‘If the fertile soil contained a large quantity of sand, in proportion to the barren soil, the process of amelioration would depend simply upon a supply of this substance; and the method would be equally simple with regard to soils deficient in clay or calcareous matter. In the application of clay, sand, loam, marl, or chalk, to lands, there are no particular chemical principles to be observed; but, when quicklime is used, great care must be taken that it is not obtained from the magnesian limestone; for in this case, as has been shown by Mr. Pennant, it is extremely injurious to land. The magnesian limestone may be distinguished from the common limestone by its greater hardness, and by the length of time that it requires for its solution in acids; and it may be analyzed by the process for carbonate of lime and magnesia. ‘When the analytical composition indicates an excess of vegetable matter as the cause of sterility, it may be destroyed by much pulverization and exposure to air, by paring and burning, or the agency of lately made quicksilver; and the defect of animal and vegetable matter must be supplied by animal or vegetable manure. The general indications of fertility and barrenness, as found by chemical experiments, must necessarily differ in different climates, and under various circumstances. The power of soils to absorb moisture, a principle essential to their productiveness, ought to be much greater in warm and dry countries, than in cold and moist ones; and the quantity of fine aluminous earth they contain should be larger. ‘From the great difference of the causes that influence the productiveness of lands, it is obvious, that, in the present state of the science, no certain system can be devised for their improvement, independent of experiment; but there are few cases in which the labor of analytical trials will not be amply repaid by the certainty with which they denote the best methods of melioration; and this will particularly happen when the defect of composition is found in the proportions of the primitive earths. In supplying animal or vegetable manure, a temporary food only is provided for plants, which is in all cases exhausted by means of a certain number of crops; but when a soil is rendered of the best possible constitution and texture with regard to its earthy parts, its fertility may be considered as permanently established. It becomes capable of attracting a very large portion of vegetable nourishment from the atmosphere, and of producing its crops with comparatively little labor and expense.’ CHAPTER XIV.――CLIMATE.[37]