100 BAIIIA BLANCA. 



these incrustations occur ; but I have nowhere 

 seen them so abundant as near Bahia Blanca. The 

 salt here, and. in other parts of Patagonia, consists 

 chiefly of sulphate of soda with some common salt. 

 As long as the ground remains moist in these sali- 

 trales (as the Spaniards improperly call them, mis- 

 taking this substance for saltpetre), nothing is to be 

 seen but an extensive plain composed of a black, 

 muddy soil, su^^porting scattered tufts of succulent 

 plants. On returning through one of these tracts, 

 after a week's hot weather, one is sui'jii'ised to see 

 square miles of the plain white, as if from a slight 

 fall of snow, here and there heaped up by the wind 

 into little drifts. This latter ajapearance is chiefly 

 caused by the salts being drawn up during the 

 slow evaporation of the moisture, round blades of 

 dead grass, stumps of wood, and pieces of broken 

 earth, instead of being crystallized at the bottoms 

 of the puddles of water. The salitrales occur ei- 

 ther on level tracts elevated only a few feet above 

 the level of the sea, or on alluvial land bordering 

 rivers. M. Parchappe* found that the saline in- 

 crustation on the plain, at the distance of some 

 miles from the sea, consisted chiefly of sulphate of 

 soda, with only seven per cent, of common salt ; 

 whilst nearer to the coast, the common salt increas- 

 ed to 37 parts in a hundred. This circumstance 

 would tempt one to believe that the sulphate of soda 

 is generated in the soil, from the muriate, left on 

 the surface during the slow and recent elevation of 

 this dry country. The whole phenomenon is well 

 worthy the attention of naturalists. Have the suc- 

 culent, salt-loving plants, which are well known to 

 contain much soda, the power of decomposing the 

 muriate 1 Does the black fetid mud, abounding 



* Voyage dans TAni^rique Merid., par M. A. d'Orbigny. Part. 

 Hist., torn, i., p, 664. 



