boulder vs scree

boulder

noun
  • A large mass of stone detached from the surrounding land. 

  • A particle greater than 256 mm in diameter, following the Wentworth scale 

  • A large marble, in children's games. 

  • A session of bouldering; involvement in bouldering. 

verb
  • To engage in bouldering. 

scree

noun
  • Loose stony debris on a slope. 

  • Similar debris made up of broken building material such as bricks, concrete, etc. 

  • A coarse sieve. 

  • A harsh, high-pitched sound or cry (as of a hawk). 

  • A slope made up of loose stony debris at the base of a cliff, mountain, etc. 

verb
  • To flatten or level concrete while still wet, and remove protruding gravel and stones from the surface. 

  • To traverse scree downhill. 

  • To make a high-pitched cry like that of a hawk. 

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