60 per cent.
In general, however, it amounts to about 10 per cent. The organic
constituents are also very variable in amount; ordinary soils of good
quality containing from 2 to 10 per cent, while in peat soils they not
unfrequently reach 30 or even 50 per cent. But these cannot be
considered _fertile_ soils. The insoluble constituents are likewise
subject to great variations, but, in the ordinary clay and sandy soils
of this country, they generally form from 70 to 85 per cent of the
whole.

The distribution of the constituents under these different heads will be
best illustrated by a few analyses of soils of good quality, and for
this purpose we shall select two, noted for the excellent crops of wheat
they produce, and for their general fertility. The analyses were made
from the upper 10 inches, and a quantity of the 10 inches immediately
subjacent was analysed as subsoil. The first is the ordinary wheat soil
of the county of Mid-Lothian, the other the alluvial soil of the Carse
of Gowrie in Perthshire, so celebrated for the abundance and luxuriance
of the crops it produces.

|------------------------------------------|-------------------
| | Mid-Lothian. | Perthshire.
|----------------------|-------------------|-------------------
| | Soil. | Subsoil. | Soil. | Subsoil.
|----------------------|--------|----------|---------|---------
|SUBSTANCES SOLUBLE | | | |
| IN WATER. | | | |
|Silica | 0.0149 | 0.0104 | 0.0072 | 0.0461
|Lime | 0.0300 | 0.0072 | 0.0184 | 0.0306
|Magnesia | 0.0097 | 0.0016 | 0.0040 | 0.0034
|Chlor. of magnesium | -- | -- | -- | 0.0033
|Potash | 0.0034 | 0.0037 | -- | --
|Soda | 0.0065 | 0.0049 | -- | --
|Chloride of potassium | -- | -- | 0.0088 | 0.0080
|Chloride of sodium | -- | -- | 0.0110 | 0.0166
|Sulphuric acid | 0.0193 | 0.0124 | 0.0089 | 0.0239
|Chlorine | trace | trace | -- | --
|Organic matters | 0.1481 | 0.2228 | 0.0608 | 0.1342
| | -------|----------|-------------------
| | 0.2319 | 0.2630 | 0.1191 | 0.2661
|----------------------|--------|----------|---------|---------
|SOLUBLE IN ACIDS. | | | |
|Silica