ANCIENT VOLCANOES. 



It is further to be noticed, that many of the craters of ancient vol- 

 canoes, are of far greater size than the present ones. Vesuvius is a 

 comparatively small cone, raised within the crater of a larger volca- 

 no. The cone of the Peak of Teneriffe, according to the descrip- 

 tion of travellers, stands within a volcanic plain, containing twelve 

 square leagues of surface, surrounded by perpendicular precipices 

 and mountains, which were the border of the ancient crater. If the 

 opinion of M. Humboldt be correct, all these craters are diminutive 

 apertures, compared with the immense chasms through which, in re- 

 mote ages, subterranean fire has forced a passage through the crust 

 of the globe. 



"The whole of the mountainous parts of Quito," he says, *' may 

 be considered as one immense volcano, occupying more than seven 

 hundred square leagues of surface, and throwing out flames by differ- 

 ent cones, known by the denominations of Cotopaxi, Tungurahua, 

 and Pichincha. In like manner," he adds, " the whole group of the 

 Canary Islands is placed as it were on one submarine volcano. The 

 fire forces a passage sometimes through one, and sometimes through 

 another of these islands. Teneriffe alone, contains in its centre an 

 immense pyramid terminated by a crater, throwing out, from one cen- 

 tury to another, lava by its flanks. In the other Canary Islands, the 

 difl!erent eruptions take place in various parts, and we no where find 

 those isolated mountains, to which volcanic efl:ects are restrained. 

 The basaltic crust formed by ancient volcanoes seems every where 

 undermined ; and the currents of lava seen at Lanzerote and Palma 

 remind us," he adds, " by every geological affinity, of the eruption 

 which took place in 1301 at the Isle of Ischia, amid the tufas of 

 Epimeo." 



In the preceding part of the present chapter, I have endeavoured 

 to give a succinct account of the most important volcanic phenomena. 

 The only formations of hard crystalline rocks in the present day are 

 volcanic; and if we trace the connection that exists between mod- 

 ern and ancient volcanic rocks, and between the latter and the rocks 

 of trap and porphyry, among the ancient rock-formations, we shall 

 extend the dominion of Pluto over a large portion of the globe. 



Many of the ancient volcanic rocks, have not flowed in currents 

 from limited apertures, like modern lavas. "The volcanic porphy- 

 ries on the back of the Cordilleras," says M. Humboldt, " are un- 

 doubtedly of igneous origin ; but the mode of their formation is not 

 like that of modern lavas, which have been erupted since the exca- 

 vation of valleys. The action of volcanic fire by an isolated cone or 

 crater of a modern volcano, differs necessarily from the action of this 

 fire, through the fractured crust of the globe." It has been observ- 

 ed by the same geologist, that the further back we can trace volca- 

 nic eruptions, the greater is the similarity between their products, and 

 the rocks which are regarded as the most ancient ; — hence, the 

 countries that have been the seats of ancient volcanoes, are particu- 



