| | ----- | ----- | ----- | | | 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 | 30 inches | | | | deep. | 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 } | | | |