112 M. Humboldt on the Waters of the Viuagre 



phyry is covered, near to Los Serillos, with a blackisli-gray 

 lime-stone traversed by veins of carbonate of" lime, and so much 

 overcharged with carbon that in some parts it stains the fingers 

 like an aluminous schist, or like the lydian * stone of" Stee- 

 ben in the Fichtelgebirge. The trachytic dome of Purace 

 which gives birth to the little river of sulphuric acid, rises out 

 of a porphyritic syenite (with common felspar), which in its 

 turn is superposed on transition granite abounding in mica. 

 This observation f, very important for the position of volcanic 

 rocks, may be made near to Santa Barbara in ascending from 

 Popayan to the village of Purace. The volcano, like the most 

 part of the great volcanos of the Andes, presents layers or 

 mantles of melted stony matter, not real currents of lava. 

 Some fragments of granular limestone, probably magnesian, 

 which I found at more than 12,790 feet high, seem to have 

 been thrown up through crevices which have since become 

 closed. They are like those of the Fosso G;««<ff of Vesuvius, 

 which owe their granular texture to volcanic fire. It is not 

 possible to go on horseback further than the cascades of the 

 Rio Vinagre. From thence we were eight hours in mounting 

 on foot to the summit of the volcano and in descending from 

 it. The weather was dreadful ; snow and hail fell. 1 had a 

 great deal of difficulty in lighting the tinder at the point of 

 the conductor of Volta's electrometer ; the balls of elder-pith 

 separated from 5 to 6 lines, and the electricity passed often 

 from positive to negative without there being any other symp- 

 tom of stomn : for thunder and lightning are (according to my 

 experience) generally very rare when we are above 12,800 or 

 14,000 feet high. The hail was white J; the hailstones, from 

 five to seven lines in diameter, composed of layers varying in 

 translucency. They were not only much flattened towards the 

 poles, but so much increased in their equatorial diameter, 

 that rings of ice separated themselves on the least shock. I 



• M. Vauquelin has recently ])rovecl by a direct analysis the presence 

 of carbon in the purest lydian stones. I had found, in a series of experi- 

 ments made on the galvanic exciters in 1798, that the lydian stones of the 

 transition schists of Steeben produced jointly with zinc the same effect as 

 graphite or carburet of iron. I have since made sonic trials to prove che- 

 mically the presence of carbon in several varieties oflydia-i otone. — Sec 

 my Experiments on the Nervous and Muscular Fibre (in German), t. ii. 

 pp.163. 



\ See an account of the whole of these phainomena of the vol(;anos of 

 Popayan in my Essai stir Ic Gisemcnl ilcs Jiocltcs, 18-3, pp. Ii2!), i;j9, 340. 



\ I have already remarked elsewhere in theyl;;);. dcChiiinc,thi\t at Paramo 

 de Guanacas, where the road from Bogota to Poj)a_' an passes to the height 

 of 14,700 feet, there has been seen fall, not snow, but rod hail. Did it inclose 

 those same germs of vegetable organization which have been discovered 

 above the polar circle ? 



had 



