It will be easily understood, that the facts we are going to state, each taken singly, prove nothing more than a change of the line in which the surface of the sea intersects the surface of the land, leaving it uncertain to which of the two the change ought really to be ascribed. Taken in combination, however, these facts may determine what each of them separately cannot ascertain. I shall first, therefore, mention some of the principal observations relative to the change above mentioned, and shall then compare them, in order to discover whether it is most probable that this change has been produced by the motion of the land or of the sea. 389. If we begin with examining the coasts of our own island, we shall find clear evidence every where, that the sea once reached higher up upon the land than it does at present. The marks of an ancient sea beach are to be seen beyond the present limits of the tide, and beds of sea shells, not mineralized, are found in the loose earth or soil, sometimes as high as thirty feet above the present level of the sea. Some of these on the shores of the Frith of Forth are very well known, and have been often mentioned. Indeed, on the shores of that frith, many monuments appear, which would seem to carry the difference between the present and the ancient level of the sea, to more than forty feet. The ground on which the Botanic Garden of Edinburgh is situated, after a thin covering of soil is removed, consists entirely of sea sand, very regularly stratified, with layers of a black carbonaceous matter, in thin lamellæ, interposed between them. Shells I believe are but rarely found in it, but it has every other appearance of a sea beach. The height of this ground above the present level of the sea is certainly not less than forty feet. 390. On almost every part of the coast where the rocks do not rise quite abrupt and precipitous from the sea, similar marks of the lowering of the sea, or the rising of the land, may be observed. On the shores opposite to ours, the same appearances are remarked. The author of the Lettre Critique to M. de Buffon, tells us, that he had found the bottom of a bason at Dunkirk, which he had reason to think was dug about 950 years ago, ten feet and a half above the present low water mark, though it must have been originally under it. The bottom of this bason is in the native chalk. From this, the same author concludes, that the sea at Dunkirk lowers its level at the rate of an inch nearly in seven years. The observation was made in 1762, (Lettre à M. le Comte de Buffon, &c. p. 55.)[201]