overburden vs slow down

overburden

verb
  • To overload or overtax. 

noun
  • A sterile stratum that lies above the stratum being investigated 

  • The rock and subsoil that lies above a mineral deposit such as a coal seam. 

slow down

verb
  • To decelerate. 

  • To reduce the velocity, speed, or tempo of something. 

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