Saturday, May 10, 2008

On the Importance of Being Precise

Yesterday I posted some of our preliminary results from the surface collection of one of the fields south of Port Tobacco. I've provided an updated version of yesterday's map, this one including the topography of the field, and I've done so to make a point.

When collecting artifacts from a field, it is a simple matter to walk back and forth, collect whatever can be seen, and then list those objects and try to determine their significance. That isn't the way the Port Tobacco team does it. We use a total station (a surveyor's instrument) to map in each oyster shell, potsherd, and stone flake. Not only do we note the object's exact location relative to our site datum (an arbitrary point from which all measurements are taken), we also note its relative elevation.

We use those elevation points to construct a topographic map of the field. With the resulting contours, we can see how the artifacts relate to such landforms as steep slopes. Note the series of oyster shells in the southern part of the southernmost field (the 'Mixed Scatter')...they lie at the foot of a steep slope, which suggests that they have been washed down hill. They may represent an archaeological site, but that site likely lies at the top of the slope in an area now wooded.

The historic site in the northeastern corner of the fields occupies a gentler slope, but even much of that material may have eroded down slope from a site that is situated beyond the field edge and into the woods.

The prehistoric sites occupy a relatively level area, just above a low-lying area to the south, an area devoid of artifacts. What the map does not show, because our measurements were confined to the cultivated field, is the wood edge some 20 ft beyond, and the top of the steep, wooded slope above the extensive marshes bordering the Port Tobacco River. Observe the linear alignment of prehistoric artifacts in the area designated 'Prehistoric Sites.' Those prehistoric sites appear to have been located with reference to the banks of the ancient Port Tobacco River before it shifted westward and before the marshes formed.

Accurate, precise mapping of artifacts is critical to the conduct of modern archaeology. The days of collecting objects and noting which field they are from, or what corner of which field, are over. We need to know precisely where a site is so we do not waste scarce resources at more intensive levels of investigation. And, if we are to call one cluster of material a site and not another cluster, or if we are to date a site to one period and not another, we need the kind of information necessary to justify those decisions to ourselves and to other scientists.



Ken Wedding said...

Thanks for the added detail.

This is a textbook example of the need for detail and precision.

Great teaching tool.

Jim said...

Thank you for your comment. As you can see, the exploration of Port Tobacco need not address purely historical issues. We can deal with anthropological and methodological concerns as well.

One measure of a successful project is its influence on how similar work is undertaken regionally, nationally, and internationally.