After being confused by these posts I decided to go up to the grave for a look!& I would like to make a couple of corrections. The inscription at St runius reads.........
Mary (not Ann)beloved wife of cpt Matthew Grose....mines.. etc etc.January 1839. ,as I have cleaned it off & read it (have pics) It is also implied by Brian Lawson & others, the Mary in the 1851 census is Matthew`s wife,clearly not,.The published Cornwall obituary for his wife Mary (Vivian) Wearn,states she died in January 1839,(as inscription), and aged 49,that also tallies with her birth year,1790.
The mystery Mary Grose in the 1851, & 1861 census, could possibly be a relative of Matthew`s? She is described in both as an annuitant,so was being looked after financially for some reason?But is definately not his wife!