As an example of a calcareous soil, forming a striking contrast to those given above, we select one from the island of Antigua, from which very large crops of sugar-cane are obtained. The soil is of great depth, and analyses of the subsoil at the depth of 18 inches and 5 feet are given. These last analyses are not so minute as that of the soil itself, the soluble matters not having been separately determined, but included in that soluble in acids.
| Surface Soil. | 18 inches deep. | 5 feet deep. | |
| SOLUBLE IN WATER. | |||
| Lime | 0·07 | ... | ... |
| Magnesia | trace | ... | ... |
| Potash | 0·06 | ... | ... |
| Soda | 0·04 | ... | ... |
| Chlorine | 0·05 | ... | ... |
| Organic matter | 0·15 | ... | ... |
| —— | |||
| 0·37 | |||
| SOLUBLE IN ACIDS. | |||
| Silica | 0·74 | ... | ... |
| Peroxide of iron | 2·22 | 1·67 | 1·87 |
| Protoxide of iron | 0·77 | 9·05 | 3·10 |
| Alumina | 1·90 | 2·52 | 4·21 |
| Lime | 10·43 | 3·04 | 25·75 |
| Magnesia | 0·20 | 0·54 | 0·51 |
| Potash | 0·03 | 0·29 | 0·28 |
| Soda | 0·02 | 0·11 | 0·16 |
| Sulphuric acid | trace | 0·02 | 0·13 |
| Phosphoric acid | 0·14 | trace | 0·04 |
| Carbonic acid | 7·38 | 0·82 | 20·23 |
| —— | —— | —— | |
| 23·83 | 18·06 | 56·28 | |
| INSOLUBLE IN ACIDS. | |||
| Silica | 41·44 | 51·24 | 27·67 |
| Protoxide of iron | 3·24 | 0·26 | 1·40 |
| Alumina | 9·00 | 1·50 | 1·00 |
| Lime | 0·08 | 0·88 | trace |
| Magnesia | 0·80 | 0·54 | trace |
| Potash | ... | 0·74 | ... |
| Soda | ... | 0·25 | ... |
| —— | —— | —— | |
| 54·56 | 55·41 | 30·07 | |
| ORGANIC MATTERS. | |||
| Humine | 1·58 } | ||
| Humic acid | 1·15 } | 12·05 | 7·49 |
| Insoluble organic matters | 7·66 } | ||
| Water | 11·13 | 14·69 | 6·06 |
| —— | —— | —— | |
| 21·52 | 26·74 | 13·55 | |
| Sum of all the constituents | 100·28 | 100·21 | 99·90 |
In this soil there is a general resemblance in the composition of the portion soluble in water to those of the wheat soils. But the part soluble in acids is distinguished by the great abundance of carbonate of lime.
The subsoil contains also a large quantity of protoxide of iron, a substance frequently found in subsoils containing much organic matter, and to which the air has imperfect access. Under these circumstances peroxide of iron is reduced to protoxide; and when present abundantly in the soil in that form, iron has been found to exercise a very injurious influence on vegetation; and it has frequently happened that when subsoils containing it have been brought up to the surface, they have in the first instance caused a manifest deterioration of the soil, although after some time, when it had become peroxidised by the action of the air, it ceased to be injurious.
The soil of Holland, from the neighbourhood of the Zuider Zee, which is an alluvial deposit from the waters of the Rhine, and produces large crops, gave the results which follow—
| Surface. | 15 inches deep. | 30 inches deep. | |
| Insoluble silica | 57·646 | 51·706 | 55·372 |
| Soluble silica | 2·340 | 2·496 | 2·286 |
| Alumina | 1·830 | 2·900 | 2·888 |
| Peroxide of iron | 9·039 | 10·305 | 11·864 |
| Protoxide of iron | 0·350 | 0·563 | 0·200 |
| Oxide of manganese | 0·288 | 0·354 | 0·284 |
| Lime | 4·092 | 5·096 | 2·480 |
| Magnesia | 0·130 | 0·140 | 0·128 |
| Potash | 1·026 | 1·430 | 1·521 |
| Soda | 1·972 | 2·069 | 1·937 |
| Ammonia | 0·060 | 0·078 | 0·075 |
| Phosphoric acid | 0·466 | 0·324 | 0·478 |
| Sulphuric acid | 0·896 | 1·104 | 0·576 |
| Carbonic acid | 6·085 | 6·940 | 4·775 |
| Chlorine | 1·240 | 1·302 | 1·418 |
| Humic acid | 2·798 | 3·991 | 3·428 |
| Crenic acid | 0·771 | 0·731 | 0·037 |
| Apocrenic acid | 0·107 | 0·160 | 0·152 |
| Other organic matters and Combined water | 8·324 | 7·700 | 9·348 |
| Loss | 0·540 | 0·611 | 0·753 |
| ——— | ——— | ——— | |
| 100·000 | 100·000 | 100·000 |
It is unnecessary to multiply analyses of fertile soils, those now given being sufficient to show their general composition. They are all characterised by the presence, in considerable quantity, of all the essential constituents of plants, in a state in which they may be readily absorbed. The absence of one or more of these substances immediately diminishes or altogether destroys the fertility of the soil; and the extent to which this occurs is illustrated by the following analysis of a soil from Pumpherston, Mid-Lothian, forming a small patch in the lower part of a field, and on which nothing would grow. Being naturally wet, it had been drained and sowed with oats, which died out about six weeks after sowing, and left a bare soil on which weeds did not show the slightest disposition to grow.