Welsh Journals

Silurian Stratigraphy was formed in Birmingham and began to tackle the problem of defining major, globally applicable subdivisions of Series and Stage rank within the Silurian System, and the boundaries between them. By 1984 that work was completed and was presented to ICS in August at the International Geological Congress in Moscow. Following ratification by IUGS, the results were published formally last June (Bassett 1985; Holland 1985). It is appropriate that almost exactly 150 years after Murchison first used the term Silurian, his 'Transition Rocks' should become the first stratigraphical System for which international agreement has been reached on both the upper and lower boundary levels, and on a full set of Series and Stage divisions between those limits. The chronostratigraphical framework for future studies is thus now firmly established. In 1986 a book will be published by the National Museum of Wales that will describe in further detail the global standards and the basis for this correlation, and in 1989 the Silurian Sub-commission will sponsor a second international symposium (in Keele, England) as a means of reviewing progress over the next few years. The occasion should prove to be a fitting celebration of the 150 years since the publication of Murchison's classic volume on the Silurian System. Continuing International Initiatives on the Cambrian System Cambrian rocks crop out on every continent. Just as the System name was launched in 1835 together with the Silurian, so the two were again linked in international recognition when the 23 August meeting in Copenhagen of the 1960 International Geological Congress confirmed the term 'Cambrian' for the lowest System of the Lower Palaeozoic. Modern studies of Cambrian geology can be regarded as beginning with a symposium on 'The Cambrian System, its Palaeogeography and the Problem of its Base' held at the 20th Session of the International Geological Congress in Mexico City in 1956; sponsorship was by ICS and the International Palaeontological Union. At the 1960 Congress there was a sectional meeting on Cambrian (and late Precambrian) stratigraphy, and the idea was first mooted of forming a Subcommission on Cambrian Stratigraphy within ICS. Further steps were taken at an informal meeting connected with the next International Congress in New Delhi in 1964, and later that year the Cambrian Subcommission was 'born'. As with the Silurian, the co-ordination of studies directed towards the establishment of global standards for the Cambrian has now become the major responsibility of the Subcommission. Problems of definition of the base and top of the Cambrian System, and of globally applicable internal subdivisions, continue to be major topics of debate within the Subcommission. In 1981 a second international symposium on the Cambrian was held, in Golden, Colorado, USA, under the auspices of the US Geological Survey as part of the Subcommission programme. Although by 1985 there has been no international agreement on standard Cambrian chronostratigraphical subdivisions and boundaries, intensive studies are under way throughout the world to resolve correlations across different facies and biogeographical realms. Beginning in 1983, the Subcommision instigated a series of correlation charts (published by IUGS) aimed at covering all known outcrop areas, and their production holds great promise for international agreement on standards in the near future. As the bicentenary year of Sedgwick's birth, and 150 years after the introduction of his System, he would surely be well pleased with the continued expansion of Cambrian investigations made through 1985. Acknowledgements. Mr. John Thackray (Geological Museum, London) and Dr. George Sevastopulo (Trinity College, Dublin) kindly provided me with information incorporated in this article. References Bassett, M.G. 1979. 100 years of Ordovician geology. Episodes, 1979(2), 18-21. Bassett, M.G. 1985. Towards a 'common language' in stratigraphy. Episodes, 8(2), 87-92. Clark, J.W. and Hughes, T.Mc. 1980. The life and letters of the Reverend Adam Sedgwick. Cambridge University Press, vol. l:i-x, 1-539; vol. 2: 1-vii, 1-640. Geikie, A. 1875. Life of Sir Roderick I. Murchison. John Murray, London, vol. 1: i-xii, 1-387; vol. 2: i-vi, 1-375. Hardy, P.D. (publisher). 1835. Proceedings of the Fifth Meeting of the British Association for the Advancement of Science, held in Dublin, during the Week from the 10th to the 15th of August, 1835, inclusive. With an Alphabetical List of Members enrolled in Dublin. Dublin, 129 pp. (+ 13 pp.). Holland, C. H. 1985. Series and Stages of the Silurian System. Episodes, 8(2), 101-103.