Discovery:
Devonian Controversy

This controversy concerns the discovery of what we now call the Devonian period in geological history. The name comes from Devon, in England, where the strata that came to typify the Devonian sequence were first identified. This discovery grew out of an often acrimonious set of negotiations among at least ten major participants (Rudwick, 1985). In the interests of simplification, we will stick to a few main characters and a sub-set of the full story. Roderick Murchison was a gentleman who had taken up geology because it afforded him a respectable hobby that could be combined with the pleasure he took in hunting. His mentor was another gentleman geologist, Adam Sedgwick, a respected president of the prestigious Geological Society. Murchison succeeded him in that post. One of the controversies in the geology of the 1830s concerned the relative importance of two methods for dating strata: fossils and rock types. Murchison, who did his fieldwork in the Yorkshire, became impressed with the heuristic value of using fossils to date strata. In contrast, Henry De la Beche, secretary of the Geological Society under Murchison in 1831, tended to favor rocks over fossils. As of 1831, younger and more recent strata were relatively well understood, but below the Carboniferous group was a large, undifferentiated area known as the Greywacke, the upper part of which was an area of "Transition limestone". Between the two was an area known as the "Old Red Sandstone" . In 1831 Murchison had a Eureka insight when he found a place where the Transition passed conformably into the Old Red. Actually, the Eureka was a myth--Murchison and at least one other geologist had observed this phenomenon before. Successful discoverers are also good at myth-making. By 1834, Murchison had developed a hypothesis: that the Old Red Sandstone was divided into three parts, the middle of which had fish, but no plants; below that, the Transition also had sea fossils, but most of the Greywacke below had none. This hypothesis had economic implications in the search for coal, which--if Murchison were right--had to exist above the Old Red. What appeared obvious in one area of England might look entirely different in another. When De la Beche did a survey in Devonshire in 1834, he found evidence to accord with his presuppositions--that fossil plants existed throughout the Greywacke, and therefore coal could be found in Greywacke as well. Murchison and De la Beche had been sparring in letters already, but now the controversy broke into the open at a meeting of the Geological Society in December of 1834. Essentially, Murchison focused on fossils--if De la Beche had found Carboniferous fossils, then he had Carboniferous strata. De la Beche, who had actually studied the rocks, felt they looked like Greywacke. Indeed, he wrote a letter to another geologist in which he depicted himself confronting Murchison and his colleagues and, pointing to his nose, announcing, "This, Gentlemen, is my Nose ", to which they responded: "My dear fellow--your account of yourself generally may be very well, but as we have classed you, before we saw you, among men without noses, you cannot possibly have a nose (Rudwick, 1985, p. 104). De la Beche initially won Sedgwick's support, in part on the grounds that Murchison had found no distinctive Greywacke fossils and therefore his case hung on the absence of fossils, rather than on the presence of a distinct variety. Murchison then back-tracked a bit, claiming there were distinct fossil plants in the Old Red, although they were too poorly preserved for clear identification. In 1835, Murchison, working in his Welsh Borderland area, labeled his Transition strata Silurian and confirmed that they contained no plant fossils. He also found a place where De la Beche had mistakenly applied the label Greywacke to Carboniferous coal-bearing strata. This piece of evidence was crucial in converting De la Beche's chief backer, Sedgwick, who now adopted Murchison's view. While Murchison was discovering the Silurian system, Sedgwick was discovering the even older Cambrian system. Murchison referred to these groups of strata as systems because he was convinced that they were general and could be found anywhere in the world where erosion, eruption or other local disruptions had not erased them. In July of 1836, Murchison and Sedgwick 'invaded' De la Beche's home ground, North Devon. They had hoped to find evidence of a discontinuity from the Carboniferous coal-bearing strata to the older Greywacke, caused by the way the strata were folded and had eroded. Instead, they found support for De la Beche's claim that there was a gradual transition. Despite the puzzling lack of an obvious disontinuity, they hypothesized a great trough of Carboniferous coal measures in the center of North Devon, which made an abrupt, unconformable transition to Silurian on the north side and Cambrian on the south.. In August of 1836, they presented their findings at a meeting of the British Association in Bristol. By the time of the meeting, Murchison had added a fourth band, or system, of strata, which he labeled 'Devonian'; on his map, these Devonian strata appeared between the Silurian and Cambrian systems north of the great Carboniferous trough in Devon. Sedgwick re-labeled these strata 'Upper Cambrian'. At this point, Murchison and Sedgqick obviously feltthere was something different about this transition from Silurian to Cambrian, but they weren't sure what. Figure 4 [Rudwick, Fig. 7.6, p. 164] compares the Sedgwick-Murchison hypothesis to De la Beche's.

