Regarding Hob’s photo
themodernantiquarian.com/post/31699/king_arthurs_round_table.html
In Mayburgh and King Arthurs Round Table by C.W. Dymond CWAAS 1890.
In the inn yard, serving as a water butt, is a circular tank of red sandstone, 38ins in diameter and about 36ins in depth, which has been called “King Arthur’s Drinking-cup.” About this object, as many another, a baseless story has been started which, unless checked, may in time, become, by repetition, a fixed tradition of the spot. I find that even some antiquarians have been misled by confiding too easily in statements made to them, to the effect that this tank was dug up on the site of the Round Table; nay, that it has been found in the very centre thereof. I myself was told this improbable tale, till on closely cross-questioning my informant,-the same who had set the story afloat, – he acknowleged that he knew nothing about it; and that he had stated as fact that which he only supposed to be so. The aforesaid man-the most ancient authority in the village, having lived there for more than 60 years-testified that it had been in the inn yard, (though not in the same position) as long as he could remember. of course, this tank has never really had any connection with the earthwork over the way.
Awww, bugger.
Mind, I think it might be that the stone used to stand outside the henge, in uncarved, pre-cup tank form. I'm sure I've seen an older ref claiming there were upright stones outside the henge. I think Camden has a first hand account ofa whole load of stuf between Mayburgh and the Table. (Having said that, I mistook the Victorian tea-room platform for a prehistoric feature, so I'm willing to admit I'm probably just being over-optimistic)
Don't give up hope Hob,
Sir William Dugales 16th century plan of the henge showed two large stones outside of the destroyed entrance, these were also mentioned by Aubrey in Monumenta Britannia but had disappeared by the time Stukeley visited some 70 odd years later.
Waterhouse speculates that there may have been more stones in or around the monument originally.
In Prehistoric Monuments of the Lake District, Tom Clare discusses the material tipped to form the present disc and states that there were substantial splinters of a large stone of 'Borrowdale igneous rock'. One of these splinters is recorded as being 0.6m long, so that the original stone must have been large. Whilst this may have been part of a cist or covering for the central burial, the geology would suggest the stone was an erratic and therefore likely to have been a boulder rather than a slab.
The source of the Old Red Sandstone is probably Geltsdale (note name) a dozen miles to the north. That would be an acceptable distance to bring the stone - but would it have been hollowed out before it travelled or after? And for a man 'who has no car', Hob, you sure get about. Remember what Holmes used to say? Watson, we'd better consult Bradshaw ...