OK, let's Undo the Top Layer.

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• Remember: The fault cuts the layers, so the fault is more recent than the layers.

This shows how the scene would have looked if the fault had moved before the layers finished depositing. This would mean that the top or most recent layer would have had to deposit on top of an irregular surface like this.

Although layers can deposit on top of an irregular surface, when they do, the irregularities are preserved. If a layer were to deposit on top of what we see here, it would have been thicker on the left and thinner on the right.

Since the layers we see today are the same thickness on both sides of the fault, an irregular surface as shown here did not appear in the past. Thus, the layer deposit is older than the fault motion.

Written by Marvin Simkin Filename undolyr1.html Last updated September 26, 2002