72 



VOLCANOES. 



remarkable eruption at the foot of the Skaptar- 

 Jokul in Iceland (11th of June to 3d of August, 

 1783), which has been described by Mackenzie 

 and Soemund Magnussen. The same difficul- 

 ties present themselves in connection with the 

 small quantities of azote that are evolved, 

 when the atmospheric air is conceived as pen- 

 etrating by the crater, or, as such an act has 

 been figuratively expressed, when the earth is 

 imagined as inspiring. So general, so deeply 

 effective, and, in reference to the interior of 

 the earth, so extensive an action as that of 

 volcanoes, cannot well have its source in the 

 chemical affinities, in the contact of individual 

 and only locally distributed substances. Mod- 

 ern geognosy prefers seeking for this source 

 in the temperature increasing with the depth 

 under every parallel of latitude, in the great in- 

 ternal heat of the globe, which is due to its 

 original consolidation, to its formation in space, 

 to the spherical contraction of vaporous matter 

 circulating in an elliptical orbit. Beside posi- 

 tive knowledge, stand Conjecture and Opinion. 

 A philosophical science of nature strives to rise 

 beyond the limited requirements of a bare de- 

 scription of nature. It consists not, as we 

 have several times reminded the reader, in the 

 barren accumulation of isolated facts. The cu- 

 rious, the inquiring spirit of man, must be suf- 

 fered to make excursions from the present into 

 the past, still to surmise what cannot be posi- 

 tively known, and to revel in the old, and, un- 

 der various shapes, ever recurring myths of ge- 

 ognosy. If we consider volcanoes as irregular 

 intermitting springs, which pour out a liquefied 

 mixture of oxidized metals, alkalies and earths, 

 that flow smoothly, silently enough, once the 

 mixture, uplifted by the vast force of com- 

 pressed vapour, finds a vent, we are involunta- 

 rily reminded of Plato's geognostical phanta- 

 sies, according to which hot springs, as well 

 as all the varieties of volcanic fiery streams, 

 are effusions of Periphlegethon, a cause uni- 

 versally present in the interior of the globe(^"). 

 Volcanoes, in their mode of distribution over 

 the surface of the earth, independently of all 

 climatic differences, are well and characteris- 

 tically referred to two classes, viz. : Central 

 volcanoes and Linear volcanoes, " according 

 as a central and common point of eruption for 

 many foci all around is established, or as sev- 

 eral vents extending in one direction, and at 

 no great distance from each other, are formed, 

 along the course apparently of a lengthened 

 fissure. Linear volcanoes, again, are of two 

 kinds : they either rise as insulated cones from 

 the bottom of the sea, and are accompanied 

 usually on one side by a primitive mountain 

 mass running in the same direction, the foot 

 of which they seem to indicate ; or they stand 

 upon the crest of the mountain chain, and form 

 its loftiest summits'^'"). The Peake of Ten- 

 eriffe, for example, is a central volcano, the 

 middle point of the volcanic group to which 

 the outbreaks of Palma and Lancerote belong. 

 The lengthened chain of the Andes, which runs 

 like a wall from Southern Chili to the north- 

 west coasts of America, here singly, there in 

 two and three parallel hnes, connected at in- 

 tervals by narrow transverse yolks, presents 

 an instance upon the grandest scale of the oc- 

 currence of linear volcanoes on dry land. The 



vicinity of active volcanoes in the line of the 

 Andes is proclaimed by the sudden appearance 

 of certain species of rocks, such as dolerite, 

 melaphyre, trachyte, andesite, and dioritic por- 

 phyry, which separate the so-called primitive 

 rocks, as well as the schistose and sandstone 

 transition strata and the tertiary or flcetz for- 

 mations. A phenomenon of this kind constant- 

 ly recurring, begot a persuasion in my mind at 

 an early period, that these sporadic rocks had 

 been the seat of volcanic phenomena, and 

 had been determined by volcanic eruptions. 

 At the foot of the great Tunguragua, near Pe 

 nipe, on the banks of the Rio Puela, I for the 

 first time, and distinctly, saw a mica schist, 

 which rested upon granite, broken through by 

 volcanic rocks. 



The linear volcanoes of the New World, 

 where they lie near to one another, are partial- 

 ly in a state of reciprocal dependance ; it is 

 even obvious that the volcanic activity has 

 been gradually advancing for centuries in par- 

 ticular determinate directions — in the Province 

 of Quito, for example, from north to south(^">. 

 The hearth or focus itself lies under the whole 

 of the elevated lands of this province ; the par- 

 ticular openings by which communications are 

 established with the atmosphere constitute the 

 mountains which we designate by special 

 names, such as Pichincha, Cotopaxi or Tun- 

 guragua, and which, by their grouping, as well 

 as by their height and form, present the grand- 

 est and most picturesque prospect that is any- 

 where to be seen within a small compass in a 

 volcanic country. As the outermost members 

 of such groups of linear volcanoes are connect- 

 ed with one another by subterraneous commu- 

 nications, as multiplied experience shows, this 

 fact reminds us of Seneca's old and truthful 

 sentence(^^^), "that the burning mountain is 

 but the passage to deeper-lying volcanic for- 

 ces." In the Mexican highlands, likewise, the 

 volcanoes (Orizaba, Popocatepetl, Jorullo, Co- 

 lima), which I have shown(^^') all to lie in one 

 direction, between 18° 59' and 19° 12' N. lati- 

 tude, appear to indicate a transverse fissure 

 extending from sea to sea, and to be mutually 

 dependant. The volcano of Jorullo broke out 

 on the 29th of September, 1759, exactly in this 

 direction, upon the same transverse fissure, 

 and rose to a height of 1580 feet above the sur- 

 rounding level. This mountain never threw 

 out but one stream of lava ; precisely like Epo- 

 meo in Isehia, in the year 1302. 



But if Jorullo, distant as it is some German 

 miles from every active volcano, be, in the 

 strictest sense of the word, a new mountain, 

 nevertheless it must not be confounded with 

 the appearance of the Monte Nuovo near Poz- 

 zuolo (19th September, 15S9), which is to be 

 reckoned among the number of upheavement 

 craters. I have already said that it were more 

 in conformity with nature to assimilate the 

 eruption of the newly produced Mexican vol- 

 cano with the upheaval of the hill of Methone 

 (now Methana), upon the peninsula of Traezene. 

 This upliftment, described by Strabo and Pau- 

 sanias, has led one of the most imaginative of 

 the Roman poets to propound views which 

 agree in a very remarkable manner with those 

 of modern geognosy : " A tumulus is seen at 

 Traezene, rugged, and without wood ; once a 



