Linda, I think you're overlooking the other obvious possibility - that an unmarried woman from a European Harris family had a son by an African-American man. Paul's research has demonstrated that the large majority of FPOC in 17th-century VA were descended from such unions. And he's turned up at least two similar relationships in Southampton County in the second half of the 18th century. Interestingly, neither of the women in those cases appears to have been prosecuted for bastardy, nor were their children bound out in infancy as the law supposedly required.
Mason is a name I don't remember running into in Southampton. Do you have names, dates or parents for your Southampton Harrises?