A relative age dating activity
If a body of granite contains unmelted inclusions of another rock, the granite is the younger rock. Granites can intrude into other rocks, even though they may be on the bottom of your geologic diagram.Look carefully for the granitic pattern (see below) and for irregular contacts between the granite and the country (preexisting) rock (see ctivity figure 2).Igneous rocks are dated according to whether they caused metamorphism in the surrounding rock (proof that they intruded into the preexisting rock), whether they cross cut preexisting rocks, or whether sediments were deposited on them after they were formed.The profile from one location is then compared with profiles from surrounding sites to determine the geologic history of a larger area.Principle of original horizontality: sedimentary layers are horizontal, or nearly so, when originally deposited.Strata that are not horizontal have been deformed by movements of the arth s crust.
Lava flows may cause contact-metamorphism with the older rocks they lie upon.
Principle of crosscutting relations: geologic features, such as faults, and igneous intrusions are younger than the rocks they cut.