Friday, October 21, 2011

Three Dimensional Mapping of Artifacts

Mapping in the 1970s, dig it man.

This week we return to the ABC’s of archaeology. We are down to the last three letters - X, Y and Z and we are going to use them all at once. Archaeology is all about mapping and X, Y, and Z represent the grid and datum coordinates used in mapping. These coordinates represent the three dimensional location of an artifact also known as provenience.

State Museum Section of Archeology volunteer Melanie mapping an FCR cluster at Fort Hunter (36Da159)

Archaeology is the scientific study of past cultural behavior through the systematic recovery and analysis of artifacts and features. The basic assumption is that artifacts and features are not randomly distributed. Their distribution or patterning is affected by a variety of cultural and natural factors. These patterns can only be revealed and understood through mapping – specifically three dimensional mapping or piece plotting. This type of excavation utilizing mapping and spatial analysis is a powerful tool in the identification of artifact patterns and their relationship to past cultural behavior.

In most upland sites, situated on residual soils, the artifact patterns have been altered through modern farming practices. Piece plotting in a plowzone is of little value. However, in alluvial settings, where artifacts are stratified, there has frequently been little post-depositional movement and artifacts are very near their original location. This is where piece plotting is important. However, mapping takes time. In today’s world dominated by compliance archaeology (for which I am a strong supporter) where time is money, many prefer to excavate in meter or half meter units using shovels, only mapping tools or very large artifacts (if they don’t end up in the screen). Some argue that post-depositional movement of artifacts is always a significant factor and piece plotting is a waste of time.

I would like to present two examples that demonstrate the contribution of three dimensional mapping of artifacts. One of the earliest cases in Eastern North America of piece plotting was conducted at the Thunderbird site in the Shenandoah Valley of Virginia. This is a stratified Paleoindian through Early Archaic site associated with a jasper quarry. The site was first tested in 1971 using three inch arbitrary levels within natural levels and ten foot squares. Initially, these were shovel skimmed. These units were producing between 800 and 1200 flakes and tools per arbitrary level. This was not surprising considering the site’s proximity to the quarry. It was assumed that these flakes represented a variety of tool making activities although the specifics were unknown. The damage to flakes due to shovel skimming or even digging with trowels was extensive and early in the first season, there was a switch to piece plotting. The use of this method was unprecedented at the time.

Hand drawn map of chipping feature at Thunderbird site (44Wr11)

 By the end of the season, several patterns were revealed that clearly document the significance and the contribution of this method. They were able to identify the types of tools that were being made, the specific flint knapping techniques being used and, in some cases, the number of flint knappers involved. Although the number of artifacts between squares did not vary greatly, piece plotting revealed that the artifacts occurred in concentrations or chipping features. Several types of chipping features were identified that were significant in understanding community patterning and stone tool manufacture. In addition, by piece plotting the artifacts, it was discovered that flakes could be refitted – cores and tools could be put back together like three dimensional jigsaw puzzles.

The most interesting feature type consisted of approximately 1500 flakes or less. These were organized into a large concentration two to three feet in diameter and a smaller pile separated by several inches of open space. The space between the two clusters represents the individual flint knappers leg print while they were sitting on the ground. The identification of chipping clusters representing one individual making a single tool (in this case a fluted projectile point) allowed archaeologists to analyze how fluted points were made and the nature of stone tool manufacture during the Paleoindian period. The piece plotting of artifacts enabled archaeologists to identify cultural patterns in the apparent chaos of thousands of flakes.

Map of Feature 75: Thunderbird site (44Wr44)

The second example of the importance of three dimensional piece plotting comes from research conducted at the Abbott Farm Complex, near Trento New Jersey. Here, fire crack-rock (FCR) was found in large quantities and mapped in great detail. The prevailing interpretation at the time was based on research conducted by Fred Kinsey in the Upper Delaware River Valley. He hypothesized that FCR was the result of large cooking hearths or fish drying racks and it was most frequently associated with the Transitional period. Again, three dimensional piece plotting demonstrated that the explanation was not that simple. There were several different patterns to the horizontal distribution of FCR. Some were tightly packed, similar to Kinsey’s scenario but others were more widely spread out. As in the chipping feature example, the mass of FCR could be divided into a series of separate events. Experimental archaeology was demonstrating that different cooking techniques produced different types of FCR. For example, stone boiling (placing heated rocks in a skin lined hole in the ground to boil water) produced a smaller more rounded FCR than roasting hearths. Also, FCR resulting from stone boiling is usually more mixed and dispersed horizontally than FCR used in cooking hearths. Again, archaeologists were able to identify separate events and different types of activities on a living floor that otherwise appeared to be a mass of artifacts.

10cm grid over FCR cluster at the City Island site (36Da12)

My point with this week’s blog is that recording the X, Y, and Z coordinates of individual artifacts can be a very useful tool in the analysis of living floors. Archaeologists have been collecting flakes and making approximate counts of FCR for over 100 years but other than their presence, not much was known about the activities they represent. To better understand these activities, their spatial arrangement and the social implications, we must apply different field and laboratory methods . If we keep collecting data in the same old way, we are not going to learning anything new. Piece plotting may require more time in the field (although the use of a total station greatly reduces that time) but the benefits far outweigh the time element in adding to our understanding of past cultural behavior.

FCR cluster resulting from hearth feature: 2011 field season Fort Hunter (36Da159)

Don't forget, just to weeks to go until the Workshops in Archaeology at the State Museum of Pennsylvania!  Click here for the program and registration form and join us for a fun and informative event Saturday, November 5th.

For more information, visit or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .

No comments:

Post a Comment