mountain pass vs tor

mountain pass

noun
  • A low point in a mountain range that allows travelers to cross the range. 

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 mountain pass and tor occurred in a corpus of books? (source: Google Ngram Viewer )