As noted in our last post, the first goal of our very busy 2015 season was to geophysically survey the large field recently added to Grand-Pré National Historic Site. Overlooking the memorial church and its surrounding gardens, this field is comparatively undeveloped, and is currently being rented for its hay crop.
But this open field must surely have been close to the bustling centre of the pre-Deportation settlement, where Charles Morris in the late 1740s observed “about 150 houses scatter’d on several small Hills.”
Any buildings that escaped the 1755 Deportation were either dismantled or repurposed by the New England colonists who took up these devastated lands in the 1760s, while the survivors, sporadically mentioned in folklore, seem to have since gone to pieces. Subterranean features may be all that remain, but these backfilled cellars, ditches, wells, and fence lines are the archaeologist’s stock in trade.
To begin the effort of building an archaeological resource inventory of the view park field, we conducted an extensive geophysical survey with our old workhorse, the Geonics EM38B. As described in previous posts, and as detailed in some of the publications in our Readings and Resources section, this instrument measures magnetic susceptibility (how easily the ground is magnetized) and electrical conductivity (how easily the ground conducts electricity), both of which properties can reveal important insights about archaeological features. The instrument is most effective in measuring the upper 50cm (20 inches) of the soil profile, which is actually where most of our evidence is found.
Deploying the EM38 requires the operator – in this case, our student archaeologists – to walk a series of parallel lines across the survey area. The data collected along these lines are later computer processed to create contour maps, which may guide us to areas of interest for higher resolution geophysical surveys (to map the anomalies in greater detail), and ultimately to archaeological test excavations (to determine what is causing the anomalous readings).
The view park field represented something of a challenge on account of its size. Measuring approximately 200m x 400m (or 656′ x 1312′), this area required a lot of footwork even with our transect intervals spaced at a relatively coarse 2m (ca. 6.5′). Not counting the steps required to set up our survey grids or to move equipment around the field, the survey team was required to walk an ambitious 40km (ca. 25 miles) of transects during the four days it took us to complete the survey.
Large scale geophysical surveys like the kind recently undertaken at Stonehenge are increasingly motorized and commonly employ global positioning systems (GPS) to maintain spatial control. We are currently looking into acquiring these technologies, but for the present we are relying on traditional (i.e. pedestrian) methods, which to date have been well suited to the smaller areas we have been tackling, and at any rate are easily mapped with a total station. At 8ha (20 acres), though, the view park field may be approaching the threshold of what we might prefer to investigate with a towed array.
For this survey, we established our survey grids by measuring from a baseline established along the eastern boundary of the field. This field boundary has been in existence from at least ca. 1761, when immigrants from Connecticut began to refashion the old French properties of Grand-Pré into a New England township called Horton, so it had the benefit of conveniently anchoring our units of study to a veritable component of the colonial landscape.
Next, we had to come up with a method that would enable our survey team to walk more-or-less parallel transects across the 200m (656′) width of open field. The course we adopted after some discussion was to erect three range poles along each survey line: one at the east end, one mid-field, and one at the west end. So long as the person carrying the instrument took care to maintain a position in visual alignment with the poles, or with the end pole and some other feature on the horizon, the transect should be accurately aligned. Additional guidance, if needed, was signalled by crew members stationed at the range poles.
To further ensure spatial control along each parallel survey line, the we inserted fiducial markers (aka “fids”) in the data stream every five metres (ca. 16.5′). Here the instrument operator took her or his lead from a teammate (affectionately called the “wheelie”) who walked alongside – just out of magnetic range – with a measuring wheel, and who kept pace and maintained alignment during the brisk stroll back and forth across the field, all the while squinting at the counter and calling out the progressively stupefying chant of “one-two-three-four-FID!” A kilometre or so of this brings one to a state that is equal parts cardio workout and mesmerism. Next time we’ll tape an infomercial.
The final member of the survey team is a note-taker, whose job it is to tally the fids and record anything out of the ordinary along the transects (e.g. operator stumbled at fid 13; metal fence post at end of line 40). These notes are occasionally very helpful when the time comes to sort through tens or even hundreds of thousands of readings to isolate those often subtle hints and traces arising from archaeological sources.
With our method in place, then, we set to work.