chalk talk vs sermon

chalk talk

noun
  • An informal lecture on an academic subject. 

  • A music hall act in which a performer makes chalk caricatures whilst reciting a monologue 

sermon

noun
  • A lengthy speech of reproval. 

  • Religious discourse; a written or spoken address on a religious or moral matter. 

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