by Kayla Marciniszyn – CART Senior Field and Lab Archaeologist
As mentioned in a previous blog post by our crew chief, Jean Cascardi, archaeologists use the science of stratigraphy to determine different cultural or natural events throughout history. We have three criteria for determining new soil layers, or strata: soil color, soil texture, and inclusions. Texture is determined by feeling how fine the particles that make up the soil are and if it can be rolled into a ball or “snake.” Inclusions refer to larger particles such as brick or gravel that may also be present into the soil. Color can be pretty tricky – one layer might seem brown to one archaeologists and reddish brown to another because everyone sees color slightly differently. As with many archaeological processes there are procedures in place to ensure data is recorded in standardized ways to facilitate analysis and comparison.
In the early 19th century, Albert H. Munsell developed the Munsell color theory in order to improve color identification in the sciences, academia, and government agencies. Today, the Munsell color system is the standard system for identifying color in soils, artifacts, rocks, etc. Archaeologists use the soil-color charts, which contain Munsell color chips, to identify changes in soil color. In the field, each time a change in soil texture or color occurs, archaeologists record the color that best matches a color chip. The color chips are classified by hue, value, and chroma. Hue is the relation to red, yellow, blue, purple, and green. Value indicates the lightness of the hue and chroma indicates strength. The soils in Colchester usually range from a 7.5YR to 10YR which is a hue of yellow-red. Once you know the basic hue, you can determine the value and chroma. Our normal topsoil layer is usually written as 10YR 2/1 or 3/1 (hue value/chroma) which is a very dark grey or black.
There are Munsell options for pinkish soils, yellow soils, green soils, and even blue soils, but unfortunately, we don’t typically come across those colors in the Mid-Atlantic.
Each layer of soil represents a change in activity by either natural events or through human activity. Tracking the soil changes allows us to interpret changes in time periods, compare information from different areas across a site and follow features within the ground. Munsells aid our ability to analyze each location and artifact. We not only take into account soils recorded by archaeologists for each soil layer, but also, soil surveys done by soil scientists. Soil types in Fairfax can be checked with the county’s Digital Map Viewer. Fairfax County also provides information about soils via the 2011 Soil Map Guide.
For more information on the Munsell color system, check out their website! http://munsell.com/about-munsell-color/
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Stratigraphy – Soils & Archaeology