So, also, the bars formed at the mouths of rivers, after having attained a certain magnitude, increase no farther, not because they cease to receive augmentations from the land, but because their diminution from the sea, increasing with their magnitude, becomes at length so great, as completely to balance those augmentations. When properly examined, therefore, the phenomena, which have been proposed as most inconsistent with the indefinite transportation of stony bodies, afford very satisfactory proofs of that operation. 383. It is true, that bodies which float in the water, when carried along on the tops of the waves towards a shelving beach, having acquired a certain velocity, are thrown farther in upon the land than the distance they would have floated to, if they had been simply sustained by the water. The depth of water, therefore, at the place where they take the ground, is not likely to be such as to float them again, and to carry them out towards the sea. They are, therefore, left behind; and this produces an appearance of a force impelling floating bodies towards the land, much greater and more general than really takes place. These observations may serve to show, how unsound the principles are from which Mr Kirwan's conclusions are deduced: they are perhaps more than is necessary for that purpose: it might have been sufficient to observe, that the increase of land on the sea shore is limited, though the augmentation from the land is certainly indefinite, a proof that the diminution from the sea is constant and equal to the increase. 384. "Mariners," says Mr Kirwan, "were accustomed, for some centuries back, to discover their situation, by the kind of earth or sand brought up by their sounding plummets; a method which would prove fallacious, if the surface of the bottom did not continue invariably the same."[198] [Footnote 198: Geol. Essays, p. 440.]