halcyon days vs old days

halcyon days

noun
  • A period of calm, usually in the past and often nostalgic. 

  • Period of calm during the winter, when storms do not occur. 

old days

noun
  • A period that was a relatively long time ago; the distant past. 

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