Wolfson College Record 2021

The living stone beneath your feet
by Jim Kennedy (EF)
The flooring blocks of the Leonard Wolfson Auditorium, café, Academic Wing and
adjacent Stallworthy Quadrangle, are made of 340 million-year old Carboniferous
Limestone from Threecastles Quarry at Kilkenny in Leinster Province, south-east
Ireland. At the time these limestones accumulated, the British Isles formed part
of the continent of Laurasia, made up of North America and Europe west of
the Urals, and lay well to the south of its present position. There was no North
Atlantic Ocean between Europe and North America at that time.
The limestone, commonly known as Irish Blue Limestone, is made up of grains of
calcite – a form of calcium carbonate – derived from the skeletons of a range of
marine organisms, and accumulated on a shallow sea floor in turbid waters. The
colour of the limestone reflects the presence of land-derived clays. The blocks in
the Stallworthy Grove and flooring the café come from a level in the sequence
where stable sea floors supported a rich fauna, dominated by corals, brachiopods
and crinoids, their calcite skeletons white against the blue-black limestone matrix.
In contrast, the flooring blocks by the Lodge desk and outside the entrance come
from a different part of the sequence, with few obvious fossils. They have a subtle
mottled appearance, the result of the carbonate sediment that was ultimately
transformed into limestone having been churned over by successive generations of
soft-bodied organisms, whose only record is their burrows.
The living stone
To return to the fossils. The corals belong to two extinct groups, known as
tabulate and rugose corals. Unlike modern reef-building corals, they probably
lacked the symbiotic organisms (zooxanthellae) that limit present-day reef
development to the photic zone (the zone of light penetration). Several types
are present. Massive colonies, built of close-packed polygonal corallites belong
to the genus Palaeosmilia. Each corallite was secreted by a single polyp, a sea
anenome-like individual. A second rugose coral, Lithostrotion, is made up of
cylindrical corallites, and appears as areas of circular sections around a centimetre
in diameter, with radiating septa within. Areas of much smaller circular sections
belong to a second species of Lithostrotion. Colonies of the tabulate coral
Michelinia have polygonal corallites, but lack septa.
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