Thursday, May 26, 2011

Update - Test Unit Excavation

This week we began excavating this season's first test units. Excavating test units is more time-consuming than digging shovel tests because a major goal of test unit excavation is to get a better idea of the area's stratigraphy, or soil layering. A basic principle of archaeological investigation is borrowed from Geology and states that new layers are deposited above old ones; as a general rule, the deeper you dig, the farther back in time you go. Therefore, test units need a high level of vertical control, which is a fancy way of saying that we dig with trowels more than we do with shovels and that we separately document each level that we excavate.

Some archaeologists prefer to start a new level whenever the soil composition or color changes, but at Arcadia, we have chosen to excavate in arbitrary 10-centimeter levels. This allows us to maintain a flat test unit floor at all times, which is important for finding stains in the ground that might otherwise have been mistaken for the start of a new level. Any of these stains could be what archaeologists call "features" such as post holes, ditches, drains, burials, trash pits, or hearths. These are assigned a different "provenience" or context number and excavated separately. We are currently excavating one block (1-meter test units in a grid) and two trenches (1-meter test units in a row.) Their locations were chosen according to the results of geophysical techniques such as soil resistivity and gradiometry that we applied last year, along with predictive models based on prior shovel test data as part of a GIS. Later posts will go over these techniques in greater detail.

Here are some of our finds this week.

This lead shot, as you can see, has been fired. Given its association with with period artifacts, it's a safe bet that the people who lived here relied on hunting local animals to supplement their diet. One thing that we find perplexing about this, however, is that other than some oyster shells from our trenches, we aren't finding as many faunal remains as we thought we would. We are on the lookout for disposal areas or middens that would tell us more about what people living here ate.

We couldn't have been happier to find this iron door hinge. While cut nails and bricks are also categorized in the "architectural" group in our database, distinctive items like hinges give us vital hints about where certain elements of a single building like doors and windows might have been. On the right side of the image are two fragments of lead-glazed stoneware, put together to demonstrate that they "cross-mend." Cross-mending ceramics is done in the lab in the off-season to link proveniences to each other archaeologically.

While some artifacts have an immediately apparent function, others can be tougher to identify. This punched metal disc could have been part of a lock, or perhaps a clothing fastener. Even though we aren't sure what this was for, it is nevertheless documented and stored for later identification.

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