carried to the sea.--Castellani, Dell Immediata Influenza delle Salce sul corso delle Acqua, i., pp. 42,43. I have contented myself with assuming less than one-half of Mengotti's estimate.] The present rate of deposit at the mouth of the Po has continued since the year 1600, the previous advance of the coast, after the year 1200, having been only one-third as rapid. The great increase of erosion and transport is ascribed by Lombardini chiefly to the destruction of the forests in the basin of that river and the valleys of its tributaries, since the beginning of the seventeenth century. [Footnote: Baumgarten, An. des Ponts et Chaussees, 1847, 1er semestre, p. 175.] We have no data to show the rate of deposit in any given century before the year 1200, and it doubtless varied according to the progress of population and the consequent extension of clearing and cultivation. The transporting power of torrents is greatest soon after their formation, because at that time their points of delivery are lower, and, of course, their general slope and velocity more rapid, than after years of erosion above, and deposit below, have depressed the beds of their mountain valleys, and elevated the channels of their lower course. Their eroding action also is most powerful at the same period, both because their mechanical force is then greatest, and because the loose earth and stones of freshly cleared forest-ground are most easily removed. Many of the Alpine valleys west of the Ticino--that of the Dora Baltea, for instance--were nearly stripped of their forests in the days of the Roman Empire, others in the Middle Ages, and, of course, there must have been, at different periods before the year 1200, epochs when the erosion and transportation of solid matter from the Alps and the Apennines were at least as great as since the year 1600.