midden vs slag heap

midden

noun
  • A refuse heap usually near a dwelling. 

  • A shelter made of vegetation and other materials by packrats. 

  • An accumulation of dried urine and fecal deposits made by hyraxes. 

  • A prehistoric pile of bones and shells. 

  • A dungheap. 

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 midden and slag heap occurred in a corpus of books? (source: Google Ngram Viewer )