In Search of Puddingstone
Field Trip to St Albans, 6th October 2013
On Sunday 6th October, nine members and four guests
visited St Albans for a Puddingstone and Sarsen Stone
walk around the city under the expert guidance of Prof.
John Catt of the Herts Geological Society. We met at the
Verulamium Roman Museum where we learnt that
Verulamium was originally an Iron Age town that
became an important Roman city with a basilica and
forum. In the 1930s Mortimer Wheeler excavated the
Roman city which extended as far as Watling Street.
The group around a puddingstone boulder
Use of Puddingstone in Churches
We first visited the nearby St Michael’s Church which had several pieces of puddingstone in the outside
walls as well as irregular courses of Roman bricks with flints between. Niches in the walls were
surrounded by facings of Totternhoe stone from the Chalk of Bedfordshire. As it is relatively soft and
easily weathered, all details of any carving had worn away. Extensive Victorian restoration had introduced
Ham Hill stone from near Yeovil for door surrounds.
Other churches in the city, St Stephen’s and St Peter’s
also have puddingstone in the walls as do many preVictorian churches in the general area, because in the
early 7th century, Pope Gregory sent out a papal edict
that any pagan talisman such as Puddingstone should be
incorporated into Christian churches. The tower of
Aldenham church which is near to an old quarry is made
almost entirely of Puddingstone and footings for
churches such as at Chesham used puddingstone taken
from a nearby stone circle for the bases of buttresses.
Different stones in St Michael's Church
Isolated puddingstone Blocks
Our walk continued looking next at a very large
isolated boulder some 4 feet high and 6 feet long
standing on a grass strip outside the old Kingsbury
Corn Mill. It was moved from the adjacent River Ver
where it was used as a stepping stone or base of a
ford in 1887 when the bridge was built. It is now used
as a boundary stone and is
visited each year at the
Beating of the Bounds by
the Lord Mayor.
Large Puddingstone boulder outside Kingsbury Mill
Other large and many smaller pieces were seen in the garden
of Kingsbury Manor next door which the owner, who allowed
us to look round, said had been there for a very long time.
Some showed beds of differing pebble size, but little evidence
of preferred
orientation of
pebbles.
Large Puddingstone boulder in
garden of Kingsbury Manor
Puddingstone boulder to protect corner of Ver cottage
At the entrance to the car park of the Blue Anchor pub, there was a large boulder incorporated into the
corner of the wall of Ver Cottage, presumably as some form of protection for the corner from abrasion by
cart wheels that may have cut close to the corner.
Another large boulder was in a private garden at
Kingsbury Lodge and was shown to us by a friend of
John Catt. This was more sarsen like than
puddingstone as it contained few pebbles. Most of
the fragments within it were of shattered black flint
and there were some white coloured
angular fragments. It was likely that
the stone had slipped down the
slope from an outlier on top of the
hill and then been placed in an
upright position.
Sarsen in garden of Kingsbury Lodge
Sarsen Setts
Sweeping away the leaves from the gutter revealed that they were made of sarsen setts. These were
produced at a “factory” at Walters Ash, Bucks. on the plateau of the Chiltern Hills where sarsen is found
in the plateau drift on top of the Chalk between the dry valleys.
Other Boulders and Stones
On the path leading to the Cathedral we encountered another
large boulder. It had the inscription “VOTA VITA MEA”
(translated as” vows of my life”) carved into it showing that it
was considerably softer than sarsen. It is thought to be a glacial
erratic of Carboniferous Limestone although it was difficult to
see evidence for this.
Erratic with carving VOTA VITA MEA
In the walls of the Cathedral we saw the outlines of the abbey
cloisters made from Totternhoe Stone from quarries owned by the Benedictine monastery. Other
interesting walls made of chalk were seen along Mount Pleasant Road forming the sides of a house dated
1831 and adjacent to Kingsbury Lodge where they had been the internal wall of part of a brewery on the
site. The chalk from these had been analysed and microfossil evidence suggests that the house wall chalk
came from more distant sources than the Redbournbury area which had
sourced the chalk in the
brewery.
Totternhoe cloisters in Cathedral wall
Chalk Clunch wall in Brewery Yard
Chalk wall of 1831 house
The Abbey church, now the Cathedral, was built on the site where St Alban, Britain’s first Christian martyr
was beheaded in 209BC on the hill outside the Roman city of Verulamium. A man called Alban, believed
to have been a Romano-British citizen of the Roman town of Verulamium around the end of the 3rd
century, gave shelter to an itinerant Christian priest, later called Amphibalus. Impressed by what he heard
Alban was converted to Christianity by him. When a period of persecution, ordered by the Emperor
Severeus, brought soldiers in search of the priest, Alban exchanged clothes with him allowing him to
escape and it was Alban who was arrested in his place.
The Benedictine monastery and abbey were built in 308AD and dedicated to St Alban whose remains
were kept in a Purbeck marble shrine. The bones were reputedly stolen by some Belgian monks in 11th or
12th century. When the bones in the shrine were examined in the 19th century they were found to be
those of an ox. The west front is made of stripy Ancaster
Stone. The Norman tower is made almost entirely from Roman
brick. Inside are pillars of Carboniferous limestone and
Purbeck marble.
On the way back to the car park we passed Ye Old Fighting
Cocks which is reputed to be the oldest pub in England. Its
interesting octagonal shape reflects its origin as a dovecote.
The Origin of Puddingstone and Sarsen
Very little Puddingstone has been found in situ, but a few outcrops have been found in Hertfordshire,
more recently during road reconstruction of the A120 and A10. It appears to be within the Palaeocene
Reading Formation, a non-marine facies that grades laterally into the marine Upnor formation. In the
shaft of an ancient flint mine at Pinner further south in Middlesex, pebble beds are seen to overlie the
Thanet beds. Records show occurrences at Radlett, south of St Albans and there are outliers to the north
west of this centring on St Albans. Whittaker found
puddingstone at the St Albans hospital site in the
late 19th century where it appears to be within the
Reading Formation, dating its formation to around
55 million years ago.
Cross section from East Herts Geology Club leaflet
Large masses of Puddingstone have been moved
by natural processes into valleys in the Chalk
surface accounting for the main occurrence in
plateau drift in the Chilterns. Studies at
Rothamsted research station in the 1960s in which
John Catt was involved, show the “Clay with flints”
form a veneer of deeply weathered Reading and
Upnor formations around Harpenden and
elsewhere.
Puddingstone is a highly silicified conglomerate composed of rounded flint pebbles cemented together by
a younger matrix of silica. The flints were eroded from the surrounding Chalk beds some 56 million years
ago in the Palaeocene-Eocene epoch and were transported by water action to beaches, where they were
rounded by wave erosion and graded by size. A lowering of sea levels and general drying during a brief
arid period known as the Palaeocene-Eocene Thermal Maximum drew out silica from surrounding rocks
into the water immersing the flint pebbles. Further drying precipitated the silica which hardened around
the pebbles, trapping them in the matrix.
Similar processes were repeated elsewhere in beds of similar and slightly younger age such as in the
Blackheath Beds of Kent and even in the Bagshot Sands.
David Turner & Ros Smith