The Edinburgh Geologist - Magazine of the Edinburgh Geological Society Issue No 64 Autumn 2018
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The Edinburgh Geologist Magazine of the Edinburgh Geological Society Issue No 64 Autumn 2018
The Edinburgh Geologist
Issue 64 Autumn 2018
Cover Illustration
The cliffs at Yesnaby, Mainland Orkney, cut into the Devonian Yesnaby
Sandstone Group. BGS image P000624. For some palaeontological
curiosities from a different part the Orkney Old Red Sandstone, see
David Leather’s article on page 20.
BGS images are reproduced by permission of the
British Geological Survey ©UKRI.
Published September 2018 by The Edinburgh Geological Society
(Charity registered in Scotland number SC008011)
www.edinburghgeolsoc.org
Editors
Phil Stone Bob McIntosh
psto@bgs.ac.uk rpm@bgs.ac.uk
British Geological Survey
The Lyell Centre, Research Avenue South, Edinburgh EH14 4AP
ISSN 0265-7244
The Edinburgh Geological Society was founded in 1834 with the twin aims of stimulating public interest in
geology and advancing geological knowledge. We organise a programme of lectures and excursions and also
publish leaflets and excursion guides. For more information about the Society and membership,
please visit www.edinburghgeolsoc.org.
editorial
Rewarding geology, Scottish islands, and odd
palaeontological furniture
An editorial ramble by Phil Stone
Over the past few decades there notes that one of the prestigious
has been dramatic growth in our awards bestowed on Holmes was the
knowledge of Scotland’s offshore Vetlesen Prize which, given its status
geology as the technical prowess of as the earth science’s ‘Nobel’ is not
the hydrocarbon industry has been nearly as well known as it deserves.
applied to exploration for oil and gas.
This kind of geology is far removed Georg Unger Vetlesen (1889–1955)
from the experiences of most of us was a Norwegian marine engineer
but the Society’s current president, involved in ship building in the
Bob Gatliff, has spent many years at United States of America. He served
the forefront of offshore geological as a commander in the U.S. Navy
investigations. For our first article for during World War II, assigned to
this issue of The Edinburgh Geologist Special Forces headquarters in
Bob has provided some background London to work with the Norwegian
to his career with the British resistance; later he became president
Geological Survey and provides us and chairman of the U.S. company
with some insight into what goes on, representing the Norwegian-
geologically, ‘offshore’. American shipping line, and then
the chairman of the board of
It’s a small step from offshore Scandinavian Airline Systems (SAS).
geological exploration to the
confirmation of sea-floor spreading His Foundation was established
and hence to the reality of plate in 1955, shortly before Vetlesen’s
tectonics. An even smaller step from death, with the Vetlesen Prize then
there reaches Arthur Holmes, and inaugurated in 1959. It is awarded
as a follow-up to our focus on ‘Fifty biennially for scientific achievement
Years of Plate Tectonics’ in EG63 resulting in a clearer understanding
Gilbert Kelling provides, as our of the Earth, its history, or its relations
second article, some reminiscences to the universe and is administered
of Holmes’ teaching at Edinburgh by Columbia University’s Lamont-
University in the 1950s. Gilbert Doherty Earth Observatory (City
1
editorial
of New York). The prize consists of of recent research findings. Arran
a cash award of $250 000 and a presents something of a microcosm
medal. Holmes was honoured in of Scottish geology (including the
1964. In a slightly ironic association, original ‘Hutton’s Unconformity’)
his immediate predecessor had and many of us will have enjoyed
been the geophysicist Sir Harold what it has to offer so Bob’s
Jeffreys — identified by Gilbert Kelling fresh insights — which have been
as one of the principal villains of the supported by a Clough Award from
continental drift controversy who EGS — are very welcome. Our
adamantly opposed the idea on second foray into Scottish geology
mechanistic grounds. I suspect that is provided by David Leather
Holmes would have found that order who takes us to Orkney, to the
of succession rather satisfying, Jeffreys Devonian Rousay Formation on
perhaps less so. the island of Westray and into the
slightly murky palaeontology of fish
coprolites —fossilised faecal pellets.
David shows what can be done with
a modern assessment, but when
thinking of the early days of coprolite
research the name that immediately
comes to mind is that of the famously
eccentric English geologist, William
Buckland (1784–1856).
Buckland’s interest had focussed
on ichthyosaur coprolites from the
Jurassic strata of the Dorset coast at
Lyme Regis, and he drew conclusions
on the diet of the animals from
The Vetlesen Medal.
the presence of crushed bone and
bits of belemnite. One outcome of
Buckland’s fascination with fossilised
For our next two articles we move excrement was the construction of
back onshore — or at least onto an extraordinary ornamental table
Scottish islands. First, Bob Gooday displaying an inlaid panel in which
describes the history of geological were set about sixty polished coprolitic
research on the isle of Arran and nodules. The table is now in the
brings it up to date with an account collection of the Lyme Regis Museum
2
editorial
and from the museum’s website you of Science and later he described
can download a full account of its collecting coprolites whilst there. The
history1 by Richard Bull — to whom, following extract from Buckland’s
together with museum director David 1836 Bridgewater Treatise is taken
Tucker, I’m indebted for permission from Richard Bull’s article:
to use the pictures.
“Mr W C Trevelyan recognised
For many years it was thought that Coprolites in the centre of nodules
the table’s coprolites had been of clay ironstone, that he found in a
sourced from the Lyme Regis area, low cliff composed of shale, belonging
but detective-work by Richard Bull, to the coal formation at Newhaven,
assisted by EGS member Mike Taylor near Leith. I visited the spot, with
and Edinburgh antique furniture this gentleman and Lord Greenock,
specialist Murdo McLeod, has proved in September 1834 and found these
otherwise. Buckland’s coprolites nodules strewed so thickly upon the
actually came from Edinburgh, from shore, that a few minutes allowed me
the Carboniferous Wardie Shales to collect more specimens than I could
outcrop on the shore of the Firth of carry. Many of these contained a fossil
Forth between Granton and Leith. fish, or a fragment of a plant, but the
Buckland had been in Edinburgh greater number had at their nucleus,
for the 1834 meeting of the British a Coprolite, exhibiting an internal
Association for the Advancement spiral structure: they were probably
derived from voracious
fishes, whose bones
are found in the same
stratum. These nodules
take a beautiful polish and
have been applied by the
lapidaries of Edinburgh to
make tables, letter presses,
Buckland’s coprolite
table-top courtesy of Lyme
Regis Museum. The inlay
panel containing the cut
and polished nodules
measures 44 cm by 59 cm.
