dition of the soil, heavy clays, especially
if undrained, and soils of a peaty nature, requiring a large
application; while on well drained and light soils a smaller quantity
suffices. Thin soils also require only a small application. The
geological origin of the soil is also not without its influence, and its
beneficial effect is peculiarly seen on granite, porphyry, and gneiss
soils, both because these are naturally deficient in lime, and because
the decompositions by which their valuable constituents are liberated
take place with extreme slowness.

The greater part of the action of lime is unquestionably dependent on
its exerting a chemical decomposition on the soil; and it acts equally
on both the great divisions of its constituents, the inorganic and the
organic. On the former, it operates by decomposing the silicates, which
form the main part of the soil, and the alkalies they contain being thus
set free, a larger supply becomes available to the plant. On the organic
constituents its effects are principally expended in promoting the
decomposition which converts their nitrogen into ammonia; and thus a
supply of food, which might remain for a long period locked up, is set
free in a state in which the plant can at once absorb it. But these
chemical decompositions are attended by a corresponding change in the
mechanical characters of the soil. Heavy clays are observed to become
lighter and more open in their texture; and those which are too rich in
organic matter have it rapidly reduced in quantity, and the excessive
lightness which it occasions diminished.

The effects of an application of lime are not generally observed
immediately, but become apparent in the course of one or two years, when
it has had time to exert its chemical influence on the soil; but from
that time its effects are seen gradually to diminish and finally to
cease entirely. The period within which this occurs necessarily varies
with the amount of the application and the nature of the soil, but it
may be said generally that lime will last from ten to fifteen years. The
cessation of its effects is due to several circumstances, partly of
course to the absorption of lime by the plants, partly to its being
washed out of the soil by the rains, and partly to its tendency to sink
to a lower level, a tendency which most practical men have had
opportunities of observing. In the latter case, deep-ploughing often
produces a marked effect, and sometimes makes