Unconformities-very long times of nondeposition and/or erosion, of which there are three basic types.
- disconformity- surface(erosion) seperating younger from older rocks. These rock layers are horizontal (parallel) to each other.
- nonconformity- erosion surface that separates old metamorphic rocks from younger sedimentary rocks.
- angular unconformity- tilted sedimentary rocks that are overlain by younger flat-lying sedimentary rocks.
Principle of inclusions- inclusions or fragments in a rock are older than the rock itself.