3
editorial
and ladies ornaments under the name
of Beetle stones from their supposed
insect origin.”
I wonder if the ladies of Edinburgh
realised what they were wearing.
The ‘supposed insect origin’ of the
‘[b]eetle stones’ derived from the
appearance of the nodules in cross-
section. The coprolites are encased in
a coating of sideritic mudstone that A selection of coprolite nodules
has been split by septarian cracks that collected recently at Wardie by
give the impression of legs. Although Richard Bull. The largest nodule
the Wardie area has been much is about 13 cm long.
developed since 1834, and the shale
exposure much reduced, it is still
possible to collect coprolite nodules book also provides an unexpected
at low tide. connection with the Edinburgh
Geological Society through its
Another name from the early history dedication to Arthur Raistrick (1896–
of British geological research, Adam 1991) who, in 1938, became only
Sedgwick, features in one of the two the second recipient of the Clough
book reviews that complete this issue Medal. That award would have most
of EG. One book, by Graham Park, probably been made on the basis of
attempts an ambitious geological Raistrick’s work on coal palynology
review of the world’s mountain belts. but his life was difficult; it took some
The second, a facsimile edition of extraordinary and unfortunate turns
Colin Speakman’s 1982 biography of and eventually he was forced away
Sedgwick (1785–1873) is well timed from geology and into industrial
to commemorate the bicentenary archaeology. The biography by John
of Sedgwick’s appointment as Marshall in Geological Society of
Woodwardian Professor at the London Special Publications 241
University of Cambridge, from which (2005) is well worth a look — but
position he became a dominating only after you have finished reading
force in British geology. Speakman’s Edinburgh Geologist.
Note 1.
www.lymeregismuseum.co.uk/related-article/bucklands-coprolite-table/
4
an introduction
An introduction
By Bob Gatliff, Edinburgh Geological Society President, 2018–2019
It was in early 1981, five years after almost entirely seismic interpretation,
I had joined the British Geological with coloured pencils and manual
Survey (BGS) in the same week that matching of the seismic to well logs.
the new office in Keyworth opened, One early project with the ‘West of
that I was reassigned to the new Shetlands’ team led to publication
Hydrocarbons Unit, which was of the first example of sequence
then operating in Grange Terrace, stratigraphy and seismic imaging of
Edinburgh. This was an exciting time, the submerged Erlend Igneous Centre
with a young group of enthusiastic (Gatliff et al, 1984).
geologists working together to
provide independent advice for the From 1988–1990 I was lucky
then Department of Energy on the enough to be posted to Tonga, to
oil industry activity on the United promote hydrocarbon exploration
Kingdom Continental Shelf. I soon in the fore-arc basin. Then, on
joined the Edinburgh Geological return to Edinburgh, I worked on
Society and am now honoured to the first computer-based seismic
be serving a term as the Society’s interpretation systems and contributed
president. Over the past few months to the regional offshore report series
I’ve been able to get to know more (Gatliff et al 1994) and the BGS
of our tremendous membership offshore mapping programme, which
and look forward to that process was recognised by the Edinburgh
continuing. Geological Society by the award of the
1993–4 Clough Medal to John Hull
As an undergraduate, just about on behalf of the Marine Geoscience
my only experience of seismic team. We continued to explore the
data was collecting refraction data geology of the deeper waters of
with a sledge hammer in the Parks Rockall and Hatton and developed
in Oxford, and my previous BGS a series of collaborative projects with
experience had been with the sand consortia of oil companies. One
and gravel resources of East Anglia highlight was taking a drill ship to the
and the Carboniferous limestones Hatton Bank and recovering core from
in Derbyshire. But from 1981 it was a dipping sequence buried by around
5
an introduction
20 m of Holocene sediments on top of
the ridge.
In 2003, I was appointed to lead
the BGS Marine and Petroleum
Programme and we developed a
new strategy based on multibeam
data to drive the next generation of
more detailed mapping. This led to
the purchase of a small coastal survey The BGS coastal survey vessel White
vessel and we now work closely with Ribbon passing under the Forth
Marine Scotland, CEFAS (Centre Railway Bridge. BGS image P741057.
for Environment, Fisheries and
Aquaculture Science), JNCC (Joint
Nature Conservation Committeee), It is now two years since BGS moved
the Crown Estate and others to out of Murchison House and into its
provide new analyses to underpin the new home at the Lyell Centre, on
definition and monitoring of marine the Heriot-Watt University campus
protected areas and other aspects of at Riccarton. In addition to the main
marine spatial planning. A key part office and laboratories, the BGS
of the current programme is working RD2 robotic drill, which can operate
with the offshore wind industry and in up to 4000 m water depth, is
this is leading to a step change in our housed in the adjacent Sir George
understanding of the Quaternary of Bruce Building, which provides
the North Sea. better engineering facilities than we
have ever enjoyed before. The new
Since 2004, BGS has led the ECORD facilities will help to keep Edinburgh
(European Consortium for Ocean as a global centre for geoscience
Research Drilling) Science Operator and I am delighted to have seen this
team and together with partners, move through successfully. Now,
we have organised a series of IODP after more than 40 years at BGS, it
expeditions. These include the first seems like a good time to retire and
deep scientific Arctic drilling, the focus on the Edinburgh Geological
use of robotic seafloor drills (on the Society.
Atlantis Massif) and a jack-up to core
the Chicxulub meteorite impact The success of the Society depends
crater (as featured on BBC Horizon on an active membership and an
and in Edinburgh Geologist No. 60). enthusiastic and dynamic Council.
6
an introduction
I am lucky to take over with the
Society in excellent shape. Each
member of the Council is making a
valuable contribution, and together
we are now well into our 5 year
strategy. Having the professional
help of Angus Miller and such an
active Council is building success and
raising the profile of the Society with
our members, academia, the public,
industry and government bodies.
