Geological Survey Of Great Britain Research Articles

The first mapping of the Moine Thrust Belt, NW Scotland: the progress of Peach, Horne and colleagues (1883–1936)

Abstract The Moine Thrust Belt in NW Scotland is fundamental for developing an understanding of complex fault systems and continental tectonics. The high-quality geological mapping, exceptional structural interpretation and insight of the late nineteenth century that underpins this is chronicled here. The Geological Survey of Great Britain mapped the thrust belt over a 14 year period, at 1:10 560, but it took five decades for the individual 1:63 360 map sheets to be published. The mapping itself was hampered by access problems, illness and prevailing weather. The deployment of expert staff to this region of few apparent economic resources threatened the status of the Geological Survey. Map publication was hindered by the transition from hand-coloured to full-colour printing, together with the restrictions of publishing to a strict grid that incorporated complex geology outside the thrust belt itself. This history of fieldwork, publication and outreach by the Geological Survey is placed in an environmental and logistical context to identify the challenges not only for the mapping itself but also in sharing the results in publication. The execution of these activities provides lessons for developing coherent interpretation in complex geology and the challenges in charting their uncertainties and alternative explanations.

BRITISH MILITARY CONTRIBUTIONS TO THE GEOLOGY OF MALTA, PART 2: THE SECOND WORLD WAR, 1939–1945

ABSTRACT During the Second World War, the central Mediterranean island of Malta was famously besieged by the Italian navy and intensively bombed by Italian and later German air forces, from June 1940 until Allied victory in North Africa in May 1943 brought an end to the siege. It was then scheduled as a staging post to support the Allied invasion of Sicily from North Africa in July 1943 and of mainland Italy from Sicily in September. From 1941 until 1945, two Tunnelling Companies Royal Engineers, overlapping in succession, excavated underground facilities safe from aerial or naval bombardment. In 1943 and then 1944–1945, two Boring Sections Royal Engineers in succession drilled wells to enhance water supplies, initially for increased troop concentrations. Borehole site selection was guided in 1943 by the Director of the Geological Survey of Great Britain (Edward Battersby Bailey: 1881–1965) and by geologists Captain Frederick William Shotton (1906–1990) and Major Gordon Lyall Paver (1913–1988). In 1944, it was guided by geologist Captain Howard Digby Roberts (1913–1971), leading a detachment from 42nd Geological Section of the South African Engineer Corps that pioneered earth resistivity surveys on the island. Overall, these military studies generated a new but unpublished geological map of the island at 1:31,680-scale and refined knowledge of its geological structure: a much faulted but otherwise near-horizontal Oligo-Miocene sedimentary sequence. Further refinement was achieved as a consequence of the 1944–1945 drilling programme, led principally by geologist Captain Thomas Owen Morris (1904–1989) of the Royal Engineers. By 1945, this had helped to develop an improved water supply system for the island, and plans to develop groundwater abstracted from a perched upper aquifer (in the Upper Coralline Limestone and underlying Greensand formations, above a ‘Blue Clay’) as well as from the main lower aquifer, near sea level (in the Globigerina Limestone and/or underlying Lower Coralline Limestone formations).

Female students of geology in Victorian Dublin

Abstract The science of geology began to thrive during the middle of the nineteenth century, with the expansion and consolidation of geological mapping of the Geological Survey of Great Britain and Ireland, and the foundation of geological societies across the islands of Britain and Ireland. As the desire for geological knowledge and understanding among the general public grew, so did the provision of lectures and courses open to the public. These public lecture series proved popular with a wide cross-section of men and women of Victorian Britain and Ireland. This paper explores the provision of geological lectures by officers of the Geological Survey of Ireland through the Museum of Irish Industry in Dublin, and the women who took these courses during the 1850s and 1860s, and completed geological examinations for London's Science and Art Department in Dublin as a result of these lectures. It provides a glimpse into the scientific and, specifically, geological interests and activities of these women at a time when it was not possible for them to become members of the geological societies in the cities in which they lived.

