Anyone new to this blog or geophysics in archaeology is recommended to read the material on the “Geophysical survey in archaeology” page.
Yesterday saw Kris, Pauline and Jim wrestling with the beast once more. It really is something one only does once in a while simply because one would die of boredom to spend too much time on it. The tick-tick-tick-tick-tick-tick-cherble cannot go fast enough. We are going to do one more day so that we have covered the whole of the house on the hill. Here are the results so far:
As we saw yesterday, the downslope wall seems to have much deeper foundations than the upslope ones. I’ll do a more detailed write-up when I have the last day’s worth of data and I can compare the images to the GPR slices.
The GPR team of Mike, Nigel, Adrian and Dave completed yet another 80x40m block. This time they headed south. The block crosses the ‘1955 ditch’, the late first century boundary of the town. Figure 2 shows a composite of time slices.
As can be seen, there is a rectangular building in the top-middle of the plot. This seems to be a simple building with four downstairs rooms, the thin one of which is probably a staircase to an upper floor. It lies parallel to the ‘1955 ditch’ which shows as a lighter band running across some of the slices from about 0m 30 to 40m 0.
The new software allows me to undertake an “overlay” analysis which produces a composite image from different time-slices. This should help see the whole of a structure when different parts of it are at different depths.
The overlay shown in Fig. 3 certainly shows part of the 1955 ditch more clearly.
One curious thing about the 1955 ditch is how varied its response in the magnetic data is. Here, the ditch shows as a strong black and white feature running across Fig. 4 from the NW corner. There is, however, quite a sudden change just at the edge of the GPR grid shown in yellow. Clearly, the ditch must have had quite a complex history and that the story of “dug c.AD 80, out of use c.AD 125″ is probably too simple. In the southern part of the town, we found a later building constructed over the line of the ditch, but here the ditch seems to have remained clear of buildings, at least for some of its length. There are some quite large circular black blobs in the magnetic data (“circular magnetic anomalies” in the jargon) which are probably large pits. A few of those show in the GPR data when one compares the two data sets carefully, but you wouldn’t notice them otherwise. Although some things show in both data sets, such as the building we found in the latest GPR results, some only show in one or other. It is definitely worth doing both.
On Wednesday we will be back at Gorhambury, one team using “the beast” and one using the GPR. We’ll be back to “normal” Earth Resistance survey on Thursday.
Many thanks to everyone who helped.