Sunday, April 21, 2013

All Mixed Up: Assessing the Triple Cortex Typology

Hello all,

Full cortex on dorsal side of an Edwards chert spall
 See video here

I was going over a few lithic coding sheets in preparation for upcoming field projects and though I'd check a few things out while making a point for an upcoming test on the blog.  Lithic coding sheets often appear very standardized, issuing group designations based on aggregate analyses and specific attribute analyses.  In following all the steps outlined in our code sheets we become comfortable that we are approaching the collection in an appropriate and meaningful manner, and that our hard work is time well spent in illustrating prehistoric behavioral patterns.  Our education and patience often pays off and lets us discuss patterning in mobility, cost-benefit decisions and different traditions of learning and acting.

Ventral side with no cortex
But, unfortunately our methods aren't always that cut and dry.  Let's have a quick chat about the Triple Cortex Typology.  This method splits an assemblage of flakes into three categories.  primary flakes have lots of cortex on the flake surface (the weathered outside of a stone). secondary flakes have less cortex than primary flakes and tertiary flakes have no cortex and lots of flake removal scars.  This method is used to infer early, middle and late stage flaking.  Some also use it to infer distance from procurement source with varying levels of success.  At this point the lithic analysts reading this are probably thinking "He makes that sound too loose, where are the cortex percentages to separate the categories"?  Well, that's a problem isn't it?  Check out a few publications and CRM coding sheets and you will often find a lack carefully defined measurements and variable percentages to construct each of these categories.  This of course leads to unreproducible data and an inability to compare patterns between studies.  Andrefsky (2005:115-118) discusses this problem in more detail in his book "Lithics: Macroscopic Approaches to Analysis".

Scatter of platform prep flakes

So that's problem number 1, that the method, while potentially helpful is often subjective. Problem number 2 is that flakes that would appear to be primary, secondary and tertiary flakes (ie, early, middle and late stage) may all be produced at the same time.  Often small chips that we would consider to be "resharpening flakes" are created during platform preparation for larger cortical flake removals.  So, While the goal may be a single large cortical flake removal from a biface, a higher volume of smaller flakes has been created in doing so.  This pattern would perhaps lead us to classify a location as a logistical site due to a higher ratio of non-cortical to cortical flakes.  The flakes produced in this case may mask the actual intention of the stone work. 

The Test:

The mixed nature of cortex/non cortex
I decided to collect a subset of flakes made during the production of a projectile point to see for myself how different levels of cortex (to which one might infer "stage") may be created in a mixed manner, rather than the nice linear trend we often read about in texts.  This is something I had noticed before but still like to do to see the variability produced.  Sure enough, the guide flakes and platform prep flakes that must be removed prior to large cortical flake removal are smaller and have little to no cortex.  I'm always a little surprised at the mixed nature of size, shape and cortex that is removed over the course of biface thinning.  Eventually the cortical flakes taper out, although often times they pop back up again when I  start working another margin of the piece.

So...what then.  How do we asses stages of production!? Isn't that a meaningful measure to infer mobility?  Yep, I still believe that understanding how and when individuals decide to further reduce stone is important.  Careful disclosure of what percentage one calls primary and secondary flakes is essential for consistent measures and can offer valuable information regarding where people are choosing to carry out specific parts of stone tool production.  Yet I also see larger importance in attempting this maneuver in a way that accepts the complex nature of flake production, where flake morphology can rarely indicate discrete "stages", but are rather a part of a continuum where multiple morphologies may be produced in a mixed fashion.

Finished dart point

Check out the video to see what I mean.  Flakes of all different cortex measures are created well into the process.  Send me your thoughts as to how we might make better sense of this dilemma.  I have opinions too, don't worry.

For more info on the problems associated with a strict adherence to primary, secondary and tertiary flake stages and distinctions between the types check out:

 Andrefsky Jr., William. 2005. Lithics: Macroscopic Approaches to Analysis. Cambridge Manuals in Archaeology. Cambridge University Press, Cambridge.

Draper, John A and Gordon A. Lothson. 1990. Test excavations at 10NP143 and 10NP292, Lower Clearwater River, West Central Idaho. Project Report 12. Pullman:Center for Northwest Anthropology, Washington State University

Sullivan, Allen P. and Kenneth Rozen. 1985. Debitage analysis and archaeological interpretation. American Antiquity. 50: 755-79



  1. I like how you provide references at the end. Ps, can I get a spacedagger too?

  2. I've noticed that the Triple Cortex classification doesn't lend itself well to archaeological assemblages made from quartz or other lithic materials which occur primarily in veins or beds.

    In Northern Ontario, we often find quartz as a primary lithic material. It is most often found in veins in the bedrock, but occasionally we can find cobbles. People would have broken apart vein quartz or cobbles in search of higher quality, micro- or crypto-crystalline forms of quartz often contained within, using this to make tools.

    Especially with vein quartz, there's no defined cortex, making the use of the triple cortex classification method a little iffy. Unfortunately, since there's a lack of data regarding quartz debitage analysis, we've had to base our classifications off of the flake size and material fineness. Larger, blockier, macrocrystalline flakes are often considered to be "primary" flakes while smaller, finer, micro- or crypto-crystalline flakes are considered to be "tertiary" flakes. We realize there are pretty obvious problems with this classification scheme, but until there are studies done with quartz, we don't have a better alternative.

    I'm hoping to take up flintknapping so I can learn a little more about quartz tool manufacture and get some data to accurately identify lithic reduction sequences. However, there's a reason people around here were using quartz as a tool stone: there's almost no chert! Until I can find some easily accessible chert, I don't think I'll be able to start knapping... :(