What happens after students excavate a test unit?

The students excavate a test unit by removing the topsoil until the sterile subsoil is reached. The subsoil zone usually contains clay and is the layer at which artifacts are no longer found. It is usually lighter in color than the topsoil. Artifacts do not sink into the soil. Instead, soil builds up over the artifacts and buries them. Decaying leaves and soil carried in by wind and water are main causes of soil buildup. Sometimes prehistoric people dug into the subsoil to create features such as fire hearths, storage pits, and trash pits. When students reach the subsoil zone, Cleveland Museum of Natural History archaeologists scrape the floor and walls of the unit clean to look for evidence of features. They then photograph and map the floor and at least one wall, even if there are no features present.



This photograph shows the west wall profile of unit N500E539. You can see the darker topsoil zone above the lighter subsoil zone. The irregular line between the two zones is caused by roots or digging by rodents such as ground hogs or chipmunks. You can also see that the topsoil zone is very thin (between 10 cm and 15 cm thick). This seems to be because this portion of the land form was never plowed. Most all of northeast Ohio was plowed at one time or another. Finding areas that have not been plowed is rare. Plow zones usually average in thickness between 20 cm and 25 cm. Plowing soil causes the artifacts contained within them to be mixed up from their original location. The Mentor Lagoons 4 site, also located near the Mentor Marsh, click here to read about this site.