I am descended from a John Atchison/Acheson who was born in Northern Ireland in 1710 and settled in Little Britain, Lancaster Co., PA, about 1735. He was married to Catherine Clark. (Both spellings appear in early PA records, but descendants in my line spell it Acheson.)
There was also an Alexander Atchison/Acheson, son of Sir Arthur, who settled in Lancaster County sometime later, but before the Revolutionary War. Alexander was the grandfather of Senator David Rice Atchison, who was the questionable "President for a day" between the terms of Polk and Taylor. They are descended from a noble Acheson family that originated in Gosford, County Haddington, Scotland in the early 1600's.
Do you have information on either of these two families, and in particular, do you know whether they were related?