Source Texts
Text
The geologic principle of cross-cutting relationships states that an intrusion is younger than the rocks through which it cuts. ____ geophysicists analyzing a given rock formation can ascertain that an igneous intrusion that bisects a layer of 358.9-million-year-old Tournaisian rock but not the 303.7-million-year-old Gzhelian rock above it is younger than the former but older than the latter.