landfill vs scoria

landfill

noun
  • A site at which refuse is buried under layers of earth. 

  • The material so disposed of. 

verb
  • To dispose of (garbage) by burying it at a landfill site. 

scoria

noun
  • Rough masses of rock formed by solidified lava, and which can be found around a volcano's crater. 

  • The slag or dross that remains after the smelting of metal from an ore. 

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