dunghill vs slag heap

dunghill

noun
  • A heap of dung, especially one for agricultural purposes. 

  • Any wretchedly mean, dirty or loathsome place, situation or condition. 

slag heap

noun
  • A man-made mound or heap formed with the waste material (slag) as a by-product of coal mining. Can also refer to the waste by-product from a foundry or furnace, formed into such a mound. 

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