THE ERUPTION OF VESUVIUS IN APRIL, 1906. 289 



scattered generally over the surface and then localized at certain 

 points. I designate these fnniaroles, of superficial origin, as sec- 

 ondary fumaroles. 



The production of breccias in this eruption of Vesuvius, built up 

 in the dry way, seemed to offer favorable conditions for their forma- 

 tion, but in no case was the temperature sufficiently high to produce 

 true secondary fumaroles. This resulted from their origin; they 

 were not formed from the new magma, but from the debris of the 

 crater. The abundance of alkaline chlorides contained in the blocks 

 of the breccia indicates that if the temperature had been favorable, 

 products of secondary fumaroles would have been abundant, 



EXHALATIONS. 



The end of the great eruptions of Vesuvius is generally signalized 

 by the release of much carbonic acid and other exhalations, which 

 become specially al)undant in the lower parts of the mountain in 

 caves, wells, and quarries. These are sometimes of fatal effect, and 

 ordinarily are injurious to vegetation. They made their appearance 

 at the end of the eruption, but not till I had left Italy. The presence 

 of asphyxiating gases during the eruption was noted at the observa- 

 tory, which at one time was invaded by them. 



OTHER I'HEXOMENA. 

 EARTH MOVEMENTS. 



Throughout the eruption violent earth movements shook the cone, 

 and were felt at times through nnich of the Vesuvian region. They 

 were particularly violent during the night of April T, the seismolog- 

 ical instruments at the observatory being greatly agitated throughout 

 this period. These movements decreased gradually toAvard the end 

 of April and it is very probable, as in the case of Mont Pelee, that 

 vil)rations of the atmosphere caused by the great explosions have 

 played some part in the destruction of buildings. The observations 

 of Baratta and ^lercalli show that a temporary elevation of the coast 

 was produced between Portici and A^ico Equense. 



ELECTRIC PHENOMENA. 



The columns of vapor and solid material ejected by the Vulcanian 

 explosions produced electric phenoinena of great intensity. They 

 began on April 4, and were especially developed in the night of April 

 8, but decreased gradually from that time, though they were notable 

 up to the 13th. G. di Paola describes the splendid sight which they 

 presented. The enormous columns, rising from the crater with a 



