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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).

This orientation is not an assumption, because in virtually all situations, it is also possible to determine the original "way up" in the stratigraphic succession from "way up indicators".

For example, wave ripples have their pointed crests on the "up" side, and more rounded troughs on the "down" side.

They are applied by geologists in the same sense that a "null hypothesis" is in statistics -- not necessarily correct, just testable.

In the last 200 or more years of their application, they are valid, but geologists do not assume they are.

However, note that because of the "principle of cross-cutting relationships", careful examination of the contact between the cave infill and the surrounding rock will reveal the true relative age relationships, as will the "principle of inclusion" if fragments of the surrounding rock are found within the infill.

Cave deposits also often have distinctive structures of their own (e.g., spelothems like stalactites and stalagmites), so it is not likely that someone could mistake them for a successional sequence of rock units. Each of them is a testable hypothesis about the relationships between rock units and their characteristics.

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In such a situation, the "principle of superposition" is easily applied, and the strata towards the bottom are older, those towards the top are younger.To search all Library collections (including American Memory) please visit loc.gov/search, or browse the full array of digitized collections at loc.gov/collections.You can also use the links below to go to the new presentations for single collections.These are often characterised as the norm, rather than the exception.I thought it would be useful to present an example where the geology is simple, and unsurprisingly, the method does work well, to show the quality of data that would have to be invalidated before a major revision of the geologic time scale could be accepted by conventional scientists.

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