Today we returned to trench 7 and continued digging down to find those illusive walls. By about 2pm we had reached the limestone bedrock and we all came to the conclusion that what we were seeing on the geophys was the underlying geology, not foundations of buildings.
However, we decided to continue for the remainder of the afternoon and even extended trench 7 by a further meter. This was most fortuitous and we came down on a group of stones that definitely were not local. After further investigation we concluded that we may have a post hole.