Glendalough is an odd place. I think it's on record that that example was thrown in or washed down in a storm. Add the fact that Glendalough has over 25 genuine bullauns I think it's a pretty safe bet to classify that particular example. That bowl is also 40cm across, which is far bigger than any river-worn one I've seen elsewhere.
There is one up stream from that which is in an earthfast boulder in the river bed that is below the water line. I would definitely put a dodgy flag on the up stream one. However, as the course of the river has moved many times it's hard to be sure that it started out in the river.
There are many river bed basins in Ireland too that are most certainly nautural. Many of them have still been sacred over the years, though - usually an early saint's knee prints. Again, being linked to an early saint does hint at the bowls being sacred beforehand, even if they are 100% natural.
A lot are associated with water, but few of them are close to fast running water, so a river-rolled-based origin is not valid for most.
This one's almost certainly got water-worn-origins, but no way are all of them natural.
As with all these things it is up to each person to have their own opinion about such things. It's easier to have a strong one when you've seen over 100 of the little buggers, though :-) As with people, so it is with websites. It's up to TMA to have a policy based on the site's opinion of bullauns and at the moment any (well most) ideas are valid.
The definition of a bullaun stone is simple - a stone with one or more large manmade/enhanced basins, usually hemi-sperical, at least 10cm in diameter.
The 10cm bit is where I personally cut them off, but the rest is pretty standard. I've seen smaller ones classed as bullauns, which I class as large cupmarks. The classification really is loose, because no one has studied and catagorised them effectively. For example, there is a group in Carlow that are conical, but still classed as bullauns. Should they be? I'm not so sure myself, but others seem to be.
