Adam Sedgwick

Adam Sedgwick (March 22, 1785 – January 27, 1873) was one of the founders of modern geology. He proposed the Devonian period of the geological timescale and later the Cambrian period. The latter proposal was based on work which he did on Welsh rock strata.

Early work

Sedgwick was one of several great figures in what has been called the Heroic Age of geology -- the time when the great geological time periods were defined, and when much exploration and fundamental research was carried out. Sedgwick's work placed him at the epicenter of one of the most heated geological controversies of his day, stemming from his work with the gentleman geologist Roderick Murchison. They explored the geology of Scotland in 1827, and in 1839 they jointly presented their researches on certain rocks in Devon, England, which had a distinctive fossil assemblage that led them to propose a new division of the geological time scale -- the Devonian. In the early 1830s, both men were working on the rocks of Wales, which were and are very difficult to work on due to extensive folding and faulting. However, they seemed to be older than most of the sedimentary rocks farther east. Murchison documented the presence of a distinctive set of fossils, one in which very few fish were found, but that included numerous different types of trilobites, brachiopods, and other such fossils. Murchison named the system of rocks containing such fossils the Silurian, after the Silures, a Celtic tribe living in the Welsh Borderlands at the time of the Romans. Sedgwick, who had been working in central Wales, proposed the existence of a separate system below the Silurian, which he named the Cambrian -- after Cambria, the Latin name for Wales. The two presented a joint paper in 1835, entitled "On the Silurian and Cambrian Systems, exhibiting the order in which the older sedimentary strata succeed each other in England and Wales."

Related Topics:
Roderick Murchison - Geology of Scotland - 1827 - 1839 - Devon - England - Fossil - Devonian - Folding - Faulting - Sedimentary rocks - Trilobites - Brachiopods - Silurian - Cambrian - 1835

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Sedgwick's upper "Cambrian" overlapped with the lower part of Murchison's "Silurian." Sedgwick had defined his "Cambrian" using physical characters of the rocks, which were unique to Wales, and had not relied extensively on fossils, which could be found everywhere. Murchison, who had used fossils extensively in defining the Silurian, claimed at first that the upper Cambrian, and then the entire Cambrian, were really parts of the Silurian. The resulting quarrel between the two men left them permanently estranged and took years to resolve. There was more than a simple matter of names involved. Both geologists wanted the honour of describing the rocks that recorded the beginning of life on Earth, for no fossils were known that were older than those of the Cambrian. Murchison felt that the fossils of Sedgwick's "Cambrian" were not different enough from his "Silurian" forms to merit the naming of a geologic time period, and it was some time before truly distinctive Cambrian fossils were documented. Today, following the solution worked out in 1879 by Sedgwick's colleague Charles Lapworth, geologists use both time periods, with a third one -- the Ordovician, also named for a Celtic tribe in Wales -- between the Cambrian and the Silurian, equivalent to the disputed "upper Cambrian-lower Silurian" beds. Each one of these is now known to be characterized by distinct fossil assemblages.

Related Topics:
Charles Lapworth - Ordovician

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