'The Virginia Magazine of History and Biography, Vol. 21, No. 4' (Oct 1913), pg. 428 states -

"Col. Thomas Slaughter (Robert, Francis, Francis, John) settled in Caroline County, Va. He was Colonel of Militia. He married Sarah Thornton, daughter of Francis and sister of Reuben Thornton by whom he had issue"

'Genealogical and Historical Notes on Culpeper County, Virginia' (1900), pg. 85 states that Thomas Slaughter, son of the second Robert Slaughter (Robert, Robert, Francis, Francis, John) married Miss Thornton.

So, we have two books of genealogy. Both must be considered somewhat authoritative since both are referred to quite frequently by genealogists. The question now is... which one is correct?