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U. S. Geological Survey, Menlo Park |
| About: : |
The stripe of light-colored pavement in this picture hasn't always been there. Originally, the pavement was all one color, but then there was a problem with the sewer line. To replace an old sewer line, workers dug a trench that cut across the old pavement, and then filled it back in with a lighter colored asphalt. The lighter stripe is younger than the darker material around it. When in the sequence do you think they painted the words "STOP" on the ground? How can you tell? |
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Copyright Ramón Arrowsmith, Arizona State University
| Location: |
Grand Canyon National Park, Arizona |
| About: |
Blocks of rock that look like stripes cutting across existing layers are also common in nature. Here, the reddish-brown layers accumulated over time. After they were laid down, hot magma pushed its way through the layers towards the surface. The dark "stripe" is where some of that magma solidified before reaching the surface. The fact that the dark layer seems to cut so cleanly through the layers is evidence that it came along after they were deposited. (It is not possible to cut layers before they exist!) |
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U.S. Department of the Interior |
U.S. Geological Survey