I believe that your Mary M. Black is connected with the Blacks that came to Union Co., Ark about 1840 from the Wilcox, Perry, Monroe Co, AL area, and before that they were in the Abbeville Co., SC area prior to 1800.If that is the case then your co-lateral families would Davis, Glenn, Calhoun, Caldwell, Russell, Rogers, Brown, Alexander.Their folks were also in the Mecklenburg Co., NC area.
They all came on a wagontrain from Al about 1840.The wagontrain stopped for awhile when they got to Farmerville, LA and most continued on the Union Co.They spent a year in Farmerville while Robert J. Black and his slaves blazed out a road to Union Co.,Ark. where there had only been rabbit trails.The dispersed from there.Robert J. Black later became an important part of the formation of Union Co. and its politics.I also think that there is something written in Goodspeed's of Union Co., Ark
Their journey was somewhat documented in Tracks & Traces - Union Co., Ark Genealogical Society 1986-87, Vol. 8-9.
I am not a Black descendent - but, am a Davis.
Hope this helped - good luck - Ruth in Portland, OR