ese 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 } | | | |
| Combined water } | 8.324 | 7.700 | 9.348 |
| Loss | 0.540 | 0.611 | 0.753 |
| | ------- | ------- | ------- |
| | 100.000 | 100.000 | 100.0