Geological controversies

Levels of disagreement in the Sedgwick-Murchison controversy

M. J. S. RUD'WICK

SUMMARY The controversy between Adam Sedgwick and graphical), methodological, theoretical and Roderick Murchison about the meaning of metaphysical levels. Their argumentative per- the 'Cambrian' and 'Silurian' systems stemmed sonalities merely accentuated their substantive from differences on the technical (i.e. strati- disagreements.

SCIENTIFIC CONTROVERSY generally takes place on several different levels simul- taneously. In this respect the famous Sedgwick-Murchison controversy is an in- structive case-study. The technical level, as summarized by Thackray (this volume, p. 367) , shows a complex history of ambiguous nomenclature and confused stratigraphical in- terpretation. The existence of an overlap between Sedgwick's "Upper Cambrian" Bala rocks and Murchison's "Lower Silurian" Llandeilo and Caradoc rocks was long concealed from both geologists (a) because Murchison misinterpreted the structure around Llandeilo and therefore inferred at first that his "Silurian" strata lay wholly above the "Cambrian"; (b) because he confused the May Hill sand- stone of "Wenlock" age with the lithologically similar (but palaeontologicaUy distinct) Caradoc sandstones, and therefore at first mistook the palaeontological character of his "Lower Silurian"; and (c) because both geologists farmed out their fossils to palaeontological specialists, and were not at first concerned to define their systems in terms of fossil faunas. The question of such definitions leads from the technical to the methodological level. Both geologists invoked the shade of William Smith (however unhistorically) to justify their stratigraphical procedures. But in Sedgwick's view Smith had always defined his formations primarily on the "sectional evidence" of super- position, and only then in terms of their characteristic fossils, while in Murchi- son's view fossils had been primary for Smith. Sedgwick claimed that he had de- fined "Cambrian" with reference to a clear succession in North Wales. Believing in a gradualistic history of life, he had always anticipated that some of the fossils in the "Silurian" would be found to extend downwards into his "Cambrian": faunal gradation was as much to be expected here as it was between the Silurian, Devonian and Carboniferous; and to alter the meaning of "Cambrian" just be- cause those strata were found to contain some "Silurian" fossils would be to upset the stability of stratigraphical nomenclature and would ultimately involve cir- cular reasoning. Murchison likewise started with a definition based on a concrete succession (hence the geographical derivation of both system names), but gradually shifted to an exclusively faunal definition of what he meant by "Silurian". Given

Jl geol. Soc. Lond. vol. x32, I976, pp. 373-375. Printed in Northern Ireland.

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that criterion, his progressive annexation of Sedgwick's "Upper Cambrian" into his own "Silurian" became logically necessary. The reason for this shift, however, must be sought at the theoretical level. Al- though the term "system" was used loosely at first by both geologists, to mean any mappable series of strata in a given region, its connotation gradually became more precise. Its overtones were those of Linnaeus's term systema naturae; in other words a geological "system" came to be understood as marking an essentially natural period in the history of life. Sedgwick believed that the only true "system" of this kind within the older rocks was the Palaeozoic, since this was separated by striking faunal distinctions from the succeeding Mesozoic; the subordinate divi- sions within the Palaeozoic did not deserve to be termed true "systems", since they manifestly graded faunally into older and newer divisions. On this inter- pretation of the term, Sedgwick argued that it was premature to term either the Cambrian or the Silurian a true natural "system" in the history of life. As already mentioned, he fully expected a faunal gradation between the two, since he be- lieved that faunal changes had generally been gradual, and he had not been con- cerned to define the "Cambrian" palaeontologically. Murchison, on the other hand, was so struck by the distinctiveness of the Silurian fauna, and by its ex- tensive discovery in many other parts of the world, that he asserted ever more strongly that it must represent a true "system" of world-wide validity. In partic- ular, its status as a "system" was confirmed by the fact that it represented a period wholly earlier than any land-plants and almost wholly earlier than any vertebrates. Having shifted to this palaeontological conception of a system, Murchison's absorption of much of the "Cambrian" then became inevitable, as already mentioned, as soon as what he regarded as distinctively "Silurian" fos- sils were discovered in Sedgwick's strata. Yet Murchison's stratigraphical im- perialism did not in fact stop at this point. When Barrande discovered in Bohemia a new and distinctive "Primordial" fauna (the Cambrian of modern geology), lying below all that had hitherto been termed "Silurian," Murchison at once annexed this too to his "Lower Silurian", despite the fact that it was quite dis- tinct in palaeontological character. Murchison was therefore not consistent even with his own overt theoretical commitment. To understand this inconsistency it is necessary to penetrate to an even deeper, metaphysical level. Both geologists shared the same directionalist picture of the history of the Earth and of life, in contradistinction to LyeU's steady-state view. They therefore believed, against Lyell, that it was both legitimate and reasonable to search for geological evidence of a true beginning to the Earth and to life on Earth. More particularly, they both believed that the fossil record could be traced back to yield evidence that life had truly had an origin within geological time. This gave the earlier Palaeozoic strata a peculiar importance. They termed the oldest known rocks "Hypozoic" or "Azoic" (i.e. 'below life', or 'without life'), and Sedgwick wanted eirenically to avoid the Cambrian-Silurian dispute by terming those strata collectively "Protozoic" (i.e. 'first life'). Sedgwickwas con- tent if clear evidence of life's origin could be demonstrated somewhere within the "Protozoic", and it was of less importance to him whether the earliest fossils of all were termed "Cambrian" or "Silurian". But Murchison ardently desired

