I have a little data on your John Black from LDS records who married Mary Elizabeth (Eliza) Adams.Mary Adams was born on 30 May 1868 in Worth County, Missouri (Probably in or near the town of Sheridan).John A. Black was also probably born in Sheridan about 1866 and was likely the son of Morgan E. Black (b. ~1827 in Kentucky) and Irene Clevenger (b. ~1844 and married Morgan Black on 11 September 1864 in Ray County, Missouri).In 1880 Morgan and Irene Black were living in Allen, Worth County, Missouri with three of their children, i.e., Charles W. (b. ~1868 in Worth County, Missouri), Noah (b.~1879 in Worth County, Missouri), and John A. (b. ~1866 in Worth County, Missouri).They were also living in Allen, Worth County, Missouri in 1870 according to the U.S. Census.There were a number of the Black Family living in Worth County during this time period including a John H. Black who was born about 1862 and was living in 1880 with his mother Catherine Black in Allen, Worth County, Missouri.Apparently John H. Black's father was no longer living as Catherine indicated in the 1880 Census that this was the case.I have found no documentation that definitely proves that John A. Black is the spouse of Mary Adams but believe that this is the likely case for you to consider. Should I find more definitive information I will contact you.