Good progress is now being made on our current project, with almost a complete cross-section of the moat having been excavated. Our work to date shows that the moat was around 1.2m deep in the middle with the blue-grey sandstone floor rising gently towards each edge. The edges of the moat seem to be formed by a vertical 'wall' of clay in front of which, sand has been used to form a slope which in turn has also been covered with a thin layer of clay.
Dating evidence from the very bottom of the moat suggests it was last cleaned out in the second half of the 17th century but after that it was allowed to silt up. Fast forward to the late 1700s and the house which stood on the island platform was demolished and the rubble put into the moat. Since then around a foot of topsoil has built up both mostly as a result of leaf litter from the nearby oak trees.
The photo above shows the north end of our trench, where the rising floor meets a wall of clay at the furthest point.
We're still working on the south end (below), having just encountered the bottom of the clay slope in which the large stone at centre is set.
This artificial colour image shows the various strata to good effect; topsoil, demolition rubble, silt, clay slope, sand, sandstone at bottom and clay 'wall' at left:
