massif vs tor

massif

noun
  • A principal mountain mass. 

  • A block of the earth's crust bounded by faults or flexures and displaced as a unit without internal change; normally consists of gneisses and schists 

tor

noun
  • A hill with such rock formation. 

  • A craggy outcrop of rock on the summit of a hill, created by the erosion and weathering of rock. 

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