married July 20 1912 in Andover, MassachusettsMargaret was 29, born in Scotlandher parents: Georg Burgess and Mary Bews
This is the evidence for the name of Margaret's (and by extension, Mary's) mother.
one tree says they were married 1878 in St Giles (presumably St Giles Cathedral in Edinburgh), citing the website ScotlandsPeoplethe other tree says they were married 29 Aug 1878 in Edinburgh, with no citation