Perhaps one area where we might
do something different is to try to
raise the profile of geology at a
Scottish level. There are some big
issues such as the decline of oil
and gas production, potential for
carbon capture and storage, new
interest in geothermal energy, and
impacts of climate change and sea Deploying the RD2 sea-floor robotic
level rise. Perhaps national academic drill. Photograph by Mike Wilson, BGS.
conferences on some of these
issues, run in collaboration with
our sister geoscience groups would References
go some way to raising the profile Gatliff, R W, et al 1994. UK offshore
of geoscience. They could lead to regional report: the geology of the
special editions of the Scottish Journal Central North Sea. (London: HMSO
of Geology. I think it is important to for British Geological Survey).
reaffirm the contribution that the
Scottish geology community makes Gatliff, R W, Hitchen, K, Ritchie J D &
in Scotland, the United Kingdom and Smythe, D K. 1984. Internal structure
around the World. of the Erlend Tertiary Volcanic
Complex, North of Shetland, as
Bob Gatliff, revealed by seismic reflection. J.
president@edinburghgeolsoc.org Geol. Soc. London. 141, 555–562.
7
arthur holmes and continental drift: some personal recollections
Arthur Holmes and Continental Drift: some
personal recollections
By Gilbert Kelling
Arthur Holmes’ early and perceptive
involvement in the continental
drift debate has, in my view, still
not received the credit that his
intervention deserves. His seminal
contributions to radiometric dating
have been recognised in some
measure (including Fellowship of the
Royal Society, the Vetlesen Award
and other prestigious Medals, and
Cherry Lewis’ 2000 biography The
Dating Game), but the pivotal role
he played in inculcating a more
‘mobilistic’ mind-set in the 20th
century earth-science community has
yet to be adequately documented
and acknowledged. The monumental
4-volume history of The Continental
Drift Controversy by Henry Frankel
(2012, Cambridge University Press)
certainly went some way towards
redressing the balance, although I
believe it still underplayed the role Edinburgh. Still a schoolboy, I was
of Sir Harold Jeffreys and some fascinated by ‘stones, fossils and
fellow geophysicists in stifling proper things’ and a near-neighbour, Col. L
geological evaluation of the hypothesis Merson Davies (ex Indian Army), an
in the UK for a couple of decades. accomplished micropalaeontologist,
suggested that I should read Holmes’
I first encountered Arthur textbook Principles of Physical
Holmes, figuratively speaking, Geology, published just a few years
in Fountainbridge Public Library, earlier, in 1944. Like many another,
8arthur holmes and continental drift: some personal recollections
delving into the Principles I found mathematics and zoology). Thus, it
myself captivated by the facts and was not until our second year of study
concepts he revealed in such a that we could experience the great
readable style. I was particularly man’s exposition, and it was well
struck by Holmes’ portrayal of a worth the wait! Holmes’ lecturing
mobile and ever-changing planet, style was like the man himself — quiet,
but one marked by order and clear and impeccably ordered — the
organisation at every level, from ideal pattern for the committed note-
mineral-forming molecules to the taker. He used illustrations (lantern-
mighty mountain chains traversing slides) liberally and effectively, while
continents. Moreover, he was the the blackboard was usually replete
Professor in EDINBURGH University! with tables and diagrams before the
start of each lecture.
A couple of years later I enrolled at
Edinburgh University for a degree Holmes taught almost all the First
course in Geology with Chemistry. In Year Introductory Geology course
those days we geologists were denied for science students and my notes
exposure to our chosen subject indicate that he touched on most of
until we had completed a first-year the topics covered in the first edition
apprenticeship in cognate sciences of his textbook but deviated slightly in
(in my case, chemistry, physics, the order of treatment. He discussed
Holmes’ original figure illustrating mantle convection as the driving force of
continental drift as published in Transactions of the Geological Society of
Glasgow, 1931 (for 1928-29), volume 18, p. 579. A slightly more sophisticated
version of the figure appeared in the Principles of Physical Geology (1944, 1965).
9arthur holmes and continental drift: some personal recollections
mountain building and the nature his ongoing debate with Sir Harold
and causes of volcanicity relatively Jeffreys on this topic: “The beginning
early in the course and it ended with of the world is clearly getting older
a discourse on earthquakes and their every year and may continue to age
causes. More significantly, the only for some time yet.”1
reference to continental drift in my
notes is an aside in lecture 3, dealing In the summer of 1954, prior
with the distribution of continents and to entering my Final Year, I was
oceans and the possibility of mantle chosen as the Edinburgh University
convection! representative on the famous
‘Students’ Geological Tour’ organised
In my second year of Geology (1953– by the Geological Society of London
54), Holmes offered a 10-lecture and funded by Shell and BP oil-
course entitled ‘Radioactivity and companies. This Tour brought
Geological Time’. This introduced us together students from around 25
to the methods and outcomes of the British universities and we were
dating methods he had pioneered taken on a 4-week marathon ‘geo-
and included some exciting practical fest’, visiting important geological
sessions where we undertook age- localities around mainland Britain.
calculations using analytical data he Apart from intellectual indigestion,
had obtained, using mineral suites my abiding memory of this trip was
from a wide range of rocks across the astonishment and dismay I felt
the globe. To be involved, even at on realising that my Department
second-hand, with determining the was regarded by most of my fellow-
age of the then-oldest known minerals trippers as a hotbed of geological
(monazites in Archaean rocks from heresy, because of the notions of
Southern Rhodesia — 2650 my), continental drift advanced by Holmes
was a highly stimulating experience! in Principles, coupled with the
Equally significant, in retrospect, was espousal of wholesale granitisation
Holmes’ casual remark concerning then being championed by his wife,
the calibration of the Phanerozoic Doris Reynolds. I was baffled by this
time-scale, which in 1954 he asserted strident opposition to continental
was based on just 5 radiometrically drift, when the geological and
dated fixed points (2 of which were palaeontological evidence seemed
stratigraphically debatable!). I also so powerful to me. However, when I
vividly recall the remark with which tried to persuade my fellows of this,
‘the Prof.’ closed a lecture dealing the invariable retort was to demand of
with the age of the Earth, referring to me what mechanism could possibly
10arthur holmes and continental drift: some personal recollections
accomplish this break-up and re-
arrangement of the Earth’s crust?
