What is "dirt bed"

Dirt \Dirt\ (d[~e]rt), n. [OE. drit; kin to Icel. drit excrement, dr[=i]ta to dung, OD. drijten to dung, AS. gedr[=i]tan.]

1. Any foul of filthy substance, as excrement, mud, dust, etc.; whatever, adhering to anything, renders it foul or unclean; earth; as, a wagonload of dirt.

   Whose waters cast up mire and dirt.
   --Is. lvii. 20.

2. Meanness; sordidness.

   Honors . . . thrown away upon dirt and infamy.
   --Melmoth.

3. In placer mining, earth, gravel, etc., before washing. Dirt bed (Geom.), a layer of clayey earth forming a stratum in a geological formation. Dirt beds are common among the coal measures. Dirt eating.

   1. The use of certain kinds of clay for food, existing among some tribes of Indians; geophagism.
      --Humboldt.

   2. (Med.) Same as Chthonophagia.

      Dirt pie, clay or mud molded by children in imitation of pastry.
      --Otway (1684).

      To eat dirt, to submit in a meanly humble manner to insults; to eat humble pie.

n. (context geology English) A layer of clayey earth forming a stratum in a geological formation.