I now have a map of the Somerset part of the Selwood Forest, from The Bounds of Selwood, Michael McGarvie, Frome Society for Local Study, 1978. This has 18 ½ pages and 118 footnotes, which seems sufficiently serious.
The map in the previous post, of the Wiltshire section, shows approximately 7/8 of the total forest; the Somerset section is a fairly narrow strip more or less following the shape of the county boundary, but for the parish of Kilmington which was then in Somerset but is now in Wiltshire and is the bit jutting out to the right and looking a bit like Wales.
Penselwood (marked with the red square), thought to be the likely site of Egbert’s Stone is right on the county border and was probably about one mile inside the forest … But, but …
Asser said, writing in 893, that Alfred rode to rally his forces ‘ad Petram Aegbryhta, quae est in orientali parte saltus qui dicitur Seluudu’; and the Anglo-Saxon Chronicle said ‘he gerad to Ecgbryhtes stane be eastan Sealwyda‘. So both accounts agree (albeit probably not independently) that Egbert’s Stone was in the eastern part of the forest. How could Penselwood, which is so close to the western boundary, be said to be in the eastern part?
It seems that right from the early days of this royal forest the two parts, in Somerset and in Wiltshire, were administered separately; so the whole of Wiltshire might have been considered the pars orientalis. But that doesn’t help, unfortunately, because Penselwood is in Somerset and doesn’t seem ever to have been in Wiltshire; even though, enticingly, it has a boundary stone at the tripoint marking the boundaries between Somerset, Wiltshire and Dorset.