History of the geological research of Wales

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From: Howells, M F. 2007. British regional geology: Wales. Keyworth, Nottingham: British Geological Survey.

Wales has had an influence in the history of geology that is inversely proportional to its size. Subsequent to the establishment of geology as a science in the late 18th century, the original subdivisions of the stratigraphical column and subdivisions at series level, particularly of the Lower Palaeozoic, are littered with the names of hamlets and villages within Wales and its borders. Early references include those to Giraldus Cambrensis, who in the 12th century, recognised pyritous shales in the vicinity of Newport, and to Leland who, in the 16th century, recognised the difference between the anthracite of the Gwendraeth valley and the coking coals of Llanelli. Later, in the early 17th century, George Owen traced the outcrop of the Lower Carboniferous limestones around the south Wales coalfield, and this formed the basis of one of the earliest geological maps. At the end of the 17th century, Gibson published illus­trations of plants from the Coal Measures near Neath. In the early 18th century, the eminent naturalist Edward Llwyd correlated, on the basis of their faunas, the (Carboniferous) lime­stones at Barry with those of Caldey Island and, most importantly, he recognised that they were different from the Jurassic limestones in south Glamorgan.

At the end of the 18th century, William Smith, the ‘father of British geology’, crossed the border into the Principality and outlined the general structure of the south Wales coalfield. He traced the outcrop of the broad elements of the Old Red Sandstone and Carboniferous on his renowned map published in 1815. In north and west Wales his observations were slightly less specific — he referred most of the rocks to ‘killas’ and ‘slate’, although he desig­nated the Coedana granite of Anglesey as igneous rock. Greenhough’s geological map of England and Wales was published in 1820, and parts of south Wales were accurate and detailed.

The most concerted, early phase of investigation began in 1831 when Adam Sedgwick and Roderick Murchison began their study of the Old Red Sandstone and the underlying Lower Paleozoic rocks that occupy most of central and north Wales; what began in concert ended in intense rivalry. Sedgwick addressed himself to unravelling the stratigraphy and structure of Snowdonia and Llŷn. In 1835, he designated the great sequence of rocks, with apparently no top or bottom, to the Cambrian, and subdivided them into Lower, Middle and Upper. Murchison, working from the Welsh borderland, divided his sequence into Upper and Lower Silurian and supposedly ‘unfossiliferous’ Cambrian; by 1839 he had published his major treatise, The Silurian System. As the work progressed it was apparent that Sedgwick’s Upper and Middle Cambrian were essentially equivalent to Murchison’s Lower Silurian and the controversy, partly on geological fact but mainly on stratigraphical terminol­ogy, was initiated. Much heat was engendered and its resolution did not occur until 1879, when both protagonists had died and Charles Lapworth proposed that the controversial beds be assigned to a newly designated Ordovician System, between the beds of the Cambrian System at Harlech and Arfon in Merionethshire and Caernarvonshire, and those of the Silurian System through Denbighshire and Montgomeryshire. The Geological Survey, presum­ably in deference to Murchison who was its Director between 1855 and 1871, continued to refer to the Ordovician as Lower Silurian into the early years of the 20th century.

Sedgwick’s map of north Wales, on the scale of one inch to eight miles, was published in 1845. One year later, Daniel Sharpe produced a map of the same area, on a scale of one inch to five and a half miles, which provided the first clear designation of the structures. The Geological Survey was founded in 1835 with Sir Henry De la Beche as Director and, in its early years, it accomplished an extraordinary amount of work in Wales. Following the publi­cation of the Geology of south Wales in its first volume of memoirs, a mapping programme, on the scale of one inch to one mile (1:63 360), was initiated with A C Ramsay, W T Aveline, A R C Selwyn and J B Jukes as surveyors, and J B Salter as palaeontologist. By 1852, the north Wales map was completed and by 1858, a geological map of Wales, on the scale of one inch to four miles, was published; this was revised in 1879. An important element of this work, which is often referred to and much admired, is a series of horizontal sections that were surveyed in the field on a scale of six inches to one mile, and display detail of the geology through some of the most remote areas of Wales.

