autochthon vs indigen

autochthon

noun
  • The earliest inhabitant of an area; an aborigine. 

  • A large mass of rock in the place of its original formation, rooted to its basement (foundation rock) as opposed to an allochthon or nappe which has shifted from the place of formation; an autochthonous rock formation. 

indigen

noun
  • An indigene or native. 

  • A plant known to be indigenous to a region, rather than a cultigen. 

How often have the words autochthon and indigen occurred in a corpus of books? (source: Google Ngram Viewer )