Mary was not a child of John and Margaret Cunningham Houston. Their 7th child was James who stayed behind while the rest of the family emigrated. This is confusing as Matthew was not exactly an infant when this will was dated, he was born in Ireland about 1730, one of the six children, Isabella, Esther, John, Matthew, Samuel and Robert, who immigrated with John and Margaret. Matthew Lyle and Esther Blair were the parents of Martha Lyle who married Matthew Houston. (Possibly Mary Blair was a relative of Esther Blair Lyle?)Matthew and Martha married about 1758, are both buried at Timber Ridge Presbyterian Church in Rockbridge Co. They had 7 children, all confusedly named the same as most of the Houstons of several generations:Matthew, John, Samuel, James, Margaret (Peggy),Esther and Robert. Three of those children added to the confusion by marrying cousins in the Houston and Gillespie lines. I believe the Moores and others mentioned were neighbors, but I don't have the survey plats at hand.