We will now observe the process of deposition a little more closely. Each of these two bottles contains the same amount of fine yellow clay, but in one the water is fresh, and in the other it is salt. At the beginning of the lesson, as you may have observed, I brought the clay in both bottles into suspension by violent agitation, and since then they have remained undisturbed. The main point is that the salt water has become quite clear, while the fresh water is still distinctly turbid, showing that the salt favors the rapid deposition of the clay. At the second lecture, a week later, these two bottles, yet undisturbed, were exhibited, and the fresh water seen to be still sensibly turbid. The fact is, the clay is not held in suspension wholly by the _motion_ of the water; but, just as in the case of dust in the atmosphere, a small portion of the medium is condensed around or adheres to each solid particle, _i.e._, each clay particle in our experiment has an atmosphere of water which moves with it and buoys it up. Now the effect of the salt is to diminish the adhesion of the water to the particles, _i.e._, to diminish their atmospheres, and consequently their buoyancy. The diminished adhesion of the salt water is well shown by the smaller drops which it forms on a glass rod. The geological importance of this principle is very great; for it is undoubtedly largely to the saltness of the sea that we owe its transparency, and the fact that the fine, clayey sediment from the land, like the coarse, is deposited near the shore. This bottle of fresh water contains some fine gravel, coarse sand, fine sand, and clay. By agitating the water, all this material is brought into suspension. Now, suddenly placing the bottle in a state of rest, we observe that the gravel falls to the bottom almost instantly, followed quickly by the coarse sand, and very soon afterward by the fine sand; and then there appears to be a pause, the fine particles of clay all remain in suspension; but finally, when the water is quite motionless, they begin to settle; they fall very slowly, however, and the water will not be clear for hours. This is a very instructive experiment. We learn from it: First, that the power of the water to hold particles in suspension is inversely proportional to the size of the particles; Second, that all materials deposited in water are assorted according to size;