GAS-ERUPTIONS 343 



cubic feet in size, which had been ejected to a distance 

 of one hundred feet. The cannon-like detonations 

 continued, but grew gradually less violent, each of 

 them being accompanied by a copious discharge of the 

 ill-smelling gas which threw the water into such com- 

 motion as to undermine the surrounding walls of 

 alluvial earth and to cause portions of them to fall into 

 the abyss. After a few days the disturbances ceased, 

 leaving as their memorial a cross-shaped chasm upwards 

 of three hundred feet in diameter, with walls rising 

 some fifteen feet above the water, which was ascertained 

 to be about one hundred feet deep. 



Many such incidents as this may have been experi- 

 enced in the history of ancient Rome. They would 

 be quite enough to fill the minds of the populace 

 with terror, and to call for a nine days' expiation and 

 lustration of the city. The traditional legend of the 

 chasm that opened in the Forum, and into which 

 Curtius threw himself in full armour to propitiate the 

 gods and save the city, may very well have been 

 founded on a real event of this nature. The lake or 

 quagmire in the Forum may have been another Lago- 

 puzzo, rent open by an outburst of gas. The subter- 

 ranean rumblings and bellowings {boati) y which were 

 accounted such dire portents in old times, were exactly 

 repeated near Monte Soracte in the autumn of 1831. 



Before we pass from this volcanic period to the 

 consideration of the next phase in the history of the 

 Campagna, it may be noted, as an interesting feature 

 in the growth of the Italian peninsula, that the sub- 

 terranean energy has been slowly dying out from north 

 to south. The volcanoes of Central Italy have long 



