muskeg vs swale

muskeg

noun
  • A terrain composed of peat bog with tussocky meadow and woody vegetation including spruce. 

swale

noun
  • A shallow, usually grassy depression sloping downward from a plains upland meadow or level vegetated ridgetop. 

  • A long narrow and shallow trough between ridges on a beach, running parallel to the coastline. 

  • Bioswale, a shallow trough dug into the land on contour (horizontally with no slope), whose purpose is to allow water time to percolate into the soil. 

  • A gutter in a candle. 

  • A low tract of moist or marshy land. 

  • A shallow troughlike depression that's created to carry water during rainstorms or snow melts; a drainage ditch. 

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