90 CHARLES DARWIN 



wood, and pieces of broken earth, instead of being crystal- 

 lized at the bottoms of the puddles of water. The salitrales 

 occur either on level tracts elevated only a few feet above 

 the level of the sea, or on alluvial land bordering rivers. 

 M. Parchappe 7 found that the saline incrustation 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 increased 

 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 phe- 

 nomenon is well worthy the attention of naturalists. Have 

 the succulent, salt-loving plants, which are well known to 

 contain much soda, the power of decomposing the muriate? 

 Does the black fetid mud, abounding with organic matter, 

 yield the sulphur and ultimately the sulphuric acid? 



Two days afterwards I again rode to the harbour: when 

 not far from our destination, my companion, the same man 

 as before, spied three people hunting on horseback. He im- 

 mediately dismounted, and watching them intently, said, 

 " They don't ride like Christians, and nobody can leave the 

 fort." The three hunters joined company, and likewise dis- 

 mounted from their horses. At last one mounted again 

 and rode over the hill out of sight. My companion said, 

 " We must now get on our horses : load your pistol ;" and he 

 looked to his own sword. I asked, " Are they Indians ? " 

 " Quien sabe? (who knows?) if there are no more than three, 

 it does not signify." It then struck me, that the one man 

 had gone over the hill to fetch the rest of his tribe. I sug- 

 gested this ; but all the answer I could extort was, " Quien 

 sabe ? " His head and eye never for a minute ceased scan- 

 ning slowly the distant horizon. I thought his uncommon 

 coolness too good a joke, and asked him why he did not 

 return home. I was startled when he answered, " We are 

 returning, but in a line so as to pass near a swamp, into 

 which we can gallop the horses as far as they can go, and 

 then trust to our own legs ; so that there is no danger." I did 



T Voyage dans 1'Amerique Merid par M. A. d'Orbigny. Part. Hist 

 torn. i. p. 664. 



