No death date listed for Mary.
Mason's symbols on stone: Square and compass with G in center. 3 linked rings.
MAY BE a match to Thomas Bernard Hamilton and his wife Mary Lethbridge - I was sent to his page on Family Search, further research is needed to see if this is indeed a match., Little Bernie
MASONIC COMPASS & SET SQUARE
3 Link Chain symbol
Mary's Death year was listed as 19--