Ramsay and his colleagues produced the first comprehensive account of the Geology of north Wales in 1866, and the second edition in 1881 presented the stratigraphy, the variable sedimentary rocks, volcanic rocks and associated intrusions, the structures and the geomorpho­logical evolution in the most extraordinary detail. It was in 1860 that Ramsay marshalled the first systematic arguments, following an earlier reference by Charles Darwin, for the effect of glacial erosion on the landscape. Towards the end of the 19th century, the Geological Survey began mapping at the scale of six inches to one mile in areas of economic importance; this work extended into the early years of the 20th century. The whole Carboniferous outcrop was remapped, between Pembrokeshire and Monmouthshire in south Wales, and from Wrexham to Shotton in north Wales; maps, sections and memoirs were published.

Following the early pioneering work of Sedgwick and Murchison, the contribution of indi­vidual researchers has continued to be a dominant feature of geological research in Wales. In 1889, A Harker published his elegant essay on the Bala volcanic rocks of Caernarvonshire in which he interpreted the detail provided by the Geological Survey’s maps and Ramsay’s memoir. Similarly, in 1895, Edward Greenly resigned his position with the Geological Survey in Scotland to work on the complex Precambrian rocks of Anglesey. Supported by his wife, Annie, he completed the mapping, on the scale of six inches to one mile, with parts mapped on the 25 inch scale. This remarkable task and partnership was lovingly described in the classic two volumes, A hand through time (1938); the map (1920) and memoir (1919), published by the Geological Survey, remain standard works of reference and the scientific testament.

The work of O T Jones, dating back to the early years of the 20th century was directed towards unravelling the Lower Palaeozoic stratigraphy and was published in a succession of papers and in his Presidential address to the Geological Society of London in 1938. His research formed the basis of both a more refined structural analysis and a palaeogeographi­cal model of an evolving geosyncline. Much of this work was accomplished with W J Pugh, who succeeded him to the Chair of Geology at Aberstwyth and later became Director of the Geological Survey. At the same time P G H Boswell systematically recorded the detail of the Silurian stratigraphy of Denbighshire, culminating with his publication, The Mid Silurian rocks of north Wales, in 1949. His studies were of mammoth proportions but seem to have been clouded by his prolonged palaeontological and sedimentological controversies with O T Jones.

Subsequent to the earliest surveys, the work of G L Elles and E M R Wood on the Ordovician and Silurian graptolite faunas laid the foundation for accurate biostratigraphical zoning, and this has continued with the palaeontological work of the Geological Survey and university researchers. Similarly, E E L Dixon clarified the stratigraphical relations of the Lower Carboniferous rocks and applied the concept of facies to the formation of different lime­stones. A E Truman’s stratigraphical zonation of the Coal Measures based on slight modifica­tions in bivalve morphology was one of the earliest evolutionary palaeontological studies. As a result of these, and other studies, there are many Welsh type-sections of the Palaeozoic sequence in Britain.

During the Second World War (1939–45), officers of the Geological Survey concen­trated on work in the coalfields, mineral resources and water supply throughout Wales. This work continued through the period of the nationalisation of the coalfields, when the survey officers worked in co-operation with geologists from the National Coal Board until the decline of the industry in the 1980s. This work formed the basis of the revision and publication of a number of geological maps, at a scale of one inch to one mile, and many of their component, uncoloured maps at six inches to one mile, together with a number of memoirs.

