SEDGWICK, ADAM (b. Dent, Yorkshire, England, 22 March 1785; d. Cambridge, England, 27 January 1873), geology.

    skill as a field geologist in the first clear analysis of the effects of diagenesis and low-grade metamorphism. In particular, his exposition of the distinction between stratification, jointing, and slaty cleavage provided the crucial technical key for the interpretation of the structure of regions with complex folding.

This had already enabled him, as early as 1832, to discover the essential structure and succession of the ancient rocks of North Wales (on his first expedition there, in 1831, he gave Charles Darwin his first training as a field geologist). In the same years Murchison was studying apparently younger “Transition” strata in the Welsh Borderland. During their first and only joint study (1834) of the relation between their two areas, Murchison assured Sedgwick that his strata (later termed “Silurian”) lay wholly above Sedgwick's “Cambrian” (so named in 1835), although there was clear -- and not unexpected -- faunal similarity between Murchison's Lower Silurian strata and Sedgwick's Upper Cambrian Bala series.

Their collaboration continued fruitfully in their solution of the anomalous problem of the slaty rocks of Devonshire, where De La Beche's discovery of Carboniferous plants in rocks of ancient appearance had seemed for a time to threaten the validity of both Murchison's and Sedgwick's stratigraphy. They worked closely in discovering first that the anomalous fossils had come from a syncline of slaty rocks of Carboniferous age, and then that the older rocks in the region were not Silurian or Cambrian but the lateral equivalents of the Old Red Sandstone, which they termed “Devonian.” This interpretation was confirmed by a joint expedition to the Continent in 1839.

Sedgwick then turned his attention back to the problem of the Cambrian strata in Wales, as part of a larger program for a synoptic work (never completed) on all the Paleozoic strata of Britain. Although he could not point to a Cambrian fauna as distinctive as Murchison's Silurian fauna, he rightly emphasized that the vast thickness of the Cambrian strata and the apparent beginning of the fossil record within them justified their status as a “system” of comparable importance. Indeed, he underlined their theoretical significance by including them with the Silurian in a broader category of “Protozoic.” He was therefore disconcerted and eventually exasperated when Murchison claimed that the upper (and fossiliferous) part of his Cambrian was nothing other than Murchison's Lower Silurian. Murchison gradually extended this claim until he had annexed virtually the whole of the Cambrian and reduced it to a synonym of Lower Silurian.

Sedgwick later was angered by what he regarded as editorial tampering with a crucial paper on the subject submitted to the Geological Society. His stratigraphical nomenclature was altered, apparently in the interests of editorial uniformity, and possibly in innocence of the massive theoretical and personal implications. Reacting with characteristic vehemence, he later broke off all dealings with the Society.

Only gradually did Sedgwick detect the root cause of the controversy. Murchison earlier had misinterpreted the order of succession of his Lower Silurian strata in their type area, so that they were not in fact younger than Sedgwick's Upper Cambrian Bala series, but of the same age. Even more seriously, Sedgwick found in 1854 that Murchison had confused some Upper Silurian strata (May Hill sandstone) with these much earlier Lower Silurian strata (Caradoc series), thus giving the Silurian faunas a spurious uniformity down into Sedgwick's Upper Cambrian.

But Murchison naturally was reluctant to admit these errors, and his position as head of the Geological Survey (from 1855) allowed him to retain his interpretation in all the Survey's official publications. What had begun as a controversy with important implications for the understanding of the earliest part of the fossil record gradually degenerated into a priority dispute between two equally obstinate old men. The conflict was not settled until much later, when the discovery of earlier faunas in Wales rehabilitated the term Cambrian for what had been Sedgwick's Lower Cambrian; and an “Ordovician” system was proposed irenically for the disputed strata (that is, Sedgwick's “Upper Cambrian” and Murchison's “Lower Silurian”) between the newly restricted Cambrian and Silurian systems.

The Geological Society acknowledged the outstanding value of Sedgwick's work in 1850 (before he was estranged from it) by awarding him their highest honor, the Wollaston Medal; and in 1863 the Royal Society, to which he had been elected in 1830, awarded him the Copley Medal.

Sedgwick was seventy-four when Darwin's Origin of Species was published, but his rejection of his pupil's evolutionary theory was not simply a consequence of old age. Thirty years earlier, while welcoming naturalistic explanations for geological events (including those responsible for “diluvial” deposits), he had felt that no purely natural mechanism could ever account for the origin of new organic