As an infant science, geology left him plenty of room for invention, and maybe for objectivity as well. His self-taught geology and enjoyment of a free life led him eventually to ramble around Wales, where he described the lowest, oldest series of sedimentary rocks he could find, and called them Cambrian.
Where Sedgwick focused on the physical nature of the rocks – we’d call that petrology and lithology today – Murchison focused more on the fossils in them. Sedgwick defined the Cambrian from its position low in the section and from its rock types, while Murchison defined strata in South Wales based on their fossils. He called that package of rock the Silurian, for an ancient Celtic tribe who lived in South Wales, the Silures. All well and good.
Murchison and Sedgwick teamed up to work in Devonshire and Cornwall, jointly announcing the Devonian Period in 1839. This was a controversy of its own, which we’ll talk about at the appropriate time… but as the friends continued to extend their work on their other units, the Cambrian and Silurian, problems developed. Sedgwick was increasingly plagued by health problems while Murchison actively extended his Silurian System.
It became evident to Murchison that some of Sedgwick’s Cambrian rocks actually contained fossils that should be classified as Silurian, so he extended his Silurian formation lower and lower in the section, taking up more and more of the Cambrian. This upset Sedgwick, although he had tacitly—or, he said later, inadvertently—approved the extension, and sometimes he denied the whole thing in harsh terms. The friendship was at an end, and the controversy pervaded British geology for the next 40 years. Everyone chose one side or the other, but on the whole Murchison’s later career was far more successful than Sedgwick’s. Murchison was knighted, and he became director of the British Geological Survey. Sedgwick, in declining health, kept a professorship, but seems to have been relegated to a by-way in British geology.
Both Sedgwick and Murchison died before their controversy was settled. It fell to English geologist Charles Lapworth to study the Cambrian and Silurian strata and to propose that it was necessary to include another time period there, embracing parts of Sedwick’s Cambrian and parts of Murchison’s Silurian. He called it the Ordovician, and we’ll be there in a couple days.
—Richard I. Gibson
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