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A Building Stones Guide to Central Manchester
Third Edition (2014)
Four self-guided walks through the city centre
Now available to purchase |
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Newsletter - September 2019
The full, illustrated newsletter is available as a pdf for download.
Text extracts are given below.
MGA and GeoLancashire field excursion to Brymbo and Llay 27 June 2019
Leaders: Tim Astrop PhD, Brymbo Heritage Project; Jason Parry, Quarry Manager Hanson Cement
Brymbo
At Brymbo are the in situ remains of a Duckmantian (Westphalian B, Pennsylvanian) 'forest', with fossil arborescent lycophyte and calamite stems in growth position. Stands of Calamites stems are said
to be very rare, (Appleton et al. 2011). The exposures are a geological SSSI.
The site is associated with a historic iron ore processing complex which includes blast furnaces. The
C19 steel works was connected to the mainline railway system and also to Minera limestone quarry,
where limekilns produced quicklime for the blast furnaces. The remains of a Hoffmann kiln, of which
there are only about three examples in the country, can be seen in the Minera quarry.
The Brymbo Heritage Project has secured funding from the Heritage Lottery Fund to create a visitor
centre and to erect a building to cover the fossil plants, which weather rapidly as soon as they are
exposed. Work on the building is expected to start soon. Currently visits are only by arrangement; for
up to date information see their website (listed in bibliography below). A number of other projects are
in hand, from growing traditional Welsh apple trees for cider-making to bee-keeping and nature conservation. An experimental bloomery is also planned, to smelt iron from siderite ore, as would have
been carried out locally in the C12 and C13. Anyone with specialist knowledge or experience of operating bloomeries please get in touch. (Do we have any members that old?)
The party of twelve met at Brymbo in lovely weather, a good start to any field excursion! After a brief
tour of the industrial archaeology we were led to an exposure of the Two Yard Coal, also known as
the Hollin mine.
The base of the exposure, which is located immediately above the unexposed Crank Coal,
contained plant stems up to about half a metre in diameter preserved in situ mudstone. Stems over
1.5m diameter have been observed. Also seen were examples of Calamites, mostly in random
orientations. Examples of Stigmaria were relatively common. Channels cutting through the
mudstone were observed in a vertical face. The pair illustrated may represent the influx of coarse-grained sandy sediment splitting around a large lycophyte stem.
Between the 'tree' exposures and the coal was a horizon containing siderite nodules, the likely
reason for the start of the local iron and steel industry. Siderite is iron carbonate, FeCO3. Some
siderite nodules contained preserved organic matter, especially rootlets. Iron stained nodules
exhibited spheroidal weathering in the fine sandstones, possibly reflecting the processes of nodule
formation.
Part of the siderite nodule shown in the figure was analysed by Hanson Cement, Ribblesdale
Works, using XRF on a fused bead. As received, the nodule contained, oxide analysis, 47%
Fe2O3. When heated to 1000°C, at which temperature the siderite has been calcined, the Fe2O3
content was 65% dry basis, equivalent to 46% iron, which is certainly ore grade. The formation of
siderite nodules is extremely complicated, but in normal circumstances they form only in non-marine environments. In reducing conditions in marine water, the activity of sulphate reducing bacte-
ria leads to the production of pyrite. Meteoric water contains very much lower levels of sulphate
than marine water and, when all the available sulphate has been used to form pyrite, bacterial activity leads to the production of siderite. In the English Westphalian siderite is quite commonly
found associated with coal seams. In many places, such as Cliviger in east Lancashire, it was
mined for use as iron ore.
Examples of enigmatic trace fossils, both in vertical and horizontal orientation, were seen in the
fine-grained sandstones beneath the channel sandstones. A discussion followed on whether these
were formed by roots or by burrowing organisms. The segments are not parallel with bedding.
However, the bifurcating example has a morphology similar to a root. A small majority of those
prepared to hazard an interpretation favoured roots, but the segmented morphology defied
explanation.
Llay Main colliery slack heap
Most of the group continued to Llay. The coal mine tip is being reworked by Hanson Cement as
raw material for cement production. It is located between Brymbo and Wrexham and is not publicly
accessible. You can read something about the mine here.
Figure 30 in the Flint Memoir is a log of the 750m deep No. 1 shaft. It shows the location of the
aforementioned Hollin and Crank coals in the Westphalian succession.
Because the tip is being reworked there was plenty of coarse rock to be picked over. Abundant
cobble sized fragments of coal were found, some extremely pyritic. Siderite nodules were also
abundant, some with well-preserved plant matter. Fragments of sandstone exhibited ripple cross-bedding.
Thanks were expressed to Jason for showing us around and explaining the use of the shale as a component of the raw material recipe for cement manufacture.
Peter del Strother
Bibliography:
Appleton et al. 2011. The Brymbo Fossil Forest. Geology Today, 27, p109-13.
BGS geological maps, 1:50,000, numbers 108 Flint and 121 Wrexham.
Brymbo website
Curtis C.D. 1975. Mineralogy, chemistry, and origin of a concretionary siderite sheet (clay-iron-
stone band) in the Westphalian of Yorkshire. Mineralogical Magazine, Vol. 40.
Davies J.R. et al. 2004. Geology of the country around Flint, BGS Memoir. (This contains a log of
Llay Main No. 1 shaft)
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Jura beige fossil identified
My piece in the June Newsletter resulted in one response from Tony North who wrote: 'I'm pretty sure it's
a sponge - see here.' Opening the
link reveals a photo of a sponge very similar to mine, but nothing more specific. This supported Peter del
Strother's thought but he "was not sure".
In the absence of any further
replies I sent the image to an
OUGS Mainland Europe friend,
Mike Malloy, who has sent me a
definitive identification of the
beastie made by Dr. Guenter Viohl,
curator of the Jura Museum in
Eichstaett for 34 years. You will be
interested to know that he
identified it as follows: "It is the
cross-section through a beaker-
shaped sponge, which are very
typical for the 'Jura Marble'
quarried in Kaldorf. Also visible in
the darker areas are the crustal
remains of bacteria which in turn,
contain lighter coloured
Tubyphites, which were sessile,
colony building, Foraminifera."
Fred Owen
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NASA and the Fiftieth Anniversary of the First Human Moon Landing
A talk by Dr James L. Green, NASA Chief Scientist, on Sunday 9 June 2019.
As you would expect, Dr. Green, as Chief Scientist of the National Aeronautics and Space Administration, is
a leading world expert on the Moon, but he, too, is being overtaken by events. Reported on the Internet
today, the Chinese Space Mission has just photographed a "Ruined City" on the dark side of the Moon. (I
learned all about this in the 1950's with Dan Dare and the Mekong in the "Eagle" Comic). Of considerably
more interest Dr. Green predicts a large ocean of water a long way underground at its South Pole.
One intriguing revelation concerns meteoric analysis. Retrieved from an earlier moon landing and brought back to earth is a meteoric fragment once embedded
in the moon's surface, which may be the only surviving evidence for the early earth before the
formation/presence of H2O. It's a complicated story which concerns the moon as well. One theory is that
the moon sheared off into orbit from the earth when the Earth collided with an early Planetesimal. (Not
exactly a planet, you understand). The collision and the explosion was so vast that fragments of early
earth were left attached to the moon. But there is so little of this early phase of the earth that scientific
instruments can no longer find it or measure it. On the contrary, the moon fragment is pure and undefiled,
uncorrupted by seismic activity as on earth.
Dr Green is preparing to send two astronauts to the moon in 2020: one male and one female.
The queue for his autograph was very long!
Charles Walker
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