Raymond Charles Casey. 10 October 1917—26 April 2016

Raymond Casey was an internationally recognized expert in two entirely different fields—geology and philately. He achieved this despite leaving school at 14. By then he was already collecting and studying fossils from his home town, Folkestone, and in 1939, despite not having a degree, he obtained a post with the Geological Survey of Great Britain in the modest role of assistant to C. J. Stubblefield. After war-time service in the RAF, he returned to the Survey in a similar role, but spent much of his ‘spare time’ researching and publishing on Lower Cretaceous palaeontology and stratigraphy. His fortunes began to change when, at the age of 38, he was admitted to Reading University to study for a doctorate. His thesis on Lower Greensand stratigraphy and palaeontology was recognized as an outstanding study that led to major publications including a nine-part monograph of the ammonite faunas. Then, in the late 1950s, he also began to study faunas from Jurassic–Cretaceous boundary beds in eastern England as part of his official work and this led to him visiting the Soviet Union on several occasions from 1963 onward. On the first visit he met the academician Nalivkin in Leningrad, who, as well as being an eminent geologist, was a keen philatelist. This led to Raymond taking an enthusiastic interest in pre-revolutionary Russian postal history, which resulted in numerous publications and awards and, after his retirement, became his main focus of interest.

About this title - Aspects of the Life and Works of Archibald Geikie

Sir Archibald Geikie (1835–1924) was one of the most distinguished and influential geologists of the late nineteenth and early twentieth centuries. He was Director-General of the Geological Survey of Great Britain, President of the Geological Society of London, President of the British Association, Trustee of the British Museum and President of the Royal Society. He was also an accomplished writer, a masterful lecturer and a talented artist who published over 200 scientific papers, books and articles. The papers in this volume examine aspects of Geikie's life and works, including his family history, his personal and professional relationships, his art, and his contributions as a field geologist and administrator. Together, they provide a deeper understanding of his life, his career and his contribution to the development of Geology as a scientific discipline. Much of the research is based on primary sources, including previously unpublished manuscripts, donated in part by members of the family to the Haslemere Educational Museum, UK.

British pioneers of the geology of Gibraltar, Part 3: E. B. Bailey and Royal Engineers 1943 to 1953

Edward Battersby Bailey (1881-1965), Director of the Geological Survey of Great Britain, visited the 6-km2 Gibraltar peninsula twice in 1943, in transit from/to England and the Mediterranean island of Malta. He spent only five days in total on Gibraltar, but submitted two influential reports to its Fortress Headquarters, guided by rock features exposed by recent quarrying. On his recommendation, a deep borehole was drilled below the northern isthmus in an attempt to locate a supposed aquifer in Cenozoic sandstones believed to extend south from Spain, and A. L. Greig (a graduate of Imperial College, London, serving locally in the ranks of the Royal Engineers) prepared a new geological map (at 1:5,280) and a report to help guide tunnel excavation within the bedrock. Between 1945 and 1948, Lieutenant (later Captain) G. B. Alexander (a graduate of the University of Cambridge also serving in the Royal Engineers) generated a much more detailed map (at 1:2,500) of the bedrock plus superficial deposits, together with associated diagrams and geotechnical reports. These unpublished documents, and fossils collected during their preparation, influenced a re-interpretation of Gibraltar (as the remnant of an overturned limb of a klippe of Early Jurassic dolomitic limestone thrust into position during the Betic-Rif Orogeny), published by Bailey in 1953. A report to accompany Alexander's map was never completed, but documents constituting the most complete record known of his Gibraltar work are now preserved within the archives of the British Geological Survey. Reserve army officers later compiled a geological map of Gibraltar (at 1:10,000) published by the Royal Engineers in 1991. Thereafter, as garrison strength became greatly reduced, work under military auspices was increasingly superseded by civilian research.

War as a catalyst for change: groundwater studies in the Geological Survey of Great Britain before 1950 and the impact of two World Wars

Abstract In the early years of the Geological Survey, staff built up a considerable understanding of the movement of groundwater, and water supply memoirs were published from 1899. During World War I, one of the tasks of the Survey was to advise on the provision of water supplies. However, this emphasis did not continue when war ended, and it was not until the 1930s that interest in groundwater began to increase. An Inland Water Survey Committee was formed and the groundwater component of its work was entrusted to the Survey. A modest Water Unit was set up in 1937, staffed by members of Field Units on rotation, but limited progress was made. At the outbreak of World War II, attitudes changed and manpower was diverted to the systematic collection of groundwater data, published in a series of Wartime Pamphlets. At the end of the war, the Water Acts imposed significant obligations on the Survey and over the next five years the systematic collection and analysis of information became a professional operation. The Unit became a Department with its own permanent staff. The war acted as a catalyst highlighting problems and initiating action to the benefit of the water industry.

