We have already observed that rains, and the currents of water they produce, continually detach from the heights of mountains sand, earth, gravel, &c. which they carry into plains, from whence the rivers convey a part of them into the sea. Plains therefore are successively filled, and by degrees raised higher, while mountains daily diminish. Joseph Blancanus relates various facts on this subject, which were of public notoriety in his time, and which prove that mountains have been considerably lowered. In the county of Derby, in England, the steeple of the village Craich was not visible in 1572 from a certain mountain, on account of the height of another which intervened; in eighty or an hundred years after, not only this steeple but every part of the church became visible from that very spot. Dr. Plot gives a similar example of a mountain between Sibbertoft and Ashby, in Northamptonshire. The rain waters not only carry with them the lightest parts of the mountains, as earth, gravel, and small stones, but even undermine and roll down large rocks, which considerably diminish the height of them. The mountains of Wales are very steep and high, and the fragments of these rocks are to be seen in large pieces at their feet, which as well as all fragments of rocks met with in vallies are the works of frosts and water. It is not mountains of sand and earth alone which the rain causes to sink, for they attack the hardest rocks, and carry with them large fragments into the vallies. In a valley in Nant-phrancon, in 1685, a part of a large rock, which rested on a narrow base, having been undermined by the waters, fell and broke in many pieces, the largest of which, in descending, tore up a considerable trench in the plain, and crossed a small river on the other side of which it stopped. It is to similar accidents we must attribute the origin of all the large stones found adjacent to the mountains. We must recollect, as before observed, that these large stones, scattered abroad, are more common in countries whose mountains are composed of sand and free-stone, than in those where their composition is marble and clay, because sand is a less solid foundation than clay. To give an idea of the quantity of earth which the rain detaches from mountains and carries into the vallies, we shall quote a circumstance related by Dr. Plot; he says, in his Natural History of Staffordshire, that 18 feet deep in the earth a great number of pieces of money had been found, coined in the reign of Edward IV. two hundred years before his time, from which he concludes that the ground which is marshy has increased above a foot in eleven years, or an inch and a twelfth every year. A similar observation occurs with respect to some trees buried seventeen feet deep from the surface under which medals of Julius Cæsar were found; so the earth, brought from the top of mountains by the waters, considerably increases the elevation of the ground of plains.