1823.] M, Humholdt on Volcanoes, 125 



between the Pacific Ocean and the town of Quito, and which 

 has become celebrated by Bouguer's earUest formula for the 

 barometer ; such also are the volcanoes that rise in the plain de 

 los Pastos, at the elevation of 10,000 feet. 



All these differently formed summits consist of trachyte, or 

 trap-porphyry, a granular rock, full of cracks and fissures, and 

 composed of glassy felspar and hornblende, but often containing 

 in addition, augite, mica, laminar felspar, and quartz. 



Where the evidence of the first eruption, and where the first 

 scaffolding, I might say, has been entirely preserved, the isolated 

 conical hills are surrounded by a high wall of rocks forming a 

 circus^ consisting of superposed strata ; such walls, or annular 

 surrounding masses, are called craters of elevation ; of these very 

 important phsenomena, Leopold von Buch, the first geognost of 

 our times, from whose works I have taken several views con- 

 tained in this i>aper, read a remarkable account, five years ago. 



The volcanoes which communicate with the atmosphere by 

 means of craters, and the conical hills of basalt and bell-shaped 

 trachytic hills without craters, the latter either low like Sarcouy, 

 or high hke Chimborazo, form different groups. A geographical 

 comparison shows, in one place, small Archipelagi, or, as it were, 

 classed systems of mountains, either with craters and currents 

 of lava, as in the Canaries and Azores, or devoid of craters and 

 real currents of lava in the Euganeans, and the Siebengebirge 

 near Bonn; or it shows, in other places, single and double 

 chains of volcanoes, connected with each other, and forming 

 tracts of many hundred miles in length, which are either 

 parallel to the direction of the mountains, as in Guatimala, 

 Peru, and Java, or in directions perpendicular to their axis, as 

 in the land of the Aztekes, where none but volcanic trachyte- 

 mountains attain the hmits of eternal snow, and those, probably, 

 have been thrust out of a fissure nearly 500 miles in length, 

 which divides the whole continent, from the Pacific Ocean to 

 the Atlantic. 



This aggregation of volcanoes either in single round groups, 

 or in double ranges, affords the most determinate proof that 

 volcanic effects do not depend upon slight causes existing near 

 the surface of the earth, but that they are great and deeply 

 founded phsenomena. The whole eastern part of the American 

 continent, which is poor in metals, is at present without craters, 

 without trachyte, probably even without basalt. All the volca- 

 noes are situated in the part opposite to Asia, in the meridian 

 line of the Andes chain, 1800 geographical miles long; the 

 whole of the elevated district of Quito is nothing but a single 

 volcanic hearth, the summits of which are Pichincha, Cotopaxi, 

 and Tunguragua. The volcanic fire now bursts forth from one, 

 and then from another of these apertures, which we are accus- 

 tomed to consider as separate volcanoes. 



The progressive motion of the fire here, in the space of three 

 centuries, turned from north to south. The earthquakes with 



