Substrata is an ambient music album by Biosphere, released in 1997 by All Saints Records. It is considered to be a classic ambient album, consistently in the top 5 in surveys on the Hyperreal ambient mailing list http://music.hyperreal.org/epsilon/info/1999_recommended_ambient.html http://music.hyperreal.org/epsilon/info/2001_classic_ambient.html http://music.hyperreal.org/epsilon/info/2003_sleepy_music.txt.

The material that the alga's holdfast is bound to.

a layer of rock or soil beneath the surface