How do Archaeologists Select Places to Excavate? The Swann House Excavations.

 

We had a busy weekend in the field at Swann House as it was our second Public Archaeology Weekend. Lots of old friends came to join in our excavations, as well as new volunteers. The weather was perfect! And, we completed a couple of units and moved on to two new ones. Before I move on to the topic at hand, if you’re interested in volunteering, we have regular Monday field and/or lab hours in Port Tobacco through August and September. Our next Public Archaeology weekend will be at the end of September. We still have to meet as a group and settle on a weekend, but I’ll let you know time and place as we get closer. For information about volunteering contact Esther Read: reade@charlescountymd.gov

Also! We have a new video about the Swann House Site (thank you Lee Ann Stone!), check us out at 

Your Charles County: Swann Site Archaeology

 

Saturday's Volunteer Crew.
Left to Right: Greg, Denise, Steve, Ned (behind Steve), Kim, Doug, Elsie,
Linda, Tim, Susanna, Leah, and Alix. A big thanks for all their hard work!

Example of an Archaeological Excavation Unit
at the Rich Hill Site in 2021.

Last week (July 16^th) I wrote about stratigraphy or the vertical/time dimension of the site, this week I’ll talk a bit about the horizontal or spatial locations on the site, or the units we excavate. What is a unit you ask? A unit is the square or rectangular hole that archaeologists excavate. But how do archaeologists select the location for the units? We have several different methods for picking a spot.

We select locations for our units across the horizontal plane of a site based on different criteria. We might pick a location due to the presence of artifacts on the surface of a plowed field or based on metal detector survey hits. Archival research in the form of maps or deeds might suggest the location of possible cultural deposits. And then there’s geophysical survey, using methods such as ground penetrating radar or a magnetometer to locate below ground remains of walls, ditches and so forth.

Tim Horsley of Horsley Archaeological Propection
with magnatometer during
Geophysical Survey of a portion of Port Tobacco in 2019
Volunteers Mary and Carol are in the background

Example of an STP

We’ve done quite a bit of geophysical work in the northern and eastern portions of Port Tobacco. We have yet to do the southwest corner of the town, which is where the Swann Site is located. We do plan to conduct some geophysical survey here in the future, but for right now we’re relying on other tried and true archaeological methods to select unit locations.

Julie and Carol excavating an STP
 at the Rich Hill Site in 2021

The first method we’re relying on is the results of the shovel test pit (STP) survey done in 2008 and 2009 by the Port Tobacco Archaeology Project. An STP is a small round hole, generally about 18 inches in diameter, that is excavated into the ground until the subsoil or substratum is reached. The subsoil is a natural soil layer that has not been disturbed by earlier cultural activities and that does not contain artifacts. STPs are excavated to different depths depending on the soil conditions. Some areas have deep soil deposits, especially along stream and river banks, while others may have almost no soil deposition due to a natural event such as erosion or a cultural activity such as grading, farming, or constuction. An STP gives an archaeologist a quick window into the past so that we can see the types of soil deposits that are present and the types of artifacts associated with them. This gives us the time dimension.

The horizontal or spatial dimension comes by analying the results of multiple STPs across a broad area. STPs are set at regular intervals - for example 30 feet apart - along transect lines. There are generally several transects set parallel to one another at regularly spaced intervals. The interval between transects generally matches the interval between STPs. The map below shows the location of STPs excavated by the Port Tobacco Archaeology Project. Not all of the STPs yielded artifacts, but many of them did.

Esther Troweling in the field units
I sprained my ankle - hence the crutches
Photo Credit: Carol Cowherd

Once the STPs are excavated the artifacts recovered in them are analyzed, counted, and mapped. The maps give us the location of concentrations and from there we can select areas within the concentrations to sample. In addition to the concentration maps produced by the Port Tobacco Archaeology Project, we used information from a metal detector survey of the former agricultual field next to the house foundation to map in the locations of other artifact concentrations. We selected the location of the first field unit in an area of artifact concentration overlap between the STP and the metal detector surveys. The second field unit location was selected because of questions that I had about the soil deposits in the first unit. These are large 5 by 5 foot units that are set adjacent to one another and cover 50 square feet. I hope to find features such as posts for fence lines or perhaps support posts for some of the outbuildings that we know were here in the late eighteenth century. We’re still working our way through both of these units. Most of the crew spent the weekend working in these units. I owe a big thank you to Elsie, Linda, Ned, Susanna, Leah, Alix, Kim, and Greg. Denise, Claudia, and Tim were in charge of the screening and Doug mowed the grass around the units.

