drumlin vs hummock

drumlin

noun
  • An elongated hill or ridge of glacial drift. 

hummock

noun
  • A ridge or hill of ice in an ice field. 

  • A fistful. 

  • A small hill; a hillock; a knoll. 

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