As Far As Quotes (page 44)
You can find virtually everybody black back as far as the 1870 census. Why 1870? That's when the ex-slaves first have surnames. But if you find your great-great-grandfather in 1870 and it says he's 50, that means he was born in 1820 and you're back to 1820 already. For an American that's pretty damned good, you know?
Henry Louis Gates