Monday, October 18, 2010
Sorting Sands of the Centuries
For me the month of October has been all about the Burch House. I spoke about our excavations there on Saturday at the ASM Board Meeting. In two weeks, I'll talk about the sedimentation processes at Port Tobacco, at the CNEHA Conference, focusing on soil samples taken from around the Burch House. We took column samples from 3 different units (see photo). Each stratum samples was split in half and one half analyzed, the other held for future processing. We developed the analysis procedure by trial and error and came up with a method to seperate different components in the soils:
First the sample is weighed. Then it is water screened using graduated geological screens with mesh sizes of .187 inches, .0937 inches, and .0469 inches. This removes and sorts gravel and tiny rocks from the sand and silt. The remainder is then water screened through a yogurt strainer, which is similar to cheese cloth. This catches coarse and medium sand grains. The water from the screen is collected during the process with very fine sand, silt, and clay particles in it. This is then poured through paper towels. The sand and silt remain in the paper towel; only the smallest particles escape.
In the end each stratum is divided into 5 fractions. Each fraction of the sample is weighed to determine the percentage of the entire sample it comprises. The data gathered from this method of soil characterization, when coupled with what is known about erosion processes, can tell us about the source of the sediments that were washed in and the velocity of the water that brought it.
Hopefully we will also be able to date major sedimentation events and see if they match up with archival information about catastrophic weather and the like.
We can also place the component percentages of the soils next to our own descriptions of the the soil as we excavated it, to see how they differ.
So for the rest of the month and a good part of what remains of the years, I'm going to be up to my elbows in Port Tobacco soil, literally.
NOTE: We will not be in the field tomorrow due to high chances of rain. We will go out some time later in the week. Stay tuned for updates!