Of course, this was a question that
Holmes himself was striving to address
at that time, as became clear in his
Final Year course devoted to ‘The
Crust of the Earth’. Here he revealed,
modified and amplified many of the
concepts and ideas expressed in the
A fragment of my notes taken during
last few chapters of his Principles. For
one of Holmes’ lectures in which
example, from my notes it seems that
he discussed the origin of volcanic
by now he had rejected the model
island arcs, integrating the latest
of a universal basaltic layer forming
geophysical results.
much of the crust and was convinced
that there were distinct compositional
and genetic differences between seismology — and in the concept of a
‘oceanic’ and ‘continental/plateau’ mobile earth.
basalts. He also cited the recently
discovered Benioff zones of the Pacific During my final year I became
rim as evidence for underthrusting of seduced by sediments and decided
oceanic crust beneath the continents. to attempt research for a PhD based
Moreover, he qualified the definition on a study of the Lower Palaeozoic
of continental sial, as presented in turbidites in the Scottish Southern
Principles, emphasizing that the ‘granitic Uplands, under the supervision of Ken
layer’ recognised by seismologists was Walton, then a recently appointed
dominated by ‘basement complexes’, lecturer in sedimentology. As a result
representing highly folded and of Ken’s advocacy, Holmes offered me
metamorphosed ancient orogenic the chance to become an Assistant in
belts that had been incorporated into the Department. This was then the
the continents over many aeons. In bottom rung on the academic ladder,
this course Holmes also introduced with responsibilities mainly concerned
us to the pioneering geophysical with the running of practical classes
work of several ‘continental’ workers, for First Year students, together with
such as the Austrian Oscar Rehm and some lectures and field classes for Arts
the Dutch group headed by Felix students, who at Edinburgh in that
Vening-Meinesz, now recognised as era were required to undertake an
pioneers in marine geophysics and elementary science class. I accepted
11arthur holmes and continental drift: some personal recollections
this offer with alacrity, not least
because the stipend was 25% higher
than a standard DSIR (governmental)
research studentship!
So, for the next year, until he retired
in 1956, I was technically required to
report to Arthur Holmes about teaching
dilemmas that included the vexed
question of how much we could reveal
to our tyro-charges about Continental
Drift, the Earth Contraction Hypothesis,
etc. In practice, Holmes (by this time an
ill man) delegated these advisory and
supervisory roles to his junior staff, and
when Fred (later Sir Frederick) Stewart
was appointed to succeed Holmes as
Regius Professor — thus maintaining
the ‘Durham connection’ — he was
happy for his Assistants to continue to
The memorial plaque to Professor
exercise a large degree of autonomy
Arthur Holmes that now graces the
in carrying out these duties.
main staircase in the Grant Institute
of Earth Sciences, University of
Despite the significant teaching load,
Edinburgh.
combined with commitment to my
PhD research, the three years that I
spent as an Assistant in Edinburgh were Note 1 … A quotation expressing a very
very enjoyable and rewarding, working similar sentiment appears on the front dust-
cover of The Dating Game (on the fold-in flap)
in a lively Department with congenial and is attributed to Holmes (1964). Then, on
colleagues who were fully committed page 234, it is repeated as having been part of
both to teaching and research. This is Holmes’ response to the presentation of the
Vetlesen Medal:
testimony to the outstanding legacy
bequeathed by Arthur Holmes. “Looking back it is a slight consolation for the
disabilities of growing old to notice that the
Gilbert Kelling Earth has grown older much more rapidly
Edinburgh University 1951–1958 than I have — from about six thousand years
when I was ten, to four or five billion years by
Latterly Professor of Geology at Keele the time I reached sixty.”
University
12arran’s volcanic past — classic geology and new ideas
Arran’s volcanic past — classic geology and new ideas
By Bob Gooday
The Isle of Arran, in the Firth of Clyde During the Upper Palaeozoic (419–
on the west coast of Scotland, has been 252 Ma), Arran moved north across
a training ground, laboratory, and site the equator, as shown by the
of pilgrimage for many geologists for sandwich of desert-environment rocks
over two centuries. For such a small (the Old and New Red Sandstones)
area, the island has spectacular and with the intervening tropical sea
incredibly diverse geology — most of and coal-swamp sediments of the
which is beautifully exposed and easily Carboniferous Succession (Fig. 1).
accessible. Many of the concepts upon
which modern geological reasoning is Around 60 Ma, during the
based were tested and refined on the Palaeogene, Europe and North
island. It is easy to think that with so America began to rift apart as the
many brilliant geologists having visited North Atlantic Ocean opened. This
the island in the past, the work is all thinned the crust, allowing a great
but done! But with recent advances amount of magmatism and volcanic
in understanding, there will always be activity, the products of which are
new ways to look at classic localities preserved throughout the western
and make new deductions about the parts of Scotland. The Palaeogene
processes occurring so far back in the igneous rocks on Arran include the
geological past. mountainous North Arran Granite
in the north, a series of intrusive sills
Arran’s half-billion-year story around the south, and the volcanic
The oldest rocks on Arran are the rocks of the Central Arran Igneous
Dalradian schists (Fig. 1), which Complex in the centre of the island
were deposited on the seafloor (Fig. 1). It is this Central Arran
around 540 million years ago (Ma) Igneous Complex which has been the
and subsequently deformed and focus of our recent research.
metamorphosed during the Caledonian
Orogeny, towards the end of which Arran — a cradle of geological
the northern and southern parts of understanding
the British Isles collided (as parts of, In 1787, Arran was visited by
respectively, Laurentia and Avalonia). Edinburgh geologist James Hutton.
