Journal of the Bath Geological Society, No. 38, 2020
33
can be given away at public events or sold to raise funds
to support geological charities.
It is likely that the collection is widely dispersed. All
organisations accepting ‘ex-Stonar School Collection’
specimens will be encouraged to acknowledge this on
specimen labels and documents.
At the time of writing, Somerset Earth Science Centre
are interested in taking some of the Stonar material to
improve their handling collections. The Centre, based at
Moons Hill Quarry, Stoke St Michael work closely with
schools, colleges, universities and community groups
across Somerset to improve their understanding of the
Natural World and in particular, the Earth Sciences. A
small collection of graptolites, collected by Philip
Curnow has also been donated to Bristol City Museum.
References
Carpenter, S. 2014. William George Cross (9 January
1919 – 30 June 2013) amateur Geologist and founder
member of Bath Geological Society – an unpublished
biography.
Thanks
I would like to start by offering my sincere gratitude to
Stonar School for relinquishing care of their geological
collection so it can be refreshed and used with the
geological community elsewhere. Elizabeth Devon,
former Head of Geology at Stonar School alerted me to
the threats facing the School geology collection and has
helped provide information about the collection and
collectors. I am indebted to Richard Ashley for finding
out more about Philip Werran Curnow. Before this
writing project began, we knew very little about Philip,
so it is has been very exciting to discover that he was a
Fellow of the Geological Society of London and a past
Curator of Geology at Bristol City Museum. I would
also like to thank Alan Bentley, friend and geologist for
helpful comments and discussions during the course of
this project and for assisting in the identification of the
fossils and minerals. Finally, I would like to thank the
many people who gave their rocks, fossils and minerals
to Stonar School and in particular, the contribution made
by Philip Werran Curnow.
-.-
‘Breaking news – meteorite impact
causes devastation near
South Gloucestershire village’
By Charles Hiscock
In this internet age we are also constantly being
bombarded by news flashes from across the world onto
our mobile phones, computers and tablets. The news
may be a few seconds old when it reaches us. Some of it
will be ‘fake news’, a scourge of modern media that
leaves us wondering if we can believe some, or all of,
that which we see or hear. The constant information and
warnings we get about ‘fake news’ prompted me to
wonder what it would have been like if instant
communications had existed in the Triassic Period.
More precisely, 214 million years ago! Hence the title of
this short article (and no, it is not ‘fake news’, it is true –
but a bit delayed and embellished!).
In 2009 I was invited by Mark Mitchelmore to have a
tour of Churchwood Quarry about a mile north of the
village of Wickwar. Mark Mitchelmore was a geologist
for Cemex UK, the owning company and operator of the
quarry. On a fine day in September we walked around
the perimeter of the quarry on the excavated level at the
top of the marine Lower Carboniferous Clifton Down
Limestone (340 mya), the material that was processed in
the quarry and sold as aggregate for the road and house
building industries. However, the Clifton Down
Limestone is overlain by first the Triassic Dolomitic
Conglomerate, a scree and alluvial fan deposit laid down
by the erosion of the Carboniferous mountains, which
grades upwards into a fine yellowish sandy matrix. This,
in turn, grades into the desert sediments of the red
Mercia Mudstone Formation. The break at the top of the
Clifton Down Limestone represents an unconformity
with a gap of about 74 million years.
In 1973 A. Kirkham was in Churchwood Quarry when
he discovered ‘unusual green spherules up to 1mm
diameter within erosional troughs along the
unconformable top of the marine, Lower Carboniferous,
Clifton Down Limestone’. The spherules were found
initially in a ‘cross bedded deposit of hard and soft silty
marls occurring discontinuously at similar stratigraphic
Fig 5. The fossil crab, Plagiophthalmus oviformis Bell. From the
Stonar School Collection and collected by Philip Curnow. The origi-
nal specimen label is missing. The accompanying form is a Natural
History Museum, London determination slip. (photo credit: Simon
Carpenter)
Journal of the Bath Geological Society, No. 38, 2020
34
levels along much of the western face of the quarry’.
