cavern vs paleohistory

cavern

noun
  • A large cave. 

  • A large, dark place or space. 

  • An underground chamber. 

verb
  • To put into a cavern. 

  • To form a cavern or deep depression in. 

paleohistory

noun
  • Synonym of archaeology 

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