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the distinction of having described the "system" which was not only anterior to land-plant and vertebrate life, but which could be shown to be the veryfirst "sys- tem" in the whole history of life. Barrande's "Primordial" therefore could not be allowed by Murchison as a possible palaeontological basis for Sedgwick's "Cam- brian" (as it was later to become) ; it too had to be annexed to his "Silurian" in order to keep the origin of life itself within that "system". But the reason for this fervent concern with the geological evidence for the origin of life can only be found in its metaphysical implications. The establishment of this crucial episode within a directionalist reconstruction of Earth-history served to refute the eternal- istic implications of a steady-state reconstruction. Life itself therefore could not be held to be self-explanatory or self-sufficient; and the highest manifestations of lifemthe moral, aesthetic and social consciousness of Manmcould not be sub- jected to a crude reductionism, but required explanation in terms of a doctrine of creation. At this deepest level Sedgwick and Murchison were united: both of them --though Sedgwick more articulatelymfeared the moral and social consequences of a "materialist" philosophy which, by claiming the self-explanatory nature of life, would end by denying the authenticity of distinctively human experience. Lastly, acting on all the four levels of controversy that have been distinguished here, there was the powerful personal factor. Both Sedgwick and Murchison were disputatious by temperament, and doubtless became progressively more obstinate with old age. But their informal letters indicate that while Sedgwick was funda- mentally good-natured about the dispute, and prepared to go far towards a peace- ful settlement, Murchison's well-known propensity for turning every scientific disagreement into a para-military "campaign" here surpassed itself. His capacity for ambition and self-aggrandisement was an embarrassment even to his con- temporaries. His refusal to admit to any stratigraphical errors, for fear they would damage his chances of scientific and social honours, was later coupled with a ruthless use of his position as Director of the Geological Survey to enforce his view of the dispute on all official geological publications. But both geologists, it is fair to add, were truly men of their own time: their disputatious tendencies mirrored an exceptionally litigious society, in which the social norms of competitive in- dividualism lent peculiar acrimony to scientific disputes. Bibliography Neither Murchison nor Sedgwick, nor the controversy between them, has yet been the subject of full-scale research at modern standards of historical scholarship. Instead of a fuU bibliography for this paper, I give references below to some of my own articles where fuller references can be found. Rtmwxez, M. J. S. 1971. Uniformity and progression: reflections on the structure of geological theory in the age of LyeU. In Duane H. D. Roller (ed.) Perspectives in the History of Sciente and Technoloeoy. Norman, Oklahoma, 209-27. 1974. Roderick Impey Murchison. Dict. Sci. Biog. 9, 582-5. 1975. Adam Sedgwick. Dict. Sci. Biog. 12, 275-9. Read at 'Geological controversies' meeting on 18 October 1972. MARTIN J. S. RUDWICK, Unit for History and Social Aspects of Science, Vrije Universiteit, De Boelelaan 1083, Amsterdam, The Netherlands.

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