cover ground vs linger

cover ground

verb
  • To do a certain amount of work; to make progress towards an end. 

linger

verb
  • To consider or contemplate for a period of time; to engage in analytic thinking or discussion. 

  • To remain alive or existent although still proceeding toward death or extinction; to die gradually. 

  • To stay or remain in a place or situation, especially as if unwilling to depart or not easily able to do so. 

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