cobblestone vs delf

cobblestone

noun
  • A rounded stone from a river bed, fit for use as ballast in ships and for paving roads. 

  • The material made from cobblestones. 

delf

noun
  • A mine, quarry, pit dug; ditch. 

  • A charge representing a square sod. 

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