Testing Hypotheses.
In Figure 13.2,
it was assumed that the dike cut the sedimentary layers (i.e., it is younger).
There is a very remote possibility that the dike was upstanding and the sediments
were deposited around the dike. How would you tell?
If the initial assumption was correct, the sedimentary
layers should be metamorphosed and there might be fingers of granite extending
into the sediment.
If the remote case was correct, the sedimentary layers would not
be metamorphosed and there could be inclusions of the granite in the sediments.
The second assumption was that the sedimentary layers
although tilted, were not overturned. Can test this by looking at sedimentary
structures:
Cross-Bedding:
cross beds are commonly cut off on the top of the bed and become parallel
to adjacent layers on the bottom.
Oscillation
Ripple Marks (symmetrical): wave-like features point to the
top of the bed.
Graded
Beds: grain-size fines upwards.
Mud Cracks:
in cross section these are wider at the top that at the bottom.