Coarse grinding costs much less than fine grinding, and it is the resulting low price that permits the heavy application. As stone varies in hardness and ability of the small particles to withstand disintegrating forces in the soil, an estimate of the difference in price between a 60-mesh limestone and a 10-mesh one could not serve as a safe guide. The buyer should know the percentages of a limestone passing through screens of various sizes before he makes a purchase, and should demand part of the saving in cost of production that attends coarse grinding. _Oyster Shell._ Ground oyster shell should be given about the same valuation as limestone. It is a lime carbonate, and the percentage of worthless material in it varies somewhat It is coarsely ground, but the large pieces disintegrate in the soil much more rapidly than limestone would do. It contains a little nitrogen and phosphoric acid, partially available, as an offset to coarseness and some lack of purity, as compared with the highest grade of fine stone. It is profitable to buy oyster shell at limestone prices if used liberally enough to furnish a supply for a term of years. The oxide, or burned shell lime, would be nearly the equivalent of burned stone if it did not change to hydrate and air-slaked forms so rapidly that it rarely is on the market in the ~full~ strength of fresh burned lime. _Hardwood Ashes._ As a source of lime, ashes have become far too expensive. The composition of ashes on the market is widely variable, dirt and moisture often accounting for much of the weight. The lime in fresh burned ashes is peculiarly effective, being finely divided and in oxide form, but the ashes on the market have much of the lime water-slaked and air-slaked. Unless analysis is made at time of purchase, a buyer should not estimate the content of lime in a ton at a value greater than assigned to one-half of a ton of limestone. The additional value of the ashes, due to the potash content, is wholly another consideration. _Marl._ No more should be paid for a ton of good chalk marl than an equal weight of fine limestone would cost. Each is a good carbonate of lime, with the same capacity for destruction of acids. _Agricultural Lime._ This variable product should not be bought unless actual composition is known, or the cost is as low as that of pulverized limestone, and even then it may be a bad purchase, the methods of the manufacturer being the determining factor. If such lime is chiefly a dumping place for low-grade stone and forkings, it has small agricultural value. _Land Plaster._ The soil wants lime in carbonate form. The oxide and hydrate change to carbonate, and therefore are good. Land plaster is a sulphate, and its tendency is to make a soil sour. It should not be considered as a means of correcting soil acidity.