The latest phase of systematic work began in the mid-1960s, when the Geological Survey (renamed the Institute of Geological Sciences and subsequently the British Geological Survey) returned to map the Lower Palaeozoic strata on a scale of six inches to one mile (1:10 560), beginning with the Silurian of Denbighshire. The work extended across the Conwy valley on to the Ordovician rocks of Snowdonia, using aerial photographs at a scale of about 1:8000 as base maps. Subsequently, the Bangor, Snowdon, Harlech, Bala and Cadair Idris 1:50 000 geological sheets were published. This work developed from a basic mapping exercise into a multidisciplinary study of the sedimentation and structure, and partic­ularly of the physical and chemical characteristics of the volcanic rocks that form such a dominant element of the Ordovician sequence. Latterly, contracts with the University of Cardiff resulted in the publication of the Aberdaron and Pwllheli sheets.

Following publication of the Denbigh (1970) and Aberystwyth (1984) 1:50 000 geolog­ical sheets, the problems of the Silurian of central Wales have been followed up systemati­cally in a transect from Aberaeron, in the west, through Rhayader into the vicinity of Builth Wells, in the east. Again the approach is multidisciplinary with stratigraphical palaeontology establishing the finest details of the stratigraphy to elucidate the complex structural evolution and the patterns of the depositional environments.

This outline of the history of geological research in Wales is extremely selective, and the omission of many names is inevitable. The reader is referred to recent memoirs (p.209–214) for a fuller bibliography. The work of Howel Williams on Snowdon formed the template for subsequent studies on the Ordovician volcanic rocks. The work of W G Fearnsides, C A Matley and T S Wilson provided a firm basis for further stratigraphical refinement of the Lower Palaeozoic stratigraphy in Merionethshire and south Caernarvonshire. In the second half of the 20th century a notable contributor was R M Shackleton, not least because he was the main catalyst in the work of N Rast, F J Fitch, R Beavon, D Wood and B Roberts. The work of T N George has left an unmistakeable signature in the geological literature of Wales and D Bassett made a lifetime commitment from his PhD research in Talerddig to his role as Director of the National Museum of Wales. Sir Alwyn Williams’ pioneering work on bra­chiopods and Ordovician palaeoecology was founded in the Bala district. The work of J R L Allen and his co-workers on the great swathe of the Devonian, Old Red Sandstone facies through south Wales and the borders has ensured its international recognition. G Kelling and his co-workers of the (former Department of Geology) University College of Wales at Swansea contributed to a clearer understanding of the clastic environments of the Carboniferous of south Wales. In recent years, the work of N H Woodcock and a succes­sion of research students at the University of Cambridge, in the unravelling of the Silurian stratigraphy in central Wales, has been clearly integrated with the work of the survey.

Bibliography

BOSWELL, P G H. 1949. The middle Silurian rocks of north Wales. (London: Edward Arnold.)

COPE, J C W, INGHAM, J K, and RAWSON, P F. 1992. Atlas of palaeogeography and litho-facies. (London: The Geological Society.)

DE LA BECHE, H T. 1866. The geology of south Wales. Memoir of the Geological Survey of Great Britain and Museum of Economic Geology in London, Vol. 3, 1–296.

HARKER, A. 1889. The Bala volcanic rocks of Caernarvonshire. (Cambridge: University Press.)

JONES, O T. 1938. Anniversary address on the evolution of a geosyncline. Quarterly Journal of the Geological Society of London, Vol. 94, lx–cx.

JONES, O T. 1956. The geological evolution of Wales and the adjacent regions. Quarterly Journal of the Geological Society of London, Vol. 111, 323–351.

Mitchell, W I (editor). 2004. The geology of Northern Ireland. Second edition. (W & G Baird Ltd, Antrim: for Geological Survey of Northern Ireland.)

MURCHISON, R I. 1839. The Silurian System. (London: Murray.)

RAMSAY, A C. 1866. On the denudation of south Wales and the adjacent counties of England. Memoir of the Geological Survey of Great Britain and Museum of Economic Geology in London, Vol. 3, 297–335.

RAMSAY, A C, SALTER, J W, and ETHERIDGE, R. 1881. The geology of north Wales. Second edition. Memoir of the Geological Survey of Great Britain. (London: HMSO.)

TRUEMAN, A E. 1924. The species concept in palaeontology. Geological Magazine, Vol. 61, 335–340.