24 | 0.71 | 0.53
|Nitrogen | 0.220 | 0.0973 | 0.21 | 0.17
|Oxygen | 4.918 | 3.1001 | 5.08 | 4.09
| |--------|----------|---------|-------
| | 10.198 | 4.8358 | 8.55 | 6.82
---------------------------------------------------------------

In examining these analyses, it is particularly worthy of notice that by
far the larger proportion of the substances soluble in water consists of
organic matter, lime, and sulphuric acid, the two last being in
combination as sulphate of lime, while some of those substances which
are usually considered to be the most important mineral constituents of
plants are present in very small quantity--potash, for instance, forming
not more than 1-25,000th of the whole soil, and phosphoric acid being
entirely absent. On the other hand, this portion contains the whole of
the chlorine which exists in the soil, and this might be anticipated
from the ready solubility in water of the compounds of that substance.

The portion soluble in acids consists of alumina and oxide of iron, both
of which are comparatively unimportant to the plant, but very important,
as we shall afterwards see, in relation to the physical properties of
the soil. The remainder of the substances soluble in acids, amounting to
from 1 and 2 per cent, is composed of some of the most essential
constituents of plants. Lime, magnesia, potash, and soda, appear again
in larger quantity than in the soluble part, and along with them we have
the phosphoric acid to the amount of from 0.2 to 0.4 per cent of the
whole soil, and sulphuric acid in much smaller quantity.

The insoluble matters differ remarkably in the two soils, that from the
Carse of Gowrie being characterised by a large quantity of potash and
soda, indicating an important difference in the materials from which
they have been formed. In the Perthshire soil it is obvious that the
felspathic element has been abundant, and that its decomposition has
been arrested at a time, when it still contained a large quantity of
alkalies. And this difference is of great practical importance, because
those soils, which contain a large quantity of potash in their insoluble
portion, have within them a source of permanent fertility, the alkali
being gradually liberated by the decomposition which is constantly in
progress, owing to the air and moisture permeating the soil. As regards
the special distribution of