Although it doesn't directly deal with digging, I would recommend the
book Con Tiki, by Thor Heyerdahl. It discusses one of many possible
sea routes for people to cross the ocean to the Americas/Polynesian
Islands.
Gerald (Gary) Smith, SSgt To be is to do - Socrates
[log in to unmask] To do is to be - Sartre
Do be do be do - Sinatra