Photograph courtesy of U.S. Geological Survey.
Geologists use cross-sections to unravel the history of an area.
This diagram shows a cross-section of Hiiaka Crater. The geology shown in the cross-section is the result of nine events. The handouts for this activity are available at the bottom of this page. A few simple geologic laws serve as guidelines for interpreting cross-sections. The Law of Original Horizontality states that sedimentary rocks, and some volcanic rocks, form as horizontal layers.