13arran’s volcanic past — classic geology and new ideas Figure 1 Geological map of Arran, after BGS 1987. He was trying to understand the to theologians, the Biblical Flood. nature of granite, and igneous Hutton was looking for evidence that rocks in general. The thought at the granite had formed from molten rock time was that all rocks had been within the Earth and had squeezed formed in the sea or, according its way into the surrounding rocks. 14
arran’s volcanic past — classic geology and new ideas
He found this evidence in several logical Map of Arran’ was published
places on the island but was not quite in 1910 (its modern counterpart at
finished with Arran. At the extreme 1:50 000 was published in 1987).
northern tip of the island, he noted The detailed petrographic work for
that gently dipping sedimentary the Geological Survey’s Arran Mem-
rocks lay on a surface of steeply oir was published by George Tyrrell
dipping metamorphic rocks (Fig. 2). (of Glasgow University) in 1928, with
This unconformity showed Hutton a contribution from Alfred Harker (of
that a huge amount of geological Cambridge University). Along with
time must have passed between the the work done around the same time
formation of these two units. He on Mull and Skye, these publications
realised that the Earth was incredibly provided detailed observations and
ancient — much older than the modern theories on how magmatic
6000 years suggested by religious and volcanic systems behaved, from
doctrine — an idea confirmed in the chemistry of their magmas, to the
1788 when he discovered the Siccar physical processes of intrusion and
Point unconformity in Berwickshire. eruption. These ideas laid the foun-
dations for all subsequent study of ac-
Around a hundred years after Hut- tive and ancient volcanic provinces.
ton’s visit, the British Geological
Survey sent geologists to start the The presence of a volcanic complex
systematic mapping of Arran. A large in central Arran was first documented
part of the work was done by Ar- by Gunn, who stated that this
chibald Geike, Ben Peach, and Wil- “focus of great volcanic activity”
liam Gunn, and the ‘One-inch Geo- was “exceptionally gigantic in its
proportions” (Gunn et al., 1901); we
would today call a volcanic system
of this size a ‘caldera’. He recognised
that the complex was made up partly
of fragmented explosive material and
partly of intrusive granitic rocks. It
was Tyrrell who classified the system
as “a ring complex of the Mull type”,
by which he meant that the volcanic
system was almost totally encircled
by a granitic ‘ring dyke’, much like
Figure 2 Hutton’s Unconformity at the Loch Bà ring intrusion that the
Newton Point near Lochranza. previously mentioned geologists, along
15arran’s volcanic past — classic geology and new ideas
with Sir Edward Bailey, had described that on such a heavily visited and
from Mull (Bailey et al., 1924). studied island, no-one saw any reason
to challenge his ideas. However,
It was Basil King (at the time also over sixty years have passed since
based at Glasgow University) who then, and in that time a huge
described the volcanic, intrusive, amount of progress has been made
and sedimentary rocks of the ‘ring by the volcanological community,
complex’ in great detail (King, in a large part thanks to the wealth
1954). He proposed a model in of observations made by specialist
which a great phase of explosive instruments at erupting volcanoes. It
activity formed a deposit of ‘tuffs and is with the benefit of this research that
agglomerates’ within the caldera, we have headed back to central Arran
which were then intruded by felsite to see what modern ideas can be
and rhyolite magmas (Fig. 3). This applied to the rocks there.
was followed by a phase of ‘resurgent
volcanism’, in which small volcanic Arran — an ongoing project
cones, comprising andesite and dacite A team of geologists from Cardiff
magmas, were built in several places University (Gooday and Kerr), the
on the caldera floor (Fig. 3). The University of Glasgow (Brown), and the
whole complex was then intruded by British Geological Survey (Goodenough)
a series of granites, including the near- have spent the last few years doing
continuous ring dyke. fieldwork on the Central Arran Igneous
Complex. This has involved making a new
King’s map of the Central Arran map of the complex and interpreting
Igneous Complex was incredibly the volcanic rocks of the caldera in
detailed, and his model of formation terms of the processes occurring at the
highly convincing. It is to his credit volcano as they were being formed.
Figure 3 Basil King’s proposed cross section of the Central Arran Igneous
Complex (King, 1954).
16arran’s volcanic past — classic geology and new ideas
A major difference between the new interaction of two or more types of
geological map of the Central Arran magma (named the Glenloig Hybrids
Igneous Complex (Fig. 4) and those on Fig. 4). It is now possible to study
of Tyrrell and King is that there is no the nature of these magmas, and how
granitic ‘ring dyke’ surrounding the they relate to other magmatic rocks
complex. There are certainly granite on Arran, using precise geochemical
intrusions around the margins of the analyses which were not available to
complex, but these are isolated from previous generations of geologists.
one another. The north and east parts
of the complex are made of intrusive The main advance, in terms of
rocks which are highly variable volcanological processes, is the
and were clearly formed from the conclusion that all of the rocks within the
Figure 4 Geological map of the Central Arran Igneous Complex. From Gooday
et al. (2018).
17arran’s volcanic past — classic geology and new ideas
mostly ignimbrites — the deposits of
pyroclastic density currents formed
during explosive eruptions — with
minor sedimentary horizons.
Together, these units have been
called the ‘Arran Volcanic Formation’.
This Formation can be divided into
separate ‘Members’, which are single
units formed during a particular
phase of activity. The main features of
these units, and their relationship to
one another, are shown in Fig. 5.
The crucial result of interpreting these
deposits as a series of individual and
identifiable units is that the caldera
system can now be discussed in
terms of volcanic processes changing
through time. The ignimbrites were
formed by a series of explosive
eruptions which involved magmas
of differing compositions, and which
had variable physical characteristics,
such as power of explosions and
temperature of ash deposits. Between
these violent volcanic episodes,
there must have been long periods
of time where surface erosion and
sediment deposition could take
place. A caldera is a low point in the
landscape, and erosion of the steep
Figure 5 Stratigraphic log through walls into the caldera during these
the units deposited inside the caldera. volcanically quieter times is shown
by the presence of conglomerates at
certain levels within the stratigraphy.
caldera formed from a series of discrete
volcanic and sedimentary events. The results of this study provide
The rocks deposited in the caldera are a useful comparison for currently
18arran’s volcanic past — classic geology and new ideas
active calderas, which can be hard to Kerr, Davie Brown, and Kathryn
study due to being filled with recent Goodenough for their help, wisdom,
volcanic or sedimentary rocks, or and patience.
water.
