disconformity vs unconformity

disconformity

noun
  • A type of unconformity in which erosion or lack of deposition has occurred between two parallel sedimentary strata. 

  • nonconformity 

unconformity

noun
  • A gap in the stratigraphic record at a site, resulting from erosion having outpaced deposition over the interval in question. 

  • A lack of conformity. 

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