Subsequently, the spherules were analysed,
photomicrographed and dated to ‘between Late
Carboniferous and Late Triassic although Triassic is
more likely’. He also considered the origin of the
spherules, suggesting that ‘they were created as molten
ejecta associated with a meteorite impact’. (Kirkham
2003 – abstract below)
In the late 1980’s Gordon Walkden was working in the
Carboniferous quarries of the Bristol area on the lizard
and small dinosaur remains that had been discovered in
the Triassic fissures in the quarries. He made a visit to
Churchwood Quarry but it proved unrewarding for the
fossil remains but he did collect ‘a lump of pink rock
with green balls in it’. He called it ‘a pretty curio with
no immediate explanation. It just went into a drawer to
await developments’. Ten years or more later, when
working on a thin section of the Cretaceous/Tertiary
impact deposit from Haiti, the penny dropped. He
realised that those little green balls he had collected
from Churchwood Quarry were the same, or similar to
the KT boundary deposit. (Walkden 2004)
I had read the both articles shortly after publication so,
in 2009 when I visited the quarry, I asked Mark
Mitchelmore about the spherulitic deposit. He said that
most had been quarried away in the intervening years
but, with a bit of luck, we might find some small pieces.
We walked around the south west face of the quarry on
the top of the limestone until reaching the graded face of
the Mercia Mudstone. Within the red rock were small
pieces of yellowish sandy rock more akin to the fine
sandy deposits at the top of the Dolomitic
Conglomerate. However, it was not plain sailing and we
had to search a lot of the material before pieces were
discovered containing the tell-tale little green balls.
Mark told me that the original deposit was loaded with
them but the pieces I was able to collect contained more
sparse numbers. The photographs in the journal reports
showed the green spherules to be abundant almost to the
exclusion of other materials. Nevertheless, the
specimens that we collected were good quality and show
the spherules very clearly, figures 1 and 2. During
lockdown I rediscovered my specimens of the green
spherules which I collected that day and they inspired
me to write this article.
Gordon Walkden’s scientific sleuthing on the green
spherules eventually led to the conclusion that they had
been formed by the impact of an asteroid at
Manicouagan in northern Canada where a 100km crater
exists from an impact that occurred during the Triassic.
By dating techniques it was possible to place the age of
the deposit at 214-215 mya.
Fake news? Well, up to a point because the impact was
2000 km away from Britain (since the Triassic, that
distance is now 4400 km due to plate tectonics and the
opening of the Atlantic Ocean). Not just up the Triassic
road from Wickwar but the result of the impact, as we
see, did leave its mark on the south Gloucestershire
village, albeit in a way not obvious or devastating to the
locals! There was no Atlantic Ocean in between us and
Canada and the terrain at the time was an arid,
windswept desert making it an ideal place for the
landfall of an asteroid with the minimum of disruption to
life on earth. There was been no major extinction
recorded at that time in the Triassic. The impact caused
melting of the rocks and ejected it into the atmosphere.
It was only over a long period that the finest ejected
material slowly returned to earth but the coarser
particles rained down across the planet a short time after
impact. They were then washed from the surface by
heavy rain storms into playa lakes, pools and wadis
where they aggregated into shallow deposits (Curtis
1982).
At the quarry, these lagoons formed in the undulating
topography of the Carboniferous limestones and
concentrated the spherules in lenses. While looking for
Fig. 1 Green spherules
Fig .2 Close up of green spherules
Journal of the Bath Geological Society, No. 38, 2020
35
the spherule samples, I found some well-preserved fossil
ripples in Mercia Mudstone, indicative of the shallow
lagoonal conditions, figure 3.
