Another fact: take a load of manure, dry it thoroughly, and weigh it. Then moisten it and apply it to the soil, and it will increase the weight of vegetation from ten to thirty or forty times its own weight when dry, and yet most of that manure may still be found in the soil. Hence it can only feed plants in a very limited degree. Its action must be on air and water, or the control it gives the soil over those elements. It is also matter of common observation that soil well manured, will continue moist for a long time after similar land by its side, but which has not been manured, is dried up. Hard coarse soils dry up very quickly, while soft, mellow, and friable ones will endure a long drought. The gases and moisture generated by the decomposition of manures produce this mellow state. Hence the necessity of having that decomposition take place under the soil, or of plowing in the manure. Another important fact bearing on this question is, that what are regarded very poor soils, such as light sandy or gravelly land, will produce good crops in a season remarkable for the frequency of showers. On such soils crops are from twice to four times as large, in a wet season as in a dry, and yet there is an addition of nothing but moisture, and in such a manner, as not to have it stand and become stagnant among the roots of the plants. Yet another evidence is in the strength of clay soils. A hard clay is very unproductive. But so disintegrated that plants can grow in it, it produces a great crop. This is because clay is of so close a texture, that when mixed with manure, turf, sand, or muck, although friable, it retains more moisture, than sand or ordinary loam. This is the reason of the superior fertility of land annually overflowed with water, as Egypt in the vicinity of the Nile. It is not that the Nile brings down deposites from the mountains of the Moon, so rich above all that is in the valleys below. The entire weight of all that a river deposites on ten acres would not equal in weight the increased vegetation of a single acre. The cause of the increased fertility is the fact that the deposite is so fine that it prevents rapid evaporation, and thus causes the soil to retain moisture for the large growth, and maturity of the plants.