CHAPTER XXII. 



ALKALI SOILS. 



Alkali Lands and Sea-shore Lands. Alkali lands proper, as 

 already stated, are wholly distinct in their nature and origin 

 from the salty lands of sea-coast marshes, past or present. 

 The latter derive their salts from sea-water that occasionally 

 overflows them, or from that which has evaporated in segre- 

 gated basins or estuaries ; and the salts impregnating them are 

 essentially " sea salts," that is, common salt, together with 

 bittern (magnesium chlorid), Epsom salt (magnesium sulfate) 

 gypsum, etc. (see chapter 2, p. 26). Very little of what would 

 be useful to vegetation or desirable as a fertilizer is contained 

 in the salts impregnating such soils ; and they are by no means 

 always intrinsically rich in plant-food, but vary greatly in this 

 respect. 



While sea-shore lands are by no means always of high fer- 

 tility even when freed from their salts, especially when very 

 sandy, it is otherwise when they occur near the mouths of 

 streams or rivers, whose finest sediments they then receive. 

 From such lands are formed the profusely productive Polders 

 of Holland and northern Germany, and the equally noted 

 " colmates " of France and Italy. These, so soon as freed 

 from salt, may be considered as possessing the same advantages 

 as " delta " alluvial lands, and from the same causes ; notably 

 the accumulation of the finest sediments derived from the 

 rivers' drainage basins. 



Origin. Alkali lands proper bear no definite relation to the 

 present sea ; they are mostly remote from it or from any other 

 sea bed, so that they have sometimes been designated as 

 " terrestrial salt lands." Their existence is in the majority of 

 cases definitely traceable to climatic conditions alone. They 

 are the natural result of a light rainfall, insufficient to leach 

 out of the land the salts that always form in it by progressive 

 weathering of the rock powder of which all soils largely con- 



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