Answers to Puzzles:
Which is older, the rock at C or the rock at E or are they the same age?
The one on the bottom must be older, since it doesn't make sense that the top one floated up in the air while the bottom one slipped under it.  Also, in the clay thought exercise, we observed that the sand layer occured first at the location of C and E, and the mud layer occured later.

This represents different environments existing at one particular place at different times.

Which is older, the rock at C or the rock at D or are they the same age?
C must be older, since, as we saw in the clay-thought-puzzle, the beach reached that location before it arrived at location D.

This represents one particular environment existing in two different locations at different times.  The significance of this is that a rock layer, although it represents one particular environment, did not all form at one time.
 

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