crag vs escarpment

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. 

escarpment

noun
  • A steep descent or declivity; steep face or edge of a ridge; ground about a fortified place, cut away nearly vertically to prevent hostile approach. 

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