We have been eagerly anticipating the arrival of Roger Anderton, the geologist, at Presaddfed. We had lots of questions for him, and he had lots of answers for us!
First, he was able to tell us that Trench A, with the lovely swirly schist, has been quarried in one area. Likewise, Trench B over another outcrop in the field is also definitely quarried. This is excellent news. However, the stones coming these quarries are not large enough to be the big schist capstone at Presaddfed.
The other type of stone at Presaddfed, including the capstone of the standing dolmen, is almost certainly a glacial erratic, as are the two uprights of the same material. Roger also suggested that the large schist capstone was a glacial erratic too, since the quartz lines on this stone are not mirrored on other schists in this field. This means that the builders of Presaddfed may have used stones lying around where they were to make the monument, and undertaken only small amounts of quarrying in order to acquire stone not available on the surface. We wonder if the stone being quarried was used as part of the construction process, perhaps to assist with lifting up the capstone/s into place prior to placing the uprights.
We opened up another trench at Presaddfed today to explore the possible outcrop/quarry close to the dolmens as shown in the geophysics, but there was no archaeology, or outcrops, to be seen in this trench.
Attention is now turning to the trench next to the dolmen in order to find evidence for construction. The weather was beautiful yesterday but a cold wind made for chilly work today.