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Earthworm Activity and Archaeological Stratigraphy

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Earthworm Activity and Archaeological Stratigraphy: A Review of Products and ProcessesIntroductionGeneral Biology of EarthwormsEarthworm Effects on ArchaeologyMaking burrowsFigure 1Figure 2Figure 4Figure 5Figure 7Figure 3Casting and burying findsFigure 6Destroying buried soilsTaking stones and seeds undergroundFigure 8Making cairnsFigure 9Making granulesFigure 10Figure 11Figure 12Figure 13Figure 14Figure 15Summary(1) Making burrows(2) Casting and burying finds(3) Destroying buried soils(4) Taking stones and seeds underground(5) Making cairns(6) Making granulesAcknowledgementsReferencesJournal of Archaeological Science (2003) 30, 135–148doi:10.1006/jasc.2001.0770Earthworm Activity and Archaeological Stratigraphy:A Review of Products and ProcessesM. G. Canti*Ancient Monuments Laboratory, Centre for Archaeology, Fort Cumberland, Eastney, PO4 9LD, U.K.(Received 14 June 2001, revised manuscript accepted 22 October 2001)The activity of earthworms has long been understood to have significant effects on archaeological stratigraphy, butmany of the details have not been fully grasped by stratigraphers or by the specialists who advise them. Althoughworms are widely known to cause the burial of finds due to surface casting, some of their other activities are lesscommonly recorded. Amongst these, their active burial of stones and seeds, their building of cairns, and theirproduction of calcium carbonate granules have mostly not been studied in any detail, and have been little exploitedfrom an interpretative point of view. This paper reviews the existing knowledge as well as presenting some recentresearch carried out into various aspects of worm actions and their relationship to taphonomy. 2002 Elsevier Science Ltd. All rights reserved.Keywords: EARTHWORM, SITE FORMATION PROCESSES, TAPHONOMY, BIOTURBATION,GRANULES, BURROWS.IntroductionHowever lofty its ideals, archaeology is still asubject that is actually carried out in the realmof earthworms. Their burrows and galleriesform and reform the matrix surrounding the hardermaterials from which we deduce whole cultures. Theiractivities push it, sort it, digest it and finally cast it,usually close to where it came from (hence we still havea subject to study), but sometimes further away. Whythen, are their effects so poorly understood by almostall branches of archaeology? Is it from fear of findingthe worst, of finding out just how destructive wormaction is? Or perhaps it stems from the distress thatmany feel on seeing their decimation during digging?Probably the answer lies in the more mundane expla-nation identified for many years by naturalists andphilosophers—they are simply too small. GilbertWhite wrote in his Natural History and Antiquities ofSelborne:‘‘The most insignificant insects and reptiles are of muchmore consequence, and have much more influence in theeconomy of Nature, than the incurious are aware of; andare mighty in their effect, from their minuteness, whichrenders them less an object of attention; and from theirnumbers and fecundity. Earth-worms, though in appear-ance a small and despicable link in the Chain of Nature,yet, if lost, would make a lamentable chasm.’’This unwarranted insignificance, seen by White asunderpinning a general failure to appreciate earth-worms’ importance, is compounded by the difficulty ofcomprehensing their slowness of action. Although weare mentally well equipped to deal with this problemtoday, in Charles Darwin’s time it was harder forpeople to see the accumulated effects that he realisedwere central to soil formation. Darwin’s (1840) paperessentially proposed that all stoneless mull topsoils (i.e.the common topsoils where the humus and mineralmaterials are thoroughly mixed) resulted from therepeated casting of earthworms gradually building up afine surface layer. Not everyone believed him. Onreading one of Darwin’s examples, Mr Fish,intheGardeners’ Chronicle of 17 April 1869 wrote:‘‘Considering their weakness, and their size, the work theyare represented to have done is stupendous . . . lifting4 inches of earth in so short a period . . . staggers one by itsmagnitude. . . . This case, like vaulting ambition, carriesone over to the other side, and instead of confirming ourfaith in the labour power of worms, tends to destroy it.’’Darwin was stung enough to use his book on thesubject (Darwin, 1881: 5) to dismiss Fish with thewords:‘‘Here we have an instance of that inability to sum upthe effects of a recurrent cause, which has often retardedthe progress of science, as formerly in the case of geology,and more recently in the principle of evolution.’’Perhaps there is a bit of Fish in us all, a tendency toclose our eyes to real processes and hope that sites aresimply fossilized. Much of the mechanics of wormaction was clearly described over forty years ago inAtkinson’s (1957) paper on the subject, yet, since then,surprisingly few people have taken on board anything*E-mail: [email protected]–4403/03/$-see front matter  2002 Elsevier Science Ltd. All rights reserved.more than the concept that there is some worm distur-bance at some sites. We know a little more now thanAtkinson did, but the additional complexity has ledonly to further field arguments and more widespreadsite myths. This paper attempts to rectify the problemby describing earthworm processes and products, aswell as exploring the long term results of their range ofactivities.General Biology of EarthwormsThere are around 3000 species of earthworm in theworld. The greatest variety is found in tropical soilswith progressively smaller numbers of species furthernorth. Thus, in France there are about 180 species(Bouche´, 1972) and in the U.K. about 25 (Sims &Gerard, 1985). Apart from size variations, most specieslook physically similar to the untrained eye. Some canbe distinguished in the field, others require microscopicexamination.Earthworms live either in the leaf litter layer or inburrows in the mineral soil, and eat almost all forms oforganic matter. They are cold-blooded and breathethrough their skin, both characteristics which makethem vulnerable to sudden environmental change.Although possessing no eyes, they are light sensitivethrough photoreceptors mainly at the head end. Thiscan be observed by taking a torch on to a lawn onwarm moist evenings after dark, where worms will beseen lying on the surface with their rear end still in theground (see Figure 1). After one or two


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