--All this, you may say, is not instruction. We ought to know exactly what lands are enriched by Gypsum, and what, if any, are not; why these are fertilized, why those are not, by a common application; how great is the profit of such application in any case; and what substitute can most nearly subserve the same ends where Gypsum is not to be had. I admit all you claim, and do not doubt that there shall yet be a Scientific Agriculture that will fully answer your requirements. As yet, however, it exists but in suggestions and fragments; and attempts to complete it by naked assertions and sweeping generalizations tend rather to mislead and disgust the young farmer than really to enlighten and guide him. At all events, I shall aim to set forth as true no more than I know, or with good reason confidently believe. I close by reiterating my belief that no farmer ever yet impoverished himself by making too much manure or by applying too much of his own manufacture. I cannot speak so confidently of _buying_ commercial fertilizers; but these I will discuss in my next chapter. XX. BONES--PHOSPHATES--GUANO. I hate to check improvement or chill the glow of Faith; yet I do so keenly apprehend that many of our people, especially among the Southern cotton-growers, are squandering money on Commercial Fertilizers, that I am bound to utter my note of warning, even though it should pass wholly unheeded. Let me make my position as clear as I can. I live in a section which has been cultivated for more than two centuries, while its proximity to a great city has tempted to crop it incessantly, exhaustively. Wheat while its original surface soil of six to twelve inches of vegetable mold (mainly composed of decayed forest-leaves) remained; then Corn and Oats; at length, Milk, Beef, and Apples--have exhausted the hill-sides and gentler slopes of Westchester County, except where they have been kept in heart by judicious culture and liberal fertilizing; and, even here, that subtle element, Phosphorus, which enters minutely but necessarily into the composition of every animal and nearly every vegetable structure has been gradually drawn away in Grain, in Milk, in Bones, and not restored to the soil by the application of ordinary manures. I am convinced that a field may be so manured as to give three tuns of Hay per acre, yet so destitute of Phosphorus that a sound, healthy animal cannot be grown therefrom. For two centuries, the tillers of Westchester County knew nothing of Chemistry or Phosphorus, and allowed the unvalued bones of their animals to be exported to fatten British meadows, without an effort to retain them. Hence, it has become absolutely essential that we buy and apply Phosphates, even though the price be high; for our land can no longer do without them. Wherever a steer or heifer can occasionally be caught gnawing or mumbling over an old bone, there Phosphates are indispensable, no matter at what cost. Better pay $100 per tun for a