Since the British Eocenes, especially of the Hampshire Basin, were mapped by the Survey, a portion of them have been separated by several writers as Oligocene. The utility of the change is not apparent in our country, where the break is seen to be purely artificial; but in other parts of Europe the Oligocenes, which embrace formations previously known as Lower Miocene, are of great importance. This change, absorbing the entire Upper Eocene fromation of the Isle of Wight, would seem alone to necessitate a reconsideration of the classification of the remainder. But the classification of the Eocene formation, invented and often modified when the beds composing it were imperfectly known, is throughout arbitrary and artificial, and scarcely yet on a scientific basis. Most of the present divisions comprise under one name the very distinct deposits formed by river, sea, or estuary, though these have been brought from quite opposite directions, and are perhaps by no means contemporaneous.