Chapter 10 The move to Melbourne University

According to E. Lim (1975), in a letter dated 15 August 1899, John Madden (1844–1918), Chancellor of the University of Melbourne wrote to the Agent General (in London) for the Colony of Victoria, asking him to invite applications for a new Chair in Geology and Mineralogy. This was necessitated by both the death of the previous holder of the Chair of Natural History (from 1854–1899), Professor Sir Frederick McCoy (1817–1899), and the creation of separate Chairs of both Chemistry and Biology, subjects that had previously been included in Natural History (Selleck 2003). This left geology teaching and research, including palaeontology, in abeyance. The emphasis was to be on ‘mineralogy so that the new Department may be brought into line with any future extensions of Mining and Engineering.’ The advertisement was placed in Nature on 28 September and applications had to be received in London by 20 October 1899. The London appointing committee consisted of four FRS's: A. Geikie, Director General of the Geological Survey of Great Britain and Ireland, J. W. Judd, Dean of the Royal College of Science, John Edward Marr (1857–1933) Woodwardian Professor of Geology at Cambridge, and Charles Lapworth (1842–1920), Professor of Geology at Birmingham. Gregory, who had (on 3 October 1899) asked for, and received from, Geikie a fine testimonial for the post, wrote to Geikie on 5 October stating that given that Geikie would be on the appointing committee in London, he would not submit the testimonial (Edinburgh University, Geikie Archives). The following day, 6 October he wrote to Lapworth asking if he would give him a testimonial, perhaps in place of Geikie's, presumably because he did not realize Lapworth was also on the committee (Lapworth archives, H22). The committee considered ‘the claims of Dr Gregory are so far above those of any of …

The Geological Structure of the North-West Highlands of Scotland – revisited: Peach et al. 100 years on

Abstract Following years of sporadic debate, in the early 1880s consensus was reached that thrust tectonics explained hitherto controversial geological field relationships in NW Scotland. This spawned a major research effort there by the Geological Survey of Great Britain that culminated in a series of highly detailed geological maps, preliminary research papers and, eventually, the publication of a memoir to the region. These works became highly influential to early-20th century geoscience, especially structural geology. Not only did they provide the first major synthesis of thrust belt structure, they also provided the basis for descriptions of fault and shear zone processes and deductive methods for unravelling tectonic histories in metamorphic basement. A common misconception is that the results arose from mapping alone, without regard to extant models and theory and this approach is held up as an ideal for fieldwork. Yet the notebooks and writings of the surveyors show the application of learning not only from other research groups but also between themselves. As with modern mapping, the Survey team created interpretations that built on contemporary knowledge. This work in turn has driven subsequent research for over 100 years, in the NW Highlands and in deformed rocks throughout the world.

Book review: 200 Years of British Hydrogeology, by J. D. Mather (ed.) (Geological Society, London, 2004) Geol Soc London Spec Publ 225, 393pp. ISBN 978-1-86239-155-0

