digging vs exploration

digging

noun
  • The action performed by a person or thing that digs. 

  • A place where ore is dug, especially certain localities in California, Australia, etc. where gold is obtained. 

exploration

noun
  • The process of penetrating, or ranging over for purposes of (especially geographical) discovery. 

  • A physical examination of a patient. 

  • The process of exploring. 

  • The (pre-)mining process of finding and determining commercially viable ore deposits (after prospecting), also called mineral exploration. 

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