There is a marriage of James Watts(Widow, of Inkpen, Berks) to Mary Hall - @ Henly - 14 Nov 1818.
But according to the 1841 census, the Mary he is with, was born in county.
He may have remarried to the Mary ? ? ? c1808, Hughenden, Bucks. after 1841.
I have checked the BucksFHS Hughenden PR. disc, and there is no Mary Hall baptised there, although there are other Hall children baptised.
I suggest a purchase of Rebecca Watts birth cert, to be on the safe side.
Steve.
