Thursday, February 3, 2011

I recently gave a paper at Southeastern Archaeological Conference SEAC that presented the preliminary results of my analysis of the Ft. Jefferson historical materials collected during Florida Archaeology Month 2008.  I thought I'd post a few pictures and findings from my analysis and show you the kind of thing we share at professional conferences (though many in the session did it more impressively than I!).

Florida Archaeology Month Poster 2009.

First, let me set the stage.  I was not there two years ago when Michele Williams was invited out by the Southeastern Archaeology Center who manages the park.  Michele was happy to respond to their request to help host a public event out at the park, let people interact with real archaeologists and ground truth some of the ground penetrating radar findings.  They excavated in the southwestern section inside the fort and recovered about 5,000 artifacts.

Last spring we had the chance to look at the artifacts after they had been washed and before they were returned to the National Park for permanent storage.  The artifacts had already been washed and sorted by general material type: metal, ceramics, glass, synthetics, and ecofacts (bone and shell).  We opened each bag and took a line of data that included material, form, weight, and measurements when appropriate.  Two other important factors were taken into consideration: function and burning.  To understand how that area of the site was used, it was important to assign a functional category to each artifact: kitchen, architectural, military, maritime.  We had over ten function groups pre-selected and adjusted as we saw a large amount of maritime artifacts in the assemblage.  If the artifact exhibited signs of being burned, we noted that as well.  A storehouse that burned in the 1850s stood on this area of the site and the park managers wanted to know if the artifacts came from that time period.

Michele Williams and Amber Weiss doing analysis.

Putting yeay nails back into the bag.

After the data were entered into the computer, I calculated dates based on the ceramics and the window glass.  All ceramics are made from clay and often decorated in a way that let us know when they were manufactured.  We use the manufacturing dates to get an average, multiply that number by the number of sherds of a certain type, and then divide by the entire assemblage number.  For example, if we had four sherds (or pieces of ceramic) that was manufactured from 1800 to 1900, we'd multiply 4 times the average of 1850 and then divide by the total number of sherds to arrive at a mean ceramic date of 1850.  In the case of Ft. Jefferson, a date of 1888 was arrived at using the mean ceramic dating formula.

Pipe stems dated too late to run formula but testiment to personal artifacts.

Mine ball recovered from the site.

Next, I did a window glass analysis based on the thickness of flat, broken fragements of glass.  Glass formulas are not new but not often applied to Florida collections.  The idea behind the formula is that window glass gets uniformally thicker over time--that the earliest window glass will be thinner, later glass will be thicker.  We measured the thickness of each glass fragment (remember they had to be flat, not curved!) and plugged the numbers into Moir's formula.  The first date I got was 1865, which is not bad considering the site was most heavily used and constructed between 1848 and 1888.  I didn't stop there though- I wanted to see if the soil in this area of the site had "integrity," or had not been mixed past the point of being archaeologically usable.  In fact my lower level dated 10 years earlier based on the window glass than then 10 cm level of soild above.  This is good!  This means that the older artifacts are still found deeper below the surface and that the site still holds a high research potential.

If anything, the analysis helped bring to light--for me at least--the long period of use of the Fort, and while it was used as a prison during the Civil War, the history of the site goes earler and later than that event.  The lighthouse was first constructed in 1826, and we found pearlware ceramic sherds that date to that time.  We also found a whisky bottle fragment and amethyst glass that told us people used and lived at the site well past the Civil War and into the early 1900s.

Ca. 1900 Maryland Planter Rye bottle.

The most surprising thing to me as a terrestrial archaeologist was the maritime artifacts.  Looking at artifacts from digs well in land, I'm not used to seeing the ship fasteners that were found at the site.  The nails and rivets looked similar to what I find on typical 19th century sites, but instead of being made of iron with chunks of rust, these maritime artifacts were made out of copper alloy and an a neat, slightly green finish. 

Brass nail indicates maritime function at site.

The other surprise that while this was supposed to be in the area of a burned storehouse, very few of the artifacts were burned, and very few matching ceramics were found--as I'd expect at a warehouse.  Instead a great variety of artifacts, notably personal artifacts, were found and give us at present a direct connection to those who used the site in the past.

If you're ever in south Florida, don't miss a chance to visit this colossal giant, the largest masonary structure in the western hemisphere.  Keep checking back with us, we'll let you know if they're planning any more digs out there in the future.

Thanks to:
April Andrade (FAU)
Paul Callsen (FAU)
Brian Conesa (ASSF)
Amber Grafft-Weiss (NE-FPAN)
Sarah Nohe (SE-FPAN)
Crystal Geiger (FAU)
Carla Hadden (NPS-SEAC)
Melissa Memory (NPS-Everglades & Dry Tortugas)
Margo Schwadron (NPS-SEAC)
South Florida National Parks Trust
And the generosity of the NPS-Dry Tortugas staff, volunteers and visitors!

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