Anyone new to this blog or geophysics in archaeology is recommended to read the material on the “Geophysical survey in archaeology” page.
Archaeologists often have skeletons in their cupboards. Sometimes they are real skeletons. Sometimes, as here, they are unfinished jobs that they haven’t quite got around to completing. There are a few surveys we have undertaken that never quite got finished, and for which there are no blog posts (shock! horror!). Way back when we got together with the Buckinghamshire Archaeological Society’s Active Archaeology Group and CVAHS to undertake some surveys at Hogshaw in Buckinghamshire. The AAG had undertaken an interesting research project on this site including topographic survey. We managed some mag (even though the mag was down to three probes) and some Earth Resistance survey (using our old system). The results were posted at the time.
The following year, in 2016, we returned and expanded the mag survey and undertook some Ground Penetrating Radar survey. We had only just started using GPR and I was still learning how to process the data. The following year, Mike and I returned with the GPR to survey another two areas. Due to problems with that data (we were distracted by lunch), that I couldn’t solve at the time, the results were put on the back burner. Fast forward two years and I am now a little more confident and have a better handle on the software. Having finished processing the awkward survey at Bovenay, I thought I would have a go at re-processing the Hogshaw data. As you might guess from the fact you are reading this post, I had some luck and so, two years late, here are the results! (See the older post for the previous results and the background to the site.)
The magnetometry survey was mainly aimed at finishing the awkward bits around the edges, and an area to the south where the landowner kindly took down his fence so we could survey across it. The results are shown in Figure 1.
At first sight the magnetic survey is rather busy and hard to interpret. This is not unusual in historic period sites where iron artefacts and fired bricks are relatively common. I have labelled the plot with some basic interpretative points (Fig. 2).
The fence line is where the farmer kindly removed the fence so we could survey. It is fascinating to see that even when the fence has gone, we still detect the line of it. Iron rust etc. washes down and permeates the soil, I guess. The platform is a large flat area in the NW corner of the site. We do not know what it is for, and the mag does not help a great deal (neither did the Earth Resistance last time).
Perhaps the most interesting feature that we detected last time is the four squares inside a square. This was quite a surprise. It looks very much like a formal garden. If it is a garden, there appears to be a line heading out westwards to an area of magnetic noise. I rather ignored that last time, but now I wonder if that is where the remains of the manor house were? It was abandoned in the 18th century.
There are two lines of very noisy magnetic readings, one along the current road and one along the northern edge. I’d like to see how these relate to the topographic features. I think they line-up with the banks, and could be lines of brick rubble. Unfortunately, the LiDAR data for this area does not cover the site, ending just under half a mile to the north (Fig. 3). Typical!
Three blocks of radar data were collected. We used SEAHA’s Mala GPR, and we thank them for the loan. The location of the three blocks are shown in Figure 4.
The southern block was surveyed in 2016 because an excavation had found a couple of stone walls in this area, and it was suggested this might be the location of the lost chapel. Figure 5 shows the top nine time slices (note that north is downwards in these images).
The first time slice shows the road nicely. Also helps build confidence when the method detects the absolutely obvious! By about the fourth slice (second row, leftmost image) the road is largely gone but there are two parallel lines running north south. Could these be our missing walls? Perhaps, but I suspect they are compacted earth either side of the fence which the farmer took down for us. The area of high amplitude reflections in the bottom-right corner (north-west) is the area of wet mud around the various temporary structures that were moved. All in all, a rather disappointing result.
The platform block was an attempt to see if we could work out the function of the platform in the NW corner of the site. Figure 6 shows nine time slices.
Again, note north! There is a vague hint of something in slice 7 (third row, first image) that might be rectangular, but it is quite low down in the sequence, and a bit amorphous. Looking at the radargrams (the original vertical slices), I cannot see anything particularly wall-like. I suspect that what little radar energy has been reflected has been greatly emphasised in these plots creating the illusion of something. Figure 7 shows slice 7 in context.
Last, but not least, is the “garden” block (Fig. 8).
In slice 1 (top left), the results just reflect the uneven surface. In slice 2 we can start to see something, but it is in slices 3 and 4 that we can see the “garden” feature quite clearly. The whole feature is about 36m across with the internal square about 12m by 12m. To the south there appears another strong linear reflection. Maybe a road to the house?
Figure 9 shows slice 3 in context. I’m glad to say that the mag and GPR data match very closely. The edging around the features must be something both magnetic and that reflects radar data. Brick is one possibility, and some form of igneous rock is another.
One might ask why I am so keen on it being a garden feature. Looking at another much grander garden, we can see many similar features (Fig. 10). The part I have outlined in red is approximately the same size as ours. The inner squares of that garden at Hatfield are 11m across, the enclosing hedge 28m by 42m, the outer edges 37m by 57m. As always, the only real way to tell is to dig a hole…
Many thanks to everyone who helped on the four days of survey, especially to the very helpful landowner. Also many thanks to Anne Rowe for commenting on the “garden” feature and sending me some very useful information. Hogshaw still has some secrets to give up!