crag vs ridgeline

crag

noun
  • A rocky outcrop; a rugged steep cliff or rock. 

  • A rough, broken fragment of rock. 

  • A partially compacted bed of gravel mixed with shells, of the Pliocene to Pleistocene epochs. 

ridgeline

noun
  • The topmost edge along a mountain ridge. 

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