There's an interesting post on the motivation for this here, http://www.levitylab.com/blog/2011/06/geology-an-interactive-primer/ http://www.levitylab.com/blog/

There's an interesting post on the motivation for this here, http://www.levitylab.com/blog/2011/06/geology-an-interactive-primer/ http://www.levitylab.com/blog/2011/06/geology-an-interactive... (note the post date).