MINERALS UNESSENTIAL OR INJURIOUS TO SOILS. 77 



tralized in any way, it can be gotten rid of only by leaching-out. This 

 process is usually accomplished in seashore lands by the action of rain, 

 or by the overflow of fresh-water streams, after the tide has been ex- 

 cluded by means of drains provided with check-valves to prevent the 

 inflow of tidewater; or else by underdrainage, and flooding when 

 possible. 



Mirabilitc, (Glauber's salt) or stilfate of soda, exists not 

 unfrequently in the soils of the arid region and sometimes en- 

 crusts extended areas of lowlands during the dry season. 

 When present in the soil it will commonly be seen blooming 

 out on the surface after a rain, in light, feathery, needle-shaped 

 crystals, sometimes to such an extent that it can be collected by 

 the handful. Subsequently, when wafted by the wind, it is 

 reduced to a fine white dust, which constitutes a goodly pro- 

 portion and sometimes the entire mass of the " alkali dust " 

 that is so annoying on the plains of Nevada, and in the desert 

 regions generally, during the hot summer. Near White Plains, 

 Nevada, it forms a thick layer of " white sand," in which the 

 foot sinks deeply, and which is carried about by the wind with 

 great ease. 



Glauber's salt is never a desirable soil-ingredient. It is 

 largely produced as a by-product in several industries, but 

 cannot be utilized for agricultural purposes to any extent. It 

 is, however, much less injurious to plant growth than common 

 salt; according to experience in California it may be considered 

 about three times less so. It constitutes the major portion 

 of what is commonly known as " white alkali," which is well 

 known to be much less injurious to crops than the " black ' : 

 kind, which contains carbonate of soda. 



Trona and Urao are natural forms of carbonate of soda or 

 salsoda. Like Glauber's salt, it commonly occurs as a surface 

 efflorescence or crust in dry or desert regions ; either from the 

 evaporation of standing water, as in the case of the soda lakes 

 of Nevada, Hungary and Egypt, or as an efflorescence on the 

 surface of the soil, as in the western United States, Mexico 

 ("urao"), North Africa ("trona"), and at many points in 

 the Old Continent. In the United States it is commonly 

 known as " black alkali," because of the black spots formed on 

 the surface by evaporation; practically the same name 