De la Beche was given an opportunity to respond at the meeting. "I was taken most deucedly in the flank, my ammunition being in my magazines, and my guns dismantled, expecting nothing but peace, I made my retreat in the best manner I could" (Rudwick, 1985, p. 166). He conceded the plausibility of the Murchison-Sedgwick re-interpretation of the north Devon strata, but argued that there was nowhere any evidence of the unconformity that should have been observed. Later, he objected to this 'slapdash' introduction of new systems into Devon by geologists who had not studied the rock as carefully as he had. He was the one professional geologist in this group, hired to do the survey--his job was on the line, as well as his reputation. Then a local geologist in Devon discovered plant fossils in strata Murchison and Sedgwick had labeled Lower Silurian. Murchison had claimed there would be no plant fossils this far down. He resolved this apparent anomaly by re-classifying these Silurian strata as Old Red Sandstone. Sedgwick laughed-off this interpretation and chided Murchison for relying too heavily on fossils. Though both authors agreed that De la Beche's hypothesis was wrong--and by this time, even De la Beche agreed it needed modification--they could no longer agree on all the details of their own hypothesis. The sticky problem of the missing unconformity remained unresolved. Fossils from the strata in contention showed strong parallels with the Carboniferous but with some additional, new fossils, none of which were from the Silurian. Nor did these fossils seem characteristic of the few that had been found in the Old Red. These fossils were found by Austen, one of the large group of talented amateur geologists who entered the controversy, and were identified by fossil specialists in London. In other words, a broadening network of actors was playing a role in this controversy, which was featured prominently in William Whewell's Presidential address to the Geological Society in February of 1838. That summer, Sedgwick read a paper which focused primarily on his Cambrian system, which had few fossils, therefore making a correlation across regions particularly difficult. Sedgwick conceded that there was no unconformity in North Devon, which meant post-Cambrian and post-Silurian strata had to go down much farther than either he or Murchison had proposed previously. Sedgwick still claimed that the bulk of the strata of Devon were upper Cambrian, but only in one location in Cornwall was he absolutely sure, and from that location he derived a few fossils characteristic of the Cambrian. In a subsequent field trip, he found these characteristic fossils in other places he had identified as Cambrian, but also ones characteristic of later periods.

