BIRDS AXD BUTTERFLIES. 233 



snowy pitch on the opposite side. Had they stumbled 

 they would either have been buried in the mingled snow 

 and ice, or would have rolled headlong down the steep. 

 The character of the rock, which was brittle and crumbling, 

 increased the difficulty of the ascent. Here and there they 

 were obliged to crawl on their hands and feet ; the sharp 

 edges of the rock wounded them, and they left behind a 

 bloody trail. They marched in single file, testing with 

 their poles the stability of the rocks before them. This 

 precaution was very necessary, as many of the rocks 

 were lying loose on the brink of the precipice. Desirous 

 of knowing how much of the mountain remained to be 

 ascended, for the summit was continually hidden from 

 their sight, Humboldt opened the barometer on a point 

 where the path was broad enough to allow two persons 

 to sit side by side : the mercury indicated a height of 

 eighteen thousand three hundred and eighty feet. The 

 temperature of the air was 98°, and that of the earth 107°. 



They proceeded for another hour, and found the rocky 

 path less steep ; the mist, however, was thicker than ever. 

 They now began to suffer severely from the extreme 

 rarefaction of the air. They breathed with difficulty, and 

 what was still more disagreeable, felt like vomiting. Their 

 heads swam, their lips and gums bled profusely, and their 

 eyelids and eyeballs were charged with blood. 



From time to time great birds, probably condors, came 

 swooping down the terrible pass, sailing grandly away ; 

 and little winged insects, resembling flies, fluttered gaily 

 around. It was impossible to catch them, owing to the 

 narrowness of the ledge ; but Humboldt judged that they 

 were Dipteras. Bonpland saw yellow butterflies, a little 

 lower down, flying very near the ground. 



