I found it with my Mine Lab CTX 3030 with the 17" coil. It was a good 15" in the mud/clay. I also was in sea water 4' deep. That ring had been there for a long time. So here is the latest on the ring.
Here is a up date on the ring : .Part 1 ..I think the ring was lost and belonged, or was passed down to, William de Blaquiere, 6Th Baron de Blaquiere of Ardkill (1856-1920), as he appears to be one of the only two family members to have crossed the Atlantic, the other being Peter Boyle de Blaquière
Peter de Blaquière - Wikipedia, the free encyclopedia. He married Lucienne Desbarats, daughter of George Desbarats, on 25 January 1888 at Christchurch Cathedral, Montreal, Quebec, Canada. So, we can assume that perhaps, for whatever reason, he landed in Maine, before making his way to Quebec, and somehow lost the family heirloom on route? He died in1920 aged 63, without surviving male issue. The motto "Tiens a la Verite" is French (the family was originally from there) and means "Hold to the Truth". It is the family motto of the de Blaquiere family. The wheat-sheaf is also a family crest associated with the de Blaquière family
Family Crest: Garb or Wheatsheaf
- Person Page 5140
...it really is a thing of beauty and has historical ties to both Ireland and Canada. I am sure that both these countries, especially Ireland would love to get the ring back and perhaps you should write to the American ambassador in Ireland, as he now stays in the former de Blaquiere family residence in Dublin (Now the American Embassy located right beside the Irish Presidents palace!! The ring does have value and you should try to research more
Part 2 ...as I stated before, it could be a family heirloom passed down from Baron (Lord) to Baron (Lord) and could have originally been presented by John de Blaquiere, 2nd Baron de Blaquiere (1776–1844), for his son William de Blaquiere, 3rd Baron de Blaquiere (1778–1851). It does have the family motto and crest on it, and was made as a seal. So, what I have written makes sense? It would have eventually arrived in the hands of William Barnard de Blaquiere, 6th Baron de Blaquiere (1856–1920) and it was he who lost it? It would never have been in the hands of his father, Peter, as he was never bestowed with the peerage (Baron Title).
...of course, the ring could have been made even earlier and the inscription was added by the 2nd Baron when he presented the ring to his son, the new 3rd Baron. This may explain the lack of important hallmarks (i.e. it was an old ring when it was inscribed)? The inscription could have been completed in Ireland by one of the finest 18th century silversmiths in Ireland; Joseph Walker (JW) and perhaps he stamped his initials and the 18 for fineness onto the ring when he inscribed it??
...all the above is just speculation really. I have tried to find paintings or photographs of the various Barons, to try and spot if they were wearing a similar ring, but have been unsuccessful (several paintings and photographs, but none showing a ring), but I am going mainly on internet research, which is not the best for this kind of search.
...once again, this probably needs professionally researched, as it is undoubtedly a historic piece. The de Blaquiere family were involved in some of the most famous historic events in the UK, Ireland, and latterly Canada. Family members also encountered famous people from history, such as Captain William Bligh (Famous because of the mutiny on the Bounty). The provenance and history behind this ring would be second to none!!!
Congratulations on finding it, and for making a well deserved banner find. 
Breezie