Shortly afterwards, Murchison published his magnum opus on the Silurian System; towards the end, he speculated that the Old Red Sandstone might be a system like the Silurian, which could be found all over the globe. As yet there were no characteristic fossils. No coincidence, De la Beche published the report of his survey shortly afterwards, and criticized the idea that local arrangments of geological strata represented systems valid globally. Furthermore, fossils were as local as strata, in the sense that a species that flourished at one time in England might flourish under the same conditions centuries or even epochs later in another part of the world. For De la Beche, the fact that species characteristic of the Carboniferous appeared in rocks he labeled Greywacke did not mean these were more recent strata; it simply meant that these species had prospered at a different time in Devon than elsewhere. Murchison had paved the way for a solution to the Devonian problem with his suggestion that the Old Red might be a system. Perhaps the questionable strata in Devonshire belonged to the Old Red. However, this new hypothesis meant making three major concessions to De la Beche: 1) There was no unconformity below the Carboniferous in Devon; instead, Carboniferous passed conformably into Old Red. 2) The fossils in the proposed Old Red in Devon were not identical to those found in the Old Red elsewhere, which meant that Murchison would have to agree that fossil evidence was not totally reliable, that there were important local variations which could make using the fossil record problematic. 3) De la Beche had even hinted that there might be Old Red sandstone in Devon, although his overall interpretation of their place and role differed from Murchison's. Finally, there was another problem. Sedgwick objected to this Old Red idea because it corresponded to strata he had labeled Cambrian--the amount of Cambrian in England was shrinking, and with it the possibility of finding more than a handful of distinctive fossils so it could be extended world-wide, like the Silurian. Murchison persuaded Sedgwick to adopt this new hypothesis and the two published a paper written by Murchison in the Philosophical Magazine. Instead of conceding his debt to De la Beche, Murchison attacked him for using parts of their re-analysis of Devon without giving him credit--and then appropriated some of De la Beche's views as if they had been his own! Specifically, Murchison pointed-out that he and Sedgwick had discovered the coal- measures trough in central Devon, but also claimed they noticed how it passed conformably into strata below, giving De la Beche no credit for this discovery. Then Murchison made a classic rhetorical move. He gave the widely-recognized fossil specialist William Lonsdale credit for realizing that "the South Devon rocks would be found to occupy an intermediate place between the carboniferous and Silurian systems" (Rudwick, 1985, p. 283). Indeed, Murchison chastised himself for not reaching the obvious solution sooner, and claimed he had relied too heavily on the character of the rocks and not enough on the fossils! This was a total rewrite of the actual history of the controversy to make it appear that the solution had been obvious all along and that it was really proposed by an authority outside of the controversy. The end of the article proposed a new Devonian system equivalent to the Old Red Sandstone that lay between Carboniferous and Silurian. Murchison conveniently glossed over many of the remaining difficulties, including the fact that there were no clear Silurian strata under the new Devonian system in Devon, nor did the new system have any truly characteristic fossils. The article was a brilliant polemic. Murchison canvassed members of the Geological Society shortly afterwards, and happily concluded that if De la Beche attempted an angry rejoinder, "we have enough powder and shot in our tumbrils to sink him" (Rudwick, 1985, p. 287). Murchison eventually apologized for some of his more pointed remarks, but made no concessions regarding the new system, which he now traced to an even more respected elder, the fossil specialist William Smith. Murchison had now placed himself firmly 'on the shoulders of giants', to adopt Newton's felicitous phrase. He conveniently ignored the contributions of lesser, Devon geologists like Robert Austen who provided much of the fossil evidence. The leading participants began to reach a consensus on this new point of view--even De la Beche concede the Devonian hypothesis had merit, especially as he felt the new synthesis vindicated some of his earlier views. But consensus was by no means universal, and could only be achieved by looking for the Devonian elsewhere. Murchison and Sedgwick traveled to the continent, where they were assisted by able European colleagues. "In the course of their long expedition, Murchison had turned most of the ancient Greywacke of the Rhineland into Devonian, only to find himself forced by the fossil evidence to turn much of it back into Silurian, leaving his confidence in the Devonian precarious if not collapsed. Sedgwick has seen his potential Cambrian annexed by the Devonian but later at least partially restored. He had totally lost confidence in the Devonian interpretation, of which he had been the nominal co-author only six months earlier. But whatever their differences, it would have been clear to both geologists that their best hope of resolving the Devonian problem, after almost five years of controversy, lay packed inside the boxes they had been sending back to London" (Rudwick, 1985, p. 329). The newly discovered Devonian system was now on its deathbed--Sedgwick renounced it, Murchison had doubts, and others would soon follow. But Lonsdale and the other fossil experts showed that there was indeed a unique, intermediate group of fossils--that some of what Murchison and Sedgwick thought was Silurian was in fact Devonian. The difficulty was that there were Silurian fossils in the Devonian strata, in addition to other new fossils that promised to be characteristic of this system. Even with this evidence, Murchison had to work hard to persuade others. He took the campaign to Russia, where he found further evidence of the three systems and found evidence for a fourth, Permian system. Who discovered the Devonian? Clearly Murchison became its champion, the one who really persuaded others that it was a system--indeed, the one most responsible for the widespread adoption of the idea of a geological system. But if one asks who first found the evidence that pointed towards a new set of strata in Devon, then the picture becomes more complex: Lonsdale, Austen, Sedgwick and even De la Beche can be said to share part of the glory. In particular, after Lonsdale's fossil analysis resurrected the Devonian, geologists moved quickly to give him credit for discovering the system. Murchison and Sedgwick had to mount a counterattack to salvage their own claims, showing that not just fossils but field evidence played an essential to establishing the Devonian. The point is, the Devonian emerged out of a complex set of negotiations involving a number of actors. In contrast, the Silurian was more clearly a Murchison discovery and the Cambrian more clearly attributable to Sedgwick.

Discovery: Devonian Controversy

Discovery:
Devonian Controversy