TRUE VOLCANOES. 403 



him, as well as for his interesting geological notices on the 

 volcanoes of the \vhole Mexican highlands, all of which he 

 has personally visited. The volcano of Toluca, whose 

 highest summit (the Pico del Frayle), though narrow and 

 difficult to climb, I ascended on the 29th September, 1803. 

 and found barometrically to be 15,166 feet high, has a totally 

 different mineralogical composition from the still active Po- 

 pocatepetl and the igneous mountain of Colima ; this must 

 not, however, be confounded with another, still higher sum- - 

 mit, called the Snow-mountain. The volcano of Toluca 

 consists, like the Peak of Orizaba, the Puy de Chaumont in 

 the Auvergne and .^Egina, of a combination of oligoclase 

 and hornblende. From this brief sketch it will be seen, 

 and it is well deserving of notice, that in the long range of 

 volcanoes which extend from ocean to ocean, there are not 

 two immediately succeeding each other which are of similar 

 mineralogical composition. 



X. THE NORTH-WESTERN DISTRICTS OF AMERICA 

 (northward of the parallel of Rio Gila) . 



In the section which treats of the volcanic action on the 

 eastern Asiatic Islands, 8 particular notice has been drawn 

 to the bow-like curve in the direction of the fissure of up- 

 beaval from which the Aleutian Islands have risen, and 

 which manifests an immediate connection between the 

 Asiatic and American continents, between the two volcanic 

 peninsulas Kamtschatka and Aliaska. At this point is the 

 outlet, or rather the northern boundary, of a mighty gulf 

 of the Pacific Ocean, which from the 150 degrees of longi- 

 tude embraced by it under the equator, narrows itself down 

 between the terminal points of these two peninsulas to 37 C 



crater, from which he then saw nothing but sulphuretted-hydrogen va- 

 pour rising in a cloud ; but Sonneschmid, who vainly attempted to 

 ascend Colima, in February, 1796, gives an account of an immense 

 ejection of ashes in the year 1770. In the month of March 1795, on 

 the other hand, red-hot scorire were visibly thrown out in a column of 

 fire at night. " To the north-west of the volcano of Colima, a vol- 

 canic branch-fissure runs along the shore of the South Sea. Extinct 

 craters and ancient lava-streams are recognised in what are called the 

 Volcanoes of Ahuacatlan (on the road from Guadalaxara to San Bias) 

 and Tepic." (Pieschel, ibid. p. 529). 

 8 See above, pp. 367372. 



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