Bibliography and further reading about geology:
Planet Earth, Grades 4-6+, by David Stewart (2002). Ages 9-12.
Geology Rocks!: 50 Hands-On Activities to Explore the Earth, by Cindy Blobaum (1999). Ages 9-12. Lively and entertaining. From Amazon, "I have used this book for my children's homeschool study, and it is FANTASTIC!"