Defining the Principle of Cross-Cutting Relationships
The Principle of Cross-Cutting Relationships is a fundamental concept in geology that states any geologic feature that cuts across another feature must be younger than the feature it cuts. In simpler terms, the cutter is younger than the cut.
Section 2: Core Components of the Principle
This principle applies to various geologic features. The feature being 'cut' is typically a rock layer or formation. The 'cutting' feature can be a fault (a fracture in the rock), an igneous intrusion (like a dike or sill where magma has pushed through), or a surface of erosion. The entire cutting feature is considered younger than any rock or feature it passes through.
Section 3: A Practical Example
Imagine observing a sequence of horizontal sedimentary rock layers. If you see a vertical sheet of igneous rock (a dike) cutting through all these layers, the Principle of Cross-Cutting Relationships tells you that the sedimentary layers were deposited first, and the igneous dike intruded later. Therefore, the dike is the younger geologic feature.
Section 4: Importance in Geology
This principle is a crucial tool for determining the relative age of rocks and events. By applying this rule, along with others like the Principle of Superposition, geologists can piece together the chronological sequence of events in a region's geological history. This helps in creating geologic maps and understanding complex geological formations without needing to know their absolute age.