References
Arran — finally all figured out? Bailey, E B, Clough, C T, Wright, W B,
Such is the nature of field geology in Richey, J E & Wilson, G V. 1924. Tertiary
and Post-Tertiary Geology of Mull,
places where forests, heather, and Loch Aline, and Oban. Memoirs of the
peat cover the landscape, that any Geological Survey of Great Britain. HMSO.
interpretation of a geological system
is exactly that — an interpretation. BGS. 1987. Arran, Scotland Special
Sheet; 1:50 000 Series; Third Solid
The observations made by the
Edition. British Geological Survey.
latest team are of the same rocks as
those studied by geologists over a Gooday, R J, Brown, D J, Goodenough,
century before. The only difference K M & Kerr, A C. 2018. The stratigraphy,
is the process of explaining those eruptive history, and collapse of the
Palaeogene Arran caldera, western
observations in the context of the Scotland: a proximal record of
current geological paradigm. Any caldera-forming eruptions. Bulletin
geologist mapping the area now or of Volcanology, 80:70. https://doi.
in the future will certainly come up org/10.1007/s00445-018-1243-z
with a different model — and we look Gunn, W, Peach, B N & Newton, E T.
forward to seeing it! It is possible (if 1901. On a remarkable volcanic vent
not almost certain) that sometime of Tertiary age in the Island of Arran,
in the next century volcanological enclosing Mesozoic fossiliferous rocks.
concepts will have evolved yet Quarterly Journal of the Geological
Society, London, 57, 226–243.
further, and this decade’s work
will start to look out-dated or even King, B C. 1954. The Ard Bheinn area
implausible. Don’t worry, we aren’t of the central igneous complex of Arran.
going to run out of geology to do any Quarterly Journal of the Geological
time soon. Society, London, 110, 323–355.
Tyrrell, G W. (1928). The geology of
Acknowledgements Arran. Memoirs of the Geological Survey
This study was undertaken as part of Great Britain. HMSO.
of my PhD at Cardiff University, and
was funded by NERC Studentship Bob Gooday
NE/L002434/1, as part of the Great School of Earth and Ocean Sciences
Western 4+ Doctoral Training Cardiff University
Partnership. I wish to thank Andrew GoodayR@cardiff.ac.uk
19a devonian coprolite from orkney and its possible fish producer
A Devonian coprolite from Orkney and its possible fish
producer
By David Leather
In the 1820s, Mary Anning collected Recently, on the island of Westray,
stones of fossilized reptile dung from Orkney, I collected or photographed
the Jurassic shore near Lyme Regis. well over 100 coprolites from lake
By 1829 William Buckland had given sediments across the island, mostly from
them the name coprolite, Greek two or three notable fish beds. The
for ‘dung stone’. About the same coprolites vary considerably in shape
time, others were discovering fossil and size as you would expect where
fish at the other end of the UK in 14 fish species have been recorded.
Devonian flagstones from the Moray They are on average 3 or 4 cm long
Firth to the Orkney Isles, and among and generally rounded in cross-
the fish, less well-documented section, varying in length from a few
coprolites. millimetres to 9.4 cm. The biggest had a
diameter of 18 mm. Many have a drawn
In 1878 Archibald Geikie named the out spiral structure, well seen on a
freshwater lake within the Orcadian weathered specimen, which may reflect
Basin, Lake Orcadie. When the lake the internal intestinal morphology,
was high enough to overflow to the like modern sharks. Most fish faeces
Rheic Ocean, fish were able to swim presumably contained crushed, half-
up rivers and colonise the desert digested bones, spines, scales, teeth
waters. Fish were by far the main and fragments of armour plate, but
inhabitants and mostly predators. among those I found, there is no clue
There was such competition, as to what they had eaten, apart from a
which appeared to be global, that rough texture on the weathered surface,
most of the fish developed armour or occasional sand grains. When freshly
plating that enshrouded the head broken, they have a black, smooth and
and shoulders, protecting the most chert-like appearance. They come from
vulnerable parts. Species included sediments that have many shallow-
an array of armoured fish, lobefins, water indicators, unlike those from
lungfish and spiny fish, with sizes the Achanarras deep lake sediments
from a few centimetres to a metre where both fish and coprolites sank to
and a half in length. the anoxic muddy depths. In the case
20a devonian coprolite from orkney and its possible fish producer
of these Westray samples, things were droppings, containing phosphates
different. and carbonates, were preserved by
salts from the rapidly evaporating lake
The palaeoclimate of Lake Orcadie waters and once stranded, may have
was a monsoon type with a strong been baked like brick clay or cement
seasonal oscillation. As the lake to become hard and solid in the
waxed and waned with the seasons, hot sun. They were not compressed
the shoreline may have migrated by later overburden, unlike the
several kilometres across the salty surrounding muds and, on becoming
mudflats. It is suggested (personal rigid they may have rolled around
view) that newly deposited fish unscathed, fallen into a mudcrack, or
Figure 1 Examples a, b and c are of the short fat round coprolites from the first
cycle of the Rousay flagstone in Westray, Orkney; (d) shows part of the scroll in a
cross section (arrowed) under a 20x binocular microscope.
21a devonian coprolite from orkney and its possible fish producer been carried along by flash floods or Rousay flagstone cycles there’s a turbidity currents without breaking close correlation between fish beds up. Today, coprolites are commonly which contain coprolites and the seen in relief on weathered flagstone, presence of sub-aerial mudcracks, where they may occur along with showing that shallow parts of the lake mudcracks or salt pseudomorphs. dried out from time to time. Interestingly they are often far from fossil fish remains. On extraction To match a coprolite with its they break up easily and only rarely producer is an almost impossible task, weather out in one piece. In the but there’s one conspicuous coprolite Figure 2 Three typical coprolites from the Rousay flagstone in Westray, including a spiral form and a larger sample 47 mm long. 22
a devonian coprolite from orkney and its possible fish producer
that is rather short, plump and round. rounded protuberances. Like many
The texture is very smooth, almost modern fish, Dipterus was likely to
shiny and it’s made up of hard have been a grazer that here fed
siliceous, flinty material with small on ‘algae’, strictly cyanobacteria, in
amounts of calcite and pyrite. the form of sessile microbial mats
or stromatolites that grew on the
These short, fat round coprolites shallow lake bed where sunlight
appear to be most frequent in fish could penetrate. Dipterus may
beds where the lungfish, Dipterus, is have also taken small crustaceans,
common. This is especially true of millipedes, worms and clam shrimps.
the first cycle of the Rousay flagstone, That both the plump coprolite and
which crops out in five localities disarticulated remains of the lungfish
across Westray. In this fish bed, Dipterus occur in the same fish bed is
Dipterus, which was about 30 or 40 some indication but not a conclusive
cm long, appears with two smaller, match between the two.
and rarer osteolepids. Dipterus had
teeth of a sort, tooth-plates on which However, on closer examination
the teeth were little more than of one of the broken coprolite
Figure 3 Gently dipping Rousay flagstones on the ‘Westside’ of Westray Orkney
allow a huge area of bedding plane surfaces to be investigated. In the distance is
the island of Rousay.
