xxxvi ^Physical and Geognostic Si((/ge8fio7is, 



Schemnitz, with the sole exception, that the trachytes " por- 

 phyres meulieres " of Bendant, are wanting here. 



As it is highly desirable that considerable time should be 

 devoted to the volcanoes of Quito, Peru, and Chili, it appears 

 uncertain whether the course of the frigate, on leaving 

 Acalpulco, will be shaped direct for Guayaquil, thus revers- 

 ing the route taken by myself, or whether she will not touch 

 at some of the central American ports — Realejo or Son- 

 sonate. The crowded series of volcanoes in Central America, 

 of which no less than eighteen, conical or dome-shaped, may 

 be considered as still in active eruption, would yield a rich 

 harvest of facts of all kinds in elucidation of the theory of 

 volcanic action, such as have never hitherto been sufficiently 

 taken advantage of. We are still in need of the minera- 

 logical determination of the rocks, while the form and 

 situation of the momitain masses have been well described 

 by Squier, Oersted, and other modern travellers. The greater 

 number, indeed, of the eruptions of scoriae and slag were 

 unaccompanied by streams of lava, as, for example, those 

 of Mount Isalco, abounding in ammonia. But recently eye- 

 witnesses have furnished us with quite different accounts 

 regarding these eruptions, in the case of several volcanoes 

 — as the Nindiri (a twin volcano with that called Mas- 

 saya), on which Dr. Scherzer has lately shed much 

 light ; the Volcano el Nuevo, erroneously called Volcano de 

 las Pilas, that of Coseguina, situated on the Great Bay of 

 Fonseca, and that of San Miguel de Rosotlan, from which 



