On a whim, I searched Google Images for "potting up" and
"potting mix":
This blog page has a good description of someone mixing up
their own potting mix out of compost, peat, and perlite:
http://tinyfarmblog.com/tag/potting-up/
An in-depth description of soilless potting mix components:
http://www.progressivegardening.com/...ernatives.html