Layered Intrusions

A layered intrusion is a set of igneous rocks emplaced into the crust of the Earth in such a way as to be exposed to eventual uplift and weathering where we can see it. Such a body is ideally defined by oldest rocks at the base and youngest rocks at the top, with the exception of any roof rocks preserved that will meet the upward layering rocks in what has been pleasantly named a sandwich horizon. Layered intrusions have important ways of revealing to us examples of phase equilibria that are fundamental. We only have to discover what these principles are.