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Snails from a midden

March 18, 2011

Below are some pictures of snails from a sample taken from a midden deposit at the site of Cladh Hallan on South Uist in the Outer Hebrides.

At this stage, I am separating the first group I want to look at from the assemblage.

Separating snails from the sample

The group I’m looking at belong to the genus Cochlicopa, which is common throughout the British Isles. There may be two species here, Cochlicopa lubrica and C. lubricella.

Cochlicopa shells

The exciting part for me is the other species left to look at in the dish though. This sample has not only an unusually high number of shells in it (there is another dish the same size from this sample), but also a lot of different species. In this context, the high number of species is quite likely to reflect a long period of relative ground surface stability. Organic waste in the midden will also have been very attractive to snails, especially the tiny Vertigo species, meaning the midden would have provided a refuge where snail populations can flourish.

The rest of the snails

Vertigo shells

6 Comments leave one →
  1. John permalink
    March 19, 2011 1:30 am

    There’s ongoing debate in the world of Texas archaeology about how to deal with land snails during excavations. Some people insist on collecting every specimen, others just do a count, and some just say they were observed (and might distinguish between a couple of different species).
    From my perspective, I can understand a geomorphologist or paleoecologist collecting snail columns and samples, because of what changes in snails can say about the environment during the site occupations. In addition, my own observations at several sites in Texas suggest that rabdotus increase particularly in levels with dense cultural deposits, and I’m pretty sure this is also a common perception, related to your mention of snails being attracted to organic waste.
    However, there are some who suggest that snails were used as food, and were intentionally harvested and represent artifacts similar to mussel shell or animal bone. Some have even collected land snail samples for dating when radiocarbon samples aren’t available, under this assumption.
    I don’t know if I have a question, per se. More just a view of different ways that land snails are thought of in Texas archaeological sites.

    • matthewlaw permalink*
      March 21, 2011 8:48 am

      Thanks so much for that John. It’s nice to hear how people deal with snails on excavations in other parts of the world. There’s quite a bit of work done on dating snails using radiocarbon (which can be problematic as the snails take in old carbonate from the bedrock to build their shells, occasionally giving rise to dates that are far too old), and also amino-acid racemization and uranium series dating). Introduced species can be useful for relative dating too if you know when they were introduced.

      I don’t think theres really a consensus on what to do with snails in British archaeology either, especially not the larger ones that you’d be more likely to see in an excavation, as these tend to have relatively low usefulness as palaeoecological indicators. Personally I think its best to collect in the field and then let an environmental archaeologist make the call whether to discard, keep or analyse the snail post-excavation. I’d be interested to know what others think.

      • John permalink
        March 22, 2011 4:15 am

        I believe that amino-acid racemization is what is generally done (when the money is available), but that’s a bit above my pay grade right now.
        As for collecting the samples, I would certainly agree with you. However, I’m sure you’re also aware (since you do contract) of budgetary constraints when it comes to certain types of expert scientific analysis, as well as issues involving curation. Ultimately, I suppose the ideal would be to have someone on staff with a specialty in environmental archaeology who can also function as a general project archaeologist.

  2. March 20, 2011 8:59 pm

    In ancient china tortoise shells were used for divination; therefor the large number of shells probably represent some form of ‘ritual’; QED.
    Can I be a Professor of Archaeology now?

    • matthewlaw permalink*
      March 21, 2011 8:39 am

      I’m sure the job offer’s in the post right now Geoff 🙂

  3. December 15, 2011 6:06 pm

    Thats an all ’round amazing post!

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