23a devonian coprolite from orkney and its possible fish producer
samples, I discovered under a 20x on inside the sample. The scroll
binocular microscope, the distinct coprolite, as the word suggests,
line of a delicate whorl (see Fig. 1d), is cylindrical like a loose roll of
as if its producer had swallowed a paper, and reflects the intestinal
gastropod. The whorl is in fact part arrangement of the fish. Scroll
of the structure of a ‘scroll coprolite’ coprolites are said to be generally
and defines more closely the group rare and thought to be the product
of fish that produced it. The spiral of lungfish (Hunt et al. p277). So,
whorl is fortuitously preserved as a this makes the match a little more
single crystal of white calcite and, on conclusive, though never certain.
turning the specimen in a bright light
source, the cleavage planes light The lungfish was a survivor and could
up, as if a light had been switched take in air when pools of water dried
up and is common
throughout the
Devonian flagstones of
Orkney, that is, in and
above the Achanarras-
Figure 4 (a)
Headshield of lungfish
Dipterus is common
in the first cycle of the
Rousay Formation,
showing squarish
upper jaw; (b) shows a
weathered lower jaw of
Dipterus which is more
angular; and (c) is a
more or less complete
Dipterus, 30 to 35 cm,
also from the first cycle
of the RF. The rounded
scales are piled over
each other, so originally
this specimen may have
been longer.
24a devonian coprolite from orkney and its possible fish producer
Figure 5 A
complete, well-
preserved though
small specimen
of Dipterus from
the Achanarras
Quarry fish bed in
Caithness.
Figure 6
Traquair’s 1895
reconstruction of
Lungfish, Dipterus.
Sandwick fish bed. Its full name is Palaeogeography, Palaeoclimatology,
Dipterus valenciennesi, named after Palaeoecology, 426, 68–74.
a town in northeast France, once Coprolites: Hunt, A P, Milàn, J, Lucas,
renowned for its fine lace — it’s nice S G, and Spielmann, J A. (eds). 2012.
to think that Mary Anning might have Vertebrate Coprolites (A collection of
decorated her bonnet with a piece of 40 papers on coprolites). New Mexico
Valenciennes lace. Museum of Natural History & Science
Bulletin, 57, 387pp.
Further reading Geology of Westray: Leather, D. 2017.
Lungfish: Den Blaauwen, J L, Demarcation of the boundary between
Barwick, R E and Campbell, K S W. Middle Devonian Upper Stromness
2005. Structure of the tooth plates Flagstone and Rousay Flagstone
of the Devonian lungfish Dipterus formations in Westray, Orkney. Scottish
valenciennesi from Caithness and the Journal of Geology, 53, 53–61.
Orkney islands. Records of the Western
Australian Museum, 23, 91–113. Photographs and specimens from the
author’s collection.
Palaeoclimate: De Vleeschouwer,
D, Leather, D, and Claeys, P. 2015.
Ripple marks indicate Mid-Devonian David Leather
palaeo-wind directions in the Orcadian Woodlands, Panorama Drive, Ilkley,
Basin (Orkney Isles, Scotland). West Yorkshire.
25book reviews
Book reviews
Mountains — The origins of the plate-tectonics. The reader will be
Earth’s mountain systems by left in no doubt as to the grand scale
Graham Park. Dunedin Academic and inter-connection of mountain
Press, Edinburgh. 2018. Hardback, ranges and the fascination that they
212 pp. Price £29.99. ISBN: 978-1- hold for the author.
78046-066-6.
The first two chapters provide
a review of the historical
development of the ideas put
forward to explain Mountain
Building (orogenesis) and introduce
the geologists who advanced that
early understanding. Chapter 3
then sets out the advances in plate
tectonic thinking, using the well-
known example of the Himalayas
to get the reader started on the
right track. Chapters 4–8 then set
Professor Graham Park has accepted out across the Alpine-Himalayan
the challenge of taking the reader mountain system and describe
on an extended excursion through the major features of these largely
the mountain belts that form continental collision features. The
the major active features on the circum-Pacific (‘Ring of Fire’) system
surface of the Earth. He examines is described in Chapters 9–12: the
the processes that have acted to complex system of plate boundaries
form these spectacular eminences, and subduction zones of the
illustrating each example with a Western Pacific, and the north and
wealth of diagrams, maps and cross- south American Cordilleran volcanic
sections, accompanied by a goodly chains and collision belts that
number of excellent colour images. border the eastern Pacific. Chapter
The book does not seek to deliver 13 deals with the hidden mountain
a comprehensive description of any chain, the largely submerged mid-
particular mountain range, rather the ocean ridges that delineate the
aim is to provide a sound and robust spreading plate boundaries. The
overview explained in the context of final chapter then compares these
26book reviews
comparatively young, and often Perhaps the greatest challenge in writing
still growing, mountainous zones this single volume will have been to
on Earth with some of the older identify, and write for, a well-defined
features recognised by geologists in target audience. The book is neither
the earlier epochs of Earth’s history, too generalised nor too specialised in
and draws parallels between the old its content, but perhaps therefore falls
and the young. This book embraces between these two stools. Rather it
a truly global subject. should be viewed as a book that will
stretch and challenge the student of
The author draws on the prodigious geology, and deliver a large volume of
academic literature of recent contemporary information. It is not, I
decades and on and his own think, a synthesis providing a ‘quick
experience and then sets out win’ or an ‘easy answer’, instead it
to distil that information into a encourages the reader to delve deeper
succinct account. No small task, and wider into this fascinating topic. If
especially when individual nations ever evidence of the huge forces and
give different names to the same dynamic processes that shape the Earth
geological feature as it crosses were needed, then mountains must be
international borders. Geology often one of the most visible and attractive
has a glorious disregard for politics! A signs of our dynamic Earth. The reader
selection of key references are given will learn much about these mountain
in support of each chapter, and a systems and will, I hope, be encouraged
very useful glossary is also supplied. to find out more.
