The formation of the alkali may be briefly described as follows: By the decomposition of the native rocks, certain salts soluble in water are formed. These salts in the present matter are chiefly sodium and potassium sulfates, chlorids and carbonates. The salts of potash together with those of lime are more tenaciously held by the soil than the soluble salts of soda, and the result of this natural affinity of the soil for soluble potash, lime and magnesian salts is seen in the formation at the surface of the earth, by the process of evaporation above described, of a crust of alkaline material which is chiefly composed of the soluble salts of soda. In countries which have a sufficient amount of rain-fall, these soluble salts are carried away either by the surface drainage or by the percolation of water through the soil, and the sodium chlorid is accumulated in this way in the waters of the ocean. But where a sufficient amount of rain-fall does not occur, these soluble salts carried down by each shower only to a certain depth rise again on the evaporation of the water, reinforced by any additional soluble material which may be found in the soil itself. The three most important ingredients of the alkali of the lands referred to are sodium chlorid, sulfate, and carbonate. When the latter salt, namely, sodium carbonate, is present in predominant quantity, it gives rise to what is popularly known as black alkali. This black color is due to the dark colored solution which sodium carbonate makes with the organic matters or humus of the soil. The black alkali is far more injurious to growing vegetation than the white alkali composed chiefly of sodium sulfate and chlorid. This black alkali has been very successfully treated by Hilgard[33] by the application of gypsum which reacting with the sodium carbonate produces calcium carbonate and sodium sulfate, thus converting the black into the white alkali and adding an ingredient in the shape of lime carbonate to stiff soils which tends to make them more pulverulent and easy of tillage. This method of treatment, however, as can be easily seen, is only palliative, the whole amount of the alkaline substances being still left in the soil, only in a less injurious form. The only perfect remedy for alkaline soils, as has been pointed out by Hilgard, is in the introduction of underdrainage in connection with irrigation. The partial irrigation of alkaline soils, affording enough moisture to carry the alkali down to and perhaps partially through the subsoil, can produce only a temporary alleviation of the difficulties produced by the alkali. Subsequent evaporation may thus increase the amount of surface incrustation. For this reason in many cases the practice of irrigation without underdrainage may completely ruin an otherwise fertile soil by slowly increasing the amount of alkali in the soil by the total amount of the alkaline material added in the waters of irrigation.