Articles from Issue Number 11/2 April 2004
Building Stones of Westminster Abbey
Led By Eric Robinson
20th February 2004
We met, on
a bitterly cold day, in Deans Yard. To our left the copingstone on the wall was
Kentish Rag laid upside down according to the cross bedding. This set the scene
for the whole experience. Eric emphasised that the Abbey is a series of
unconformities and we saw them everywhere.
As a
newcomer to geology I imagine that an experienced geologist can just look at a
stone and know what it is but the delivery records have been kept and are not
only invaluable for identification but also inform about hidden stones such as
the fifty-five hundredweight of chalk used to pack the vaults.
Westminster Abbey stands on a gravel sand island strip in the Thames near one of
the few crossing places. You might not think that it would be stable enough. The
abbey does not have an under croft but under the raised Pavement it is perfectly
dry. It is on the edge though as St Margaret’s Church, a stone’s throw to the
north is off the eyot and has serious damp problems whilst under Parliament
Square there are lenses of quick sand below the London Tertiary’s (which the
test boreholes missed) that caused the new underground line builders to over run
and nearly cost Hopkins, the architect of Portcullis House, his reputation quite
undeservedly. The wall, to the right of the entrance from Deans Yard, is of
Reigate Stone. This stone from the Upper Greensand is easy to dress but,
unfortunately, it is glauconitic so now the blocks are well rounded,
particularly around the joints (we were told that the mortar might be one of the
culprits). Down pipes around the cathedral cause particularly bad erosion and
here galletting has been used possibly as an early remedy. Even the galletts are
standing proud now though.
Inside the
gatehouse there are bigger blocks of Reigate Stone. It was also used for the
vaulting. The condition is much better although the odd piece has flaked away.
But take care when you look. Often the walls have a preservative coat perhaps of
lime wash). To the left a huge block of beautifully carved Carrara Marble
standing on a breccia base celebrates a naval skirmish. The detail is crisp
although one lizard has lost its head. We could appreciate why sculptors favour
this marble. The benching in the cloister, originally of Bath Stone, has had a
fair amount of wear so has been repaired. But one repair has rudist bivalve
shells in it so must have come from an older source, possibly France. The
cloister itself is quite open and there is a marked difference in the condition
of exposed and sheltered stones.
We saw
unconformities in abundance in the Chapter House wall from the Cloister. The
yellowish stones at the base are magnesian limestone transported by sea from the
Humber. There is white Bath Stone and Chilmark Stone above. We examined Chapter
House wall in more detail from the east and Eric pointed out the characteristic
blisters formed as the glauconitic Chilmark Stone erodes. Chilmark stone is the
Wiltshire facies of Portland Stone and was chosen by Sir George Gilbert Scott.
It was an unsuccessful choice though and has been systematically replaced by
Portland Stone since 1900.
In the
nave itself we looked at a selection of monuments to past geologists, Buckland
and Lyell.
The small
Purbeck Marble columns attached to the main columns in the south transept are
interesting. The seam is no more than about a meter thick and yet some are about
double that height. The smaller columns are carved from vertical blocks and some
clay-rich bands in the marble have worn into grooves and notches. The longer
unbroken columns are actually length bedded. Look upwards in the Nave to see
more Purbeck Marble pillars. The clerestory and vaulting are Reigate Stone.
After a
brief prayer for peace we had our main treat. The shrine to Edward the
Confessor, with royal tombs grouped in a horse shoe around, lies behind the
altar screen. In front is the raised Great Pavement. Henry III visited the pope
in 1259 and saw the Cosmati pavement being built there and returned home with a
bag of bits and pieces to have his own built. This whole area would at one time
have been patterned with small tesserae of coloured stone or ceramic. The Great
Pavement itself is incised into a bed of Purbeck Marble.
Although
damaged this is the most complete Cosmati pavement known. Oliver Cromwell
allowed his horses on it and the Lords caused more damage in1953 at the
coronation. Perhaps most surprisingly the rubber underlay of the carpet, laid
specifically to protect it, cut off its air supply causing even more damage and
left black bits behind as well. Conservators are hard at work restoring it. Eric
has recast his fingerprints using spit to clean it and even less appropriate
human activities are said to work well but cleaning is difficult. Shoes off
before stepping on it – see how privileged we were! We stood back to appreciate
the geometric design of the Great Pavement, also known as the End of the World
Pavement. It predicts the world to end in 19683 years time. I am not sure what
the starting date is though.
After a
hot soup in the very cold cloisters we passed modern monuments.
There was
still time for a final look outside. The top of the West Front looks as crisp as
the architectural drawing Eric showed us, where it is faced by white Portland
stone. At the bottom to the side are more Reigate Stone and Kentish Rag.
Round the
corner in the North Nave buttresses is the piéce de resistance of
unconformities. A couple of courses at the bottom consist of older, reused
masonry. Above this there is a wide course of Cornish Granite. Oolitic Chilmark
stone sits unconformably on the granite followed by a yellow shelly oolite from
Normandy and more oolite. At head height it is Bath Stone. Our last view of the
cathedral was the Henry VIIth
Chapel tacked on to the east end. This is highly decorated Bath Stone.
Eric not
only gave us an idea of the fabric of Westminster Abbey and its contents but
also passed on his enthusiasm by adding anecdotes a plenty which made us realise
that this church is a gigantic living organism rather than just an historic
building. We thoroughly enjoyed our tour and look forward to seeing the restored
Great Pavement.
We are
grateful to Eric for making the effort to get out of bed so early on such a
bitterly cold winter’s day to come up from Frome to be with us.
Diana
Wrench
