crag vs ore

crag

noun
  • A rough, broken fragment of rock. 

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

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

ore

noun
  • Rock or other material that contains valuable or utilitarian materials; primarily a rock containing metals or gems for which it is typically mined and processed. 

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