308 Salt Lakes paet n. 



confined to, though, most abundant on, the low muddy 

 flats ; for I noticed some ona calcareous plain between 

 thirty and forty feet above the sea, and even a little 

 occurs in still higher valleys. Low alluvial tracts in 

 the valleys of the rivers Kegro and Colorado are also 

 encrusted, and in the latter valley such spaces appeared 

 to be occasionally overflowed by the river. I observed 

 saline incrustations in some of the valleys of southern 

 Patagonia. At Port Desire a low, flat, muddy valley 

 was thickly incrusted by salts, which on analysis by 

 I\Ir. T. Reeks, are found to consist of a mixture of sul- 

 phate and muriate of soda, with carbonate of lime and 

 earthy matter. On the western side of the continent, 

 the southern coasts are much too humid for this phe- 

 nomenon ; but in northern Chile I again met with 

 similar incrustations. On the hardened mud, in parts 

 of the broad, flat -bottomed valley of Copiapo, the saline 

 matter incrusts the ground to the thickness of some 

 inches : specimens, sent by Mr. Bingley to Apothe- 

 caries' Hall for analysis, were said to consist of 'car- 

 bonate and sulphate of soda. Much sulphate of soda is 

 found in the desert of Atacama. In all parts of S. 

 America, the saline incrustations occur most frequently 

 on low damp surfaces of mud, where the climate is 

 rather dry ; and these low surfaces have, in almost 

 every case, been upraised above the level of the sea, 

 within the recent period. 



Salt-lakes of Patagonia and La Plata,. — Salinas, 

 or natural salt-lakes, occur in various formations on the 

 eastern side of the continent, — in the argillaceo-calca- 

 reous deposit of the Pampas, in the sandstone of the 

 Rio Negro, where they are very numerous, in the pumi- 

 ceous and other beds of the Patagonian tertiary forma- 

 tion, and in small primary districts in the midst of this 

 latter formation. Port S. Julian is the most southerly 