The subject book (Mather 2004) is a very well written compendium of papers by various authors on key people and topics, which describe the evolution of the practice of hydrogeology in Great Britain. Summaries of contributions of distinguished hydrogeologists have been published previously, especially contributions from other European countries and America, but none, to the author’s knowledge, are as thorough and detailed as presented in this book about the British hydrogeologists. The book has an overview which nicely summarizes the 24 papers. It appears that the evolution of British hydrogeology essentially had two primary periods. The first was characterized by prominent individuals who made significant contributions, starting with William Smith (1769–1839) who, among other things, showed the relationship of springs to stratigraphy in 1799. Robert Stephenson (1803–1859), an engineer, wrote a hydrogeologic report on the London water supply and accurately described the shape of the cone of depression around a pumped well. The Reverend James Clutterbuck (1801–1885) noted how groundwater pumping affected surface water and saline intrusion beneath London; he is considered the father of English hydrogeology. Joseph Prestwich (1812–1896) apparently was the first to show hydrogeological information on a British geological map; and, John Snow (1813–1858) discovered that cholera was spread by contaminated drinking water. The second primary period in the evolution of British hydrogeology was one in which the majority of the contributions were made primarily through employees of various government organizations, beginning in about 1870 with scientists in the Geological Survey of Great Britain. William Whitaker (1836–1925) was a meticulous compiler of well logs and other groundwater information during his work with the Geological Survey. Whitaker was also involved later in his career as a consultant on proving a source of well pollution using a lithium chloride tracer. Joseph Lucas (1846–1926) is claimed to be the first person to have used the term “hydrogeology” in its modern context, was the first to refer to himself as a hydrogeologist, and drew the first British maps showing groundwater level contours. Lastly, Charles de Rance (1847–1906) produced a book surveying the water supplied to each town and sanitation authority in England and Wales which included a hydrogeological map showing the permeability of the strata. Hydrogeologic research was rather limited in the latter part of the nineteenth century but covered diverse segments, mostly conceptual or empirical in nature, such as intergranular and fracture flow, recharge, water balances, specific yield, and unsaturated flow. Especially intriguing are the solute transport experiments of Issac Roberts in 1879. It was also surprising to learn that the famous British scientist, John Dalton, constructed what was perhaps the first soil lysimeter to quantify infiltration as a percentage of precipitation in 1799, and the results of this work were applied about 90 years later in quantitative assessments of water resource availability. It was not until 1937 that there was a formal water unit within the Geological Survey. In response to major legislation, 1945 began an era of resource assessment. Research, however, within the Geological Survey seems to have begun in earnest after 1963 on aquifer properties, modeling, and hydrogeochemistry including applications to groundwater contamination. Prior to this time, much of the hydrogeological work was more descriptive in nature. Perhaps the most notable British contribution to the entire field of quantitative hydrogeology was from Norman Boulton (1899–1984), a civil engineering professor, who pioneered work in aquifer mechanics. He is best known for his “delayed yield” equations on the behavior of pumped unconfined aquifers. Mather’s book points out Received: 27 March 2009 /Accepted: 12 May 2009 Published online: 23 June 2009

Obituary: Denys Barker Smith 1929-2007

Denys Barker Smith was bom on 9th April 1929 in Wybun- bury, Cheshire, the son of James Ramsay Smith, the local village headmaster, and Ida Mary Smith, also a teacher. He attended his father's school from 1934–1940, and from 1940–1947 was a pupil at Nantwich and Acton Grammar School, Cheshire. There he excelled in geography and geology, inspired by his teacher, Mr Gowdridge, who encouraged his interest in maps, landscape and topography. These interests led Denys to study geology at the University of Birmingham, from where he graduated with First Class Honours in 1950. University was followed by National Service (1951–1953), during which, as a Captain in the Royal Engineers, he was responsible for compiling mobility maps. He remained on the reserve of Scientific Officers until 1964. In 1953, he joined the Geological Survey of Great Britain, being appointed as Scientific Officer and based in the Newcastle Office. Denys transferred to the Leeds Office of the Geological Survey in and remained there until 1976. During his early career, Denys was engaged primarily on the field survey of eastern Co. Durham, embracing the indus­trial areas of lower Tyneside, Wearside and Teeside and the intervening coalfield areas, working mainly on the Permian Magnesian Limestone on the Sunderland and Durham geological map sheets. In 1958, he published ‘Some Observa­tions on the Magnesian Limestone reefs of north-eastern Durham’ in the Bulletin of the Geological Survey of Great Britain , the first of over 70 papers published throughout his scientific career. He was promoted to Principal Geologist in steadily increasing his national and international repu­tation as an expert on the Permian rocks of north east England and maintaining a steady flow of papers on the subject. In 1961, he completed the survey of the Magnesian Limestone on the Stockton 1:50 K Sheet, and in 1965 …

The role of the British Geological Survey in the history of geoconservation

Abstract Over its 172 year history, the British Geological Survey (formerly the Geological Survey of Great Britain) has, through underpinning core activities, its archive and databases and its experienced field staff, provided the geological basis for geoconservation. Evolving activities of the Survey from primary survey and collecting to revision mapping to 3D/4D-modelling reflect changing national needs. In turn, BGS has developed its capability to provide new geological interpretations and a range of publications raising the profile of Earth sciences, both for professionals and for the popular market. Today, BGS's input through networks to geodiversity projects and to newly designated regions such as Geoparks marks a major transition towards a proactive geoconservation agenda in the twenty-first century.

