Welsh Journals

'Transition Rocks and Grauwacke' — The Silurian and Cambrian Systems through 150 years Michael G. Bassett The terms Silurian and Cambrian were first published in a geological sense in 1835. This article (a reprint with minor emendations of an article in the December 1985 issue of Episodes: International Geoscience Newsmagazine) reviews the historical background to the concept and early application of these stratigraphical divisions, and their international status after 150 years of development. The author, Dr. Michael G. Bassett, Keeper of Geology at the National Museum of Wales, was Secretary-General of the International Commission on Stratigraphy within the International Union of Geological Sciences from 1976 to 1984. Dublin, Ireland, was the setting for the fifth annual meeting of the British Association for the Advancement of Science in August 1835. On Friday, August 14th, the Reverend Professor Adam Sedgwick and Mr. Roderick Impey Murchison (Figs. 1, 2) read a communication to the final session of the Geology and Geography Section entitled 'On Fig. 1 Adam Sedgwick (1785-1873) aged 47. the Silurian and Cambrian Systems, exhibiting the order in which the older Sedimentary Strata succeed each other in England and Wales'. Sedgwick read the details of the Cambrian rocks as established by his research, whilst Murchison discussed the basis for his Silurian stratigraphy; this presentation, by the seemingly unlikely combination of a Cambridge University professor/clergyman and an ex-soldier turned amateur geologist, was the first announcement at a formal scientific meeting of the terminology and relationships of the major stratigraphical units that were to become accepted universally as the lower and upper divisions of System rank within the Lower Palaeozoic rocks. The official proceedings of the Dublin meeting were not published until 1836, but two separate reports appeared in 1835, the first being privately printed in Dublin in September (Hardy 1835; see also Morrell & Thackray 1981, p. 185), and the second distributed to a wider scientific audience in the Fig. 2 Roderick Murchison (1792-1871) probably aged 55