I am reposting this query in the great expectations that it will reach someone out there who can help me.

My ancestor, Margaret Johnston, was born about 1825 in Ireland to James Johnston and Margaret Jane Groves. She married James McDonald in Gloucester Township, Carleton County, Ontario on Dec 17, 1845. They had children James in 1846 and Sarah in 1849. Then they disappeared. In 1874, Margaret, widow, did a land transaction in Gloucester and her residence was Morristown, New York.
Since then, I have found this family which I strongly feel is the correct family in 1850.

1850 St. Lawrence Co. census. Living in Oswegatchie, St. Lawrence Co., NY were the following.
James McDonald 27 years Laborer born Canada
Margaret McDonald 25 yrs Canada
James McDonald 3 yrs Canada
Margaret McDonald 2yrs Canada
Sarah McDonald 1 yr Canada
George McDonald 3/12 NY

then in 1870, this MAY be the same family in Morristown
James McDonald 46 yrs. (abt 1824)Born Canada Laborer
Margaret McDonald 43 yrs. (abt 1827)Born (shows Canada)
House wife
Angus McDonald 13 yrs. Born NY
Robert McDonald 11 yrs. Born NY
Sarah Jane McDonald 9 yrs. Born NY
Catherine McDonald 7 yrs. Born NY
Allen McDonald 4 yrs. Born NY

So James must have died between 1870 and 1874, probably Morristown.
Now, I have found this, which may or may not be the son James and mother Margaret in Brier Hill Cemetery, Morristown.

http://freepages.genealogy.rootsweb.com/~stlawgen/CEMETERY/B...
McDonald Monument
James McDonald, d. Jan 24, 1872; AE 26 yrs, 1 mo, 13 dys
Maria C., wife of James McDonald, d. Aug 18, 1886 AE 46 yrs, 1 mo
Clara Eveline, dau, d. Aug 13, 1871 Aged 10 mos

Margaret, wife of James McDonald, Mother, 1823-1895

If anyone can elaborate on any of this, such as find the death of James between 1870 and 1874, or Margaret in 1895, or the marriage of son James and Maria, or the births of any of Margaret's children, I would be so grateful.
Thank you
Peggy