argillic vs earthen

argillic

adj
  • Of or pertaining to clay or clay minerals. 

noun
  • A soil of this kind. 

earthen

adj
  • Made of clay (especially said of pottery). 

  • Made of earth or mud. 

verb
  • to provide or add soil to 

  • to make earthly or earthlike 

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