Fired bricks and concrete are derived from earth, but structures built from these materials are usually not considered earth structures. - please add a reference
Lindauer & Blitz 1997, pp. 169ff. - Lindauer & Blitz 1997, p. 169ff.
Snell 2004, p. 27-28. - Snell 2004, pp. 27-28.
Elleh 1998, p. 47. Harv error: link from #CITEREFElleh1998 doesn't point to any citation. (f you install
this, HarvErrors are easy to notice.)
Porterfield 2004, p. 39. Harv error: link from #CITEREFPorterfield2004 doesn't point to any citation.
Sources
Elleh, Nnamdi (1997). African Architecture: Evolution and Transformation. McGraw-Hill.
ISBN978-0-07-021506-1. Harv error: There is no link pointing to this citation. The anchor is named CITEREFElleh1997.
Porterfield, Jason (2004-05). The Homestead Act of 1862: A Primary Source History of the Settlement of the American Heartland in the Late 19th Century. The Rosen Publishing Group.
ISBN978-1-4042-0178-1. Retrieved 2014-04-27. Harv error: There is no link pointing to this citation. The anchor is named CITEREFPorterfield.