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Natural & Accidental Breakage

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  • Natural & Accidental Breakage


    Several researchers have sought to determine whether natural fractures arising from “trampling” can mimic intentional flaking or retouch. In this context, “trampling” means someone (human or potentially another animal) walking over a flake, whether isolated or in a heap of material. The results are interesting and have important implications for artifact identification since the short answer to the question is “yes”.

    Human Trampling as an Agent of Lithic Artifact Edge Modification

    McBrearty et al published “Tools Underfoot: Human Trampling as an Agent of Lithic Artifact Edge Modification” in American Antiquity vol. 63 no. 1 in 1998 which you can download here:

    The main question she and her co-workers addressed was: “can trampling produce edge damage that mimics deliberate retouch?” Although the question was posed in the context of European Palaeolithic Mousterian (Neanderthal) denticulate knife/scrapers the conclusions are equally valid elsewhere.
    The authors’ main conclusions were that:

    1. Artifact lithic raw material, artefact density and substrate (ie the nature of the ground surface on which the artefacts were laying) all contributed to edge modification to some degree but substrate had the major effect - ie harder surfaces.

    2. Trampling does tranform flakes into “pseudo-tools” to the extent that they can then be “classified” as formal tools using  standard typology.

    Experimental Production of Bending and Radial Flake Fractures and implications for lithic technologies

    Thomas A. Jennings published “Experimental Production of Bending and Radial Flake Fractures and implications for lithic technologies” in the Journal of Archaeological Science in 2011, which you can download here:

    Jennings seeks to answer the question of whether “bending” and radially broken flakes in Paleoindian lithic assemblages can be reliably attributed to intentional tool production as opposed to scavenged flakes from reduction processes. More importantly, he goes on to try and answer the question of whether either of those processes can be distinguished from accidental breakage arising from “trampling”… ie people (or potentially other animals) walking over flakes of stone.

    He compared three sets of flakes which he had produced himself: (a) intentionally fractured by percussion; (b) incidentally fractured, but produced from intentional bifacial reduction of a core; (c) broken by trampling.

    The trampled flakes were produced as follows. Twenty Edwards chert flakes were individually placed on a dry, hardened, silty-clay soil surface and he then simply stepped on each of them. If they broke, he gathered up the fragments for analysis. If they didn’t, he stacked them in piles of three and stepped on them again to simulate “flake-on-flake” trampling as might happen in a pile of lithic debris. Anything with breaks larger than 1cm from the second attempt were also gathered up for analysis.
    His main conclusions were:

    1. Intentional fracturing can be distinguished from incidental fracturing in reduction flakes by the presence of point of impact markers, break angles close to 90 degrees and high percentages of bend and radial breaks.

    2. Fractures from intentional flaking can be distinguished from trampled flakes by their high percentages of radial breaks.

    3. It may not be possible to identify intentional fractures in bifacial reduction flakes which have been severely affected by flake-on-flake trampling.
    Last edited by painshill; 01-28-2016, 09:26 AM.
    I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.

  • #2

    “Starch fracture” is the term used to describe a particular kind of prismatic columnar fracture seen in glassy siliceous rocks such as flints and cherts. It’s so called because it resembles the fractures seen if you mix starch and water into a stiff paste, let it dry and then break it.

    Typical corn starch colonnade (shown inverted), grown with a constant evaporation rate – picture from “Order and disorder in columnar joints” by Lucas Goehring and Stephen W. Morris: Department of Physics, University of Toronto.

    Although fractures of this type are a characteristic of some lithic artefacts (especially blade-flake technology) they are the most common natural feature mistaken for human modification of lithic items. Here’s a typical example:

    Picture from Wellcome Images website.

    Although such fractures do arise from knapping, they are also often the result of frost or extreme temperature change where expansion or expansion/contraction creates enough stress along planes in the rock to cause a long flake to detach.

    Natural fractures of this kind are almost impossible to distinguish from those created by knapping unless an obvious striking platform, bulb or point of percussion aligned to the flake scar is still present. Aligned conchoidal ripples and radial cracks are not in themselves sufficient indications of human modification unless they are strongly enough defined to indicate the use of hard-hammer percussion. Those kinds of shocking indications will also arise from natural detachment caused thermal stress in amorphous, glassy rocks. Naturally detached flakes tend to leave a scar that has more curvature in profile than from knapping, but it’s not a conclusive diagnostic and also depends on the structural nature of the lithic.

