downland vs hummock

downland

noun
  • An area of rolling hills (downs), often grassy pasture over chalk or limestone. 

hummock

noun
  • A small hill; a hillock; a knoll. 

  • A fistful. 

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

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