Friday, March 2, 2012

History of the Fort in Cross Section

During our November 2011 excavations at Fort de Chartres (see February 29 2012 post) we uncovered a segment of a large, deep, wall trench that once supported vertical logs that formed a palisade wall of the fort. The profile or cross section of the ditch told quite a story – and is a good example of how and why we read soils the way we do in such features.

  • On the western edge of the trench, Zone A was a sandy clay soil that contained no artifacts. This zone probably reflects the dirt excavated in 1732, which was backfilled against the new, upright logs.
  • Zone B represents a posthole affiliated with that initial palisade wall.
  • Sometime after the construction of the fort, parts of the palisade wall were repaired, including the portion uncovered by our excavations. This repair involved the removal of some of the original posts, and the redigging or expansion of the wall trench that support the uprights. That rebuilding activity is represented by Zone C, an old topsoil that was backfilled against a second line of posts.
  • Also associated with that replacement post setting is Zone D, which fills the eastern edge of the expanded palisade trench. This soil was similar to Zone C, but was greasier and more heavily laden with animal bones and other artifacts. This suggests that the soils used to backfill the trench (from what was the inside of the fort) were more contaminated with occupation-related debris. In other words the ground surface inside the fort was more littered with trash that just outside of the palisade walls.
  • Finally, Zones E/F represents the fill of a posthole associated with the replacement palisade wall. This was old topsoil that fell into the posthole when the fort was dismantled, sometime during the 1750s. 

So, visible in this unit was the initial 1732 construction of the fort, a circa 1740s repair episode, and the dismantling of the fort sometime in the 1750s. The palisade trench was about three feet deep, and supported a wall that was probably about 10-12 feet tall. Traces of charcoal at the bases of both lines of postholes suggest that they were partially carbonized before they were set, to slow the decay of the wooden posts once they were in the ground. Mineral (manganese) staining was also visible at the base of some of these posts, as well as across the base of the wall trench. This suggests that water often collected at the base of the palisade trench, at least in places. That's why we draw profiles....

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