grey matter vs profundity

grey matter

noun
  • Brains; a person's ability to think. 

  • A collection of cell bodies and (usually) dendritic connections, in contrast to white matter. 

  • Literal brains as a general substance. 

profundity

noun
  • Deep intellect or insight. 

  • A great depth. 

  • The state of being profound or abstruse. 

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