    It’s not unusual to find artefacts which have starch fractures with both natural and human origins – the natural ones having been produced after deposition of the artefact. Here’s such an example – scraper, where the planar base and probably the side scars are knapping features but the dorsal scars (in the second picture) are likely a mixture of the two.

    Starch Fractures (natural -and- man-made) – picture from UK Portable Antiquities Scheme website.
    Last edited by painshill; 01-28-2016, 09:27 AM.
    I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.


    • #3

      Strange linear marks on pieces of stone created by glacial movement are sometimes mistakenly believed to be engravings produced by Native Americans.

      It is often incorrectly assumed that glacial scarring can be distinguished by a series of parallel scratches on a flat surface but that’s far from the case. You might find such scratches on a piece of bedrock that was immobile as a glacier passed over it. You might also find them on slabs of rock loosed from the bedrock as a result of the extreme pressures created by the ice. But loose cobbles and smaller broken rock fragments are usually tumbled during glacial movement such that all faces are usually scarred and those scars may criss-cross one another and even form something that could be mistaken for an intentional design.

      Another feature common to cobbles transported by glaciers is they may exhibit what looks like “faceting”, with straight edges created by pressure or frost fracturing which have subsequently rounded off by abrasion. Here’s a typical example:

      Glacial Scratching -and- pseudo-faceted edges on cobble from W Pennsylvania [pic by Callan Bentley]

      Geographic Occurrence

      A counter argument sometimes raised is “but I’m not in a glacial area”. It has to be remembered that when most people think of glaciation, they have in mind the most recent period – generally known as the “Wisconsin Glaciation” or the “Last/Late Glacial Maximum”, which at its extreme around 21,000-25,000 years ago covered these areas of North America:

      The initials C, K and L designate the Cordilleran, Keewatin and Labrador ice sheets. The latter two conjoined, forming the massive Laurentide ice sheet in the high latitudes of central and eastern America with the Cordilleran to the west and an occasional ice-free corridor between them.

      That, however, is not the only glacial event for North America – there were other earlier glaciations for which we don’t know the exact timings or the extent of the ice sheets. Even for the most recent period it’s worth bearing in mind that as the ice retreated, huge quantities of melt-water formed massive lakes with torrential rivers reaching their way to the sea in various places. Those rivers also transported glacial material considerable distances from the edge of the ice sheet.
      Last edited by painshill; 01-28-2016, 09:28 AM.
      I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.


      • #4

        What are Eoliths?

        The term “eolith” derives from the Greek “eos” (“dawn”) and “lithos” (“stone”), so also known as “dawn-stones”. These terms are generally used to describe crudely chipped flint nodules and cobbles which are claimed to be much earlier evidence of humans than conventional archaeology can accept.

        The first such items were collected in Kent in England by the amateur archaeologist Benjamin Harrison in 1885, although the term was coined by J. Allen Browne in 1892 following publication of Harrison’s finds in 1891 by Sir Joseph Prestwich. The term has subsequently been extended to similar items found elsewhere in strata that pre-date the known existence of humans or have improbably early dates.

        Further examples were found in the early 20th Century by J. Reid Moir in East Anglia (England) and in mainland Europe by Aimé Louis Rutot and H. Klaatsch. In part, these finds helped support the “authenticity” of the “hominid” fossil jaw and cranial fragments known as “Piltdown Man” found in 1912 in East Sussex, England. Long considered “suspect”, the fossils were exposed as fakes in 1953.

        Drawings from “On the Discovery of a Palaeolithic Human Skull and Mandible in Flint-Bearing Gravel Overlying the Wealden (Hastings Beds) at Piltdown, Fletching (Sussex)” by Charles Dawson, F.S.A., F.G.S. and Arthur Smith Woodward, LL.D., F.R.S., Secr. G.S.” 1912

        Modern Interpretation

        Eoliths are now generally regarded as having been produced by natural geological processes such as glaciation. The French archaeologist Marcellin Boule first suggested this in 1905 and Samuel Hazzledine Warren provided confirmation from experimental work, published later that year in: “On the origin of “Eolithic” flints by natural causes, especially by the foundering of drifts” in the Journal of the Royal Antrhopological Institute of Great Britain and Ireland.
        Last edited by painshill; 01-28-2016, 09:29 AM.
        I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.