"Dating the fossils by the layer they are found in and dating the layers by the fossils they contain."
Do you have a source for this contention?
How do you know how old each layers is? Well do you not say, “we know this layer is this old because of the fossils in it?”
Source, The Science museum in Boston, the one in Portland, Maine and that great big one in Washington goes by the name of smith something or other.
Go to a museum and just ask them:
How do you know the age of these fossils?
Later ask them "How do you know the age of these layers?"
See what you get for an answer. Let me know if you find a museum or reachers that says other than I have stated.
I call it circular logic others call it circular reasoning.