270 COSMOS. 



of Tuxtla, not even an extinct trachytic cone has been 

 discovered ; in this quarter, granite abounding in quartz 

 and mica-schist predominate. 



The volcanoes of Central America do not crown the ad- 

 jacent mountain chains, but rise along the foot of the 

 latter, usually completely separated from each other. The 

 greatest elevations lie at the two extremities of the series. 

 Towards the South, in Costa Rica, both seas are visible 

 from the summit of the Irasu (the volcano of Cartago), 

 to which, besides its elevation (11,081 feet), its central 

 position contributes. To the south-east of Cartago there 

 stand mountains of ten or eleven thousand feet : the 

 CUriqui (11,262 feet) and the Pico Blanco (11,740 feet). 

 We know nothing of the nature of their rock, but they 

 are probably unopened trachytic cones. Further towards 

 the south-east, the elevations diminish in Yeragua to six 

 and five thousand feet. This appears also to be the 

 average height of the volcanoes of Nicaragua and San Sal- 

 vador; but towards the north-western extremity of the 

 whole series, not far from the new city of Guatemala, two 

 volcanoes again rise above 13,000 feet. The maxima con- 

 sequently fall into the third group of my attempted hyp- 

 sometric classification of volcanoes, coinciding with Etna 

 and the Peak of Teneriffe, whilst the greater number of 

 the heights lying between the two extremities, scarcely 

 exceed Vesuvius by 2000 feet. The volcanoes of Mexico, 

 New Granada, and Quito belong to the fifth group, and 

 usually attain an elevation of more than 17,000 feet. 



Although the continent of Central America increases 

 considerably in breadth from the isthmus of Panama, 

 through Veragua, Costa Rica, and Nicaragua, to the lati- 

 tude of 11^, the great area of the lake of Nicaragua and 

 the small elevation of its surface (scarcely 128 feet 64 above 

 the two seas), gives rise to such a degradation of the land 

 exactly in this district, that by it an overflow of air from 

 the Caribbean Sea into the Great South Sea is often caused, 

 bringing danger to the voyager in the so-called Pacific 



84 Even under the Spanish Government in 1781, the Spanish engi- 

 neer, Don Jose" Galisteo, had found for the surface of the Laguna of 

 Nicaragua an elevation only six feet greater than that given by Baily in hia 

 different levellings in 1838 (Humboldt, Relation Historique. t. iii, p. 321). 