The book is lavishly illustrated with The author has packed a tremendous
hardly a page lacking one or more amount of information into these
figures. Some stunning views of the 212 pages, and whilst an expert may
spectacular mountain topography debate the interpretation offered
accompanies the diagrams – but for any particular feature or region,
perhaps some images of the equally I came across no striking errors. The
stunning rocks that can result from book will take time to digest and is
the processes that build these undoubtedly one to be consulted
mountains would have added to many times over. Some readers may
the impact overall. The diagrams find it hard to resist marking their
are well-drawn with accurate keys own annotations onto the glossy,
and helpful captions, whilst the beautifully-produced pages.
page size means that they are clearly
reproduced at a generous scale. Graham Leslie
27book reviews
Adam Sedgwick —Geologist and
It says much for the author’s skill that at
Dalesman (Facsimile edition) by no point is the reader left bewildered
Colin Speakman. Gritstone Writers by apparent anachronisms.
Cooperative and The Yorkshire
Geological Society, Hebden Bridge. Although Sedgwick is undoubtedly
2018. Paperback, 145 pp. Price £12, best known for his geological
ISBN 978-0-9955609-4-9. contributions and pre-eminence at
Cambridge University, Speakman
ranges much more widely. In four
introductory ‘themes’ he takes his
subject, a fellow Dalesman with few
advantages in life save innate talent,
a determination to succeed, and the
fortuitous influence of able teachers,
from rural Yorkshire to a University
Fellowship. Near the end of the book
two ‘themes’ cover the contrasting
activities of the older Sedgwick. There
was an extraordinary involvement
with Queen Victoria and Prince Albert
which transformed the supposed
Colin Speakman’s biography of reactionary into a radical activist
Adam Sedgewick (1785–1873), a promoting reforms to the university
legendary figure in British geology, was curriculum. Then, in ‘retirement’,
first published in 1982. A definitive Sedgwick championed the rights of
work, it has been out-of-print for his local Dentdale community.
several years, so this new facsimile
edition is most welcome. The main Five geological ‘themes’ form
text is unchanged, but the opportunity the middle section of the book.
has been taken to improve the print Sedgwick’s opportunistic conversion
quality of the excellent figures, whilst from mathematics to geology seems
introductory pages have been brought to have been partly a smart career
up-to-date. The book is described as move but perhaps was also driven
‘a biography in twelve themes’ and the by a need for outdoor therapy to
approach works well in that the very counter chronic depression. Whatever
different aspects of Sedgwick’s life are the motive, in 1818, he was elected
explored in full without the disruption Woodwardian Professor of Geology
of contemporary but unrelated events. although the position, as Speakman
28book reviews
emphasises, carried little associated Be that as it may, I doubt that any of
prestige. Nevertheless, and despite the protagonists would approve of the
his lack of formal training, Sedgwick description of the critical graptolites as
soon became a powerful force in “minute pencil-like organisms”.
British geological circles.
The second of the controversial
Sedgwick ranged widely across England themes, Darwinian evolution by natural
in his geological researches, but selection, saw Sedgwick in prominent
Speakman rightly highlights one of his opposition; a sad irony given his
discoveries from 1822, in the hitherto early influence on Darwin’s scientific
intractable rocks of the English Lake development. Like the dispute with
District. There, Sedgwick recognised Murchison, it has been the subject of
the true relationship between bedding, much research and commentary, with
cleavage and jointing; informed a plethora of publications on both
structural interpretations could then issues post-dating the 1982 publication
follow. Later, as an established senior of Speakman’s book. Two that spring
figure, Sedgwick met the up-and- to mind are James Secord’s 1986
coming Roderick Murchison and, book Controversy in Geology: The
perhaps surprisingly, a firm friendship Cambrian-Silurian Dispute, and Sandra
developed. So much so, that the Herbert’s 2005 book Charles Darwin,
two men toured the Highlands of Geologist. As an addition to the 2018
Scotland, explored the Alps and jointly facsimile edition a complete review of
published scientific papers. Their the more recent literature would have
subsequent falling-out over the relative been too much to ask, but it is a shame
extent of Silurian and Cambrian that the opportunity was not taken to
rocks in Wales enlivens the first of draw attention to the more important
Speakman’s two ‘controversy themes’; recent contributions by means of a
the second is Sedgwick’s reaction to supplementary bibliography.
Darwin and The Origin of Species.
That omission aside, it is still difficult
For the first of these two great to fault Speakman’s biography. It is
scientific controversies Speakman a beautifully crafted assessment of
sides firmly with Sedgwick as the Sedgwick’s life and demonstrates that
aggrieved party, as early as page three there was much more to the man
he has dismissed the “apologists of than can be gleaned from two famous
Murchison” and regards Lapworth’s controversies.
Ordovician interpolation as more to
Sedgwick’s liking than to Murchison’s. Phil Stone
29This issue: No. 64, Autumn 2018
1 Editorial ramble
Rewarding geology, Scottish islands, and odd
palaeontological furniture
5 An introduction
By Bob Gatliff, Edinburgh Geological Society President,
2018–2019
8 Arthur Holmes and Continental Drift: some
personal recollections
By Gilbert Kelling
13 Arran’s volcanic past — classic geology and new
ideas
By Bob Gooday
20 A Devonian coprolite from Orkney and its possible
fish producer
By David Leather
26 Book reviews
Mountains — The origins of the Earth’s mountain
systems
Adam Sedgwick — Geologist and Dalesman
All previous issues are available online at
www.edinburghgeolsoc.org/publications.
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ISSN 0265-7244You can also read
