238 COSMOS., 



and the saute direction, as, for instance, from north to south 

 in the province of Quito. * The focus of the volcanic action 

 lies below the whole of the highlands of this province ; the only 

 channels of communication with the atmosphere are, however, 

 those mountains which we designate by special names, as the 

 mountains of Pichincha, Cotopaxi, and Tunguragua, and which 

 from their grouping, elevation, and form, constitute the grandest 

 and most picturesque spectacle to be found in any volcanic 

 district of an equally limited extent. Experience shows us 

 in many instances, that the extremities of such groups of vol- 

 canic chains are connected together by subterranean commu- 

 nications ; and this fact reminds us of the ancient and true 

 expression made use of by Seneca,f that the igneous mountain 

 is only the issue of the more deeply-seated volcanic forces. In 

 the Mexican highlands a mutual dependence is also observed 

 to exist among the volcanic mountains Orizaba, Popocatepetl, 

 Jorullo, and Colima ; and I have shown J that they all lie in 

 one direction between 18 59' and 19 12' north lat. ; and are 

 situated in a transverse fissure running from sea to sea. The 

 volcano of Jorullo broke forth on the 29th of September, 1 759, 

 exactly in this direction, and over the same transverse fissure, 

 being elevated to a height of 1604 feet above the level of the 

 surrounding plain. The mountain only once emitted an eruption 

 of lava, in the same manner as is recorded of Mount Epomeo 



* Humboldt, Oeognost. Beobacli. uber die Vulkane des Hochlandes 

 von Quito, in Poggend. Annal. der Physik, bd. xliv. s. 194.,_ 



t Seneca, while he speaks very clearly regarding the problematical 

 sinking of Etna, says in his 79th Letter : " Though this might happen, 

 not because the mountain's height is lowered, but because the fires are 

 weakened and do not blaze out with their former vehemence ; and for 

 which reason it is that such vast clouds of smoke are not seen in the 

 day time. Yet neither of these seem incredible, for the mountain may 

 possibly be consumed by being daily devoured, and the fire not be so 

 large as formerly, since it is not self-generated here, but is kindled in the 

 distant bowels of the earth, and there rages, being fed with continual fuel, 

 not with that of the mountain, through which it only makes its passage." 

 The subterranean communication, " by galleries," between the volcanoes 

 of Sicily, Lipari, Pithecusa (Ischia), and Vesuvius, " of the last of which 

 we may conjecture that it formerly burned and presented a fiery circle," 

 seems fully understood by Strabo (lib. i. pp. 247 and 248). He terms 

 the whole district " subigneous." 



.$ Humboldt, Essai politique sur la Nouv. Espagne, t. ii. pp. 173- 

 175. 



