1. The formation of alkali soils is primarily a question of soluble salt accumulation. Those processes which bring about the accumulation of soluble salts in soils also tend to cause the accumulation of CaCO3. Under certain conditions simple calcium silicates may also be precipitated in alkali soils. Hilgard's researches were concerned chiefly with the soluble salts. On the other hand, more recent investigators have emphasised the base-exchange aspects of the subject. Sodium salts tend to react with the clay and humus constituents of the soil, converting them into Na-absorption compounds. These components produce extremely adverse conditions in the soil.

2. Under certain conditions alkali soils tend to pass through four evolutionary stages, namely, salinisation, alkalinisation, desalinisation, and degradation. As to whether or not an alkali soil will pass beyond the salinisation stage, depends on the composition of the soluble salts that accumulate in it. Where sodium salts predominate, more or less alkalinisation of the exchange complex has taken place. However, this is not true where soluble calcium is relatively abundant.

3. Desalinisation (by leaching, whether natural or artificial) of alkalinised soil is usually accompanied by the formation of Na2CO3 and by pronounced deflocculation. If CaCO3 be present, the formation of Na2CO3 is accompanied by the replacement of absorbed sodium by calcium. Under these conditions the degradation stage will not be attained. If CaCO3 be absent, base-unsaturated constituents arise under leaching conditions, and more or less of the inorganic-exchange complex becomes decomposed into simple oxides.