The Sustainability of Geological Mapmaking: The Case of the Geological Survey of Great Britain

Henry De la Beche's leadership of the Geological Survey of Great Britain in the second quarter of the nineteenth century led to the establishment of a number of key institutions which ensured the Survey of survival beyond the initial phase of geological mapmaking. Considered as a finite activity serving only to fix on paper the spatial distribution of an unchanging physical resource, geological mapmaking alone was never a secure basis for institutional or disciplinary development. The actions taken by De la Beche in the 1830s and 1840s, at a time when public and politicians alike were suspicious of government-funded science, were echoed 150 years later by successors who served governments with similar doubts about non-commercial scientific activity. Whether buried within an empire of public institutions, illuminated in museum collections which spoke of utilitarian value, or conceptualised as an income-generating database of rare data, the continuation of geological mapmaking in Britain relied upon a relationship to, and relevance for, a wider world of politics and practice. Seen in the long view, the British Geological Survey demonstrates that a nation can only make and re-make geological maps if that activity can be submerged within, or repackaged as, a new strategically-valued socio-economic initiative.

Conditions of Employment and Work Practices in the Early Years of the Geological Survey of Great Britain

This paper provides information about the conditions of employment and concomitant work practices of the early years of the Geological Survey of Great Britain. It is chiefly based on a series of pamphlets issued by the successive Survey Directors. These set down the conditions of employment for the organization's staff members, but they also provide insights into the day-to-day workings of the Survey, its gradual enlargement, and its modes of bureaucratic control. They also provide some insight into the ethos of the Survey, and the kind of career and the nature of the work that the organization could offer its staff. Evidence is put forward as to the reason why the series of printed regulations was initiated. The Survey provides a useful early example of the nature and practice of government science, organized according to bureaucratic principles.

The development of groundwater in the UK between 1935 and 1965 — the role of the Geological Survey of Great Britain

Abstract After the drought of 1933–1934 the Geological Survey became responsible, under the Inland Water Survey, for collecting and collating data on groundwater. In 1935 a Water Unit was formed for this purpose. Following the Water Act of 1945, the Survey advised the Government on aspects of the Act relating to groundwater. The Act led to the introduction of quantitative hydrogeology in England and Wales. The groundwater resources of the main aquifers were assessed, well hydraulic theory was applied to British aquifers, and geophysical techniques and new instrumentation introduced.

Stevenson Buchan (1907–1996): field geologist, hydrogeologist and administrator

Abstract Stevenson Buchan, a Scot educated at Aberdeen University, joined the Geological Survey of Great Britain in 1931. Assigned to the Southern District Unit he became involved in hydrogeology when he revised the 6-inch to the mile maps of Greater London. This led to the publication of a memoir on the water supply of the County of London in 1938. During the war he was involved in the search for water and coal. Appointed Head of a new Water Department when hostilities ceased he was given responsibility for overseeing the statutory obligations placed on the Survey by recent Water Acts. He developed around him a group of able colleagues creating the first groundwater research group of any size in the UK. Promoted to Assistant Director in 1960, he was very active internationally and in his role as an enabler and administrator played an important role in the development of hydrogeology in the UK.

Jack Ineson (1917–1970) The instigator of quantitative hydrogeology in Britain

Abstract Jack Ineson will always be associated with introducing quantitative methods to British hydrogeology. A geologist with a sound knowledge of mathematics and statistics, unusual for the time, he seized the opportunity in 1948 to apply to British aquifers the burgeoning theory of well hydraulics initiated by Theis. Ineson’s career was mainly spent with the Geological Survey of Great Britain, now the British Geological Survey, but in the period 1965–1970 as Chief Geologist of the Water Resources Board. It was, however, a relatively short career with the start postponed by the Second World War and tragically truncated in June 1970 as a direct consequence of his experiences in the war.

OBITUARY: SIR KINGSLEY CHARLES DUNHAM (1910–2001)

Sir Kingsley Dunham, one of the leading figures in British Geology of the latter half of the twentieth century, died at Durham on the 5th of April, 2001. He was born at Sturminster Newton, Dorset, in 1910. His father was an estate manager and the family moved north to Brancepeth, near Durham City, while he was still young. Dunham's early education was at Brancepeth School and later at the Durham Johnston School. Strongly supported and encouraged by his parents, he obtained matriculation and entrance to Hatfield College at Durham University. A talented musician (organ and pianoforte), he was awarded a college organ scholarship and played the organ in the college chapel. He intended to read Chemistry, but came under the spell of Arthur Holmes, the then Professor of Geology, a man of great ability and now widely regarded as one of the most distinguished geologists of the twentieth century. Kingsley Dunham was captivated by the eloquence of geological processes and patterns, often at the bounds of knowledge, as taught by Holmes. He changed to the Honours Geology course and completed his first degree. After graduating, Dunham was offered a postgraduate studentship at Durham University to work under Holmes, and he chose to study the distribution of vein minerals in the Northern Pennine Orefield, a topic that he continued to research for the rest of his life. He was awarded a PhD in 1932, and a Commonwealth Fund Fellowship to work on mineralogy at Harvard University. He travelled widely in North America and completed a geological survey of the Organ Mountains with the New Mexico Bureau of Mines. Returning to Britain in 1934, Dunham obtained one of the few posts available at that time as a geologist in the Geological Survey of Great Britain. His first assignment was to map the …

