There is an appearance that formerly the island of Great Britain was part of the continent, and that England was joined to France; the similarity of the stones on the two coasts, and the narrowness of this strait seem plainly to indicate it. By supposing, says Dr. Wallis, "that England formerly communicated with France, by an isthmus between Dover and Calais, it must follow that the sea would be carried against both sides of it with great violence by the tides twice in every twenty-four hours, the German ocean, which is between England and Holland, striking of it on the eastern side, and that of France on the west, would be sufficient in time to wear away so narrow a neck of land, as we have supposed. The tides acting with great violence, not only against this isthmus but also against the coasts of France and England, must have washed away a great quantity of sand, earth, and clay, from every part against which the sea was forced: but, being stopt in its course, it would not deposite, as might be supposed, their sediments against this isthmus, but transported them into the great plain that now forms Romney Marsh, which is eight miles long by four broad; for whosoever has seen this plain, cannot doubt but that it was formerly covered with the sea, as it would be still overflowed by spring tides if it was not for the Dikes of Dimchurch." The German sea must have acted in the same manner against this isthmus, and the coasts of England and Flanders would convey its sediments into Holland and Zealand, the ground of which, though formerly covered with water, is now forty feet above. On the coast of England, the German sea must have filled up that large valley, where the river Stour actually flows for more than 20 miles, beginning at Sandwich, passing Canterbury, Chatham, Chilham as far as Ashford. At this place the ground is much higher than it was formerly, since at Chatham the bones of an hippopotamus were found seventeen feet deep in the earth, together with anchors and marine shells. It is very probable the sea may form new land, by bringing and depositing, at particular places, sand, earth, mud, &c. for in the island of Orkney, which is adjacent to Romney Marsh, there was a tract of low land continually in danger of being inundated by the river Rother; but in less than 60 years this ground has been considerably elevated by quantities of earth and mud being brought thither every tide, and the channel through which it enters, in less than fifty years has deepened so much as to admit of the reception of large vessels, whereas at that time it was a ford over which people might pass.