Appearance overwhelms content in this poorly designed title in the I Didn’t Know That series. Too many feature icons (projects, true/false questions, search-and-find activities) engulf the factual information and result in a book that’s confusing and difficult to follow. Oliver covers dormant and extinct volcanoes, mud baths, magma, hot springs, magnetic forces, and other fascinating aspects of the topic, but the content doesn’t flow, and some of the more interesting details are simply swept aside. (glossary, index) (Nonfiction. 6-8)