In 2015, Mount Vernon archaeologists excavated 73 5' by 5' test units, covering an area of 1,825 square feet, and recorded a total of 21 burial features. This brings the total number of burials found in the cemetery to 46.
The 21 burials located during the 2015 field season were identified by 3 characteristic: shape, soil compositions, and orientation.
Though each grave shaft was unique, most are filled with yellowish clayey soil. The pale, light-brown silty clay soil surrounding each grave shaft is relatively uniform across the site. The contrasts between the two soil types made it possible for archaeologists to distinguish between grave shafts and the surrounding, undisturbed soil.
Grave shafts in Slave Cemetery. Facing SE.
Based on the lengths and widths of each grave, archaeologists believe that 14 of the 21 burials likely belong to infants or children, while the remaining seven grave shafts are adult interments. Of particular interest is that eight of these small burials occur in a single defined row near the western slope of the site.
It is unclear if this grouping means that this area of the cemetery was intentionally set aside for children, or if it speaks to an event in which a number of small children passed away around the same time, and were therefore buried next to one another.
In an effort to further define the boundaries of the cemetery, archaeologists excavated ten 5x5 ft. test units on the southern and western slopes of the site. These test units did not reveal any burials features. This allows archaeologists to say with a high degree of certainty that in this area of the cemetery, burials appear to be contained on the level space atop the ridge.
Just as in 2014, one component of the 2015 field season was to test the results of a geophysical survey that was conducted on the site in 1985. This original survey involved the use of Ground-Penetrating Radar (GPR) and detected 30 below-ground disturbances in the section of the cemetery currently being studied today. Archaeologists have been able to test 27 of these 30 radar readings to date. Of these 27 readings, 22 correspond with a grave shaft found archaeologically. Further, 15 additional graves have been located through archaeology that were not detected with GPR in 1985.
Prehistoric artifacts continue to be found throughout the project area, revealing evidence of the Native American presence at Mount Vernon that predates the Washington family tenure.
Prehistoric artifacts discovered in the Slave Cemetery
The majority of these artifacts consist of flakes and lithic debitage from the production of various stone tools on the site.
Though it is difficult to determine the occupation range of the site, several Savannah River type points have been found, which date to the Late Archaic period (5000 – 3000 BP). Of particular interest in 2016 was the discovery of a celt, a type of stone axe made by grinding the rock with an abrasive stone to form a smooth, sharp cutting edge.