This comprehensive site explores a number of soil related topics. A glossary of soil terms, formation of soils, and classification of soils are just of a few of the topics found on this this.

This program uses a scenario with fictional detective characters to present plant growth to learners. While the unit focuses on the basic needs and parts of plants, the topics of plant classification and adaptations, soil formation and...

A wonderfully detailed introduction to the topic of wind erosion and landforms. Contains many illustrations and maps which show the concepts that are presented in the text.

This site is a personal site from John W. Kimball, a Harvard Professor, that contains a brief definition of both topsoil and subsoil. A drawing supplements the text.