For example, the principle of superposition is based, fundamentally, on gravity.
They are the "initial working hypotheses" to be tested further by data.
Using these principles, it is possible to construct an interpretation of the sequence of events for any geological situation, even on other planets (e.g., a crater impact can cut into an older, pre-existing surface, or craters may overlap, revealing their relative ages).
An early summary of them is found in Charles Lyell's .
In no way are they meant to imply there are no exceptions.
They are applied by geologists in the same sense that a "null hypothesis" is in statistics -- not necessarily correct, just testable.