atid the stibtoraneom Lakes of Pur ace. 1 1 1 



gi-eat quantity of cai'bonic acid. When it was merely remem- 

 bered tliat the sources of the Vinagre are very hot, this opinion 

 ouo-ht to have been abandoned. I boiled some water taken 

 from die cascade ; and I found, after the ebullition, the same 

 acid taste and the same precipitates as in the unboiled water. 

 At this period I had very few re-agents left. 



The nitrate of silver* gave a white and milky precipitate, 

 indicating the presence of muriates. The presence of iron was 

 shown by the prussiate of lime, that of lime by the oxalate of 

 potash. When the water was weighed with great care in the 

 office of the mint of Popayan, the weight of an equal quantity 

 of the water of the Vinagre was found to be to that of distilled 

 water as 2735i gr. to 2731 gr.; that is to say, that the specific 

 gravity of the water of the cascade was 1,0015. 



The waters which I describe, and of which M. Rivero has 

 given the first analysis, must not be confounded with those of 

 the two subterraneous lakes which we have found near the sum- 

 mit of the volcano; one is 14,356 feet high, the other, above 

 the snows, 15,475 feet. This volcano of Purace is a dome of 

 semivitreous trachyte, of a blueish grey and having a conchoidal 

 fracture. It does not present a great crater at its summit, 

 but several little mouths. It differs very much from the 

 neighbouring volcano, the Sotara, which is of a conical form, 

 and which has thrown out an immense quantity of obsidians. 

 These masses, covering the plains of Julumito, are balls or 

 tears of obsidian, the surface of which is often tubercular. 

 They present, what I have seen nowhere else in the two hemi- 

 spheres, all the shades of colour, from deep black to that of an 

 artificial glass entirely colourless. It may appear surprismg 

 to see that this deprivation of colour has not been accompanied 

 by any inflation or porosity The obsidians of Sotara are 

 mixed with fragments of enamel which resemble the porcelain 

 of Reaumur, and adhering to which I have found masses of 

 felspar which have resisted fusion. 



Here, as in the Andes of Quito, as at Mexico and at the 

 Canary Islands, the system of basaltic rocks lies far from the 

 trachytes which form the volcanos of Purace and of Soltara. 

 The basalts of the Tetilla of Julumito belong only to the left 

 bank of the Cauca. They rise from transition porphyries free 

 from aiigite, conUvining some hornblende, a very little quartz 

 in small crystals embedded in the mass, and a felspar which 

 passes from the common to the vitreous variety. This por- 



♦ The coniohu presence of the sulphuric and muriatic acids has also 



been observed by M. Vauquclin in the water which M. LcBchenault had 



taken from the crater-lake of Mount Idienne \n Java {Journal de fhy- 



siqur, I. Ixv. p. 40(5.) Sec Phil. Mi»g. vol. xlii. pp. 126, 182. 



^ phyry 



