h to permit an application sufficient for a considerable
term of years, so that it will contain all the fine material needed at
once. In that case the coarser material may be expected to meet later
need, and may be even more desirable for such purpose, as it would not
be subject to leaching.

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 sam