper Greensand inner porch doorway and plasterwork above is stained green by mould. When used internally and can be kept dry, this stone is coloured grey, see the original Chantry/Aisle to follow. Photo: PB

The porch is a 19th century construction, with Bath Stone archway on the outside. The again fine-grained, Upper Greensand, inner door-frame just retains its colouration.

In the eastern example, between the Unio shell casts, concentrations of the freshwater Viviparus snail can also be seen. Taken together, still "best evidence" that such weathered stone is a Purbeck Marble. Photo: PB

The restructuring of 1859 can be identified by the use of the Corallian oolite in the archway to the tower, several pieces of the same stone in the western nave archway, the eastern and southern walls of the chancel, including a sedilia, the doorway in the vestry, and the southern window frames inside. The outer window frames are variously Heathstone, Purbeck Burr, Greensand and Bath Stone.

A brass inlaid Purbeck Marble ledger slab in the chancel. Photo: PB

Bennett’s memorial slab of Purbeck limestone is at the foot of the chancel steps. JT

Seen from the Chancel, by way of the wooden Chancel screen, is the Norman- style Tower archway renewed 1836 with an oolitic limestone as shown herewith. Photo: PB

The tomb-top has been so well cared for, that it outshines today’s commercially polished sample placed upon it. Photo: PB

The 19th century yellow-toned Bath Stone highlights the porch door-furnishings and all south-facing windows. PB

The exterior walls are largely of Heathstone which could have been obtained in the southern part of the parish, from the hill known as Henbury, where the Poole Formation is at present being dug for building sand. The London Clay Formation is found at depth in the current excavation. Both of these Formations yield occasional concretions of iron-cemented sandstone known as Heathstones. They are so variable in colour, iron content and quality of sand as to be impossible to identify precisely. This same hill continues westward into Lytchett Matravers parish, and thence into Morden parish, yielding concretions of Heathstone in many places.

Heathstone is difficult to identify precisely, but came from the Poole Formation/London Clay concretions on hill to the south of the village. JT

A 1cm x 1cm LED metric-scaled magnifier, set here against a turbulent marine-deposited Purbeck Burr block, one of just a few set centrally above the eastern church wall’s string line. This allows one to see the fine shell of bivalve Neomioden. PB

The spar prominent Bath Stone, oolitic but quite shelly, shown here in the vestry door frame, is set in 19th century strictly-coursed Dorset stone and against the north aisle’s wholly traditional mixture of stone - using the largest for foundation courses and quoins. PB

This lower magnification shows another feature of Bath Stone. The thick sparitic cement is far stronger and more resistant than the ooidal grains themselves; so the grains commonly break out leaving cavities termed “spar prominent”. Depending on the direction of light falling on them, these cavities stand out strongly and allow this stone to be quickly identified under any hand lens. PB

In 1859 the tower was heightened with the addition of pinnacles, which appear to be Ham Hill Stone (from the ground view). This castellation was often created in the 19th century in Ham Hill Stone.

North aisle Greensand and Heathstone buttress, arrowed shows frosted off weathering to some of the Greensand, caused by growth and expansion of ice crystals in the most fine- grained areas. Photo: PB

Left and right (or west and east) of the porch are these two very weathered medieval tomb lids. Horseshoe shaped Unio bivalve fossils are easily seen in the eastern one. Photo: PB

 Both the north aisle and the chancel were lengthened eastwards in the 14th century, with higher and wider archways. The first is all Heathstone, and the next, partly in the chancel, is built of well sorted fine-grained Upper Greensand. The final, smaller arch on the north side of the chancel was built as part of the 1859 re-structuring, and is of the Corallian oolite known as Marnhull Stone. The tower fell down in 1804, and was rebuilt the following year with Heathstone and Purbeck limestone. The corner buttresses and the quoins again include much well sorted fine-grained Upper Greensand. The sandstone appears finer than Upper Greensand, and includes large grains of glauconite. From the transport point of view Shaftesbury is as near to the River Stour as is Marnhull and it would be possible to bring stone down the river or its valley. Sturminster means – ‘large church by the Stour’.

One 15th century arch remains, built of fine-grained Upper Greensand, but the arch to the right, in the chancel, is part of the 19th century restoration using Corallian Marnhull limestone. JT

A view of the north arcade from the west. JT

A closer view of the cladding of the north arcade columns that are so large the congregation in the north aisle cannot see the altar. Photo: JT

Monuments in the church are: in the porch two grave slabs, one of Purbeck Marble, the other of a Purbeck limestone not yet identified: in the chancel on the south side a ledger slab of Belgian Black: in the centre of the chancel a ledger slab of Purbeck Marble with an inset brass: on the north side of the chancel a table tomb topped with polished Purbeck limestone: at the chancel steps a small square of polished Purbeck limestone with inset brass.

The font (see left).  Historic England records the font bowl as "Purbeck (c.1400) an octagonal bowl with coupled arches to each face, (Victorian re-decorated) and supported on a narrow column, which rests on a 13th century inverted bowl (itself re-cut)." The bowl is of a hard and coarse sparite shelly bioclastic limestone (not Purbeck Marble).  The pillar is a calcarenite with spheroids; probably an 1836 Corallian oolite restoration. The base looks to be lime-wash coated Upper Greensand.  Common on many fonts; whitewash had originally, and even when washed clean, blended the colours of the various upgrades and repairs using whatever new stone was added. Photo: PB

The archway ooids, many slightly oxidised a rusty colour, all cemented still in place, so neither “grain nor spar prominent” ,are set in a finer grained sparite cement. This is the early 19th century restoration stone now seen throughout the church and the new Chancel archway below. Photo: PB

The Victorian chancel archway stone and wall-cladding match the Tower-arch stone. It surrounds a table-top tomb of Purbeck Grub that is natural stone, front-faced and with a very polished ledger top. Photo: PB

Text and photos by PB and JT, July 2017