assart vs morass

assart

noun
  • Forest land cleared for agriculture. 

verb
  • To clear forest land for agriculture; remove stumps. 

morass

noun
  • A tract of soft, wet ground; a marsh; a fen. 

  • Anything that entraps or makes progress difficult. 

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