In the first volume, published in 1881, 
Charles Libby had this to say:  


"So far as discovered,-

The immigrant's sons numbered.........8................sons
Their sons numbered..................25.............grandsons
Their sons numbered.................105..........gt-grandsons
Their sons numbered.................288......gt-gt-grandsons
Their sons numbered.................772..gt-gt-gt-grandsons"

"If, as it natural to suppose, the daughters in all the generations,
on average, have had as numerous progeny as the sons, the
whole number of the immigrant's descendants cannot be less
than 300,000."

Wow!