Algae remains

• A light soil consisting of siliceous diatom remains and often used as a filtering material

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Infusorial \In`fu*so"ri*al\, a. (Zo["o]l.) Belonging to the Infusoria; composed of, or containing, Infusoria; as, infusorial earth. Infusorial earth (Geol.), a deposit of fine, usually white, siliceous material, composed mainly of the shells of the microscopic ...

Wiktionary Word definitions in Wiktionary
n. (context geology English) A fine, powdery earth formed from the skeletons of diatoms

WordNet Word definitions in WordNet
n. a light soil consisting of siliceous diatom remains and often used as a filtering material [syn: diatomaceous earth , kieselguhr ]