Principle of Cross-Cutting Relationships

A relative-dating principle stating that a geological feature which cuts through another, a fault, a fracture, an igneous intrusion, must be younger than the feature it cuts. Nicolas Steno's 1669 Dissertationis prodromus, the same short work that stated original horizontality and superposition, contains an early statement of the idea; James Hutton formulated it more explicitly in Theory of the Earth (1795), and Charles Lyell folded it into the systematic relative-dating toolkit of Principles of Geology (1830). Alongside superposition, original horizontality and faunal succession, it lets a geologist read the order of events in a rock face with no instrument at all, and it still anchors radiometric dating today: a rock unit crossed by a datable dike or vein has its own age bracketed between older and younger bounds. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/