1223. In ascertaining the composition of faulty soils, with a view to their improvement by adding to their constituent parts, any particular ingredient the want or excess of which is the cause of their unproductiveness should be particularly attended to; if possible, they should be compared with fertile soils in the same neighbourhood, and in similar situations, as the difference of the composition may, in many cases, indicate the most proper methods of improvement. If, on washing a sterile soil, it is found to contain an excess of the salts of iron, or any acid matter, it may be ameliorated by the application of quicklime. A soil of good apparent texture, containing too great a proportion of sulphate of iron, will be sterile; but the obvious remedy is a top-dressing with lime, which converts the sulphate into manure. If there be an excess of calcareous matter in the soil, it may be improved by the application of sand or clay. Soils too abundant in sand are benefited by the use of clay, or marl, or vegetable matter. Light sands are often benefited by a dressing of peat, and peats by a dressing of sand; though the former is in its nature but a temporary improvement. When peats are acid, or contain ferruginous salts, calcareous matter is absolutely necessary to bring them into cultivation. The best natural soils are those of which the materials have been derived from different strata, which have been minutely divided by air and water, and are intimately blended together; and in improving soils artificially, the cultivator cannot do better than imitate the processes of nature.