Volcanoes in the different regions of the Earth. 32T 



Teyde, Tunguragua, and Cotopaxi. I have observed them 

 rising from the size of the lovi^est hills to 17,700 feet above th6 

 level of the sea. But close to these conical mountains, there al- 

 so occur permanent apertures, forming regular communications 

 with the interior of the earth, on long serrated chains, not at the 

 middle of their mural summit, but at their extremity, and near 

 the declivity. Of this kind is Pichincha, which rises between 

 the great ocean and the city of Quito, and which Bouguer''s ba- 

 rometrical formulae have long rendered celebrated. Such also 

 are the volcanoes which rise on the Steppe de los Pastos, which 

 is 10,000 feet high. All these summits, of varied forms, are 

 composed of trachyte, formerly named trap porphyry, a granu- 

 lar fissured rock, formed of glassy felspar and hornblende, and 

 in which augite, mica, laminar felspar, and quartz, also occur. 

 In places where the evidences of the first eruption I might say 

 of the ancient volcanic scaffolding, are preserved entire, the iso- 

 lated conical mountain is surroundtd, in the form of an amphi- 

 theatre, with a great wall, constructed of rocky strata, super- 

 imposed upon each other. These walls or circumvallations are 

 the remains of craters of elevation, a phenomenon worthy of 

 attention, respecting which the first geologist of our times, M. 

 Leopold Von Buch, in his writings, from which I have borrowed 

 several ideas stated in the present memoir, has presented such 

 interesting views. 



The volcanoes which communicate with the atmosphere by 

 permanent apertures, the basaltic cones or domes of trachyte, 

 destitute of crater, sometimes low like Sarcouy, and sometimes 

 elevated like Chimborazo, form various groups. Comparative 

 geography shews us, on the one hand, small archipelagoes, and 

 entire systems of volcanic mountains, with their craters and cur- 

 rents of lava, resembling those of the Canary Islands, and the 

 Azores ; and, on the other, mountains without craters, and with- 

 out currents of lava, properly so called, as the Euganeans, and 

 the (Siebengebirge) seven mountains of Bonn. Moreover, it 

 shews us volcanoes arranged in single or double hnes, and extend- 

 ing to several hundreds of leagues, sometimes parallel to the axis 

 of the chain, as in Guatemala, Peru, and Java; sometimes cutting 

 it perpendicularly, as in the country of the Azteques, where tra- 

 chytic mountains, which vomit fire, alone attain the height of 



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