TRUE VOLCANOES. 309 



heaval of this isolated mountain, 13,553 feet in height, may 

 have caused the formation of the Loma de Tablas. During 

 such an upheaval, longitudinal fissures and net-works of fis- 

 sures may be produced far and wide by folding of the soil, 

 and from these molten masses may have poured directly, 

 sometimes as dense masses, and sometimes as scoriaceous 

 lava, without any formation of true mountain platforms 

 (open cones or craters of elevation). Do we not seek in vain 

 in the great mountains of basalt and porphyritic slate for 

 central points (crater mountains), or lower, cireumvallated, 

 circular chasms, to which their common production might be 

 ascribed? The careful separation of that which is genet- 

 ically different in phenomena the formation of conical 

 mountains with permanently open craters and lateral open- 

 ings ; of circumvallated craters of elevation and Maars ; of 

 upraised, closed, bell-shaped mountains or open cones, or 

 matters poured out from coalescent fissures is a gain to sci- 

 ence. It is so because the multiplicity of opinions which is 

 necessarily called forth by an enlarged horizon of observa- 

 tion, and the strict critical comparison of that which exists 

 with that which is asserted to be the only mode of produc- 

 tion, are most powerful inducements to investigation. Even 

 upon European soil, however, on the island of Eubrea, so rich 

 in hot springs, a vast lava stream has been poured out,* 

 within the historical period, from a chasm in the great plain 

 of Lelanton, at a distance from any mountain. 



In the volcanic group of Central America, which follows 

 the Mexican group toward the south, and in which eighteen 

 conical and bell-shaped mountains may be regarded as still 

 active, four (Nindiri, El Nuevo, Conseguina, and San Miguel 

 de Bosotlan) have been recognized as producing lava.f The 

 mountains of the third volcanic group, that of Popayan and 

 Quito, have already for more than a century enjoyed the rep- 

 utation of furnishing no lava streams, but only incoherent, 

 glowing scoriaceous masses, thrown out of the single sum- 

 mital crater, and often rolling down in a linear arrangement. 

 This was even the opinion^ of La Condamine, when he left 



* Strabo, lib. i., p. 58 ; lib. vi., p. 269, ed. Casaubon ; Cosmos, vol. i., 

 p. 237, and vol. v., p. 215. 



t See page 263. 



j "I have never known," says La Condamine, "lava-like matter in 

 America, although M. Bouguer and myself have encamped for whole 

 weeks and months upon the volcanoes, and especially upon those of 

 Pichincha, Cotopaxi, and Chimborazo. Upon these mountains I have 

 only seen traces of calcination, without liquefaction. Nevertheless, the 



