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