It is reassuring that the coins in both these cases are being offered to the museum.
While handing it to someone at the museum is of course the obviously right thing to do from a responsible viewpoint I would point out for those unaware that it is an offence to remove an artefact of any description from the World Heritage Site. Technically I guess one would have to bring something to the attention of the authorities from the site or from a practical view take it direct to the museum. In the case of something found on Silbury it is complicated by the fact it would actually be owned by Lord Avebury, who fortunately wants anything like this put into the museum.
A Geo II coin is evidence if found on the slopes or at the base and the location can be corroborated. Well done for finding it.
In case anyone finds anything and doesn't have it to hand the number of the museum is 01672-539250 but do specifically ask for the Curator or leave her a message.
Meanwhile I will attempt to find out what the actual procedure is supposed to be and post it.
VBB