258 ANNUAL OF SCIENTIFIC DISCOVERY. 



Last autumn I received a parcel of " efflorescences," from the soil of the 

 desert, between the head waters of the Missouri River, bordering on the 

 eastern flank of the Rocky Mountains, from Lieutenant Grover, U. S. A., who 

 conducted a party engaged in a reconnoissance of that region. The earth, of 

 many square miles of surface, is covered by a gray saline frosting, which ex- 

 ists so abundantly that vegetation does not appear, and the features of steril- 

 ity are so widely displayed as to cause a true desert. Chemical analysis 

 proved the efflorescence to be sulphate of soda, with minute traces of sulphate 

 of lime and common salt, mixed with fine sand, to which the gray color was 

 due ; no other saline compound was present. The sulphate of soda was nearly 

 anhydrous, being, in fact, thenardite, but evidently formed from a hydrous salt 

 by desiccation. No distinct crystals were included in the specimen received. 

 The occurrence of this salt, as an abundant exudation from the soil, is inter- 

 esting in a mineralogical view ; and its presence, under the form of an efflor- 

 escence, illustrates the physical law, in accordance with which saline waters 

 rise through the soil, and in evaporating from the surface, leave their saline 

 parts at that point, thus forming deserts. It has been long known to me that 

 the water of the Missouri River contains sulphate of soda, and the presence 

 of this salt in the water occasions a change in the composition of the water of 

 the Mississippi River, after these waters become mixed, below St. Louis. 



The water of the upper Mississippi contains a large amount of organic 

 matter, of a kind which, in changing its composition, out of contact with air, 

 attracts oxygen powerfully, and will decompose oxydized bodies. The dark 

 color of the buried salt is due to the presence of sulphuret of iron, formed 

 from the oxyd of iron of an ocherous clay, reduced and rendered a sulphate 

 of iron, by the presence of sulphates of soda and lime in the water. So abund- 

 ant is this organic matter, that the silt of the Mississippi water, after having 

 been kept ten years, has the power of decomposing alkaline sulphates, and 

 forming the sulphate of iron with the sulphur of the sulphate, while the soda, 

 in presence of carbonate of lime and carbonic acid, is eliminated as a sesqui or 

 bicarbonate of soda. Below St. Louis the turbid water of the Mississippi 

 contains, as its characteristic salt, the bicarbonate of soda ; and its suspended 

 matter being deposited by rest, we always find in the clear water this alkaline 

 salt, constituting a large part of the whole saline matter. I have been able 

 to trace the steps of the production of the bicarbonate of soda from the sul- 

 phate of soda, by the silt of this river in my vessels. The sulphate of iron, 

 also produced at the same time, oxydizes in free air, becoming oxyd of iron 

 and free sulphur. Sulphates are not the final result of the oxydation of basic 

 sulphates usually. The clay-colored cliffs and banks of the Mississippi exhibit 

 the oxydized state of the small portion of iron oxyd, one of its constituents, 

 while the dark, and even black, color of the buried mass beneath the surface, 

 is due to the reduced, and generally sulphureted, state of the iron, a condi- 

 tion caused by the changing organic matter. Until the discovery of the exist- 

 ence of sulphate of soda in the soil washed by the tributaries of the Mississippi, 

 its origin in the water was a subject of doubt, and in this connection the. new 

 fact becomes important. Regarding the immense body of water discharged 

 by the Mississippi, as a diluted solution of bicarbonate of soda, which falls 



