The Lower and Upper Carboniferous owe their names to the deepest theoretical tenet of geology – the Principle of Superposition. This states that the new stuff is on top of the old stuff. It is credited to Niels Stensen (a Dane, who like many intellectuals of the day usually went by a Latinized version of his name, in his case Nicolaus Steno) in the mid-seventeenth century. Sometimes, because the Earth is active and throws material about by faulting and folding, the older rocks end up on top of the younger ones. But the geologist would still call the older ones “lower” and the newer ones “upper'