e locality in many sections of the country.
Some of these inferior marls have had so much clay and sand mixed with
the lime carbonate that dressings must be heavy. The best lime marls
provide excellent material for the correction of soil acidity, the
actual value per ton being practically the same as that of the finest
pulverized limestone. Some dealers in marl make extravagant claims for
their goods, but any farmer may easily put these claims to the test and
learn that he should not expect more than a fairly good carbonate of
lime can do.

Marl improves the physical condition of stiff soils only when used in
large amount per acre, and this is true of any carbonate form, such as
limestone. Little effect upon physical condition should be expected from
the light application usually given when marl is purchased and
transported some distance to the farm. The chalk marl on the market is
used to correct soil acidity, and at the best it is worth only what good
lime carbonate is worth. It has no hidden virtues, and cannot take the
place of fertilizers. It is an excellent means of meeting the
lime-requirement of land when bought right, and its fine division makes
it distinctly superior to coarse stone.

There should be no confusion of a lime marl with the so-called "green
sand" marl. The latter is low in lime, and may be acid, the value of the
marl being in a considerable percentage of plant food contained.

_Oyster Shell._ Ground oyster shell is a good source of carbonate of
lime. The percentage falls below that of limestone, but in addition
there is a little nitrogen and phosphoric acid. An analysis of a good
quality of oyster shell, as found on the market, will show 90% carbonate
of lime.

Burned oyster shell has something near the same composition as lime made
from stone, but it goes back to hydrate and air-slaked forms rapidly.
There is no large amount of burned shell lime on the market, the
material known as shell lime being the ground shell, or lime carbonate.

_Wood Ashes._ A large supply of lime in excellent form was afforded by
hardwood ashes, but this product has ceased to have any important value
to our agriculture. The chief supply on the market is low in quality,
containing moisture and dirt in considerable amount, the form of lime
being changed from an oxide to the hydrate and carbonate.

_Gas Lime._ Prof. E. B. Voorhees, in "First Principles of Agriculture,"
says: "Gas lime is also frequently used as manure