24 Jul Digging into the Past: The Fowler Clark Farm
Back in December, guest blogger Dr. John Steinberg of the Fiske Center for Archeological Research at UMass Boston wrote about his survey work at the Fowler Clark Farm in Mattapan which HBI recently acquired. Using ground penetrating radar (GPR), the UMass team surveyed all of the open space at the farm to determine if there were any likely areas that had been undisturbed since the house was built (circa 1786) where archaeological artifacts might be found. Today Dr. Steinberg reports on his team?s findings.
After dragging two geophysical instruments across all the open space at the Fowler-Clark farm in Mattapan last year and analyzing the resulting data, we determined that most of the front and back yards at the Fowler-Clark lot were very disturbed by earlier occupants of the site. Upon a detailed analysis of the data, two areas stood out as having potential preservation, so our team from UMass Boston Fiske Center for Archaeological Research returned to the site this spring to excavate two shovel test pits. The shovel test pits revealed that there are, in fact, two small, very deep layers that are preserved, potentially from the earliest occupations.
The first targeted excavation (TE#2) is right in the front of the barn/Carriage house. The cobblestone driveway actually goes over part of it. The area is just at the end of the GPR line that the UMass Boston graduate students are about to traverse in Figure 1. In the raw data you can see the outline of the stone driveway (blue box in Figure 2) over the preserved surface in both A-A? and B-B?. The preserved surface in TE#2 (Figure 4) turned out to be an ash layer with the top of that ash layer about 70 cm (25 in) below the ground surface (Figure 5). There was almost nothing of interest in the fill layer above the ash layer.
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| Figure 1) UMass Boston graduate students pulling the GPR with 500 MHz antenna. At the end of thiS transect (A=A?) they will be on top of TE #2. |
In the raw data you can see the outline of the stone driveway (blue box in Figure 2) over the preserved surface in both A-A? and B-B?. The preserved surface in TE#2 (Figure 4) turned out to be an ash layer with the top of that ash layer about 70 cm (25 in) below the ground surface (Figure 5). There was almost nothing of interest in the fill layer above the ash layer.
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| Figure 2) Examples of raw data (sometimes called radargrams) from the GPR. Strong reflectors produce a distinct series of black and white lines. The purple box in A-A? outlines a preserved surface. |
The second (TE#3) is in the front yard by the corner of Hosmer and Norfolk Streets. The preserved layer can be seen in the raw data in transect F-F? (Figure 2 denoted by the red arrows). This find is a little more exciting as this is potentially a preserved surface from the first European occupants of the site. About 90 cm (35+ inches) down, (Figure 6) we identified a rich organic layer (Figure 7). Again there were almost no artifacts above this layer. What this means is that the original surface of the land in the front yard (or ?A? horizon) used to be almost 3 feet lower than it is today. How, why and when the grade of the front yard was raised so significantly is anyone?s guess.
Both of these layers are interesting, considering the poor state of preservation of this yard. Using GPR technology in combination with excavation allows us to see more and disturb less than with archaeology alone.
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Figure 3) Overlay (composite) depth-slice GPR image. The raw data (examples above)
are sliced at different layers to create a map of the subsurface. Strong reflectors
are shown in red. Transect A-A? (being walked in the top picture and its raw
data displayed in the middle picture).
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Figure 4) TE#2 the surface 70 cm (28 in) down, after cutting through the ash layer
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Figure 5) The Ash layer, identified in the GPR, in the shovel test pit profile.
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Figure 6) TE#3 showing the organic layer identified in the GPR
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Figure 7) Top of preserved surface in TE#3
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