606 POPULAR SCIENCE MONTHLY. 



value of vast land areas thus far considered either irreclaimable 

 or adapted only to scanty pasturage. 



Without going into technical details or figures, the case may 

 be stated thus : Soils are formed from rocks by the physical and 

 chemical agencies commonly comprehended in the term weather- 

 ing, which includes both their pulverization and chemical decom- 

 position by atmospheric action. Both actions, but more espe- 

 cially the chemical one, continue in the soil itself ; the last named 

 in an accelerated measure, so as to give rise to the farmers' prac- 

 tice of "fallowing" that is, leaving the land exposed to the 

 action of the air in a well-tilled but unplanted condition, with a 

 view to increasing the succeeding year's crop by the additional 

 amount of plant food rendered available, during the fallow, from 

 the soil itself. 



This weathering process is accompanied by the formation of 

 new compounds out of the minerals originally composing the 

 rock. Some of these, such as zeolites and clay, are insoluble in 

 water, and therefore remain in the soil, forming a " reserve " of 

 plant food that may be drawn upon gradually by plants ; while 

 another portion, containing especially the compounds of the al- 

 kalies, potash and soda, are easily soluble in water. Where the 

 rainfall is abundant, these soluble substances are currently car- 

 ried into the country drainage, and through the rivers into the 

 ocean ; which shows in its saline portion (about three and a half 

 per cent) the average composition of the matters permanently 

 leached out of the land. Most of this is common salt chloride 

 of sodium but a large portion, if not all, of the other elements 

 known are represented in sea water in a greater or less propor- 

 tion. Among these, potash, lime, magnesia, sulphuric and a trifle 

 of phosphoric acids require mention here. 



Where, on the contrary, the rainfall is insufficient to carry 

 the soluble compounds formed in the weathering of the soil 

 mass into the country drainage, those compounds must of neces- 

 sity remain and accumulate in the soil. They then constitute 

 what in the western United States is now universally known as 

 "alkali." 



" Alkali " is not, then, as is popularly supposed, something for- 

 eign to the soil, imposed as a special affliction upon the dwellers 

 in the arid or irrigation regions. It is the normal product of soil- 

 formation and soil- weathering everywhere ; but in the humid 

 regions it appears only in the bottom and stream waters, and is 

 not perceived in the soil itself. 



Nor does it in either climatic region consist only of salts inju- 

 rious or useless to vegetation. Its origin, as well as the chemical 

 nature of sea water, proves that it should contain the useful or 

 plant-food ingredients as well ; and direct analysis amply confirms 



