M. Humboldt on two Attempts to ascend Chimborazo. 311 



is associated true diorite-porphyry, a mixture of black horn- 

 blende (without augite) and white glassy albite, a rock which 

 reminds one of the beautiful columnar masses of Pisoje near 

 Popayan, and of the Mexican volcano of Toluca; which also, I 

 ascended. Some of the pieces of augite-porphyry, which I found 

 as high up as 18,000 feet upon the ridge of rock leading to- 

 wards the summit, for the most part in loose pieces, of from 12 

 to 14 inches in diameter, are minutely porous, and red in colour. 

 These pieces have shining vesicular cavities. The blackest arc 

 sometimes light, like pumice-stones, and as if recently changed by 

 fire. They have not, however, flown in streams like lava, but have 

 probably been thrust out through fissures, on the side of the earlier 

 raised-up dome-shaped mountain. The whole table-land of the 

 province of Quito has always been considered by me as a great 

 volcanic area. Tungurahua, Cotopaxi, Pichincha, with their 

 craters, are only different openings of this area. If volcanism, 

 in the broadest sense of the word, marks all the appearances 

 which depend on the reaction of the interior of a planet 

 on its oxydized surface, this part of the high land is more 

 exposed than any other in the tropical region of South Ame- 

 rica, to the effect of this volcanism. The volcanic powers 

 rage also, under the domes of augite-porphyry, which, like 

 that of Chimborazo, have no crater. Three days after our 

 expedition, we heard, in New Riobamba, at one o'clock a. m., 

 a raging subterranean crash (hramido) that was accompanied 

 by no concussion. Three hours later, there followed a vio- 

 lent earthquake, without any preceding noise. Similar bra- 

 m'ldos, coming, as it is supposed, from Chimborazo, were per- 

 ceived some days before at Calpi. Nearer to this mountain- 

 Colossus, in the village of San Juan, they are extremely frequent. 

 They excite the attention of the natives no more, than distant 

 thunder out of a deeply-clouded sky docs in our northern zone. 

 These are the few fugitive remarks on two ascents of Chim- 

 borazo, whicli I have allowt-d myself to communicate from an 

 unprintcd journal. Where Nature is so mighty and so vast, 

 and our endeavours arc purely scientific, the exhibition of any 

 ornament in language may well be spared. 



