In no way are they meant to imply there are no exceptions.
For example, the principle of superposition is based, fundamentally, on gravity.
Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another.The following data might be compromised if you continue: 1. Further action on this computer or any other device on your network might reveal private information and involve serious risks. Code: 055BCCAC9FEC Internet Security Alert : Your Computer Might Be Infected By Harmful Viruses. The following data might be compromised if you continue: 1. The principle of superposition therefore has a clear implication for the age of a vertical succession of strata.There are situations where it potentially fails -- for example, in cave deposits.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.They are applied by geologists in the same sense that a "null hypothesis" is in statistics -- not necessarily correct, just testable.The most common rocks observed in this form are sedimentary rocks (derived from what were formerly sediments), and extrusive igneous rocks (e.g., lavas, volcanic ash, and other formerly molten rocks extruded onto the Earth's surface).The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy".To get to that point, there is also a historical discussion and description of non-radiometric dating methods.The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods" in the Age of the Earth FAQ and Isochron Dating FAQ).