Units Close to the Foundations
One of the trench features has been excavated,
the other appears as the dark soil stain under the
pink string between the two units.
Carol found the Creamware in the dark stain.
The post hole is in the lower right corner

I picked the location for two 3 by 3 foot units (covering a total of 18 square feet) just off the south side of the house foundation based on documentary evidence. According to the architectural description of the house in the Maryland Historical Trust’s Inventory of Historic Properties the house had a shed addition on the south side. There is no description of the shed addition in the 1784 probate assessment of the house, so it must have been constructed after that date. We found several features in the two units and this past weekend Carol finished the last feature. There was a post mold (or the remnants of a rotted post) and two narrow trenches running east/west across the two units. One of the trenches produced a tiny fragment of Creamware. I don’t know what the trenches were used for, but the Creamware suggests that the trench predates the shed addition. I will probably open another unit along this line of trenches, which I don’t think are scars from plowing. The plow scars run north/south across the bottom of the field units, not east/west like the trenches in these two units.

Finally, we put three units in the house foundation. The Port Tobacco Archaeological Project excavated a unit in the northeast corner of the foundation in 2009 and encountered fill thrown into the cellar hole after the house was abandoned and razed. We wanted to further sample the interior of the cellar and look at the construction methods used for the brick chimney and pents and how they articulated with the stone foundation wall.

Northeast Corner of the Stone Foundation of Swann House
The Port Tobacco Archaeological Project put a unit in this corner in 2009.

Base of the Hearth or Fireplace Units
The brick wall of the side of the hearth is on the 
right side of the photograph

We opened two adjacent units at the base of the chimney inside the cellar hearth (fire place) on the west side of the house. These two units measure in total 7 feet east/west by 3 feet north/south, and cover 21 square feet. In these two units, which are almost 3 feet deep, Steve and James encountered fill under the collapsed chimney at the base of the units that dates to the period 1910 through 1920 . This gives us a Terminus Post Quem (TPQ) date, meaning the chimney could not have collapsed before 1920 because there are artifacts dating to 1920 or earlier under the chimney bricks. We are still excavating these units.

The photograph shows the base of the hearth. Two pails were thrown into the hearth, along with bottles, an old boot, and other trash before the chimney was collapsed inside the unit.

The third unit is in one of the chimney pents. Many houses in Southern Maryland have chimney pents that are located between two gable end chimneys. This is not the case at  Swann House, where there was one gable end chimney on the west side of the house that had a pent on either side of it. According to the 1784 probate assessment of the house there should also be a chimney on the east side of the house that has two pents. There is some brick on the surface on the east side of the foundation, but we have yet to investigate that side.

Example of a Chimney Pent at the Barnes-Compton House in Port Tobacco
The area between the two chimneys may have been used as closets,
small rooms, or for general stoage.
An entrance to the cellar is between the bases of the two chimneys.
Stag Hall is on the right and Mount Bleak is in the background on the left.

Swann House Pent
There is pent on either side
of the single end chimney

The pent unit has been interesting. According to the 1784 probate assessment there are four closets in the house, that were probably located in the pents – one on either side of the two chimneys on the first floor on the house. We’re in the part of the pent that extends below the ground. Steve and Kathy spent the weekend excavating inside the pent and discovered that there is no access into the pent from the cellar as the stone foundation wall of the house extends across the east side of the pent. Our excavation indicates that there is no opening into the pent from either the north or west sides of the house, both of these sides of the pent are solid brick walls. The final wall of the pent, on the south side, is adjacent to the basement fireplace wall and the chimney, so there’s no access there either. It appears that the pent is totally enclosed below the first floor of the house.

Mortar Patch on the North Side of the pent

 

However, the twentieth-century photograph of the house shows extensive mortar patching on the north side of the chimney. Could this possibly indicate an opening that has been filled in? Or is it simply patch work on a chimney pent in deteriorating condition? The interior of the pent was full of rubble: chipped stone pieces from the foundation stones, partial brick, burned oyster shell, and mortar. Each of these was dumped into the pent as a discrete layer of stone, or shell, or mortar. There was not much brick, but one partial brick was covered with mortar. Each of the layers appears to be a wheel barrow dump, the debris forms sloping piles within the pent and the direction of the slope indicates that the wheel barrows were bought into the house and dumped into the pent. We think we’re at the base of the fill, as we’re on top of a thick clay layer. We haven’t finished excavating the pent, but will be finishing up hopefully next week. We also haven’t recovered any artifacts other than a very heavily rusted nail that is currently unidentified as to type - that is eighteenth-century wrought or later nineteenth-century machine cut. 

 

Chimney Pent unit
The trowel is pointing north

The photograph of the chimney pent unit (above) shows the unit where we left off yesterday. The north brick wall shows no sign of extensive patching, but there is evidence of patching on  the east wall. The stone directly below the sign board on the east wall has mortar patching on it and there is a layer of mortar directly below it on the floor of the level. The south wall is a soil bulk left in place so that we will be able to record the soil profile and have a record of the important vertical/time information from this unit. Once that information is recorded we’ll removed the bulk. I’m holding off on a final interpretation of what the rubble is associated with, construction or patch work, until we finish excavating the interior of the pent. 

Lab work for all the artifacts that we gathered continued today at lab. I’ll have some updates next week! Below is a photograph of Sunday’s crew.

Sunday's Crew: Kathy, Ned, Carol, Claudia, Elsie, Esther (behind Elsie) and Steve.