270 Volcanoes, 



But on the 28th of that month the noises were agam heard; 

 and, during that and the following day, a space of ground 

 from three to four miles in extent was elevated in the form 

 of a bladder. At the same time, flames issued from a space 

 about half a square league in superficies, and large fragments 

 of rocks were ejected. The rivers of Cuitimba and San 

 Pedro were precipitated into the chasm, and seemed to in- 

 crease the violence of the eruption. From the plain thou- 

 sands of little cones, called hornitos (ovens) by the natives, 

 were formed, and columns of smoke were projected. In 

 the midst of this, in the line of the chasm, bearing N.N.E. 

 to S.S.W., six larger cones were thrown up, the least being 

 three hundred feet above the level of the plain : JoruUo, 

 the largest, is sixteen hundred feet. From this elevation 

 immense quantities of basalt, lava, and fragments of primitive 

 rocks were ejected, almost without intermission, till the fol- 

 lowing February, when the action became less violent. 



Humboldt visited this mountain twenty years after the 

 eruption, and the lava was then in a heated state. Since 

 that time it has been again active ; but, although it was so 

 long ago as 1819, no authentic information concerning its 

 phenomena has reached us. 



Before we pass on to the consideration of subaqueous 

 volcanoes, it will not be unnecessary to remark that there 

 are two classes of phenomena usually attending aerial erup- 

 tion, which are generally either partially described, or 

 altogether overlooked, by those who detail volcanic pheno- 

 mena. We refer to the electrical state of the atmosphere, 

 and the alteration in the level of the surrounding waters. 

 But as these effects of volcanic activity may perhaps lead to 

 the establishment of some rational explanation of its cause, 

 we hope that future observers will carefully examine them, 

 and endeavour to overcome those difficulties which necessarily 

 oppose their experiments. 



The number of subaqueous volcanoes with which we are 

 acquainted is very small. When we consider how much the 

 greater portion of the surface of our globe is covered by 

 water, we may at first be surprised at this fact ; but we must 

 remember that it does not arise from the inactivity of the 

 volcanic agent beneath our seas, but from the elevation of 

 cones above its level. An eruption of any considerable vio- 

 lence must of necessity form an elevation that will come 

 under the class of aerial volcanoes, and hence it is that the 

 majority of these are in islands. 



There is much difficulty in obtaining specific information 

 of the phenomena which attend the activity of subaqueous 



