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You can see that the curb is offset: the bottom half does not line up with the top half.As it turns out, the famous San Andreas fault runs below the curb at this location, which has caused the curb to be broken and displaced.Due to that discovery, Smith was able to recognize the order that the rocks were formed.Sixteen years after his discovery, he published a geological map of England showing the rocks of different geologic time eras.As he continued his job as a surveyor, he found the same patterns across England.
Imagine cutting a slice of bread from a whole loaf.Because of cross-cutting relationships, the cut that divides the slice from the rest of the loaf is younger than the loaf itself (the loaf had to exist before it could be cut).When investigating rocks in the field, geologists commonly observe features such as igneous intrusions or faults that cut through other rocks.Taughannock Falls near Trumansburg, New York, illustrating the Principle of Superposition. Superposition is observed not only in rocks, but also in our daily lives. The trash at the bottom was thrown out earlier than the trash that lies above it; the trash at the bottom is therefore older (and likely smellier! Or, think about a stack of old magazines or newspapers that might be sitting in your home or garage: most likely, the newspapers at the bottom of the pile have dates on them that are older than the newspapers at the top of the pile.The photograph below was captured at Volcano National Park on the Big Island of Hawaii.