highland vs hummock

highland

noun
  • A high area; land that is higher than surrounding areas. 

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 highland and hummock occurred in a corpus of books? (source: Google Ngram Viewer )