Sir (Cyril) James Stubblefield. 6 September 1901 – 23 October 1999

Cyril James Stubblefield was an internationally renowned palaeontologist who, in his long career in the Geological Survey of Great Britain, rose to become its Director, and who was elected to be the leading geologist in the country as President of the Geological Society of London. A tribute to Sir James Stubblefield–as he became–by Dr M.A. Calver (1981), a colleague and Chief Palaeontologist, Institute of Geological Sciences, celebrated Sir James's 80th birthday and gave a list of his publications. H.E. Wilson's lively history (Wilson 1985) of the 150 years of the British Geological Survey, as the Institute of Geological Sciences was renamed in 1984, has much information on the years spanning Sir James's career. The personal tribute by Dr R. Casey, F.R.S. (Casey 2000), gives a unique insight into service in the Geological Survey during those years. Here I have supplemented the account by Calver, using autobiographical notes compiled by Stubblefield, and the complete bibliography includes publications (additional to those listed by Calver) compiled by Dr P.A. Sabine, formerly Deputy Director of the Institute.

Geochemical Evolution of the Tertiary Mull Volcano, Western Scotland

The early Tertiary Mull volcano, western Scotland, is one of the most dissected and best exposed igneous complexes of the North Atlantic Province. The new and published geochemical data enable us to chart the magmatic evolution of the Mull volcano from the oldest lavas through the intrusive rocks of three overlapping igneous centres, to the youngest dykes. In this study, we identify four successive magma types within the remnant volcano. The earliest type—the Mull Plateau Group—comprises mildly alkaline basaltic rocks with steep chondrite-normalized rare earth element (REE) patterns. This type is succeeded, within the lava succession and dyke swarm, by the Coire Gorm magma type with essentially flat chondrite-normalized REE patterns. A third magma type represented within the lava and dykes—the Central Mull Tholeiites—is more depleted in incompatible trace elements than the preceding types and has flat to LREE-depleted chondrite-normalized patterns. The major intrusions and cone sheets of Mull Centre 1 and early Centre 2 belong to this magma type. Midway through the igneous activity associated with Centre 2, the magma type changed to become more alkalic and more enriched in incompatible trace elements. This magma type (the Late Mull type) is found to persist through the cone sheets and major intrusions of Centre 3, to the youngest dykes. These changes in magma composition were related to variations in the mantle source and depth of partial melting beneath Mull, and/or differences in the efficiency of melt pooling before ascent through the lithosphere. With the exception of the early Staffa magma sub-type (part of the Mull Plateau Group), the location of magma chambers, in which the bulk of contamination occurred, changed with time from deep (lower-crustal Lewisian gneiss) to shallow (upper-crustal Moine schist). Intermediate members of the Plateau Group and the Late Mull magma type are enriched in Fe, Ti and P relative to the Central Mull Tholeiites. We attribute this difference to the more alkalic nature of these suites, lower fO2, and the formation of Fe3+−P complexes in the magma. The intermediate rocks were important in magma mixing processes, with two types of mixing identified on Mull: (1) cryptic mixing between basalts and low-Fe intermediate magmas, typified by lavas and early basic cone sheets of the Central Mull Tholeiite magma type; (2) observable mingling between rhyolitic magmas and high-Fe intermediate magmas of the Late Mull type, shown by the mixed-magma bodies of the Glen More and Loch Bà ring dykes. The main factor in determining which type of mixing occurred appears to have been the density contrast between the various magmas. ‘It may safely be maintained that Mull includes the most complicated igneous centre as yet accorded detailed examination anywhere in the world’ (Bailey et al., 1924, Memoir of the Geological Survey of Great Britain, Scotland, HMSO, Edinburgh, 1924).