In 2020 the only evidence of the effect of the impact
about 214 mya, 20,000 km from Wickwar, lies in
various museum collections and the scientific papers
written about it. Nevertheless, it is a sober reminder that
these events do happen albeit rarely and that, maybe
sometime in the future there will be a similar deposit of
little green balls over the village of Wickwar. Now, that
would be true news!
References
Curtis, M. T. 1982. Playa cycles in the Mercia Mudstone
(Keuper Marl) of Aust Cliff, Avon. Bristol Naturalists’
Society, 4, 13-32
Kirkham, A. 2003. Glauconitic spherules from the
Triassic of the Bristol area, SW England: probable
microtektite pseudomorphs. Proceedings of the
Geologists’ Association 114, 11-21. https://
doi.org/10.1016/S0016-7878(03)80025-1
Walkden, G. 2004. Deep Impact, Planet Earth Autumn
2004, 16-18. The headline of which reads “Gordon
Walkden has managed to link a mysterious layer of rock
in a Gloucestershire quarry to a disastrous asteroid
impact, a pretty unusual feat of science” https://
webarchive.nationalarchives.gov.uk/20130701153851/
http://www.nerc.ac.uk/publications/planetearth/2004/
autumn/
-.-
Equatorial Rain-Forests in Bath:
Fossil Coal-Measure Plants from
Twerton - Radstock
Maurice Tucker, School of Earth Sciences, Bristol
University, Bristol BS8 1RJ.
Introduction
This article discusses the Carboniferous rocks in the area
of Bath – particularly the Coal Measures which were
exploited in the 18
th
and 19
th
centuries in the area
between Twerton and Newton St Loe. Evidence for the
former coal mining activity is scant in western Bath but
fragments of shale with fossil plants, as well as pieces of
coal, siderite and sandstone derived from the old tips can
be found. There is plenty of evidence of mining farther
south / southwest in the Radstock area and coal tips are
still present and accessible for collecting fossils.
Carboniferous rocks in the Bath region
One is accustomed to Jurassic sedimentary rocks in the
Bath area but it is also possible to see Carboniferous
rocks, and not just in the pavements of Bath either,
which are of Pennant Sandstone in many places. This
very hard, weather-resistant Upper Carboniferous stone
was exploited at Willsbridge, just 8 km northwest of
Bath, and farther afield (e.g. Hanham, Downend, and
Temple Cloud). If interested, you could visit the old
Pennant Sandstone quarries and exposures on your way
to Longwell Green in the nature reserve of the Siston
Brook valley at Willsbridge Mill (Grid Ref ST666 708)
or the fine exposures along the old railway line, now a
cycle track, just past Bitton towards Bristol. These
outcrops are of Downend Sandstone, the lower part of
the Pennant Sandstone Formation, a clean quartzitic-
lithic-micaceous arenite with largescale cross-bedding
and channel structures, deposited by major rivers
flowing from south to north, 310-15 Ma ago. However,
samples of other Upper Carboniferous coal measure
facies, along with plant fossils, can be collected from old
coal tips in the region. The nearest site, perhaps
surprisingly, is near Twerton and a little farther afield to
the south old tips can still be seen in the region of
Radstock. The Radstock Museum of Somerset Coalfield
Life (radstockmuseum.co.uk) has many spectacular
fossil plants on display as well as artefacts from the
mining activities and a reconstruction of a coal mine; it
is well worth a visit.
Coal mining history and geological context
Coal has been mined in the Somerset coalfield since
Roman times, but it was not until the late 1600s that is
became a major industry with more than 60 pits working
over the next four centuries. Peak production was in the
late 19
th
and early 20
th
centuries but from then on it
steadily declined until Nationalisation in 1947 when
there were only 12 pits left. The last two, Kilmersdon
and Lower Writhlington, near Radstock, closed in 1973.
At the surface there are two small areas of Upper
Carboniferous rocks in the Somerset coalfield, in the
vicinity of Pensford and around Nettlebridge; otherwise
they occur below the Triassic and Jurassic cover. Some
Fig. 3 Ripples in Mercia Mudstone
