Now we have, I hope, a better idea of the position the strata we have been specially studying occupy in the geological history, and shall understand the relation the strata we may find elsewhere bear to those in the Isle of Wight and the neighbouring south of England. After this sketch of what went before our Island story, we must see what followed at the end of the Oligocene period. We said that there are no strata in the British Isles representing the next period, the Miocene. But it was a period of great importance in the world's history. Great stratified deposits were laid down in France and Switzerland and elsewhere, and it was a great age of mountain building. The Alps and the Himalaya, largely composed of Cretaceous and Eocene rocks, were upheaved into great mountain ranges. It is probable that during much of the period the British Isles were dry land, and that great denudation of the land took place. But in the first part of the period at all events this part of the world must have been under water, and strata have been laid down, which have since been denuded away. For our soft Oligocene strata, if exposed to rain and river action during the long Miocene period and the time which followed, would surely have been entirely swept away. The Miocene was succeeded by the Pliocene, when the strata called the Crag, which cover the surface of Norfolk and Suffolk, were formed. They are marine deposits with sea shells, of which a considerable proportion of species still survive.